Accepted Manuscript Textile wastewater treatment: aerobic granular sludge vs activated sludge systems Adriana Maria Lotito, Marco De Sanctis, Claudio Di Iaconi, Giovanni Bergna
PII:
S0043-1354(14)00095-5
DOI:
10.1016/j.watres.2014.01.055
Reference:
WR 10458
To appear in:
Water Research
Received Date: 20 October 2013 Revised Date:
21 December 2013
Accepted Date: 27 January 2014
Please cite this article as: Lotito, A.M., De Sanctis, M., Di Iaconi, C., Bergna, G., Textile wastewater treatment: aerobic granular sludge vs activated sludge systems, Water Research (2014), doi: 10.1016/ j.watres.2014.01.055. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
Textile wastewater treatment: aerobic granular sludge vs activated sludge
2
systems
3
Adriana Maria Lotitoa,*, Marco De Sanctisb, Claudio Di Iaconib,*, Giovanni Bergnac
4
a
Department of Water Engineering and Chemistry, Politecnico di Bari, via Orabona 4, 70125 – Bari, Italy
5
b
CNR-IRSA, Water Research Institute - National Research Council, viale De Blasio 5, 70132 – Bari, Italy
6
c
CIDA S.p.A., via Laghetto 1, 22073 – Fino Mornasco (CO), Italy
SC
RI PT
1
7 * Corresponding authors:
9
Adriana Maria Lotito: e-mail address: [email protected]; Tel: +393403005056;
M AN U
8
10
Claudio Di Iaconi: e-mail address: [email protected]; Tel: +390805820525; Fax:
11
+390805313365
12
Abstract
14
Textile effluents are characterised by high content of recalcitrant compounds and are often
15
discharged (together with municipal wastewater to increase their treatability) into centralized
16
wastewater treatment plants with a complex treatment scheme. This paper reports the results
17
achieved adopting a granular sludge system (sequencing batch biofilter granular reactor – SBBGR)
18
to treat mixed municipal-textile wastewater. Thanks to high average removals in SBBGR (82.1%
19
chemical oxygen demand, 94.7% total suspended solids, 87.5% total Kjeldahl nitrogen, 77.1%
20
surfactants), the Italian limits for discharge into a water receiver can be complied with the
21
biological stage alone. The comparison with the performance of the centralized plant treating the
22
same wastewater has showed that SBBGR system is able to produce an effluent of comparable
AC C
EP
TE D
13
ACCEPTED MANUSCRIPT
23
quality with a simpler treatment scheme, a much lower hydraulic residence time (11 h against 30 h)
24
and a lower sludge production.
RI PT
25 26
Keywords
27
textile effluents; SBBGR treatment; centralized treatment plant; ozonation; sludge
28
production
SC
29
1. Introduction
31
The textile sector is of great importance in the European economy: the manufacture of
32
textiles, clothing and leather was the main activity of over 267,000 enterprises in the
33
Member States in 2006 (European Commission, 2009) and textiles and wearing apparel
34
accounted for about 3.6% of the EU-27 manufacturing in terms of value added and 6.3% in
35
terms of employment in 2008 (European Commission, 2011). In particular, Italy is the
36
leading producer, generating about one third (33.6%) of EU-27 value added in this sector in
37
2006, followed by Germany (12.1%), France (11.6%), Spain (9.2%) and the United
38
Kingdom (7.8%) (European Commission, 2009). Moreover, Italy is the only specialised
39
State, as in 2006 this sector contributed 3.4% of the value added generated in its non-
40
financial business economy, three times the average contribution recorded across the EU-27
41
(European Commission, 2009).
42
An important environmental issue related to such a relevant economic sector is the
43
production and discharge of big volumes of highly polluted wastewater, due to the
44
consumption of about 100-200 l of water per kg of textile product (Bechtold et al., 2004)
AC C
EP
TE D
M AN U
30
2
ACCEPTED MANUSCRIPT
and to the use of an immense range of materials and chemicals (dyes, process aids and
46
finishing products) in the production chain (Correia et al., 1994).
47
Despite on-site treatment can be the optimal solution to promote water recycle, such an
48
option is generally not affordable for small enterprises, especially those working on the
49
most polluting processing stages (dyeing, printing and finishing steps): in fact, any
50
conventional treatment method applied individually is usually not capable to successfully
51
remove all the diverse pollutants present in textile wastewater and to tackle the large
52
variability in composition, producing limited results in terms of overall reduction in organic
53
matter, nutrients and colour (Demmin and Uhrich, 1998; Fongsatitkul et al., 2004; Soares et
54
al., 2006; Lau and Ismail, 2009). Thus, the usual treatment scheme consists of a
55
combination of biological and physico-chemical processes like chemical precipitation,
56
coagulation-flocculation, adsorption on activated carbons, ion-exchange, electrochemical
57
processes, etc. (Chen et al., 2005; Sreedhar Reddy and Kotaiah, 2006; Ramesh-Babu et al.,
58
2007; Somensi et al., 2010). Due to the complexity of the sequence of treatments, to the
59
need for large areas and to the high capital and operating costs (Ramesh-Babu et al., 2007),
60
it is often necessary to treat effluents in centralized plants rather than on-site at each
61
factory.
62
Hence, most of the wastewater from the textile industry is currently mixed and discharged
63
to municipal wastewater treatment plants with little or even no pre-treatment (Libra and
64
Sosath, 2003). In fact, when centralized treatment is performed, the joint treatment with
65
municipal wastewater is considered to be the optimum alternative, as it can help to solve
66
many difficulties such as the extreme fluctuations in flow and wastewater composition
AC C
EP
TE D
M AN U
SC
RI PT
45
3
ACCEPTED MANUSCRIPT
(Grau, 1991). Moreover, the municipal contribution supplies nitrogen and phosphorus
68
(necessary for the biological process) and increases the biodegradable fraction of the
69
wastewater (Grau, 1991). The domestic component is expected to provide some buffering
70
in terms of the characteristics of the combined flow and, therefore, to enable an easier
71
treatment of combined wastewater compared to individual treatment of industrial effluents
72
on their own (Ng, 2006). The combined treatment of industrial and domestic wastewater
73
could represent an economically-feasible alternative in which the degradation of organic
74
pollutants is favoured by dilution and adaptation ability of the activated sludge (Del Borghi
75
et al., 2003).
76
However, due to the high amount of hydrophobic compounds present in the textile
77
component, the biological stage of the centralized plant often suffers from sludge bulking
78
and foaming problems (Bortone et al., 1995; Mino, 1995). Furthermore, a tertiary treatment
79
stage is required to remove refractory compounds and colour, with a consequent increase in
80
treatment scheme complexity and capital and operating costs. This stage is often based on a
81
coagulation-flocculation treatment followed by ozonation.
82
In order to simplify the treatment scheme and reduce treatment costs, the use of more
83
efficient innovative technologies in the existing centralized wastewater treatment plants is a
84
research field of major interest, especially in countries like Italy, in which the textile
85
industry is mainly composed of numerous small and medium-sized enterprises, which are
86
specialized on specific productions or processing steps and are located in some areas
87
known as textile districts.
AC C
EP
TE D
M AN U
SC
RI PT
67
4
ACCEPTED MANUSCRIPT
The aim of this paper is to prove the suitability of an innovative biological system
89
(sequencing batch biofilter granular reactor – SBBGR) for the treatment of textile
90
wastewaters mixed with municipal ones. The SBBGR system consists of a single basin into
91
which the wastewater is fed, treated and then discharged. It combines the advantages of
92
attached biomass systems (greater robustness and compactness) with those of periodic
93
systems (greater flexibility and stability). SBBGR is, however, a unique system in virtue of
94
the particular type of biomass growing in it (a mixture of biofilm and granules packed in a
95
filling material) which allows a greater retention of the biomass in the reactor (up to one
96
order of magnitude higher than that recorded in conventional biological systems). As a
97
result, remarkable improvements in substrate conversion capacities and sludge production
98
are achieved (Di Iaconi et al., 2010).
99
In this paper, the performance of SBBGR system is compared with the one of the full scale
100
wastewater treatment plant in which the wastewater is currently treated (Alto Seveso, Fino
101
Mornasco, Como, Italy). A detailed analysis, which includes also biomass characterization,
102
shows the peculiar advantages of SBBGR.
SC
M AN U
TE D
EP
103
RI PT
88
2. Materials and methods
105
2.1. Como textile district
106
Mixed municipal-textile wastewater was taken from the centralized wastewater treatment
107
plant (WWTP) Alto Seveso (Fino Mornasco, Italy), located in the textile district of Como.
108
This wide district includes about 1040 industries located in 27 towns, mainly devoted to the
109
treatment of silk and silky fibres. The activity is mostly based on a high number of small
AC C
104
5
ACCEPTED MANUSCRIPT
specialized factories operating on a single stage of the entire textile processing chain (i.e.,
111
twisting, weaving, dyeing, printing, finishing, etc.). The predominant activities are those
112
related to dyeing, printing and finishing operations, which are also the most polluting stages
113
in the textile chain. The produced wastewater is treated in several wastewater treatment
114
plants (the largest four plants globally treat about 100,000 m3 per day, considering both
115
textile and domestic contribution).
SC
RI PT
110
116
2.2. Lab-scale SBBGR
118
The experimental campaign was carried out using a lab-scale SBBGR prototype (Figure 1),
119
which consisted of a 1 m Plexiglas cylinder with internal diameter of 190 mm. The bottom
120
of the reactor (microbial bed; volume: 9 l) was filled with plastic support material for
121
biomass development (wheel shaped plastic elements KMT-k1 from Kaldnes, Norway; 10
122
mm diameter, 7 mm height, 630 m2/m3 specific surface, 950 kg/m3 density, 0.75 porosity)
123
packed between two sieves. In order to start-up the reactor, activated sludge from a local
124
municipal WWTP was used as inoculum.
125
The operation of the reactor was based on treatment cycles, each consisting of three
126
consecutive phases (namely filling, reaction and drawing). During the filling phase (few
127
minutes), a fixed volume of wastewater was added from the bottom of the reactor to the
128
liquid volume retained from the previous treatment cycle using a peristaltic pump. In the
129
reaction phase, the filled wastewater was continuously aerated (with the exception of the
130
first hour for denitrification) by air injection through porous stones placed close to the
131
upper sieve and recycled through the biomass supporting material using a recycle pump, in
AC C
EP
TE D
M AN U
117
6
ACCEPTED MANUSCRIPT
order to obtain a homogeneous distribution of substrate and oxygen. Finally, the treated
133
wastewater was discharged by gravity using a port located in the liquid phase over the bed
134
through the opening of a motorized valve (duration of the drawing phase: 15 min).
135
A pressure meter at the bottom of the reactor was used to measure biofilter head losses due
136
to biomass growth and entrapped suspended solids contained in the influent and to plan a
137
washing step with compressed air to decrease head loss down to the low set-point,
138
whenever a fixed head loss value was reached (high set-point).
SC
RI PT
132
M AN U
139
2.3. Alto Seveso wastewater treatment plant
141
The Alto Seveso WWTP treats about 8 million m3/year and serves around 80,000
142
population equivalents (PEs), with a civil contribution of 30,000 PEs and an industrial one
143
of 50,000 PEs. The industrial wastewater mostly comes from textile industries (97%), and
144
in particular from printing factories (38%), dyeing factories (28%) and factories in which
145
both dyeing and printing operations are performed (31%).
146
The treatment scheme consists of numerous steps, which encompass preliminary, biological
147
and tertiary treatments (the total hydraulic retention time of the latter two is about 30 hours)
148
(Figure 2). The preliminary treatments (grit removal, screening, sand removal) are intended
149
to remove coarse suspended matters such as grit, sand and rags, pieces of fabric, fibres,
150
yarns. The biological compartment consists of a conventional activated sludge plant
151
composed of a pre-denitrification stage, followed by biological oxidation and secondary
152
settling. Ozone is dosed on part of the recycle from the secondary settler to the biological
153
basin in order to reduce sludge production and to solve some operational problems due to
AC C
EP
TE D
140
7
ACCEPTED MANUSCRIPT
filamentous bacteria growth and consequent biological foam (sludge bulking problems and
155
hindered sedimentation). Then, tertiary treatments (coagulation-flocculation, clarification
156
and ozonation) are required to remove suspended solids, recalcitrant compounds and
157
colour.
RI PT
154
158
2.4. Treatment performance
160
The influent to the biological compartment of the Alto Seveso WWTP, after preliminary
161
treatments to remove grit, sand and coarse material, was used in our tests. The experimental
162
SBBGR campaign lasted 200 days. During the first 3 months of the experimentation
163
particular attention was paid to the generation of the particular biomass of SBBGR (i.e., a
164
mixture of biofilm and granules packed in the filling material) by operating with a high
165
value of hydraulic retention time (HRT), i.e. 25-30 h, and 8 h-treatment cycles. Thanks to
166
the design of the reactor, granulation is simply achieved using such a slow increasing step-
167
feed approach: more details about the start-up of a SBBGR can be found in De Sanctis et al.
168
(2010). Afterwards, in order to evaluate the maximum treatment capability of the system,
169
the HRT was progressively reduced down to 11 h and the OLR increased up to 2
170
kgCOD/m3⋅d by increasing the wastewater volume fed to plant and reducing the duration of
171
the cycle from 8 to 6 h. During this final experimental period, feeding, reaction phase and
172
drawing lasted 15, 330 and 15 minutes, respectively.
173
Treatment performance was evaluated by measuring several parameters of influent and
174
effluent, two or three times per week. Chemical oxygen demand (COD), biochemical
175
oxygen demand (BOD5), total and volatile suspended solids (TSS and VSS), total Kjeldahl
AC C
EP
TE D
M AN U
SC
159
8
ACCEPTED MANUSCRIPT
nitrogen (TKN), ammonia (N-NH4+), total phosphorus (P) and pH were determined using
177
standard methods (APHA, 1998). Total nitrogen (TN) was measured by means of a carbon
178
analyzer (model 5050) with an additional total nitrogen measuring unit (model TNM-1) by
179
Shimadzu Co Japan. Oxidised nitrogen (N-NOx) was calculated as the difference between
180
TN and TKN. Total surfactants were calculated by summing anionic (MBAS; 5540 C), non
181
ionic (LCK 333 of Dr. Lange; DEV H23) and cationic (LCK 331 of Dr. Lange; DEV H 20)
182
surfactants. Colour removal was evaluated as decolourization percentage, measuring the
183
absorbance of the samples in quartz cuvettes with a 1 cm path-length at three wavelengths
184
(426 nm, 558 nm and 660 nm).
185
Biomass concentration in the reactor was determined at the end of the experimental
186
campaign, detaching representative samples of biomass (microbial samples) from three
187
heights of the microbial bed (top, medium and bottom). The sampled bed volume was
188
evaluated as the fraction of carrier elements with respect to 1023, that is the number of
189
carrier elements per litre of bed. The sludge present on the removed carriers was collected
190
in a known volume of tap water, and TSS and VSS were measured.
191
The specific sludge production (SSP) was calculated on the basis of the balance of sludge
192
produced and COD removed during the 200 days of experimentation. Therefore, SSP
193
(gTSS/gCODremoved) was calculated dividing the amount of sludge produced (i.e., biomass
194
accumulation in the reactor bed + solids lost with the effluent + biomass samples) by the
195
amount of COD removed. It should be noted, however, that this is an overestimated value
196
because it includes even the start-up period of the plant characterized by low sludge ages.
AC C
EP
TE D
M AN U
SC
RI PT
176
197
9
ACCEPTED MANUSCRIPT
2.5. Sludge characterization
199
Sludge dewaterability was assessed by determining the capillary suction time (CST, UNI
200
EN 14701-1) and the specific resistance to filtration (SRF, UNI EN 14701-2) of raw sludge
201
samples, without any coagulant addition.
202
CST was measured on the original sludge samples and after stirring at 1000 rpm using a
203
standard stirrer for 10 s, 40 s and 100 s in order to evaluate floc strength, i.e. the ability of
204
flocs to resist erosion (this type of test is particularly suitable to define the capability of
205
sludge to resist the stresses it is exposed to during centrifugation).
206
SRF was measured at three values of pressure (50 kPa, 150 kPa and 350 kPa) in order to
207
determine the compressibility factor s, according to:
208
P SRF = SRF0 P0
209
where P is the applied pressure, P0 is the atmospheric pressure and SRF0 is the value of
210
SRF at P0.
s
TE D
M AN U
SC
RI PT
198
211
2.6. Microbiological characterization
213
Representative samples of biomass were taken from both the Alto Seveso WWTP and the
214
laboratory scale SBBGR to analyse biomass microbial composition. The analysis was
215
performed on two samples from Alto Seveso WWTP (one from the denitrification basin
216
and one from the oxidation basin) and three samples from lab-scale SBBGR (taken at the
217
end of the experimental campaign from three bed heights). Moreover, the inoculum used to
218
start up the SBBGR was analysed.
AC C
EP
212
10
ACCEPTED MANUSCRIPT
Biological activity and the main microbial components were scrutinized through
220
fluorescence in situ hybridization (FISH) analysis, performed according to the procedure
221
described by Amann et al. (1995). Biomass samples were fixed in ethanol (for Gram
222
positive characterization) or paraformaldehyde and ethanol (for Gram negative
223
characterization) and stored at -20 °C. Oligonucleotide probes specific for Alpha-, Beta-,
224
Gamma- and Delta-proteobacteria (ALF968, Bet-42a, Gam-42a and Delta495mix probes,
225
respectively), Flavobacteria (CF319a probe), Actinobacteria (HGC69A), Firmicutes
226
(LGC354mix), Chloroflexi (CFX1223), TM7 division (TM7905), Planctomycetes (Pla46),
227
Thauera/Azoarcus group (THAU646 and AZO644), Alcaligenes-Bordetella (ALBO577)
228
and Archaea (ARC915) were used. Ammonia (Nso1225 probe) and nitrite oxidisers
229
(Ntspa662 and NIT3 probes) were also monitored by FISH. All the hybridizations with
230
group specific probes were carried out simultaneously with probes EUB338, EUB338-II
231
and EUB338-III combined in a mixture (EUB338mix) for the detection of most bacteria
232
and with DAPI staining for the quantification the total number of cells. In order to estimate
233
the amount of bacteria from the total number of cells, DAPI was directly added to the
234
hybridization buffer at a final concentration of 1 µg/ml.
235
Details on oligonucleotide probes are available at probeBase (Loy et al., 2007). All the
236
probes were synthesized with 5’-FITC and -Cy3 labels and purchased from MWG AG
237
Biotech (Germany). Slides were examined under an epifluorescence microscope (Olympus
238
BX51).
239
All microscopic analyses of SBBGR samples were performed on crushed biomass (biofilm
240
and granules). The ratio of bacteria (EUB338mix) over the total number of cells (DAPI
AC C
EP
TE D
M AN U
SC
RI PT
219
11
ACCEPTED MANUSCRIPT
stained cells) was considered as a gross parameter to assess the overall physiological state
242
of bacterial communities and define biomass activity (De Sanctis et al., 2010). In fact,
243
DAPI staining detects all the cells containing DNA (active, not active or even dead).
244
Differently, cell detection by FISH requires that the cell contains at least 103 copies of 16S
245
rRNA (ribosomal RNA) and the presence of several ribosomes approximately indicates that
246
cells are metabolically active.
SC
RI PT
241
247
3. Results and discussion
249
3.1. Treatment performance
250
As reported in paragraph 2.4, after the generation of the particular SBBGR biomass, the
251
HRT was progressively reduced down to 11 h by increasing the hydraulic loading (i.e., by
252
increasing the wastewater volume fed to the plant). Reactor performances (in terms of
253
average values ± standard deviation, and value range) recorded at this value of HRT are
254
summarized in Table 1.
255
The performance of the reactor was really good for all the analysed parameters. COD and
256
TSS concentrations in the effluent from SBBGR were, on average, 42 ± 9 mg/l and 4 ± 2
257
mg/l, respectively, always far below the Italian limits for discharge (125 mg/l and 35 mg/l,
258
respectively), and high percentages of removal were achieved. These results are particularly
259
interesting if considering that the biological stage of centralized plants treating wastewater
260
with high textile contribution often suffers from sludge bulking and foaming problems
261
(Bortone et al., 1995; Mino, 1995).
AC C
EP
TE D
M AN U
248
12
ACCEPTED MANUSCRIPT
Regarding nitrogen, the plant was able to remove 87.5 ± 5.3% of TKN with a residual
263
concentration in the effluent of 4.9 ± 2.4 mg/l, indicating that a stable nitrification process
264
was established, with average concentrations of oxidised nitrogen in the effluent of 7.6 ±
265
4.5 mg/l, contrary to what usually detected in biological systems treating textile
266
wastewater, where the nitrifying biomass activity is usually reduced because of the many
267
textile inhibitory compounds (Rozzi et al., 1999; Bortone et al., 1997). Nitrogen balance
268
also highlights the existence of a somewhat extended denitrification process, although no
269
final anoxic phase was included in the treatment cycle. In fact, less than 1 mg/l of TKN was
270
required for biomass growth, considering a nitrogen request of about 4.5 mgN/gCODremoved,
271
calculated by multiplying sludge production (0.15 gTSS/gCODremoved; see paragraph 3.2)
272
and measured N biomass content (0.03 gN/gTSS).
273
Surfactant removal was satisfactory in terms of both removal percentage (up to 85.4%) and
274
effluent concentration (1.1 ± 0.3 mg/l, always below the limit of 2 mg/l). Despite the
275
removal of colour was not as high as the one observed for all the other parameters, effluent
276
colour was always sufficiently low to allow direct discharge (i.e., colour was not visible
277
after a 20-fold dilution of the sample).
278
Interesting considerations can be formulated if the trends recorded during a typical
279
treatment cycle are observed (Figure 3): while the removal of COD, TSS and total
280
surfactants was nearly completed in 2.5 hours, the removal of nitrogen and colour continued
281
to occur till the end of the cycle. The analysis of COD and TSS removal shows that the
282
system could afford even lower HRT values, as constant COD and TSS values as low as 50
283
and 5 mg/l were measured after only about 2.5 hours. However, as ammonia continued to be
AC C
EP
TE D
M AN U
SC
RI PT
262
13
ACCEPTED MANUSCRIPT
removed throughout the whole cycle duration, nitrogen removal is the limiting step that
285
influences the choice of the maximum OLR and minimum HRT to be adopted, as a further
286
reduction of the HRT below 11 h would not allow the removal of ammonia to be
287
satisfactory.
288
The effectiveness of SBBGR can be appreciated if treatment results are compared with
289
those achieved in the Alto Seveso WWTP in the same period. Table 2 shows effluent
290
concentrations and removal efficiencies of the different treatment stages of Alto Seveso
291
WWTP (i.e., effluent after the biological compartment, effluent after the coagulation-
292
flocculation-clarification stage and final effluent after ozone treatment). While influent
293
and effluent concentrations of the full-scale plant are measured for the daily 24-h flow-
294
proportional composite samples, concentrations after the biological compartment and after
295
coagulation-flocculation-clarification are determined for instantaneous grab samples.
296
As can be seen, the quality of the effluent after SBBGR treatment was much better than
297
the one after the biological compartment of the full scale WWTP. Except for colour,
298
SBBGR assured the attainment of effluent concentrations similar (COD, TKN, NH4+) or
299
even better (TSS, NOx) than the ones of the final effluent after coagulation-flocculation-
300
clarification and ozonation. It is worth underlining that such a result is achieved with a
301
much lower HRT (i.e., 11 hours in SBBGR against about 30 hours in the full scale
302
WWTP), which means lower reactor volumes. Moreover, no chemical dosage was
303
necessary in SBBGR against about 2 mg/l of Al as aluminium salt and 0.8 mg/l of
304
polyeloctrolyte in the coagulation-flocculation-clarification stage and about 8 mg/l of
AC C
EP
TE D
M AN U
SC
RI PT
284
14
ACCEPTED MANUSCRIPT
ozone (of which about 2 mg/l are used in the recycle from the secondary settler to the
306
nitrification tank) in Alto Seveso WWTP.
307
The better performance of SBBGR compared to Alto Seveso WWTP can be ascribed to
308
the particular type of biomass growing in the first system consisting of a mixture of
309
biofilm and granules, completely packed in the filling material of the reactor. This allows
310
a greater retention of the biomass in the system and then a much higher biomass age
311
(higher than 150 d). The packed biomass acts as a filtering medium to remove suspended
312
particulate matter (and the associated COD) from the wastewater whereas the high age of
313
the biomass allows the hydrolysis of the captured solids to produce soluble organic
314
compounds which are then removed by the same biomass.
315
SBBGR results can be also compared with those of Lubello and Gori (2004), who
316
evaluated the efficiency of a membrane bioreactor (MBR) as a treatment capable to
317
substitute a full-scale centralized WWTP (Baciacavallo, Prato, Italy) whose characteristics
318
are similar to the ones of Alto Seveso WWTP. In fact, also the wastewater considered in
319
that study has mainly textile industry origin (80%), with a contribution of domestic
320
wastewater of about 20%. The treatment scheme is based on preliminary treatments
321
(screening, degritting), followed by primary (coagulation–flocculation, primary settling),
322
secondary (biological oxidation, secondary settling) and tertiary ones (clariflocculation,
323
ozonation). Good performances were achieved with MBR, leading to effluent COD values
324
around 60 mg/l independent of inlet loads, complete nitrification (with no nitrite
325
accumulation), good surfactant removal and low permeate absorbance values, with a global
326
removal efficiency similar or higher than the one of the full treatment chain of Baciacavallo
AC C
EP
TE D
M AN U
SC
RI PT
305
15
ACCEPTED MANUSCRIPT
WWTP. A monthly chemical cleaning was, however, carried out in MBR whereas no
328
washing steps were required for SBBGR over 200 days of operation. Moreover, the HRT
329
was about 17-25 h in MBR against 11 h in SBBGR.
RI PT
327
330
3.2. Sludge production and characterization
332
Owing to the up-flow operation of SBBGR, a stratified distribution of biomass was noticed
333
(Table 3). Moreover, also the ratio between the volatile and the total solid content was
334
slightly higher at the bottom and lower at the top: since organic loading is the highest at the
335
filter inlet, bacteria growth and bioactivity are the highest at the filter inlet (Liu et al.,
336
2008). Biomass concentration values in SBBGR are much higher than those measured in
337
the biological compartment of the full-scale WWTP (about 7 kgTSS/m3, which is already
338
quite high for a conventional activated sludge treatment, thanks to ozone dosage in the
339
sludge recycle).
340
The calculated sludge production for SBBGR was 0.15 kgTSS/kgCODremoved, considering
341
also the sludge accumulated in the reactor during the start-up period. If biomass
342
accumulation is not taken into account (as this contribution is practically negligible in
343
steady-state operation) an even lower value of 0.05 kgTSS/kgCODremoved is achieved. These
344
values are remarkably lower than the one of the centralized WWTP Alto Seveso, which
345
amounts to 0.28 ± 0.02 kgTSS/kgCODremoved in the biological compartment, despite the use
346
of ozone to reduce sludge production. Moreover, the global sludge production of the full-
347
scale WWTP is further increased by the chemical sludge produced in the coagulation-
348
flocculation-clarification stage.
AC C
EP
TE D
M AN U
SC
331
16
ACCEPTED MANUSCRIPT
Sludge physical properties for SBBGR and full-scale plant are shown in Table 4.
350
Sludge dewaterability for SBBGR and WTTP sludge is similar. The slightly higher CST
351
values for the sludge sample from the full-scale WWTP are due to the higher sludge
352
content; in fact, the measured values normalized to the solids content are very similar for
353
the two sludge types. The CST values after 100 s of stirring increased by about only 20%
354
with respect to the original sludge sample for both sludge types, indicating the possibility to
355
effectively centrifuge the sludge as it does not break in smaller flocs.
356
Very good filterability was observed, with SRF values below 1013 m/kg for both sludge
357
samples. Bearing in mind that an already conditioned sludge sample is considered to filter
358
well if SRF is lower than 1012 m/kg, the achieved results show a good filterability without
359
conditioning, especially for SBBGR sludge. However, the compressibility factor s close to
360
unity indicates that, despite the good filterability, filtration under pressure is not
361
convenient, as the volume of filtrate does not increase when the pressure is increased.
TE D
M AN U
SC
RI PT
349
362
3.3. Microbiological characterization
364
The results of microbial characterization of the biomass coming from SBBGR and full-
365
scale plant are reported in Table 5.
366
The change in biomass structure from the activated sludge used as inoculum to SBBGR
367
biomass caused a reduction of the active bacterial fraction from 85% to about 45%. Such a
368
reduction is a consequence of both the high sludge age and the low specific biomass
369
organic load (kgCOD/kgVSS.d) in the lab-scale SBBGR compared with activated sludge
370
systems. In more detail, biomass activity was lower at the bottom of the reactor (40%) than
AC C
EP
363
17
ACCEPTED MANUSCRIPT
at the top (50%), because of the higher biomass concentration (40 gTSS/lbed) and, therefore,
372
the lower specific biomass organic load. Nevertheless, the fact that the active biomass
373
fraction in this study is similar to the one observed in other SBBGR systems treating
374
synthetic and real municipal wastewater (Di Iaconi et al. 2010; De Sanctis et al. 2010)
375
indicates the absence of biomass inhibition from the tested mixed municipal-textile
376
wastewater.
377
The analysis of microbial community by means of group-specific probes allowed the
378
identification of about 70-80% of the bacteria in the lab-scale SBBGR and more than 90%
379
in the SBBGR inoculum. SBBGR biomass was quite selected, with Betaproteobacteria
380
representing more than 40% of the active bacteria in the system. Among the bacterial
381
domain the other relevant groups were Actinobacteria and Alphaproteobacteria.
382
Furthermore, a low concentration of Archaea was found (2% of total biomass): however,
383
due to their low concentration, the composition of this domain was not further investigated.
384
The application of more specific probes confirmed the presence of nitrifying and
385
denitrifying bacteria in the system. In particular the first ones represented about 3% and the
386
second ones about 6% of active bacteria in the reactor. Such percentages, apparently low,
387
are in agreement with the efficient nitrogen removal achieved in the lab-scale SBBGR
388
because they correspond to about 0.4 and 0.7 gVSS/lbed of nitrifying and denitrifying
389
bacteria in the reactor, respectively.
390
The analysis of the Alto Seveso WWTP biomass did not show significant differences
391
between the nitrification and denitrification basins in terms of both biomass activity and
392
composition, in agreement with the biological plant scheme that does not include a settler
AC C
EP
TE D
M AN U
SC
RI PT
371
18
ACCEPTED MANUSCRIPT
between the denitrification and the oxidation reactors (single sludge process). The active
394
bacterial fraction represented about 85% of total biomass in both basins: although a high
395
level of bacterial activity should not be expected for a plant treating an industrial
396
wastewater like textile effluents, such a value could be due to the domestic wastewater
397
contribution (about 30% of the influent volume) and to the ozone dosage on the
398
recirculation stream, which could both increase the amount of ready biodegradable COD
399
and reduce the concentration of potential inhibitory compounds in the WWTP influent.
400
However, it must be highlighted that, although the active bacterial fraction in SBBGR is
401
lower than that in Alto Seveso WWTP biomass (i.e., 45% vs 85%), the concentration of
402
active biomass is actually greater in SBBGR thanks to its higher total concentration (5-6
403
times higher). The screening with group-specific probes allowed the identification of about
404
100% of the bacteria in the plant and revealed that the biomass was characterized by higher
405
biodiversity with respect to the SBBGR system. Nevertheless, the three main bacterial
406
groups were the same observed in SBBGR (i.e. Beta- and Alphaproteobacteria and
407
Actinobacteria). According to the nitrogen removal performances of the system, a high
408
amount of nitrifying and denitrifying bacteria was found; the first ones were more abundant
409
in the nitrification tank while the second ones dominated in the denitrification tank.
AC C
EP
TE D
M AN U
SC
RI PT
393
410 411
4. Conclusions
412
SBBGR is suitable for the upgrade of WWTPs treating mixed municipal-textile wastewater
413
because:
414
•
it assures very good treatment results at a low HRT (11 h); 19
ACCEPTED MANUSCRIPT
415
•
ascribable to the high biomass age in the system;
416
•
the sludge shows interesting dewatering and filterability properties.
RI PT
417
it is characterized by a low sludge production (lower than 0.15 kg TSS/kgCODremoved)
SBBGR is more effective than currently adopted treatment solutions: in the full-scale plant
419
treating the same wastewater similar results are achieved only with a more complex
420
treatment (biological treatment, coagulation-flocculation and ozonation), with a higher
421
HRT and sludge production.
SC
418
M AN U
422
Acknowledgements
424
This study was financially supported by Lariana Depur s.p.a., a company operating the
425
wastewater treatment plant Alto Seveso in the textile industrial district of Como (Italy).
426
The authors would like to express their gratitude to Dr. Guido Del Moro and Annalisa
427
Mancini for their support.
428
TE D
423
References
430
Amann, R.I., Ludwig, W., Schleifer, K.-H., 1995. Phylogenetic identification and in situ
431
detection of individual microbial cells without cultivation. Microbiol. Mol. Biol. R. 59,
432
143-169.
433
APHA, AWWA, American Public Health Association and American Water Works
434
Association, 1998. Standard Methods for the Examination of Water and Wastewater, 20th
435
ed. Water Environment Federation, Washington DC.
AC C
EP
429
20
ACCEPTED MANUSCRIPT
Bechtold, T., Burtscher, E., Hung, Y.-T., 2004. Treatment of textile wastes. In: Wang, L.K.,
437
Hung, Y.-T., Lo, H.H., Yapijakis, C. (Eds.), Handbook of industrial and hazardous wastes
438
treatment, 2nd ed. Marcel Dekker Inc., New York, pp. 379-414.
439
Bortone, G., Cech, J.S., Bianchi, R., Tilche, A., 1995. Effects of an anaerobic zone in a
440
textile wastewater treatment plant. Water Sci. Technol. 32(9-10), 133-140.
441
Bortone, G., Gemelli, S., Tilche, A., Bianchi, R., Bergna, G., 1997. A new approach to the
442
evaluation of biological treatability of industrial wastewater for the implementation of the
443
“waste design” concept. Water Sci. Technol. 36(2-3), 81-90.
444
Chen, X., Shen, Z., Zhu, X., Fan, Y., Wang, W., 2005. Advanced treatment of textile
445
wastewater for reuse using electrochemical oxidation and membrane filtration. Water SA
446
31(1), 127-132.
447
Correia, V.M., Stephenson, T., Judd, S.J., 1994. Characterisation of textile wastewaters - a
448
review. Environ. Technol. 15, 917-929.
449
De Sanctis, M., Di Iaconi, C., Lopez, A., Rossetti, S., 2010. Granular biomass structure and
450
population dynamics in Sequencing Batch Biofilter Granular Reactor (SBBGR).
451
Bioresource Technol. 101, 2152-2158.
452
Del Borghi, A., Binaghi, L., Converti, A., Del Borghi, M., 2003. Combined treatment of
453
leachate from sanitary landfill and municipal wastewater by activated sludge. Chem.
454
Biochem. Eng. Q. 17(4), 277-283.
455
Demmin, T.R., Uhrich, K.D., 1988. Improving carpet wastewater treatment. Am. Dyest.
456
Rep. 77(6), 13-18.
AC C
EP
TE D
M AN U
SC
RI PT
436
21
ACCEPTED MANUSCRIPT
Di Iaconi, C., De Sanctis, M., Rossetti, S., Ramadori, R., 2010. SBBGR technology for
458
minimising excess sludge production in biological processes. Water Res. 44 (6), 1825-
459
1832.
460
European Commission, 2009. European Business – Facts and figures. Eurostat Statistical
461
Books. Office for Official Publications of the European Communities, Luxembourg.
462
European Commission, 2011. Eurostat Pocketbooks - Key figures on European business
463
with a special feature on SMEs. Publications Office of the European Union, Luxembourg.
464
Fongsatitkul, P., Elefsiniotis, P., Yamasmit, A., Yamasmit, N., 2004. Use of sequencing
465
batch reactors and Fenton's reagent to treat a wastewater from a textile industry. Biochem.
466
Eng. J. 21, 213-220.
467
Grau, P., 1991. Textile industry wastewaters treatment. Water Sci. Technol. 24(1), 97-103.
468
Lau, W.J., Ismail, A.F., 2009. Polymeric nanofiltration membranes for textile dye
469
wastewater treatment: preparation, performance evaluation, transport modelling and fouling
470
control - a review. Desalination 245, 321-348.
471
Libra, J.A., Sosath, F., 2003. Combination of biological and chemical processes for the
472
treatment of textile wastewater containing reactive dyes. J. Chem. Technol. Biot. 78, 1149-
473
1156.
474
Liu, F., Zhao, C.C., Zhao, D.F., Liu, G.H., 2008. Tertiary treatment of textile wastewater
475
with combined media biological aerated filter (CMBAF) at different hydraulic loadings and
476
dissolved oxygen concentrations. J. Hazard. Mater. 160, 161-167.
AC C
EP
TE D
M AN U
SC
RI PT
457
22
ACCEPTED MANUSCRIPT
Loy, A., Maixner, F., Wagner, M., Horn, M., 2007. ProbeBase - an online resource for
478
rRNA-targeted oligonucleotide probes: new features 2007. Nucleic Acids Res. 35, D800-
479
D804.
480
Lubello, C., Gori, R., 2004. Membrane bio-reactor for advanced textile wastewater
481
treatment and reuse. Water Sci. Technol. 50(2), 113-119.
482
Mino, T., 1995. Survey on filamentous micro-organisms in activated sludge processes in
483
Bangkok, Thailand. Water Sci. Technol. 31(9), 193-202.
484
Ng, W.J., 2006. Industrial wastewater treatment. Imperial College Press, London.
485
Ramesh Babu, B., Parande, A.K., Raghu, S., Prem Kumar ,T., 2007. Cotton textile
486
processing: waste generation and effluent treatment. J. Cotton Sci. 11, 141-153.
487
Rozzi, A., Ficara, E., Cellamare, C., Bortone, G., 1999. Characterization of textile
488
wastewater and other industrial wastewaters by respirometric and titration biosensors.
489
Water Sci. Technol. 40(1), 161-168.
490
Soares, O.S.G.P., Orfao, J.J.M., Portela, D., Vieira, A., Pereira, M.F.R., 2006. Ozonation of
491
textile effluents and dye solutions under continuous operation: influence of operating
492
parameters. J. Hazard. Mater. B137, 1664-1673.
493
Somensi, C.A., Simionatto, E.L., Bertoli, S.L., Wisniewski, A., Radetski, C.M., 2010. Use
494
of ozone in a pilot-scale plant for textile wastewater pre-treatment: physico-chemical
495
efficiency, degradation byproducts dentification and environmental toxicity of treated
496
wastewater. J. Hazard. Mater. 175, 235-240.
AC C
EP
TE D
M AN U
SC
RI PT
477
23
ACCEPTED MANUSCRIPT
Sreedhar Reddy, S., Kotaiah, B., 2006. Comparative evaluation of commercial and sewage
498
sludge based activated carbons for the removal of textile dyes from aqueous solutions. Iran.
499
J. Environ. Healt. 3(4), 239-246.
500
UNI EN 14701-1, 2006. Characterisation of sludges - Filtration properties - Part 1:
501
Capillary suction time (CST).
502
UNI EN 14701-2, 2006. Characterization of sludges - Filtration properties - Part 2:
503
Determination of the specific resistance to filtration.
AC C
EP
TE D
M AN U
504
SC
RI PT
497
24
ACCEPTED MANUSCRIPT
Figure captions
506
Figure 1 – Sketch of the lab-scale SBBGR
507
Figure 2 – Sketch of the Alto Seveso WWTP
508
Figure 3 – Trends recorded during a typical treatment cycle of SBBGR: a) COD
509
concentration (continuous line) and removal (dashed line); b) TSS concentration
510
(continuous line) and removal (dashed line); c) total surfactants concentration (continuous
511
line) and removal (dashed line); d) nitrogen concentrations (TN, TKN, N-NH4+ and N-
512
NOx-; continuous lines) and TN removal (dashed line); e) colour removal at 426, 558 and
513
660 nm
AC C
EP
TE D
M AN U
SC
RI PT
505
25
ACCEPTED MANUSCRIPT
Table 1 – Treatment results achieved with SBBGR at a HRT of 11 h
NH4+
NOx Total surfactants
Colour (426 nm)
Colour (558 nm)
AC C
EP
Colour (660 nm)
Range 186 ÷ 352 22 ÷ 52 76.9 ÷ 88.2 53 ÷ 134 2÷9 92.8 ÷ 96.3 28.8 ÷ 39.7 1.7 ÷ 8.1 79.6 ÷ 94.0 21.7 ÷ 29.4 0 ÷ 4.5 84.0 ÷ 100 0.2 ÷ 0.3 1.5 ÷ 14.7 1.5 ÷ 7.6 0.7 ÷ 1.5 64.9 ÷ 85.4 0.028 ÷ 0.041 0.017 ÷ 0.026 23.5 ÷ 44.1 0.013 ÷ 0.023 0.007 ÷ 0.013 31.6 ÷ 52.2 0.010 ÷ 0.014 0.005 ÷ 0.006 40.0 ÷ 64.3
RI PT
SC
TKN
Mean value 249 ± 65 42 ± 9 82.1 ± 3.6 87 ± 36 4±2 94.7 ± 1.1 34.2 ± 5.1 4.9 ± 2.4 87.5 ± 5.3 25.6 ± 3.4 1.7 ± 2.2 95.0 ± 7.4 0.2 ± 0.1 7.6 ± 4.5 4.7 ± 2.5 1.1 ± 0.3 77.1 ± 7.6 0.035 ± 0.005 0.022 ± 0.003 33.9 ± 8.0 0.019 ± 0.004 0.011 ± 0.002 41.9 ± 6.9 0.012 ± 0.002 0.006 ± 0.001 52.6 ± 9.8
M AN U
TSS
influent (mg/l) effluent (mg/l) removal efficiency (%) influent (mg/l) effluent (mg/l) removal efficiency (%) influent (mgN/l) effluent (mgN/l) removal efficiency (%) influent (mgN/l) effluent (mgN/l) removal efficiency (%) influent (mgN/l) effluent (mgN/l) influent (mg/l) effluent (mg/l) removal efficiency (%) influent (abs) effluent (abs) removal efficiency (%) influent (abs) effluent (abs) removal efficiency (%) influent (abs) effluent (abs) removal efficiency (%)
TE D
Parameter COD
ACCEPTED MANUSCRIPT
Table 2 – Performance of the Alto Seveso WWTP (average values ± standard deviation).
TKN
NH4+
NOx-
AC C
EP
TE D
Colour
RI PT
TSS
influent [mg/l] effluent [mg/l] removal [%] influent [mg/l] effluent [mg/l] removal [%] influent [mgN/l] effluent [mgN/l] removal [%] influent [mgN/l] effluent [mgN/l] removal [%] influent [mgN/l] effluent [mgN/l] 426 nm: removal [%] 558 nm: removal [%] 660 nm: removal [%]
SC
COD
M AN U
Parameter
Alto Seveso WWTP After After After biological coagulation ozonation compartment flocculation (final effluent) clarification 241 ± 56 52 ± 25 40 ± 20 66 ± 24 77.9 ± 7.4 82.4 ± 9.5 71.5 ± 9.2 80 ± 17 23 ± 9 19 ± 6 16 ± 7 73.0 ± 7.8 80.2 ± 7.9 68.3 ± 10.5 31.9 ± 7.6 4.7 ± 2.4 85.1 ± 7.1 19.9 ± 6.0 1.4 ± 1.7 1.3 ± 2.4 94.1 ± 8.8 93.2 ± 7.7 1.9 ± 1.1 11.1 ± 1.4 11.1 ± 2.7 40.4 ± 17.5 67.4 ± 16.8 32.9 ± 17.2 37.1 ± 19.0 42.8 ± 19.7 73.7 ± 16.3 50.9 ± 16.7 76.0 ± 14.9 41.8 ± 19.6
ACCEPTED MANUSCRIPT
Table 3 – Biomass concentration in SBBGR VSS concentration [kgVSS/m3]
VSS/TSS [%]
Top
26.0
19.3
74.2
Medium
29.9
22.7
Bottom
39.8
30.7
RI PT
TSS concentration [kgTSS/m3]
76.0 77.1
AC C
EP
TE D
M AN U
SC
REACTOR POSITION
ACCEPTED MANUSCRIPT
Table 4 – Physical characterization of SBBGR and Alto Seveso WWTP sludge. TSS [g/l]
SBBGR WWTP
11.1 16.9
0s 16.0 25.8
CST [s] 10 s 40 s 17.9 18.5 27.9 30.4
100 s 19.3 30.7
50 kPa 5.5 . 1011 1.9 . 1012
SRF [m/kg] 150 kPa 350 kPa 2.5 . 1012 4.1 . 1012 5.4 . 1012 1.2 . 1013
AC C
EP
TE D
M AN U
SC
RI PT
SLUDGE
s 1.000006 1.000007
ACCEPTED MANUSCRIPT
Table 5 – Microbial characterization of SBBGR and Alto Seveso WWTP biomass by FISH analysis (n.d. = not detected). Target microbial group / total DAPI stained biomass [%]
Ammonia-oxidizing bacteria Nitrite-oxidizing bacteria Denitrifying bacteria (Thauera + Azoarcus + Alcaligenes-Bordetella) Sulphate-reducing bacteria
83 15 28 31 n.d. 3 ≤ 0.5 ≤ 0.5 9
≤ 0.5
5
4
≤ 0.5 3
≤ 0.5 1
3 ≤ 0.5
1 4
n.d.
n.d.
n.d.
n.d.
2
2
3
5
85 16 19 20 n.d. 20 ≤ 0.5 n.d. 10
49 8 8 17 n.d. 1 1 n.d. 4
41 5 3 20 n.d. 1 1 n.d. ≤ 0.5
40 6 3 18 n.d. ≤ 0.5 n.d. n.d. ≤ 0.5
2
1
1
n.d. 0.7
1 4
n.d.
n.d.
3
2
SC
Top
RI PT 85 15 29 30 n.d. 4 ≤ 0.5 ≤ 0.5 10
Medium
EP AC C
Denitrification basin
Bottom
TE D
Archaea
Nitrification basin
Inoculum
M AN U
Bacteria Actinobacteria Alphaproteobacteria Betaproteobacteria Chloroflexi Gammaproteobacteria Deltaproteobacteria Firmicutes Flavobacteria
Alto Seveso WWTP
SBBGR
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
SBBGR is suitable to treat mixed municipal-textile wastewater
•
very good treatment results can be achieved at a low HRT (11 h)
•
a low sludge quantity with interesting dewaterability and filterability is produced
•
SBBGR can effectively replace a complex 30-h HRT treatment scheme
AC C
EP
TE D
M AN U
SC
RI PT
•
PII:
S0043-1354(14)00095-5
DOI:
10.1016/j.watres.2014.01.055
Reference:
WR 10458
To appear in:
Water Research
Received Date: 20 October 2013 Revised Date:
21 December 2013
Accepted Date: 27 January 2014
Please cite this article as: Lotito, A.M., De Sanctis, M., Di Iaconi, C., Bergna, G., Textile wastewater treatment: aerobic granular sludge vs activated sludge systems, Water Research (2014), doi: 10.1016/ j.watres.2014.01.055. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
Textile wastewater treatment: aerobic granular sludge vs activated sludge
2
systems
3
Adriana Maria Lotitoa,*, Marco De Sanctisb, Claudio Di Iaconib,*, Giovanni Bergnac
4
a
Department of Water Engineering and Chemistry, Politecnico di Bari, via Orabona 4, 70125 – Bari, Italy
5
b
CNR-IRSA, Water Research Institute - National Research Council, viale De Blasio 5, 70132 – Bari, Italy
6
c
CIDA S.p.A., via Laghetto 1, 22073 – Fino Mornasco (CO), Italy
SC
RI PT
1
7 * Corresponding authors:
9
Adriana Maria Lotito: e-mail address: [email protected]; Tel: +393403005056;
M AN U
8
10
Claudio Di Iaconi: e-mail address: [email protected]; Tel: +390805820525; Fax:
11
+390805313365
12
Abstract
14
Textile effluents are characterised by high content of recalcitrant compounds and are often
15
discharged (together with municipal wastewater to increase their treatability) into centralized
16
wastewater treatment plants with a complex treatment scheme. This paper reports the results
17
achieved adopting a granular sludge system (sequencing batch biofilter granular reactor – SBBGR)
18
to treat mixed municipal-textile wastewater. Thanks to high average removals in SBBGR (82.1%
19
chemical oxygen demand, 94.7% total suspended solids, 87.5% total Kjeldahl nitrogen, 77.1%
20
surfactants), the Italian limits for discharge into a water receiver can be complied with the
21
biological stage alone. The comparison with the performance of the centralized plant treating the
22
same wastewater has showed that SBBGR system is able to produce an effluent of comparable
AC C
EP
TE D
13
ACCEPTED MANUSCRIPT
23
quality with a simpler treatment scheme, a much lower hydraulic residence time (11 h against 30 h)
24
and a lower sludge production.
RI PT
25 26
Keywords
27
textile effluents; SBBGR treatment; centralized treatment plant; ozonation; sludge
28
production
SC
29
1. Introduction
31
The textile sector is of great importance in the European economy: the manufacture of
32
textiles, clothing and leather was the main activity of over 267,000 enterprises in the
33
Member States in 2006 (European Commission, 2009) and textiles and wearing apparel
34
accounted for about 3.6% of the EU-27 manufacturing in terms of value added and 6.3% in
35
terms of employment in 2008 (European Commission, 2011). In particular, Italy is the
36
leading producer, generating about one third (33.6%) of EU-27 value added in this sector in
37
2006, followed by Germany (12.1%), France (11.6%), Spain (9.2%) and the United
38
Kingdom (7.8%) (European Commission, 2009). Moreover, Italy is the only specialised
39
State, as in 2006 this sector contributed 3.4% of the value added generated in its non-
40
financial business economy, three times the average contribution recorded across the EU-27
41
(European Commission, 2009).
42
An important environmental issue related to such a relevant economic sector is the
43
production and discharge of big volumes of highly polluted wastewater, due to the
44
consumption of about 100-200 l of water per kg of textile product (Bechtold et al., 2004)
AC C
EP
TE D
M AN U
30
2
ACCEPTED MANUSCRIPT
and to the use of an immense range of materials and chemicals (dyes, process aids and
46
finishing products) in the production chain (Correia et al., 1994).
47
Despite on-site treatment can be the optimal solution to promote water recycle, such an
48
option is generally not affordable for small enterprises, especially those working on the
49
most polluting processing stages (dyeing, printing and finishing steps): in fact, any
50
conventional treatment method applied individually is usually not capable to successfully
51
remove all the diverse pollutants present in textile wastewater and to tackle the large
52
variability in composition, producing limited results in terms of overall reduction in organic
53
matter, nutrients and colour (Demmin and Uhrich, 1998; Fongsatitkul et al., 2004; Soares et
54
al., 2006; Lau and Ismail, 2009). Thus, the usual treatment scheme consists of a
55
combination of biological and physico-chemical processes like chemical precipitation,
56
coagulation-flocculation, adsorption on activated carbons, ion-exchange, electrochemical
57
processes, etc. (Chen et al., 2005; Sreedhar Reddy and Kotaiah, 2006; Ramesh-Babu et al.,
58
2007; Somensi et al., 2010). Due to the complexity of the sequence of treatments, to the
59
need for large areas and to the high capital and operating costs (Ramesh-Babu et al., 2007),
60
it is often necessary to treat effluents in centralized plants rather than on-site at each
61
factory.
62
Hence, most of the wastewater from the textile industry is currently mixed and discharged
63
to municipal wastewater treatment plants with little or even no pre-treatment (Libra and
64
Sosath, 2003). In fact, when centralized treatment is performed, the joint treatment with
65
municipal wastewater is considered to be the optimum alternative, as it can help to solve
66
many difficulties such as the extreme fluctuations in flow and wastewater composition
AC C
EP
TE D
M AN U
SC
RI PT
45
3
ACCEPTED MANUSCRIPT
(Grau, 1991). Moreover, the municipal contribution supplies nitrogen and phosphorus
68
(necessary for the biological process) and increases the biodegradable fraction of the
69
wastewater (Grau, 1991). The domestic component is expected to provide some buffering
70
in terms of the characteristics of the combined flow and, therefore, to enable an easier
71
treatment of combined wastewater compared to individual treatment of industrial effluents
72
on their own (Ng, 2006). The combined treatment of industrial and domestic wastewater
73
could represent an economically-feasible alternative in which the degradation of organic
74
pollutants is favoured by dilution and adaptation ability of the activated sludge (Del Borghi
75
et al., 2003).
76
However, due to the high amount of hydrophobic compounds present in the textile
77
component, the biological stage of the centralized plant often suffers from sludge bulking
78
and foaming problems (Bortone et al., 1995; Mino, 1995). Furthermore, a tertiary treatment
79
stage is required to remove refractory compounds and colour, with a consequent increase in
80
treatment scheme complexity and capital and operating costs. This stage is often based on a
81
coagulation-flocculation treatment followed by ozonation.
82
In order to simplify the treatment scheme and reduce treatment costs, the use of more
83
efficient innovative technologies in the existing centralized wastewater treatment plants is a
84
research field of major interest, especially in countries like Italy, in which the textile
85
industry is mainly composed of numerous small and medium-sized enterprises, which are
86
specialized on specific productions or processing steps and are located in some areas
87
known as textile districts.
AC C
EP
TE D
M AN U
SC
RI PT
67
4
ACCEPTED MANUSCRIPT
The aim of this paper is to prove the suitability of an innovative biological system
89
(sequencing batch biofilter granular reactor – SBBGR) for the treatment of textile
90
wastewaters mixed with municipal ones. The SBBGR system consists of a single basin into
91
which the wastewater is fed, treated and then discharged. It combines the advantages of
92
attached biomass systems (greater robustness and compactness) with those of periodic
93
systems (greater flexibility and stability). SBBGR is, however, a unique system in virtue of
94
the particular type of biomass growing in it (a mixture of biofilm and granules packed in a
95
filling material) which allows a greater retention of the biomass in the reactor (up to one
96
order of magnitude higher than that recorded in conventional biological systems). As a
97
result, remarkable improvements in substrate conversion capacities and sludge production
98
are achieved (Di Iaconi et al., 2010).
99
In this paper, the performance of SBBGR system is compared with the one of the full scale
100
wastewater treatment plant in which the wastewater is currently treated (Alto Seveso, Fino
101
Mornasco, Como, Italy). A detailed analysis, which includes also biomass characterization,
102
shows the peculiar advantages of SBBGR.
SC
M AN U
TE D
EP
103
RI PT
88
2. Materials and methods
105
2.1. Como textile district
106
Mixed municipal-textile wastewater was taken from the centralized wastewater treatment
107
plant (WWTP) Alto Seveso (Fino Mornasco, Italy), located in the textile district of Como.
108
This wide district includes about 1040 industries located in 27 towns, mainly devoted to the
109
treatment of silk and silky fibres. The activity is mostly based on a high number of small
AC C
104
5
ACCEPTED MANUSCRIPT
specialized factories operating on a single stage of the entire textile processing chain (i.e.,
111
twisting, weaving, dyeing, printing, finishing, etc.). The predominant activities are those
112
related to dyeing, printing and finishing operations, which are also the most polluting stages
113
in the textile chain. The produced wastewater is treated in several wastewater treatment
114
plants (the largest four plants globally treat about 100,000 m3 per day, considering both
115
textile and domestic contribution).
SC
RI PT
110
116
2.2. Lab-scale SBBGR
118
The experimental campaign was carried out using a lab-scale SBBGR prototype (Figure 1),
119
which consisted of a 1 m Plexiglas cylinder with internal diameter of 190 mm. The bottom
120
of the reactor (microbial bed; volume: 9 l) was filled with plastic support material for
121
biomass development (wheel shaped plastic elements KMT-k1 from Kaldnes, Norway; 10
122
mm diameter, 7 mm height, 630 m2/m3 specific surface, 950 kg/m3 density, 0.75 porosity)
123
packed between two sieves. In order to start-up the reactor, activated sludge from a local
124
municipal WWTP was used as inoculum.
125
The operation of the reactor was based on treatment cycles, each consisting of three
126
consecutive phases (namely filling, reaction and drawing). During the filling phase (few
127
minutes), a fixed volume of wastewater was added from the bottom of the reactor to the
128
liquid volume retained from the previous treatment cycle using a peristaltic pump. In the
129
reaction phase, the filled wastewater was continuously aerated (with the exception of the
130
first hour for denitrification) by air injection through porous stones placed close to the
131
upper sieve and recycled through the biomass supporting material using a recycle pump, in
AC C
EP
TE D
M AN U
117
6
ACCEPTED MANUSCRIPT
order to obtain a homogeneous distribution of substrate and oxygen. Finally, the treated
133
wastewater was discharged by gravity using a port located in the liquid phase over the bed
134
through the opening of a motorized valve (duration of the drawing phase: 15 min).
135
A pressure meter at the bottom of the reactor was used to measure biofilter head losses due
136
to biomass growth and entrapped suspended solids contained in the influent and to plan a
137
washing step with compressed air to decrease head loss down to the low set-point,
138
whenever a fixed head loss value was reached (high set-point).
SC
RI PT
132
M AN U
139
2.3. Alto Seveso wastewater treatment plant
141
The Alto Seveso WWTP treats about 8 million m3/year and serves around 80,000
142
population equivalents (PEs), with a civil contribution of 30,000 PEs and an industrial one
143
of 50,000 PEs. The industrial wastewater mostly comes from textile industries (97%), and
144
in particular from printing factories (38%), dyeing factories (28%) and factories in which
145
both dyeing and printing operations are performed (31%).
146
The treatment scheme consists of numerous steps, which encompass preliminary, biological
147
and tertiary treatments (the total hydraulic retention time of the latter two is about 30 hours)
148
(Figure 2). The preliminary treatments (grit removal, screening, sand removal) are intended
149
to remove coarse suspended matters such as grit, sand and rags, pieces of fabric, fibres,
150
yarns. The biological compartment consists of a conventional activated sludge plant
151
composed of a pre-denitrification stage, followed by biological oxidation and secondary
152
settling. Ozone is dosed on part of the recycle from the secondary settler to the biological
153
basin in order to reduce sludge production and to solve some operational problems due to
AC C
EP
TE D
140
7
ACCEPTED MANUSCRIPT
filamentous bacteria growth and consequent biological foam (sludge bulking problems and
155
hindered sedimentation). Then, tertiary treatments (coagulation-flocculation, clarification
156
and ozonation) are required to remove suspended solids, recalcitrant compounds and
157
colour.
RI PT
154
158
2.4. Treatment performance
160
The influent to the biological compartment of the Alto Seveso WWTP, after preliminary
161
treatments to remove grit, sand and coarse material, was used in our tests. The experimental
162
SBBGR campaign lasted 200 days. During the first 3 months of the experimentation
163
particular attention was paid to the generation of the particular biomass of SBBGR (i.e., a
164
mixture of biofilm and granules packed in the filling material) by operating with a high
165
value of hydraulic retention time (HRT), i.e. 25-30 h, and 8 h-treatment cycles. Thanks to
166
the design of the reactor, granulation is simply achieved using such a slow increasing step-
167
feed approach: more details about the start-up of a SBBGR can be found in De Sanctis et al.
168
(2010). Afterwards, in order to evaluate the maximum treatment capability of the system,
169
the HRT was progressively reduced down to 11 h and the OLR increased up to 2
170
kgCOD/m3⋅d by increasing the wastewater volume fed to plant and reducing the duration of
171
the cycle from 8 to 6 h. During this final experimental period, feeding, reaction phase and
172
drawing lasted 15, 330 and 15 minutes, respectively.
173
Treatment performance was evaluated by measuring several parameters of influent and
174
effluent, two or three times per week. Chemical oxygen demand (COD), biochemical
175
oxygen demand (BOD5), total and volatile suspended solids (TSS and VSS), total Kjeldahl
AC C
EP
TE D
M AN U
SC
159
8
ACCEPTED MANUSCRIPT
nitrogen (TKN), ammonia (N-NH4+), total phosphorus (P) and pH were determined using
177
standard methods (APHA, 1998). Total nitrogen (TN) was measured by means of a carbon
178
analyzer (model 5050) with an additional total nitrogen measuring unit (model TNM-1) by
179
Shimadzu Co Japan. Oxidised nitrogen (N-NOx) was calculated as the difference between
180
TN and TKN. Total surfactants were calculated by summing anionic (MBAS; 5540 C), non
181
ionic (LCK 333 of Dr. Lange; DEV H23) and cationic (LCK 331 of Dr. Lange; DEV H 20)
182
surfactants. Colour removal was evaluated as decolourization percentage, measuring the
183
absorbance of the samples in quartz cuvettes with a 1 cm path-length at three wavelengths
184
(426 nm, 558 nm and 660 nm).
185
Biomass concentration in the reactor was determined at the end of the experimental
186
campaign, detaching representative samples of biomass (microbial samples) from three
187
heights of the microbial bed (top, medium and bottom). The sampled bed volume was
188
evaluated as the fraction of carrier elements with respect to 1023, that is the number of
189
carrier elements per litre of bed. The sludge present on the removed carriers was collected
190
in a known volume of tap water, and TSS and VSS were measured.
191
The specific sludge production (SSP) was calculated on the basis of the balance of sludge
192
produced and COD removed during the 200 days of experimentation. Therefore, SSP
193
(gTSS/gCODremoved) was calculated dividing the amount of sludge produced (i.e., biomass
194
accumulation in the reactor bed + solids lost with the effluent + biomass samples) by the
195
amount of COD removed. It should be noted, however, that this is an overestimated value
196
because it includes even the start-up period of the plant characterized by low sludge ages.
AC C
EP
TE D
M AN U
SC
RI PT
176
197
9
ACCEPTED MANUSCRIPT
2.5. Sludge characterization
199
Sludge dewaterability was assessed by determining the capillary suction time (CST, UNI
200
EN 14701-1) and the specific resistance to filtration (SRF, UNI EN 14701-2) of raw sludge
201
samples, without any coagulant addition.
202
CST was measured on the original sludge samples and after stirring at 1000 rpm using a
203
standard stirrer for 10 s, 40 s and 100 s in order to evaluate floc strength, i.e. the ability of
204
flocs to resist erosion (this type of test is particularly suitable to define the capability of
205
sludge to resist the stresses it is exposed to during centrifugation).
206
SRF was measured at three values of pressure (50 kPa, 150 kPa and 350 kPa) in order to
207
determine the compressibility factor s, according to:
208
P SRF = SRF0 P0
209
where P is the applied pressure, P0 is the atmospheric pressure and SRF0 is the value of
210
SRF at P0.
s
TE D
M AN U
SC
RI PT
198
211
2.6. Microbiological characterization
213
Representative samples of biomass were taken from both the Alto Seveso WWTP and the
214
laboratory scale SBBGR to analyse biomass microbial composition. The analysis was
215
performed on two samples from Alto Seveso WWTP (one from the denitrification basin
216
and one from the oxidation basin) and three samples from lab-scale SBBGR (taken at the
217
end of the experimental campaign from three bed heights). Moreover, the inoculum used to
218
start up the SBBGR was analysed.
AC C
EP
212
10
ACCEPTED MANUSCRIPT
Biological activity and the main microbial components were scrutinized through
220
fluorescence in situ hybridization (FISH) analysis, performed according to the procedure
221
described by Amann et al. (1995). Biomass samples were fixed in ethanol (for Gram
222
positive characterization) or paraformaldehyde and ethanol (for Gram negative
223
characterization) and stored at -20 °C. Oligonucleotide probes specific for Alpha-, Beta-,
224
Gamma- and Delta-proteobacteria (ALF968, Bet-42a, Gam-42a and Delta495mix probes,
225
respectively), Flavobacteria (CF319a probe), Actinobacteria (HGC69A), Firmicutes
226
(LGC354mix), Chloroflexi (CFX1223), TM7 division (TM7905), Planctomycetes (Pla46),
227
Thauera/Azoarcus group (THAU646 and AZO644), Alcaligenes-Bordetella (ALBO577)
228
and Archaea (ARC915) were used. Ammonia (Nso1225 probe) and nitrite oxidisers
229
(Ntspa662 and NIT3 probes) were also monitored by FISH. All the hybridizations with
230
group specific probes were carried out simultaneously with probes EUB338, EUB338-II
231
and EUB338-III combined in a mixture (EUB338mix) for the detection of most bacteria
232
and with DAPI staining for the quantification the total number of cells. In order to estimate
233
the amount of bacteria from the total number of cells, DAPI was directly added to the
234
hybridization buffer at a final concentration of 1 µg/ml.
235
Details on oligonucleotide probes are available at probeBase (Loy et al., 2007). All the
236
probes were synthesized with 5’-FITC and -Cy3 labels and purchased from MWG AG
237
Biotech (Germany). Slides were examined under an epifluorescence microscope (Olympus
238
BX51).
239
All microscopic analyses of SBBGR samples were performed on crushed biomass (biofilm
240
and granules). The ratio of bacteria (EUB338mix) over the total number of cells (DAPI
AC C
EP
TE D
M AN U
SC
RI PT
219
11
ACCEPTED MANUSCRIPT
stained cells) was considered as a gross parameter to assess the overall physiological state
242
of bacterial communities and define biomass activity (De Sanctis et al., 2010). In fact,
243
DAPI staining detects all the cells containing DNA (active, not active or even dead).
244
Differently, cell detection by FISH requires that the cell contains at least 103 copies of 16S
245
rRNA (ribosomal RNA) and the presence of several ribosomes approximately indicates that
246
cells are metabolically active.
SC
RI PT
241
247
3. Results and discussion
249
3.1. Treatment performance
250
As reported in paragraph 2.4, after the generation of the particular SBBGR biomass, the
251
HRT was progressively reduced down to 11 h by increasing the hydraulic loading (i.e., by
252
increasing the wastewater volume fed to the plant). Reactor performances (in terms of
253
average values ± standard deviation, and value range) recorded at this value of HRT are
254
summarized in Table 1.
255
The performance of the reactor was really good for all the analysed parameters. COD and
256
TSS concentrations in the effluent from SBBGR were, on average, 42 ± 9 mg/l and 4 ± 2
257
mg/l, respectively, always far below the Italian limits for discharge (125 mg/l and 35 mg/l,
258
respectively), and high percentages of removal were achieved. These results are particularly
259
interesting if considering that the biological stage of centralized plants treating wastewater
260
with high textile contribution often suffers from sludge bulking and foaming problems
261
(Bortone et al., 1995; Mino, 1995).
AC C
EP
TE D
M AN U
248
12
ACCEPTED MANUSCRIPT
Regarding nitrogen, the plant was able to remove 87.5 ± 5.3% of TKN with a residual
263
concentration in the effluent of 4.9 ± 2.4 mg/l, indicating that a stable nitrification process
264
was established, with average concentrations of oxidised nitrogen in the effluent of 7.6 ±
265
4.5 mg/l, contrary to what usually detected in biological systems treating textile
266
wastewater, where the nitrifying biomass activity is usually reduced because of the many
267
textile inhibitory compounds (Rozzi et al., 1999; Bortone et al., 1997). Nitrogen balance
268
also highlights the existence of a somewhat extended denitrification process, although no
269
final anoxic phase was included in the treatment cycle. In fact, less than 1 mg/l of TKN was
270
required for biomass growth, considering a nitrogen request of about 4.5 mgN/gCODremoved,
271
calculated by multiplying sludge production (0.15 gTSS/gCODremoved; see paragraph 3.2)
272
and measured N biomass content (0.03 gN/gTSS).
273
Surfactant removal was satisfactory in terms of both removal percentage (up to 85.4%) and
274
effluent concentration (1.1 ± 0.3 mg/l, always below the limit of 2 mg/l). Despite the
275
removal of colour was not as high as the one observed for all the other parameters, effluent
276
colour was always sufficiently low to allow direct discharge (i.e., colour was not visible
277
after a 20-fold dilution of the sample).
278
Interesting considerations can be formulated if the trends recorded during a typical
279
treatment cycle are observed (Figure 3): while the removal of COD, TSS and total
280
surfactants was nearly completed in 2.5 hours, the removal of nitrogen and colour continued
281
to occur till the end of the cycle. The analysis of COD and TSS removal shows that the
282
system could afford even lower HRT values, as constant COD and TSS values as low as 50
283
and 5 mg/l were measured after only about 2.5 hours. However, as ammonia continued to be
AC C
EP
TE D
M AN U
SC
RI PT
262
13
ACCEPTED MANUSCRIPT
removed throughout the whole cycle duration, nitrogen removal is the limiting step that
285
influences the choice of the maximum OLR and minimum HRT to be adopted, as a further
286
reduction of the HRT below 11 h would not allow the removal of ammonia to be
287
satisfactory.
288
The effectiveness of SBBGR can be appreciated if treatment results are compared with
289
those achieved in the Alto Seveso WWTP in the same period. Table 2 shows effluent
290
concentrations and removal efficiencies of the different treatment stages of Alto Seveso
291
WWTP (i.e., effluent after the biological compartment, effluent after the coagulation-
292
flocculation-clarification stage and final effluent after ozone treatment). While influent
293
and effluent concentrations of the full-scale plant are measured for the daily 24-h flow-
294
proportional composite samples, concentrations after the biological compartment and after
295
coagulation-flocculation-clarification are determined for instantaneous grab samples.
296
As can be seen, the quality of the effluent after SBBGR treatment was much better than
297
the one after the biological compartment of the full scale WWTP. Except for colour,
298
SBBGR assured the attainment of effluent concentrations similar (COD, TKN, NH4+) or
299
even better (TSS, NOx) than the ones of the final effluent after coagulation-flocculation-
300
clarification and ozonation. It is worth underlining that such a result is achieved with a
301
much lower HRT (i.e., 11 hours in SBBGR against about 30 hours in the full scale
302
WWTP), which means lower reactor volumes. Moreover, no chemical dosage was
303
necessary in SBBGR against about 2 mg/l of Al as aluminium salt and 0.8 mg/l of
304
polyeloctrolyte in the coagulation-flocculation-clarification stage and about 8 mg/l of
AC C
EP
TE D
M AN U
SC
RI PT
284
14
ACCEPTED MANUSCRIPT
ozone (of which about 2 mg/l are used in the recycle from the secondary settler to the
306
nitrification tank) in Alto Seveso WWTP.
307
The better performance of SBBGR compared to Alto Seveso WWTP can be ascribed to
308
the particular type of biomass growing in the first system consisting of a mixture of
309
biofilm and granules, completely packed in the filling material of the reactor. This allows
310
a greater retention of the biomass in the system and then a much higher biomass age
311
(higher than 150 d). The packed biomass acts as a filtering medium to remove suspended
312
particulate matter (and the associated COD) from the wastewater whereas the high age of
313
the biomass allows the hydrolysis of the captured solids to produce soluble organic
314
compounds which are then removed by the same biomass.
315
SBBGR results can be also compared with those of Lubello and Gori (2004), who
316
evaluated the efficiency of a membrane bioreactor (MBR) as a treatment capable to
317
substitute a full-scale centralized WWTP (Baciacavallo, Prato, Italy) whose characteristics
318
are similar to the ones of Alto Seveso WWTP. In fact, also the wastewater considered in
319
that study has mainly textile industry origin (80%), with a contribution of domestic
320
wastewater of about 20%. The treatment scheme is based on preliminary treatments
321
(screening, degritting), followed by primary (coagulation–flocculation, primary settling),
322
secondary (biological oxidation, secondary settling) and tertiary ones (clariflocculation,
323
ozonation). Good performances were achieved with MBR, leading to effluent COD values
324
around 60 mg/l independent of inlet loads, complete nitrification (with no nitrite
325
accumulation), good surfactant removal and low permeate absorbance values, with a global
326
removal efficiency similar or higher than the one of the full treatment chain of Baciacavallo
AC C
EP
TE D
M AN U
SC
RI PT
305
15
ACCEPTED MANUSCRIPT
WWTP. A monthly chemical cleaning was, however, carried out in MBR whereas no
328
washing steps were required for SBBGR over 200 days of operation. Moreover, the HRT
329
was about 17-25 h in MBR against 11 h in SBBGR.
RI PT
327
330
3.2. Sludge production and characterization
332
Owing to the up-flow operation of SBBGR, a stratified distribution of biomass was noticed
333
(Table 3). Moreover, also the ratio between the volatile and the total solid content was
334
slightly higher at the bottom and lower at the top: since organic loading is the highest at the
335
filter inlet, bacteria growth and bioactivity are the highest at the filter inlet (Liu et al.,
336
2008). Biomass concentration values in SBBGR are much higher than those measured in
337
the biological compartment of the full-scale WWTP (about 7 kgTSS/m3, which is already
338
quite high for a conventional activated sludge treatment, thanks to ozone dosage in the
339
sludge recycle).
340
The calculated sludge production for SBBGR was 0.15 kgTSS/kgCODremoved, considering
341
also the sludge accumulated in the reactor during the start-up period. If biomass
342
accumulation is not taken into account (as this contribution is practically negligible in
343
steady-state operation) an even lower value of 0.05 kgTSS/kgCODremoved is achieved. These
344
values are remarkably lower than the one of the centralized WWTP Alto Seveso, which
345
amounts to 0.28 ± 0.02 kgTSS/kgCODremoved in the biological compartment, despite the use
346
of ozone to reduce sludge production. Moreover, the global sludge production of the full-
347
scale WWTP is further increased by the chemical sludge produced in the coagulation-
348
flocculation-clarification stage.
AC C
EP
TE D
M AN U
SC
331
16
ACCEPTED MANUSCRIPT
Sludge physical properties for SBBGR and full-scale plant are shown in Table 4.
350
Sludge dewaterability for SBBGR and WTTP sludge is similar. The slightly higher CST
351
values for the sludge sample from the full-scale WWTP are due to the higher sludge
352
content; in fact, the measured values normalized to the solids content are very similar for
353
the two sludge types. The CST values after 100 s of stirring increased by about only 20%
354
with respect to the original sludge sample for both sludge types, indicating the possibility to
355
effectively centrifuge the sludge as it does not break in smaller flocs.
356
Very good filterability was observed, with SRF values below 1013 m/kg for both sludge
357
samples. Bearing in mind that an already conditioned sludge sample is considered to filter
358
well if SRF is lower than 1012 m/kg, the achieved results show a good filterability without
359
conditioning, especially for SBBGR sludge. However, the compressibility factor s close to
360
unity indicates that, despite the good filterability, filtration under pressure is not
361
convenient, as the volume of filtrate does not increase when the pressure is increased.
TE D
M AN U
SC
RI PT
349
362
3.3. Microbiological characterization
364
The results of microbial characterization of the biomass coming from SBBGR and full-
365
scale plant are reported in Table 5.
366
The change in biomass structure from the activated sludge used as inoculum to SBBGR
367
biomass caused a reduction of the active bacterial fraction from 85% to about 45%. Such a
368
reduction is a consequence of both the high sludge age and the low specific biomass
369
organic load (kgCOD/kgVSS.d) in the lab-scale SBBGR compared with activated sludge
370
systems. In more detail, biomass activity was lower at the bottom of the reactor (40%) than
AC C
EP
363
17
ACCEPTED MANUSCRIPT
at the top (50%), because of the higher biomass concentration (40 gTSS/lbed) and, therefore,
372
the lower specific biomass organic load. Nevertheless, the fact that the active biomass
373
fraction in this study is similar to the one observed in other SBBGR systems treating
374
synthetic and real municipal wastewater (Di Iaconi et al. 2010; De Sanctis et al. 2010)
375
indicates the absence of biomass inhibition from the tested mixed municipal-textile
376
wastewater.
377
The analysis of microbial community by means of group-specific probes allowed the
378
identification of about 70-80% of the bacteria in the lab-scale SBBGR and more than 90%
379
in the SBBGR inoculum. SBBGR biomass was quite selected, with Betaproteobacteria
380
representing more than 40% of the active bacteria in the system. Among the bacterial
381
domain the other relevant groups were Actinobacteria and Alphaproteobacteria.
382
Furthermore, a low concentration of Archaea was found (2% of total biomass): however,
383
due to their low concentration, the composition of this domain was not further investigated.
384
The application of more specific probes confirmed the presence of nitrifying and
385
denitrifying bacteria in the system. In particular the first ones represented about 3% and the
386
second ones about 6% of active bacteria in the reactor. Such percentages, apparently low,
387
are in agreement with the efficient nitrogen removal achieved in the lab-scale SBBGR
388
because they correspond to about 0.4 and 0.7 gVSS/lbed of nitrifying and denitrifying
389
bacteria in the reactor, respectively.
390
The analysis of the Alto Seveso WWTP biomass did not show significant differences
391
between the nitrification and denitrification basins in terms of both biomass activity and
392
composition, in agreement with the biological plant scheme that does not include a settler
AC C
EP
TE D
M AN U
SC
RI PT
371
18
ACCEPTED MANUSCRIPT
between the denitrification and the oxidation reactors (single sludge process). The active
394
bacterial fraction represented about 85% of total biomass in both basins: although a high
395
level of bacterial activity should not be expected for a plant treating an industrial
396
wastewater like textile effluents, such a value could be due to the domestic wastewater
397
contribution (about 30% of the influent volume) and to the ozone dosage on the
398
recirculation stream, which could both increase the amount of ready biodegradable COD
399
and reduce the concentration of potential inhibitory compounds in the WWTP influent.
400
However, it must be highlighted that, although the active bacterial fraction in SBBGR is
401
lower than that in Alto Seveso WWTP biomass (i.e., 45% vs 85%), the concentration of
402
active biomass is actually greater in SBBGR thanks to its higher total concentration (5-6
403
times higher). The screening with group-specific probes allowed the identification of about
404
100% of the bacteria in the plant and revealed that the biomass was characterized by higher
405
biodiversity with respect to the SBBGR system. Nevertheless, the three main bacterial
406
groups were the same observed in SBBGR (i.e. Beta- and Alphaproteobacteria and
407
Actinobacteria). According to the nitrogen removal performances of the system, a high
408
amount of nitrifying and denitrifying bacteria was found; the first ones were more abundant
409
in the nitrification tank while the second ones dominated in the denitrification tank.
AC C
EP
TE D
M AN U
SC
RI PT
393
410 411
4. Conclusions
412
SBBGR is suitable for the upgrade of WWTPs treating mixed municipal-textile wastewater
413
because:
414
•
it assures very good treatment results at a low HRT (11 h); 19
ACCEPTED MANUSCRIPT
415
•
ascribable to the high biomass age in the system;
416
•
the sludge shows interesting dewatering and filterability properties.
RI PT
417
it is characterized by a low sludge production (lower than 0.15 kg TSS/kgCODremoved)
SBBGR is more effective than currently adopted treatment solutions: in the full-scale plant
419
treating the same wastewater similar results are achieved only with a more complex
420
treatment (biological treatment, coagulation-flocculation and ozonation), with a higher
421
HRT and sludge production.
SC
418
M AN U
422
Acknowledgements
424
This study was financially supported by Lariana Depur s.p.a., a company operating the
425
wastewater treatment plant Alto Seveso in the textile industrial district of Como (Italy).
426
The authors would like to express their gratitude to Dr. Guido Del Moro and Annalisa
427
Mancini for their support.
428
TE D
423
References
430
Amann, R.I., Ludwig, W., Schleifer, K.-H., 1995. Phylogenetic identification and in situ
431
detection of individual microbial cells without cultivation. Microbiol. Mol. Biol. R. 59,
432
143-169.
433
APHA, AWWA, American Public Health Association and American Water Works
434
Association, 1998. Standard Methods for the Examination of Water and Wastewater, 20th
435
ed. Water Environment Federation, Washington DC.
AC C
EP
429
20
ACCEPTED MANUSCRIPT
Bechtold, T., Burtscher, E., Hung, Y.-T., 2004. Treatment of textile wastes. In: Wang, L.K.,
437
Hung, Y.-T., Lo, H.H., Yapijakis, C. (Eds.), Handbook of industrial and hazardous wastes
438
treatment, 2nd ed. Marcel Dekker Inc., New York, pp. 379-414.
439
Bortone, G., Cech, J.S., Bianchi, R., Tilche, A., 1995. Effects of an anaerobic zone in a
440
textile wastewater treatment plant. Water Sci. Technol. 32(9-10), 133-140.
441
Bortone, G., Gemelli, S., Tilche, A., Bianchi, R., Bergna, G., 1997. A new approach to the
442
evaluation of biological treatability of industrial wastewater for the implementation of the
443
“waste design” concept. Water Sci. Technol. 36(2-3), 81-90.
444
Chen, X., Shen, Z., Zhu, X., Fan, Y., Wang, W., 2005. Advanced treatment of textile
445
wastewater for reuse using electrochemical oxidation and membrane filtration. Water SA
446
31(1), 127-132.
447
Correia, V.M., Stephenson, T., Judd, S.J., 1994. Characterisation of textile wastewaters - a
448
review. Environ. Technol. 15, 917-929.
449
De Sanctis, M., Di Iaconi, C., Lopez, A., Rossetti, S., 2010. Granular biomass structure and
450
population dynamics in Sequencing Batch Biofilter Granular Reactor (SBBGR).
451
Bioresource Technol. 101, 2152-2158.
452
Del Borghi, A., Binaghi, L., Converti, A., Del Borghi, M., 2003. Combined treatment of
453
leachate from sanitary landfill and municipal wastewater by activated sludge. Chem.
454
Biochem. Eng. Q. 17(4), 277-283.
455
Demmin, T.R., Uhrich, K.D., 1988. Improving carpet wastewater treatment. Am. Dyest.
456
Rep. 77(6), 13-18.
AC C
EP
TE D
M AN U
SC
RI PT
436
21
ACCEPTED MANUSCRIPT
Di Iaconi, C., De Sanctis, M., Rossetti, S., Ramadori, R., 2010. SBBGR technology for
458
minimising excess sludge production in biological processes. Water Res. 44 (6), 1825-
459
1832.
460
European Commission, 2009. European Business – Facts and figures. Eurostat Statistical
461
Books. Office for Official Publications of the European Communities, Luxembourg.
462
European Commission, 2011. Eurostat Pocketbooks - Key figures on European business
463
with a special feature on SMEs. Publications Office of the European Union, Luxembourg.
464
Fongsatitkul, P., Elefsiniotis, P., Yamasmit, A., Yamasmit, N., 2004. Use of sequencing
465
batch reactors and Fenton's reagent to treat a wastewater from a textile industry. Biochem.
466
Eng. J. 21, 213-220.
467
Grau, P., 1991. Textile industry wastewaters treatment. Water Sci. Technol. 24(1), 97-103.
468
Lau, W.J., Ismail, A.F., 2009. Polymeric nanofiltration membranes for textile dye
469
wastewater treatment: preparation, performance evaluation, transport modelling and fouling
470
control - a review. Desalination 245, 321-348.
471
Libra, J.A., Sosath, F., 2003. Combination of biological and chemical processes for the
472
treatment of textile wastewater containing reactive dyes. J. Chem. Technol. Biot. 78, 1149-
473
1156.
474
Liu, F., Zhao, C.C., Zhao, D.F., Liu, G.H., 2008. Tertiary treatment of textile wastewater
475
with combined media biological aerated filter (CMBAF) at different hydraulic loadings and
476
dissolved oxygen concentrations. J. Hazard. Mater. 160, 161-167.
AC C
EP
TE D
M AN U
SC
RI PT
457
22
ACCEPTED MANUSCRIPT
Loy, A., Maixner, F., Wagner, M., Horn, M., 2007. ProbeBase - an online resource for
478
rRNA-targeted oligonucleotide probes: new features 2007. Nucleic Acids Res. 35, D800-
479
D804.
480
Lubello, C., Gori, R., 2004. Membrane bio-reactor for advanced textile wastewater
481
treatment and reuse. Water Sci. Technol. 50(2), 113-119.
482
Mino, T., 1995. Survey on filamentous micro-organisms in activated sludge processes in
483
Bangkok, Thailand. Water Sci. Technol. 31(9), 193-202.
484
Ng, W.J., 2006. Industrial wastewater treatment. Imperial College Press, London.
485
Ramesh Babu, B., Parande, A.K., Raghu, S., Prem Kumar ,T., 2007. Cotton textile
486
processing: waste generation and effluent treatment. J. Cotton Sci. 11, 141-153.
487
Rozzi, A., Ficara, E., Cellamare, C., Bortone, G., 1999. Characterization of textile
488
wastewater and other industrial wastewaters by respirometric and titration biosensors.
489
Water Sci. Technol. 40(1), 161-168.
490
Soares, O.S.G.P., Orfao, J.J.M., Portela, D., Vieira, A., Pereira, M.F.R., 2006. Ozonation of
491
textile effluents and dye solutions under continuous operation: influence of operating
492
parameters. J. Hazard. Mater. B137, 1664-1673.
493
Somensi, C.A., Simionatto, E.L., Bertoli, S.L., Wisniewski, A., Radetski, C.M., 2010. Use
494
of ozone in a pilot-scale plant for textile wastewater pre-treatment: physico-chemical
495
efficiency, degradation byproducts dentification and environmental toxicity of treated
496
wastewater. J. Hazard. Mater. 175, 235-240.
AC C
EP
TE D
M AN U
SC
RI PT
477
23
ACCEPTED MANUSCRIPT
Sreedhar Reddy, S., Kotaiah, B., 2006. Comparative evaluation of commercial and sewage
498
sludge based activated carbons for the removal of textile dyes from aqueous solutions. Iran.
499
J. Environ. Healt. 3(4), 239-246.
500
UNI EN 14701-1, 2006. Characterisation of sludges - Filtration properties - Part 1:
501
Capillary suction time (CST).
502
UNI EN 14701-2, 2006. Characterization of sludges - Filtration properties - Part 2:
503
Determination of the specific resistance to filtration.
AC C
EP
TE D
M AN U
504
SC
RI PT
497
24
ACCEPTED MANUSCRIPT
Figure captions
506
Figure 1 – Sketch of the lab-scale SBBGR
507
Figure 2 – Sketch of the Alto Seveso WWTP
508
Figure 3 – Trends recorded during a typical treatment cycle of SBBGR: a) COD
509
concentration (continuous line) and removal (dashed line); b) TSS concentration
510
(continuous line) and removal (dashed line); c) total surfactants concentration (continuous
511
line) and removal (dashed line); d) nitrogen concentrations (TN, TKN, N-NH4+ and N-
512
NOx-; continuous lines) and TN removal (dashed line); e) colour removal at 426, 558 and
513
660 nm
AC C
EP
TE D
M AN U
SC
RI PT
505
25
ACCEPTED MANUSCRIPT
Table 1 – Treatment results achieved with SBBGR at a HRT of 11 h
NH4+
NOx Total surfactants
Colour (426 nm)
Colour (558 nm)
AC C
EP
Colour (660 nm)
Range 186 ÷ 352 22 ÷ 52 76.9 ÷ 88.2 53 ÷ 134 2÷9 92.8 ÷ 96.3 28.8 ÷ 39.7 1.7 ÷ 8.1 79.6 ÷ 94.0 21.7 ÷ 29.4 0 ÷ 4.5 84.0 ÷ 100 0.2 ÷ 0.3 1.5 ÷ 14.7 1.5 ÷ 7.6 0.7 ÷ 1.5 64.9 ÷ 85.4 0.028 ÷ 0.041 0.017 ÷ 0.026 23.5 ÷ 44.1 0.013 ÷ 0.023 0.007 ÷ 0.013 31.6 ÷ 52.2 0.010 ÷ 0.014 0.005 ÷ 0.006 40.0 ÷ 64.3
RI PT
SC
TKN
Mean value 249 ± 65 42 ± 9 82.1 ± 3.6 87 ± 36 4±2 94.7 ± 1.1 34.2 ± 5.1 4.9 ± 2.4 87.5 ± 5.3 25.6 ± 3.4 1.7 ± 2.2 95.0 ± 7.4 0.2 ± 0.1 7.6 ± 4.5 4.7 ± 2.5 1.1 ± 0.3 77.1 ± 7.6 0.035 ± 0.005 0.022 ± 0.003 33.9 ± 8.0 0.019 ± 0.004 0.011 ± 0.002 41.9 ± 6.9 0.012 ± 0.002 0.006 ± 0.001 52.6 ± 9.8
M AN U
TSS
influent (mg/l) effluent (mg/l) removal efficiency (%) influent (mg/l) effluent (mg/l) removal efficiency (%) influent (mgN/l) effluent (mgN/l) removal efficiency (%) influent (mgN/l) effluent (mgN/l) removal efficiency (%) influent (mgN/l) effluent (mgN/l) influent (mg/l) effluent (mg/l) removal efficiency (%) influent (abs) effluent (abs) removal efficiency (%) influent (abs) effluent (abs) removal efficiency (%) influent (abs) effluent (abs) removal efficiency (%)
TE D
Parameter COD
ACCEPTED MANUSCRIPT
Table 2 – Performance of the Alto Seveso WWTP (average values ± standard deviation).
TKN
NH4+
NOx-
AC C
EP
TE D
Colour
RI PT
TSS
influent [mg/l] effluent [mg/l] removal [%] influent [mg/l] effluent [mg/l] removal [%] influent [mgN/l] effluent [mgN/l] removal [%] influent [mgN/l] effluent [mgN/l] removal [%] influent [mgN/l] effluent [mgN/l] 426 nm: removal [%] 558 nm: removal [%] 660 nm: removal [%]
SC
COD
M AN U
Parameter
Alto Seveso WWTP After After After biological coagulation ozonation compartment flocculation (final effluent) clarification 241 ± 56 52 ± 25 40 ± 20 66 ± 24 77.9 ± 7.4 82.4 ± 9.5 71.5 ± 9.2 80 ± 17 23 ± 9 19 ± 6 16 ± 7 73.0 ± 7.8 80.2 ± 7.9 68.3 ± 10.5 31.9 ± 7.6 4.7 ± 2.4 85.1 ± 7.1 19.9 ± 6.0 1.4 ± 1.7 1.3 ± 2.4 94.1 ± 8.8 93.2 ± 7.7 1.9 ± 1.1 11.1 ± 1.4 11.1 ± 2.7 40.4 ± 17.5 67.4 ± 16.8 32.9 ± 17.2 37.1 ± 19.0 42.8 ± 19.7 73.7 ± 16.3 50.9 ± 16.7 76.0 ± 14.9 41.8 ± 19.6
ACCEPTED MANUSCRIPT
Table 3 – Biomass concentration in SBBGR VSS concentration [kgVSS/m3]
VSS/TSS [%]
Top
26.0
19.3
74.2
Medium
29.9
22.7
Bottom
39.8
30.7
RI PT
TSS concentration [kgTSS/m3]
76.0 77.1
AC C
EP
TE D
M AN U
SC
REACTOR POSITION
ACCEPTED MANUSCRIPT
Table 4 – Physical characterization of SBBGR and Alto Seveso WWTP sludge. TSS [g/l]
SBBGR WWTP
11.1 16.9
0s 16.0 25.8
CST [s] 10 s 40 s 17.9 18.5 27.9 30.4
100 s 19.3 30.7
50 kPa 5.5 . 1011 1.9 . 1012
SRF [m/kg] 150 kPa 350 kPa 2.5 . 1012 4.1 . 1012 5.4 . 1012 1.2 . 1013
AC C
EP
TE D
M AN U
SC
RI PT
SLUDGE
s 1.000006 1.000007
ACCEPTED MANUSCRIPT
Table 5 – Microbial characterization of SBBGR and Alto Seveso WWTP biomass by FISH analysis (n.d. = not detected). Target microbial group / total DAPI stained biomass [%]
Ammonia-oxidizing bacteria Nitrite-oxidizing bacteria Denitrifying bacteria (Thauera + Azoarcus + Alcaligenes-Bordetella) Sulphate-reducing bacteria
83 15 28 31 n.d. 3 ≤ 0.5 ≤ 0.5 9
≤ 0.5
5
4
≤ 0.5 3
≤ 0.5 1
3 ≤ 0.5
1 4
n.d.
n.d.
n.d.
n.d.
2
2
3
5
85 16 19 20 n.d. 20 ≤ 0.5 n.d. 10
49 8 8 17 n.d. 1 1 n.d. 4
41 5 3 20 n.d. 1 1 n.d. ≤ 0.5
40 6 3 18 n.d. ≤ 0.5 n.d. n.d. ≤ 0.5
2
1
1
n.d. 0.7
1 4
n.d.
n.d.
3
2
SC
Top
RI PT 85 15 29 30 n.d. 4 ≤ 0.5 ≤ 0.5 10
Medium
EP AC C
Denitrification basin
Bottom
TE D
Archaea
Nitrification basin
Inoculum
M AN U
Bacteria Actinobacteria Alphaproteobacteria Betaproteobacteria Chloroflexi Gammaproteobacteria Deltaproteobacteria Firmicutes Flavobacteria
Alto Seveso WWTP
SBBGR
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT
SBBGR is suitable to treat mixed municipal-textile wastewater
•
very good treatment results can be achieved at a low HRT (11 h)
•
a low sludge quantity with interesting dewaterability and filterability is produced
•
SBBGR can effectively replace a complex 30-h HRT treatment scheme
AC C
EP
TE D
M AN U
SC
RI PT
•
