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Effectiveness of dairy wastewater treatment in a bioreactor based on the integrated technology of activated sludge and hydrophyte system a
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M. Dębowski , M. Zieliński , M. Krzemieniewski , M. Rokicka & K. Kupczyk
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Department of Environment Engineering, University of Warmia and Mazury in Olsztyn, Al. Warszawska 117a, Olsztyn 10-720, Poland Published online: 06 Jan 2014.
To cite this article: M. Dębowski, M. Zieliński, M. Krzemieniewski, M. Rokicka & K. Kupczyk (2014) Effectiveness of dairy wastewater treatment in a bioreactor based on the integrated technology of activated sludge and hydrophyte system, Environmental Technology, 35:11, 1350-1357, DOI: 10.1080/09593330.2013.868528 To link to this article: http://dx.doi.org/10.1080/09593330.2013.868528
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Environmental Technology, 2014 Vol. 35, No. 11, 1350–1357, http://dx.doi.org/10.1080/09593330.2013.868528
Effectiveness of dairy wastewater treatment in a bioreactor based on the integrated technology of activated sludge and hydrophyte system M. De˛bowski, M. Zieli´nski, M. Krzemieniewski, M. Rokicka∗ and K. Kupczyk Department of Environment Engineering, University of Warmia and Mazury in Olsztyn, Al. Warszawska 117a, Olsztyn 10-720, Poland
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(Received 31 May 2013; accepted 14 November 2013 ) The aim of this study was to determine the effectiveness of dairy wastewater treatment in the integrated technology based on the simultaneous use of the activated sludge method (AS) and a hydrophyte system (HS) (AS–HS), in this case, common reed (Phragmites australis) or common cattail (Typha latifolia). Experiments were conducted in an innovative reactor exploited in the fractional-technical scale at the loads of 0.05 mg BOD5 /mg.d.m. d (biochemical oxygen demand) and 0.10 mg BOD5 /mg.d.m d. The AS–HS enabled improving the removal effectiveness of biogenes characterized by concentrations of Ntot. , N-NH4 and Ptot. . In contrast, the integrated system had no significant reducing effect either on concentrations of organic compounds characterized by BOD5 and chemical oxygen demand parameters or on the structure of AS in the sequencing batch-type reactors. Keywords: dairy wastewaters; sequencing batch reactor; hydrophyte system; wastewater treatment
1. Introduction As indicated by the literature data, dairy wastewaters are characterized by chemical oxygen demand (COD) concentration ranging from 800 to 7000 mg O2 /l and by high concentrations of biogenes. [1–4] Commonly applied methods of contaminants removal are based on aerobic and anaerobic biological systems. [5–7] Owing to benefits of running the treatment processes in one tank, sequencing batch reactors (SBRs) are also widely exploited in many treatment plants.[8–10] The main restraint of this technology, however, is the low efficiency of nitrogen and phosphorus compounds removal that results mainly from the insufficient quantity of available carbon.[11–13] Hence, a tangible need emerges for solutions that would improve the technological and economic effectiveness of typical SBRs. An alternative solution presented in this work involves the integration of an SBR with a hydrophyte system (HS). Papers published so far have described the co-action of bacterial microflora with hydrophytes in typical hydrobotanical wastewater treatment plants,[10,14–17] with common reed, osier, common cattail and duckweed used most commonly to this end.[16,18] The functioning of plant communities has been shown to have an immediate effect on the effective removal of nitrogen and phosphorus compounds necessary for hydrophytes development and biomass growth.[19] The analysis of these processes has inspired us to undertake a research aimed at evaluating the possibility and validity of integrating the SBR with a plant system. Therefore, the goal of this study was to determine the effectiveness of dairy ∗ Corresponding
author. Email: [email protected]
© 2013 Taylor & Francis
wastewater treatment in the integrated technology based on the concomitant used of the activated sludge (AS) method and a HS.[20]
2.
Methodology
Experiments were carried out in the system exploited in the fractional-technical scale. Research works were divided into three series with the applied technology of wastewater treatment used as a criterion of division. In series I, the experimental system was based only on AS. In series II, the functioning of the AS was integrated with common reed (Phragmites australis), whereas in series III the wastewater treatment process by the AS was integrated with common cattail (Typha latifolia). Each experimental series was run in two variants differing in the loading of AS with a feedstock of wastewaters, i.e. A1 = 0.05 mg BOD5 /mg.d.m. d (biochemical oxygen demand) in the first variant (variant 1) and A2 = 0.10 mg BOD5 /mg.d.m. d in the second variant (variant 2). The experimental design is presented in Figure 1. The experiment was run for 8 months in six reactors simultaneously. A single reactor in the form of a cylinder (2.0 m total height × internal diameter of 0.2 m) was made of transparent Plexiglas (Figure 2). The reactor was divided into two sections according to the function performed: the bottom section – the tank of activated sludge (AST) and the upper section – the tank of the hydrophyte system (HST). The tanks were partitioned with a supporting grid used to
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Figure 1.
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Experimental design.
which when opened enabled free gas exchange between the tank and the environment. Alongside the reactor, ports were installed in 25-cm spacing, which enabled collecting gas samples from the HST and wastewater samples from the AST. The gas ports allowed for recirculation of gases from a selected height to the AST via the aerating pump. Technical parameters of a single research installation were as follows:
Total height Active height Height of AST Height of HST Internal diameter Active volume of the AST Active volume of the hydrophyte growth tank
Figure 2. Scheme of a single research installation. (1) AST, (2) HST, (3) plant-supporting grid, (4) stirrer, (5) aerating pump in tight case, (6) aerator, (7) ventilation valve, (8) gas sampling ports, (9) discharge of treated wastewaters, (10) tank with crude wastewaters, (11) stems and leaves of tested aquatic plants and (12) roots of tested aquatic plants.
place plant shoots. Each tank was 1.0 m high. At the bottom of AST, a magnetic stirrer was fixed that was induced with a drive mounted in the reactor’s axis beneath its bottom. Above the magnetic stirrer, at the height of 50 mm, an aerating diffuser was fixed that was supplied with compressed air. An aerating pump with the yield of 150 l/h was located inside a tight case. A sucking port enabled feeding of gases from the HST. At the height of 60 cm, the AST had a release port (φ 1/4 ) with a ball valve used to discharge the treated wastewaters. Above, at the height of 70 cm, there was an inlet of raw wastewaters in the form of a pipe (φ 1/4 ) ended with an intermediate tank with a valve. Both sections of the AST and HST reactors were joined tightly. The AST was filled with liquid to the level of the supporting grid used to place plant rhizomes. In the dome of the HST, a ventilation valve (1 in diameter) was mounted
Htot. = 220 cm Hact. = 200 cm HAST = 100 cm Hr = 100 cm Dint. = 20 cm Vo = 31.4 dm3 Vo = 47.1 dm3
The experimental system consisted of six single, identical reactors fixed on a common frame at the southern-exposure window. The distance between the successive columns was 35 cm. Throughout the experiment, the thermal conditions were kept at a stable level of 21 ± 2◦ C, which assured identical and comparable conditions for hydrophytes growth. The AST was functioning as a SBR. The reactor’s working cycle spanned for 1 day including: 2 h – the phase of raw wastewaters batch feeding and mixing, 20 h – the aeration phase and 2 h – sedimentation and discharge of treated wastewaters (Figure 3). Experiments were carried out with the use of model dairy wastewaters prepared from milk powder. Depending on the experimental variant, from 1.0 to 2.0 g of skim milk powder were dissolved in 1.0 l of tap water. In both variants, 10 l/d of raw wastewaters were fed to the reactor. In both cases, the hydraulic loading was identical, whereas the concentration of contaminants in wastewaters was successively increased. The characteristics of raw wastewaters used in both experimental variants were presented in Table 1. The seedlings of common reed (P. australis) and common cattail (T. latifolia) used in experiment originated from own culture, which assured the selection of uniform plant material for comparative analyses. Standardized single shoots of the plants (ca. 1.0 m in height) were selected for the study and placed in the reactors together with their
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Figure 3.
M. De˛bowski et al.
Scheme of AST working cycle.
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Table 1.
Characteristics of crude wastewaters.
Parameter BOD5 COD Ntot. Ptot. pH Total suspended solids
Table 2.
A1 = 0.05 mg BOD5 /mgd.m. d
A2 = 0.10 mgBOD5 /mgd.m. d
Unit
Mean
SD
Mean
SD
mg O2 /l mg O2 /l mg N/l mg P/l – mg/l
1503.6 2140.9 95.6 23.7 7.19 11.3
192.5 221.7 7.3 2.6 0.11 1.1
3012.6 4282.3 191.7 48.2 7.06 12.9
258.3 299.7 9.6 3.3 0.14 1.6
Characteristics of rhizomes of hydrophytes used in the experiment. Common reed (P. australis)
Parameter Fresh mass height dry matter organic dry matter
Common cattail (T. latifolia)
Unit
Mean
SD
Mean
SD
mean
SD
mean
SD
g f.m. Cm g d.m./g f.m. g o.d.m./g d.m.
253.1 98.4 0.221 0.210
23.9 7.3 0.018 0.027
250.9 101.6 0.221 0.210
19.7 3.9 0.018 0.027
248.6 104.8 0.218 0.219
36.1 5.2 0.029 0.016
250.2 99.6 0.221 0.219
26.3 13.7 0.018 0.016
rhizomes and root system. A single batch of seedlings were from 4 to 6 plants in the case of common reed and from 3 to 5 plants in the case of common tail. The characteristics of biomass of the plant material used in the study were presented in Table 2. The crude and treated wastewaters were analysed once a day by means of cuvette tests (Germany). The following indicators of contamination were determined in the study period: COD, total nitrogen, ammonia nitrogen and total phosphorus. Determinations were carried out with a DR 5000 spectrophotometer and with an HT 200 s mineralizer. Measurements of BOD5 were conducted with the Oxi-top control system by WTW Company (Germany). An oxygen probe with a recorder (Endress Hauser) was used for continuous monitoring of oxygen content in the AST The content of total suspended solids in crude and treated wastewaters was determined with the gravimetric method. The pH value was measured with a VWR 1000L pH-meter. Before being fed to reactors, the plant material was analysed for moisture content and dry matter content. To this end, plants were selected at random from the seedlings
to be used in the experiment, and subjected to analyses (grinding → drying → analysis). After each experimental variant, the plants were removed from the reactors and subjected to analogous gravimetric analyses of water and dry matter contents. The plant material was also subjected to elementary carbon analysis using a Flesh 200 elemental analysed by Thermo Company. In addition, the length of the aerial parts of the plants was measured at the onset and at the end of each experimental variant. Microscope observations were made throughout the study to analyse the impact of the applied technology on changes in biocoenoses of AS in the subsequent variants of the experiment. Quantity of assimilated CO2 was determined by the following Equation (1): mCO2 =
mTOC × MCO2 (g), MC
(1)
where mCO2 is the quantity of assimilated CO2 (g); mTOC the content of total organic carbon (TOC) in biomass growth (g)];MCO2 the molecular weight of CO2 (g/mol) and MC the molecular weight of C (g/mol).
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The statistical analysis of results was carried out using STATISTICA 10.0 PL package. The hypothesis on the distribution of each analysed variable was verified with the Shapiro–Wilk W test. One-way analysis of variance was conducted to determine the significance of differences between mean values. In order to determine the significance of differences between the analysed variables, the Tukey’s honestly significant difference (HSD) test was used. In the above tests, the level of significance was adopted at α = 0.05.
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3. Results Irrespective of the applied experimental variant, a similar course of the biodegradation process of organic compounds was observed in the exploited technological system that was analogous for both species of hydrophytes. The efficiency of BOD5 reduction was high and ranged from 98.7% in variant 2 of series III to 99.1% in variant 1 of series II. The value of BOD5 in the effluent fitted within the range of 9.02–15.06 mg O2 /l Figure 4). The loading of the exploited technological system was observed to have a significant effect on COD value in the treated wastewaters. In variant 2, the COD value in the effluent ranged from 51.39 to 59.95 mg O2 /l. In contrast, significantly lower COD values were determined in variant 1, which oscillated around 20.0 mg O2 /l irrespective of the experimental series (Figure 5).
In variant 1 of series I, the concentration of total nitrogen reached 16.06 mg Ntot. /l, whereas the exploitation of the technological system at the loading of 0.05 g BOD5 /gd.m . d resulted in the final total nitrogen concentration at 32.78 mg Ntot. /l. A tangibly higher, comparable efficiency of Ntot. removal was noted for the reactors exploited in series II and series III. In variant 1 of series II, the efficiency of Ntot. removal accounted for 88.4%, which enabled reaching the concentration of 11.08 mg Ntot. /l. The comparable treatment efficiency was observed in variant 2, which resulted in Ntot. concentration at the level of 22.42 mg Ntot. /l (Figure 6). Statistically comparable final effects were achieved in series II. In the case of N-NH4 , the effectiveness of its removal was very high and fitted within a narrow range of 99.6–99.81% irrespective of the technological variant. Concentrations of ammonia nitrogen in the effluent were very low in all variants and ranged from 0.01 to 0.03 mg N-NH4 /l (Figure 7). The experiments demonstrated a significant effect of hydrophytes introduction to the treatment process on the efficiency of Ptot. removal. Tanks loading in variant 1 enabled achieving Ptot . concentration in the effluent at: 9.15 mg/l in series I, at 7.51 mg/l in series II and at 7.56 mg/l in series III. In variant 2, comparable concentrations of total phosphorus accounting for 15.70 mg Ptot. /l were observed in the series with hydrophytes. In the control reactor, in series I variant 2 the mean concentration of total phosphorus in the effluent was at 19.18 mg Ptot. /l (Figure 8).
Figure 4.
Value of BOD5 in the effluent.
Figure 6.
Concentration of Ntot. in the effluent.
Figure 5.
Value of COD in the effluent.
Figure 7.
Concentration of N-NH4 in the effluent.
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Figure 8.
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Concentration of Ptot. in the effluent.
The pH value of the treated wastewaters was close to neutral. It was at a similar level irrespective of the analysed experimental variant and ranged from 7.03 to 7.12 (Figure 9). Also, no differences were noted in the concentration of total suspended solids in the effluent. In the successive variants of series I, it reached 11.72 and 10.03 mgd.m ./l, in series II it ranged from 12.74 mgd.m ./l in variant 1 to 11.62 mgd.m ./l in variant 2, whereas in series III values of this parameter oscillated around 13.00 mgd.m ./l in both variants (Figure 10). Irrespective of the hydrophyte species applied, no statistically significant changes were observed in oxygen concentration in the exploited tanks, which at the aeration phase reached ca. 1.9 mg O2 /l (Figures 11 and 12).
Figure 11. Course of changes in oxygen concentration in the AST, A = 0.05 mg BOD5 /mgd.m. d.
Figure 12. Course of changes in oxygen concentration in the AST, A = 0.10 mg BOD5 /mgd.m. d.
Figure 9.
Figure 10. ent.
The pH value in the effluent.
Concentration of total suspended solids in the efflu-
The microscope observations made throughout the study and their analysis enable to conclude that biocoenosis of the AS in the exploited biofilters contained a significant number of ciliates, and low counts of flagellates (Synura uvella, Euglena viridis and Codonosiga botrytis) and amoebas (Amoeba proteus, Arcella vulgaris and Difflugia oblonga). Floccules had light-brown colour. In some reactors, mainly those integrated with hydrophytes, filamentous fungi occurred as well. Irrespective of the analysed technological variant, analyses showed no intensive growth of filamentous bacteria, which is often the case in installations based on the AS method. This group of microorganisms – constituting a negative element of the biocoenosis of AS microflora as seen from the technological perspective – was represented by Sphaerotilus natans, which however did not result in swelling, foaming or expansion of the sludge during the treatment process and sedimentation. It may be concluded that the species composition of microflora in the investigated AS, in the subsequent biofilters, was not diversified. Analyses confirmed the presence of bacteria belonging to Bacillus and Achromobacter genera as well as of Pseudomonas putida and Pseudomonas fluorescens. In the AS, bacteria of the Alcaligenes and
Environmental Technology Table 3.
Results of microscope observations of AS in the experiment. Series I
Parameter
Variant 1
Series II Variant 2
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Sludge colour Light-brown Light-brown Follicles structure Compact, regular Compact, regular Follicles shape Non-branched, Slightly branched, spherical lobularspherical Follicles stability Stable Stable Follicles size 240 290 (μm) Plant and animal Numerous Numerous organisms Filamentous Sparse Relatively bacteria numerous 4.9 × 1011 Eubacteria 1.7 × 109 Table 4.
Series II III
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Variant 1
Series III Variant 2
Variant 1
Variant 2
Light-brown Light-brown Compact, regular Compact, regular Non-branched, Slightly branched, spherical lobularspherical Stable Stable 190 240
Light-brown Light-brown Compact, regular Compact, regular Non-branched, Non-branched, spherical spherical Stable 210
Stable 200
Numerous
Numerous
Numerous
Numerous
Sparse
Relatively numerous 5.7 × 1011
Sparse
Sparse
6.2 × 1010
4.2 × 1012
3.1 × 1010
Growth of hydrophytes biomass and effectiveness of CO2 absorption in the experiment.
Variant
Mass of biomass at the beginning of experiment (g f.w.)
Growth of biomass at the end of experiment (g f.w.)
Growth of biomass at the end of experiment (%)
Content of TOC in biomass growth (g)
Quantity of assimilated CO2 (g)
1 2 1 2
253.1 250.9 248.6 250.2
43.03 47.67 34.80 30.02
17.11 18.82 14.37 11.80
3.44 3.81 3.15 2.71
12.60 13.96 11.54 9.96
Flavobacterium genera were also abundant, which confirmed that the wastewaters contained high quantities of proteins and products of their hydrolysis (Table 3). The presence of E. viridis and C. botrytis, fungi: Fusarium avenaceum, Sclerotinia fructigenia, and Trichoderma viride, as well as sedentary ciliates: Opercularia articulata, and Vorticella convallaria and free-swimming ciliates: Aspidisca costata, Oxytricha ludibunda, and Spirostomum ambiguum, may indicate good condition of the AS. Prolonged exploitation of the technological systems had also a direct impact on rotifers emergence in the sludge that could have contributed to the loss of AS biomass. Likewise, at the beginning/end of treatment process, the follicles were lightbrown and small. A reduction was observed in the count of filamentous bacteria. The characteristics of AS obtained based on the microscope observations were presented in Table 4. The analysis of hydrophytes biomass growth conducted in the experiment showed that the higher effectiveness of biomass growth was noted for common reed irrespective of the technological variant. In variant 1, the value of this parameter reached 43.03 g fresh weight (f.w.), which constituted higher biomass of hydrophyte about 17.11%. In variant 2, the biomass of common reed increased 47.67 g f.w., i.e. by 18.82% (Table 4). In the series III based on common cattail, the respective increase reached 14.37% in variant 1 and 11.80% in variant 2.
4. Discussion The search for modifications in the SBR systems stem mainly from the necessity of improving the effectiveness of biogenes removal.[21,22] An example in this case was an attempt of integrating SBR with a circulation ditch that enabled the removal of 96.6% of N-NH4 . For comparison, the efficiency of N-NH4 removal in the AS–HS system ranged from 99.6% to 99.81% depending on variant. The analysis of the novel solution tested in the study showed that the achieved effectiveness of the treatment process was also significantly higher than the values obtained in typical HSs.[23] The vertical-flow hydrobotanical systems described in the literature assured N-NH4 removal with the efficiency approximating 72%.[24] Works addressing the improvement of the SBR effectiveness demonstrated process temperature to be directly responsible for the final outcomes of the treatment process.[25,26] A temperature of 20◦ C and additional aeration applied in the treatment process of dairy wastewater with N-NH4 content of 300 mg/l resulted in 93% efficiency of this indicator removal.[27] Corresponding results were also reported elsewhere.[28,29] In turn, in the system with hydrophyte filters based on P. australis, Da˛browski [30] recorded the efficiency of N-NH4 removal at 93.2%.[30] In thus-far conducted studies, processes of biogenes removal in SBRs were intensified via modifications of process duration and methods of wastewaters aeration.[31] The
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latter modification, however, enabled achieving barely 70% effectiveness of N-NH4 removal.[9,10] In addition, the preliminary aeration was proved not to affect the efficiency of Ptot. removal from dairy wastewaters.[32] Nearly 90% effectiveness of phosphorus removal is achieved upon the use of chemical coagulants that may, however, lead to secondary contamination of wastewaters.[33] The AS–HS system enabled Ptot. reduction to 65%. Experiments reported in this work proved the significant effect of hydrophytes introduction to the treatment process on the effectiveness of total phosphorus removal. The high removal effectiveness in the AS–HS system was noted for organic compounds and suspended solids. The achieved COD values ranged from 51.39 to 59.95 mg O2 /l at the loading of 0.05 mg BOD5 /mgd.m. d, and indicated over 96% reduction in the value of this parameter. It confirms the thesis that the application of the AS–HS system yields significantly better effects compared with those obtained in typical bioreactors.[34] An alternative solution includes the use of inorganic coagulants, however in this case the efficiency of COD removal does not exceed 70%.[3] Higher effectiveness of COD removal (from 70% to 80%) was achieved as a result of modifications in the SBR aeration systems.[35] In contrast, as reported by Tocchi,[36] the reduction of COD value decreases to 70% in the systems with additional aeration, compared with values between 88% and 94% achieved in the system without aeration.[36]
5. Conclusions An attempt was undertaken in this study to determine the effect of applying hydrobotanical systems based on common reed and common cattail on the improvement of the effectiveness of wastewater treatment processes in ASTs. The analysis of results obtained in the study enables to conclude that the investigated technology is a perspective solution that may limit or eliminate drawbacks of standard methods based on aerobic degradation of contaminants present in wastewaters. The analysed reactor enabled improving the effectiveness of removal of biogenes characterized by concentrations of Ntot. , N-NH4 and Ptot. . The technological effects achieved were comparable irrespective of the hydrophyte species (common reed or common cattail) used in the exploited system. The application of hydrophytes had no significant reducing effect on BOD5 and COD concentrations. The microbiological characteristics of the AS enable to conclude that the applied technological modifications of the system for wastewater treatment had no effect on the condition of biocoenoses of microorganisms taking part in the treatment process. Also, no effect was found for the loading of biofilters with organic compounds on significant changes in the species composition that determines the community of AS microflora. Microscope analyses of the AS allow for a conclusion that the microflora participating
in the removal of contaminants was in good condition and was characterized by high sedimentation capability. The AS–HS system consisted of a cylindrical AS chamber. Inside the chamber, there were inflow of raw wastewater and aeration diffusers in the bottom. The mixing system was located above that. The outflow of treated wastewater was located at the upper part of the chamber. Frame construction was used to fix the aquatic vegetation at the surface of AS liquid with the plant roots submerged in the AS. The upper part of the chamber was made of transparent material and the air outflow from the chamber was through the upper part of the cover. Funding The presented study was funded by the National Science Centre, Poland, conducted in the project [N N523 620839]. References [1] Banu JR, Anandan S, Kaliappan S, Yeom I-T. Treatment of dairy wastewater using anaerobic and solar photocatalytic methods. Sol Energy. 2008;82(9):812–819. [2] Britz TJ, van Schalkwyk C, Hung Y-T. Treatment of dairy processing wastewaters. In: Yapijakis C, Hung Y-T, Lo HH, Wang LK, editors. Waste treatment in the food processing industry. Boca Raton, FL: CRC Press; 2006. [3] Kushwaha JP, Srivastava VC, Mall ID. Organics removal from dairy wastewater by electrochemical treatment and residue disposal. Sep Purif Technol. 2010;76(2):198–205. [4] Janczukowicz W, Zieli´nski M, De˛bowski M, Pesta J. Estimation of biodegradability rate of pollutants in sewage from selected sections of dairy. Environ Prot Eng. 2007;33(1): 77–88. [5] Grady W Jr, Daigger G, Lim H. Biological wastewater treatment. 2nd ed. Basel: Marcel Dekker; 1999. [6] Kassab G, Halalsheh M, Klapwijk A, Fayyad M, van Lier JB. Sequential anaerobic–aerobic treatment for domestic wastewater. Bioresour Technol. 2010;101(10):3299–3310. [7] Janczukowicz W, Zieli´nski M, Debowski M. Biodegradability evaluation of dairy effluents originated in selected sections of dairy production. Bioresour Technol. 2007;99(10): 4199–4205. [8] Fernandes H, Jungles MK, Hoffmann H, Antonio RV, Costa RHR. Full-scale sequencing batch reactor (SBR) for domestic wastewater: performance and diversity of microbial communities. Bioresour Technol. 2013;132:262–268. [9] Guo JH, Peng YZ, Wang SY, Zheng YN, Huang HJ, Ge SJ. Effective and robust partial nitrification to nitrite by realtime aeration duration control in an SBR treating domestic wastewater. Process Biochem. 2009;44(9):979–985. [10] Rodríguez DA, Pino N, Panuela G. Monitoring the removal of nitrogen by applying a nitrification–denitrification process in a sequencing batch reactor (SBR). Bioresour Technol. 2011;102(3):2316–2321. [11] Guerrero J, Guisasola A, Baeza JA. The nature of the carbon source rules the competition between PAO and denitrifiers in systems for simultaneous biological nitrogen and phosphorus removal. Water Res. 2011;45(16):4793–4802. [12] Patel J, Nakhla G. Interaction of denitrification on P removal in anoxic P removal systems. Desalination. 2006;201:82–99. [13] D¸ebowski M, Krzemieniewski M, Zieli´nski M, Dudek M, Grala A. Respirometric studies on the effectiveness of biogas
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Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Effectiveness of dairy wastewater treatment in a bioreactor based on the integrated technology of activated sludge and hydrophyte system a
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M. Dębowski , M. Zieliński , M. Krzemieniewski , M. Rokicka & K. Kupczyk
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Department of Environment Engineering, University of Warmia and Mazury in Olsztyn, Al. Warszawska 117a, Olsztyn 10-720, Poland Published online: 06 Jan 2014.
To cite this article: M. Dębowski, M. Zieliński, M. Krzemieniewski, M. Rokicka & K. Kupczyk (2014) Effectiveness of dairy wastewater treatment in a bioreactor based on the integrated technology of activated sludge and hydrophyte system, Environmental Technology, 35:11, 1350-1357, DOI: 10.1080/09593330.2013.868528 To link to this article: http://dx.doi.org/10.1080/09593330.2013.868528
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Environmental Technology, 2014 Vol. 35, No. 11, 1350–1357, http://dx.doi.org/10.1080/09593330.2013.868528
Effectiveness of dairy wastewater treatment in a bioreactor based on the integrated technology of activated sludge and hydrophyte system M. De˛bowski, M. Zieli´nski, M. Krzemieniewski, M. Rokicka∗ and K. Kupczyk Department of Environment Engineering, University of Warmia and Mazury in Olsztyn, Al. Warszawska 117a, Olsztyn 10-720, Poland
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(Received 31 May 2013; accepted 14 November 2013 ) The aim of this study was to determine the effectiveness of dairy wastewater treatment in the integrated technology based on the simultaneous use of the activated sludge method (AS) and a hydrophyte system (HS) (AS–HS), in this case, common reed (Phragmites australis) or common cattail (Typha latifolia). Experiments were conducted in an innovative reactor exploited in the fractional-technical scale at the loads of 0.05 mg BOD5 /mg.d.m. d (biochemical oxygen demand) and 0.10 mg BOD5 /mg.d.m d. The AS–HS enabled improving the removal effectiveness of biogenes characterized by concentrations of Ntot. , N-NH4 and Ptot. . In contrast, the integrated system had no significant reducing effect either on concentrations of organic compounds characterized by BOD5 and chemical oxygen demand parameters or on the structure of AS in the sequencing batch-type reactors. Keywords: dairy wastewaters; sequencing batch reactor; hydrophyte system; wastewater treatment
1. Introduction As indicated by the literature data, dairy wastewaters are characterized by chemical oxygen demand (COD) concentration ranging from 800 to 7000 mg O2 /l and by high concentrations of biogenes. [1–4] Commonly applied methods of contaminants removal are based on aerobic and anaerobic biological systems. [5–7] Owing to benefits of running the treatment processes in one tank, sequencing batch reactors (SBRs) are also widely exploited in many treatment plants.[8–10] The main restraint of this technology, however, is the low efficiency of nitrogen and phosphorus compounds removal that results mainly from the insufficient quantity of available carbon.[11–13] Hence, a tangible need emerges for solutions that would improve the technological and economic effectiveness of typical SBRs. An alternative solution presented in this work involves the integration of an SBR with a hydrophyte system (HS). Papers published so far have described the co-action of bacterial microflora with hydrophytes in typical hydrobotanical wastewater treatment plants,[10,14–17] with common reed, osier, common cattail and duckweed used most commonly to this end.[16,18] The functioning of plant communities has been shown to have an immediate effect on the effective removal of nitrogen and phosphorus compounds necessary for hydrophytes development and biomass growth.[19] The analysis of these processes has inspired us to undertake a research aimed at evaluating the possibility and validity of integrating the SBR with a plant system. Therefore, the goal of this study was to determine the effectiveness of dairy ∗ Corresponding
author. Email: [email protected]
© 2013 Taylor & Francis
wastewater treatment in the integrated technology based on the concomitant used of the activated sludge (AS) method and a HS.[20]
2.
Methodology
Experiments were carried out in the system exploited in the fractional-technical scale. Research works were divided into three series with the applied technology of wastewater treatment used as a criterion of division. In series I, the experimental system was based only on AS. In series II, the functioning of the AS was integrated with common reed (Phragmites australis), whereas in series III the wastewater treatment process by the AS was integrated with common cattail (Typha latifolia). Each experimental series was run in two variants differing in the loading of AS with a feedstock of wastewaters, i.e. A1 = 0.05 mg BOD5 /mg.d.m. d (biochemical oxygen demand) in the first variant (variant 1) and A2 = 0.10 mg BOD5 /mg.d.m. d in the second variant (variant 2). The experimental design is presented in Figure 1. The experiment was run for 8 months in six reactors simultaneously. A single reactor in the form of a cylinder (2.0 m total height × internal diameter of 0.2 m) was made of transparent Plexiglas (Figure 2). The reactor was divided into two sections according to the function performed: the bottom section – the tank of activated sludge (AST) and the upper section – the tank of the hydrophyte system (HST). The tanks were partitioned with a supporting grid used to
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Figure 1.
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Experimental design.
which when opened enabled free gas exchange between the tank and the environment. Alongside the reactor, ports were installed in 25-cm spacing, which enabled collecting gas samples from the HST and wastewater samples from the AST. The gas ports allowed for recirculation of gases from a selected height to the AST via the aerating pump. Technical parameters of a single research installation were as follows:
Total height Active height Height of AST Height of HST Internal diameter Active volume of the AST Active volume of the hydrophyte growth tank
Figure 2. Scheme of a single research installation. (1) AST, (2) HST, (3) plant-supporting grid, (4) stirrer, (5) aerating pump in tight case, (6) aerator, (7) ventilation valve, (8) gas sampling ports, (9) discharge of treated wastewaters, (10) tank with crude wastewaters, (11) stems and leaves of tested aquatic plants and (12) roots of tested aquatic plants.
place plant shoots. Each tank was 1.0 m high. At the bottom of AST, a magnetic stirrer was fixed that was induced with a drive mounted in the reactor’s axis beneath its bottom. Above the magnetic stirrer, at the height of 50 mm, an aerating diffuser was fixed that was supplied with compressed air. An aerating pump with the yield of 150 l/h was located inside a tight case. A sucking port enabled feeding of gases from the HST. At the height of 60 cm, the AST had a release port (φ 1/4 ) with a ball valve used to discharge the treated wastewaters. Above, at the height of 70 cm, there was an inlet of raw wastewaters in the form of a pipe (φ 1/4 ) ended with an intermediate tank with a valve. Both sections of the AST and HST reactors were joined tightly. The AST was filled with liquid to the level of the supporting grid used to place plant rhizomes. In the dome of the HST, a ventilation valve (1 in diameter) was mounted
Htot. = 220 cm Hact. = 200 cm HAST = 100 cm Hr = 100 cm Dint. = 20 cm Vo = 31.4 dm3 Vo = 47.1 dm3
The experimental system consisted of six single, identical reactors fixed on a common frame at the southern-exposure window. The distance between the successive columns was 35 cm. Throughout the experiment, the thermal conditions were kept at a stable level of 21 ± 2◦ C, which assured identical and comparable conditions for hydrophytes growth. The AST was functioning as a SBR. The reactor’s working cycle spanned for 1 day including: 2 h – the phase of raw wastewaters batch feeding and mixing, 20 h – the aeration phase and 2 h – sedimentation and discharge of treated wastewaters (Figure 3). Experiments were carried out with the use of model dairy wastewaters prepared from milk powder. Depending on the experimental variant, from 1.0 to 2.0 g of skim milk powder were dissolved in 1.0 l of tap water. In both variants, 10 l/d of raw wastewaters were fed to the reactor. In both cases, the hydraulic loading was identical, whereas the concentration of contaminants in wastewaters was successively increased. The characteristics of raw wastewaters used in both experimental variants were presented in Table 1. The seedlings of common reed (P. australis) and common cattail (T. latifolia) used in experiment originated from own culture, which assured the selection of uniform plant material for comparative analyses. Standardized single shoots of the plants (ca. 1.0 m in height) were selected for the study and placed in the reactors together with their
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Figure 3.
M. De˛bowski et al.
Scheme of AST working cycle.
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Table 1.
Characteristics of crude wastewaters.
Parameter BOD5 COD Ntot. Ptot. pH Total suspended solids
Table 2.
A1 = 0.05 mg BOD5 /mgd.m. d
A2 = 0.10 mgBOD5 /mgd.m. d
Unit
Mean
SD
Mean
SD
mg O2 /l mg O2 /l mg N/l mg P/l – mg/l
1503.6 2140.9 95.6 23.7 7.19 11.3
192.5 221.7 7.3 2.6 0.11 1.1
3012.6 4282.3 191.7 48.2 7.06 12.9
258.3 299.7 9.6 3.3 0.14 1.6
Characteristics of rhizomes of hydrophytes used in the experiment. Common reed (P. australis)
Parameter Fresh mass height dry matter organic dry matter
Common cattail (T. latifolia)
Unit
Mean
SD
Mean
SD
mean
SD
mean
SD
g f.m. Cm g d.m./g f.m. g o.d.m./g d.m.
253.1 98.4 0.221 0.210
23.9 7.3 0.018 0.027
250.9 101.6 0.221 0.210
19.7 3.9 0.018 0.027
248.6 104.8 0.218 0.219
36.1 5.2 0.029 0.016
250.2 99.6 0.221 0.219
26.3 13.7 0.018 0.016
rhizomes and root system. A single batch of seedlings were from 4 to 6 plants in the case of common reed and from 3 to 5 plants in the case of common tail. The characteristics of biomass of the plant material used in the study were presented in Table 2. The crude and treated wastewaters were analysed once a day by means of cuvette tests (Germany). The following indicators of contamination were determined in the study period: COD, total nitrogen, ammonia nitrogen and total phosphorus. Determinations were carried out with a DR 5000 spectrophotometer and with an HT 200 s mineralizer. Measurements of BOD5 were conducted with the Oxi-top control system by WTW Company (Germany). An oxygen probe with a recorder (Endress Hauser) was used for continuous monitoring of oxygen content in the AST The content of total suspended solids in crude and treated wastewaters was determined with the gravimetric method. The pH value was measured with a VWR 1000L pH-meter. Before being fed to reactors, the plant material was analysed for moisture content and dry matter content. To this end, plants were selected at random from the seedlings
to be used in the experiment, and subjected to analyses (grinding → drying → analysis). After each experimental variant, the plants were removed from the reactors and subjected to analogous gravimetric analyses of water and dry matter contents. The plant material was also subjected to elementary carbon analysis using a Flesh 200 elemental analysed by Thermo Company. In addition, the length of the aerial parts of the plants was measured at the onset and at the end of each experimental variant. Microscope observations were made throughout the study to analyse the impact of the applied technology on changes in biocoenoses of AS in the subsequent variants of the experiment. Quantity of assimilated CO2 was determined by the following Equation (1): mCO2 =
mTOC × MCO2 (g), MC
(1)
where mCO2 is the quantity of assimilated CO2 (g); mTOC the content of total organic carbon (TOC) in biomass growth (g)];MCO2 the molecular weight of CO2 (g/mol) and MC the molecular weight of C (g/mol).
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The statistical analysis of results was carried out using STATISTICA 10.0 PL package. The hypothesis on the distribution of each analysed variable was verified with the Shapiro–Wilk W test. One-way analysis of variance was conducted to determine the significance of differences between mean values. In order to determine the significance of differences between the analysed variables, the Tukey’s honestly significant difference (HSD) test was used. In the above tests, the level of significance was adopted at α = 0.05.
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3. Results Irrespective of the applied experimental variant, a similar course of the biodegradation process of organic compounds was observed in the exploited technological system that was analogous for both species of hydrophytes. The efficiency of BOD5 reduction was high and ranged from 98.7% in variant 2 of series III to 99.1% in variant 1 of series II. The value of BOD5 in the effluent fitted within the range of 9.02–15.06 mg O2 /l Figure 4). The loading of the exploited technological system was observed to have a significant effect on COD value in the treated wastewaters. In variant 2, the COD value in the effluent ranged from 51.39 to 59.95 mg O2 /l. In contrast, significantly lower COD values were determined in variant 1, which oscillated around 20.0 mg O2 /l irrespective of the experimental series (Figure 5).
In variant 1 of series I, the concentration of total nitrogen reached 16.06 mg Ntot. /l, whereas the exploitation of the technological system at the loading of 0.05 g BOD5 /gd.m . d resulted in the final total nitrogen concentration at 32.78 mg Ntot. /l. A tangibly higher, comparable efficiency of Ntot. removal was noted for the reactors exploited in series II and series III. In variant 1 of series II, the efficiency of Ntot. removal accounted for 88.4%, which enabled reaching the concentration of 11.08 mg Ntot. /l. The comparable treatment efficiency was observed in variant 2, which resulted in Ntot. concentration at the level of 22.42 mg Ntot. /l (Figure 6). Statistically comparable final effects were achieved in series II. In the case of N-NH4 , the effectiveness of its removal was very high and fitted within a narrow range of 99.6–99.81% irrespective of the technological variant. Concentrations of ammonia nitrogen in the effluent were very low in all variants and ranged from 0.01 to 0.03 mg N-NH4 /l (Figure 7). The experiments demonstrated a significant effect of hydrophytes introduction to the treatment process on the efficiency of Ptot. removal. Tanks loading in variant 1 enabled achieving Ptot . concentration in the effluent at: 9.15 mg/l in series I, at 7.51 mg/l in series II and at 7.56 mg/l in series III. In variant 2, comparable concentrations of total phosphorus accounting for 15.70 mg Ptot. /l were observed in the series with hydrophytes. In the control reactor, in series I variant 2 the mean concentration of total phosphorus in the effluent was at 19.18 mg Ptot. /l (Figure 8).
Figure 4.
Value of BOD5 in the effluent.
Figure 6.
Concentration of Ntot. in the effluent.
Figure 5.
Value of COD in the effluent.
Figure 7.
Concentration of N-NH4 in the effluent.
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Figure 8.
M. De˛bowski et al.
Concentration of Ptot. in the effluent.
The pH value of the treated wastewaters was close to neutral. It was at a similar level irrespective of the analysed experimental variant and ranged from 7.03 to 7.12 (Figure 9). Also, no differences were noted in the concentration of total suspended solids in the effluent. In the successive variants of series I, it reached 11.72 and 10.03 mgd.m ./l, in series II it ranged from 12.74 mgd.m ./l in variant 1 to 11.62 mgd.m ./l in variant 2, whereas in series III values of this parameter oscillated around 13.00 mgd.m ./l in both variants (Figure 10). Irrespective of the hydrophyte species applied, no statistically significant changes were observed in oxygen concentration in the exploited tanks, which at the aeration phase reached ca. 1.9 mg O2 /l (Figures 11 and 12).
Figure 11. Course of changes in oxygen concentration in the AST, A = 0.05 mg BOD5 /mgd.m. d.
Figure 12. Course of changes in oxygen concentration in the AST, A = 0.10 mg BOD5 /mgd.m. d.
Figure 9.
Figure 10. ent.
The pH value in the effluent.
Concentration of total suspended solids in the efflu-
The microscope observations made throughout the study and their analysis enable to conclude that biocoenosis of the AS in the exploited biofilters contained a significant number of ciliates, and low counts of flagellates (Synura uvella, Euglena viridis and Codonosiga botrytis) and amoebas (Amoeba proteus, Arcella vulgaris and Difflugia oblonga). Floccules had light-brown colour. In some reactors, mainly those integrated with hydrophytes, filamentous fungi occurred as well. Irrespective of the analysed technological variant, analyses showed no intensive growth of filamentous bacteria, which is often the case in installations based on the AS method. This group of microorganisms – constituting a negative element of the biocoenosis of AS microflora as seen from the technological perspective – was represented by Sphaerotilus natans, which however did not result in swelling, foaming or expansion of the sludge during the treatment process and sedimentation. It may be concluded that the species composition of microflora in the investigated AS, in the subsequent biofilters, was not diversified. Analyses confirmed the presence of bacteria belonging to Bacillus and Achromobacter genera as well as of Pseudomonas putida and Pseudomonas fluorescens. In the AS, bacteria of the Alcaligenes and
Environmental Technology Table 3.
Results of microscope observations of AS in the experiment. Series I
Parameter
Variant 1
Series II Variant 2
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Sludge colour Light-brown Light-brown Follicles structure Compact, regular Compact, regular Follicles shape Non-branched, Slightly branched, spherical lobularspherical Follicles stability Stable Stable Follicles size 240 290 (μm) Plant and animal Numerous Numerous organisms Filamentous Sparse Relatively bacteria numerous 4.9 × 1011 Eubacteria 1.7 × 109 Table 4.
Series II III
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Variant 1
Series III Variant 2
Variant 1
Variant 2
Light-brown Light-brown Compact, regular Compact, regular Non-branched, Slightly branched, spherical lobularspherical Stable Stable 190 240
Light-brown Light-brown Compact, regular Compact, regular Non-branched, Non-branched, spherical spherical Stable 210
Stable 200
Numerous
Numerous
Numerous
Numerous
Sparse
Relatively numerous 5.7 × 1011
Sparse
Sparse
6.2 × 1010
4.2 × 1012
3.1 × 1010
Growth of hydrophytes biomass and effectiveness of CO2 absorption in the experiment.
Variant
Mass of biomass at the beginning of experiment (g f.w.)
Growth of biomass at the end of experiment (g f.w.)
Growth of biomass at the end of experiment (%)
Content of TOC in biomass growth (g)
Quantity of assimilated CO2 (g)
1 2 1 2
253.1 250.9 248.6 250.2
43.03 47.67 34.80 30.02
17.11 18.82 14.37 11.80
3.44 3.81 3.15 2.71
12.60 13.96 11.54 9.96
Flavobacterium genera were also abundant, which confirmed that the wastewaters contained high quantities of proteins and products of their hydrolysis (Table 3). The presence of E. viridis and C. botrytis, fungi: Fusarium avenaceum, Sclerotinia fructigenia, and Trichoderma viride, as well as sedentary ciliates: Opercularia articulata, and Vorticella convallaria and free-swimming ciliates: Aspidisca costata, Oxytricha ludibunda, and Spirostomum ambiguum, may indicate good condition of the AS. Prolonged exploitation of the technological systems had also a direct impact on rotifers emergence in the sludge that could have contributed to the loss of AS biomass. Likewise, at the beginning/end of treatment process, the follicles were lightbrown and small. A reduction was observed in the count of filamentous bacteria. The characteristics of AS obtained based on the microscope observations were presented in Table 4. The analysis of hydrophytes biomass growth conducted in the experiment showed that the higher effectiveness of biomass growth was noted for common reed irrespective of the technological variant. In variant 1, the value of this parameter reached 43.03 g fresh weight (f.w.), which constituted higher biomass of hydrophyte about 17.11%. In variant 2, the biomass of common reed increased 47.67 g f.w., i.e. by 18.82% (Table 4). In the series III based on common cattail, the respective increase reached 14.37% in variant 1 and 11.80% in variant 2.
4. Discussion The search for modifications in the SBR systems stem mainly from the necessity of improving the effectiveness of biogenes removal.[21,22] An example in this case was an attempt of integrating SBR with a circulation ditch that enabled the removal of 96.6% of N-NH4 . For comparison, the efficiency of N-NH4 removal in the AS–HS system ranged from 99.6% to 99.81% depending on variant. The analysis of the novel solution tested in the study showed that the achieved effectiveness of the treatment process was also significantly higher than the values obtained in typical HSs.[23] The vertical-flow hydrobotanical systems described in the literature assured N-NH4 removal with the efficiency approximating 72%.[24] Works addressing the improvement of the SBR effectiveness demonstrated process temperature to be directly responsible for the final outcomes of the treatment process.[25,26] A temperature of 20◦ C and additional aeration applied in the treatment process of dairy wastewater with N-NH4 content of 300 mg/l resulted in 93% efficiency of this indicator removal.[27] Corresponding results were also reported elsewhere.[28,29] In turn, in the system with hydrophyte filters based on P. australis, Da˛browski [30] recorded the efficiency of N-NH4 removal at 93.2%.[30] In thus-far conducted studies, processes of biogenes removal in SBRs were intensified via modifications of process duration and methods of wastewaters aeration.[31] The
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latter modification, however, enabled achieving barely 70% effectiveness of N-NH4 removal.[9,10] In addition, the preliminary aeration was proved not to affect the efficiency of Ptot. removal from dairy wastewaters.[32] Nearly 90% effectiveness of phosphorus removal is achieved upon the use of chemical coagulants that may, however, lead to secondary contamination of wastewaters.[33] The AS–HS system enabled Ptot. reduction to 65%. Experiments reported in this work proved the significant effect of hydrophytes introduction to the treatment process on the effectiveness of total phosphorus removal. The high removal effectiveness in the AS–HS system was noted for organic compounds and suspended solids. The achieved COD values ranged from 51.39 to 59.95 mg O2 /l at the loading of 0.05 mg BOD5 /mgd.m. d, and indicated over 96% reduction in the value of this parameter. It confirms the thesis that the application of the AS–HS system yields significantly better effects compared with those obtained in typical bioreactors.[34] An alternative solution includes the use of inorganic coagulants, however in this case the efficiency of COD removal does not exceed 70%.[3] Higher effectiveness of COD removal (from 70% to 80%) was achieved as a result of modifications in the SBR aeration systems.[35] In contrast, as reported by Tocchi,[36] the reduction of COD value decreases to 70% in the systems with additional aeration, compared with values between 88% and 94% achieved in the system without aeration.[36]
5. Conclusions An attempt was undertaken in this study to determine the effect of applying hydrobotanical systems based on common reed and common cattail on the improvement of the effectiveness of wastewater treatment processes in ASTs. The analysis of results obtained in the study enables to conclude that the investigated technology is a perspective solution that may limit or eliminate drawbacks of standard methods based on aerobic degradation of contaminants present in wastewaters. The analysed reactor enabled improving the effectiveness of removal of biogenes characterized by concentrations of Ntot. , N-NH4 and Ptot. . The technological effects achieved were comparable irrespective of the hydrophyte species (common reed or common cattail) used in the exploited system. The application of hydrophytes had no significant reducing effect on BOD5 and COD concentrations. The microbiological characteristics of the AS enable to conclude that the applied technological modifications of the system for wastewater treatment had no effect on the condition of biocoenoses of microorganisms taking part in the treatment process. Also, no effect was found for the loading of biofilters with organic compounds on significant changes in the species composition that determines the community of AS microflora. Microscope analyses of the AS allow for a conclusion that the microflora participating
in the removal of contaminants was in good condition and was characterized by high sedimentation capability. The AS–HS system consisted of a cylindrical AS chamber. Inside the chamber, there were inflow of raw wastewater and aeration diffusers in the bottom. The mixing system was located above that. The outflow of treated wastewater was located at the upper part of the chamber. Frame construction was used to fix the aquatic vegetation at the surface of AS liquid with the plant roots submerged in the AS. The upper part of the chamber was made of transparent material and the air outflow from the chamber was through the upper part of the cover. Funding The presented study was funded by the National Science Centre, Poland, conducted in the project [N N523 620839]. References [1] Banu JR, Anandan S, Kaliappan S, Yeom I-T. Treatment of dairy wastewater using anaerobic and solar photocatalytic methods. Sol Energy. 2008;82(9):812–819. [2] Britz TJ, van Schalkwyk C, Hung Y-T. Treatment of dairy processing wastewaters. In: Yapijakis C, Hung Y-T, Lo HH, Wang LK, editors. Waste treatment in the food processing industry. Boca Raton, FL: CRC Press; 2006. [3] Kushwaha JP, Srivastava VC, Mall ID. Organics removal from dairy wastewater by electrochemical treatment and residue disposal. Sep Purif Technol. 2010;76(2):198–205. [4] Janczukowicz W, Zieli´nski M, De˛bowski M, Pesta J. Estimation of biodegradability rate of pollutants in sewage from selected sections of dairy. Environ Prot Eng. 2007;33(1): 77–88. [5] Grady W Jr, Daigger G, Lim H. Biological wastewater treatment. 2nd ed. Basel: Marcel Dekker; 1999. [6] Kassab G, Halalsheh M, Klapwijk A, Fayyad M, van Lier JB. Sequential anaerobic–aerobic treatment for domestic wastewater. Bioresour Technol. 2010;101(10):3299–3310. [7] Janczukowicz W, Zieli´nski M, Debowski M. Biodegradability evaluation of dairy effluents originated in selected sections of dairy production. Bioresour Technol. 2007;99(10): 4199–4205. [8] Fernandes H, Jungles MK, Hoffmann H, Antonio RV, Costa RHR. Full-scale sequencing batch reactor (SBR) for domestic wastewater: performance and diversity of microbial communities. Bioresour Technol. 2013;132:262–268. [9] Guo JH, Peng YZ, Wang SY, Zheng YN, Huang HJ, Ge SJ. Effective and robust partial nitrification to nitrite by realtime aeration duration control in an SBR treating domestic wastewater. Process Biochem. 2009;44(9):979–985. [10] Rodríguez DA, Pino N, Panuela G. Monitoring the removal of nitrogen by applying a nitrification–denitrification process in a sequencing batch reactor (SBR). Bioresour Technol. 2011;102(3):2316–2321. [11] Guerrero J, Guisasola A, Baeza JA. The nature of the carbon source rules the competition between PAO and denitrifiers in systems for simultaneous biological nitrogen and phosphorus removal. Water Res. 2011;45(16):4793–4802. [12] Patel J, Nakhla G. Interaction of denitrification on P removal in anoxic P removal systems. Desalination. 2006;201:82–99. [13] D¸ebowski M, Krzemieniewski M, Zieli´nski M, Dudek M, Grala A. Respirometric studies on the effectiveness of biogas
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