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© IWA Publishing 2014 Water Science & Technology
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Aerobic co-treatment of landfill leachate and domestic wastewater – are slowly biodegradable organics removed or simply diluted? R. Campos, F. M. Ferraz, E. M. Vieira and J. Povinelli
ABSTRACT This study investigated the co-treatment of landfill leachate/domestic wastewater in bench-scale activated sludge (AS) reactors to determine whether the slowly biodegradable organic matter (SBOM) was removed rather than diluted. The AS reactors were loaded with mixtures of raw leachate and leachate that was pretreated by air stripping. The tested volumetric ratios were 0%, 0.2%, 2% and 5%. For all of the tested conditions, the reactors performed better when pretreated leachate was used rather than raw leachate, and the best volumetric ratio was 2%. The following removals were obtained: 97% for the biochemical oxygen demand (BOD5,20), 79% for total suspended solids, 77% for dissolved organic carbon and 84% for soluble chemical oxygen demand. Most of the pretreated leachate SBOM (65%) was removed rather than diluted or adsorbed into the sludge, as confirmed by Fourier transform infrared (FTIR) spectroscopy analyses. Key words
| activated sludge reactors, air stripping, FTIR spectroscopy, landfill leachate, organic
R. Campos F. M. Ferraz (corresponding author) J. Povinelli Departamento de Hidráulica e Saneamento, Escola de Engenharia de São Carlos, Universidade de São Paulo, Av. Trabalhador São Carlense, 400, CEP 13566-590 São Carlos, São Paulo, Brasil E-mail: [email protected] E. M. Vieira Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São Carlense, 400, CEP 13566-590 São Carlos, São Paulo, Brasil
matter removal
INTRODUCTION Leachate is a pollutant wastewater that is generated by sanitary landfills. Its characteristics may vary depending on the type of landfilled waste and the climate conditions. The primary constituents of leachates include inorganic salts, heavy metals, ammonia and organic matter. Leachates can be classified as young or old, as follows: young leachates contain low total ammoniacal nitrogen (TAN) concentrations and biodegradable organic matter, and old leachates contain high TAN concentrations, slowly biodegradable and refractory organic matter, such as humic substances (Renou et al. ; Contrera et al. ). Among conventional treatments, the co-treatment of leachate and domestic wastewater is a cost-attractive and advantageous alternative that has been adopted worldwide (Çeçen & Aktaş ; Hasar et al. ; Capodici et al. ; Ferraz et al. ). Leachate is co-treated with domestic wastewater primarily in aerobic-based processes, and the tested volumetric ratios of the leachate generally vary from 0.2% to 5%. Satisfactory reductions (up to 90%) in chemical oxygen demand (COD) and TAN have been reported (Çeçen & Aktaş ; Capodici et al. ; Ferraz et al. ). Drewnowski () reported the removal of particulate and colloidal slowly biodegradable organic matter doi: 10.2166/wst.2014.439
(SBOM) from domestic wastewater by hydrolysis followed by aerobic biodegradation, which was indirectly assessed by measuring the oxygen utilization rate. Compared with domestic wastewater, old leachates present a major content of complex organic matter (Frimmel & Abbt-Braun ; Rodríguez et al. ). Nonetheless, despite the promising results regarding the aerobic co-treatment of leachate, it is unclear whether the old leachates’ dissolved SBOM was removed via biodegradation rather than dilution. This questioning motivated the current research, which aimed to analyze the co-treatment of leachate/domestic wastewater in bench-scale activated sludge (AS) reactors, focusing on the behavior of the SBOM during the co-treatment.
MATERIALS AND METHODS Wastewaters and synthetic substrate The following wastewaters were used in this experiment: domestic wastewater, raw leachate and leachate pretreated by air stripping (for TAN removal). The physicochemical
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Aerobic co-treatment of landfill leachate and domestic wastewater
characterization of wastewaters was determined by Ferraz et al. (). An old leachate was collected from the municipal sanitary landfill of São Carlos, São Paulo state, Brazil. The leachate pretreatment by air stripping was described by Ferraz et al. (). To eliminate the interference of domestic wastewater when assessing the leachate SBOM behavior during aerobic co-treatment, lactose was substituted for domestic wastewater in two experiments. Lactose is an easily biodegradable substrate, so when the leachates were added to lactose, they were the only source of SBOM. A 1 g L1 solution of lactose was produced by dissolving lactose in biochemical oxygen demand (BOD) dilution water that was prepared with the seed (domestic wastewater) and nutrients according to Standard Methods (APHA, AWA, WEF ). Raw and pretreated leachates were added to domestic wastewater at volumetric ratios of 0% (control), 0.2%, 2% and 5%. The volumetric ratio that corresponded to the best organic matter removal was selected for the experiments with lactose.
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Analytical procedures Physicochemical and spectroscopic analyses The following parameters were measured according to Standard Methods (APHA, AWA, WEF ): BOD5,20 (Hach BODTrakII respirometric apparatus), method 5210 B; dissolved organic carbon (DOC) (Shimadzu TOC 5000 A Analyzer), method 5310 B; solid content, method 2540; and soluble chemical oxygen demand (SCOD) (Hach COD reactor 45600-00/Hach DR 2010 spectrophotometer), colorimetric method 5220 D. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups that were present in the leachate structure. A Bomem B-102 FTIR spectrometer was used to record the FTIR spectra from KBr pallets containing approximately 1 mg of a lyophilized sample and 100 mg of KBr. The FTIR spectra were obtained by collecting 16 scans over a wavenumber range of 4,000–400 cm1 at a resolution of 4 cm1. The spectra were plotted in Origin 8.0 (Origin Lab). Determining the leachate SBOM removal
Bench-scale AS reactors Ten bench-scale AS reactors were used, consisting of 10-L working volume tanks made of acrylic. In the experiments conducted using domestic wastewater, seven reactors were inoculated with 2.5 L of AS that was obtained from a wastewater treatment plant, containing approximately 3,000 mg L1 of volatile suspended solids (VSS). During the start-up period, the reactors were aerated and only loaded with domestic wastewater for 5 days. The experiments with lactose were conducted exclusively to assess the behavior of the leachate SBOM during the aerobic co-treatment without interference from domestic wastewater SBOM. Consequently, the reactors were not inoculated with aerobic sludge, which could contain SBOM. The sources of microorganisms in the aeration tanks included the BOD dilution water and the leachates. Consequently, the concentration of VSS in the aeration tanks was as low as 100 mg L1. The reactors were operated under room temperature (≈20 C) for 20 days, which exceeds the typical hydraulic retention time that is adopted by wastewater treatment plants. However, this operational time was adopted, because it includes the range in which organic matter oxidation reached 95–99% in the BOD tests (Metcalf & Eddy ). W
Due to the difficulties associated with directly determining the SBOM from wastewaters (Drewnowski ), a standardized method is lacking. In this research, the SBOM was indirectly determined as follows: discounting the DOC of domestic wastewater from the DOC of the mixtures containing leachate, the influent leachate SBOM was determined. Applying the same procedure for effluent samples, the leachate inert organic matter (Si) was determined. These procedures were also valid for the experiments with lactose. Thus, the leachate SBOM removal efficiency was determined according to Equation (1): Removal (%) ¼ 100 ×
SBOM Si SBOM
(1)
RESULTS AND DISCUSSION BOD5,20, TSS, DOC and SCOD removal In the experiments using domestic wastewater, the AS reactors were operated under the following conditions: an average concentration of mixed liquor volatile suspended solids (MLVSS) of 3,000 mg L1; sludge volumetric index
366 349 80 84 49 40
160 125 66 77 44 23
53 85 74 79 16 10
172 142 94 97 10 5
)
249 252 78 81 42 35
131 100 82 83 14 13
99 48 66 81 23 11
6 3
97 98
165 166
1
(mg L (%) )
203 180 90 18
81 78 83 12
65 58 86 10
184 168 98 3
)
1 2 SCOD
RL/DW PTL/DW
1 2 DOC
RL/DW PTL/DW
1 2 TSS
RL/DW PTL/DW
1 2 BOD5,20
RL/DW PTL/DW
Experiments Variable
Mixtures
W
187
69
59
140
1
(mg L
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BOD5,20: biochemical oxygen demand (5-day test at 20 C); TSS: total suspended solids; DOC: dissolved organic carbon; SCOD: soluble chemical oxygen demand; RL: raw leachate; PTL: pretreated leachate; DW: domestic wastewater.
44 48 202 180
52 71 77 37
52 57 25 40
12 7
93 95
(%)
Effluent ) 1
(mg L
Influent Removal
|
1
(mg L
Influent
(%)
Effluent
Removal Influent
Effluent
Removal
Influent
Effluent
(%)
5% 2% 0.2% 0%
Volumetric ratios
below 100 mL g1; and a food to microorganism (F/M) ratio of 0.02 kgBOD kgMLVSS1 d1, which was a very low ratio caused by the low strength of domestic wastewater. In the aerobic co-treatment with domestic wastewater, the interference of raw and pretreated leachates was negligible at a volumetric ratio of 0.2%: the total amounts of BOD5,20 (98%) and DOC (80%) removed were equal to those removed in the control reactor (Table 1). Loaded with leachates at a volumetric ratio of 2%, the reactors efficiently removed the BOD5,20, total suspended solids (TSS) and SCOD and were only 10% less effective than the control reactor (Table 1). Using a volumetric ratio of 5% directly affected the TSS, DOC and SCOD removals, resulting in removal rates that were approximately 34%–51% less than the removal rates in the control reactor (Table 1). In a previous study, a young leachate was co-treated with synthetic domestic wastewater in a 2-L AS reactor containing 2,100 mgMLVSS L1 (Çeçen & Aktaş ). For a volumetric ratio of 5%, the SCOD removal was 89%, and the refractory SCOD in treated effluent was 100 mgO2 L1, which were twice as large as the values obtained in the current study for raw leachate (Table 1). The comparison between the studies highlighted that organic matter is much more easily removed from young leachates than from old leachates. For the three tested volumetric ratios (0.2%, 2% and 5%), the majority of organic matter was removed with pretreated leachate (experiment 2) rather than raw leachate (experiment 1). This finding potentially resulted from the lower humic substance content in pretreated leachate compared with raw leachate. Lime was added to raw leachate before the air stripping pretreatment. In addition, Renou et al. () reported that humic substances could be partially removed from leachate by co-precipitation with CaCO3. Co-precipitation occurs when organic substances adsorb onto the surface of growing CaCO3 crystals (Liao & Randtke ). At a pH of 11, the functional groups of the humic substances dissociate and quickly react with Caþ, followed by co-precipitation with CaCO3 (Liao & Randtke ; Renou et al. ). The lactose experiments allowed for the evaluation of the co-treatment process when the leachates were the only source of SBOM. According to the best results from experiments 1 and 2, a volumetric leachate ratio of 2% was tested in experiments 3 and 4. As expected for such an easily biodegradable substrate, in the control reactor, lactose was almost completely removed (Table 2). The aerobic reactors sufficiently removed the organic matter when the leachates were added at a volumetric ratio of 2%. However, their performances differed from the control reactor by less than 10% (Table 2).
Water Science & Technology
Removal
Aerobic co-treatment of landfill leachate and domestic wastewater
Organic matter removal from the co-treatment of leachates and domestic wastewater after 20 days of aeration
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Table 1
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Table 2
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Organic matter removal from the co-treatment of leachates and lactose solution after 20 days of aeration
Volumetric ratios 0%
2%
Influent
Effluent
Removal
Influent
(%)
(mg L
0
100
715 650
6 4
99 99
120
11
91
100 70
30 13
70 81
RL/LAC PTL/LAC
352
9
97
373 371
20 15
94 96
RL/LAC PTL/LAC
1,042
27
97
1,207 1,195
103 70
91 94
1
Variable
Experiments
Mixtures
(mg L
BOD5,20
3 4
RL/LAC PTL/LAC
528
TSS
3 4
RL/LAC PTL/LAC
DOC
3 4
SCOD
3 4
)
1
Effluent
Removal
)
(%)
W
BOD5,20, biochemical oxygen demand (5-day test at 20 C); TSS, total suspended solids; DOC, dissolved organic carbon; SCOD, soluble chemical oxygen demand; LAC, lactose; RL, raw leachate; PTL, pretreated leachate.
W
Assessment of leachate SBOM removal In previous studies, it was observed that COD was further removed by adsorption when powdered activated carbon or zeolite was added to aeration tanks (Çeçen & Aktaş ; Mojiri et al. ). Thus, it was not clear whether the leachate SBOM would be biodegraded or diluted in the absence of adsorbents. According to Table 3, the best results were obtained when pretreated leachate was used rather than raw leachate. In experiments 1 and 2, most of the SBOM was removed from the mixtures that contained pretreated leachate at volumetric ratios of 0.2% and 2% (89% and 65%, respectively; Table 3). Even at the volumetric ratio of 5% of pretreated leachate, SBOM was removed (55%). Except for raw leachate at a volumetric ratio of 5%, the SBOM was satisfactorily removed in all tested conditions, a result supported by two recent studies based on kinetic parameters. Drewnowski (), studying the aerobic degradation of domestic wastewater (operational temperature, Table 3
|
20 C), determined yield coefficients for the heterotrophic biomass (YH) in the range of 0.62–0.72 mg VSS mg COD1. A very similar range of YH (0.64–0.68 mg VSS mg COD1) was determined, at an operational temperature of 20 C, by Capodici et al. () in their study on leachate co-treatment. The similarity between ranges of YH highlights the ability of aerobic biomass to assimilate the organic content of leachate. The operational conditions tested in the lactose experiments guaranteed that the leachates were the only sources of SBOM. As shown in Table 3, the leachates’ SBOM removal efficiencies and rates were nearly identical to those obtained in the domestic wastewater experiments. Thus, the results obtained in experiments 1 and 2 were validated by experiments 3 and 4. W
FTIR spectroscopic analysis of the raw and treated samples To better evaluate the leachate SBOM removal, the raw and treated samples from the reactors that were loaded with
Assessment of leachates’ slowly biodegradable organic matter (SBOM) removal over 20 days of aeration
Experiments
1
2
3
4
Raw leachate/lactose
Pretreated leachate/lactose
Raw leachate/domestic
Pretreated leachate/
Mixture of wastewaters
wastewater
domestic wastewater
Volumetric ratios (%)
0.2
2
5
0.2
2
5
2
2
Influent SBOM
12
62
91
9
31
56
21
19
Inert organic matter
2
32
65
1
11
25
11
6
SBOM removal (%)
83
48
29
89
65
55
48
68
SBOM removal rate (d1)
0.09
0.03
0.02
0.11
0.05
0.04
0.03
0.06
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leachates at a volumetric ratio of 2% were analyzed by FTIR spectroscopy. As shown in Figures 1(a)–1(c), the absorption bands that were observed in the domestic wastewater spectrum were also found in the spectra of the influent samples that contained leachates at a volumetric ratio of 2%. Nonetheless, the absorption intensities in the spectra from the samples containing leachates were greater than the intensities detected for the domestic wastewater. The band at 875 cm1 was intrinsic to the leachates and was related to the C–O out-of-plane deformation of carbonates (Smidt & Meissl ). After 20 days of aeration, most of the absorption bands in the raw domestic wastewater spectra were not detected in the treated effluent of the control reactor. This finding confirmed that the organic matter was oxidized (Figure 1(a)).
Figure 1
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When comparing the influent and effluent sample spectra from the reactors that were loaded with raw leachate/domestic wastewater (Figure 1(b)) and pretreated leachate/domestic wastewater (Figure 1(c)) mixtures, the oxidation of the following components was observed: alcohols or phenols (3,400 cm1); aliphatic methylene (2,900–2,800 cm1); aromatic C ¼ C bonds (1,600 cm1); carboxylic acid/carboxylate ions (1,400 cm1); polysaccharides (1,130 cm1); and organic nitrogen to nitrate (2,400 and 1,382 cm1) (Liang et al. ; Silverstein et al. ; Smidt & Meissl ). However, this oxidation was more effective when the pretreated leachate was used rather than the raw leachate. For example, the absorption intensity at 3,400 cm1 decreased by only 7% in the raw leachate spectra, but it decreased by 39% in the pretreated leachate spectra (Figures 1(b) and 1(c)).
FTIR spectra of the influent and effluent samples for the reactors loaded with (a) domestic wastewater (DW), (b) a mixture of raw leachate/domestic wastewater (RL/DW) at a volumetric ratio of 2% and (c) a mixture of pretreated leachate/domestic wastewater (PTL/DW) at a volumetric ratio of 2%.
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Regarding the lactose experiments, most of the absorption bands found in the raw lactose spectrum either were not detected or had lower absorption intensities in the treated effluents of the control reactor, which confirmed that organic matter oxidation occurred (Figure 2(a)). The remaining bands in the spectra from the treated lactose included the following: 3,400 cm1 with an absorption intensity that decreased by 84%; 1,100–1,050 cm1, which resulted from the remaining polysaccharides; and 620 cm1, which resulted from the S–O angular deformation of inorganic sulfate (caused by the MnSO4 used to prepare BOD dilution water in which powdered lactose was dissolved) or from the out-of-plane O–H deformation of alcohols. The presence of alcohols may result from the aerobic fermentation of lactose (Silveira et al. ). The FTIR spectra of the raw leachate/lactose and the pretreated leachate/lactose presented the same bands as the lactose spectra, but with greater absorption intensities
Figure 2
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(Figures 2(b) and 2(c)). Due to the removal of organic matter, most of the bands detected in the raw samples were not detected in the treated samples. In the spectra presented in Figures 2(b) and 2(c), the following components were oxidized: alcohols or phenols (3,400 cm1); aliphatic methylene (2,900 cm1); carboxylic acids and ketones (1,700 cm1); aromatic C ¼ C bonds (1,600 cm1); carboxylic acid/carboxylate ions (1,400 cm1); polysaccharides (1,050 cm1) and amines (700 and 780 cm1) (Silverstein et al. ; Smidt & Meissl ; Liang et al. ). The remaining bands were the same as those detected in the spectra of the treated lactose, except the band at 1,265 cm1 (C–O vibrations of carboxylic acids and C–N vibrations of amines and amides). In a previous study regarding the decomposition of waste materials (Smidt & Meissl ), this absorption band was attributed to the mono-molecules that originated from the degradation of the macromolecules.
FTIR spectra of the influent and effluent samples for the reactors loaded with (a) lactose (LAC), (b) a mixture of raw leachate/lactose (RL/LAC) at a volumetric ratio of 2%, (c) a mixture of pretreated leachate/lactose (PTL/LAC) at a volumetric ratio of 2% and (d) sludge samples from the control reactor and the reactors loaded with raw and pretreated leachate at a volumetric ratio of 2%.
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Ferraz et al. () used FTIR spectroscopy to analyze sludge samples that were used for a submerged aerobic biofilter start-up and samples that were acquired after the cotreatment of pretreated leachate and domestic wastewater at a volumetric ratio of 2%. The spectra were identical, which confirmed that the organic matter was primarily biodegraded rather than adsorbed to the sludge. The spectra shown in Figure 2(d) correspond with these findings. The spectra were identical for the sludge samples that were developed in the reactors that were loaded with lactose, raw leachate/ lactose 2% and pretreated leachate/lactose 2%. The FTIR spectroscopic analyses indicated that the leachate SBOM was primarily biodegraded rather than adsorbed or diluted. If dilution had occurred, the influent and effluent FTIR spectra would be identical, which did not occur in this study.
CONCLUSIONS The co-treatment of domestic wastewater and landfill leachate was successfully performed in AS reactors that were operated in batches. The AS reactors performed better when pretreated leachate was used at a volumetric ratio of 2%. It was determined that most (65%) of the pretreated leachate SBOM was removed rather than diluted, as confirmed by FTIR analyses.
ACKNOWLEDGEMENTS The authors would like to thank the São Paulo Research Foundation (grant numbers 2010/51955-2 and 2011/ 50627-4) and the National Council for Scientific and Technological Development (grant numbers 141710/2010-1 and 303083/2010-7) for their financial support. We also thank the anonymous reviewers for their helpful comments.
REFERENCES Capodici, M., Di Trapani, D. & Viviani, G. Co-treatment of landfill leachate in laboratory-scale sequencing batch reactors: analysis of system performance and biomass activity by means of respirometric techniques. Water Sci. Technol. 69 (6), 1267–1274.
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Çeçen, F. & Aktaş, O. Aerobic co-treatment of landfill leachate with domestic wastewater. Environ. Eng. Sci. 21 (3), 303–312. Contrera, R. C., Sarti, A., Castro, M. C. A. A., Foresti, E., Zaiat, M. & Shalch, V. Ethanol addition as a strategy for start-up and acclimation of an AnSBBR for the treatment of landfill leachate. Process Biochem. 48, 1767–1777. Drewnowski, J. The impact of slowly biodegradable organic compounds on the oxygen uptake rate in activated sludge systems. Water Sci. Technol. 69 (6), 1136–1144. Ferraz, F. M., Povinelli, J., Pozzi, E., Vieira, E. M. & Trofino, J. C. Co-treatment of landfill leachate and domestic wastewater using a submerged aerobic biofilter. J. Environ. Manage. 141, 9–15. Frimmel, F. H. & Abbt-Braun, G. Basic characterization of reference NOM from Central Europe – similarities and differences. Environ. Int. 25 (23), 191–207. Hasar, H., Ipek, U. & Kinaci, C. Joint treatment of landfill leachate with municipal wastewater by submerged membrane bioreactor. Water Sci. Technol. 60 (12), 3121–3127. Liang, Z., Liu, J. X. & Li, J. Decomposition and mineralization of aquatic humic substances (AHS) in treating landfill leachate using the ANAMMOX process. Chemosphere 74, 1315–1320. Liao, M. Y. & Randtke, S. J. Predicting the removal of soluble organic contaminants by lime softening. Water Res. 20 (1), 27–35. Metcalf, Eddy. Wastewater Engineering: Treatment and Reuse. 4th international edn, McGraw-Hill, New York. Mojiri, A., Aziz, H. A., Zaman, N. Q. & Aziz, S. Q. Powdered ZELIAC augmented sequencing batch reactors (SBR) process for co-treatment of landfill leachate and domestic wastewater. J. Environ. Manage. 139, 1–14. Renou, S., Poulain, S., Givaudan, J. G. & Moulin, P. Amelioration of ultrafiltration process by lime treatment: case of landfill leachate. Desalination 249 (1), 72–82. Rodríguez, J., Castrillón, L., Marañón, E., Sastre, H. & Fernández, E. Removal of non-biodegradable organic matter from landfill leachates by adsorption. Water Res. 38, 3297–3303. Silveira, W. B., Passos, F. J. V., Mantovani, H. C. & Passos, F. M. L. Ethanol production from cheese whey permeate by Kluyveromyces marxianus UFV-3: a flux analysis of oxidoreductive metabolism as a function of lactose concentration and oxygen levels. Enzyme Microb. Technol. 36, 930–936. Silverstein, R. M., Webster, F. X. & Kiemle, D. J. Spectrometric Identification of Organic Compounds. 7th edn, John Wiley & Sons, New York. Smidt, E. & Meissl, K. The applicability of Fourier transform infrared (FTIR) spectroscopy in waste management. Waste Manage. 27, 268–276. Standard Methods for the Examination of Water and Wastewater 22nd edn, APHA – American Public Health Association, AWWA – American Water Works Association, WEF – Water Environment Federation, Washington, DC.
First received 7 August 2014; accepted in revised form 20 October 2014. Available online 30 October 2014
© IWA Publishing 2014 Water Science & Technology
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Aerobic co-treatment of landfill leachate and domestic wastewater – are slowly biodegradable organics removed or simply diluted? R. Campos, F. M. Ferraz, E. M. Vieira and J. Povinelli
ABSTRACT This study investigated the co-treatment of landfill leachate/domestic wastewater in bench-scale activated sludge (AS) reactors to determine whether the slowly biodegradable organic matter (SBOM) was removed rather than diluted. The AS reactors were loaded with mixtures of raw leachate and leachate that was pretreated by air stripping. The tested volumetric ratios were 0%, 0.2%, 2% and 5%. For all of the tested conditions, the reactors performed better when pretreated leachate was used rather than raw leachate, and the best volumetric ratio was 2%. The following removals were obtained: 97% for the biochemical oxygen demand (BOD5,20), 79% for total suspended solids, 77% for dissolved organic carbon and 84% for soluble chemical oxygen demand. Most of the pretreated leachate SBOM (65%) was removed rather than diluted or adsorbed into the sludge, as confirmed by Fourier transform infrared (FTIR) spectroscopy analyses. Key words
| activated sludge reactors, air stripping, FTIR spectroscopy, landfill leachate, organic
R. Campos F. M. Ferraz (corresponding author) J. Povinelli Departamento de Hidráulica e Saneamento, Escola de Engenharia de São Carlos, Universidade de São Paulo, Av. Trabalhador São Carlense, 400, CEP 13566-590 São Carlos, São Paulo, Brasil E-mail: [email protected] E. M. Vieira Instituto de Química de São Carlos, Universidade de São Paulo, Av. Trabalhador São Carlense, 400, CEP 13566-590 São Carlos, São Paulo, Brasil
matter removal
INTRODUCTION Leachate is a pollutant wastewater that is generated by sanitary landfills. Its characteristics may vary depending on the type of landfilled waste and the climate conditions. The primary constituents of leachates include inorganic salts, heavy metals, ammonia and organic matter. Leachates can be classified as young or old, as follows: young leachates contain low total ammoniacal nitrogen (TAN) concentrations and biodegradable organic matter, and old leachates contain high TAN concentrations, slowly biodegradable and refractory organic matter, such as humic substances (Renou et al. ; Contrera et al. ). Among conventional treatments, the co-treatment of leachate and domestic wastewater is a cost-attractive and advantageous alternative that has been adopted worldwide (Çeçen & Aktaş ; Hasar et al. ; Capodici et al. ; Ferraz et al. ). Leachate is co-treated with domestic wastewater primarily in aerobic-based processes, and the tested volumetric ratios of the leachate generally vary from 0.2% to 5%. Satisfactory reductions (up to 90%) in chemical oxygen demand (COD) and TAN have been reported (Çeçen & Aktaş ; Capodici et al. ; Ferraz et al. ). Drewnowski () reported the removal of particulate and colloidal slowly biodegradable organic matter doi: 10.2166/wst.2014.439
(SBOM) from domestic wastewater by hydrolysis followed by aerobic biodegradation, which was indirectly assessed by measuring the oxygen utilization rate. Compared with domestic wastewater, old leachates present a major content of complex organic matter (Frimmel & Abbt-Braun ; Rodríguez et al. ). Nonetheless, despite the promising results regarding the aerobic co-treatment of leachate, it is unclear whether the old leachates’ dissolved SBOM was removed via biodegradation rather than dilution. This questioning motivated the current research, which aimed to analyze the co-treatment of leachate/domestic wastewater in bench-scale activated sludge (AS) reactors, focusing on the behavior of the SBOM during the co-treatment.
MATERIALS AND METHODS Wastewaters and synthetic substrate The following wastewaters were used in this experiment: domestic wastewater, raw leachate and leachate pretreated by air stripping (for TAN removal). The physicochemical
1942
R. Campos et al.
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Aerobic co-treatment of landfill leachate and domestic wastewater
characterization of wastewaters was determined by Ferraz et al. (). An old leachate was collected from the municipal sanitary landfill of São Carlos, São Paulo state, Brazil. The leachate pretreatment by air stripping was described by Ferraz et al. (). To eliminate the interference of domestic wastewater when assessing the leachate SBOM behavior during aerobic co-treatment, lactose was substituted for domestic wastewater in two experiments. Lactose is an easily biodegradable substrate, so when the leachates were added to lactose, they were the only source of SBOM. A 1 g L1 solution of lactose was produced by dissolving lactose in biochemical oxygen demand (BOD) dilution water that was prepared with the seed (domestic wastewater) and nutrients according to Standard Methods (APHA, AWA, WEF ). Raw and pretreated leachates were added to domestic wastewater at volumetric ratios of 0% (control), 0.2%, 2% and 5%. The volumetric ratio that corresponded to the best organic matter removal was selected for the experiments with lactose.
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Analytical procedures Physicochemical and spectroscopic analyses The following parameters were measured according to Standard Methods (APHA, AWA, WEF ): BOD5,20 (Hach BODTrakII respirometric apparatus), method 5210 B; dissolved organic carbon (DOC) (Shimadzu TOC 5000 A Analyzer), method 5310 B; solid content, method 2540; and soluble chemical oxygen demand (SCOD) (Hach COD reactor 45600-00/Hach DR 2010 spectrophotometer), colorimetric method 5220 D. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups that were present in the leachate structure. A Bomem B-102 FTIR spectrometer was used to record the FTIR spectra from KBr pallets containing approximately 1 mg of a lyophilized sample and 100 mg of KBr. The FTIR spectra were obtained by collecting 16 scans over a wavenumber range of 4,000–400 cm1 at a resolution of 4 cm1. The spectra were plotted in Origin 8.0 (Origin Lab). Determining the leachate SBOM removal
Bench-scale AS reactors Ten bench-scale AS reactors were used, consisting of 10-L working volume tanks made of acrylic. In the experiments conducted using domestic wastewater, seven reactors were inoculated with 2.5 L of AS that was obtained from a wastewater treatment plant, containing approximately 3,000 mg L1 of volatile suspended solids (VSS). During the start-up period, the reactors were aerated and only loaded with domestic wastewater for 5 days. The experiments with lactose were conducted exclusively to assess the behavior of the leachate SBOM during the aerobic co-treatment without interference from domestic wastewater SBOM. Consequently, the reactors were not inoculated with aerobic sludge, which could contain SBOM. The sources of microorganisms in the aeration tanks included the BOD dilution water and the leachates. Consequently, the concentration of VSS in the aeration tanks was as low as 100 mg L1. The reactors were operated under room temperature (≈20 C) for 20 days, which exceeds the typical hydraulic retention time that is adopted by wastewater treatment plants. However, this operational time was adopted, because it includes the range in which organic matter oxidation reached 95–99% in the BOD tests (Metcalf & Eddy ). W
Due to the difficulties associated with directly determining the SBOM from wastewaters (Drewnowski ), a standardized method is lacking. In this research, the SBOM was indirectly determined as follows: discounting the DOC of domestic wastewater from the DOC of the mixtures containing leachate, the influent leachate SBOM was determined. Applying the same procedure for effluent samples, the leachate inert organic matter (Si) was determined. These procedures were also valid for the experiments with lactose. Thus, the leachate SBOM removal efficiency was determined according to Equation (1): Removal (%) ¼ 100 ×
SBOM Si SBOM
(1)
RESULTS AND DISCUSSION BOD5,20, TSS, DOC and SCOD removal In the experiments using domestic wastewater, the AS reactors were operated under the following conditions: an average concentration of mixed liquor volatile suspended solids (MLVSS) of 3,000 mg L1; sludge volumetric index
366 349 80 84 49 40
160 125 66 77 44 23
53 85 74 79 16 10
172 142 94 97 10 5
)
249 252 78 81 42 35
131 100 82 83 14 13
99 48 66 81 23 11
6 3
97 98
165 166
1
(mg L (%) )
203 180 90 18
81 78 83 12
65 58 86 10
184 168 98 3
)
1 2 SCOD
RL/DW PTL/DW
1 2 DOC
RL/DW PTL/DW
1 2 TSS
RL/DW PTL/DW
1 2 BOD5,20
RL/DW PTL/DW
Experiments Variable
Mixtures
W
187
69
59
140
1
(mg L
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BOD5,20: biochemical oxygen demand (5-day test at 20 C); TSS: total suspended solids; DOC: dissolved organic carbon; SCOD: soluble chemical oxygen demand; RL: raw leachate; PTL: pretreated leachate; DW: domestic wastewater.
44 48 202 180
52 71 77 37
52 57 25 40
12 7
93 95
(%)
Effluent ) 1
(mg L
Influent Removal
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1
(mg L
Influent
(%)
Effluent
Removal Influent
Effluent
Removal
Influent
Effluent
(%)
5% 2% 0.2% 0%
Volumetric ratios
below 100 mL g1; and a food to microorganism (F/M) ratio of 0.02 kgBOD kgMLVSS1 d1, which was a very low ratio caused by the low strength of domestic wastewater. In the aerobic co-treatment with domestic wastewater, the interference of raw and pretreated leachates was negligible at a volumetric ratio of 0.2%: the total amounts of BOD5,20 (98%) and DOC (80%) removed were equal to those removed in the control reactor (Table 1). Loaded with leachates at a volumetric ratio of 2%, the reactors efficiently removed the BOD5,20, total suspended solids (TSS) and SCOD and were only 10% less effective than the control reactor (Table 1). Using a volumetric ratio of 5% directly affected the TSS, DOC and SCOD removals, resulting in removal rates that were approximately 34%–51% less than the removal rates in the control reactor (Table 1). In a previous study, a young leachate was co-treated with synthetic domestic wastewater in a 2-L AS reactor containing 2,100 mgMLVSS L1 (Çeçen & Aktaş ). For a volumetric ratio of 5%, the SCOD removal was 89%, and the refractory SCOD in treated effluent was 100 mgO2 L1, which were twice as large as the values obtained in the current study for raw leachate (Table 1). The comparison between the studies highlighted that organic matter is much more easily removed from young leachates than from old leachates. For the three tested volumetric ratios (0.2%, 2% and 5%), the majority of organic matter was removed with pretreated leachate (experiment 2) rather than raw leachate (experiment 1). This finding potentially resulted from the lower humic substance content in pretreated leachate compared with raw leachate. Lime was added to raw leachate before the air stripping pretreatment. In addition, Renou et al. () reported that humic substances could be partially removed from leachate by co-precipitation with CaCO3. Co-precipitation occurs when organic substances adsorb onto the surface of growing CaCO3 crystals (Liao & Randtke ). At a pH of 11, the functional groups of the humic substances dissociate and quickly react with Caþ, followed by co-precipitation with CaCO3 (Liao & Randtke ; Renou et al. ). The lactose experiments allowed for the evaluation of the co-treatment process when the leachates were the only source of SBOM. According to the best results from experiments 1 and 2, a volumetric leachate ratio of 2% was tested in experiments 3 and 4. As expected for such an easily biodegradable substrate, in the control reactor, lactose was almost completely removed (Table 2). The aerobic reactors sufficiently removed the organic matter when the leachates were added at a volumetric ratio of 2%. However, their performances differed from the control reactor by less than 10% (Table 2).
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Removal
Aerobic co-treatment of landfill leachate and domestic wastewater
Organic matter removal from the co-treatment of leachates and domestic wastewater after 20 days of aeration
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Table 1
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Table 2
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Organic matter removal from the co-treatment of leachates and lactose solution after 20 days of aeration
Volumetric ratios 0%
2%
Influent
Effluent
Removal
Influent
(%)
(mg L
0
100
715 650
6 4
99 99
120
11
91
100 70
30 13
70 81
RL/LAC PTL/LAC
352
9
97
373 371
20 15
94 96
RL/LAC PTL/LAC
1,042
27
97
1,207 1,195
103 70
91 94
1
Variable
Experiments
Mixtures
(mg L
BOD5,20
3 4
RL/LAC PTL/LAC
528
TSS
3 4
RL/LAC PTL/LAC
DOC
3 4
SCOD
3 4
)
1
Effluent
Removal
)
(%)
W
BOD5,20, biochemical oxygen demand (5-day test at 20 C); TSS, total suspended solids; DOC, dissolved organic carbon; SCOD, soluble chemical oxygen demand; LAC, lactose; RL, raw leachate; PTL, pretreated leachate.
W
Assessment of leachate SBOM removal In previous studies, it was observed that COD was further removed by adsorption when powdered activated carbon or zeolite was added to aeration tanks (Çeçen & Aktaş ; Mojiri et al. ). Thus, it was not clear whether the leachate SBOM would be biodegraded or diluted in the absence of adsorbents. According to Table 3, the best results were obtained when pretreated leachate was used rather than raw leachate. In experiments 1 and 2, most of the SBOM was removed from the mixtures that contained pretreated leachate at volumetric ratios of 0.2% and 2% (89% and 65%, respectively; Table 3). Even at the volumetric ratio of 5% of pretreated leachate, SBOM was removed (55%). Except for raw leachate at a volumetric ratio of 5%, the SBOM was satisfactorily removed in all tested conditions, a result supported by two recent studies based on kinetic parameters. Drewnowski (), studying the aerobic degradation of domestic wastewater (operational temperature, Table 3
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20 C), determined yield coefficients for the heterotrophic biomass (YH) in the range of 0.62–0.72 mg VSS mg COD1. A very similar range of YH (0.64–0.68 mg VSS mg COD1) was determined, at an operational temperature of 20 C, by Capodici et al. () in their study on leachate co-treatment. The similarity between ranges of YH highlights the ability of aerobic biomass to assimilate the organic content of leachate. The operational conditions tested in the lactose experiments guaranteed that the leachates were the only sources of SBOM. As shown in Table 3, the leachates’ SBOM removal efficiencies and rates were nearly identical to those obtained in the domestic wastewater experiments. Thus, the results obtained in experiments 1 and 2 were validated by experiments 3 and 4. W
FTIR spectroscopic analysis of the raw and treated samples To better evaluate the leachate SBOM removal, the raw and treated samples from the reactors that were loaded with
Assessment of leachates’ slowly biodegradable organic matter (SBOM) removal over 20 days of aeration
Experiments
1
2
3
4
Raw leachate/lactose
Pretreated leachate/lactose
Raw leachate/domestic
Pretreated leachate/
Mixture of wastewaters
wastewater
domestic wastewater
Volumetric ratios (%)
0.2
2
5
0.2
2
5
2
2
Influent SBOM
12
62
91
9
31
56
21
19
Inert organic matter
2
32
65
1
11
25
11
6
SBOM removal (%)
83
48
29
89
65
55
48
68
SBOM removal rate (d1)
0.09
0.03
0.02
0.11
0.05
0.04
0.03
0.06
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leachates at a volumetric ratio of 2% were analyzed by FTIR spectroscopy. As shown in Figures 1(a)–1(c), the absorption bands that were observed in the domestic wastewater spectrum were also found in the spectra of the influent samples that contained leachates at a volumetric ratio of 2%. Nonetheless, the absorption intensities in the spectra from the samples containing leachates were greater than the intensities detected for the domestic wastewater. The band at 875 cm1 was intrinsic to the leachates and was related to the C–O out-of-plane deformation of carbonates (Smidt & Meissl ). After 20 days of aeration, most of the absorption bands in the raw domestic wastewater spectra were not detected in the treated effluent of the control reactor. This finding confirmed that the organic matter was oxidized (Figure 1(a)).
Figure 1
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When comparing the influent and effluent sample spectra from the reactors that were loaded with raw leachate/domestic wastewater (Figure 1(b)) and pretreated leachate/domestic wastewater (Figure 1(c)) mixtures, the oxidation of the following components was observed: alcohols or phenols (3,400 cm1); aliphatic methylene (2,900–2,800 cm1); aromatic C ¼ C bonds (1,600 cm1); carboxylic acid/carboxylate ions (1,400 cm1); polysaccharides (1,130 cm1); and organic nitrogen to nitrate (2,400 and 1,382 cm1) (Liang et al. ; Silverstein et al. ; Smidt & Meissl ). However, this oxidation was more effective when the pretreated leachate was used rather than the raw leachate. For example, the absorption intensity at 3,400 cm1 decreased by only 7% in the raw leachate spectra, but it decreased by 39% in the pretreated leachate spectra (Figures 1(b) and 1(c)).
FTIR spectra of the influent and effluent samples for the reactors loaded with (a) domestic wastewater (DW), (b) a mixture of raw leachate/domestic wastewater (RL/DW) at a volumetric ratio of 2% and (c) a mixture of pretreated leachate/domestic wastewater (PTL/DW) at a volumetric ratio of 2%.
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Regarding the lactose experiments, most of the absorption bands found in the raw lactose spectrum either were not detected or had lower absorption intensities in the treated effluents of the control reactor, which confirmed that organic matter oxidation occurred (Figure 2(a)). The remaining bands in the spectra from the treated lactose included the following: 3,400 cm1 with an absorption intensity that decreased by 84%; 1,100–1,050 cm1, which resulted from the remaining polysaccharides; and 620 cm1, which resulted from the S–O angular deformation of inorganic sulfate (caused by the MnSO4 used to prepare BOD dilution water in which powdered lactose was dissolved) or from the out-of-plane O–H deformation of alcohols. The presence of alcohols may result from the aerobic fermentation of lactose (Silveira et al. ). The FTIR spectra of the raw leachate/lactose and the pretreated leachate/lactose presented the same bands as the lactose spectra, but with greater absorption intensities
Figure 2
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(Figures 2(b) and 2(c)). Due to the removal of organic matter, most of the bands detected in the raw samples were not detected in the treated samples. In the spectra presented in Figures 2(b) and 2(c), the following components were oxidized: alcohols or phenols (3,400 cm1); aliphatic methylene (2,900 cm1); carboxylic acids and ketones (1,700 cm1); aromatic C ¼ C bonds (1,600 cm1); carboxylic acid/carboxylate ions (1,400 cm1); polysaccharides (1,050 cm1) and amines (700 and 780 cm1) (Silverstein et al. ; Smidt & Meissl ; Liang et al. ). The remaining bands were the same as those detected in the spectra of the treated lactose, except the band at 1,265 cm1 (C–O vibrations of carboxylic acids and C–N vibrations of amines and amides). In a previous study regarding the decomposition of waste materials (Smidt & Meissl ), this absorption band was attributed to the mono-molecules that originated from the degradation of the macromolecules.
FTIR spectra of the influent and effluent samples for the reactors loaded with (a) lactose (LAC), (b) a mixture of raw leachate/lactose (RL/LAC) at a volumetric ratio of 2%, (c) a mixture of pretreated leachate/lactose (PTL/LAC) at a volumetric ratio of 2% and (d) sludge samples from the control reactor and the reactors loaded with raw and pretreated leachate at a volumetric ratio of 2%.
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Ferraz et al. () used FTIR spectroscopy to analyze sludge samples that were used for a submerged aerobic biofilter start-up and samples that were acquired after the cotreatment of pretreated leachate and domestic wastewater at a volumetric ratio of 2%. The spectra were identical, which confirmed that the organic matter was primarily biodegraded rather than adsorbed to the sludge. The spectra shown in Figure 2(d) correspond with these findings. The spectra were identical for the sludge samples that were developed in the reactors that were loaded with lactose, raw leachate/ lactose 2% and pretreated leachate/lactose 2%. The FTIR spectroscopic analyses indicated that the leachate SBOM was primarily biodegraded rather than adsorbed or diluted. If dilution had occurred, the influent and effluent FTIR spectra would be identical, which did not occur in this study.
CONCLUSIONS The co-treatment of domestic wastewater and landfill leachate was successfully performed in AS reactors that were operated in batches. The AS reactors performed better when pretreated leachate was used at a volumetric ratio of 2%. It was determined that most (65%) of the pretreated leachate SBOM was removed rather than diluted, as confirmed by FTIR analyses.
ACKNOWLEDGEMENTS The authors would like to thank the São Paulo Research Foundation (grant numbers 2010/51955-2 and 2011/ 50627-4) and the National Council for Scientific and Technological Development (grant numbers 141710/2010-1 and 303083/2010-7) for their financial support. We also thank the anonymous reviewers for their helpful comments.
REFERENCES Capodici, M., Di Trapani, D. & Viviani, G. Co-treatment of landfill leachate in laboratory-scale sequencing batch reactors: analysis of system performance and biomass activity by means of respirometric techniques. Water Sci. Technol. 69 (6), 1267–1274.
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Çeçen, F. & Aktaş, O. Aerobic co-treatment of landfill leachate with domestic wastewater. Environ. Eng. Sci. 21 (3), 303–312. Contrera, R. C., Sarti, A., Castro, M. C. A. A., Foresti, E., Zaiat, M. & Shalch, V. Ethanol addition as a strategy for start-up and acclimation of an AnSBBR for the treatment of landfill leachate. Process Biochem. 48, 1767–1777. Drewnowski, J. The impact of slowly biodegradable organic compounds on the oxygen uptake rate in activated sludge systems. Water Sci. Technol. 69 (6), 1136–1144. Ferraz, F. M., Povinelli, J., Pozzi, E., Vieira, E. M. & Trofino, J. C. Co-treatment of landfill leachate and domestic wastewater using a submerged aerobic biofilter. J. Environ. Manage. 141, 9–15. Frimmel, F. H. & Abbt-Braun, G. Basic characterization of reference NOM from Central Europe – similarities and differences. Environ. Int. 25 (23), 191–207. Hasar, H., Ipek, U. & Kinaci, C. Joint treatment of landfill leachate with municipal wastewater by submerged membrane bioreactor. Water Sci. Technol. 60 (12), 3121–3127. Liang, Z., Liu, J. X. & Li, J. Decomposition and mineralization of aquatic humic substances (AHS) in treating landfill leachate using the ANAMMOX process. Chemosphere 74, 1315–1320. Liao, M. Y. & Randtke, S. J. Predicting the removal of soluble organic contaminants by lime softening. Water Res. 20 (1), 27–35. Metcalf, Eddy. Wastewater Engineering: Treatment and Reuse. 4th international edn, McGraw-Hill, New York. Mojiri, A., Aziz, H. A., Zaman, N. Q. & Aziz, S. Q. Powdered ZELIAC augmented sequencing batch reactors (SBR) process for co-treatment of landfill leachate and domestic wastewater. J. Environ. Manage. 139, 1–14. Renou, S., Poulain, S., Givaudan, J. G. & Moulin, P. Amelioration of ultrafiltration process by lime treatment: case of landfill leachate. Desalination 249 (1), 72–82. Rodríguez, J., Castrillón, L., Marañón, E., Sastre, H. & Fernández, E. Removal of non-biodegradable organic matter from landfill leachates by adsorption. Water Res. 38, 3297–3303. Silveira, W. B., Passos, F. J. V., Mantovani, H. C. & Passos, F. M. L. Ethanol production from cheese whey permeate by Kluyveromyces marxianus UFV-3: a flux analysis of oxidoreductive metabolism as a function of lactose concentration and oxygen levels. Enzyme Microb. Technol. 36, 930–936. Silverstein, R. M., Webster, F. X. & Kiemle, D. J. Spectrometric Identification of Organic Compounds. 7th edn, John Wiley & Sons, New York. Smidt, E. & Meissl, K. The applicability of Fourier transform infrared (FTIR) spectroscopy in waste management. Waste Manage. 27, 268–276. Standard Methods for the Examination of Water and Wastewater 22nd edn, APHA – American Public Health Association, AWWA – American Water Works Association, WEF – Water Environment Federation, Washington, DC.
First received 7 August 2014; accepted in revised form 20 October 2014. Available online 30 October 2014
