Journal of Environmental Management 141 (2014) 9e15
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Co-treatment of landfill leachate and domestic wastewater using a submerged aerobic biofilter F.M. Ferraz a, *, J. Povinelli a, E. Pozzi a, E.M. Vieira b, J.C. Trofino a a Departamento de Hidráulica e Saneamento, Escola de Engenharia de São Carlos, Universidade de São Paulo, Av.Trabalhador Sao Carlense, 400, CEP 13566-590 Sao Carlos, São Paulo, Brazil b Instituto de Química de São Carlos, Universidade de São Paulo, Av.Trabalhador Sao Carlense, 400, CEP 13566-590 Sao Carlos, Sao Paulo, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 October 2013 Received in revised form 24 March 2014 Accepted 29 March 2014 Available online
This study used a pilot-scale submerged aerobic biofilter (SAB) to evaluate the co-treatment of domestic wastewater and landfill leachate that was pre-treated by air stripping. The leachate tested volumetric ratios were 0, 2, and 5%. At a hydraulic retention time of 24 h, the SAB was best operated with a volumetric ratio of 2% and removed 98% of the biochemical oxygen demand (BOD), 80% of the chemical oxygen demand (COD) and dissolved organic carbon (DOC), and 90% of the total suspended solids (TSS). A proposed method, which we called the “equivalent in humic acid” (Eq.HA) approach, indicated that the hardly biodegradable organic matter in leachate was removed by partial degradation (71% of DOC Eq.HA removal). Adding leachate at a volumetric ratio of 5%, the concentration of the hardly biodegradable organic matter was decreased primarily as a result of dilution rather than biodegradation, which was confirmed by Fourier transform infrared (FTIR) spectroscopy. The total ammoniacal nitrogen (TAN) was mostly removed (90%) by nitrification, and the SAB performances at the volumetric ratios of 0 and 2% were equal. For the three tested volumetric ratios of leachate (0, 2, and 5%), the concentrations of heavy metals in the treated samples were below the local limits. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: FTIR spectroscopy Humic substances India ink reverse stain Municipal solid waste Organic matter removal Sanitary landfill leachate
1. Introduction Many studies have demonstrated that sanitary landfills generate leachate, a pollutant wastewater that contains inorganic salts, heavy metals, TAN, biodegradable organics, and refractory compounds such as humic substances. Leachate typically presents a dark colour that can be attributed to the humic substances (Kjeldsen et al., 2002; Renou et al., 2008; Wu et al., 2011). Leachate is classified as old when its characteristics include low BOD/COD ratios (0.3e0.01) and high TAN concentrations, but it is important to remember that these characteristics are not necessarily associated with the age of the landfills (Renou et al., 2008). TAN is one of the most important constituents of old leachate because of its possible toxicity to ammonia and nitrite-oxidising bacteria, which are used in biological treatment (Gabarró et al., 2012; Renou et al., 2008; Xu et al., 2010; Yusof et al., 2010). Prior knowledge of the above-mentioned characteristics is mandatory when selecting a successful treatment technology for landfill leachate. The available technologies are based on biological,
* Corresponding author. E-mail address: [email protected] (F.M. Ferraz). http://dx.doi.org/10.1016/j.jenvman.2014.03.022 0301-4797/Ó 2014 Elsevier Ltd. All rights reserved.
physicochemical, advanced oxidation (AOP), and membrane filtration processes (Marañón et al., 2010; Renou et al., 2008; Xu et al., 2010; Yusof et al., 2010). To optimise the efficiency of the treatments and meet the regional discharge limits for landfill leachate, most of the cited processes have been combined. Leachate treatment using air stripping/AOP/biological processes resulted in 99% COD removal (Nurisepehr et al., 2012). Similar values were obtained for COD, colour, and nutrient removal from leachate treatment as a result of applying sequencing batch reactors (SBR)/coagulation/Fenton/biological aerated filtering (Wu et al., 2011). Nonetheless, combined processes can be very costly because they require chemicals and electricity to produce high-quality treated leachate. It was reported that the operating costs of combining an SBR with ozonation or photo-Fenton were, respectively, 125% and 63% higher than the operating costs of an SBR treating leachate (Cassano et al., 2011). Regarding the low-cost options that may be associated with obtaining a good final effluent quality, the co-treatment of leachate with domestic wastewater can be highlighted. This treatment alternative is advantageous because it can be employed in an existing wastewater treatment plant (WWTP) and can thus avoid the need to invest in a new facility. Because leachate is generally
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added to domestic wastewater at volumetric ratios that do not exceed 10%, the biological processes are less susceptible to the toxic effects of high TAN concentrations (Borghi et al., 2003; Çeçen and Aktas, 2004; Fudala-Ksiazek et al., 2011; Renou et al., 2008; Yu et al., 2010). Most papers reporting leachate co-treatment with domestic wastewater have considered the use of activated sludge reactors. For volumetric ratios of leachate varying from 0.2 to 5%, the COD removals ranged from 80 to 92% (Çeçen and Aktas, 2004; FudalaKsiazek et al., 2010, 2011; Yu et al., 2010). Despite the important contributions of the previous studies, none of those studies clarified whether the hardly biodegradable organic matter of old leachates was indeed removed by biodegradation with the organic content of domestic wastewater or whether this matter was instead diluted. Thus, the main objective of this study was to investigate whether the hardly biodegradable organic matter of old leachate was simply diluted or actually biodegraded with domestic wastewater. Differing from previous studies, this study evaluated the cotreatment of old leachate with domestic wastewater in pilot-scale submerged aerobic biofilters (SABs), which are known to offer better solid retention compared with activated sludge reactors (Gálvez et al., 2009; Metcalf and Eddy, 2003). 2. Material and methods 2.1. Wastewaters 2.1.1. Landfill leachate This study used leachate from the municipal sanitary landfill of Sao Carlos, a medium-sized city located in Sao Paulo, Brazil, that has approximately 220,463 inhabitants and generates 160 tons of municipal solid waste per day. This municipal landfill has been in operation for 22 years and receives domestic solid waste containing organic matter (60% by mass), as well as glass, paper, plastic, and metals, though the city has a recycling program. The sampling point was located at the landfill treatment pond. Before being mixed with domestic wastewater, the leachate was pre-treated by air stripping (for TAN removal) according to the procedures described by Ferraz et al. (2013a). Initially, the pH was adjusted to 11 by lime addition; the leachate was then recirculated in an aerated packed tower until its TAN concentration was reduced to approximately 100e150 mg L1 (Ferraz et al., 2013a). The leachate used in this study was classified as old, primarily because of its high TAN concentration and extremely low BOD/COD ratio of 0.1 (Table 1). The pre-treated leachate obtained through air stripping presented the same BOD/COD ratio as did the raw leachate. These extremely low BOD/COD ratios can be associated with the presence of the hardly biodegradable organics, such as humic and fulvic acids (Renou et al., 2008), which seem to remain in leachates that have been pre-treated by a pH adjustment with lime and air stripping (Ferraz et al., 2013a). 2.1.2. Domestic wastewater Domestic wastewater was collected from the sewer system located in the neighbourhood of the University of Sao Paulo (EESC/ USP) campus. This wastewater presented a large content of biodegradable organic matter compared with that of the leachate, resulting in BOD/COD ratios varying from 0.5 to 0.6 (Table 1). 2.1.3. Mixture leachate/domestic wastewater Leachate was added to domestic wastewater at volumetric ratios of 2 and 5%.
Table 1 Physico-chemical characterization of wastewaters used in the experiments (adapted from Ferraz et al. (2013b)). Parameter
Raw leachate
Pre-treated leachate
Sanitary sewage
Min
Min
Min
Max
pH 8.3 9.0 Total alkalinity 6000 7570 1 (mg CaCO3 L ) 28,300 Conductivity (mS cm1) 14,800 BOD5,20 (mgO2 L1) 433 588 CODtotal (mgO2 L1) 4425 4860 TKN (mg L1 N) 920 977 TAN (mg L1 N) 790 821 1 130 156 Organic-N (mg L ) 1 TS (mg L ) 8446 15,980 4974 8447 TVS (mg L1) TFS (mg L1) 3472 7533 TDS (mg L1) 8247 15,565
9.5 2649 8450 218 2772 12 9 3 6558 5749 2118 6248
Max
11 6.4 5000 111 12,300 304 3900 250 150 100 9140 6976 3778 8700
363 115 216 29 27 2 562 120 172 495
Max 7.6 200 505 269 440 50 37 13 1078 390 202 1003
BOD: biochemical oxygen demand; COD: chemical oxygen demand; Min: minimum; Max: maximum; TAN: total ammoniacal nitrogen; TKN: total Kjeldahl nitrogen; TS: total solids; TVS: total volatile solids; TFS: total fixed solids; TDS: total dissolved solids.
2.2. Pilot-scale submerged aerobic biofilters (SABs) One of the SABs consisted of a PVC tube with a diameter of 38 cm, a height of 200 cm, and a working volume of 178 L. As shown in Figure S1 (Supplementary data), this reactor was divided into five modules. Two of these modules were packed with polyethylene corrugated Raschig rings, which were 1.5 cm in diameter and 5 cm in length. Each of these modules was inoculated with 25 L of activated sludge biomass. Another SAB that was inoculated similarly to the first one and packed with the same material was used as a control reactor. This reactor was loaded only with domestic wastewater and had a working volume of 75 L (Figure S1). The two SABs were operated under a continuous-flow regime, with an hydraulic retention time (HRT) of 24 h. Compressed air was injected into the SABs at a rate of 500 L h1, and the dissolved oxygen concentration inside the five modules was maintained above 2 mg L1. 2.3. Analytical procedures The following parameters were measured according to the Standard Methods for the Examination of Water and Wastewater (APHA, AWA and WEF, 2012): BOD5, 20 (Hach BODTrakII respirometric apparatus), method 5210 B; COD (Hach COD reactor 4560000/Hach DR 2010 spectrophotometer), colourimetric method 5220 D; conductivity, method 2510 B; DOC (Shimadzu TOC 5000 A Analyser), method 5310 B; nitrate, method 4500 C e NO 3 (Shimadzu UV-160A spectrophotometer); solid content, method 2540; total alkalinity, method 2320 B; TAN (Büchi distillation unit B-339), method 4500 C e NH3 Nitrogen; total heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) (Varian AA240 FS atomic absorption spectrophotometer), methods 3111 B and D; and total Kjeldahl nitrogen (TKN) (Büchi digestion unit B-426), method 4500 C e Norg Nitrogen. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups present in the leachate structure. FTIR spectra were recorded from KBr pallets containing approximately 1 mg of a lyophilised sample and 100 mg of KBr. A BOMEM B-102 FTIR spectrometer was used. The FTIR spectra were obtained over the wavenumber range of 4000 to 400 cm1, at a resolution of 4 cm1, and in 16 scans. The spectra were plotted in Origin 8.0 (OriginLab).
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2.4. Assessment of the hardly biodegradable organic matter removal
D1
Based on the previous literature, it is unclear whether the hardly biodegradable organic matter in leachate is removed through biodegradation or whether its concentration is reduced in treated effluent due to the effects of dilution that are observed during cotreatment with domestic wastewater. In a previous study (Ferraz et al., 2013b), we proposed a method called the “equivalent in humic acid” (Eq.HA) approach to quantify the hardly biodegradable organic matter under aerobic conditions. When the alkalinity is determined in a sample, the result is expressed in terms of mg CaCO3 L1; however, this result does not mean that the sample only contains CaCO3. Other species such as OH or HCO 3 may be present in that sample. Analogously, expressing the DOC as Eq.HA does not mean that a sample contains exclusively humic acid: fulvic acid and other hardly biodegradable substances that may be present in that sample are represented in the measurement of DOC Eq.HA. In the current study, a calibration curve was built using eight different humic acid (SigmaeAldrich) concentrations (5e 300 mg L1), and the amount of DOC was subsequently measured (Fig. 1). As summarized in Figure S2 (Supplementary data), the DOC values of the influent samples of the two SABs are measured first. By inserting the measured DOC values into the calibration curve, the DOC in terms of Eq.HA can be obtained for domestic wastewater (term “x1” in Figure S2a) and for the mixture of leachate/domestic wastewater (term “x2” in Figure S2a). The hardly biodegradable organic matter in the mixture, which results from the addition of leachate to the domestic wastewater (D1), can be tentatively determined as follows:
D1 ¼ x2 x1 ;
(1)
i.e., the hardly biodegradable DOC of the domestic wastewater, which is used as a blank, is discounted. Analogously, this procedure was applied to the samples treated by the SABs (Figure S2b). Thus, the refractory organic matter in the treated mixture, which was produced by the addition of leachate to domestic wastewater (D2), can be determined in mg L1 as follows:
D2 ¼ y2 y1
11
D D2 DOC Eq:HA removalð%Þ ¼ 100* 1
(2)
The DOC Eq.HA removal is determined according to Equation (3):
(3)
For the control SAB, the DOC Eq.HA removal can be obtained using Equation (4):
x y1 Control DOC Eq:HA removalð%Þ ¼ 100* 1 x1
(4)
The results can be interpreted as follows: -
if D2 ¼ 0, the SAB completely removed the DOC Eq.HA; if D1 > D2 and D2 > 0, the DOC Eq.HA was partially removed; and if D1 ¼ D2, the activated sludge reactors could not remove the DOC Eq.HA.
2.5. Microscopic examination A microscopic examination was performed to observe the possible toxic effects of leachate with respect to microfaunal diversity when it is added to domestic wastewater. The India ink reverse stain test was applied to mixed liquor samples, focusing on a qualitative analysis of dissolved carbon, according to Jenkins et al. (2003). In this test, the India ink penetrates the free dissolved carbon portion of the samples, staining the microscope slide black, while portions containing dissolved carbon particles exhibit a brownish yellow colour. In normal flocs, small, clear points are typically observed, with a predominance of blackstained areas (Jenkins et al., 2003). An alternative approach for obtaining a quantitative response from the India ink reverse stain test is proposed in this study. The method consists of classifying the tonalities observed on microscope slides using the Image Pro-Plus software, as shown in Fig. 2. The light-yellow portions on the microscope slides are classified as “class 1”, the brown yellow portions as “class 2”, and the black portions as “class 3”. Using the software, the percentage of the area occupied by each “class” on a microscope slide can be assessed. Our interest was focused on the large light-yellow portions (“class 1”). All microscope observations were performed at a magnification of 100, zero contrast, a sharpness of þ7, zero red and blue levels, and a manual exposure mode varying from 1/1000 to 1/250, depending on the intensity of the bright areas in each sample. This result may offer a quantitative answer to the question of how effective the SABs were in removing DOC. The advantage of this procedure is that it can be used as a preliminary analysis preceding COD determinations, for example, in addition to offering a rapid assessment. It is also a simple, safe, and inexpensive control tool because microscopes are often available at wastewater treatment plant facilities. 2.6. Statistical analysis The performances of the two SABs with respect to organic matter and nitrogen removal were compared using an analysis of variance (ANOVA) to verify whether the differences between the reactors’ performance were random or whether they were caused by leachate interference. 3. Results and discussion 3.1. Organic matter removal
Fig. 1. “Equivalent in humic acid” calibration curve.
The steady-state condition was reached in 50 days for the three tested volumetric ratios (0, 2, and 5%). Confirming the advantage of SABs with respect to solid retention, Fig. 3a shows that excellent performance was achieved in
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Fig. 2. (a) India ink reverse stain test and (b) proposed method for tonality classification.
terms of TSS removal. At a volumetric ratio of 2%, there was negligible interference from the leachate in the aerobic biomass: the TSS removal (90% on average) was equal to that of the control SAB. When fed with leachate at a volumetric ratio of 5%, the SAB removed approximately 80% of TSS. Based on an ANOVA at a
significance level of 0.01, the average removals for the volumetric ratio of 0, 2, and 5% were significantly different (F ¼ 5.3 and F critical ¼ 5.2). The control SAB operating with an organic loading rate (OLR) of 0.340 kg COD m3 d1 removed 98% of the BOD, 80% of the COD and
Fig. 3. Organic matter removal profile: (a) TSS; (b) SCOD; (c) BOD; (d) DOC; and (e) DOC Eq.HA.
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83% of the DOC (Fig. 3bed). The OLR increased to 0.4 kg COD m3 d1 due to the addition of leachate to the domestic wastewater at a volumetric ratio of 2%; in this case, the SAB removed 98% of the BOD and 80% of both the COD and DOC. At a volumetric ratio of 5% and an OLR of 0.5 kg COD m3 d1, the SAB removals were 98% of the BOD, 76% of the COD, and 75% of the DOC (Fig. 3bed). For the three tested volumetric ratios (0, 2, and 5%), the average BOD of the treated effluents was less than 10 mg O2 L1, thus meeting the discharge standard established by the Brazilian environmental law CONAMA 430/2011 (Brazilian Ministry of the Environment, 2011). Based on an ANOVA at a significance level of 0.01, there was no statistically significant difference (F ¼ 0.9 and F critical ¼ 5) in the average removals of BOD, COD, or DOC when the SAB was fed with leachate/domestic wastewater at volumetric ratios of 0, 2, and 5%. 3.1.1. Application of the proposed equivalent in humic acid (Eq.HA) method and FTIR spectroscopic analysis Using Equation (1)e(4), the concentrations of the hardly biodegradable organics, which were altered by adding leachate to domestic wastewater, were calculated before and after this biological treatment. Fig. 4e shows that the SAB performance in the removal of hardly biodegradable organic matter decreased as the volumetric ratio of leachate increased from 2 to 5%. The addition of leachate to domestic wastewater at a volumetric ratio of 2% resulted in a BOD/COD ratio of 0.5, and the same ratio was obtained for the domestic wastewater. However, the SAB fed with leachate at a volumetric ratio of 2% removed 71% of the DOC Eq.HA, whereas 90% was removed in the control SAB. For the mixture containing leachate at the volumetric ratio of 5%, the BOD/COD ratio decreased to 0.4. Consequently, the DOC Eq.HA removal decreased to 62% for the volumetric ratio of 5%. Additionally, at a significance level of 0.01, an ANOVA showed that the differences between the DOC Eq.HA removal rates were statistically significant (F ¼ 9 and F critical ¼ 5) for the volumetric ratios of 0, 2, and 5%. lu (2001) evaluated the co-treatment of Çeçen and Çakırog leachate (COD 2431 mg O2 L1) with synthetic domestic wastewater in 2-L activated sludge reactors. Using a control reactor that was fed only with synthetic domestic wastewater, the authors assessed the contribution of leachate at a volumetric ratio of 10% to the influent COD (250 mg O2 L1) and the inert COD in the treated effluent (210 mg O2 L1). The inert COD in the treated effluent corresponded to 56% of the initial COD. In our study, using a volumetric ratio of 2%, which was one-fifth lu (2001), the of the volumetric ratio used by Çeçen and Çakırog refractory DOC was 11%. This value also represented one-fifth of the refractory COD obtained by the above-mentioned authors. Such consistent results confirm that the proposed Eq.HA method was valid for non-synthetic wastewaters. As shown in Fig. 4a, the following absorption bands that were found in the domestic wastewater spectra were also found in the influent samples containing leachate at volumetric ratios of 2 and 5%: 3400 cm1, due to the OH stretching of alcohols or phenols; 1600 cm1, due to aromatic C]C bonds; 1400 cm1, due to the C] O stretching of carboxylate ions; and 1150 cm1, due to the CeO stretching of polysaccharides. Absorption bands caused by the addition of leachate to domestic wastewater were observed at 2900 cm1, due to the CeH stretching of aliphatic methylene, and 1500 cm1, due to aromatic C]C bonds (Liang et al., 2009; Silverstein et al., 2005; Smidt and Meissl, 2007; Stevenson, 1994). For a 24-h HRT, most of the absorption bands found in the spectrum of the raw domestic wastewater (volumetric ratio 0%) were not detected in the treated effluent of the control SAB (Fig. 4a).
Fig. 4. FTIR spectra of (a) SABs influent and effluent samples, (b) sludge samples from the control SAB, and (c) sludge samples from the SAB fed with leachate at volumetric ratios of 2 and 5%.
An absorption band at 1384 cm1 was observed (Fig. 4a) and was likely due to nitrate because nitrogen was removed from the effluent via nitrification (Smidt and Meissl, 2007). As demonstrated by the COD and DOC measurements, some refractory organic matter remained in the treated effluent, causing the appearance of a band at 1150 cm1 and the permanence of the absorption band at 3400 cm1, although the latter band had a significantly lower intensity compared with that of the raw domestic wastewater (Fig. 4a). For the mixture leachate/domestic wastewater at a volumetric ratio of 2%, the spectrum of the treated effluent was equal to that of
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the control SAB (Fig. 4a); this confirmed the organic matter removal, as evaluated using physicochemical parameters. Nonetheless, the addition of leachate at a volumetric ratio of 5% interfered with the SAB performance in hardly biodegradable organic matter removal, and the spectra of the influent and effluent samples were identical (Fig. 4a). To verify whether the removal of hardly biodegradable organic matter was caused by their adsorption into the sludge, samples of the sludge used for the SAB start-up and samples of the end of operation were acquired and analysed through FTIR spectroscopy. As shown in Fig. 4b, for the control SAB, the spectra of the sludge used for the start-up and those of the sludge after the end of operation were identical. The same is true for the SAB operated with leachate at a volumetric ratio of 2% (Fig. 4c), confirming that neither dilution nor adsorption into the sludge was the primary cause for the disappearance of the hardly biodegradable organic matter. No distinct differences were observed in the sludge spectra when the VR of the leachate increased from 2 to 5% (Fig. 4c). Based on the Eq.HA method results and FTIR spectroscopic analysis, the hardly biodegradable organic matter was partially biodegraded (71%) when leachate was added at a volumetric ratio of 2%. If dilution had caused decreases in the hardly biodegradable organic matter concentration, the FTIR spectra of the SAB influent and effluent samples would have been identical, as observed for the volumetric ratio of 5%. 3.1.2. Organic carbon evaluation using the India ink test In agreement with the measured DOC concentration in the treated SAB effluents (Fig. 3d), the proposed procedure applied to the India ink test to assess the percentage of DOC in microscope slides showed that the DOC in the control SAB sludge was only 0.46%. At volumetric ratios of 2 and 5%, the areas corresponding to the DOC were 3.4 and 4.5%, respectively. A good correlation coefficient (R2) was obtained between the measured DOC concentrations and the percentage of DOC in the SAB biomass for the three tested leachate volumetric ratios (Fig. 5). Thus, the proposed procedure based on the tonalities of the India ink test can provide a simple and low-cost preliminary evaluation of the organic matter removal in the SABs. Nonetheless, this procedure was not intended to replace physicochemical analyses such as COD or DOC.
Fig. 5. Relation between DOC measurements and the percentage of DOC obtained as a quantitative response from the India ink test.
by the Brazilian environmental law CONAMA n 430/2011. As shown in Table S1 (Supplementary data), after the co-treatment, the concentration of heavy metals was even further below these limits. 4. Conclusion The co-treatment of domestic wastewater and landfill leachate that was pre-treated by air stripping was successfully performed in
3.2. Nitrogen removal As the steady-state was reached, the SAB performances for TAN removal at volumetric ratios of 0, 2, and 5% were 91, 90, and 88%, respectively (Fig. 6a). Based on an ANOVA at a significance level of 0.01, the differences among the average TAN removals were random; thus, the results were statistically identical (F ¼ 0.1 and F critical ¼ 5), and the interference of leachate at the tested volumetric ratios was negligible. Fig. 6b also shows that nitrogen removal was primarily caused by nitrification rather than ammonia stripping because the majority of the removed TAN was oxidised to nitrate. The average nitrification effectiveness was 83% for the volumetric ratio of 0%, and it was 77% for the volumetric ratios of 2 and 5%. At a significance level of 0.01, the ANOVA showed that these performances were not significantly different (F ¼ 1.4 and F critical ¼ 5.1). 3.3. Heavy metals Prior to the aerobic treatment, the concentration of heavy metals in the samples of domestic wastewater and leachate/domestic wastewater at volumetric ratios of 2 and 5% was already below the discharge limits for wastewaters that were established
Fig. 6. Nitrogen removal measured by (a) TAN, (b) nitrification, and (c) FA profiling, along with the co-treatment.
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a pilot-scale SAB operated with a 24-h HRT. The SAB showed optimal performance when the volumetric ratio of the leachate was 2%, at which point the organic matter and nitrogen removals were equal to those of the control reactor: 98% of the BOD, 80% of the COD and DOC, and 90% of the TSS. The proposed Eq.HA method allowed us to conclude that the concentrations of the hardly biodegradable organic matter in the leachate were most likely decreased as a result of partial degradation (71% of DOC Eq.HA removal) instead of dilution, which was confirmed by FTIR analysis. The proposed method, which is based on a tonality classification of the India ink test, allowed for the quantitative assessment of DOC using microscopic examinations. The TAN was mostly removed (90%) by nitrification, and the SAB performances at volumetric ratios of 0 and 2% on TAN removal were identical. For the three tested volumetric ratios of leachate (0, 2, and 5%), the concentration of heavy metals in treated samples was lower than the local limits. Acknowledgements The authors would like to thank São Paulo Research Foundation (grant numbers 2010/51955-2 and 2011/50627-4) and CNPq (grant numbers: 303083/2010-7 and 141710/2010-1) for financial support. We also thank the anonymous reviewers for their helpful comments. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2014.03.022. References APHA e American Public Health Association, AWWA e American Water Works Association, WEF e Water Environment Federation, 2012. Standard Methods for the Examination of Water and Wastewater, twenty-second ed. APHA, AWWA, WEF, Washington. Borghi, A. Del, Binaghi, L., Converti, A., Borghi, M. Del, 2003. Combined treatment of leachate from sanitary landfill and municipal wastewater by activated sludge. Chem. Biochem. Eng. Q. 17, 277e283. Brazilian Ministry of the Environment [Internet], 2011. Available from: http://www. mma.gov.br/port/conama/legiabre.cfm?codlegi¼646. Cassano, D., Zapata, A., Brunetti, G., Del Moro, G., Di Iacomi, C., Oller, I., Malato, S., Mascolo, G., 2011. Comparison of several combined/integrated biological-AOPs setups for the treatment of municipal landfill leachate: minimization of operating costs and effluent toxicity. Chem. Eng. J. 172, 250e257. Çeçen, F., Aktas, Ö., 2004. Aerobic co-treatment of landfill leachate with domestic wastewater. Environ. Eng. Sci. 21, 303e312. lu, D., 2001. Impact of landfill leachate on the co-treatment of Çeçen, F., Çakırog domestic wastewater. Biotechnol. Lett., 821e826. Ferraz, F.M., Povinelli, J., Maria Vieira, E., 2013a. Ammonia removal from landfill leachate by air stripping and absorption. Environ. Technol.. http://dx.doi.org/ 10.1080/09593330.2013.767283.
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Ferraz, F.M., Campos, R., Povinelli, J., Ferraz, H.J.M., 2013b. Assessment of hardly biodegradable organics removal in co-treatment of landfill leachate and domestic wastewater. In: Proceedings of the Fourteenth International Waste Management and Landfill Symposium. IWWG, Cagliari. Fudala-Ksiazek, S., Luczkiewicz, A., Jankowska, K., Kulbat, E., Czerwionka, K., Quant, B., Olanczuk-Neyman, K., 2010. Combined treatment of landfill leachates with wastewater in a sequencing batch reactor (SBR). In: Proceedings of the Second International Conference on Hazardous and Industrial Waste Management, Crete, Greece. Fudala-Ksiazek, S., Luczkiewicz, A., Quant, B., Olanczukneyman, K., 2011. The effectiveness of nitrification and denitrification with co-treatment wastewater with landfill leachate. In: Proceedings of the Thirteenth International Waste Management and Landfill Symposium, Sardinia, Italy. Gabarró, J., Ganigué, R., Gich, F., Ruscalleda, M., Balaguer, M.D., Colprim, J., 2012. Effect of temperature on AOB activity of a partial nitritation SBR treating landfill leachate with extremely high nitrogen concentration. Bioresour. Technol. 126, 283e289. Gálvez, a, Giusti, L., Zamorano, M., Ramos-Ridao, A.F., 2009. Stability and efficiency of biofilms for landfill leachate treatment. Bioresour. Technol. 100, 4895e4898. Jenkins, D., Richard, M.G., Daigger, G., 2003. Manual on the Causes and Control of Activated Sludge Bulking, Foaming and Other Solids Separation Problems. Lewis Publishing, Boca Raton. Kjeldsen, P., Barlaz, M.A., Rooker, A.P., Baun, A., Ledin, A., Christensen, T.H., 2002. Present and long-term composition of MSW landfill leachate: a review. Critical Rev. Environ. Sci. Technol. 32, 297e336. Liang, Z., Liu, J.X., Li, J., 2009. Decomposition and mineralization of aquatic humic substances (AHS) in treating landfill leachate using the Anammox process. Chemosphere 74, 1315e1320. Marañón, E., Castrillón, L., Fernández-Nava, Y., Fernández-Méndez, A., FernándezSánchez, A., 2010. Colour, turbidity and COD removal from old landfill leachate by coagulation-flocculation treatment. Waste Manag. Res. 28, 731e737. Metcalf, Eddy, 2003. Wastewater Engineering: Treatment and Reuse, fourth international ed. McGraw-Hill, New York. Nurisepehr, M., Jorfi, S., Rezaei Kalantary, R., Akbari, H., Soltani, R.D.C., Samaei, M., 2012. Sequencing treatment of landfill leachate using ammonia stripping, Fenton oxidation and biological treatment. Waste Manag. Res. 30, 883e887. Renou, S., Givaudan, J.G., Poulain, S., Dirassouyan, F., Moulin, P., 2008. Landfill leachate treatment: review and opportunity. J. Hazard. Mater. 150, 468e493. Silverstein, R.M., Webster, F.X., Kiemle, D.J., 2005. Spectrometric Identification of Organic Compounds, seventh ed. John Wily & Sons, New York. Smidt, E., Meissl, K., 2007. The applicability of Fourier transform infrared (FT-IR) spectroscopy in waste management. Waste Manag. 27, 268e276. Stevenson, F.J., 1994. Humus Chemistry: Genesis, Composition, Reactions. John Wily & Sons, New York. Wu, Y., Zhou, S., Ye, X., Chen, D., Zheng, K., Qin, F., 2011. Transformation of pollutants in landfill leachate treated by a combined sequence batch reactor, coagulation, Fenton oxidation and biological aerated filter technology. Process Saf. Environ. Prot. 89, 112e120. Xu, Z.-Y., Zeng, G.-M., Yang, Z.-H., Xiao, Y., Cao, M., Sun, H.-S., Ji, L.-L., Chen, Y., 2010. Biological treatment of landfill leachate with the integration of partial nitrification, anaerobic ammonium oxidation and heterotrophic denitrification. Bioresour. Technol. 101, 79e86. Yu, J., Zhou, S., Wang, W., 2010. Combined treatment of domestic wastewater with landfill leachate by using A2/O process. J. Hazard. Mater. 178, 81e88. Yusof, N., Hassan, M.A., Phang, L.Y., Tabatabaei, M., Othman, M.R., Mori, M., Wakisaka, M., Sakai, K., Shirai, Y., 2010. Nitrification of ammonium-rich sanitary landfill leachate. Waste Manag. 30, 100e109.
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Co-treatment of landfill leachate and domestic wastewater using a submerged aerobic biofilter F.M. Ferraz a, *, J. Povinelli a, E. Pozzi a, E.M. Vieira b, J.C. Trofino a a Departamento de Hidráulica e Saneamento, Escola de Engenharia de São Carlos, Universidade de São Paulo, Av.Trabalhador Sao Carlense, 400, CEP 13566-590 Sao Carlos, São Paulo, Brazil b Instituto de Química de São Carlos, Universidade de São Paulo, Av.Trabalhador Sao Carlense, 400, CEP 13566-590 Sao Carlos, Sao Paulo, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 October 2013 Received in revised form 24 March 2014 Accepted 29 March 2014 Available online
This study used a pilot-scale submerged aerobic biofilter (SAB) to evaluate the co-treatment of domestic wastewater and landfill leachate that was pre-treated by air stripping. The leachate tested volumetric ratios were 0, 2, and 5%. At a hydraulic retention time of 24 h, the SAB was best operated with a volumetric ratio of 2% and removed 98% of the biochemical oxygen demand (BOD), 80% of the chemical oxygen demand (COD) and dissolved organic carbon (DOC), and 90% of the total suspended solids (TSS). A proposed method, which we called the “equivalent in humic acid” (Eq.HA) approach, indicated that the hardly biodegradable organic matter in leachate was removed by partial degradation (71% of DOC Eq.HA removal). Adding leachate at a volumetric ratio of 5%, the concentration of the hardly biodegradable organic matter was decreased primarily as a result of dilution rather than biodegradation, which was confirmed by Fourier transform infrared (FTIR) spectroscopy. The total ammoniacal nitrogen (TAN) was mostly removed (90%) by nitrification, and the SAB performances at the volumetric ratios of 0 and 2% were equal. For the three tested volumetric ratios of leachate (0, 2, and 5%), the concentrations of heavy metals in the treated samples were below the local limits. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: FTIR spectroscopy Humic substances India ink reverse stain Municipal solid waste Organic matter removal Sanitary landfill leachate
1. Introduction Many studies have demonstrated that sanitary landfills generate leachate, a pollutant wastewater that contains inorganic salts, heavy metals, TAN, biodegradable organics, and refractory compounds such as humic substances. Leachate typically presents a dark colour that can be attributed to the humic substances (Kjeldsen et al., 2002; Renou et al., 2008; Wu et al., 2011). Leachate is classified as old when its characteristics include low BOD/COD ratios (0.3e0.01) and high TAN concentrations, but it is important to remember that these characteristics are not necessarily associated with the age of the landfills (Renou et al., 2008). TAN is one of the most important constituents of old leachate because of its possible toxicity to ammonia and nitrite-oxidising bacteria, which are used in biological treatment (Gabarró et al., 2012; Renou et al., 2008; Xu et al., 2010; Yusof et al., 2010). Prior knowledge of the above-mentioned characteristics is mandatory when selecting a successful treatment technology for landfill leachate. The available technologies are based on biological,
* Corresponding author. E-mail address: [email protected] (F.M. Ferraz). http://dx.doi.org/10.1016/j.jenvman.2014.03.022 0301-4797/Ó 2014 Elsevier Ltd. All rights reserved.
physicochemical, advanced oxidation (AOP), and membrane filtration processes (Marañón et al., 2010; Renou et al., 2008; Xu et al., 2010; Yusof et al., 2010). To optimise the efficiency of the treatments and meet the regional discharge limits for landfill leachate, most of the cited processes have been combined. Leachate treatment using air stripping/AOP/biological processes resulted in 99% COD removal (Nurisepehr et al., 2012). Similar values were obtained for COD, colour, and nutrient removal from leachate treatment as a result of applying sequencing batch reactors (SBR)/coagulation/Fenton/biological aerated filtering (Wu et al., 2011). Nonetheless, combined processes can be very costly because they require chemicals and electricity to produce high-quality treated leachate. It was reported that the operating costs of combining an SBR with ozonation or photo-Fenton were, respectively, 125% and 63% higher than the operating costs of an SBR treating leachate (Cassano et al., 2011). Regarding the low-cost options that may be associated with obtaining a good final effluent quality, the co-treatment of leachate with domestic wastewater can be highlighted. This treatment alternative is advantageous because it can be employed in an existing wastewater treatment plant (WWTP) and can thus avoid the need to invest in a new facility. Because leachate is generally
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added to domestic wastewater at volumetric ratios that do not exceed 10%, the biological processes are less susceptible to the toxic effects of high TAN concentrations (Borghi et al., 2003; Çeçen and Aktas, 2004; Fudala-Ksiazek et al., 2011; Renou et al., 2008; Yu et al., 2010). Most papers reporting leachate co-treatment with domestic wastewater have considered the use of activated sludge reactors. For volumetric ratios of leachate varying from 0.2 to 5%, the COD removals ranged from 80 to 92% (Çeçen and Aktas, 2004; FudalaKsiazek et al., 2010, 2011; Yu et al., 2010). Despite the important contributions of the previous studies, none of those studies clarified whether the hardly biodegradable organic matter of old leachates was indeed removed by biodegradation with the organic content of domestic wastewater or whether this matter was instead diluted. Thus, the main objective of this study was to investigate whether the hardly biodegradable organic matter of old leachate was simply diluted or actually biodegraded with domestic wastewater. Differing from previous studies, this study evaluated the cotreatment of old leachate with domestic wastewater in pilot-scale submerged aerobic biofilters (SABs), which are known to offer better solid retention compared with activated sludge reactors (Gálvez et al., 2009; Metcalf and Eddy, 2003). 2. Material and methods 2.1. Wastewaters 2.1.1. Landfill leachate This study used leachate from the municipal sanitary landfill of Sao Carlos, a medium-sized city located in Sao Paulo, Brazil, that has approximately 220,463 inhabitants and generates 160 tons of municipal solid waste per day. This municipal landfill has been in operation for 22 years and receives domestic solid waste containing organic matter (60% by mass), as well as glass, paper, plastic, and metals, though the city has a recycling program. The sampling point was located at the landfill treatment pond. Before being mixed with domestic wastewater, the leachate was pre-treated by air stripping (for TAN removal) according to the procedures described by Ferraz et al. (2013a). Initially, the pH was adjusted to 11 by lime addition; the leachate was then recirculated in an aerated packed tower until its TAN concentration was reduced to approximately 100e150 mg L1 (Ferraz et al., 2013a). The leachate used in this study was classified as old, primarily because of its high TAN concentration and extremely low BOD/COD ratio of 0.1 (Table 1). The pre-treated leachate obtained through air stripping presented the same BOD/COD ratio as did the raw leachate. These extremely low BOD/COD ratios can be associated with the presence of the hardly biodegradable organics, such as humic and fulvic acids (Renou et al., 2008), which seem to remain in leachates that have been pre-treated by a pH adjustment with lime and air stripping (Ferraz et al., 2013a). 2.1.2. Domestic wastewater Domestic wastewater was collected from the sewer system located in the neighbourhood of the University of Sao Paulo (EESC/ USP) campus. This wastewater presented a large content of biodegradable organic matter compared with that of the leachate, resulting in BOD/COD ratios varying from 0.5 to 0.6 (Table 1). 2.1.3. Mixture leachate/domestic wastewater Leachate was added to domestic wastewater at volumetric ratios of 2 and 5%.
Table 1 Physico-chemical characterization of wastewaters used in the experiments (adapted from Ferraz et al. (2013b)). Parameter
Raw leachate
Pre-treated leachate
Sanitary sewage
Min
Min
Min
Max
pH 8.3 9.0 Total alkalinity 6000 7570 1 (mg CaCO3 L ) 28,300 Conductivity (mS cm1) 14,800 BOD5,20 (mgO2 L1) 433 588 CODtotal (mgO2 L1) 4425 4860 TKN (mg L1 N) 920 977 TAN (mg L1 N) 790 821 1 130 156 Organic-N (mg L ) 1 TS (mg L ) 8446 15,980 4974 8447 TVS (mg L1) TFS (mg L1) 3472 7533 TDS (mg L1) 8247 15,565
9.5 2649 8450 218 2772 12 9 3 6558 5749 2118 6248
Max
11 6.4 5000 111 12,300 304 3900 250 150 100 9140 6976 3778 8700
363 115 216 29 27 2 562 120 172 495
Max 7.6 200 505 269 440 50 37 13 1078 390 202 1003
BOD: biochemical oxygen demand; COD: chemical oxygen demand; Min: minimum; Max: maximum; TAN: total ammoniacal nitrogen; TKN: total Kjeldahl nitrogen; TS: total solids; TVS: total volatile solids; TFS: total fixed solids; TDS: total dissolved solids.
2.2. Pilot-scale submerged aerobic biofilters (SABs) One of the SABs consisted of a PVC tube with a diameter of 38 cm, a height of 200 cm, and a working volume of 178 L. As shown in Figure S1 (Supplementary data), this reactor was divided into five modules. Two of these modules were packed with polyethylene corrugated Raschig rings, which were 1.5 cm in diameter and 5 cm in length. Each of these modules was inoculated with 25 L of activated sludge biomass. Another SAB that was inoculated similarly to the first one and packed with the same material was used as a control reactor. This reactor was loaded only with domestic wastewater and had a working volume of 75 L (Figure S1). The two SABs were operated under a continuous-flow regime, with an hydraulic retention time (HRT) of 24 h. Compressed air was injected into the SABs at a rate of 500 L h1, and the dissolved oxygen concentration inside the five modules was maintained above 2 mg L1. 2.3. Analytical procedures The following parameters were measured according to the Standard Methods for the Examination of Water and Wastewater (APHA, AWA and WEF, 2012): BOD5, 20 (Hach BODTrakII respirometric apparatus), method 5210 B; COD (Hach COD reactor 4560000/Hach DR 2010 spectrophotometer), colourimetric method 5220 D; conductivity, method 2510 B; DOC (Shimadzu TOC 5000 A Analyser), method 5310 B; nitrate, method 4500 C e NO 3 (Shimadzu UV-160A spectrophotometer); solid content, method 2540; total alkalinity, method 2320 B; TAN (Büchi distillation unit B-339), method 4500 C e NH3 Nitrogen; total heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) (Varian AA240 FS atomic absorption spectrophotometer), methods 3111 B and D; and total Kjeldahl nitrogen (TKN) (Büchi digestion unit B-426), method 4500 C e Norg Nitrogen. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups present in the leachate structure. FTIR spectra were recorded from KBr pallets containing approximately 1 mg of a lyophilised sample and 100 mg of KBr. A BOMEM B-102 FTIR spectrometer was used. The FTIR spectra were obtained over the wavenumber range of 4000 to 400 cm1, at a resolution of 4 cm1, and in 16 scans. The spectra were plotted in Origin 8.0 (OriginLab).
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2.4. Assessment of the hardly biodegradable organic matter removal
D1
Based on the previous literature, it is unclear whether the hardly biodegradable organic matter in leachate is removed through biodegradation or whether its concentration is reduced in treated effluent due to the effects of dilution that are observed during cotreatment with domestic wastewater. In a previous study (Ferraz et al., 2013b), we proposed a method called the “equivalent in humic acid” (Eq.HA) approach to quantify the hardly biodegradable organic matter under aerobic conditions. When the alkalinity is determined in a sample, the result is expressed in terms of mg CaCO3 L1; however, this result does not mean that the sample only contains CaCO3. Other species such as OH or HCO 3 may be present in that sample. Analogously, expressing the DOC as Eq.HA does not mean that a sample contains exclusively humic acid: fulvic acid and other hardly biodegradable substances that may be present in that sample are represented in the measurement of DOC Eq.HA. In the current study, a calibration curve was built using eight different humic acid (SigmaeAldrich) concentrations (5e 300 mg L1), and the amount of DOC was subsequently measured (Fig. 1). As summarized in Figure S2 (Supplementary data), the DOC values of the influent samples of the two SABs are measured first. By inserting the measured DOC values into the calibration curve, the DOC in terms of Eq.HA can be obtained for domestic wastewater (term “x1” in Figure S2a) and for the mixture of leachate/domestic wastewater (term “x2” in Figure S2a). The hardly biodegradable organic matter in the mixture, which results from the addition of leachate to the domestic wastewater (D1), can be tentatively determined as follows:
D1 ¼ x2 x1 ;
(1)
i.e., the hardly biodegradable DOC of the domestic wastewater, which is used as a blank, is discounted. Analogously, this procedure was applied to the samples treated by the SABs (Figure S2b). Thus, the refractory organic matter in the treated mixture, which was produced by the addition of leachate to domestic wastewater (D2), can be determined in mg L1 as follows:
D2 ¼ y2 y1
11
D D2 DOC Eq:HA removalð%Þ ¼ 100* 1
(2)
The DOC Eq.HA removal is determined according to Equation (3):
(3)
For the control SAB, the DOC Eq.HA removal can be obtained using Equation (4):
x y1 Control DOC Eq:HA removalð%Þ ¼ 100* 1 x1
(4)
The results can be interpreted as follows: -
if D2 ¼ 0, the SAB completely removed the DOC Eq.HA; if D1 > D2 and D2 > 0, the DOC Eq.HA was partially removed; and if D1 ¼ D2, the activated sludge reactors could not remove the DOC Eq.HA.
2.5. Microscopic examination A microscopic examination was performed to observe the possible toxic effects of leachate with respect to microfaunal diversity when it is added to domestic wastewater. The India ink reverse stain test was applied to mixed liquor samples, focusing on a qualitative analysis of dissolved carbon, according to Jenkins et al. (2003). In this test, the India ink penetrates the free dissolved carbon portion of the samples, staining the microscope slide black, while portions containing dissolved carbon particles exhibit a brownish yellow colour. In normal flocs, small, clear points are typically observed, with a predominance of blackstained areas (Jenkins et al., 2003). An alternative approach for obtaining a quantitative response from the India ink reverse stain test is proposed in this study. The method consists of classifying the tonalities observed on microscope slides using the Image Pro-Plus software, as shown in Fig. 2. The light-yellow portions on the microscope slides are classified as “class 1”, the brown yellow portions as “class 2”, and the black portions as “class 3”. Using the software, the percentage of the area occupied by each “class” on a microscope slide can be assessed. Our interest was focused on the large light-yellow portions (“class 1”). All microscope observations were performed at a magnification of 100, zero contrast, a sharpness of þ7, zero red and blue levels, and a manual exposure mode varying from 1/1000 to 1/250, depending on the intensity of the bright areas in each sample. This result may offer a quantitative answer to the question of how effective the SABs were in removing DOC. The advantage of this procedure is that it can be used as a preliminary analysis preceding COD determinations, for example, in addition to offering a rapid assessment. It is also a simple, safe, and inexpensive control tool because microscopes are often available at wastewater treatment plant facilities. 2.6. Statistical analysis The performances of the two SABs with respect to organic matter and nitrogen removal were compared using an analysis of variance (ANOVA) to verify whether the differences between the reactors’ performance were random or whether they were caused by leachate interference. 3. Results and discussion 3.1. Organic matter removal
Fig. 1. “Equivalent in humic acid” calibration curve.
The steady-state condition was reached in 50 days for the three tested volumetric ratios (0, 2, and 5%). Confirming the advantage of SABs with respect to solid retention, Fig. 3a shows that excellent performance was achieved in
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Fig. 2. (a) India ink reverse stain test and (b) proposed method for tonality classification.
terms of TSS removal. At a volumetric ratio of 2%, there was negligible interference from the leachate in the aerobic biomass: the TSS removal (90% on average) was equal to that of the control SAB. When fed with leachate at a volumetric ratio of 5%, the SAB removed approximately 80% of TSS. Based on an ANOVA at a
significance level of 0.01, the average removals for the volumetric ratio of 0, 2, and 5% were significantly different (F ¼ 5.3 and F critical ¼ 5.2). The control SAB operating with an organic loading rate (OLR) of 0.340 kg COD m3 d1 removed 98% of the BOD, 80% of the COD and
Fig. 3. Organic matter removal profile: (a) TSS; (b) SCOD; (c) BOD; (d) DOC; and (e) DOC Eq.HA.
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13
83% of the DOC (Fig. 3bed). The OLR increased to 0.4 kg COD m3 d1 due to the addition of leachate to the domestic wastewater at a volumetric ratio of 2%; in this case, the SAB removed 98% of the BOD and 80% of both the COD and DOC. At a volumetric ratio of 5% and an OLR of 0.5 kg COD m3 d1, the SAB removals were 98% of the BOD, 76% of the COD, and 75% of the DOC (Fig. 3bed). For the three tested volumetric ratios (0, 2, and 5%), the average BOD of the treated effluents was less than 10 mg O2 L1, thus meeting the discharge standard established by the Brazilian environmental law CONAMA 430/2011 (Brazilian Ministry of the Environment, 2011). Based on an ANOVA at a significance level of 0.01, there was no statistically significant difference (F ¼ 0.9 and F critical ¼ 5) in the average removals of BOD, COD, or DOC when the SAB was fed with leachate/domestic wastewater at volumetric ratios of 0, 2, and 5%. 3.1.1. Application of the proposed equivalent in humic acid (Eq.HA) method and FTIR spectroscopic analysis Using Equation (1)e(4), the concentrations of the hardly biodegradable organics, which were altered by adding leachate to domestic wastewater, were calculated before and after this biological treatment. Fig. 4e shows that the SAB performance in the removal of hardly biodegradable organic matter decreased as the volumetric ratio of leachate increased from 2 to 5%. The addition of leachate to domestic wastewater at a volumetric ratio of 2% resulted in a BOD/COD ratio of 0.5, and the same ratio was obtained for the domestic wastewater. However, the SAB fed with leachate at a volumetric ratio of 2% removed 71% of the DOC Eq.HA, whereas 90% was removed in the control SAB. For the mixture containing leachate at the volumetric ratio of 5%, the BOD/COD ratio decreased to 0.4. Consequently, the DOC Eq.HA removal decreased to 62% for the volumetric ratio of 5%. Additionally, at a significance level of 0.01, an ANOVA showed that the differences between the DOC Eq.HA removal rates were statistically significant (F ¼ 9 and F critical ¼ 5) for the volumetric ratios of 0, 2, and 5%. lu (2001) evaluated the co-treatment of Çeçen and Çakırog leachate (COD 2431 mg O2 L1) with synthetic domestic wastewater in 2-L activated sludge reactors. Using a control reactor that was fed only with synthetic domestic wastewater, the authors assessed the contribution of leachate at a volumetric ratio of 10% to the influent COD (250 mg O2 L1) and the inert COD in the treated effluent (210 mg O2 L1). The inert COD in the treated effluent corresponded to 56% of the initial COD. In our study, using a volumetric ratio of 2%, which was one-fifth lu (2001), the of the volumetric ratio used by Çeçen and Çakırog refractory DOC was 11%. This value also represented one-fifth of the refractory COD obtained by the above-mentioned authors. Such consistent results confirm that the proposed Eq.HA method was valid for non-synthetic wastewaters. As shown in Fig. 4a, the following absorption bands that were found in the domestic wastewater spectra were also found in the influent samples containing leachate at volumetric ratios of 2 and 5%: 3400 cm1, due to the OH stretching of alcohols or phenols; 1600 cm1, due to aromatic C]C bonds; 1400 cm1, due to the C] O stretching of carboxylate ions; and 1150 cm1, due to the CeO stretching of polysaccharides. Absorption bands caused by the addition of leachate to domestic wastewater were observed at 2900 cm1, due to the CeH stretching of aliphatic methylene, and 1500 cm1, due to aromatic C]C bonds (Liang et al., 2009; Silverstein et al., 2005; Smidt and Meissl, 2007; Stevenson, 1994). For a 24-h HRT, most of the absorption bands found in the spectrum of the raw domestic wastewater (volumetric ratio 0%) were not detected in the treated effluent of the control SAB (Fig. 4a).
Fig. 4. FTIR spectra of (a) SABs influent and effluent samples, (b) sludge samples from the control SAB, and (c) sludge samples from the SAB fed with leachate at volumetric ratios of 2 and 5%.
An absorption band at 1384 cm1 was observed (Fig. 4a) and was likely due to nitrate because nitrogen was removed from the effluent via nitrification (Smidt and Meissl, 2007). As demonstrated by the COD and DOC measurements, some refractory organic matter remained in the treated effluent, causing the appearance of a band at 1150 cm1 and the permanence of the absorption band at 3400 cm1, although the latter band had a significantly lower intensity compared with that of the raw domestic wastewater (Fig. 4a). For the mixture leachate/domestic wastewater at a volumetric ratio of 2%, the spectrum of the treated effluent was equal to that of
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the control SAB (Fig. 4a); this confirmed the organic matter removal, as evaluated using physicochemical parameters. Nonetheless, the addition of leachate at a volumetric ratio of 5% interfered with the SAB performance in hardly biodegradable organic matter removal, and the spectra of the influent and effluent samples were identical (Fig. 4a). To verify whether the removal of hardly biodegradable organic matter was caused by their adsorption into the sludge, samples of the sludge used for the SAB start-up and samples of the end of operation were acquired and analysed through FTIR spectroscopy. As shown in Fig. 4b, for the control SAB, the spectra of the sludge used for the start-up and those of the sludge after the end of operation were identical. The same is true for the SAB operated with leachate at a volumetric ratio of 2% (Fig. 4c), confirming that neither dilution nor adsorption into the sludge was the primary cause for the disappearance of the hardly biodegradable organic matter. No distinct differences were observed in the sludge spectra when the VR of the leachate increased from 2 to 5% (Fig. 4c). Based on the Eq.HA method results and FTIR spectroscopic analysis, the hardly biodegradable organic matter was partially biodegraded (71%) when leachate was added at a volumetric ratio of 2%. If dilution had caused decreases in the hardly biodegradable organic matter concentration, the FTIR spectra of the SAB influent and effluent samples would have been identical, as observed for the volumetric ratio of 5%. 3.1.2. Organic carbon evaluation using the India ink test In agreement with the measured DOC concentration in the treated SAB effluents (Fig. 3d), the proposed procedure applied to the India ink test to assess the percentage of DOC in microscope slides showed that the DOC in the control SAB sludge was only 0.46%. At volumetric ratios of 2 and 5%, the areas corresponding to the DOC were 3.4 and 4.5%, respectively. A good correlation coefficient (R2) was obtained between the measured DOC concentrations and the percentage of DOC in the SAB biomass for the three tested leachate volumetric ratios (Fig. 5). Thus, the proposed procedure based on the tonalities of the India ink test can provide a simple and low-cost preliminary evaluation of the organic matter removal in the SABs. Nonetheless, this procedure was not intended to replace physicochemical analyses such as COD or DOC.
Fig. 5. Relation between DOC measurements and the percentage of DOC obtained as a quantitative response from the India ink test.
by the Brazilian environmental law CONAMA n 430/2011. As shown in Table S1 (Supplementary data), after the co-treatment, the concentration of heavy metals was even further below these limits. 4. Conclusion The co-treatment of domestic wastewater and landfill leachate that was pre-treated by air stripping was successfully performed in
3.2. Nitrogen removal As the steady-state was reached, the SAB performances for TAN removal at volumetric ratios of 0, 2, and 5% were 91, 90, and 88%, respectively (Fig. 6a). Based on an ANOVA at a significance level of 0.01, the differences among the average TAN removals were random; thus, the results were statistically identical (F ¼ 0.1 and F critical ¼ 5), and the interference of leachate at the tested volumetric ratios was negligible. Fig. 6b also shows that nitrogen removal was primarily caused by nitrification rather than ammonia stripping because the majority of the removed TAN was oxidised to nitrate. The average nitrification effectiveness was 83% for the volumetric ratio of 0%, and it was 77% for the volumetric ratios of 2 and 5%. At a significance level of 0.01, the ANOVA showed that these performances were not significantly different (F ¼ 1.4 and F critical ¼ 5.1). 3.3. Heavy metals Prior to the aerobic treatment, the concentration of heavy metals in the samples of domestic wastewater and leachate/domestic wastewater at volumetric ratios of 2 and 5% was already below the discharge limits for wastewaters that were established
Fig. 6. Nitrogen removal measured by (a) TAN, (b) nitrification, and (c) FA profiling, along with the co-treatment.
F.M. Ferraz et al. / Journal of Environmental Management 141 (2014) 9e15
a pilot-scale SAB operated with a 24-h HRT. The SAB showed optimal performance when the volumetric ratio of the leachate was 2%, at which point the organic matter and nitrogen removals were equal to those of the control reactor: 98% of the BOD, 80% of the COD and DOC, and 90% of the TSS. The proposed Eq.HA method allowed us to conclude that the concentrations of the hardly biodegradable organic matter in the leachate were most likely decreased as a result of partial degradation (71% of DOC Eq.HA removal) instead of dilution, which was confirmed by FTIR analysis. The proposed method, which is based on a tonality classification of the India ink test, allowed for the quantitative assessment of DOC using microscopic examinations. The TAN was mostly removed (90%) by nitrification, and the SAB performances at volumetric ratios of 0 and 2% on TAN removal were identical. For the three tested volumetric ratios of leachate (0, 2, and 5%), the concentration of heavy metals in treated samples was lower than the local limits. Acknowledgements The authors would like to thank São Paulo Research Foundation (grant numbers 2010/51955-2 and 2011/50627-4) and CNPq (grant numbers: 303083/2010-7 and 141710/2010-1) for financial support. We also thank the anonymous reviewers for their helpful comments. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2014.03.022. References APHA e American Public Health Association, AWWA e American Water Works Association, WEF e Water Environment Federation, 2012. Standard Methods for the Examination of Water and Wastewater, twenty-second ed. APHA, AWWA, WEF, Washington. Borghi, A. Del, Binaghi, L., Converti, A., Borghi, M. Del, 2003. Combined treatment of leachate from sanitary landfill and municipal wastewater by activated sludge. Chem. Biochem. Eng. Q. 17, 277e283. Brazilian Ministry of the Environment [Internet], 2011. Available from: http://www. mma.gov.br/port/conama/legiabre.cfm?codlegi¼646. Cassano, D., Zapata, A., Brunetti, G., Del Moro, G., Di Iacomi, C., Oller, I., Malato, S., Mascolo, G., 2011. Comparison of several combined/integrated biological-AOPs setups for the treatment of municipal landfill leachate: minimization of operating costs and effluent toxicity. Chem. Eng. J. 172, 250e257. Çeçen, F., Aktas, Ö., 2004. Aerobic co-treatment of landfill leachate with domestic wastewater. Environ. Eng. Sci. 21, 303e312. lu, D., 2001. Impact of landfill leachate on the co-treatment of Çeçen, F., Çakırog domestic wastewater. Biotechnol. Lett., 821e826. Ferraz, F.M., Povinelli, J., Maria Vieira, E., 2013a. Ammonia removal from landfill leachate by air stripping and absorption. Environ. Technol.. http://dx.doi.org/ 10.1080/09593330.2013.767283.
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