Waste Management & Research http://wmr.sagepub.com/

Enhancing biogas production from anaerobic biodegradation of the organic fraction of municipal solid waste through leachate blending and recirculation Arjun Nair, Majid Sartaj, Kevin Kennedy and Nuno MG Coelho Waste Manag Res published online 14 August 2014 DOI: 10.1177/0734242X14546036 The online version of this article can be found at: http://wmr.sagepub.com/content/early/2014/08/14/0734242X14546036

Published by: http://www.sagepublications.com

On behalf of:

International Solid Waste Association

Additional services and information for Waste Management & Research can be found at: Email Alerts: http://wmr.sagepub.com/cgi/alerts Subscriptions: http://wmr.sagepub.com/subscriptions Reprints: http://www.sagepub.com/journalsReprints.nav Permissions: http://www.sagepub.com/journalsPermissions.nav Citations: http://wmr.sagepub.com/content/early/2014/08/14/0734242X14546036.refs.html

>> OnlineFirst Version of Record - Aug 14, 2014 What is This?

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

546036

research-article2014

WMR0010.1177/0734242X14546036Waste Management & ResearchNair et al.

Original Article

Enhancing biogas production from anaerobic biodegradation of the organic fraction of municipal solid waste through leachate blending and recirculation

Waste Management & Research 1­–8 © The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734242X14546036 wmr.sagepub.com

Arjun Nair, Majid Sartaj, Kevin Kennedy and Nuno MG Coelho

Abstract Leachate recirculation has a profound advantage on biodegradation of the organic fraction of municipal solid waste in landfills. Mature leachate from older sections of landfills (>10 years) and young leachate were blended and added to organic fraction of municipal solid waste in a series of biomethane potential assay experiments with different mixing ratios of mature and young leachate and their effect on biogas production was monitored. The improvement in biogas production was in the range of 19%–41% depending on the ratio of mixing old and new leachate. The results are conclusive that the biogas generation could be improved by blending the old and new leachate in a bioreactor landfill system as compared with a conventional system employed in bioreactor landfills today for recirculating the same age leachate. Keywords Anaerobic digestion, biodegradability, bioreactor landfills, biomethane potential, leachate recirculation

Introduction In modern engineered landfills, the biogas and leachate produced through the anaerobic degradation of organic fraction of municipal solid waste (OFMSW) are collected to prevent the release of methane, which has a high greenhouse gas potential (Abouelenien et al., 2010), and the contamination of groundwater by the highly contaminated leachate (Bashir et al., 2010). Biogas can then be utilised to generate energy and leachate is treated on-site before being discarded. Bioreactor landfills are a development of regulated landfills where leachate is commonly collected and recirculated back through the waste material. The research on bioreactor landfilling technology in some countries is an emerging field, with many studies aimed at recirculation of leachate within the landfill for improving the rate of biodegradation of the waste. Leachate recirculation improves distribution of enzymes and nutrient transfer to the microbial population (Bilgili et al., 2007), which increases their growth rate. It also increases the moisture within the waste, which is essential for microbial biodegradation. Recirculating the leachate solubilises organics in the waste, which in turn accelerates the biodegradation process (Manfredi and Christensen, 2009; Morris et al., 2003; Sun et al., 2011). It has also been reported that the toxicity levels in the leachate from bioreactor landfills are significantly lower than those of regular landfills that do not practice recirculation owing to dilution of inhibitory compounds (Bilgili et al., 2007; USEPA, 2013).

The leachate generated in landfills varies in strength and composition depending on several factors, but the most significant is the age of the landfill (Peng et al., 2008; Sartaj et al., 2010). Leachate types can be generally divided into young leachate and old (mature) leachate. Young leachate is produced in a portion of a landfill with recently landfilled municipal solid waste (MSW). Typically, this type of leachate has extremely high concentrations of chemical oxygen demand (COD), ammonia and volatile fatty acids (VFAs), along with a low pH. COD concentrations up to 80,000 mg L−1 (Wang et al., 2006) and ammonia concentrations as high as 13,000 mg L−1 have been reported for young leachate (Renou et al., 2008). Ammonia inhibition has been reported to occur in the range of 1500–3000 mg L−1 of total ammonia nitrogen (TAN) (Liu et al., 2012). In water, ammonia exists in two forms: un-ionised ammonia, NH3, and ionised ammonium, NH4+, with NH3 being the form that is toxic to living organisms. The relative concentration of each of these forms is primarily a function of pH and temperature. It is common in aquatic chemistry to refer to and express the sum of the two as simply ammonia or TAN. The very Department of Civil Engineering, University of Ottawa, Ottawa, Ontario, Canada Corresponding author: Majid Sartaj, Department of Civil Engineering, University of Ottawa, 161 Louis-Pasteur Ottawa, ON Ontario K1N 6N5 Canada. Email: [email protected]

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

2

Waste Management & Research

high concentrations of VFAs, caused by active acidogenesis occurring in the early stages of landfill operation (acidogenesis phase), cause a drop in the pH value. This, along with high concentrations of ammonia, inhibits methanogenic bacteria and restricts the potential biogas and methane production (Abouelenien et al., 2010; Berge et al., 2006; Francois et al., 2007; Peng et al., 2008). For this reason, the maximum production of biogas is only achieved when conditions suitable for methanogenesis develop. It is also reported that ammonia tends to accumulate since there is no degradation pathway for ammonia in anaerobic systems. Recirculating leachate increases the rate of ammonification, resulting in accumulation of higher levels of NH3, which intensifies the toxicity of the leachate to aquatic species (Berge et al., 2006; He et al., 2007; Wang et al., 2006). Mature leachate has markedly different characteristics. With the exception of ammonia, the concentration of all components of leachate increases rapidly during the initial (0–2 years) and young (3–5 years) phases and then starts to decline as the landfill matures through to the final old stages (>10 years). COD content in old leachate is considerably lower than that of young leachate as is the case with the VFAs. Mature landfill leachate has a higher pH as a result of decreased VFAs concentration and alkalinity production by methanogenesis. Older leachate has also a more balanced mixture of acidogenic and methanogenic microorganisms, with a significant increase of active methanogens when compared with young leachate (Kim and Pohland, 2003; Reinhart, 1996). Contrary to COD or VFAs, the concentration of some amphoteric heavy metals (like Cu, Zn, Pb) is usually higher in old leachate than in young leachate, which can prevent old leachate from being treated in municipal wastewater treatment plants without a pre-treatment step (Li et al., 2009). As mentioned above, in a recently landfilled waste material, recirculating the produced leachate causes the accumulation of ammonia and VFAs with a subsequent decrease of pH and inhibition of methanogenic activity and even greater accumulation of VFAs, which could result in reduced biogas production. An interesting and potentially advantageous option is to recirculate old leachate, or a mixture of old and new, to the newer portions of the landfill. Old leachate will have a more balanced mix of anaerobic microbial consortia (with a significantly higher presence of methanogens), a low VFAs content, a higher pH and a higher alkalinity and, consequently, if mixed with young leachate and recirculated through young waste cells, could decrease the negative effects caused by low pH, high concentrations of ammonia and excess VFAs accumulations inside new sections of the landfill. This option might considerably reduce the time necessary to achieve a high and stable biogas production in a landfill, while at the same time reducing the strength of the collected leachate. At the same time, new leachate, or a mixture of old and new, could also be recirculated to an old section of the landfill where substrate is scarce but microbial consortia is well developed and balanced (a more balanced mixture of acidogenic and methanogenic microorganisms).

The objective of this study was then to investigate and assess the hypothesis that mixing different blends of mature and young leachate could enhance biodegradation and biogas production in bioreactor landfills. It is hypothesised that while the mature leachate portion supplies microorganisms that are starved of substrate, the young leachate portion brings in the substrate. As a result of the symbiotic substrate–microorganisms mixture, the leachate would not have to be continually modified before reinjection into the bioreactor landfill. It was hypothesised that recirculating a mixture of old and new leachate could decrease the time required to reach a high methane production stage and, as a consequence, reduce length of time required to stabilise the waste while increasing the methane yield in the process.

Materials and methods To assess and test the hypothesis of feasibility of enhancing anaerobic degradation of OFMSW and biogas production by blending young and mature leachate before recycling, a series of biomethane potential (BMP) assay experiments, under a controlled and accelerated environment, was conducted as explained below.

OFMSW A mixture simulating the OFMSW was prepared in the laboratory to be used in the experiments as a model waste to minimise compositional variation seen in a real OFMSW. The model OFMSW (M-OFMSW) composition was similar to the one reported by Shahriari et al. (2012). This mixture was intended to simulate kitchen waste and industrial food processing waste and had a similar composition of protein, carbohydrates, vegetables and fat as the Canada Food Guide (CFG, 2011), thus was representative of Canadian kitchen waste. The composition of this mixture in weight percentage consisted of cooked rice (27.5%), cooked pasta (17.5%), carrot (11%), apple (11%), banana (11%), cooked ground beef (10%), dog food (10%) and cabbage (2%). To reduce the particle size, M-OFMSW was placed in a Kitchen Aid food processor (PowerPro II, 500 W) for 30 s at high speed and stored at 4 °C until being used.

Source of leachate Mature landfill leachate aged between 15–25 years was obtained from the municipal landfill at Carp Road, Carp, Ontario. The leachate was collected, transported to the laboratory, stored at a temperature of –4 °C, and thawed at 35 °C whenever required. A sample of the leachate was sent for analysis to Exova Testing Laboratories (Colonnade Road, Ottawa, Canada) and its characteristics are shown in Table 1. Young leachate was generated in the laboratory by continuously percolating tap water under anaerobic conditions through 100 L of loosely packed MSW in a column at a recirculation rate of 3 L h−1 and three recirculation cycles a day. MSW was collected from the Lafleche Environmental landfill facility at Moose

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

3

Nair et al. Table 1.  Characteristics of the mature and young leachate (in mg L−1). Parameter

Mature leachate

Young leachate

Alkalinity as CaCO3 Biochemical oxygen demand (BOD5) Chemical oxygen demand (COD) TAN (total ammonia nitrogen) VFA (as acetic acid) Total solids Volatile solids pH

8200 85 11,040 1410 868.4 96 22 8.9

5300 22,500 56,800 2360 19,514 287 230 5.4

Table 2.  BMP experimental set-up. BMP test

Code

Leachate blend volume (mL)

Leachate blend composition

OFMSW (g)

Buffered distilled water (mL)

I

3N0O 2N1O 1N2O 0N3O Control Inoculum 3N0O 2N1O 1N2O 0N3O

10 10 10 10 0 0 30 30 30 30

100% young 66.6% young; 33.3% old 33.3% young; 66.6% old 100% old – – 100% young 66.6% young; 33.3% old 33.3% young; 66.6% old 100% old

3 3 3 3 3 0 0 0 0 0

100 100 100 100 110 110 100 100 100 100

II

BMP: biomethane potential; OFMSW: organic fraction of municipal solid waste. 70 mL of inoculum (anaerobic sludge) added to all bottles.

Creek, Ontario. Organic waste (from the green box programme in Ontario) was collected following hand sorting from the output of the shredder at the solid waste processing facility, transported and stored at University of Ottawa, at –4 °C until being used. The composition of young leachate generated is shown in Table 1.

BMP experiments In order to study the hypothesis put forward in this study, two sets of BMP tests were conducted. Kimax® glass bottles (250 mL) capped with butyl rubber stoppers were used to perform mesophilic BMP assays. The total working volume was 200 mL consisting of OFMSW and leachate (discussed below) and included 70 mL of mesophilic anaerobic inoculums. Anaerobic sludge collected from a local wastewater treatment plant was used as inoculum. Equal portions of NaHCO3 and KHCO3 were added to each bottle to achieve an alkalinity concentration of between 4000 and 6000 mg L−1 (as CaCO3). The bottles were subsequently sparged with nitrogen gas for two minutes to produce anaerobic conditions and then sealed. Assay bottles were brought to atmospheric pressure prior to incubation by inserting a BD 21G1½ needle connected to a U-tube manometer, allowing the bottle pressure to equilibrate with atmospheric pressure. Bottles were incubated at 35  °C ±1  °C in a New Brunswick Scientific Controlled Environment Incubator Shaker model G-25 at 80 r min−1, to keep bacteria and substrate in suspension. The measurement of the gas

produced by the batch BMP bottles were monitored on a daily basis using a tube manometer. The tests performed, as well as the set-up of each bottle, are shown in Table 2. All tests were performed in duplicates and continued until the biogas production ceased. The first set of tests (BMP test I) was done in order to investigate the effect of blending young and mature leachate on anaerobic digestion of OFMSW. The codes in Table 2 refer to the mixing ratios of young and old leachate. For example, 2N1O corresponds to 2 portions new leachate and 1 portion old leachate. Two additional BMP tests, duplicated, were conducted as control with OFMSW or inoculum only. The control reactor with inoculum represents BMP of inoculum alone, while the control reactor with OFMSW contains inoculum and OFMSW. This control reactor simulates a batch BMP assay of a conventional regulated landfill with no recirculation. To isolate the contribution from degradation of leachate and the degradation of OFMSW, BMP test II was carried out with the same set-up as test I, but without the addition of OFMSW.

Analytical procedures The biogas produced was measured with a manometer on a daily basis. Gas samples were analysed for gas composition (N2, CO2 and CH4) with a thermal conductivity gas chromatograph (series 400, Gow-Mac Instrument Co., USA) on a

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

4

Waste Management & Research

Figure 1.  Average cumulative biogas production for batch test I. OFMSW: organic fraction of municipal solid waste.

weekly basis. The detector, injection port and column temperatures were 130 °C, 130 °C and 120 °C, respectively, and the carrier gas was helium at an inflow rate of 30 mL min−1. Leachate samples were analysed in triplicates for COD, ammonia nitrogen (NH3-N); in duplicates for total alkalinity and VFAs. COD was measured with the reactor digestion method (5220-D; APHA, 2005) using TNTplus™822 highrange reagent vials (Method 8000, Hach, USA). TAN was measured with the salicylate method using TNTplus™ 832 reagent vials (Method 10205, Hach, USA). The Hach DR 5000 UV-VIS spectrophotometer was used to analyse the reagent vials of COD and ammonia. The Hach DR200 heating block for COD vials was used to heat and digest the Hach TNT 822 test vials. VFAs were measured using the gas chromatographic method (5560-D; APHA, 2005) with an Agilent-6890 gas chromatograph (HP-Agilent Technologies, Inc., USA) equipped with a flame ionization detector. Total alkalinity was determined by titration to pH = 4.50 (2320-B; APHA, 2005). The pH value was measured using a Fisher Accumet model XL25 dual channel pH/ion meter equipped with a glass electrode.

Results and discussion The objective of BMP test I was to evaluate if blending old and young leachate would enhance anaerobic biodegradation of OFMSW either by changing the rate or the yield in biogas production. It was expected that different blends of mature and young leachate would have different biodegradability characteristics per se, because of the difference in organic content and general composition between the two types of leachate. The cumulative biogas production for BMP test I is shown in Figure 1. The results are the average

of duplicate samples. The standard deviation of results was on average 8.2%. All test bottles with leachate added produced more biogas than the test bottles with OFMSW only, which was somewhat expected owing to the increased organic load contributed by young leachate in particular. However, it should be noted that the biogas generated in batch test I would be representative of the biogas contribution from the leachate, inoculum, as well as the OFMSW. The biogas generated from the leachate blends component (analysed from batch test II) was then subtracted from the total biogas generated in batch test I, to get the actual or net biogas production from the OFMSW. Based on the results from this data, it would be possible to infer whether or not the leachate blending had any significant effect and enhancement on anaerobic biodegradation of OFMSW. To isolate the effects of leachate and OFMSW, BMP test II was performed. In these tests, only leachate was added to the bottles as a source of organic substrate (in addition to inoculum, which was the same), so the biogas produced would be reflective of the contribution of leachate and inoculum in biogas production. The results of the test are shown in Figure 2 and are the average values of two replicates. Biogas production was proportional to the amount of new leachate present as the BMP tests with 100% old leachate produced very low amounts of biogas owing to minimal amounts of biodegradable substrate (BOD5 of only 85 mg L−1 for a total COD of 11,040 mg L−1). Young leachate, on the contrary, had a higher total COD along with a higher amount of biodegradable substrate (BOD5 of 22,500 mg L−1), so it was not surprising to see that tests with 100% young leachate (3N0O) produced the largest amount of biogas. The rest of the test bottles also showed proportionality between biogas production and fraction of young leachate, since the blend with a

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

5

Nair et al.

Figure 2.  Average cumulative biogas production from pure leachate blends – batch test II.

Figure 3.  Average cumulative net biogas production from OFMSW. OFMSW: organic fraction of municipal solid waste.

higher proportion of young leachate produced more biogas. The bottles with the blends 0N3O, 1N2O, 2N1O and 3N0O produced 120 mL, 321 mL, 767 mL and 1487 mL of biogas, respectively. However, it was observed that biogas production for the tests with higher proportions of young leachate, i.e. 3N0O and 2N1O, was a bit erratic, with visible periods of very small biogas production. These periods could be owing to the

exhaustion of an easy-to-degrade substrate and the necessary period of adjustment to a newer substrate (Gonzalez-Gil and Kleerebezem, 2002). These adjustment periods can be longer because of the high concentrations of VFAs and ammonia, and lower pH (Gallert and Winter, 1997). The biogas produced initially contained as little as 20% methane for the first four days, following which the methane

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

6

Waste Management & Research

content increased to 60% and stayed consistent for 14 days at 61.4%. The final plot of net biogas production, shown in Figure 3, was obtained by subtracting the corrected contribution of inoculum and leachate in biogas production (based on a common denominator, i.e. the same volume of added leachate) from the corresponding values in Figure 1. This gave an account of the biogas production from OFMSW alone. These results clearly showed that blending mature and new leachate had a positive effect on biogas production. The reactors with higher proportions of mature leachate, i.e. 0N3O and 1N2O, had higher total biogas productions compared with 2N1O and 3N0O, which had lower proportions of mature leachate. Old leachate had a very low biodegradable organic matter content, so the increase in biogas yield, even for the test with 100% old leachate, was probably owing not to increased organic load but most likely to a greater amount of methanogens, buffering capacity and nutrients. The tests with 100% young leachate (3N0O) could be thought of as representing a conventional bioreactor landfill once the newly generated leachate was recirculated (with no leachate blending). The additional biogas generation observed in Figure 1 for this mix was caused presumably by the high COD load of the leachate (56,800 mg L−1). During start-up, the measured COD concentration was highest in the bottles containing 100% young leachate of all the bottles. TAN also had the highest amount at the start of the test for 100% young leachate bottles, along with propionic acid and butyric acid. As stated earlier, ammonia could act as an inhibitor of methanogenesis at high concentrations and propionic acid is known to be more difficult to degrade into methane than acetate. These facts could explain the lowest net biogas production for tests with 100% new leachate and OFMSW, even though organic substrate was present at a higher concentration. Further evidence of inhibitory effects was the accumulation of both propionic and acetic acids when comparing the initial and final concentrations of these VFAs. The final concentration of acetic acid was 1360 mg L−1, which was very high, and propionic acid reached a final concentration of 650 mg L−1. In a balanced anaerobic media, almost all the acetic acid is transformed into methane, and accumulation of propionic acid to such high levels is not reported. On the other extreme, as shown in Figure 3, the bottles with 100% old leachate also generated more biogas than the bottles with only OFMSW, even though the biodegradable organic material added by the mature leachate was almost negligible. Net biogas production was 47% higher than the test with OFMSW only, showing the advantage of recirculating a mature leachate even if it contained almost no biodegradable organic substrate. The biogas production curve showed a steep slope during the initial week, beyond which there was a lag phase prevailing for a few days. This indicated a phase shift from acidogenesis to methanogenesis. The methanogenic phase was very consistent, as observed from the smoother curve compared with the control. The initial concentration of COD, ammonia and VFAs were significantly lower than those measured for the test with 100%

young leachate. In fact, COD was lowest for this test compared with all the other tests, as expected, since old leachate has a considerably smaller COD concentration. The COD removed only 47% of the initial COD present for 100% old leachate, compared with 54% for 100% young leachate, which showed that a greater proportion of the initial COD in the old leachate is not biodegradable. However, this fact does not prevent old leachate from having a positive effect given the increase in biogas yield when digested with OFMSW. The tests that used a mixture of old and young leachate gave more satisfactory results in terms of biogas production and faster biodegradation (visible in the steeper biogas production curve). The results suggest that 100% mature leachate mix (0N3O) was the best leachate combination to use since it produced the most net biogas. However, from a practical perspective, the leachate blend 1N2O would also be a suitable option owing to the following reasons. 1. The results showed that the difference in cumulative biogas production between 0N3O and 1N2O was negligible (less than 3%). 2. The leachate blends 1N2O had a higher COD content. Hence, the total organic loading can be more efficiently increased with this leachate blend over the 100% mature (0N3O) leachate in a working bioreactor landfill. As a result there will be higher potential for biogas production. 3. By blending old and new leachate, the new leachate is treated and managed at the same time in terms of organic contents. If only mature leachate were to be used in a large scale operational bioreactor landfill for recycling, the generated leachate would need to be treated before disposal. 4. This study was based on enhancing biogas production via leachate blending, wherein the leachate mix 0N3O contained only mature leachate and was not a blend. Results from BMP tests I and II were further aggregated in order to evaluate the effect that mixing different blends of leachate had on OFMSW degradation and vice-versa. The first batch test I was able to provide information about degradation of OFMSW alone and OFMSW mixed with leachate; while test II was capable of evaluating the potential biogas production and biodegradability of leachate blends as a single substrate. Biogas productions for each mixture (OFMSW + leachate blend) were then compared against the sum of independent biogas productions, which was calculated as the sum of three factors: (1) the biogas produced when OFMSW was degraded as a single substrate; (2) the biogas produced when a given leachate blend is degraded as the single substrate; and (3) the biogas produced when inoculum was degraded as a single substrate. A comparison of the values is given in Figure 4. Results indicate that the presence of mature leachate enhanced the total biogas attainable from biodegradation of OFMSW and leachate. This could be thought of as a synergistic effect, since the total biogas production in tests with a leachate blend

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

7

Nair et al. 1200

Average Cumulaitve Biogas volume (mL)

1000

1113 1012 879

967

926

873

800

724

658

600 400 268

243 200

139

0 3N 0O

2N 1O

1N 2O

0N 3O

mixture biogas producon

-200 -233 -400

sum of independent biogas producons balance

Figure 4.  Average biogas productions for each condition and balance.

including mature leachate was always more than the sum of the parts (the sum of the biogas production when separately degrading OFMSW only, leachate only and inoculum only). The enhancement or synergistic effect was proportional to the amount of mature leachate in the leachate blend, since the smallest improvement was seen in the test 2N1O with one-third mature leachate blend (139 mL, a 19% increase compared with the sum of the independent biogas productions), while the highest was recorded when degrading OFMSW with 100% mature leachate in test 0N3O (268 mL, a 41% increase). In the case of 100% young leachate (test 3N0O), mixing OFMSW with leachate had a detrimental effect in biodegradability since less biogas was obtained by digesting the mixture than if both fractions were degraded separately. The decrease was substantial and 233 mL (−21%) less biogas was produced. This decrease could be mainly attributed to a combination of high VFAs (especially propionic acid) and low pH, which decrease the activity of methanogens. On the other hand, the positive effect of mature leachate presence, observed through a higher gas production in batch bottles with higher fractions of mature leachate, might be owing to, as hypothesised, the presence of the mature leachate having a stabilisation effect on the system that was probably brought about by the higher pH (pH of mature leachate was 8.9) and also the fact that it contained more microbial consortium (especially methanogens) than young leachate. The VFAs concentration was also significantly lower in the mature leachate. The acetic acid concentration for the mature leachate was at 868 mg L−1 compared with 19,514 mg L−1 for the young leachate. Several studies conducted on mature leachate substantiate the advantages of recirculation of leachate at a higher pH (7–9) (Berge et al., 2005; Chugh et al., 1998). With an increased pH alone, studies have shown that there was an earlier phase shift

into a methanogenic phase from acidogenesis. The mature leachate used in this study had an ammonia level of 1410 mg TAN L−1, which was high compared with the mature leachate used in other studies (in the range of 6–500 mg L−1) (Chugh et al., 1998). This value was close to the toxic levels for methanogenesis that was stated to occur at concentrations of over 1500 mg L−1 (Karakashev et al., 2005).

Conclusions The reported series of batch tests were able to provide some insights into the advantages of blending young and mature leachate with OFMSW. Results show that higher biogas production rates were obtained by leachate recirculation and when blending the old and new leachate with OFMSW was implemented. The results are conclusive that biogas generation could be improved by blending the old and new leachate before recirculating into a bioreactor landfill. This is probably mainly owing to the accumulation of VFAs at the start of the test for 100% young leachate. The degree of improvement can be maximised by blending fractions of old and young leachate. The smallest improvement was seen in the test 2N1O with a one-third mature leachate blend (19% increase), while the highest was recorded when degrading OFMSW with 100% mature leachate (41% increase) in test 0N3O. Despite the fact that young leachate has a larger amount of biodegradable substrate, a higher amount of old leachate increased the synergistic effect of mixing leachate and OFMSW, most likely owing to greater amounts of methanogens and buffering capacity of old leachate. These reported tests showed that landfills that recirculate young leachate only are wasting some of the energetic potential present in the waste. An additional benefit of adding mature leachate to the recirculating mix is that the

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

8

Waste Management & Research

methanogenesis will start earlier in landfills recirculated with these blends and waste will degrade to a further extent.

Declaration of conflicting interests The authors declare that there is no conflict of interest.

Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

References Abouelenien F, Fujiwara W, Namba Y, et al. (2010) Improved methane fermentation of chicken manure via ammonia removal by biogas recycle. Bioresource Technology 101: 6368–6373. APHA (2005) Standard Methods for the Examination of Water and Wastewater (21st edn). Washington DC: American Public Health Association. Bashir MJK, Aziz HA, Yusoff MS, et al. (2010) Application of response surface methodology (RSM) for optimization of ammoniacal nitrogen removal from semi-aerobic landfill leachate using ion exchange resin. Desalination 254: 154–161. Berge ND, Reinhart DR, Dietz J, et al. (2006) In situ ammonia removal in bioreactor landfill leachate. Waste Management 26: 334–343. Berge ND, Reinhart DR and Townsend TG (2005) The fate of nitrogen in bioreactor landfills. Critical Reviews in Environmental Science and Technology 35: 365–399. Bilgili MS, Demir A and Ozkaya B (2007) Influence of leachate recirculation on aerobic and anaerobic decomposition of solid wastes. Journal of Hazardous Materials 143: 177–183. CFG (2011) Canada’s food guide. Available at: www.hc-sc.gc.ca/fn-an/ alt_formats/hpfb-dgpsa/pdf/food-guide-aliment/view_eatwell_vue_ bienmang_e.pdf. (accessed 15 October 2013). Chugh S, Clarke W, Pullammanappallil P, et al. (1998) Effect of recirculated leachate volume on MSW degradation. Waste Management & Research 16: 564–573. Francois V, Feuillade G, Matejka G, et al. (2007) Leachate recirculation effects on waste degradation: Study on columns. Waste Management 27: 1259–1272. Gallert C and Winter J (1997) Mesophilic and thermophilic anaerobic digestion of source-sorted organic wastes: effect of ammonia on glucose degradation and methane production. Applied Microbiology and Biotechnology 48: 405–410. Gonzalez-Gil G and Kleerebezem R (2002) Assessment of metabolic properties and kinetic parameters of methanogenic sludge by on-line methane

production rate measurements. Applied Microbiology and Biotechnology 58: 248–254. He P, Qu X, Shao L, et al. (2007) Leachate pre-treatment for enhancing organic matter conversion in landfill bioreactor. Journal of Hazardous Materials 142: 288–296. Karakashev D, Batstone DJ and Angelidaki I (2005) Influence of environmental conditions on methanogenic compositions in anaerobic biogas reactors. Applied and Environmental Microbiology 71: 331–338. Kim J and Pohland FG (2003) Process enhancement in anaerobic bioreactor landfills. Water Science and Technology 48(4): 29–36. Li HS, Zhou SQ, Sun YB, et al. (2009) Advanced treatment of landfill leachate by a new combination process in a full-scale plant. Journal of Hazardous Materials 172(1): 408–415. Liu J, Luo J, Zhou J, et al. (2012) Inhibitory effect of high-strength ammonia nitrogen on bio-treatment of landfill leachate using EGSB reactor under mesophilic and atmospheric conditions. Bioresource Technology 113: 239–243. Manfredi S and Christensen TH (2009) Environmental assessment of solid waste landfilling technologies by means of LCA-modeling. Waste Management 29: 32–43. Morris JWF, Vasuki NC, Baker JA, et al. (2003) Findings from long-term monitoring studies at MSW landfill facilities with leachate recirculation. Waste Management 23: 653–666. Peng Y, Zhang S, Zeng W, et al. (2008) Organic removal by denitritation and methanogenesis and nitrogen removal by nitritation from landfill leachate. Water Research 42: 883–892. Reinhart D (1996) Full-scale experiences with leachate recirculating landfills: case studies. Waste Management & Research 14: 347–365. Renou S, Givaudan JG, Poulain S, et al. (2008) Landfill leachate treatment: Review and opportunity. Journal of Hazardous Materials 150: 468–493. Sartaj M, Ahmadifar M and Jashni AK (2010) Assessment of in-situ aerobic treatment of municipal landfill leachate at laboratory scale. Iranaian Journal of Science & Technology, Transactions B, Engineering 34(B1): 107–116. Shahriari H, Warith M, Hamoda M, et al. (2012) Anaerobic digestion of organic fraction of municipal solid waste combining two pretreatment modalities, high temperature microwave and hydrogen peroxide. Waste Management 32: 41–52. Sun Y, Sun X and Zhao Y (2011) Comparison of semi-aerobic and anaerobic degradation of refuse with recirculation after leachate treatment by aged refuse bioreactor. Waste Management 31: 1202–1209. USEPA (2013) Wastes – Municipal Solid Waste. Available at: http://www. epa.gov/osw/nonhaz/municipal/landfill/bioreactors.htm. (accessed on 15 October 2013). Wang Q, Matsufuji Y, Dong L, et al. (2006) Research on leachate recirculation from different types of landfills. Waste Management 26: 815–824.

Downloaded from wmr.sagepub.com at University of Sussex Library on August 24, 2014

Enhancing biogas production from anaerobic biodegradation of the organic fraction of municipal solid waste through leachate blending and recirculation.

Leachate recirculation has a profound advantage on biodegradation of the organic fraction of municipal solid waste in landfills. Mature leachate from ...
1009KB Sizes 0 Downloads 6 Views