Impact of leachate recirculation and recirculation volume on stabilization of municipal solid wastes in simulated anaerobic bioreactors

The effects of leachate recirculation and the recirculation rate on the anaerobic treatment of domestic solid waste was investigated in three simulated landfill anaerobic bioreactors. A single pass reactor was operated without leachate recirculation while the other two reactors were operated with leachate recirculation. The leachate recirculation rate was 9 l/day (13% of the reactor volume) in Reactor₉, while the recirculation rate was 21 l/day (30% of the reactor volume), in Reactor₂₁. pH, chemical oxygen demand (COD), volatile fatty acids (VFA), ammonium–nitrogen (NH₄–N) total and methane gas measurements in leachate samples were regularly monitored. After 220 days of anaerobic incubation, it was observed that the pH, COD, VFA concentrations, methane gas productions and methane percentages in Reactor₉ were better than the single pass reactor and Reactor₂₁. When the leachate recirculation rate was increased to three times a decrease in pH, and an increase in VFA and COD concentrations were observed in Reactor₂₁. The COD values were measured as 47 000, 39 000 and 52 000 mg/l while the VFA concentrations were 15 000, 13 000 and 21 000 mg/l, respectively, in single pass, Reactor₉ and Reactor₂₁ after 220 days of anaerobic incubation. The values of pH were 5.89, 6.44 and 6.16, respectively, after anaerobic incubation. The mean methane percentages of single pass reactor, Reactor₉ and Reactor₂₁ were 30, 50 and 40%, respectively, after 50 days of incubation. Leachate recirculation reduced the waste stabilization time and was effective in enhancing methane gas production and improving leachate. However, leachate recirculation was not effective in removing ammonia from the leachate. The amounts of COD recovered by methane were 62.9, 162.3 and 94.6 g for single pass, Reactor₉ and Reactor₂₁, respectively, at the end of 220 days of anaerobic incubation.     

Comparison of aerobic and anaerobic degradation of municipal solid waste in bioreactor landfills

Two landfill bioreactors were operated under aerobic and anaerobic conditions in a thermo-insulated room at a constant temperature of 32 °C. Reactors were filled with 19.5 kg of shredded synthetic solid waste prepared according to the average municipal solid waste compositions determined in Istanbul and operated under wet-tomb management strategy by using leachate recirculation. Aerobic conditions in the reactor were developed by using an air compressor. The results of experiments indicated that aerobic reactor had higher organic, nitrogen, phosphorus and alkali metal removal efficiencies than the anaerobic one. Furthermore, stabilization time considerably decreased when using aerobic processes with leachate recirculation compared to the anaerobic system with the same recirculation scheme.     

Behavior of dimethyl phthalate (DMP) in simulated landfill bioreactors with different operation modes

The behavior of dimethyl phthalate (DMP) from municipal solid waste (MSW) in the leachate and refuse of two simulated landfill bioreactors was compared. In one reactor, the leachate was circulated between a landfill and a methanogenic reactor, while the other reactor was operated using direct recirculation of the leachate. The results revealed that the original concentration of DMP in the refuse was approximately 3.3 μg g⁻¹, and the concentration decreased greatly during decomposition of the waste in both reactors. The major loss of DMP from the landfill occurred in an active methanogenic environment in the later period, while the environment was acidic due to a high concentration of chemical oxygen demand (COD), volatile fatty acids (VFA), and contained a large volume of biologically degradable material (BDM) during the early stage. In addition, a high correlation was found between the residual DMP concentrations and the BDM of the refuse in both systems. Circulating the leachate between the landfill and a methanogenic reactor resulted in an increase in the biodegradability of MSW and the degree of waste stabilization. Furthermore, the removal of DMP was enhanced 14% in the landfill that was operated in conjunction with the methanogenic reactor when compared to the landfill in which there was direct leachate recirculation.     

生物反应器填埋场系统渗滤液的脱氮性能

利用填埋场垂直分布的好氧-缺氧-厌氧的独特生态环境,并采用填埋垃圾上层间歇曝气充氧的方式,研究了生物反应器填埋场系统渗滤液的脱N性能.结果表明,填埋垃圾上层间歇曝气充氧,促进了填埋垃圾层硝化细菌和反硝化细菌的生长,且可使反硝化细菌的数量比普通的填埋垃圾层高4～13个数量级,硝化细菌的最大数量可达到10⁹个·g^-1;营建了填埋场内硝化、反硝化等脱N反应的生物环境,有利于回流渗滤液含N化合物的去除.试验结束时,其渗滤液NH₄⁺-N和TN浓度分别为186和289 mg·L^-1,仅为对照的18%和26％.此外,填埋垃圾上层间歇曝气充氧也有利于填埋垃圾的降解,提高垃圾的稳定化效果.     

Source reduction of the landfill leachate strength in a functional layer embedded landfill (FLEL)

In order to reduce the leachate strength from landfill at source, a novel landfill, functional layer embedded landfill, was developed through the introduction of the functional layers, and a comparative study was conducted between the functional layer embedded landfill (FLEL, R1) and the conventional landfill (CL, R2). It was found that the pollutant in leachate effluent from R1 was 20-50%, 14-43% and 33-75% of that from R2, in terms of COD, TN and NH₃-N. The cumulative movement of waste settlement was about 16.4 and 13.1 cm in R1 and R2 under the test period of 1 years, resulting in 13.7% and 10.9% of the original landfill height. Therefore, FLEL could save the land area and the cost of the leachate treatment process due to the reduction of leachate strength, and more waste could be disposed in landfill through the acceleration of the MSW degradation process, comparing to the CL.     

Effluent recirculation to improve perchlorate reduction in a fixed biofilm reactor

The effect of effluent recirculation on perchlorate reduction in a nominally plug-flow fixed biofilm reactor was studied in two cases: influent concentrations of 10 and 400 microg/L at low hydraulic loading rates (1.9 and 37.5 m(3)/m(2)/day without and with recirculation, respectively) and after a step increase in perchlorate concentration to 1,000 microg/L at the higher hydraulic loading rate (5 and 100 m(3)/m(2)/day without and with recirculation, respectively). Complete perchlorate reduction was sustained for influent concentrations of 400 and 10 microg/L in both flow regimes at the lower hydraulic loading rates. Reactor tracer profiles showed that biofilm diffusion had a more significant effect on mass transfer in the plug flow reactor compared with recirculation. The recirculation bioreactor acclimated more rapidly to increased hydraulic and perchlorate mass loading rates with significantly lower effluent perchlorate compared to the plug flow reactor: 16 microg/L versus 46 microg/L, respectively, although complete perchlorate removal was not achieved in either flow regime after 21 days acclimation to the higher loading. Total biofilm mass was more uniformly distributed in the recirculation reactor which may have contributed to better performance under increased perchlorate loading.     

Co-digestion of intermediate landfill leachate and sewage sludge as a method of leachate utilization

This study examines the co-digestion of intermediate landfill leachate and sewage sludge from a municipal wastewater treatment plant. Application of leachate as a co-fermentation component increased the concentrations of soluble organic compounds (expressed as total organic carbon), ammonium nitrogen, and alkalinity in the digester influents.The biogas yield obtained from the co-fermentation of a 20:1 sewage sludge: intermediate leachate mixture was 1.30 m³ per kg of removed volatile solids (VS), while that from a 10:1 mixture was 1.24 m³ per kg of removed VS. These values exceeded the biogas yield for the sludge alone by 13% and 8%, respectively. The leachate addition influenced the proportion of methane to a minor extent. Increased methane yields of 16.9% and 6.2% per kg of removed VS were found for the two sewage sluge:intermediate leachate mixtures, respectively.     

Acidophilic degradation of methanol by a methanogenic enrichment culture

Abstract An acidophilic methanogenic enrichment culture was obtained in a continuous up-flow anaerobic sludge blanket reactor operated at pH 4.2 with methanol as the sole carbon source. The specific methylotrophic methanogenic activity of the enriched reactor sludge at pH 5 was 3.57 g COD g⁻¹ volatile suspended solids day⁻¹ and the apparent doubling time of the biomass was 15.8 h. Acidic conditions were obligatory, since the enrichment culture was not able to produce methane or to grow at pH 7. Based on morphological characteristics, the dominant methanogenic species in the enrichment culture was a Methanosarcina .     

Start-up procedures and analysis of heavy metals inhibition on methanogenic activity in EGSB reactor

The effectiveness of operating an industrial UASB reactor, treating wastewater from the beer industry, with flows containing heavy metals was evaluated. A pilot-scale UASB reactor, already used to simulate the industrial reactor, was unsuccessfully employed. An easy start-up was obtained arranging it as an EGSB reactor. Considerations about this modification are reported. The effects of Cu(II), Ni(II) and Cr(III) ions on the anaerobic activity were analyzed by measurements of methane production rate and COD removal. The employed biomass was the sludge of the industrial UASB reactor, while a solution of ethanol and sodium acetate with COD of 3000 mg/L and a heavy metal concentration of 50 mg/L were continuously fed. Experimental results proved higher biomass sensitivity for copper and much slighter for nickel and chromium. Moreover, copper inhibition has been demonstrated to be less significant if a metal-free feed was provided to the system before copper addition.     

Anaerobic digestion of food waste in a hybrid anaerobic solid–liquid system with leachate recirculation in an acidogenic reactor

Recirculation of the leachate in the acidogenic reactor was proposed to enhance anaerobic digestion of food waste in the hybrid anaerobic solid–liquid (HASL) system. Recirculation of the leachate in the acidogenic reactor provided better conditions for extraction of organic matter from the treated food waste and buffering capacity to prevent excessive acidification in the acidogenic reactor. It ensured faster supply of nutrients in the methanogenic reactor in experiment. The highest dissolved COD and VFA concentrations in the leachate from the acidogenic reactor were reached for shorter time and were 16,670 mg/l and 9450 mg/l in control and 18,614 mg/l and 11,094 mg/l in experiment, respectively. Recycling of the leachate in the acidogenic reactor intensified anaerobic digestion of food waste and diminished time needed to produce the same quantity of methane by 40% in comparison with anaerobic digestion of food waste without recirculation.     

Diversity and structure of the archaeal community in the leachate of a full-scale recirculating landfill as examined by direct 16S rRNA gene sequence retrieval

The diversity and structure of the archaeal community in the effluent leachate from a full-scale recirculating landfill was characterized by direct 16S rRNA gene (16S rDNA) retrieval. Total-community DNA was extracted from the microbial assemblages in the landfill leachate, and archaeal 16S rDNAs were amplified with a universally conserved primer and an Archaea-specific primer. The amplification product was then used to construct a 16S rDNA clone library, and 70 randomly selected archaeal clones in the library were grouped by restriction fragment length polymorphism (RFLP) analysis. Sequencing and phylogenetic analysis of representatives from each unique RFLP type showed that the archaeal library was dominated by methanogen-like rDNAs. Represented in the kingdom of Euryarchaeota were phylotypes highly similar to the methanogenic genera Methanoculleus, Methanosarcina, Methanocorpusculum, Methanospirillum and Methanogenium, where the clone distribution was 48, 11, 3, 1 and 1, respectively. No sequences related to known Methanosaeta spp. were retrieved. Four rDNA clones were not affiliated with the known methanogenic Archaea, but instead, they were clustered with the uncultured archaeal sequences recently recovered from anaerobic habitats. Two chimeric sequences were identified among the clones analyzed.     

Photoelectrochemical treatment of landfill leachate in a continuous flow reactor

Leachate from a municipal landfill site, which has been treated by biological process, was treated by photoelectrochemical oxidation in a pilot scale flow reactor, using DSA anode and UV light irradiation. At a current density of 67.1 mA/cm² and 2.5 h reaction time, the removal rates achieved were for 74.1% COD, 41.6% for TOC, and 94.5% for ammonium in the electrolysis process with UV light irradiation. In comparison, the removal rates of COD, TOC, and ammonium were decreased in the individual electrolysis process, respectively. The increase induced by the UV light irradiation was analyzed. The removal rates increased with the increase of current densities in the photoelectrochemical process. Combined with UV–vis spectra and gas chromatography–mass spectroscopy analysis, it is believed that the organic contaminants were efficiently mineralized into small molecular acids. At the meantime, the concentrations of metal ions in the landfill leachate were largely reduced.     

Powdered activated carbon added biological treatment of pre-treated landfill leachate in a fed-batch reactor

Biological treatment of landfill leachate usually results in low treatment efficiencies because of high chemical oxygen demand (COD), high ammonium-N content and also presence of toxic compounds such as heavy metals. A landfill leachate with high COD content was pre-treated by coagulation-flocculation followed by air stripping of ammonia at pH = 12. Pre-treated leachate was biologically treated in an aeration tank operated in fed-batch mode with and without addition of powdered activated carbon (PAC). PAC at 2 g l^–1 improved COD and ammonium-N removals resulting in nearly 86% COD and 26% NH₄-N removal.     

The role of phase separation and feed cycle length in leach beds coupled to methanogenic reactors for digestion of a solid substrate (Part 1): Optimisation of reactors' performance

A two-phase system composed by a leach bed and a methanogenic reactor was modified for the first time to improve volumetric substrate degradation and methane yields from a complex substrate (maize; Zeamays). The system, which was operated for consecutive feed cycles of different durations for 120 days, was highly flexible and its performance improved by altering operational conditions. Daily substrate degradation was higher the shorter the feed cycle, reaching 8.5 g TS_destroyed d⁻¹ (7-day feed cycle) but the overall substrate degradation was higher by up to 55% when longer feed cycles (14 and 28 days) were applied. The same occurred with volumetric methane yields, reaching 0.839 m³ (m³)⁻¹ d⁻¹. The system performed better than others on specific methane yields, reaching 0.434 m³ kg⁻¹ TS_added, in the 14-day and 28-day systems. The UASB and AF designs performed similarly as second stage reactors on methane yields, SCOD and VFA removal efficiencies.     

Biological sulphide oxidation in a fed-batch reactor

This study shows that, in a sulphide-oxidizing bioreactor with a mixed culture of Thiobacilli, the formation of sulphur and sulphate as end-products from the oxidation of sulphide can be controiledinstantaneously and reversibiy by the amount of oxygen supplied. It was found that at sulphide loading rates of up to 2.33 mmol7/L . h, both products can be formed already at oxygen concentrations below 0.1 mg/L. Because the microorganisms tend to form sulphate rather than forming sulphur, the oxygen concentration is not appropriate to optimize the sulphur production. Within less than 2 h, the system can be switched reversibly from sulphur to sulphate formation by adjusting the oxygen flow. This is below the minimum doubling time (2.85 h) of, e.g., Thiobacillus neapolitanus and Thiobacillus 0,(18) which indicates that one metabolic type of organism can probably perform both reactions. Under highly oxygen-limited circumstances, that is, at an oxygen/sulphide consumption ratio below 0.7 mol . h(-1) mol . h(-1) thiosulphate is abundantly formed. Because the chemical sulphide oxidation results mainly in the formation of thiosulphate, it is concluded that, under these circumstances, the biological oxidation capacity of the system is lower than the chemical oxidation capacity. The oxidation rate of the chemical sulphide oxidation can be described by a first-order process (k =-0.87 h(-1)).(c) 1995 John Wiley & Sons, Inc.     

Bioremediation of leachate from a green waste composting facility using waste-derived filter media

The evaluation of two waste-derived materials used to treat compost leachate by biofiltration is described in this paper. Nine biofilters were constructed using 240 l, high density polyethylene containers. Three containers were filled without compaction with 200l of each of three types of filter media. Waste-derived filter media (compost and oversize) were compared to a mineral control (granite chips). The filters were fed with compost leachate from a typical green waste composting facility at hydraulic loading rates ranging from 0.05 m3/m3/day to 0.5 m3/m3/day over a period of twelve months. The oversize medium emerged as the most effective demonstrating characteristics of consistency of effluent quality and resilience to stress. The oversize medium produced an effluent of <10mg/l ammoniacal nitrogen on >95% of sampling occasions. The organic component of compost leachate was dominated by compounds that proved to be recalcitrant to biodegradation. The solids content of the treated effluent remained too high to be acceptable for direct discharge to a watercourse without further treatment and if discharge to a watercourse is to be considered, a polishing stage (e.g., reed bed) able to remove solids and dampen occasional peaks of ammoniacal nitrogen should be employed.     

Anaerobic degradation of 3-aminobenzoate by a newly isolated sulfate reducer and a methanogenic enrichment culture

A new rod-shaped, gram-negative, non-sporing sulfate reducer, strain mAB1, was enriched and isolated from marine sediment samples with 3-aminobenzoate as sole electron and carbon source. Strain mAB1 degraded 3-aminobenzoate completely to CO₂ and NH₃ with stoichiometric reduction of sulfate to sulfide. Cells contained carbon monoxide dehydrogenase, cytochromes, and sulfite reductase P582. Strain mAB1 degraded also benzoate, 4-aminobenzoate, hydroxybenzoates, and some aliphatic compounds. Besides sulfates, also sulfite was reduced with 3-aminobenzoate as electron donor, but not thiosulfate, sulfur, nitrate, or fumarate. The strain grew in sulfide-reduced mineral medium supplemented with 7 vitamins. Strain mAB1 was tentatively affiliated with the genus Desulfobacterium. Experiments with dense cell supsensions showed benzoate accumulation during 3-aminobenzoate degradation under conditions of sulfate limitation or cyanide inhibition. 3-Aminobenzoate was activated to 3-aminobenzoyl-CoA by cell extracts in the presence of ATP, coenzyme A, and Mg²⁺. Acitivity of 3-aminobenzoyl-CoA synthetase was 16 nmol per min and mg protein, with a K_M for 3-aminobenzoate lower than 50 M. Cell extract of 3-aminobenzoate-grown cells activated also 3-hydroxybenzoate (31.7 nmol per min and mg protein) and benzoate (2.3 nmol per min and mg protein), but not 2-aminobenzoate or 4-aminobenzoate. In the presence of NADH of NADPH, 3-aminobenzoyl-CoA was further metabolized to a not yet identified reduced product.Freshwater enrichments with 3-aminobenzoate in the absence of an extenal electron acceptor led to a stable methanogenic enrichment culture consisting of three types of bacteria. 3-Aminobenzoate was degraded completely to CO₂ and stoichiometric amounts of CH₄, with intermediary acetate accumulation.