Review on landfill gas formation from leachate biodegradation

Landfill waste management is a very crucial procedure in handling Municipal Solid Waste (MSW) because it may create significant environmental issues if it is not managed properly. Landfill leachate and landfill gas (LFG) is part of the landfill waste management which triggered lot of researchers especially in terms of the environmental implications associated with the movement of the gasses during the waste constituents’ processes. Hence, this paper review is aiming to understand the behaviour of leachate itself as a decomposition agent in producing landfill gas (biogas). Biogas is naturally produced by anaerobic bacteria through anaerobic digestion which is affected by operating parameters and substrate characteristic. The results indicate that temperature, pH, and C/N ratio of leachate are the important factors that could increase the production of biogas with high content of methane. Furthermore, in terms of microbial activity during anaerobic digestion process, hydrogenotrophic and acetoclastic methanogen are the dominant substrate that contribute in producing methane gas as the final product. Firmicutes and Bacteroidetes are the common fermentative bacteria that had been found during fermentation process in hydrolysis and acidogenic phases. While, methanobacterial, methanococcal, methanomicrobial, methanosarcinal, and methanopyral are being classified as orders among 65 types of methanogenic archaea during methanogenesis stage. Overall, the relationships between operating parameters and microbial structure are important aspects that need to be considered in order to optimize the production of methane gas.

Enhancing Phenol Conversion Rates in Saline Anaerobic Membrane Bioreactor Using Acetate and Butyrate as Additional Carbon and Energy Sources

Phenolic industrial wastewater, such as those from coal gasification, are considered a challenge for conventional anaerobic wastewater treatment systems because of its extreme characteristics such as presence of recalcitrant compounds, high toxicity, and salinity. However, anaerobic membrane bioreactors (AnMBRs) are considered of potential interest since they retain all micro-organism that are required for conversion of the complex organics. In this study, the degradation of phenol as main carbon and energy source (CES) in AnMBRs at high salinity (8.0 g Na+⋅L–1) was evaluated, as well as the effect of acetate and an acetate-butyrate mixture as additional CES on the specific phenol conversion rate and microbial community structure. Three different experiments in two lab-scale (6.5 L) AnMBRs (35°C) were conducted. The first reactor (R1) was fed with phenol as the main CES, the second reactor was fed with phenol and either acetate [2 g COD⋅L–1], or a 2:1 acetate-butyrate [2 g COD⋅L–1] mixture as additional CES. Results showed that phenol conversion could not be sustained when phenol was the sole CES. In contrast, when the reactor was fed with acetate or an acetate-butyrate mixture, specific phenol conversion rates of 115 and 210 mgPh⋅gVSS–1 d–1, were found, respectively. The syntrophic phenol degrader Syntrophorhabdus sp. and the acetoclastic methanogen Methanosaeta sp. were the dominant bacteria and archaea, respectively, with corresponding relative abundances of up to 63 and 26%. The findings showed that dosage of additional CES allowed the development of a highly active phenol-degrading biomass, potentially improving the treatment of industrial and chemical wastewaters.

Analysis of microbial community structure and diversity in the thermophilic anaerobic digestion of waste activated sludge

The microbial community structures in the thermophilic anaerobic digestion (TAD) of waste activated sludge (WAS) and WAS were analyzed with molecular biological techniques including real-time polymerase chain reaction (PCR) and cloning. The microbial community of TAD had less diversity than that of WAS, and the sequences obtained in WAS were not present in TAD by the cloning analysis. In the TAD bacterial clone library, 97.5% of total clones were affiliated with the phylum Firmicutes and 73.1% with the genus Coprothermobacter. Real-time PCR and cloning analysis revealed that the number of Methanosarcina thermophila, which is an acetoclastic methanogen, is larger than that of Methanoculleus thermophilus, which is a hydrogenotrophic methanogen, in terms of the numbers of copies of 16S ribosomal DNA (rDNA).

Changes of microbial characteristics of retained sludge during low-temperature operation of an EGSB reactor for low-strength wastewater treatment

In this study, a lab scale EGSB reactor was operated for 400 days to investigate the influence of temperature-decrease on the microbial characteristic of retained sludge. The EGSB reactor was started-up at 15°C seeding with 20°C-grown granular sludge. The influent COD of synthetic wastewater was set at 0.6–0.8 gCOD/L. The process-temperature was stepwise reduced from 15°C to 5°C during 400 days operation. Decrease of temperature of the reactor from 15°C to 10°C caused the decline of COD removal efficiency. However, continuous operation of the EGSB reactor led the efficient treatment of wastewater (70% of COD removal, 50% of methane recovery) at 10°C. We confirmed that the both acetate-fed and hydrogen-fed methanogenic activities of retained sludge clearly increased under 15 to 20°C. Changes of microbial profiles of methanogenic bacteria were analyzed by 16S rDNA-targeted DGGE analysis and cloning. It shows that genus Methanospirillum as hydrogen-utilizing methanogen proliferated due to low temperature operation of the reactor. On the other hand, genus Methanosaeta presented in abundance as acetoclastic-methanogen throughout the experiment.

Use of the ADM1 to investigate the effects of acetoclastic methanogen population dynamics on mesophilic digester stability

The ADM1 was employed to assess the effect of variations in solids hydrolysis and acetoclastic methanogen process characterizations on municipal digester stability relating to excess acetate utilization capacity. First-order single- and dual-pathway hydrolysis rate functions and single and competitive acetoclastic methanogen rate functions were implemented in the ADM1. The acetate capacity number (ACN), defined as the ratio between the maximum acetate utilization rate and the average acetate production rate, was used to index digester instability. Simulations of a single CSTR at steady state indicate a similar ACN can be obtained with a 12-day SRT digester dominated by Methanosarcina sp and a 24-day SRT digester dominated by Methanosaeta sp. An increase in ACN with a decrease in SRT representing Methanosarcina sp. selection was observed for particulate feed loadings from 40 g COD/L to 90 g COD/L. Feeding frequency and dual-pathway hydrolysis were found to have less effect on the ACN than the competitive acetoclastic model structure.

Molecular Characterization of a Dechlorinating Community Resulting from In Situ Biostimulation in a Trichloroethene-Contaminated Deep, Fractured Basalt Aquifer and Comparison to a Derivative Laboratory Culture

ABSTRACT Sodium lactate additions to a trichloroethene (TCE) residual source area in deep, fractured basalt at a U.S. Department of Energy site have resulted in the enrichment of the indigenous microbial community, the complete dechlorination of nearly all aqueous-phase TCE to ethene, and the continued depletion of the residual source since 1999. The bacterial and archaeal consortia in groundwater obtained from the residual source were assessed by using PCR-amplified 16S rRNA genes. A clone library of bacterial amplicons was predominated by those from members of the class Clostridia (57 of 93 clones), of which a phylotype most similar to that of the homoacetogen Acetobacterium sp. strain HAAP-1 was most abundant (32 of 93 clones). The remaining Bacteria consisted of phylotypes affiliated with Sphingobacteria, Bacteroides, Spirochaetes, Mollicutes, and Proteobacteria and candidate divisions OP11 and OP3. The two proteobacterial phylotypes were most similar to those of the known dechlorinators Trichlorobacter thiogenes and Sulfurospirillum multivorans. Although not represented by the bacterial clones generated with broad-specificity bacterial primers, a Dehalococcoides-like phylotype was identified with genus-specific primers. Only four distinct phylotypes were detected in the groundwater archaeal library, including predominantly a clone affiliated with the strictly acetoclastic methanogen Methanosaeta concilii (24 of 43 clones). A mixed culture that completely dechlorinates TCE to ethene was enriched from this groundwater, and both communities were characterized by terminal restriction fragment length polymorphism (T-RFLP). According to T-RFLP, the laboratory enrichment community was less diverse overall than the groundwater community, with 22 unique phylotypes as opposed to 43 and a higher percentage of Clostridia, including the Acetobacterium population. Bioreactor archaeal structure was very similar to that of the groundwater community, suggesting that methane is generated primarily via the acetoclastic pathway, using acetate generated by lactate fermentation and acetogenesis in both systems.

Phylogenetic Characterization of Methanogenic Assemblages in Eutrophic and Oligotrophic Areas of the Florida Everglades

ABSTRACT Agricultural activities have produced well-documented changes in the Florida Everglades, including establishment of a gradient in phosphorus concentrations in Water Conservation Area 2A (WCA-2A) of the northern Everglades. An effect of increased phosphorus concentrations is increased methanogenesis in the eutrophic regions compared to the oligotrophic regions of WCA-2A. The goal of this study was to identify relationships between eutrophication and composition and activity of methanogenic assemblages in WCA-2A soils. Distributions of two genes associated with methanogens were characterized in soils taken from WCA-2A: the archaeal 16S rRNA gene and the methyl coenzyme M reductase gene. The richness of methanogen phylotypes was greater in eutrophic than in oligotrophic sites, and sequences related to previously cultivated and uncultivated methanogens were found. A preferential selection for the order Methanomicrobiales was observed in mcrA clone libraries, suggesting primer bias for this group. A greater diversity within the Methanomicrobiales was observed in mcrA clone libraries than in 16S rRNA gene libraries. 16S rRNA phylogenetic analyses revealed a dominance of clones related to Methanosaeta spp., an acetoclastic methanogen dominant in environments with low acetate concentrations. A significant number of clones were related to Methanomicrobiales, an order characterized by species utilizing hydrogen and formate as methanogenic substrates. No representatives of the orders Methanobacteriales and Methanococcales were found in any 16S rRNA clone library, although some Methanobacteriales were found in mcrA libraries. Hydrogenotrophs are the dominant methanogens in WCA-2A, and acetoclastic methanogen genotypes that proliferate in low acetate concentrations outnumber those that typically dominate in higher acetate concentrations.