High Methane Production Potential Research Articles

Syntrophic Jiont of Sulfate-Reducing Bacteria and Hydrogen-Producing Acetogen Stimulated Methane Production from Waste Activated Sludge Digestion

Anaerobic digestion of waste-activated sludge (WAS) towards biogas recovery is constrained by the limited hydrolysis and inhibited acetogenesis steps that hinder subsequent energy recovery. This study employed Fe(VI)/S(IV) oxidation to enhance the WAS solubilization and coupled it with the syntrophic interaction of hydrogen-producing acetogen (HPA) and sulfate-reducing bacteria (SRB) to stimulate the successive procedure towards methane production. Results showed that the dosage ratio of HPA-SRB to WAS (H-S-W) with 1:1:50 outperformed with the highest methane production potential (11.63 ± 1.87 mL CH4/(g VSS·d). Meanwhile, the efficient and sequential process from acetogenesis to methanogenesis stimulated by HPA-SRB was evidenced by a significant decrease of 30.2% in the acetate concentration. The microbial community structure further manifested the crucial role of HPA-SRB with increased abundance of Desulfobulbus (2.07%), Syntrophomonas (1.24%) and Smithella (1.63%), which stimulated acetophilic methanogen boost with Methanobacterium dominating with 77.51% in H-S-W100. Furthermore, the positive syntrophic relationships among HPA-SRB and acetophilic methanogens towards methane production were confirmed via molecular ecological network and canonical correspondence analysis. This study highlighted the syntrophic cooperation of the mixed consortia of HPA and SRB on methane production based on Fe(VI)/S(IV) pretreatment and provided the theoretical and technical basis for the potential implementation of novel methanogenesis technology for WAS treatment.

Heat-enhanced sulfite pretreatment improves the release of soluble substances and the stimulation of methanogenic pathways for anaerobic digestion of waste activated sludge

Waste activated sludge pretreatment is effective in improving sludge hydrolysis rate and methane production. Our previous study revealed that sulfite could be a viable method for sludge pretreatment. To further improve methane production, this study employed an integrated strategy by combining sulfite and heat pretreatment. WAS from a local full-scale plant was pretreated with heat-enhanced sulfite pretreatment (HESP) at 25, 35, 55 °C. Compared with the control (no sulfite, 25 °C), soluble substances (e.g., chemical oxygen demand, protein, polysaccharides, nitrogen and phosphorus) could be significantly enhanced by the absence of sulfite and the increasing temperature. A variation of − 8.32–19.90% in cumulative methane production was observed. Moreover, methane production could be significantly enhanced by 14.15% at sulfite of 300 mg S/L and temperature of 35 °C, while kinetic analysis showed that the highest methane production potential (1.43 times of the control) was obtained at this level. Besides, the microbial structure and pathways reveal that HESP promotes the enrichment of methanogenic bacteria and facilitates methanogenic metabolism. The findings of this study suggest that the HESP could be promising in enhancing methane production, particularly considering the reuse of sulfite-laden industrial wastes and the heat as the by-products of the anaerobic digestion plant with biogas power generation, but certain experimental conditions should be verified case by case.

Process Performance and Functional Microbial Community in the Anaerobic Digestion of Chicken Manure: A Review

Anaerobic digestion is one of the most widely used treatment methods for animal manure. Chicken manure has high methane production potential and is thus a suitable substrate for biogas plants. However, high nitrogen content inhibits the metabolism of anaerobic microorganisms and thus hinders methane production from chicken manure. Enhancing the performance of anaerobic digestion for chicken manure is indeed a long-standing challenge. This review presents new insights into maintaining methanogens’ activities, the decomposition of acetate, and the dynamics of methanogenic pathways under high ammonia stress. This review also analyzed the possible strategies for alleviating ammonia inhibition effects, including supplementing trace elements, co-digestion with nitrogen-less materials, in-situ ammonia removal, and long adaptation of anaerobic consortia to ammonia stress. The insights obtained in this paper may provide helpful information for a better understanding of anaerobic digestion technology for chicken manure and other nitrogen-rich waste and wastewater.

The Improvement of Rice Straw Anaerobic Co-Digestion with Swine Wastewater by Solar/Fe(II)/PS Pretreatment

Rice straw (RS) is among the agricultural waste products with the highest methane production potential in the world, but the refractory complex structure and high carbon-to-nitrogen ratio of RS cause low methane conversion efficiency and limit its widespread application in anaerobic digestion. In this study, Solar/Fe (II)/persulfate (PS) pretreatment of RS was investigated to improve microbial accessibility, and anaerobic co-digestion combined pretreated RS and swine wastewater (SW) were evaluated to improve the efficiency of anaerobic digestion. The results showed that the Solar/Fe (II)/PS pretreatment could disrupt the structure of RS and promote the reduction of sugar content, increasing microbial accessibility to RS. When all the components of the pretreated RS (including the use of the solution remaining from the pretreatment) were anaerobically co-digested with SW, the cumulative biogas production and cumulative methane production reached 252.10 mL/g·VS and 163.71 mL/g·VS, 19.18% and 36.97% higher than the anaerobic co-digestion of untreated RS and SW, respectively. The anaerobic co-digestion of the Solar/Fe (II)/PS-pretreated RS with SW is a promising approach to achieving the utilization of RS components and maximizing methane yields, providing a cost-effective and pollution-free method for the production of high-quality bioenergy from agricultural waste.

Anaerobic Fermentation of Combined Chicken Manure and Straw on a Sequencing Batch Reactor: Analysis of Stability and Numerical Modeling

Anaerobic fermentation experiments were performed using combinations of chicken manure and straw at a temperature of 37±0.5 °C for 70 d. In this investigation, system stability and methane production were analyzed using the Logistic model. According to our results, the highest cumulative methane yield was 292.87 mL/g VS at a straw ratio of 3%. This value was 17.43% higher than the one obtained using pure chicken manure. In addition, a positive correlation between ammonia concentration and content of chicken manure was observed. At the end of the reaction, pH values in the four groups were between 7.0 and 8.0. However, pH in the M2 group was significantly higher than that observed in the rest of the groups. Data also indicated that hydrolase activities were positively correlated with SCOD concentrations. In this context, cellulase activity reached the highest value on day 40. Proteinase activity presented two peaks on days 20 and 40. In the case of lipase, activities and amylase initially increased and later decreased, but the change is small. According to the results of the Logistic model, the highest methane production potential was of 404.41 mL/g VS, at a straw proportion of 3%. In addition, the highest daily methane yield was 6.13 mL/g VS.

Continuous Anaerobic Treatment of the Aqueous Phase of Hydrothermal Liquefaction from Spirulina Using a Horizontal-Flow Anaerobic Immobilized Biomass (HAIB) Reactor

Anaerobic digestion is a possibility for post-hydrothermal liquefaction wastewater (PHWW) treatment because this wastewater is rich in nutrients and organic compounds. However, the PHWW presents many toxic compounds. A strategy for the anaerobic treatment of toxic compounds is using biomass adhered to inert supports forming biofilms, which can offer more resistance to the microorganism and protection from such compounds. The continuous treatment of PHWW is the essential key to obtaining a sustainable hydrothermal liquefaction process. In this work, the use of immobilized biomass was evaluated for the anaerobic degradation of PHWW from Spirulina in batch assays and continuous treatment. Higher methane production potential and volatile fatty acid mass balance showed the advantages of using biomass immobilized in polyurethane foam. Continuous treatment in a horizontal-flow anaerobic immobilized biomass (HAIB) reactor reached chemical organic demand (COD) removal efficiencies of 67% and 58% for volumetric organic load rates of 0.8 and 1.6 g COD.L−1.d−1, respectively. After 200 days of continuous treatment, Anaerobaculum and Coprothermobacter, fermentative proteolytic genera of bacteria with potential for hydrogen production, were favored.

Determination of Commercially Available Biogas Production Capacity and Effects on Methane Capture in Tekirdağ Province

This research was carried out in farms which have 100 and more cows with commercial biogas production capacity, in 2019 in Tekirdağ. This is because it is stated that if the livestock enterprises have at least 100 animals, biogas production can be realized economically. The distribution and number of farms with this feature in districts were provided from Tekirdağ Food, Agriculture and Livestock Provincial Directorate. Biogas is generally used by converting it to heat and electrical energy. While it is used mostly for heating purposes in small farms, electricity and heat energy are provided in CHP units in large farms. Total methane production potential and energy value were calculated as 22466 Nm3day-1 and 81756.4 MWhyear-1, respectively. The highest methane production potential and energy value is in Muratlı district and the least is in Çerkezköy district. It was determined that 42512.48 MWhyear-1 useful heat energy and in CHP unit 28614.17 MWhyear-1 electricity energy and 19784.65 MWhyear-1additional heat energy could be obtained from methane produced by anaerobic fermentation. It is determined that 19067.56 tonsCO2eyear-1 of methane will be released if the manure is stored outdoors. It was determined that methane emission could be reduced by 1087.13 tons CO2eyear-1 if the nitrogen was used in fermentation residues instead of the chemical fertilizer. Total methane retention in the use of methane for heat purposes will be 31590.55 tons CO2eyear-1. Methane emissions will be reduced by 12522.99 tons CO2eyear-1 when used for heat purposes, than the conditions in which the manure is stored outdoors. When methane is used in the CHP unit to provide electricity and heat energy, total methane retention is calculated as 38467.6 tons CO2eyear-1, and the decrease in methane emission is calculated as 19400 tons CO2eyear-1. In animal husbandry enterprises that are located in Tekirdağ and are commercially producing, evaluation of manure without long-term storage by means of anaerobic digestion is important in terms of meeting of the energy requirement and reducing methane emission and the government should encourage enterprises in this regard.

Bio-Energy Recovery from Canola Oil and Wastewater as Co-Substrates

The attention to renewable energy increasing as a result of global energy security problems, climate change, and environmental pollution, therefore we found that the rates of renewable energy applications are increasing progressively over the years. In general canola oil can be utilized as an energy source through transesterification which increases its value. This research is aimed to appreciate the feasibility of using canola oil with the wastewater through biological technology. Canola oil should induce high methane production potential but this does not happen without certain drawbacks. For this purpose, canola oil was co-anaerobic digested with wastewater under different loading rates, a continuous stirred tank reactor (CSTR) was used for anaerobic digestion, and the experiment was conducted for 60 days at 37˚C. Hence, evaluate digestion conditions, stability, and affect the overall operational efficiency depending on canola oil characteristics.The results showed that it was noticed that the biogas production varied from 620.12 –1569.20 l/kgots.day depending on OLR 1-3 goTS l -1 d-1.The highest biogas production was 47 l/day with methane content 69.19% when the loading rate was 3 goTS l -1 d-1.Co-digested canola oil with wastewater produce a methane yield that may reach up to 47 l/day with methane content 69.19%, the highest one produced by 3 g oTS l -1 d-1 While increasing loading rate lead to increase VFA, decrease pH level and the production.The ratio of output /input energy reached to1.9 if canola oil used as biogas substrate but be 1.3 when canola oil used as biodiesel source.

Microbial Community Analysis of Digested Liquids Exhibiting Different Methane Production Potential in Methane Fermentation of Swine Feces.

Batch methane fermentation was conducted using seed sludge collected from six methane fermentation facilities. Swine feces were centrifuged and autoclaved, followed by its use as a substrate for methanogenesis. This "swine feces supernatant medium" facilitates the cultivation of the microbes of the seed sludge, sampling of the digested liquid using a syringe, and subculturing of the digested liquid in a subsequent medium using a syringe. Through 15 subcultures, digested liquids with high and low methane production potential were obtained, which were named "H-DS" and "L-DS," respectively. On the day 10 of cultivation, chemical oxygen demand (COD) of H-DS significantly decreased by 31% and that of L-DS did not differ significantly compared with that on the day 0 of cultivation. Acetic acid concentration of H-DS (1009mg/L) was significantly lower than that of L-DS (2686mg/L). These chemical characteristics indicate that organics decomposition in L-DS was not successful and suggest that H-DS has high relative abundance of bacteria decomposing organic matter and methanogen utilizing acetic acid compared with those in L-DS. Microbial community analysis revealed that Shannon index of H-DS was significantly higher than that of L-DS, and the relative abundance of acetogenic bacteria (e.g., Syntrophomonas) and acetic acid-utilizing methanogen (Methanosarcina) in H-DS was significantly higher than that in L-DS. Thus, the high methane production potential of H-DS might be attributable to the smooth flow from acetogenesis to methanogenesis step in the methane fermentation, compared with the case of L-DS.

Anaerobic treatment of LCFA-containing synthetic dairy wastewater at 20 °C: Process performance and microbial community dynamics.

Facilitating anaerobic degradation of long-chain fatty acids (LCFA) is key for tapping the high methane production potential of the fats, oil and grease (FOG) content of dairy wastewaters. In this study, the feasibility of using high-rate granular sludge reactors for the treatment of mixed LCFA-containing synthetic dairy wastewater (SDW) was assessed at 20 °C. The effects of the LCFA concentration (33-45% of COD) and organic loading rates (2-3 gCOD/L·d) were determined using three parallel expanded granular sludge bed reactors. For the first time, long term anaerobic treatment of LCFA-containing feed at 20 °C was shown to be feasible and was linked to the microbial community dynamics in high-rate reactors. During a two-month operation, a soluble COD removal of 84-91% and COD to methane conversion of 44-51% was obtained. However, granular sludge flotation and washout occurred after two months in all reactors without volatile fatty acids (VFA) accumulation, emphasizing the need for sludge retention for long-term granular sludge reactor operation with LCFA-containing feed at low ambient temperatures. The temporal shifts in microbial community structure were studied in the high-rate treatment of SDW, and the process disturbances (elevated LCFA loading, LCFA accumulation, and batch operation) were found to decrease the microbial community diversity. The relative abundance of Methanosaeta increased with higher LCFA accumulation in the settled and flotation layer granules in the three reactors, therefore, acetoclastic methanogenesis was found to be crucial for the high-rate treatment of SDW at 20 °C. This study provides an initial understanding of the continuous anaerobic treatment of LCFA-containing industrial wastewaters at low ambient temperatures.

Biogas generation from by-products of edible oil processing: a review of opportunities, challenges and strategies

Edible oil processing by-products can be used to produce a renewable fuel called biogas through anaerobic digestion technology. In this process, the physicochemical characteristics of the substrates dictate the process conditions, stability and microbial profile. All these, in turn, affect the overall digester design and operational efficiency. Most edible oil processing by-products tend to exhibit comparatively similar physicochemical properties, allowing for echo studies to be conducted on them. Naturally, residual fats and oils in edible oil by-products should induce high methane production potential. However, this does not occur without certain drawbacks. In this work, a review is conducted on biogas systems that use edible oil processing by-products as substrates for anaerobic digestion. Anaerobic digestion opportunities and challenges associated with these substrates are identified by analysis of factors that affect anaerobic digestion. The factors are scrutinised under different sub-headings, viz., substrate physicochemical composition, process conditions and parameters. Knowledge gaps are identified. Additionally, strategies for resolving some of the highlighted challenges while leveraging opportunities identified are discussed.

Sludge blanket anaerobic baffled reactor for source-separated blackwater treatment.

The performance of a sludge blanket anaerobic baffled reactor was tested as an integrated treatment system for source-separated blackwater. The system consists of a stirred equalization tank, a buffer inlet tank, and two identical reactors, each with a working volume of 16.4 L, operated in parallel. Both reactors run at 3-days hydraulic retention time with different intermittent pulse feeding. Pulse lengths of 12 and 24 seconds per feed were set with respective rates of 114 L h-1 and 52 L h-1 for the short-pulse fed reactor (RI) and the long-pulse fed reactor (RII). Stable performance of the reactors was attained after 120 and 90 days, for RI and RII, respectively. After stable conditions attained, total chemical oxygen demand (COD) removal efficiency stabilized above 78%. Biogas production ranged from 0.52 to 1.16 L d-1 L-1 reactor volume, with 67-82% methane concentration and an average conversion of 0.69 ± 0.2 and 0.73 ± 0.2 g CH4-COD g-1CODin for RI and RII, respectively. The results imply that source-separated blackwater can be treated effectively in an anaerobic sludge blanket process on average loading rate of 2.3 ± 0.5 g COD d-1 L-1 reactor volume with high methane production potential and more than 80% removal of organic and particulate matter.

Effect of magnetite powder on anaerobic co-digestion of pig manure and wheat straw

This study investigated the effects of different amounts of magnetite powder (i.e., 0g, 1.5g, 3g, 4.5g, 6g) on the anaerobic co-digestion of pig manure (PM) and wheat straw (WS). The variations in pH, alkalinity, cellulase activity (CEA), dehydrogenase activity (DHA) and methane production, were analyzed by phases. Correlation of the activities of the two enzymes with methane production was also analyzed, and the Gompertz model was used to evaluate the efficiency of anaerobic digestion (AD) with the addition of magnetite powder. The results showed that magnetite powder had significant effects on the anaerobic co-digestion of PM and WS. The maximum total methane production with the addition of 3g of magnetite powder was 195mL/g total solids (TS), an increase of 72.1%. The CEA and DHA increased with magnetite powder in the ranges of 1.5–4.5g, 1.5–6g, respectively, while the methane production showed a better correlation with DHA than with CEA. Using the Gompertz model, the efficiency of AD was optimal when adding 3g magnetite powder, with higher methane production potential (206mL/g TS), shorter lag-phase time (14.9d) and shorter AD period (44d).

Feasibility study of a centralized biogas plant performance in a dairy farming area

In this feasibility study, the anaerobic co-digestion of different organic wastes obtained from a dairy farming area in Hokkaido prefecture, Japan was investigated with the objective of building a centralized biogas plant. The daily organic wastes generated from the study area were 210 t/day, comprised of 90% barn wastes and 10% wastewater sludge and feed residue of total mixed ration. The wastes can be categorized into high VS/TS ratio which is easily biodegradable and low VS/TS ratio which is hardly biodegradable. The methane yield of each substrate was investigated in a batch experiment followed by a continuous experiment at mesophilic temperature. Compared to other organic wastes, higher methane production potential were obtained from dairy manures with the highest yield, resulting in 0.19 m3/kgVS, from dairy manure slurry. Moreover, a longer hydrolysis rate constant (7.2 days) was observed with dairy manure slurry rather than beef cattle manure (3.4 days). Due to the mixture of substrates in the continuous experiment, the methane yield increased significantly (0.35 m3/kgVS), reaching almost double of that observed during batch experiments. The average biogas production performance was 39.26 m3 per m3 of added substrate. This illustrates the potential economic viability of the prospective centralized biogas plant.

High methane production potential of activated sludge accumulating polyhydroxyalkanoates in anaerobic digestion

A technique for using waste activated sludge (WAS) accumulating intracellular storage materials was studied for enhancing methane production through anaerobic digestion. Model WAS samples with various contents of poly-β-hydroxyalkanoates (PHAs) were used for anaerobic digestion tests. Methane production during 32 d from WAS with PHA content of 290mgg⿿1 of dry mass was higher by 30% than that from WAS with PHA content of 30mgg⿿1. Kinetic models showed that PHAs have a higher biogas production rate constant and a higher biogas yield than microbial cells of WAS in anaerobic digestion. An increase of 10mgg⿿1 of the PHA content in WAS increased biogas production of 2.6mLg⿿1-VSadded and methane production of 2.4mLg⿿1-VSadded. Results show that PHA-accumulating WAS has high potential for methane production in anaerobic digestion.

Nutrient composition, in vitro true digestibility (IVTD) and methane production potential of fodder tree leaves

This work was carried out to estimate the nutrient composition and methane production potential of various tree leaves to develop a database on methane production. Highest organic matter (OM) content was recorded in cashew leaves (96.87%) and lowest value was recorded in mulberry leaves (86.03%). Ether extract (EE) content of various tree leaves ranged from 0.54 to 8.74%. Neutral detergent fibre (NDF) was highest in velvel leaves (65.03%) and lowest in Murungai leaves (19.48%). Lowest in vitro true digestibility was observed in velvel leaves (41.59%) and highest value was observed in maramalli leaves (75.59%). Mulberry leaves had lowest methane production potential at half life (t1/2) (0.21 ml/100 mg truly digested substrate) and highest methane production potential at half life (t1/2) was recorded in velvel leaves (1.98 ml/100 mg truly digested substrate). Agathi leaves had highest (P<0.05) methane production potential at 24 h (2.72 ml/100 mg truly digested substrate) compared to all other tree leaves. It can be concluded that average OM, EE and NDF content of various tree leaves was 90.83, 4.67 and 40.53%, respectively. Average methane production potential of different tree leaves at half life and 24 h was 0.93 and 1.55 ml /100 mg truly digested substrate, respectively.

Influence of deflocculation on microwave disintegration and anaerobic biodegradability of waste activated sludge

In the present study, the potential benefits of deflocculation on microwave pretreatment of waste activated sludge were investigated. Deflocculation in the absence of cell lysis was achieved through the removal of extra polymeric substances (EPS) by sodium citrate (0.1g sodium citrate/g suspended solids), and DNA was used as a marker for monitoring cell lysis. Subsequent microwave pretreatment yielded a chemical oxygen demand (COD) solubilisation of 31% and 21%, suspended solids (SS) reduction of 37% and 22%, for deflocculated and flocculated sludge, respectively, with energy input of 14,000kJ/kg TS. When microwave pretreated sludge was subjected to anaerobic fermentation, greater accumulation of volatile fatty acid (860mg/L) was noticed in deflocculated sludge, indicating better hydrolysis. Among the samples subjected to BMP (Biochemical methane potential test), deflocculated microwave pretreated sludge showed better amenability towards anaerobic digestion with high methane production potential of 0.615L (gVS)−1.

Control Strategies for Enhancement of Anaerobic Digestion of Food Waste

Food waste management has become an important issue from the environmental, economic, and social points of view due to the fast increase of food waste production and serious environmental pollution. Food waste is considered to be an attractive feedstock of anaerobic digestion and has attracted worldwide attention because of its good biodegradability and high methane production potential. However, in practice, anaerobic digestion system of food waste often shows poor performance and stability, which greatly limited the development of anaerobic digestion process of food waste. In order to obtain high treatment efficiency and satisfactory methane yield, many researchers employed various control strategies for anaerobic digestion of food waste including pretreatment, additive agent addition, two-phase anaerobic digestion, and anaerobic co-digestion. Therefore, this article is intended to review the control strategies for anaerobic digestion process that have been developed for methane production from food waste.

Comparison of methane production potential, biodegradability, and kinetics of different organic substrates

The methane production potential, biodegradability, and kinetics of a wide range of organic substrates were determined using a unified and simple method. Results showed that feedstocks that contained high energy density and easily degradable substrates exhibited high methane production potential and biodegradability. Lignocellulosic biomass with high content of fibrous compositions had low methane yield and biodegradability. Feedstocks with high lignin content (≥ 15%, on a TS basis) had low first-order rate constant (0.05-0.06 1/d) compared to others. A negative linear correlation between lignin content and experimental methane yield (or biodegradability) was found for lignocellulosic and manure wastes. This could be used as a fast method to predict the methane production potential and biodegradability of fiber-rich substrates. The findings of this study provided a database for the conversion efficiency of different organic substrates and might be useful for applications of biomethane potential assay and anaerobic digestion in the future.

Anaerobic co-digestion of municipal wastewater sludge and restaurant grease

Co-digestion has drawn much attention because of its potential to increase biogas production among other benefits. Restaurant grease has high energy content and methane production potential and so is a promising substrate for co-digestion with municipal wastewater sludge. Anaerobic co-digestion of municipal wastewater sludge and restaurant grease was investigated at laboratory-scale under mesophilic conditions (37 °C). Increasing the chemical oxygen demand (COD) loading rate of the test digester by 387% (organic loading rate 4.235 kg VS/m3/d) relative to the control digester led to a 467% increase in daily biogas production, a 25.2% increase in methane yield (based on volatile solids (VS) destruction), a 29.8% increase in COD removal and a 27.2% increase in VS reduction. The biogas methane content ranged from 62.6 to 66.2% (v/v). No negative effect of the grease addition was observed in the test digester performance under the conditions investigated. The increases in biogas production and methane yield indicated enhanced digestion performance. In addition, partial alkalinity and pH proved to be good indicators of digester stability.