Two-phase Anaerobic Digestion System Research Articles

Assessing two-phase anaerobic digestion systems for demand-driven electricity and biobutanol transport fuel at a large distillery

Decarbonisation of industry will necessitate innovative technological solutions that allow for both reduced carbon footprint and security of supply. Biogas systems can allow electricity production on-demand. This study evaluated and compared different two-phase anaerobic digestion systems for continuous volatile fatty acid (VFAs) production and demand-driven biogas production at a whiskey distillery using by-products as feedstock. The systems analysed were a two-phase continuously stirred tank reactor (CSTR) and a leach bed-expanded granular sludge bed reactor (LBR-EGSB) system. Both systems exhibited continuous VFA production (up to 10.4 g. L−1VFA made up of primarily butyric acid and acetic acid) and rapid biogas production, achieving peak flow rates within 30 min. The peak biogas production from the demand-driven EGSB was 3.1 L. L−1reactor. d−1 compared to the CSTR, which recorded 1.8 L. L−1reactor. d−1. Three kinetic models of both systems were assessed, which were able to describe the cumulative biogas production. A theoretical evaluation of processing butyric acid into biobutanol, to be blended with diesel, could produce a more sustainable transport fuel than diesel, reducing distillery-associated transport emissions by 16%.

A Novel Batched Four-Stage–Two-Phase Anaerobic Digestion System to Facilitate Methane Production from Rice Straw and Cow Manure with Low Inoculum/Substrate Ratios

In order to improve the performance of methane production from agro-waste, a batched four-stage–two-phase anaerobic digestion (4S2P-AD) system was designed to combine the advantages of both anaerobic co-digestion (co-AD) and two-phase AD. The initial separation of two phases was performed using rice straw (RS) as a feedstock in acidogenic phase and cow manure (CM) in methanogenic phase at low inoculum/substrate (I/S) ratios of 0.5 and 0.2 and a high organic loading of 60 g volatile solid (VS)/L. The periodic round-trip reflux of leachate during the 4S2P-AD process facilitated re-inoculation throughout the four stages. The results showed that this round-trip reflux also dispersed toxic ammonia, balanced the carbon/nitrogen ratio, unified the microbial community structure, and led to the selection of Methanosarcina (relative abundance > 80%) as the dominant methanogens. With the abilities to overcome volatile fatty acid accumulation, shorten lag times, improve biodegradability, and foster synergistic effects, it was verified that the 4S2P-AD process can maintain efficient and stable methanogenesis from high-solid lignocellulosic feedstock. The averaged methane production throughout the four stages of 4S2P-AD was 234 mL/g VS. This result is 96% higher than the averaged methane production obtained from the four one-step AD groups using mono-feedstock, and 91% higher than that obtained using co-feedstock. This study provides a scientific reference for the development of new processes of bio-methane production from agro-waste with a high fermentation capacity and stability in the future.

Environmental life cycle assessment of treatment and management strategies for food waste and sewage sludge

A consequential life cycle assessment (LCA) was utilized to compare the environmental impacts of food waste and sewage sludge management strategies. The strategies included a novel two-phase anaerobic digestion (AD) system and alternatives including landfill, waste-to-energy, composting, anaerobic membrane bioreactor, and conventional AD (wet continuous stirred-tank reactor [CSTR]). The co-management of food waste with sewage sludge was also considered for the two-phase AD system and for a conventional AD reactor. A multidimensional LCA approach was taken, considering the five-midpoint impact categories of global warming, smog, human health particulate, acidification, and eutrophication estimated using the U.S. EPA Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts. Co-management of food waste and sewage sludge using the novel two-phase AD system was shown to maximize energy recovery and had a net global warming benefit while reducing other environmental impacts compared with the alternative management strategies. It had similar relative environmental advantages across all categories as conventional AD, with the advantage of a smaller physical footprint. However, both approaches featured net environmental burdens when the background electric grid intensity fell below 0.25 kg CO2-eq kWh−1, as could be expected in a decarbonized electric future. Upgrading the biogas produced from AD to renewable natural gas can displace the use of fossil natural gas for other non-electricity energy requirements that are difficult to decarbonize and may extend the time period of significant environmental benefits of utilizing AD for organic waste management. Treatment of the nutrient-rich supernatant generated by the novel two-phase AD system could be an obstacle for utilities with stringent nutrient discharge limits. Future research and full-scale implementation are needed to demonstrate the benefits of the two-phase AD system predicted through this analysis.

Pilot-scale two-phase anaerobic digestion of deoiled food waste and waste activated sludge: Effects of mixing ratios and functional analysis

Anaerobic co-digestion of deoiled food waste (dFW) and waste activated sludge (WAS) can address the challenges derived from mono-digestion of FW. In the present study, a pilot-scale methanogenic bioreactor of a two-phase anaerobic digestion system was developed to explore the impact of dFW/WAS volatile solids ratios on the overall performance, microbial community, and metabolic pathways. Besides, the tech-economic of the system was analyzed. The results showed that the degradation efficiency of soluble chemical oxygen demand (SCOD) was more than 84.90% for all the dFW/WAS ratios (v/v) (1:0, 39:1, 29:1, 19:1 and 9:1). Moreover, the dominant genus of bacteria and archaea with different ratios were Lactobacillus (66.84–98.44%) and Methanosaeta (53.66–80.09%), respectively. Co-digestion of dFW and WAS (29: 1 in v/v ratios) obtained the highest yield of methane (0.41 L CH4/Ladded) with approximately 90% of SCOD being removed. In the pilot-scale experiment, the co-digestion of FW and WAS makes positive contribution to reusing solid waste for improving solid management.

Anaerobic digestion of liquid dairy manure pretreated by the microwave-enhanced advanced oxidation process

ABSTRACT The microwave-enhanced advanced oxidation process (MW-AOP) was utilized for the treatment of liquid dairy manure, prior to anaerobic digestion (AD). A significant amount of soluble chemical oxygen demand (SCOD) was formed in the treated solution, but there was no or little increase in volatile fatty acid (VFA). In this study, up-flow anaerobic sludge blanket (UASB) reactors were used in both the conventional AD system and as the methane phase reactor in a two-phase anaerobic digestion (TPAD) system. Both AD systems were capable of operating at very short hydraulic retention times (HRTs) to as low as about 3 days, and very high methane production rates were achieved. However, much higher methane production was obtained in the TPAD system. The phase separation of the acidogenesis and the methanogenesis in the TPAD system not only increased methane production but also maintained reactor stability throughout the experimental period. Thus, the combination of MW-AOP treatment and TPAD appears to be an effective means of energy recovery from dairy manure.

Regulation of acidogenic fermentation through exogenous additives for promoting carbon conversion of food waste in two-phase anaerobic system

In this study, exogenous Megasphaera elsdenii inoculum and acetate supplementation were introduced at the acidogenic phase to regulate the acidogenic fermentation pathway and assess their effects on food waste (FW) carbon conversion in two-phase anaerobic digestion (AD) system. These two additives significantly accelerated organic removal efficiency and subsequently increased FW hydrolysis and acidogenesis by 16% and 35%, respectively. As expected, two exogenous additives promoted butyrate fermentation during FW acidogenesis. With regard to the role of exogenous additives, both hydrogen and butyrate yields increased by over 60%. This desired increment resulted in a 25% increase in methane production. The overall carbon conversion from FW in the integrated two-phase AD system was enhanced by biochemical additives, which was 1.3-fold higher than that in control without any additives. Collectively, findings demonstrate the feasibility of regulating acidogenic fermentation via exogenous biochemical additives and its benefits on FW carbon conversion during AD process.

System performance and functional analysis for the methanogenic bioreactor of a two-phase anaerobic digestion system: The effect of influent sulfate

In this study, a lab-scale bioreactor was built to investigate the influence of sulfate on the overall performance, microbial community, and metabolic pathways in the methanogenic bioreactor of a two-phase anaerobic digestion system. The results demonstrated that by gradually cultivating the sludge of the methanogenic bioreactor, a chemical oxygen demand (COD) degradation efficiency of over 65% was achieved for sulfate contents from 10,000 mg/L to 30,000 mg/L. The sulfate reduction performance could only be maintained at a high level for influent COD/sulfate ratios no less than 1.88. In addition, the methane production rate (MPR) decreased from 0.92 L/L/d to 0.28 L/L/d, and the proportion of methane in biogas dropped from 51% to 33% when the influent sulfate exceeded 30,000 mg/L. High-throughput sequencing coupled with PICRUSt2 revealed that the dissimilatory sulfate process could be enhanced by sulfate within 30,000 mg/L. While an amount of greater than 5000 mg/L sulfate remarkably inhibited the assimilatory sulfate reduction process, and this inhibition was induced by the down-regulation of the cysNC, cysC, cysI and cysJ genes. For the methanogenic process, sulfate contents within 30,000 mg/L had no obvious impact on all of the acetoclastic, hydrogenotrophic, and methylotrophic methanogenesis processes, but serious suppression was observed for sulfate amounts greater than 30,000 mg/L. This inhibition primarily originated from the decrease in mcrA, mcrB, and mcrG genes that regulate the conversion of methylcoenzyme M to methane, the last step of all three methanogenesis pathways.

Effect of nitrite on hydrolysis-acidification, biogas production and microbial community in semi-continuous two-phase anaerobic digestion of sewage sludge

Previous study found that the pre-treatment of sewage sludge with nitrite improves the biogas production during the mono/two-phase anaerobic digestion (AD) using batch biochemical methane potential tests. In this study, the effects of nitrite on hydrolysis-acidification, biogas production, volatile solids destruction and microbial composition in semi-continuous two-phase AD of sewage sludge were investigated. The addition of nitrite promotes sludge organic matter solubilization (+484%) and VFAs production (+98.9%), and causes an increase in the VS degradation rate during the AD process (+8.7%). The comparison of biogas production from the acidogenic and methanogenic reactors with or without the addition of nitrite implies that the nitrite has no significant effect on the overall biogas production of two-phase sludge AD process. High-throughput sequencing analysis shows that the microbial communities of bacteria and archaea in two-phase AD reactors significantly changes after the addition of nitrite. Vulcanibacillus (bacteria) and Candidatus Methanofastidiosum (archaea) become the dominant genera in the acidogenic and methanogenic reactors with the nitrite respectively. These findings provide new insights about using nitrite to promote the organic matter degradation of sewage sludge in a semi-continuous two-phase AD system.

Enhanced methane yield through sludge two-phase anaerobic digestion process with the addition of calcium hypochlorite

This study investigated the effects of calcium hypochlorite (Ca(ClO)2) on biomethane generation from sludge two-phase anaerobic digestion system. In first (acidogenic) phase, volatile fatty acids (VFAs) were largely generated when pretreated by Ca(ClO)2, while the methane yield was severely inhibited. In second (methanogenic) phase, the methane yield was observably enhanced by Ca(ClO)2. Further calculation showed that the total methane yield from the two phases was firstly promoted from 156.0 ± 4.5 to 269.9 ± 5.2 mL when Ca(ClO)2 dosage enhanced from 0 to 1.6 g/L, which then reduced to 235.4 ± 5.5 mL when Ca(ClO)2 content reached 2.0 g/L. Mechanism analysis showed that the suppression of Ca(ClO)2 on coenzyme F420 activity was relieved in methanogenic phase, and the abundances of functional microbes in methanogenic phase were enriched when added with Ca(ClO)2. The Ca(ClO)2-based method well realized the balance between efficacy and economy, possessing outstanding potential for large-scale applications.

Start-up phase optimization of two-phase anaerobic digestion of food waste: Effects of organic loading rate and hydraulic retention time

The effects of organic loading rate (OLR) and hydraulic retention time (HRT) on the dynamics of acidogenic and methanogenic processes in two-phase anaerobic digestion (TPAD) of food waste (FW) were investigated to determine the start-up operational conditions. Seven arrangements of TPAD systems under mesophilic conditions were evaluated, each containing one acidogenic reactor and one methanogenic reactor. The work analyzed two HRTs (2 and 3 days) and four OLRs (2, 3, 4 and 5 kgVS.m−3.d−1). The 2D5KG system obtained VS and COD removal of 68% and 72%; SMP of 273 Lmethane.kg.VS−1. The 3D4KG system obtained VS and COD removal of 70 and 66%; SMP of 252 Lmethane.kg.VS−1. Valeric acid predominated in the acidogenic reactor in both HRT and OLR evaluated, followed by butyric acid. In the methanogenic reactor, the main methane production route was the butyric acid conversion into acetic acid and finally methane. Higher OLR benefits the methane production. The microbiological profile indicated the pathway of methanogenesis by acetoclastic methanogenesis. The canonical correlation analysis allowed to verify that the groups are independent and, therefore, the variables analyzed in the acidogenic reactor have an influence on the methanogenic reactor.

Enhanced biomethane production from corn straw by a novel anaerobic digestion strategy with mechanochemical pretreatment

The biomethane production from lignocellulose via anaerobic digestion has always suffered from low carbon conversion rate, due to the stubborn structure of lignocellulose and the inefficiency of the current anaerobic digestion systems. The integrated two-phase anaerobic reactor can form a highly efficient anaerobic digestion system with an upper acidogenic phase and a lower methanogenic phase. However, the acidogenic phase can be overaccelerated, leading to acidification failure of the whole digestion system. In this study, the acidogenesis liquid digestate (ALD) generated from the acidogenic phase was applied to impregnate corn straw coupled with disc refining (DR) to enhance biomethane production by forming a thorough and stable integrated two-phase anaerobic system. The concentration of volatile fatty acids in the acidogenic phase is adjusted by this pretreatment technology to approximately match the efficiency of methanogenic bacteria in the methanogenic phase. The acetic acid in ALD was proved to be an effective acid to swell lignocellulose and improved the performance of the acid impregnation coupled with disc refining (AIDR) pretreatment. A 47.13% higher biomethane yield was obtained from corn straw after AIDR pretreatment. Moreover, energy conversion efficiency and economic analysis indicated this anaerobic digestion process with AIDR pretreatment had a $ 21.06 ton−1 higher net profit than that without any pretreatment. This novel anaerobic digestion process creates a synergistic processing technology that integrates biomass pretreatment with a two-phase anaerobic digestion system, resulting in destroying the compact structure of lignocellulose, enhancing biomethane production efficiency, and improving the economic competitiveness of biomass conversion to biomethane.

Optimization of water replacement during leachate recirculation for two-phase food waste anaerobic digestion system with off-gas diversion

An integrated two-phase AD with acidogenic off-gas diversion from a leach bed reactor to an upflow anaerobic sludge blanket was developed for improving methane production. However, this system had its own technical limitation such as mass transfer efficiency for solid-state treatment. In order to optimize the mass transfer in this two phase AD system, leachate recirculation with various water replacement rates regulating the total solids contents (TS) at 12.5%, 15%, and 17.5% was aim to investigate its effect on methane generation. The solubilization of food waste was increased with decreasing TS content, while the enzymatic hydrolysis showed the opposite trend. A TS contents of 15% presented the best acidogenic performance with the highest hydrogen yield of 30.3 L H2/kg VSadded, which subsequently resulted in the highest methane production. The present study provides an easy approach to enhance food waste degradation in acidogenic phase and energy conversion in methanogenic phase simultaneously.

The efficiencies and capacities of carbon conversion in fruit and vegetable waste two-phase anaerobic digestion: Ethanol-path vs. butyrate-path

To rapidly treat and stably utilize great quantities of fruit and vegetable waste (FVW), the strategies in anaerobic digestion pattern have been constantly improved. In this work, the efficiencies and capacities of carbon conversion in different FVW anaerobic digestion systems were studied. Compared to butyrate-path (BD) two-phase and single-phase anaerobic digestion (SD), the ethanol-path two-phase anaerobic digestion (ED) system showed the highest rate of converting insoluble into soluble carbon formation (82.2%) and methane yield conversed from soluble carbon which is 0.14 gCODCH4 (gVSS d)−1. It was also found that the coexistence of Bacillus and Methanococcus in the methanogenic phase maintained fatty acids and methane generation. The advantage of carbon conversion efficiency in ED can be elucidated from the highest acetification rate (704.10 mgCOD (L h)−1) which means more converted acetate can be smoothly used for methane generation. Compared to methanogenesis converted from butyrate and propionate, the thermodynamic condition of methanogenesis converted from ethanol was more feasible. Also, the highest capacity of max methane production (197773.7 mL) of ED was simulated. ED might be an efficient and advantageous option for FVW methane digestion. Furthermore, comparison of acidogenic product and methane in conversion efficiency revealed that fatty acids should think as ideal anaerobic product rather than methane.

PH regulation of the first phase could enhance the energy recovery from two-phase anaerobic digestion of food waste.

The effect of pH regulation in phase I on hydrolysis and acidogenesis rate, metabolites production, microbial community, and the overall energy recovery efficiency during two-phase anaerobic digestion (AD) of food waste (FW) was investigated. pH strongly affected the acidogenesis rate and the yield of the fermentation products. The highest acidogenesis efficiency (60.4%) and total volatile fatty acids (VFA)/ethanol concentration (12.4g/L) were obtained at pH 8 during phase I. Microbial community analysis revealed that Clostridium IV was enriched at pH 8, relating to the accumulation of butyrate. Also, Clostridium sensu stricto played a crucial role in hydrogen production and was abundant at pH 6, resulting in the highest hydrogen yield (212.2ml/gVS). In phase II, the highest cumulative methane yield (412.6ml/gVS) was obtained at pH 8. By considering the hydrogen and methane production stages, the highest energy yield (22.8kJ/gVS, corresponding to a 76.4% recovery efficiency) was generated at pH 8, which indicates that pH 8 was optimal for energy recovery during two-phase AD of FW. Overall, the results demonstrated the possibility of increasing the energy recovery from FW by regulating the pH in the hydrolysis/acidogenesis phase based on the two-phase AD system. PRACTITIONER POINTS: pH 8 was suitable for hydrolysis, acidogenesis, and methanogenesis. High hydrogen yields were obtained at pH 5-8 (about 200ml/d). Clostridium sensu stricto might have played a crucial role in hydrogen production. High methane production (about 400ml/gVS) was obtained at pH 7-9. pH 8 was optimal for energy recovery from FW with an efficiency of 76.4% (22.8kJ/gVS).

Innovations in anaerobic digestion: a model-based study

BackgroundIncreasing the efficiency of the biogas production process is possible by modifying the technological installations of the biogas plant. In this study, specific solutions based on a mathematical model that lead to favorable results were proposed. Three configurations were considered: classical anaerobic digestion (AD) and its two modifications, two-phase AD (TPAD) and autogenerative high-pressure digestion (AHPD). The model has been validated based on measurements from a biogas plant located in Poland. Afterward, the TPAD and AHPD concepts were numerically tested for the same volume and feeding conditions.ResultsThe TPAD system increased the overall biogas production from 9.06 to 9.59%, depending on the feedstock composition, while the content of methane was slightly lower in the whole production chain. On the other hand, the AHPD provided the best purity of the produced fuel, in which a methane content value of 82.13% was reached. At the same time, the overpressure leads to a decrease of around 7.5% in the volumetric production efficiency. The study indicated that the dilution of maize silage with pig manure, instead of water, can have significant benefits in the selected configurations. The content of pig slurry strengthens the impact of the selected process modifications—in the first case, by increasing the production efficiency, and in the second, by improving the methane content in the biogas.ConclusionsThe proposed mathematical model of the AD process proved to be a valuable tool for the description and design of biogas plant. The analysis shows that the overall impact of the presented process modifications is mutually opposite. The feedstock composition has a moderate and unsteady impact on the production profile, in the tested modifications. The dilution with pig manure, instead of water, leads to a slightly better efficiency in the classical configuration. For the TPAD process, the trend is very similar, but the AHPD biogas plant indicates a reverse tendency. Overall, the recommendation from this article is to use the AHPD concept if the composition of the biogas is the most important. In the case in which the performance is the most important factor, it is favorable to use the TPAD configuration.

Effect of liquid digestate recirculation on the ethanol-type two-phase semi-continuous anaerobic digestion system of food waste

This study set up four groups for semi-continuous 150-days experiment to explore the effect of liquid digestate recirculation on the food waste ethanol-type anaerobic digestion system. Results showed that this operation improved the maximum organic load rates to 6.0 g-VS·L−1·d−1, and increased the average alkalinity of methanogenic phase under high load condition by 1.3 times. Total volatile fatty acids/total alkalinity (threshold value was approximately 0.5) could be used as an early warning indicator of methanogenic phase instability. Besides, approximately 64.5% of bacterial species in the hydrolysed acidified phase of ethanol-type liquid digestate recirculation group originated from the recirculated liquid digestate, which enriched the diversity of microbial community, thereby improving the hydrolysis acidification efficiency. Therefore, liquid digestate recirculation improved the stability of system in terms of alkalinity and microecology and then increased the maximum organic load rates.

Two Phase Anaerobic Digestion System of Municipal Solid Waste by Utilizing Microaeration and Granular Activated Carbon

In an anaerobic digestion (AD) process, the hydrolysis phase is often limited when substrates with high concentrations of solids are used. We hypothesized that applying micro-aeration in the hydrolysis phase and the application of granular activated carbon (GAC) in the methanogenesis phase could make the AD process more efficient. A packed bed reactor (PBR) coupled with an up-flow anaerobic sludge blanket (UASB) was conducted, and its effects on methane generation were evaluated. The micro-aeration rate applied in PBR was 254 L-air/kg-Total solids (TS)-d was compared with a control reactor. Micro-aeration showed that it reduced the hydrolysis time and increased the organic matter solubilization as chemical oxygen demand (COD) increasing 200%, with a volatile fatty acids (VFAs) increment higher than 300%, compared to the control reactor (without aeration). Our findings revealed that the implementations of microaeration and GAC in the two-phase AD system could enhance methane production by reducing hydrolysis time, increasing solid waste solubilization.

Effect of solid–liquid separation enhanced by low-temperature hydrolysis in methanogenic phase on two-phase anaerobic sludge digestion system

In this study, a mesophilic two-phase anaerobic digestion system was used to treat waste activated sludge at the temperature of 35 ± 1 °C. The internal structure of the anaerobic sequencing batch reactor (methanogenic phase) has been improved by providing a solid–liquid separation plate, and a continuous-flow stirred tank reactor was employed as the acidogenic phase. The results of the study indicate that solid–liquid separation can be achieved in the methanogenic phase, and the low-temperature hydrolysis pretreatment can enhance solid–liquid separation capability. The separation of solids retention time and hydraulic retention time was also achieved in methanogenic phase, and the solids retention time was extended, which effectively improved the anaerobic digestion performance of the system. The organic concentration and total solids concentration in the methanogenic reactor were significantly different in height. The bottom of the reactor formed an area of high solids and low organic precipitation, while the upper part of the reactor formed a clear water area. The suspended solids concentration in the reactor clear water area was maintained at 359 ± 84 to 533 ± 93 mg/L, and the better solid–liquid separation effect was obtained inside the methanogenic phase. The maximum biogas yield was 258 ± 3 mL/g with the maximum volatile solids degradation rates of 59.43% in the system in Stage 3. Considering the efficiency of anaerobic digestion and the operating costs, the operating condition of Stage 4 (the designed hydraulic retention time was 10.67 d, the feed sludge was thermally pretreated, and its volume was 3 L) in this test is the optimal.

A mini-review on the metabolic pathways of food waste two-phase anaerobic digestion system.

Food waste (FW) disposal has become a global social, environmental, and economic problem. The current practice of landfilling is undesirable due to its potential emission of greenhouse gas, nutrient recycling, and pollution of water resources. Anaerobic digestion (AD), particularly two-phase AD is a promising option to manage FW and recover energy in the form of methane and obtain value-added by-products. However, most current review literature focuses on operating conditions while often placing little emphasis on improving conversion efficiency through regulating intermediate products. The AD process involves complex metabolic reactions carried out by several microbial groups. Therefore, understanding of these metabolic pathways existing in AD is the key to design effective strategies for enrichment of specific microbial groups which can produce desired intermediates for methane production, which can possibly be achieved by an understanding of the influence of critical process parameters on these metabolic pathways. Thus, it is the aim of this review to describe the effect of process conditions on underlying metabolic pathways in order to allow an efficient manipulation of these pathways for enhancing methane production.

Influence of Temperature on Biogas Production Efficiency and Microbial Community in a Two-Phase Anaerobic Digestion System

In this study, the influence of temperature on biogas production efficiency and the microbial community structure was investigated in a two-phase anaerobic digestion reactor for co-digestion of cow manure and corn straw. The results illustrated that the contents of solluted chemical oxygen demand (SCOD) and volatile fatty acid (VFA) in the acidogenic phase and biogas production in the methanogenic phase maintained relatively higher levels at temperatures ranging from 35–25 °C. The methane content of biogas production could be maintained higher than 50% at temperatures above 25 °C. The microbial community structure analysis indicated that the dominant functional bacteria were Acinetobacter, Acetitomaculum, and Bacillus in the acidogenic phase and Cenarchaeum in the methanogenic phase at 35–25 °C. However, the performances of the acidogenic phase and the methanogenic phase could be significantly decreased at a lower temperature of 20 °C, and microbial activity was inhibited obviously. Accordingly, a low temperature was adverse for the performance of the acidogenic and methanogenic phases, while moderate temperatures above 25 °C were more conducive to high biogas production efficiency.