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Anaerobic digestion is a technology that converts complex organic matter into another form of matter, from which energy can be more easily extracted. The stability and digestion of anaerobic co‐digestion with multiple raw materials as substrates is better than the performance of anaerobic mono‐digestion. In the past two decades, there has been a large amount of literature on how to improve the performance of methane production in the anaerobic co‐digestion process, but few systematic reviews have been conducted. This paper summarizes the factors affecting the development of anaerobic co‐digestion. The process parameters, substrate optimization strategy, microbial community, and model application for improving anaerobic co‐digestion performance were systematically analyzed. Methane purification technology and policies to support digestion projects are also discussed. At present, the technological process is basically mature, but the interaction between various parameters can be studied in depth. Methane purification technology expands the market for the biogas industry and increases its economic benefits. Policy is the key to promoting process technology and the methane market. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

This study investigated the effects of different amounts of magnetite powder (i.e., 0 g, 1.5 g, 3 g, 4.5 g, 6 g) 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 3 g of magnetite powder was 195 mL/g total solids (TS), an increase of 72.1%. The CEA and DHA increased with magnetite powder in the ranges of 1.5–4.5 g, 1.5–6 g, 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 3 g magnetite powder, with higher methane production potential (206 mL/g TS), shorter lag-phase time (14.9 d) and shorter AD period (44 d). [ABSTRACT FROM AUTHOR]

Goat manure (GM) is an excellent raw material for anaerobic digestion because of its high total nitrogen content and fermentation stability. Several comparative assays were conducted on the anaerobic co-digestion of GM with three crop residues (CRs), namely, wheat straw (WS), corn stalks (CS) and rice straw (RS), under different mixing ratios. All digesters were implemented simultaneously under mesophilic temperature at 35±1 °C with a total solid concentration of 8%. Result showed that the combination of GM with CS or RS significantly improved biogas production at all carbon-to-nitrogen (C/N) ratios. GM/CS (30:70), GM/CS (70:30), GM/RS (30:70) and GM/RS (50:50) produced the highest biogas yields from different co-substrates (14840, 16023, 15608 and 15698 mL, respectively) after 55 d of fermentation. Biogas yields of GM/WS 30:70 (C/N 35.61), GM/CS 70:30 (C/N 21.19) and GM/RS 50:50 (C/N 26.23) were 1.62, 2.11 and 1.83 times higher than that of CRs, respectively. These values were determined to be the optimal C/N ratios for co-digestion. However, compared with treatments of GM/CS and GM/RS treatments, biogas generated from GM/WS was only slightly higher than the single digestion of GM or WS. This result was caused by the high total carbon content (35.83%) and lignin content (24.34%) in WS, which inhibited biodegradation. [ABSTRACT FROM AUTHOR]

Dairy manure (DM), chicken manure (CM) and wheat straw were used to investigate the possibility of optimizing the methane (CH4) potentials in anaerobic co-digestion of multiple substrates. Response surface methodology (RSM) was used to evaluate the individual and interactive effects of four variables [carbon/nitrogen (C/N) ratio, the feeding composition (DM/CM), initial substrate loading and inoculum-to-substrate ratio (ISR)] in the digestion process. All four variables had significant effects on CH4 potentials. Interactive effects of C/N and DM/CM ratios, C/N ratio and ISR, initial substrate loading and ISR were significant The optimum conditions were a C/N ratio of 26.31, a DM/CM ratio of 42.96:57.04, an initial loading of 15.90 g volatile solids (VS)/l and an ISR ratio of 2.34, with the maximum CH4 potential being 394 ml/g VS. The RSM model was appropriate for optimizing CH4 production in the process of anaerobic co-digestion of multiple substrates. [ABSTRACT FROM AUTHOR]

Ecological stoichiometry (C:N:P ratios) has been widely used to indicated the complicated microbial ecology system and microbial community, however, limited researches have been done in the anaerobic digestion process. In this study, different responses of microbial community to C:N:P stoichiometry were investigated. Results showed that bacterial diversity were higher than archaea; Beta diversity was decreased then remained stable and strongly correlated to C:N:P ratios, while it was not significant for alpha diversity. Furthermore, considering the archaeal dominant order, Methanomicrobiales showed no significant correlation with C:N:P stoichiometric ratios, but closely related to C, Methanosarcinales was positively influenced by C:N ratio, and Methanobacteriales was significantly and negatively impacted by N:P ratio. For bacteria, Clostridiales and Sphaerochaetales closely and positively related to N, Bacteroidales significantly and negatively related to P, but positively to C:N ratio, and Spirochaetales positively related to C. Moreover, changes of microbial taxa were significantly correlated with all considered process variables, which explained 94.1% and 96.6% of total variation in archaea and bacteria taxa, respectively. It is worthy note that these results could be used to predict the process performance and indicate the complicated microbial community by using the simple C:N, C:P and N:P ratios. • As digestion prolonged, C:N ratio decreased, while C:P and N:P increased. • Microbial diversity strongly related to process properties and C:N:P ratios. • Both archaeal and bacterial dominant order significantly responded to C:N:P ratios. • Process variables explained 94.1% (archaea) and 96.6% (bacteria) of total variation. [ABSTRACT FROM AUTHOR]

Abstract Although many studies have been done about anaerobic digestion of corn straw, the insight of process performance focusing on biogas production and systematic parameters still needs to be further investigated. This paper investigated biogas production, synergistic correlations of systematic parameters and their correlations based on the effects of total solid (TS) content and initial pH on the digestion performance of corn straw. Results demonstrated that biogas production was significantly correlated with systematic parameters, and the best digestion performance was found at TS content of 4% and initial pH 7.5. Furthermore, the ratio of inoculum to substrate (I/S) should be an indicator for forecasting process performance. The significant synergistic correlations of each kind parameter were also achieved. Moreover, three different synergistic effect pathways of I/S, pH, volatile fatty acid (VFA), hydrolysis rate (k), biogas production potential (P), the maximum biogas production rate (R max) and lag phase (λ) were concluded: (1) I/S→pH (R2 = 0.841, P < 0.01)→k (R2 = 0.831, P < 0.01)→R max (R2 = 0.818, P < 0.01), (2) I/S→pH (R2 = 0.841, P < 0.01)→P (R2 = 0.920, P < 0.01) and (3) I/S→VFA (R2 = −948, P < 0.01)→λ (R2 = −0.662, P < 0.05). Taken together, this report will be a basis for further study of industrial anaerobic digestion of corn straw. Highlights • TS content of 4% with initial pH 7.5 could be an appropriate adjusting measure. • I/S and VS were the main operating parameters influencing other parameters. • The significant synergistic correlations of each kind parameter were achieved. • Three different synergistic effect pathways of these parameters were concluded. [ABSTRACT FROM AUTHOR]

Kinetic characteristics play an important role in anaerobic digestion system for representing biogas production performance, however, its relationship with anaerobic digestion process parameters (i. e., volatile fatty acids, total ammonia nitrogen, pH and total alkalinity) and operational conditions remains poorly understood. To illustrate the linkage of kinetic parameters with process parameters and swine manure content and initial pH, and the effects of swine manure content and initial pH on anaerobic digestion performance, substrate properties, accumulative biogas production, specific biogas production rate and process parameters were analyzed under different treatments. Additionally, the effects of swine manure and initial pH on hydrolysis constant, lag phase, biogas production potential and the maximum biogas production rate were investigated. The results revealed that volatile solid and C:N ratio were significantly decreased with swine manure content increased which were considered as operational conditions with initial pH following the linkage illustration. Furthermore, accumulative biogas production, biogas production rate, final pH, total ammonia nitrogen and hydrolysis constant were increased with swine manure content and initial pH increased, while volatile fatty acids and lag phase showed the opposite trend. The results showed that these operational conditions significantly influenced process parameters and kinetic parameters, with close correlations were observed. Lag phase closely correlated with VFA which was closely correlated with C:N ratio. Therefore, C:N ratio impacted kinetic parameters via effecting VFA, while initial pH directly influenced kinetic parameters. Meanwhile, the correlation of kinetic parameters with C:N ratio was stronger than initial pH. Therefore, C:N ratio should be an indicator for estimating process performance, time the bacteria's acclimatization to the new environment and biogas production. Taken together, these findings provide a scientific theory for estimating anaerobic digestion performance. [ABSTRACT FROM AUTHOR]

With the rising demand for renewable energy and environmental protection, anaerobic digestion of biogas technology has attracted considerable attention within the scientific community. This paper presents a comprehensive review of research achievements on anaerobic digestion developments for biogas production. The review includes a discussion of factors affecting efficiency (temperature, pH, C/N ratio, OLR and retention time), accelerants (greenery biomass, biological pure culture and inorganic additives), reactors (conventional anaerobic reactors, sludge retention reactors and anaerobic membrane reactors) and biogas AD processes (lignocellulose waste, municipal solid waste, food waste, livestock manure and waste activated sludge) based on substrate characteristics and discusses the application of each forementioned aspect. The factors affecting efficiency are crucial to anaerobic digestion, because they play a major role in biogas production and determine the metabolic conditions for microorganism growth. As an additive, an accelerant is not only regarded as a nutrient resource, but can also improve biodegradability. The focus of reactor design is the sufficient utilization of a substrate by changing the feeding method and enhancing the attachment to biomass. The optimal digestion process balances the optimal digest conditions with the cost-optimal input/output ratio. Additionally, establishment of theoretical and technological studies should emphasize practicality based on laboratory-scale experiments because further development of biogas plants would allow for a transition from household to medium- and large-scale projects; therefore, improving stability and efficiency are recommended for advancing AD research. [ABSTRACT FROM AUTHOR]

This study investigated the effects of different initial pH (6.0, 6.5, 7.0, 7.5 and 8.0) and uncontrolled initial pH (CK) on the lab-scale anaerobic co-digestion of kitchen waste (KW) with cow manure (CM). The variations of pH, alkalinity, volatile fatty acids (VFAs) and total ammonia nitrogen (NH 4 + –N) were analyzed. The modified Gompertz equation was used for selecting the optimal initial pH through comprehensive evaluation of methane production potential, degradation of volatile solids (VS), and lag-phase time. The results showed that CK and the fermentation with initial pH of 6.0 failed. The pH values of the rest treatments reached 7.7–7.9 with significantly increased methane production. The predicted lag-phase times of treatments with initial pH of 6.5 and 7.5 were 21 and 22 days, which were 10 days shorter than the treatments with initial pH of 7.0 and 8.0, respectively. The maximum methane production potential (8579 mL) and VS degradation rate (179.8 mL/g VS) were obtained when the initial pH was 7.5, which is recommended for co-digestion of KW and CM. [ABSTRACT FROM AUTHOR]

Abstract: To investigate the feasibility of statistical methods in optimizing the feeding composition in anaerobic co-digestion, a simplex-centroid mixture design (SCMD) and central composite design (CCD) were evaluated with methane potential as the response variable. Dairy manure, chicken manure, swine manure and rice straw (RS) were selected as raw materials and two kinds of manures and RS were mixed in each blend. Each component served as an independent variable in the SCMD and CCD and involved two factors, the manure and C/N ratios. Co-digestion of three-component substrates resulted in higher methane potentials than single and two-component substrates. In response surface plots, SCMD showed the interactions among each component in the co-substrates and CCD presented the interaction between the ratio of manures and the C/N ratio. SCMD and CCD are both suitable methods for optimizing the feeding composition during anaerobic co-digestion. [Copyright &y& Elsevier]

Abstract: This study investigated the possibilities of improving methane yield from anaerobic digestion of multi-component substrates, using a mixture of dairy manure (DM), chicken manure (CM) and wheat straw (WS), based on optimized feeding composition and the C/N ratio. Co-digestion of DM, CM and WS performed better in methane potential than individual digestion. A larger synergetic effect in co-digestion of DM, CM and WS was found than in mixtures of single manures with WS. As the C/N ratio increased, methane potential initially increased and then declined. C/N ratios of 25:1 and 30:1 had better digestion performance with stable pH and low concentrations of total ammonium nitrogen and free NH3. Maximum methane potential was achieved with DM/CM of 40.3:59.7 and a C/N ratio of 27.2:1 after optimization using response surface methodology. The results suggested that better performance of anaerobic co-digestion can be fulfilled by optimizing feeding composition and the C/N ratio. [Copyright &y& Elsevier]

Review: 150 refs. [ABSTRACT FROM AUTHOR]