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As the by-product of the vinegar production process, a large number of vinegar residue has been abandoned and caused a serious environmental pollution. Anaerobic digestion has been proved to be able to dispose and convert vinegar residue into bioenergy but still need to improve the efficiency. This study applied central composite design of response surface methodology to investigate the influences of feed to inoculum ratio, organic loading, and initial pH on methane production and optimize anaerobic digestion condition. The maximum methane yield of 203.91 mL gVS-1 and biodegradability of 46.99% were obtained at feed to inoculum ratio of 0.5, organic loading of 31.49 gVS L-1, and initial pH of 7.29, which was considered as the best condition. It has a very significant improvement of 69.48% for methane production and 52.02% for biodegradability compared with our previous study. Additionally, a high methane yield of 182.09 mL gVS-1 was obtained at feed to inoculum ratio of 1.5, organic loading of 46.22 gVS L-1, and initial pH of 7.32. And it is more appropriate to apply this condition in industrial application owing to the high feed to inoculum ratio and organic loading. Besides, a significant interaction was found between feed to inoculum ratio and organic loading. This study maximized the methane production of vinegar residue and made a good foundation for further study and future industrial application.

Enormous amounts of vegetable residues are wasted annually, causing many environmental problems due to their high moisture and organic contents. In this study, the methane production potential of 20 kinds of typical leafy vegetable residues in China were explored using a unified method. A connection between the biochemical components and the methane yields of these vegetables was well established which could be used to predict biogas performance in practice. A high volatile solid/total solid (VS/TS) ratio and hemicellulose content exhibited a positive impact on the biogas yield while lignin had a negative impact. In addition, three kinetic models were used to describe the methane production process of these agro-wastes. The systematic comparison of the methane production potentials of these leafy vegetables shown in this study will not only serve as a reference for basic research on anaerobic digestion but also provide useful data and information for agro-industrial applications of vegetable residues in future work.

California is the leading dairy state in the United States. The total sale of milk and its products represents about $6.3 billion annually out of the $50 billion generated from all agricultural production in the state. However, methane emissions from dairy manure and enteric fermentation represented nearly half of all annual methane emissions in California, with dairy manure accounting for 25%, and enteric fermentation for 20%. Methane emissions originating from manure are produced primarily from anaerobic settling basins and lagoons, which are the most common manure storage systems in the state. To achieve sustainability on dairy farms and to comply with state regulations for air and climate pollutants, dairy farms have implemented technologies such as anaerobic digestion and alternative manure management technologies. In addition, governmental incentive programs have been deployed to partially fund these technologies for eligible dairies in the state. The present article reviews the design and operations, effectiveness, and economics of the most common technologies employed in Californian dairies in reducing methane emissions. The technologies studied include anaerobic digesters, mechanical separators, compost-bedded pack barns, manure vacuuming followed by drying, and weeping walls. The current status and estimated effectiveness of government incentive programs are reviewed and recommendations for improvements presented. Finally, future trends and research needs for mitigating the emissions in Californian dairies are identified. [ABSTRACT FROM AUTHOR]

In order to reduce emissions of greenhouse gases, related global warming and dependency on fossil fuels, it is crucial to promote the uses of renewable energy, and conversion of biomass and organic waste into energy sources. In many parts of the world, a substantial increase in efforts for the conversion of waste into energy is currently being observed. Specifically, biogas technology has been emphasized for the conversion of animal waste into biomethane/biogas because livestock waste is considered to be a substantial source of ambient greenhouse gases, causing climate change. While biogas technology, an anerobic process to convert livestock waste into biogas, is promoted in both developed and developing countries, this review article is focused on improving our existing understanding of small-scale biogas technology and relevance of this technology in rural environment of India. A thorough review research has been performed to gather the information on livestock population, manure production, and potential of biogas technology in India to provide a wholistic information. A summary of the financial supports facilitated by various agencies, the cost of biogas plants, potential uses, and potential challenges in the dissemination of biogas technology in India has been discussed in this study. We anticipate that the data and interpretation provided here will help in understanding the scope of biogas technology in India and will help in formulating the policies which will support the implementation of biogas technologies in developing countries. [ABSTRACT FROM AUTHOR]

Antibiotic resistance genes (ARGs) are emerging contaminants causing serious global health concern. Interventions to address this concern include improving our understanding of methods for treating waste material of human and animal origin that are known to harbor ARGs. Anaerobic digestion is a commonly used process for treating dairy manure, and although effective in reducing ARGs, its mechanism of action is not clear. In this study, we used three ARGs to conducted a longitudinal bench scale anaerobic digestion experiment with various temperatures (28, 36, 44, and 52°C) in triplicate using fresh dairy manure for 30 days to evaluate the reduction of gene abundance. Three ARGs and two mobile genetic elements (MGEs) were studied: sulfonamide resistance gene (sulII), tetracycline resistance genes (tetW), macrolide-lincosamide-streptogramin B (MLSB) superfamily resistance genes (ermF), class 1 integrase gene (intI1), and transposase gene (tnpA). Genes were quantified by real-time quantitative PCR. Results show that the thermophilic anaerobic digestion (52°C) significantly reduced (p < 0.05) the absolute abundance of sulII (95%), intI1 (95%), tnpA (77%) and 16S rRNA gene (76%) after 30 days of digestion. A modified Collins–Selleck model was used to fit the decay curve, and results suggest that the gene reduction during the startup phase of anaerobic digestion (first 5 days) was faster than the later stage, and reductions in the first five days were more than 50% for most genes. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is an effective way to utilize the abundant resource of corn stover (CS). In this light, Ca(OH)2pretreatment alone, steam explosion (SE) pretreatment alone, and co-pretreatment of Ca(OH)2and SE were applied to improve the digestion efficiency of CS. Results showed that AD of co-pretreated CS with 1.0% Ca(OH)2and SE at 1.5 MPa achieved the highest cumulative methane yield of, which was 61.54% significantly higher (p < .01) than untreated CS. The biodegradability value of CS after co-pretreatment enhanced from 43.03% to 69.52%. Methane yield could be well fitted by the first-order model and the modified Gompertz model. In addition, composition and structural changes of CS after pretreatment were analyzed by a fiber analyzer, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The validated results indicated that co-pretreatment of Ca(OH)2and SE was efficient to improve the digestion performance of CS and might be a suitable method for agricultural waste pretreatment in the future AD industry. [ABSTRACT FROM PUBLISHER]

Agricultural residues, such as lignocellulosic materials (LM), are the most attractive renewable bioenergy sources and are abundantly found in nature. Anaerobic digestion has been extensively studied for the effective utilization of LM for biogas production. Experimental investigation of physiochemical changes that occur during pretreatment is needed for developing mechanistic and effective models that can be employed for the rational design of pretreatment processes. Various-cutting edge pretreatment technologies (physical, chemical and biological) are being tested on the pilot scale. These different pretreatment methods are widely described in this paper, among them, microaerobic pretreatment (MP) has gained attention as a potential pretreatment method for the degradation of LM, which just requires a limited amount of oxygen (or air) supplied directly during the pretreatment step. MP involves microbial communities under mild conditions (temperature and pressure), uses fewer enzymes and less energy for methane production, and is probably the most promising and environmentally friendly technique in the long run. Moreover, it is technically and economically feasible to use microorganisms instead of expensive chemicals, biological enzymes or mechanical equipment. The information provided in this paper, will endow readers with the background knowledge necessary for finding a promising solution to methane production. [ABSTRACT FROM AUTHOR]

Vinegar residue is the by-product in the vinegar production process. The large amount of vinegar residue has caused a serious environmental problem owing to its acidity and corrosiveness. Anaerobic digestion is an effective way to convert agricultural waste into bioenergy, and a previous study showed that vinegar residue could be treated by anaerobic digestion but still had room to improve digestion efficiency. In this study, steam explosion at pressure of 0.8, 1.2, and 1.5 MPa and residence time of 5, 10, 15, and 20 min were used to pretreat vinegar residue to improve methane production, respectively. Scanning electron microscopy and X-ray diffraction analyses were applied to validate structural changes of vinegar residue after steam explosion. Results showed that steam explosion pretreatment could destroy the structure of lignocellulose by removing the hemicellulose and lignin, and improve the methane yield effectively. Steam explosion-treated vinegar residue at 0.8 MPa for 5 min produced the highest methane yield of 153.58 mL gVS-1, which was 27.65% (significant, α < 0.05) more than untreated vinegar residue (120.31 mL gVS-1). The analyses of pH, total ammonia-nitrogen, total alkalinity, and volatile fatty acids showed that steam explosion did not influence the stability of anaerobic digestion. This study suggested that steam explosion pretreatment on vinegar residue might be a promising approach and it is worth further study to improve the efficiency of vinegar residue waste utilisation. [ABSTRACT FROM AUTHOR]

Getting over recalcitrance of lignocellulose is effective way to fuel production from lignocellulosic biomass. In current work, different pretreatments were applied to enhance the digestibility of corn stover (CS). Results showed that steam explosion (SE)-treated CS produced maximal methane yield (223.2 mL/g vs ) at 1.2 MPa for 10 min, which was 55.2% more than untreated (143.8 mL/g vs ). Whereas 1.5% KOH-treated CS produced maximum methane yield of 208.6 mL/g vs , and significantly ( α < 0.05) improved 45.1% with respect to untreated. Sequent pretreatment of potassium hydroxide and steam explosion (SPPE) (1.5% KOH-1.2 MPa, 10 min) achieved a very significant ( α < 0.01) improvement (80.0%) of methane yield (258.8 mL/g vs ) compared with untreated CS. Methane production could be well explained by the first-order and modified Gompertz models. Besides, SEM, FTIR, and XRD analyses validated structural changes of CS after SPPE. SPPE might be a promising method to pretreat CS in the future AD industry. [ABSTRACT FROM AUTHOR]

Commercial digesters handling complex waste and organic overloading often encounter unbalanced conditions or failures. With limited studies on the digester recovery from an industry-based waste stream, a complex and high-strength digestate containing up to 79 g COD l−1 from acidified commercial digester was investigated for biochar and alkaline treatments. The addition of biochar and calcium hydroxide successfully decomposed excessive volatile fatty acid up to 18.9 ± 2.5 g l−1 and resumed methane production. The maximum methane yield was obtained from the digester amended with biochar (373.4 ± 6.0 ml g COD−1), followed by calcium hydroxide (350.1 ± 2.5 ml g COD−1). Calcium hydroxide treatment showed a shorter lag phase than the biochar by 44%. Methane production could not be recovered by using sodium hydroxide or untreated digester. This study provides a strategic approach to justify the use of alkalis for restoring sour digesters from industry-based waste streams. • Alkali additives recovered sour digester with initial 79 gCOD l−1 and 19 gVFA l−1. • Sour digestate taken from upset commercial digester presented complex waste stream. • Biochar and calcium hydroxide successfully recovered methane production. • Key process parameters are crucial to justify suitable alkaline treatment. [ABSTRACT FROM AUTHOR]

Highlights: [•] Co-digestion of CM and CS were investigated under batch and continuous conditions. [•] CSTR showed stable methane yield of 223±7mL/gVSadded at OLR of 4gVS/L/d. [•] Post-digestion of digestate gave extra energy yield up to 2.6MJ/kgVSadded. [•] Pyrolysis of digestate could produce valuable pyrolysis gas with LCV of 10.9MJ/m3. [ABSTRACT FROM AUTHOR]

Abstract: The anaerobic digestion of onion residual from an onion processing plant was studied under batch-fed and continuously-fed mesophilic (35 ± 2 °C) conditions in an Anaerobic Phased Solids (APS) Digester. The batch digestion tests were performed at an initial loading of 2.8 gVS L−1 and retention time of 14 days. The biogas and methane yields, and volatile solids reduction from the onion residual were determined to be 0.69 ± 0.06 L gVS−1, 0.38 ± 0.05 L CH4 gVS−1, and 64 ± 17%, respectively. Continuous digestion tests were carried out at organic loading rates (OLRs) of 0.5–2.0 gVS L−1 d−1. Hydrated lime (Ca(OH)2) was added to the APS-Digester along with the onion residual at 16 mg Ca(OH)2 gVS−1 to control the pH of the biogasification reactor above 7.0. At steady state the average biogas yields were 0.51, 0.56, and 0.62 L gVS−1 for the OLRs of 0.5, 1.0, and 2.0 gVS L−1 d−1 respectively. The methane yields at steady state were 0.29, 0.32, and 0.31 L CH4 gVS−1 for the OLRs of 0.5, 1.0, and 2.0 gVS L−1 d−1 respectively. The study shows that the digestion of onion residual required proper alkalinity and pH control, which was possible through the use of caustic chemicals. However, such chemicals will begin to have an inhibitory effect on the microbial population at high loading rates, and therefore alternative operational parameters are needed. [Copyright &y& Elsevier]

Abstract: A process model was developed to predict the mass and energy balance for a full-scale (115td−1) high-solids anaerobic digester using research data from lab and pilot scale (1–3000kgd−1 wet waste) systems. Costs and revenues were estimated in consultation with industry partners and the 20-year project cash flow, net present worth (NPW), simple payback, internal rate of return, and revenue requirements were calculated. The NPW was used to compare scenarios in order to determine the financial viability of using a generator for heat and electricity or a pressure swing adsorption unit for converting biogas to compressed natural gas (CNG). The full-scale digester consisted of five 786m3 reactors (one biogasification reactor and four hydrolysis reactors) treating a 50:50 mix (volatile solids basis) of food and green waste, of which 17% became biogas, 32% residual solids, and 51% wastewater. The NPW of the projects were similar whether producing electricity or CNG, as long as the parasitic energy demand was satisfied with the biogas produced. When producing electricity only, the power output was 1.2MW, 7% of which was consumed parasitically. When producing CNG, the system produced 2hm3 y−1 natural gas after converting 22% of the biogas to heat and electricity which supplied the parasitic energy demand. The digester system was financially viable whether producing electricity or CNG for discount rates of up to 13%y−1 without considering debt (all capital was considered equity), heat sales, feed-in tariffs or tax credits. [Copyright &y& Elsevier]

Abstract: This research was conducted to develop an integrated rotary drum reactor (RDR)-anaerobic-phased solids (APS) digester system for the treatment of municipal solid waste (MSW) to produce biogas energy and achieve waste reduction. A commercial RDR facility was used to provide a 3-d pretreatment and sufficient separation of the organics from MSW and then the organics were digested in a laboratory APS-digester system for biogas production. The organics generated from the RDR contained 50% total solids (TS) and 36% volatile solids (VS) on wet basis. The APS-digester was started at an organic loading rate (OLR) of 3.1gVSL−1 d−1 and operated at three higher OLRs of 4.6, 7.7 and 9.2gVSL−1 d−1. At the OLR of 9.2gVSL−1 d−1 the system biogas production rate was 3.5LL−1 d−1 and the biogas and methane yields were 0.38 and 0.19LgVS−1, respectively. Anaerobic digestion resulted in 38% TS reduction and 53% VS reduction in the organic solids. It was found that the total VFA concentration reached a peak value of 15,000mgL−1 as acetic acid in the first 3d of batch digestion and later decreased to about 500mgL−1. The APS-digester system remained stable at each OLRs for over 100d with the pH in the hydrolysis reactors in the range of 7.3–7.8 and the pH in the biogasification reactor in 7.9–8.1. The residual solids after the digestion had a high heating value of 14.7kJgTS−1. [Copyright &y& Elsevier]

Abstract: Biogas and methane yields of food and green wastes and their mixture were determined using batch anaerobic digesters at mesophilic (35±2°C) and thermophilic (50±2°C) temperatures. The mixture was composed of 50% food waste and 50% green waste, based on the volatile solids (VS) initially added to the reactors. The thermophilic digestion tests were performed with four different feed to inoculum (F/I) ratios (i.e., 1.6, 3.1, 4.0 and 5.0) and the mesophilic digestion was conducted at one F/I (3.1). The results showed that the F/I significantly affected the biogas production rate. At four F/Is tested, after 25days of thermophilic digestion, the biogas yield was determined to be 778, 742, 784 and 396mL/g VS for food waste, respectively; 631, 529, 524 and 407mL/g VS for green waste, respectively; and 716, 613, 671 and 555mL/g VS for the mixture, respectively. About 80% of the biogas production was obtained during the first 10days of digestion. At the F/I of 3.1, the biogas and methane yields from mesophilic digestion of food waste, green waste and their mixture were lower than the yields obtained at thermophilic temperature. The biogas yields were 430, 372 and 358mL/g VS, respectively, and the methane yields were 245, 206, and 185mL/g VS, respectively. [Copyright &y& Elsevier]

Abstract: The effects of the addition of enzyme products containing cellulase, hemicellulase, and β-glucosidase to anaerobic digestion systems were studied using Jose Tall Wheat Grass (wheat grass) as a model substrate. Anaerobic digestion tests were performed using batch reactors operated at 50°C. The application of enzyme products in three digestion configurations were simulated and investigated: (1) enzyme addition to a single-stage digester, (2) pre-treatment of wheat grass with enzymes followed by a single-stage anaerobic digestion, and (3) enzyme addition to the first stage (hydrolysis and acidification) of a two-stage digestion system. The enzyme products showed positive effects on the solubilization of wheat grass when used alone to treat the wheat grass. However, no significant differences in biogas and methane yields, and volatile solids reduction resulted when the enzyme products were tested in the anaerobic digestion systems. This reveals that the microorganisms present in the inoculum were effective in carrying out the digestion of wheat grass. The types of microorganisms present in the inoculum were identified using 16S rRNA sequence analysis. A comparison of the sequences between the different inocula revealed that the prevalent operational taxonomic units were similar, but that the acidified inoculum contained a higher percentage of the species Thermotogae. [Copyright &y& Elsevier]

Abstract: The co-digestion of onion juice and aerobic wastewater sludge produced from an onion processor using an anaerobic mixed biofilm reactor (AMBR) was investigated for biogas energy production potential and waste treatment. Two experiments were conducted to study the performance of an AMBR at different organic loading rates (OLRs) using different mixtures of onion juice and aerobic sludge. In the first experiment, the OLR was increased from 1.24 to 4.37gVS/L/d by increasing the amount of onion juice in the feed mixture while maintaining a constant amount of aerobic sludge. When the OLR reached 4.37gVS/L/d, the AMBR failed as indicated by decreased biogas production and pH. Increase of carbon to nitrogen ratio (C/N) from 13.7 to 20.3 and lack of proper alkalinity were suspected to be the causes for the failure. In the second experiment, the C/N of the feed mixture was maintained at about 15 while the OLR was increased from 1.40 to 3.60gVS/L/d. The digester showed stable performance. The average biogas and methane yields of the two experiments were 0.62±0.05L/gVS and 0.37±0.08L/gVS, respectively. It was concluded that the C/N of about 15 was recommended for treating the mixture of onion juice and aerobic sludge. [Copyright &y& Elsevier]

Abstract: Food waste collected in the City of San Francisco, California, was characterized for its potential for use as a feedstock for anaerobic digestion processes. The daily and weekly variations of food waste composition over a two-month period were measured. The anaerobic digestibility and biogas and methane yields of the food waste were evaluated using batch anaerobic digestion tests performed at 50°C. The daily average moisture content (MC) and the ratio of volatile solids to total solids (VS/TS) determined from a week-long sampling were 70% and 83%, respectively, while the weekly average MC and VS/TS were 74% and 87%, respectively. The nutrient content analysis showed that the food waste contained well balanced nutrients for anaerobic microorganisms. The methane yield was determined to be 348 and 435mL/gVS, respectively, after 10 and 28 days of digestion. The average methane content of biogas was 73%. The average VS destruction was 81% at the end of the 28-day digestion test. The results of this study indicate that the food waste is a highly desirable substrate for anaerobic digesters with regards to its high biodegradability and methane yield. [Copyright &y& Elsevier]

Abstract To improve the methane production of wheat straw (WS), the mono-pretreatment (MP) and co-pretreatment (CP) of WS with KOH and Ca(OH) 2 were conducted in this study. The results showed that the MP with KOH presented better effects than the MP with Ca(OH) 2. However, the CP with 2% KOH combined with 1% Ca(OH) 2 displayed similar effects to those of the MP with 3% KOH, obtaining the cumulative methane yield of 239.8 mL g VS −1 and an improved biodegradability from 56.37% of raw WS to 66.10%. Methane production and kinetic analyses suggested that 2% KOH combined with 1% Ca(OH) 2 was the ideal condition of alkaline pretreatment for anaerobic digestion of WS. The mechanism for the improvement in methane production was clearly described by biochemical component, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analyses. Moreover, preliminary economics and energy potential analyses also confirmed that alkaline co-pretreatment was a reasonable method, which not only gave important guidance for future utilization of WS waste but also showed useful reference for the efficient pretreatment of other lignocellulosic wastes. Graphical abstract Image 1 Highlights • 2% KOH combined with 1% Ca(OH) 2 could replace 3% KOH to pretreat WS before AD. • The highest CMY and B D of WS were 239.8 mL g VS −1 and 66.10%, respectively. • Alkaline co-pretreatment was more economically reasonable than mono-pretreatment. • Energy potential for AD of WS after co-pretreatment was 5.09 × 1012 MJ/year. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) of vinegar residue was investigated in continuously stirred tank reactor (CSTR). The influence of organic loading rate (OLR) and effluent recirculation on AD performance of vinegar residue was tested. Five OLRs, 1.0, 1.5, 2.0, 2.5, and 3.0 g vs L −1 d −1 , were used. The highest volumetric methane productivity of 581.88 mL L −1 was achieved at OLR of 2.5 g vs L −1 d −1 . Effluent reflux ratio was set as 50%, the results showed that effluent recirculation could effectively neutralize the acidity of vinegar residue, raise the pH of the feedstock, and enhance the buffering capacity of the AD system. Anaerobic digestion of vinegar residue could be a promising way not only for converting this waste into gas energy but also alleviating environmental pollution which might be useful for future industrial application. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) has been proven to be an effective green technology for producing biomethane while reducing environmental pollution. The interspecies electron transfer (IET) processes in AD are critical for acetogenesis and methanogenesis, and these IET processes are carried out via mediated interspecies electron transfer (MIET) and direct interspecies electron transfer (DIET). The latter has recently become a topic of significant interest, considering its potential to allow diffusion-free electron transfer during the AD process steps. To date, different multi-heme c-type cytochromes, electrically conductive pili (e-pili), and other relevant accessories during DIET between microorganisms of different natures have been reported. Additionally, several studies have been carried out on metagenomics and metatranscriptomics for better detection of DIET, the role of DIET's stimulation in alleviating stressed conditions, such as high organic loading rates (OLR) and low pH, and the stimulation mechanisms of DIET in mixed cultures and co-cultures by various conductive materials. Keeping in view this significant research progress, this study provides in-depth insights into the DIET-active microbial community, DIET mechanisms of different species, utilization of various approaches for stimulating DIET, characterization approaches for effectively detecting DIET, and potential future research directions. This study can help accelerate the field's research progress, enable a better understanding of DIET in complex microbial communities, and allow its utilization to alleviate various inhibitions in complex AD processes. [Display omitted] [ABSTRACT FROM AUTHOR]

This study quantifies the financial and environmental impacts of a microalgal bioenergy system that attempts to maximize circular flows by recovering and reusing the carbon, nutrients, and water within the system. The system produces microalgal biomass using liquid digestate of an anaerobic digester that processes 45 metric tons of food waste and generates 28.6 m3 of permeate daily in California, and three energy production scenarios from the biomass are considered: producing biodiesel, electricity, and both. In all scenarios, the resulting energy products delivered only modest reductions in environmental impacts as measured by carbon dioxide equivalent emissions. The carbon intensities (CIs) of biodiesel from this study were 91.0 gCO 2 e/MJ and 93.3 gCO 2 e/MJ, which were lower than 94.71 gCO 2 e/MJ of conventional petroleum diesel, and the CI of electricity from this study was 70.6 gCO 2 e/MJ, lower than the average electricity grid CI in California (82.92 gCO 2 e/MJ). The economic analysis results show that generating electricity alone can be profitable, while biodiesel produced via this system is not cost competitive with conventional diesel due to high capital expenses. Thus, generating electricity in lieu of biodiesel appears to be a better option to maximize the use of waste flows and supply lower-carbon energy. [Display omitted] • Permeate from a digester had sufficient nutrients for microalgae cultivation. • Combining anaerobic digestion and microalgae limitedly reduced environmental impacts. • Electricity generation better than biodiesel financially and environmentally. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this research was to develop an integrated process to produce biogas and high-quality particleboard using saline creeping wild ryegrass (CWR), Leymus triticoides through anaerobic digestion (AD). Besides producing biogas, AD also serves as a pretreatment method to remove the wax layer of CWR for improving binding capability and then the residue is used to produce high-quality particleboard. CWR was digested for three time periods, 15, 22, and 33 days with the volatile solid (VS) loading of 10g-VS/L-sludge and the food to microorganism (F/M) ratio of 1.41. The highest biogas yield after digestion for 33 days was 251mL/g-VS, which is corresponded to energy of 8419BTU/kg-dry CWR. The highest methane content of biogas was 63%. Compared with particleboards manufactured from urea formaldehyde (UF) and untreated CWR, the mechanical and long-term (24h) water resistance properties of particleboards made from UF and 33-day AD CWR residue were statistically significantly improved, except for modulus of elasticity (MOE). For example, the modulus of rupture (MOR) was increased by 39%. The results indicated that the integrated process could be a cost-effective and environmentally friendly method for producing bioenergy and particleboard with agricultural residues. [Copyright &y& Elsevier]

This study was conducted to determine the characteristics and biogas production potential of organic materials separated from municipal solid wastes using a rotary drum reactor (RDR) process. Four different types of wastes were first pretreated with a commercial RDR system at different retention times (1, 2 and 3 d) and the organic fractions were tested with batch anaerobic digesters with 2.6gVSL−1 initial loading. The four types of waste were: municipal solid waste (MSW), a mixture of MSW and paper waste, a mixture of MSW and biosolids, and a mixture of paper and biosolids. After 20 d of thermophilic digestion (50±1°C), it was found that the biogas yields of the above materials were in the range of 457–557mLgVS−1 and the biogas contained 57.3–60.6% methane. The total solid and volatile solid reductions ranged from 50.2% to 65.0% and 51.8% to 66.8%, respectively. For each material, the change of retention time in the RDR from 1 to 3d did not show significant (α =0.05) influence on the biogas yields of the recovered organic materials. Further studies are needed to determine the minimum retention time requirements in the RDR system to achieve effective separation of organic from inorganic materials and produce suitable feedstock for anaerobic digesters. [Copyright &y& Elsevier]

The effect of bioaugmentation with different microorganisms on anaerobic digestion to mitigate the ammonia inhibition problem was investigated. Seven pure strains of microorganisms (including obligate aceticlastic methanogen, facultative aceticlastic methanogen, hydrogenotrophic methanogen, syntrophic acetate oxidizing bacteria (SAOB) were selected and thirteen bioaugmentation approaches were tested. Bioaugmentation with hydrogenotrophic methanogen Methanobrevibacter smithii (MBS) and SAOB Syntrophaceticu schinkii together was the optimal choice, methane production (MP) was 71.1% higher than that in Blank, the activity of hydrogenotrophic methanogenesis was greatly heightened according to specific methanogenic activity analysis. Bioaugmentation with facultative aceticlastic methanogen Methanosarcina barkeri (MSB) alone without SAOB addition was also proven efficient (MP was 59.7% higher than that in Blank), both aceticlastic and hydrogenotrophic methanogenesis were enhanced. Further evaluation with carbon isotope fractionations analysis indicated that balancing the activities of the aceticlastic and hydrogenotrophic methanogenic pathways is of great importance. 16s rRNA gene sequencing results showed that Methanobacterium spp. and Methanosaeta spp. were the dominant archaea in all 14 reactors. Nevertheless, bioaugmentation with Methanosaeta spp. did not result in a positive effect on MP. On the other hand, Methanobrevibacter spp. and Methanosarcina spp. were non-dominant archaea (even after bioaugmentation with MBS or MSB, the relative abundances were still poor (<2%)), but displayed pivotal roles in determining the overall microbial consortium and, in turn, improved the overall performance. Graphical abstract Image 1 Highlights • Bioaugmentation could achieve 71% increased methane production (MP). • Bioaugmentation with Syntrophaceticu smithii + Methanobrevibacter spp. was optimum. • Methanosarcina spp. bioaugmented alone was efficient with 59.7% increased MP. • Enhancement of both aceticlastic and hydrogenotrophic methanogenesis is important. • Methanobrevibacter and Methanosarcina spp. were non-dominant but important archaea. [ABSTRACT FROM AUTHOR]

Highlights • Swine slaughterhouse waste produced a maximum methane yield of 999.2 mL/g VS. • Lipid hydrolysis led to serious accumulation of linoleic, oleic and palmitic acids. • Increase of palmitic acid produced by degradation of oleic acid was observed. • Predominant microorganisms were Clostridium , Syntrophomonas and Methanospirillum. Abstract This study investigated methane production, long-chain fatty acids (LCFAs) profile, and predominant microorganisms in anaerobic digestion (AD) of lipid-rich swine slaughterhouse waste (SSW). The maximum methane yield was 999.2 mL/g VS. LCFAs, as inhibitory hydrolysis products, accumulated first to 1165 mg/L on day 3, and then decreased sharply to 125.7 mg/L on day 9, and finally were degraded to 20 mg/L on day 27. Linoleic acid (C18:2), oleic acid (C18:1) and palmitic acid (C16:0) were the dominant LCFAs. The easy conversion of C18:1 to C16:0 compared with difficult degradation of C16:0 resulted in an increase of C16:0 on day 4–6. Predominant microorganisms were Clostridium , Syntrophomonas and Methanospirillum. This study proved the high methane potential of lipid-rich SSW and gained insights into the degradation process by analysis of intermediates of LCFAs and predominant microorganisms. The results can provide valuable guidance for efficient utilization of this waste to produce methane in future. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is the most abundant natural resource with high biomethane potential. However, complex structure of lignocellulosic biomass has hampered the efficient utilization of this bioresource. Previous studies have investigated the overall anaerobic digestion performance of lignocellulosic biomass, but the individual participation of each lignocellulosic component during anaerobic digestion remained unclear. Thus, this study investigated the methane production characteristics of cellulose, hemicellulose, lignin and their mixtures along with the microbial communities involved in anaerobic digestion. The results showed that the biomethane potential of cellulose was higher than that of hemicellulose; however, hemicellulose was hydrolysed more quickly than cellulose, while lignin was very difficult to be digested. The higher concentrations of acetic, n -butyric and n -valeric acids hydrolysed from the hemicellulose resulted in a lower pH and more severe inhibition on methane production than that of cellulose, and the methanogenesis gradually recovered after pH adjustment. The co-digestion of cellulose and hemicellulose increased the methane yield and biodegradability compared to mono-digestions. The addition of lignin to cellulose brought more significant decrease in the methane yield of cellulose than that of hemicellulose. Substrate-related bacteria such as Clostridium sensu stricto , Lutaonella , Cloacibacillus and Christensenella showed higher relative abundance in cellulose digestate, and sugar-fermenting bacteria such as Saccharofermentans , Petrimonas and Levilinea were more rich in the digestate of hemicellulose. Moreover, methanogenic Methanospirillum and Methanothrix likely contributed to the methane production of cellulose, while aciduric methanogens from Methanobrevibacter , Methanomassiliicoccus , Methanobacterium and Methanoculleus contributed to that of hemicellulose. This study provides a deeper understanding of the mechanism in the bioconversion of lignocellulosic biomass during anaerobic digestion. [ABSTRACT FROM AUTHOR]

The effects of ammonia on methane production, methanogenesis pathway, microbial community, and reactor performance were investigated in this study. More than 20% of methane production loss was observed in mesophilic and thermophilic reactors when the ammonia level exceeded 2 and 5 g NH 4 + -N/L, respectively. The volatile fatty acid (VFA) data indicated that acetogenesis and methanogenesis are strongly influenced by ammonia inhibition under the mesophilic condition, while methanogenesis was mainly affected under thermophilic condition. No evident methanogenesis pathway shift was found in the mesophilic reactor, whereas the increase in NH 4 + -N concentration to more than 5 g/L led to a clear shift from aceticlastic to complex and flexible pathways, thereby significantly enriching the hydrogenotrophic pathway in the thermophilic reactor. The function and response of the microbial community to ammonia inhibition were consistent despite the difference in population and diversity under mesophilic and thermophilic conditions. [ABSTRACT FROM AUTHOR]

Municipal solid waste (MSW) contains a large fraction of biodegradable organic materials. When disposed in landfills, these materials can cause adverse environmental impact due to gaseous emissions and leachate generation. This study was performed with an aim of effectively separating the biodegradable materials from a Mechanical Biological Treatment (MBT) facility and treating them in well-controlled anaerobic digesters for biogas production. The rotary drum reactor (RDR) process (a sub-process of the MBT facilities studied in the present work) was evaluated as an MSW pretreatment technology for separating and preparing the biodegradable materials in MSW to be used as feedstock for anaerobic digestion. The RDR processes used in six commercial MSW treatment plants located in the USA were surveyed and sampled. The samples of the biodegradable materials produced by the RDR process were analyzed for chemical and physical characteristics as well as anaerobically digested in the laboratory using batch reactors under thermophilic conditions. The moisture content, TS, VS and C/N of the samples varied between 64.7 and 44.4%, 55.6 to 35.3%, 27.0 to 41.3% and 24.5 to 42.7, respectively. The biogas yield was measured to be between 533.0 and 675.6 mL g −1 VS after 20 days of digestion. Approximately 90% of the biogas was produced during the first 13 days. The average methane content of the biogas was between 58.0 and 59.9%. The results indicated that the biodegradable materials separated from MSW using the RDR processes could be used as an excellent feedstock for anaerobic digestion. The digester residues may be further processed for compost production or further energy recovery by using thermal conversion processes such as combustion or gasification. [ABSTRACT FROM AUTHOR]

Nut residues are common wastes which abandoned with more than 5 million tons in China annually. In this study, anaerobic digestion (AD) was firstly applied to treat 18 kinds of nut residues and their characterization, methane production, and kinetics were comprehensively investigated. Results implied that nut residues with low lignin content, high lipid and carbohydrate contents, such as lotus seed shells (expressed the highest biodegradability of 95.11% among others), showed good performance in AD. Kinetic analysis proved that modified Gompertz and Cone model were well fitted to describe the AD process of nut residues. Multiple linear regression equation was developed to determine the correlation between experimental methane yield and biochemical compositions of different nut residues, based on which, the highest cumulative methane yield could be predicted. The findings of this research provided useful knowledge for bioconversion of nut waste to renewable energy, and also showed a promising possibility for practical industrial application in future. [ABSTRACT FROM AUTHOR]

A large amount of sheep dung (SD) produced on farms in China is a potential feedstock for production of clean energy in the form of biogas. Similarly, waste paper can be a notable energy source that is worth exploiting. In this study, we assessed the feasibility of co-digesting nitrogen-rich SD with the carbon-rich corrugated board (CB) or waste office paper (OP) in varying volatile solids (VS) ratios, to produce methane. Synergistic effect of co-digesting SD with CB and SD with OP on methane production was found in this study. The highest methane yields of 151.62 and 198.85 mL/g-VS were obtained during the co-digestions of SD with CB at 4:1 ratio (SDCB) and SD with OP at 2:3 ratio (SDOP), respectively. High-throughput 16 S rRNA gene sequencing demonstrated that the microbial diversity and richness in SDCB and SDOP co-digests were higher than in SD and OP mono-digests, respectively. Characteristic bacteria and archaea in the digests were strongly substrate-related and might contribute to methane production. The validated results indicated that methane production through anaerobic co-digestion of SD and waste paper can be an efficient way that could not only reduce environmental pollution but also contribute to methane production. [ABSTRACT FROM AUTHOR]

This study systematically investigated the anaerobic digestibility of durian shell and focused on maximizing the methane yield using response surface methodology. Results showed in the feedstock to inoculum (F/I) ratio range of 0.2–2, a lower value was preferred. Meanwhile the methane yield showed a sharp rise first followed by a decline as the organic loading (OL) increased from 3 to 27 g VS/L. The highest experimental methane yield (EMY) was calculated to be 170.6 ml/g VS at F/I ratio of 0.2 and organic loading of 20.45 g VS/L. To make the combination of F/I ratio and OL more practical, 0.5 was set as the optimum F/I ratio, when the highest EMY was obtained to be 165.0 ml/g VS at the OL of 20.45 g VS/L. Characteristics of final effluent implied the anaerobic system was stable. This study is important to promote the application of durian shell into anaerobic digestion from theory to practice. [ABSTRACT FROM AUTHOR]

Huge amounts of fruit residues are produced and abandoned annually. The high moisture and organic contents of these residues makes them a big problem to the environment. Conversely, they are a potential resource to the world. Anaerobic digestion is a good way to utilize these organic wastes. In this study, the biomethane conversion performances of a large number of fruit residues were determined and compared using batch anaerobic digestion, a reliable and easily accessible method. The results showed that some fruit residues containing high contents of lipids and carbohydrates, such as loquat peels and rambutan seeds, were well fit for anaerobic digestion. Contrarily, residues with high lignin content were strongly recommended not to be used as a single substrate for methane production. Multiple linear regression model was adopted to simulate the correlation between the organic component of these fruit residues and their experimental methane yield, through which the experimental methane yield could probably be predicted for any other fruit residues. Four kinetic models were used to predict the batch anaerobic digestion process of different fruit residues. It was shown that the modified Gompertz and Cone models were better fit for the fruit residues compared to the first-order and Fitzhugh models. The first findings of this study could provide useful reference and guidance for future studies regarding the applications and potential utilization of fruit residues. [ABSTRACT FROM AUTHOR]

A pretreatment process for wheat straw using potassium hydroxide (KOH) and recycled black liquor as a treatment reagent was developed and the minimum fresh chemical and water requirement were determined. Black liquor recycling in the pretreatment process resulted in a 75% reduction in fresh water use and 25% in KOH use, when compared to no recycling. It was found that after five batches of treatment, the concentrations of reducing sugar, chemical oxygen demand (COD), and K + in black liquor, reached stable levels. During the pretreatment with black liquor recycling, 32–35% lignin was reduced in wheat straw. The pretreated straw showed reducing sugar yield of 336–366 mg g −1 [total solid (TS)] and methane yield of 290–303 mg g −1 [volatile solid (VS)] when subjected to enzymatic hydrolysis and anaerobic digestion, respectively. [ABSTRACT FROM AUTHOR]

The pretreatment of wheat straw with potassium hydroxide (KOH) at ambient temperature (20 °C) was investigated. The pretreatment effects on chemical composition and physical structures, and subsequent enzymatic hydrolysis and anaerobic digestion were evaluated. Wheat straw at 10% total solids (TS) was treated with KOH solution for 24 h at a wide range of KOH loadings from 2% to 50% (w/w dry basis). Higher KOH loading resulted in higher lignin reduction from the straw and chemical oxygen demand (COD) in the resulting black liquor. Maximum lignin reduction of 54.7% was observed at 50% KOH loading. In comparison to untreated straw, specific hydrolysis yields achieved 14.0–92.3% over the range of 2–50% KOH loading, and methane yields increased 16.7–77.5% for KOH loadings of 10–50%, respectively. Accounting for losses during pretreatment, 20% KOH loading resulted in maximum overall reducing sugar yield and methane yield and therefore is the recommended loading for pretreatment under these conditions. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) is a widely applied technology for treating organic wastes to generate renewable energy in the form of biogas. The effectiveness of AD process depends on many factors, among which the most important is the presence of active and healthy microbial community in the anaerobic digesters, which needs to be explored. However, the deciphering of microbial populations and their functions during the AD process of different materials is still incomplete, which restricts the understanding of its long-term performance under different operational conditions. This review describes the type, morphology, functions, and specific growth conditions of commonly found hydrolytic, acidogenic, acetogenic bacteria, and archaea during the AD process. The effects of microbes on the performance and stability of the digestion process are also presented. Furthermore, the article offers a deep understanding of the AD management strategies for the enhancement of methane production and the efficiency of the energy conversion process of various organic wastes. Unlabelled Image • Systematic study on roles of bacteria and archaea participating in four stages of anaerobic digestion is given. • Microbial ecology of digesters is strongly affected by temperature, organic loading rate, and F/I ratio. • The review gives deep understanding of the anaerobic digestion strategies to enhance methane production. [ABSTRACT FROM AUTHOR]

1 – Microbial synthesis reaction zone; 2 – Gas-liquid mixing zone; 3 – Aeration buffer zone; 4 – Gas-solid–liquid separation zone; 5 – Liquid circulating tube; 6 – Import of organic mixture; 7 – Gas inlet; 8 – Sludge discharge zone; 9 – Aerator; 10 – Uniform water distribution device; 11 – Gas-phase stabilization zone; 12 – Gas circulating pipe; 13 – Gas outlet. • ADM1 was modified and extended for syngas biomethanation simulation. • ADM1_modified was established based on lab-scale reactors and R2 all > 0.86. • Pilot-scale reactor data was used for model validation. • Gene sequencing and model simulation obtained similar methanogenic pathway results. The Anaerobic Digestion Model No.1 (ADM1) was extended for simulation of syngas biomethanation from lab-scale to pilot-scale, with the development of the gas–liquid mass transfer, the inhibition equations, and the biochemical reaction of CO and H 2. In the lab-scale reactor, after increasing the syngas flow rate and syngas loading, the syngas conversion efficiency into methane increased from less than 68% to over 95%. The ADM1_modified was developed based on lab-scale data, and the simulation values fitted the experimental results well with R2 values higher than 0.86. The data from the pilot-scale reactor was then used for model validation, and methane production (MP) predictions matched well with the measured data (R2 > 0.83). Methanogenic pathways were further explored and compared by using high-throughput 16S rRNA gene sequencing and the ADM1_modified simulation, and the results from the two methods were highly similar. The established ADM1_modified could be used to describe or predict the syngas biomethanation process macroscopically and microscopically. [ABSTRACT FROM AUTHOR]

• Bioaugmentation was confirmed stable to mitigate ammonia inhibition in long-term operation. • 49% increment was achieved in MSH + SS + MBS with both two pathways enhanced. • Bioaugmentation stains should be properly selected to achieve a synergistic effect. • Methanosarcina spp. performed different methanogenic pathway in different bottles. • Methanogenic pathway simulated by ADM1 is consistent with the microbial analysis. The effect of different bioaugmentation strategies on anaerobic digestion related to the alleviation of ammonia inhibition was investigated in a long-term operation. The long-term operation confirmed that bioaugmentation is a stable method. A 35% increase in methane production (MP) was observed in bottles bioaugmented with Methanosarcina barkeri (MSB) or Syntrophaceticu schinkii (SS) + Methanobrevibacter smithii (MBS), and a 49% increment was obtained from the bottles bioaugmented with Methanosaeta harundinacea (MSH) + SS + MBS. Results suggest that the enhancement in both aceticlastic and hydrogenotrophic methanogenic pathways should be considered, and bioaugmentation strain should be properly selected to achieve a synergistic effect. The microbial community analysis indicated Methanosarcina spp. was the dominant archaea. Combined with specific methanogenic activity and carbon isotope fractionation analysis, it was suggested that Methanosarcina spp. performed differently in methanogenic pathways in different bottles. The abundance of COG and total enzymes in the bottles with high MP (MSB and MSH + SS + MBS) was higher than that in the other bottles. The ratio of the functional enzyme tetrahydromethanopterin S-methyltransferase subunit H (EC 2.1.1.86) to formylmethanofuran dehydrogenase subunit E (EC 1.2.99.5) and the relative abundance of enolase (EC 1.2.1.2) confirmed the aceticlastic methanogenic pathway of MSB in Group 1 and the pathway enhancement balance in MSH + SS + MBS. The modified Anaerobic Digestion Model No.1 including syntrophic acetate oxidation was used for simulation with R2 > 0.96. Simulated contribution rate data indicated that the hydrogenotrophic methanogenic pathway was dominant while both two pathways got strengthened, which is consistent with the findings of the microbial analysis. [ABSTRACT FROM AUTHOR]

An integrated treatment system with co-fermentation of food waste (FW) and syngas generated from digestate pyrolysis was verified as a promising approach to improve biofuel recovery. Syngas was injected and co-fermented with the FW at different injection volumes starting from 560 mL (Stage II). More stable methane production (MP) was exhibited in the thermophilic reactor than the mesophilic reactor. As syngas injection volume gradually increased to 5300 mL in stage V, the MP in the thermophilic reactor was about 22% higher than that in the mesophilic reactor. It was calculated that the syngas was not only almost stoichiometrically converted into CH 4 but also accelerated the digestion process of FW, resulting in the improvement of biofuel recovery. The different pathways of syngas biomethanation under the different temperatures were revealed by 16S rRNA genes analysis. Methanosaeta spp. was dominant in the mesophilic reactor and CO and H 2 could be converted into acetate and then CH 4. On the other hand, hydrogenotrophic methanogens were dominant in the thermophilic reactor indicating that CO may be converted with H 2 as the intermediary. This integrated treatment system has the potential for industrial applications and provides a useful approach for the development of a circular bio-economy. Image 1 • Anaerobic digestion, digestate pyrolysis and syngas biomethanation were integrated. • Syngas was almost stoichiometrically converted into CH 4 when co-fermented with FW. • Syngas accelerated the biodegradation of FW, leading to enhanced CH 4 production. • Hydrogenotrophic methanogens were dominant in thermophilic reactor. • Aceticlastic methanogen Methanosaeta spp. was dominant in mesophilic reactor. [ABSTRACT FROM AUTHOR]

• The OL and F/I ratio of tobacco stalks for AD were optimized via RSM. • Various pretreatments for improving methane yield from TS 116 were examined. • AHP pretreated TS 116 achieved the highest methane yield. This work firstly investigated the suitable organic loading (OL) and feed to inoculum (F/I) ratio of three kinds of tobacco stalks (TS 116 , TS 99 , and TS 85) during anaerobic digestion (AD) via response surface methodology (RSM). The highest experimental methane yield (EMY) of 148.1 mL/g VS was achieved from TS 116 at OL of 20.2 g VS/L and F/I ratio of 1.1. To further increase EMY, various pretreatments including alkaline hydrogen peroxide (AHP), NaOH, KOH, Ca(OH) 2 , HCl, and oxalic acid (H 2 C 2 O 4) were implemented on TS 116. Results showed that AHP was most effective, and the maximal EMY of 350.7 mL/g VS and biodegradability (B d) of 81.4% were obtained from 7% AHP pretreated TS 116 , which increased by 105.6% than untreated. XRD, FTIR, and SEM analyses evidenced that the structure of AHP pretreated TS 116 was strongly disrupted. This study lays the foundation for applying this waste into AD in future applications. [ABSTRACT FROM AUTHOR]