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• Inhibition of lignin in AD was ranked as: hydrolytic bacteria < acidogens < acetogens. • Lignin extraction was optimized without compromising carbohydrate utilization. • Liquid hot water treatment prior to alkali pretreatment was essential to preserve sugars. • 80% of lignin was recovered, with 35% being biologically utilizable. This study emphasized the synergistic production of bioprocessible lignin and carbohydrates during a sequential liquid hot water and alkali pretreatment of lignocellulose, facilitating their subsequent individual fermentation. Increasing the dose of alkaline lignin from 0 to 8 g/L inhibited cell growth in anaerobic digestion, with varying levels of inhibition observed in the following order: hydrolytic bacteria < acidogens < acetogens. Alkali pretreatment was adapted to maximize yields of bioprocessible lignin liquor without compromising utilization of the carbohydrates. Increasing the NaOH dose from 50 to 200 mg/g-feedstock monotonically improved lignin yields, but further increases in alkali loading led to a decline in lignin recovery. Volatile fatty acids production from anaerobic digestion of the carbohydrate moiety consistently increased with higher NaOH doses. The optimal conditions for maximizing lignin yields were determined to be 105 °C for 30 min, with NaOH loading in the range of 150–200 mg/g-feedstock, resulting in approximately 80 % lignin recovery, of which 35 % was biologically utilizable. Liquid hot water treatment prior to alkali pretreatment was confirmed as necessary to preserve carbohydrates of 0.1 g/g-feedstock at a low temperature of 70 °C. These findings are crucial for economically producing bioprocessible lignin without carbohydrate loss, a key step towards achieving full lignocellulose valorization. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass wastes are abundant resources that are usually valorized for methane-rich biogas via anaerobic digestion. Conversion of lignocellulose into volatile fatty acids (VFA) rather than biogas is attracting attention due to the higher value-added products that come with VFA utilization. This review consolidated the latest studies associated with characteristics of lignocellulosic biomass, the effects of process parameters during acidogenic fermentation, and the intensification strategies to accumulate more VFA. The differences between anaerobic digestion technology and acidogenic fermentation technology were discussed. Performance-enhancing strategies surveyed included (1) alkaline fermentation; (2) co-digestion and high solid-state fermentation; (3) pretreatments; (4) use of high loading rate and short retention time; (5) integration with electrochemical technology, and (6) adoption of membrane bioreactors. The recommended operations include: mesophilic temperature (thermophilic for high loading rate fermentation), C/N ratio (20–40), OLR (< 12 g volatile solids (VS)/(L·d)), and the maximum HRT (8–12 days), alkaline fermentation, membrane technology or electrodialysis recovery. Lastly, perspectives were put into place based on critical analysis on status of acidogenic fermentation of lignocellulosic biomass wastes for VFA production. Highlights: Strategies to enhance acidogenic fermentation of lignocellulosic biomass presented. Optimal parameters for anaerobic digestion and acidogenic fermentation are compared. Challenges of electrochemical fermentation of lignocellulosic biomass are discussed. Membrane technology and its further optimization are effective for VFAs extraction. [ABSTRACT FROM AUTHOR]

• Combined activated carbon supplement and feedstock microwave pretreatment studied. • Joint implementation effective in mitigating antibiotic resistance genes issue. • Average methane yield and CH 4 percentage increased by 10–41% and 6–29%, respectively. • Bacterial genus Treponema and methanogen genus Methanosarcina selectively enriched. • KEGG cluster and genome functional analysis validated enhanced microbial activity. Antibiotic resistance genes (ARGs) stemming from animal manure pose adverse impacts on human health and ecology and consequently cost more to treat the anaerobic digestate after manure fermentation. To jointly reduce the ARGs and improve the methane yield during anaerobic digestion (AD) of chicken manure, microwave pretreatment of manure and activated carbon supplementation were simultaneously applied and evaluated in an anaerobic digester (R1). For comparison, three other digesters, a digester (R2) fed with raw chicken manure without activated carbon, a digester (M1) fed with microwave-pretreated chicken manure and without activated carbon, and a digester (M2) fed with raw chicken manure supplemented with activated carbon, were operated in parallel. The results showed that after 47 days of AD operation, R1 achieved an 87–95% ARGs removal rate, significantly higher than that of R2 (34–58%). As the loading rate was 5.8–7.0 g volatile solids (VS)/L, the average methane yield of R1 was 0.287 L/g VS, which was 1.4-fold, 1.3-fold and 1.1-fold higher than that of R2, M1 and M2, respectively. The increased methane yield was ascribed to the combined effect of feedstock microwave pretreatment and activated carbon supplementation. Pyrosequencing analysis showed that the dominant bacterial phyla were Firmicutes , Bacteroidetes and Proteobacteria while the dominant archaeal genus were Methanosarcina , Methanothrix , Methanolinea , Methanomassiliicoccus , Methanospirillum , Methanoregula and Methanobacterium. The KEGG cluster analysis and functional analysis of genome from archaeal communities demonstrated that the dominant functions enhanced by substrate microwave pretreatment and activated carbon supplementation were linked to amino acid metabolism, carbohydrate metabolism, cell communication, energy metabolism, signaling molecules and interaction, and signal transduction. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Synergy of activated carbon and encapsulated trace element additive was studied. • Joint addition increased average methane yield by 12–23%. • Additives increased Ni bioavailability by 11–23% by increasing water soluble form. • Growth of hydrolytic, acidogenic and acetogenic bacteria selectively enhanced. • Joint addition enriched beneficial methanogens like Methanolinea and Methanosarcina. Abstract Laboratory semi-continuous anaerobic digestion (AD) experiments were performed to investigate the effects of different supplements on the AD performance of food waste, specifically activated carbon (AC), encapsulated trace element additive (ETEA) and a combination of AC + ETEA. Results indicated that the operation stability of AD was enhanced through the addition of the additives. Compared with the control digester without any additive, AC, ETEA, and AC + ETEA increased the average methane yield by 34%, 22% and 50%, respectively. Chemical speciation analyses indicated that AC + ETEA supplementation increased the proportion of water soluble form of Ni by 11–23%, compared to ETEA single addition. Real-time PCR analyses showed that AC and ETEA supplementation synergistically facilitated the growth of bacterial and archaeal communities. Microbial community structure analysis revealed that AC + ETEA favored the enrichment of hydrolytic, acidogenic and acetogenic bacteria and methanogens. [ABSTRACT FROM AUTHOR]

Abstract Complex microbial communities in anaerobic digestion (AD) system play a vital role in the production of biogas. An in-depth understanding of the microbial compositions, diversity/similarity, metabolic networks, functional gene patterns, and relations between biodiversity and system functions at the genome level could help to optimize microbial productivity and contribute to enhancement of AD process. The study of microbial communities has been revolutionized in recent years with the development of high-throughput sequencing technologies. Analysis of high-throughput sequencing data and a suitable bioinformatics analysis approach therefore plays a very critical role in the investigation of microbial metagenome. The present article reviews the overall procedure of processing metagenomics data of microbial communities for revealing metagenomics characterization using bioinformatics approaches. This includes (1) introduction of application case summary, (2) DNA extraction and high-throughput pyrosequencing, (3) processing metagenomics data using function-based bioinformatics platforms and tools, and (4) several specific bioinformatics analysis of anaerobic microbial communities. Key findings on anaerobic digestion via bioinformatics analysis are summarized. Limitations and future potential of bioinformatics approaches for analysis of metagenomics information of microbial communities are also discussed, with the hope of promoting its further development. Finally, a big-data-based precision fermentation platform using artificial neural network is proposed for integrating the bioinformatics data of microbial communities with performance of anaerobic digesters to facilitate the usage of huge metagenomics data. Graphical abstract fx1 Highlights • Biogas-producing microbial communities were analyzed using bioinformatic tools. • Comprehensive microbial community investigation aimed to optimize digestion process. • Challenges involved data storage, processing technique, reliability and application. • Collaboration of biological and computer sciences can contribute to problem solving. • A big-data-based fermentation platform by artificial neural network was proposed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A joint pretreatment method for yard waste using sludge and food waste was proposed. • An increase of 20.3–53.1% was achieved in reduction of cellulose and hemicellulose. • 23% cellulose crystallinity decreased during pretreatment period due to food waste. • Methane yield increased by 35% by co-pretreatment of sludge and 10 wt% food waste. • Bacteria Sphaerochaeta and Cellulosibacter were selectively enriched by 5–10 times. Abstract Solid waste treatment through anaerobic digestion (AD) technology contributes to energy recycling and reuse of various solid organic wastes. However, yard waste (YW) is generally recalcitrant to AD due to the presence of high cellulose and hemicellulose content, which are difficult to be hydrolyzed. In this study, to enhance hydrolysis efficiency, YW was biologically pretreated with digested sludge and supplemented with food waste (FW) before AD process. Effects of FW supplementation on pH, SCOD, cellulose and hemicellulose content and cellulose crystallinity were examined. The optimal amount of FW supplementation was determined to be 10 wt%. An increase of 6.5–20.3% in cellulose reduction and an increase of 14.8–53.1% in hemicellulose reduction in digesters was achieved within the optimal pretreatment time of 4 days. After hydrolysis, cellulose crystallinity decreased by 23% from 71% in the control digester, which was responsible for improved biodegradability of cellulose in YW. FT-IR analysis of hydrolysis mixture confirmed that partial hydrogen bonds were destroyed in digesters with supplementation of 10 wt% FW, leading to a higher extent of degradation of the feedstock. In the batch AD of FW supplemented YW, results indicated that methane yield was 35% higher than that of the control digester without FW supplementation. Pyrosequencing analysis indicated that the abundance of bacterial genus Sphaerochaeta and Cellulosibacter in subsequent digestion were enhanced by 10- and 5-folds by 10 wt% FW supplementation, respectively, and were deemed to be responsible for the enhanced anaerobic digestion performance. [ABSTRACT FROM AUTHOR]

A novel compact three-stage anaerobic digester (TSAD) was developed for high-efficiency anaerobic digestion of food waste and methane production. Through structure optimization by having three separate chambers in a single-stage anaerobic digester, hydrolysis, acidogenesis and methanogenesis were independently optimized with concomitant improvement in anaerobic digestion performance. Compared to traditional one-stage and two-stage anaerobic digesters, TSAD had a 24–54% higher methane yield at a high organic loading rate of 10 g VS FW /L. A higher volatile solid reduction rate of 83.5 ± 1.3% was also achieved in TSAD. Even at high organic loading, TSAD still presented a high buffering ability when the one-stage and two-stage digesters had already soured and failed. Pyrosequencing analysis indicated that the bacterial community in TSAD is more diverse than the control digesters. Multi-function methanogens Methanosarcina and some dominant populations with the function of acetogenesis, amino-acid-utilization and symbiosis were found to selectively enrich in TSAD. [ABSTRACT FROM AUTHOR]

• Mesophilic vs. thermophilic anaerobic digestion (MAD, TAD) of soybean curd residue. • Maximum available organic loading rate was 3.3 gVS/L for both MAD and TAD digesters. • Compared to MAD, average methane yield and VS removal of TAD were 20% and 8% higher. • Bacteroidetes dominated in MAD digester while Defluviitoga enriched in TAD digester. • Enriched hydrogenotrophic Methanothermobacter correlated well with TAD performance. To find the optimal operation parameters and provide an explanation of methanogenic pathway for methane production in mesophilic (35 °C) and thermophilic (55 °C) anaerobic digestion (MAD, TAD) of soybean curd residue (SCR), MAD and MAD were contrastively investigated for 95 days. The maximum available OLR was identified as 3.3 gVS/L for both MAD and TAD. Compared to MAD, TAD exhibited a 20% higher average methane yield (0.591 L/gVS) and a 7.5% higher volatile solids removal efficiency (74.1 ± 10.4%). Bacterial phyla Bacteroidetes , Firmicutes and Proteobacteria dominated in MAD digesters while genus Defluviitoga was selectively enriched in TAD digesters due to higher temperature and organic loading pressure. Principal coordinates analysis of methanogen community showed that both temperature and OLR were crucial environmental variables shifting the taxonomic patterns of the methanogens. The enriched methanogen genus Methanothermobacter (93%) with a hydrogenotrophic methanogenic pathway had a close correlation with the TAD performance. [ABSTRACT FROM AUTHOR]

Eco-friendly delivery carrier of trace metals is very significant to appropriate metal supplementation to improve metal bioavailability and prevent metal precipitation in anaerobic digesters. A novel encapsulated form of dry water (DW) additive was synthesized by the high-speed mixing of nickel ions solution with hydrophobic silica nanoparticles and was characterized using scanning electron microscope (SEM), nuclear magnetic resonance (NMR) and particle size analyzer. Nickel (Ni) was chosen as a model trace element. The encapsulated structure of DW additive and the feasibility of controlled release of Ni ions from DW additive in pure water and anaerobic digesters were verified. The optimal mixing speed for the highest methane yield of digesters with DW additive was determined as 800–1000 rpm. By varying stirring speed, controlled release of trace metal element (Ni) into digester was easily achieved during anaerobic digestion of food waste. The results showed that nickel ions delivery via DW additive significantly enhanced the metal bioavailability by 18.9–42.6% and process stability during 59 days of operation, resulting in an increase of 11.6–31.8% in methane yields compared to the controls. Pyrosequencing analysis indicated that bacterial communities were dominated by phyla Firmicutes , Bacteroidetes , Proteobacteria , Chloroflexi and Spirochaetes while methanogenic genus Methanolinea , Methanoculleus , Methanothrix , Methanomassiliicoccus and Methanospirillum were more abundant in archaea communities. Further, phyla Bacteroidetes , Proteobacteria and Methanoculleus were selectively enriched by the DW additive. Results indicated that it was feasible to apply the method of DW additive supplementation to enhance anaerobic digestion of food waste for biogas production by improving metal bioavailability. Image 100004 • An encapsulated dry water (DW) additive was developed for trace element delivery. • Shear stress-based controlled release of Ni2+ was achieved by varying stirring rate. • Bioavailability of nickel ions was enhanced by 19–43% via DW additive for delivery. • Methane yield increased by 12–32% due to DW additive compared to the controls. • Phyla Bacteroidetes , Proteobacteria and Methanoculleus were enriched by DW additive. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Batch study on effects of disposable plastics on food waste digestion. • PS and PP inhibited biogas production from food waste more than HDPE and WC. • Increased surface area of plastics led to greater reduction in methane yield. • Reduced contact of microbes and food waste lowered methane production. • No obvious changes to microbial consortia of food waste with or without plastics. Abstract A common challenge for the anaerobic digestion (AD) of food waste (FW) is the contamination by disposable plastic materials and utensils. The objective of this batch study was to investigate the effects of disposable plastic materials – polystyrene (PS), polypropylene (PP), high density polyethylene (HDPE) and wooden chopsticks (WC) on the AD of FW. Results showed that methane production from the AD of FW was inhibited to different extents when different materials were present in FW. PS and PP were found to reduce methane production from food waste more than HDPE and WC. The reduction in methane production was hypothesized to be due to the production of toxic plastic by-products or due to reduced contact between microbes and FW. Pyrosequencing and Field Emission Scanning Electron Microscope (FESEM) results indicated that the reduction in methane production was more likely due to the interference of good contact necessary between microbes and FW for biodegradation, and that the biological processes of AD were not affected by the contamination of plastics. Greater reductions in methane yields were also observed when the surface areas of the disposable materials were increased. Studying the effects of disposable materials on the AD of FW would provide plant operators with more information that could optimise the process of resource recovery from food waste. [ABSTRACT FROM AUTHOR]

Effects of activated carbon (AC) supplementation on anaerobic digestion (AD) of food waste were elucidated in lab- and pilot-scales. Lab-scale AD was performed in 1 L and 8 L digesters, while pilot-scale AD was conducted in a 1000 L digester. Based on the optimal dose of 15 g AC per working volume derived from the 1 L digester, for the same AC dosage in the 8 L digester, an improved operation stability coupled with a higher methane yield was achieved even when digesters without AC supplementation failed after 59 days due to accumulation of substantial organic intermediates. At the same time, color removal from the liquid phase of the digestate was dramatically enhanced and the particle size of the digestate solids was increased by 53% through AC supplementation after running for 59 days. Pyrosequencing of 16S rRNA gene showed the abundance of predominant phyla Firmicutes , Elusimicrobia and Proteobacteria selectively enhanced by 1.7-fold, 2.9-fold and 2.1-fold, respectively. Pilot-scale digester without AC gave an average methane yield of 0.466 L⋅(gVS) −1 ⋅d −1 at a composition of 53–61% v/v methane. With AC augmentation, an increase of 41% in methane yield was achieved in the 1000 L digester under optimal organic loading rate (1.6 g VS FW ·L −1 ·d −1 ). [ABSTRACT FROM AUTHOR]

[Display omitted] • Simplified inputs for pretreatment, post-pretreatment and methanogenesis arrest. • Enhanced VFA production without methanogenesis inhibitors. • Explored interplay between pH, cell viability/functionality, and VFA production. • Avoided costs in post-pretreatment and methanogenesis arrest. The pursuit of affordable biofuels necessitates continuous refinement of valorization strategies, focusing on cost-effective feedstocks, accessible bioprocessing, and high-quality products. High energy input required during various stages, including pretreatment, post-pretreatment, and methanogenesis arrest, impeded the economic lignocellulose-derived biofuels production from anaerobic digestion (AD). Addressing this challenge, an upstream process integrating synergistic alkali pretreatment and arrested AD was proposed. Results demonstrated that an optimum reactor pH 10 yielded a volatile fatty acids (VFA) titer of 3.6 gCOD/L, only 23% lower than using methanogenesis inhibitor. The study further explored the interplay between initial pH, cell viability/functionality, and VFA production by assessing cell viability and cell population demographics. This integrated approach demonstrated a VFA yield of 364 gVFA/kgTS substrate at a cost of just USD 0.2/kgVFA, encompassing post-pretreatment and methanogenesis arrest, which underscores the viability of combining pretreatment and methanogenesis arrest for cost effective and scalable biofuels production. [ABSTRACT FROM AUTHOR]

The effects of activated carbon (AC) on methane production and the fate of antibiotic resistance genes (ARGs) were evaluated through comparing the anaerobic digestion performance and transformation of ARGs among anaerobic mono-digestion of food waste, co-digestion of food waste and chicken manure, and co-digestion of food waste and waste activated sludge. Results showed that adding AC in anaerobic digesters improved methane yield by at least double through the enrichment of bacteria and archaea. Conventional digestion process showed ability in removing certain types of ARGs, such as tet A, tet X, sul 1, sul 2, cml A, flo R, and intl 1. Supplementing AC in anaerobic digester enhanced the removal of most of the ARGs in mono-digestion of food waste. The effects tended to be minimal in co-digestion of co-substrates such as chicken manure and waste activated sludge, both of which contain a certain amount of antibiotics. [ABSTRACT FROM AUTHOR]

Effects of activated carbon (AC) addition on biogas production, bacterial pathogens removal and antibiotic resistance genes (ARGs) during anaerobic digestion (AD) for food waste were investigated. Results indicate that anaerobic digesters with AC addition (R1) maintained stable operation with methane yield of 0.35 L CH 4 /L/g VS at high organic loading rate of 4.38 g VS FW /L/d while the control digesters displayed less stability and caused acidification. Some specific dominant bacteria were enriched in R1, resulting in a lower microbial biodiversity. A total of 11 bacterial pathogens and 12 ARGs was detected in the sludge samples. Compared to the control, adding AC enhanced the AD process by decreasing the relative abundance of bacterial pathogens by 18%. Moreover, AC supplementation also facilitated reduction of abundant ARGs, including tetA , tetM , tetW , tetO , tetQ , sul2 and tetX . This study may provide an ecological treatment method for AD with the addition of AC. [ABSTRACT FROM AUTHOR]

• Thermophilic food waste digestion with varied particle size of biochar was examined. • All examined biochars (<50 μm to 3 cm) significantly improved methane production. • Bacteria Thermotogae and methanogens Methanothermobacter & Methanosarcina enriched. • The synergy of hydrogenotrophic and acetoclastic methanogenic pathways was achieved. • Both technical and economic feasibility of adding biochar strategy were validated. Effectiveness of biochar addition to enhance thermophilic semi-continuous anaerobic digestion (AD) of food waste for methane production was investigated with a focus on dosage and particle size of biochar, pilot-scale application and elucidation of methanogenic pathways. Optimal dosage range of biochar was determined as 7.5 to 15 g per L working volume based on lab-scale batch AD. Effects of biochar with different particle sizes at a model dosage of 15 g/L were evaluated in a semi-continuous AD experiment, results of which showed that all the examined biochars with different particle sizes (<50 μm to 3 cm) substantially enhanced the average methane yields (0.465–0.543 L/gVS) compared to control digesters which failed due to overloading (≥3.04 gVS/L/d). No significant difference in methane yields, however, was observed among digesters with different particle sizes of biochars, except for 1–3 cm. The core reason for this phenomenon was that the biochars with different particle sizes had similar properties (e.g. density, surface area and pore size) and that the floating of large particle size (1–3 cm) of biochar with a density of 847 kg/m3 was not conducive to microbial growth. Metagenomic analysis was performed to determine the predominant microbial species and to explain the main methanogenic pathways in biochar-amended digesters using 16S rRNA sequencing. In the biochar-amended digester, bacterial phylum Thermotogae containing a major genus of Defluviitoga was selectively enriched with gradual increase of organic loadings, while simultaneously enriched methanogen genera Methanothermobacter and Methanosarcina , which showed a synergy of hydrogenotrophic and acetoclastic methanogenic pathways, jointly enhanced the methane productivity. Both technical feasibility and economic feasibility of adding biochar with simple pretreatment (e.g. smash) were validated in the pilot-scale thermophilic semi-continuous AD operations. [ABSTRACT FROM AUTHOR]

• Both CFD modelling and experiments optimized the mixing conditions in digesters. • The optimal mixing time was reduced to 2 mins/hr. • Intermittent mixing is an alternative strategy to reduce energy consumption. • Energy performance of an anaerobic digestion waste-to-energy system was simulated. • Intermittent mixing is efficient to generate sufficient biogas for net energy output. This study investigates the effect of different mixing strategies on anaerobic digestion of food waste in order to make the anaerobic digestion waste-to-energy process more energy efficient. Results showed that intermittent mixing is an alternative strategy to continuous mixing or unmixing for high efficient biogas production and energy saving. Through computational fluid dynamics modelling of fluid flow in anaerobic digesters, the mixing time was optimized to 2 mins/hr, at which point the reaction mixture is almost entirely homogeneous. The results of the model was validated with the experimental data. At an organic loading rate of 2.4 g VS FW /L/day, the semi-continuously mixed reactor maintains a higher specific methane yield of 437 mL CH 4 /g VS FW in comparison with the other controls. In addition, the semi-continuously mixed reactor has a larger proportion of Bacteroides and Methanocuelles. Based on the results of the bench scale experiment, the energy balance of the hybrid AD waste-to-energy system was simulated and evaluated. The calculated AD efficiency of the semi-continuously mixed reactor is 74.4%, which is higher than the AD efficiencies of the continuously mixed (66.9%) and unmixed reactors (14.9%). The energy balance investigated the electricity generated and the net heat output generated, in addition to self-sustaining and meeting the energy requirements of the various AD processes investigated. Based on the analysis, it was found the semi-continuous mixing is more energy efficient and sustainable to generate sufficient biogas output for the energy system to provide a net positive heat and electricity output. [ABSTRACT FROM AUTHOR]

Highlights • Microalgae growth was inhibited at NH 4 +-N concentrations above 100 mg/L. • Microalgae growth in digestate was suppressed by high NH 4 +-N and competing microbes. • Nitrification based pre-treatment was effective in alleviating NH 4 +-N toxicity. • Excellent nitrogen and phosphorus recovery from nitrified digestate by microalgae. • Integrated nitrification and algae cultivation possible using membrane bioreactors. Abstract High ammonium concentration is considered a major challenge in cultivating autotrophic microalgae in anaerobic digestate. In this research, the feasibility of applying nitrification as pretreatment to alleviate ammonium toxicity on microalgae was investigated. Batch experiments conducted in synthetic medium showed that microalgae growth was inhibited at NH 4 +-N > 100 mg/L, but NO 3 −-N was benign at concentrations as high as 350 mg/L. Microalgae growth in 2–50% digestate (v/v) was also affected adversely by invading heterotrophic microorganisms. Digestate pre-treatment using activated sludge mitigated these challenges by converting NH 4 +-N to NO 3 −-N, and reducing organics content in the digestate. Microalgae exhibited excellent growth and nutrients removal in nitrified digestate (5–30% mixed with municipal wastewater) in batch mode. For example, COD, NH 4 +-N, NO 3 −-N and PO 4 3−-P removal in 10% digestate using two-stage bacterial-microalgal process were 87%, 100%, 30% and 77%, respectively. In continuous mode, using a microalgae-based membrane photobioreactor (MPBR) operating downstream to membrane bioreactor (MBR), 91% COD, 97% NH 4 +-N and >99% PO 4 3−-P could be continuously removed from 10% digestate. Although NH 4 +-N removal in the process was mainly through nitrification, total nitrogen removal was >75% at steady state. The effects of lower NH 4 +-N toxicity in the MPBR was also manifested in terms of high microalgae biomass accumulation of about 5 g/L. These results indicate that nitrification can be a promising pretreatment for anaerobic digestate for use in microalgae cultivation. [ABSTRACT FROM AUTHOR]

A hybrid biological and thermal waste-to-energy system in lab-scale level of application was developed to combine a 1000 L anaerobic digester and a 10 KW gasifier for solid organic wastes treatment and energy generation. Energy performance of the single system (anaerobic digestion (AD) and gasification) and the integrated AD – gasification system treating blended food waste (FW) and medium-sized woods chips (WCs) by cutting or chipping were studied. The results showed that the methane yield of AD of FW was 0.52 L CH 4 /g VS/d with a volatile solid reduction rate of 85%. Producer gas with over 34% of CH 4 , H 2, and CO was generated from gasification of WCs with biochar as a by-product. A small amount of the methane-rich gas generated from AD were mixed with a large amount of producer gas generated from gasification in a gas storage tank, improving the heating value of the producer gas. The waste heat generated from the gasification of WCs was used for the heat preservation of AD, increasing the overall energy efficiency of the integrated AD-gasification system. When the treatment capacity ratio of AD to gasification is below 0.4, the integrated AD - gasification system can operate with a self-supply heat recovery system. [ABSTRACT FROM AUTHOR]

The effects of biological co-pretreatment on biogas production from anaerobic co-digestion of food waste (FW) and waste activated sludge (WAS) were investigated. FW and WAS underwent anaerobic co-pretreatment to improve hydrolysis efficiency followed by co-digestion. Results showed that the methane yield from co-digestion of co-pretreated FW and WAS was 24.6% higher than that of control substrates without pretreatment. An increase of 10.1% in solids reduction was achieved in the anaerobic digester under the optimum pretreatment time of 24 h. Compared to mono-digestion of FW with pretreatment, the combination of anaerobic co-digestion and co-pretreatment of FW and WAS resulted in a higher treatment performance and methane production due to synergistic effects of pH amendment and enhancement of WAS particles solubilization. Pyrosequencing analysis indicated that anaerobic co-pretreatment reduced the abundance of filamentous bacteria of genus Levilinea in the subsequent co-digestion, which was liable to cause a decrease in anaerobic digestion performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano-biochar application was studied for anaerobic digestion of orange peel waste. • Sewage sludge derived biochar had the highest performance among different biochars. • Nano-biochar facilitated electron transfer, hydrogen transfer and nutrition supply. • Successfully rescued failed digester relied on restore of microbial communities. • Restored key microbes included phylum Hydrogenispora and genus Methanosarcina. Nano-biochar application was investigated for anaerobic digestion of orange peel waste. The application for methane production focused on the optimization of biochar feedstock, rescue of failed digesters, and microbial succession analysis. It showed that sewage sludge (SS) derived biochar had the highest performance enhancement among the different feedstocks, which could be ascribed to the improvement of electron transfer, interspecies hydrogen transfer, and supply of trace elements. Subsequently, nano SS biochar-amended digestate was evaluated for rescuing failed digesters, and the experimental results indicated its positive roles through gradual bioaugmentation operation. The dynamic analysis of microbial succession indicated the successful application was through the mechanism of restoring partially the functional microbial communities. The major reconstruction of functional microorganisms included bacteria phyla Hydrogenispora (24.5%) and Defluviitoga (18.8%) as well as methanogenic genera of Methanosarcina (41.5%) and Methanobacterium (27.3%). These findings would contribute to rescuing failed anaerobic digesters by bioaugmentation with biochar-amended digestate. [ABSTRACT FROM AUTHOR]

To manage the mixture of food waste and plastic waste, a hybrid biological and thermal system was investigated for converting plastic-containing food waste (PCFW) into renewable energy, focusing on performance evaluation, microbial community analysis, and energy balance assessment. The results showed that anaerobic digestion (AD) of food waste, polyethylene (PE)-containing food waste, polystyrene (PS)-containing food waste, and polypropylene (PP)-containing food waste generated a methane yield of 520.8, 395.6, 504.2, and 479.8 mL CH 4 /gVS, respectively. CO 2 gasification of all the plastic-containing digestate produced more syngas than pure digestate gasification. Syngas from PS-digestate reached the maximum yield of 20.78 mol/kg. During the digestate-derived-biochar-amended AD of PCFW, the methane yields in the biochars-amended digesters were 6–30% higher than those of the control digesters. Bioinformatic analysis of microbial communities confirmed the significant difference between control and biochar-amended digesters in terms of bacterial and methanogenic compositions. The enhanced methane yields in biochars-amended digesters could be partially ascribed to the selective enrichment of genus Methanosarcina , leading to an improved equilibrium between hydrogenotrophic and acetoclastic methanogenesis pathways. Moreover, energy balance assessment demonstrated that the hybrid biological and thermal conversion system can be a promising technical option for the treatment of PCFW and recovery of renewable biofuels (i.e., biogas and syngas) and bioresource (i.e., biochar) on an industrial scale. [Display omitted] • A hybrid bio/thermal system for plastic-containing food waste conversion to energy. • Plastic/digestate gasification produced higher syngas yields than pure digestate. • Gasification biochar enhanced methane yield by 6–30% in the AD processes. • Biochar shifted methanogens toward a balance of two flexible methanogenic pathways. • Average profit of PCFW treatment via the hybrid system is 20.7–64.2 US$/ton waste. [ABSTRACT FROM AUTHOR]

• A decentralized system was set up to transfer food waste to electricity and heat. • 30 kg food waste produced a methane yield of 0.55 L CH 4 /g VS in a current system. • A scale-up system was simulated to output 74.80kWh electricity at 500 kg feed per day. • Electrical and thermal energy outputs of optimized system increased by 135% and 87%. Biogas derived from the decentralized anaerobic digestion (AD) of food waste may be used to generate electrical and thermal energy for nearby residents through combined heat and power generation technology. A mobile food-waste-to-energy system in conjunction with an anaerobic digester and biogas engine was developed for food waste (FW) treatment and energy output. The scale-up was simulated to explore the methane yield and energy flow at different ambient temperatures of 0 °C, 10 °C, 20 °C, 30 °C and different feedstock of 200 kg, 500 kg FW. Accordingly, the results demonstrated that the installed system with a 1 m3 digester had a methane yield of 0.55L CH 4 /g VS when the feedstock load was 30 kg FW/d and the Organic Load Rate (OLR) was 5.4 g VS /L, while the thermal and electrical efficiencies of this system were 31% and 16%, respectively. The corresponding exhaust gas of the thermal energy from the biogas combustion was recovered by a heat exchanger in order to keep the digester at mesophilic conditions. The simulations carried out on the scale-up systems under loads of 200 kg FW/d and 500 kg FW/d achieved a thermal energy balance at different ambient temperatures of 0 °C, 10 °C, 20 °C and 30 °C. Improvements were proposed in the optimized system by optimizing pre-treatment facilities as well as the AD reactor, biogas engine and heat exchanger. The net thermal and electrical energy output of the optimized system at 500 kg FW/d were 175.93kWh and 163.90kWh, respectively. The energy generated by the FW-to-energy system illustrated by the Sankey diagrams depicts that was enough for operation without the need of extra heat and a power supply, moreover, the surplus energy may be utilized for its neighboring communities. In addition, the optimized system under the same OLR were increased by 87% and 135%, regards the thermal and electrical energy outputs, respectively in comparison with the current system. [ABSTRACT FROM AUTHOR]

• Mixing and activated carbon nexus was studied in thermophilic anaerobic digestion. • The optimum mixing time of 120 s/h were obtained via CFD modelling. • Coupling of activated carbon and semi-continuous mixing increased by 20% of CH 4. • Starting-up strategy - continuous mixing followed by intermittent mixing. • Metabolic pathways and functional genes of microbial communities were analyzed. This study evaluated the mixing – activate carbon nexus in anaerobic digestion with the aim of accelerating start-up of thermophilic anaerobic co-digestion of food waste and chicken manure using mesophilic anaerobic sludge as inoculum. Results showed that the methane yield in the continuous stirred reactor is 71.3% higher than that of intermittent agitated reactor, and the addition of activated carbon can further improve the yield of methane by 18.2%. Continuous mixing mode followed by intermittent mixing was proved to be an alternative strategy to accelerate start-up of thermophilic anaerobic digestion. The optimum mixing time of 120 s/hour were obtained using computational fluid dynamics modeling. Analysis of genomic annotation metabolism indicated that the addition of activated carbon enhanced the dominant metabolism pathways of amino acid, methane and energy. Results of enzymes gene expression suggested that carbohydrates esterases, glycoside hydrolases and glycosyl transferases were dominant, respectively. [ABSTRACT FROM AUTHOR]

• Algal biochar enhanced co-digestion of algal biomass and food waste for biomethane. • 75% algal biomass + 25% food waste mixture co-digestion showed a synergistic effect. • Average methane yields enhanced by 12–54% due to 15 g/L of algal biochar amendment. • Proteiniphilum enriched in mesophilic reactor like Defluviitoga in thermophilic one. • Biochar shifted methanogens towards a balance of two flexible methanogenic pathways. The impact of algal biochar addition on mesophilic and thermophilic anaerobic co-digestion of algal biomass and food waste was investigated with a focus on semi-continuous operations and functional microbial communities. Under batch co-digestion, the highest co-digestion synergy was observed for a mixture of 25% food waste and 75% algal biomass. During semi-continuous co-digestion of 25% food waste-75% algal biomass mixture, biochar amended digesters exhibited a 12–54% increase in average methane yield (275.8–394.6 mL/gVS) compared to the controls. Elevated temperature induced narrow distributions of volatile fatty acids (VFAs) by inhibiting the production of branched VFAs. Genus Proteiniphilum was selectively enriched by 3.2 folds in mesophilic digesters with biochar amendment while genus Defluviitoga was selectively enriched in thermophilic digesters due to elevated temperature. Methanogenic communities were significantly different in mesophilic and thermophilic digesters. Biochar amendment contributed to shifts in the predominant methanogens leading to a more balanced state of two methanogenic pathways. [ABSTRACT FROM AUTHOR]