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Concentrating organic matter in sludge and converting it into methane through anaerobic bioconversion can improve resource recovery from domestic wastewater. Enhanced membrane coagulation (EMC) is highly efficient at concentrating organic matter, but residual coagulants (aluminum salts) can obstruct bioconversion by blocking microbial access. Limited research exists on evaluating EMC sludge bioconversion performance and addressing coagulant inhibition. This study proposes alkaline pre-fermentation to break down HO-Al-P backbones in coagulated sludge flocs, thereby improving hydrolysis and organic acid production for anaerobic digestion. Among the tested alkaline conditions (pH 9, pH 10, pH 11), pre-fermentation at pH 11 released the most organic matter (4710.0 mg/L SCOD), 20.4 times higher than without alkaline treatment. At pH 11, phosphate (61 mg/L PO43−–P) and organic acid production (2728.1 mg COD/L, with nearly 50% acetic acid) peaked, resulting in superior volatile solids removal (65.2%) and methane production (185.8 mL/g VS) during anaerobic digestion. Alkaline pre-fermentation favored alkali-tolerant bacteria such as Firmicutes and Actinobacteria, especially at pH 11, while neutrophilic Proteobacteria were suppressed. Trichococcus and Bifidobacterium, known acid producers, dominated under all conditions, with their abundance increasing at higher pH levels. Anaerobic digestion enriched fermentative bacteria like Chloroflexi and Synergistota (e.g., Thermovirga), especially in high pH reactors. Methanothrix, an acetoclastic methanogen, became the dominant methanogenic archaeon, indicating that methane production from EMC sludge primarily followed the acetoclastic methanogenesis pathway. Our findings demonstrate that alkaline pre-fermentation at pH 11 significantly enhances the hydrolysis efficiency of EMC sludge for methane recovery. [ABSTRACT FROM AUTHOR]

The approach offers the feasibility of coupling pyrolysis and AD for the energy enhancement and resource utilization of residues from biologically treated FW. 2 Standalone treatment technology for FW and DBFs 2.1 AD process AD technology is promising because of its competence in recovering bioenergy products from biomass or bio-solid wastes ([5]). 3 Individual technology challenges in the disposal of FW and DBFs 3.1 AD challenges in FW and DBFs AD has been a widely investigated organic waste/biomass waste/FW processing route in recent years because of its potential for producing reasonable amounts of fuel gas in the form of H SB 2 sb and CH SB 4 sb for energy applications ([122], [43], [45], [6], [36]). 2.1.2 Factors influencing the AD process of FW AD is an efficient and globally applied technique that exploits the abilities of microbial metabolic activity to convert waste organic fractions to biogas ([113]). Keywords: anaerobic digestion; difficult-to-biodegrade fractions; food waste; integration process; pyrolysis EN anaerobic digestion difficult-to-biodegrade fractions food waste integration process pyrolysis 35 53 19 01/18/22 20220101 NES 220101 1 Introduction Global interest in biomass-based energy and upgrade is increasing. The European Union is the global front-runner in biogas electricity generation, with over 10 GW installed capacity and approximately 17,400 biogas plants (the global biogas capacity in 2015 was 15 GW) ([101]). [Extracted from the article]

[Display omitted] • The superiority of ethanol-path anaerobic digestion was clarified via various means. • Liquid product presents higher recovery potential than gas product in carbon flux view. • The dominant microorganisms in the anaerobic digestion system are identified. To rapidly treat and stably utilize great quantities of fruit and vegetable waste (FVW), the strategies in anaerobic digestion pattern have been constantly improved. In this work, the efficiencies and capacities of carbon conversion in different FVW anaerobic digestion systems were studied. Compared to butyrate-path (BD) two-phase and single-phase anaerobic digestion (SD), the ethanol-path two-phase anaerobic digestion (ED) system showed the highest rate of converting insoluble into soluble carbon formation (82.2%) and methane yield conversed from soluble carbon which is 0.14 gCOD CH4 (gVSS d)−1. It was also found that the coexistence of Bacillus and Methanococcus in the methanogenic phase maintained fatty acids and methane generation. The advantage of carbon conversion efficiency in ED can be elucidated from the highest acetification rate (704.10 mgCOD (L h)−1) which means more converted acetate can be smoothly used for methane generation. Compared to methanogenesis converted from butyrate and propionate, the thermodynamic condition of methanogenesis converted from ethanol was more feasible. Also, the highest capacity of max methane production (197773.7 mL) of ED was simulated. ED might be an efficient and advantageous option for FVW methane digestion. Furthermore, comparison of acidogenic product and methane in conversion efficiency revealed that fatty acids should think as ideal anaerobic product rather than methane. [ABSTRACT FROM AUTHOR]

Food waste (FW) is a severe environmental problem all over the world, and the recalcitrant organic residues (ROR) from FW treatment plant operations are also a critical environmental issue due to unsustainable treatment and disposal techniques. Requirements for FW and ROR complete exploitation with the establishment of recycling‐renewable technologies are very crucial. This paper review AD and pyrolysis as two promising technologies to degrade FW and its residues, creating numerous renewable bioenergy yields with value‐added. Existing oil/tar application methods in the AD suffered from various problems such as microorganism toxicity and limited productivity. Future upgrading techniques considering the second‐stage pyrolysis process to decompose oil/tars for syngas with high hydrogen content and enhanced bio‐methanation in the AD were addressed. Simultaneous pyrolysis by‐product recycle in the AD during the valorization of FW are aimed to have the features of sustainability toward increased bioenergy production, reactor efficiency, and agricultural application. [ABSTRACT FROM AUTHOR]

The application of an enhanced membrane coagulation reactor (E-MCR) for sewage concentration and energy recovery through anaerobic digestion (AD) was investigated. The results show that the addition of powder-activated carbon (PAC) and polyaluminum chloride (PACl) enhanced the sewage concentration efficiency and minimized the membrane fouling. The reactor was operated for 100 d with 70 d without severe fouling. The flux of 6 L/(m2 h) with sludge retention time of 2 d recorded a long-term stable performance and recovered concentrates with about 6000-9800 mg/L of chemical oxygen demand (COD) values. The concentrate was used as feed for AD using a continuous stirred tank reactor. The results show that at a thermophilic temperature of 35°C, a high biogas yield was achieved at 20 and 30 d hydraulic retention time (HRT). Meanwhile, biogas yields of 10, 220, and 295 mL/(gCOD) were achieved at 10, 20, and 30 d HRT, respectively. The addition of PAC/PACl and the low flux condition enhanced the concentration efficiency and minimized the membrane fouling during the long-term operation. Thus, with the optimization of the operation, E-MCR becomes a promising option for sewage concentration and energy recovery. [ABSTRACT FROM AUTHOR]

This study investigated the efficiency of biogas production from sewage concentrate through anaerobic digestion. A continuous stirred tank reactor with a 900-mL working volume was used. The experiment was designed to investigate the influence of organic loading rate on the efficiency of biogas production and to determine the most suitable organic loading rate condition for methane production from sewage concentrate by using continuous stirred tank reactor. The reactor was operated at different organic loading rates of 1.8, 0.8, and 0.6 gCOD/(L.d). The methane composition of the biogas produced from the treatment organic loading rate (OLR). The beginning of the experiment recorded low methane production because of the high organic loading rate. However, the later part of the experiment recorded high and stable biogas production because of the relatively low OLR. Results suggested that a 0.6 gCOD/(L.d) OLR was the most efficient setup parameter for ideal methane production from sewage concentrate by using continuous stirred tank reactor. [ABSTRACT FROM AUTHOR]

Hydrogenotrophic methanogenesis has been proved to be a feasible biological method for biogas upgrading. To improve its performance, the feasibility of typical anaerobic granules as the inoculum was investigated in both batch and continuous experiments. The results from batch experiments showed that glucose-acclimated granules seemed to perform better than granules acclimated to acidified products (AP, i.e. acetate, propionate and ethanol) inin situbiogas upgrading systems and a slightly higher H2consumption rate (1.5 mmol H2 g VSS−1 h−1) was obtained for glucose-acclimated granules. For AP-acclimated granules, the inhibition on anaerobic digestion and pH increase (up to 9.55±0.16) took place, and the upgrading performance was adversely affected. In contrast, better performance for AP-acclimated granules was observed inex situsystems, possibly due to their higher hydrogenotrophic methanogenic activities (HMA). Moreover, when gas–liquid mass transfer limitations were alleviated, the upgrading performance was significantly improved (three-fold) for both glucose-acclimated and AP-acclimated granules. The HMA of anaerobic granules could be further enhanced to improve biogas upgrading performance via continuous cultivation with H2/CO2as the sole substrate. During the three months' cultivation, secondary granulation and microbial population shift were observed, but anaerobic granules still remained intact and their HMA increased from 0.2 to 0.6 g COD g VSS−1 d−1. It indicated that the formation of hydrogenotrophic methanogenic granules, a new type of anaerobic granules specialized for high-rate hydrogenotrophic methanogenesis and biogas upgrading, might be possible. Conclusively, anaerobic granules showed great potential for biogas upgrading. [ABSTRACT FROM PUBLISHER]

Innovative methods for biogas upgrading based on biological/in-situ concepts have started to arouse considerable interest. Bioelectrochemical removal of CO 2 for biogas upgrading was proposed here and demonstrated in both batch and continuous experiments. The in-situ biogas upgrading system seemed to perform better than the ex-situ one, but CO 2 content was kept below 10% in both systems. The in-situ system’s performance was further enhanced under continuous operation. Hydrogenotrophic methanogenesis and alkali production with CO 2 absorption could be major contributors to biogas upgrading. Molecular studies showed that all the biocathodes associated with biogas upgrading were dominated by sequences most similar to the same hydrogenotrophic methanogen species, Methanobacterium petrolearium (97–99% sequence identity). Conclusively, bioelectrochemical removal of CO 2 showed great potential for biogas upgrading. [ABSTRACT FROM AUTHOR]

[Display omitted] • BGD from the iron-making process was first utilized as an accelerant in AD. • BGD accelerant (0.5–2.5 wt.%) can increase methane yield by 22.6%–51.3%. • Digestate with 2 wt.% BGD showed optimal stability (57.9%) and fertility (4.86%). • The electron transfer ability of the AD system was enhanced with BGD. • A strategy for understanding BGD added to boost AD performance was proposed. Plenty of refractory and environmentally hazardous bag-filter gas dust (BGD) is produced in the iron-making process. The effects of untreated BGD on anaerobic digestion (AD) with cattle manure were investigated. The BGD had the potential to boost the methane yield and digestate utilization considerably. The digester with 2.0 wt% BGD gained the highest methane yield (256.3 mL/g VS) and chemical oxygen demand removal rate (56.8%), 51.3% and 20.1% higher than that (169.4 mL/g VS, 47.3%) of the control group, respectively. The digestates with BGD possessed a utilization potential with the stability of 49.5–57.9% and fertility of 4.65–4.86%. Electrochemical measurements demonstrated that 2.0 wt% BGD improved the electron transport capacity of the AD system and increased the limiting current and redox peak current by 40.3% and 12.9%, respectively. A strategy for understanding the BGD reinforcing methanogenesis was proposed. This work also provides a technical support for recycling the BGD. [ABSTRACT FROM AUTHOR]

[Display omitted] • CQDs-0.36 MF group achieved best CH 4 yield (348.9 mL/g VS) and H 2 yield (9.9 mL/g VS). • Digestate of CQDs-0.36 MF group showed acceptable thermal stability and fertility. • The IET process was enhanced by the synergistic effect of CQDs and MF. • MF and CQDs enriched hydrogenotrophic methanogens and electrotrophic methanogens. Anaerobic digestion shows great potential for biomass energy recovery, however, the low electron transfer efficiency between microorganisms limits overall anaerobic digestion performance. In this work, aloe peel-derived carbon dots (carbon quantum dots, CQDs) were designed and investigated as accelerants for anaerobic digestion systems under an applied magnetic field to promote the interspecific electron transfer (IET) efficiency in methane and hydrogen production processes. Compared with the control group (188.9 mL/g VS, 4.2 mL/g VS, 34.7 %, and 26.3 %), the applied magnetic field (5 mT) significantly increased methane yield (256.1 mL/g VS), hydrogen yield (7.0 mL/g VS), total chemical oxygen demand reduction (41.7 %), and energy conversion efficiency (35.7 %). The introduction of the CQDs (0.18–0.45 wt.%) under a magnetic field (5 mT) has further positive effects on digestion performance. The experimental group incorporating 0.36 wt.% CQDs under a 5 mT magnetic field obtained the highest methane yield (348.9 mL/g VS), hydrogen yield (9.9 mL/g VS), and total chemical oxygen demand reduction (58.4 %), and thus the energy recovery efficiency was increased by 85 % compared with control group. The digestate incorporating 0.36 wt.% CQDs exhibited excellent thermal stability (59.71 %) and total nutrient content (38.17 g/kg), and has great potential as a main ingredient in compound fertilizer. The potential role of the magnetic field and CQDs in enhancing hydrogen interspecies electron transfer (HIET) and direct interspecies electron transfer (DIET) for methane and hydrogen production is further illustrated, providing a feasible solution for improving energy recovery from biomass. [ABSTRACT FROM AUTHOR]

• Introduction of binary and ternary TEs can improve biogas yield by 66.52–76.32%. • Three kinetic models (FOM, LM, and MGM) are employed to predict biogas yield. • Predicted data (0.32–5.3%) of LM and MGM are closer to measured data than FOM. • Coats-Redfern fitting proves TEs reduce activation energy of digestate (3.9–26.2%). • The selected kinetic models fit well with the experimental data (R2 > 0.98). The effects of binary and ternary trace elements (TEs) (Fe/Co, Fe/Ni, and Fe/Co/Ni) on the anaerobic digestion (AD) of cattle manure were investigated using kinetic models (first-order, logistic, modified Gompertz, and Coats-Redfern) and experimental measurements. Binary and ternary TEs can significantly improve the biogas production rate and yield potential. The deviation between the predicted and measured data for biogas yield with logistic model (2.1%–5.3%) and modified Gompertz model (0.32%–2.9%) was smaller than that with first-order kinetic model (6.9%–9.9%). The Coats-Redfern model fitting indicated that the activation energy of digestates with trace elements during pyrolysis was reduced by 3.9%–26.2% compared with the control group. Meanwhile, digestates with TEs showed remarkable fertility (5.72%–5.95%). The combination of kinetic models and experimental measurements can effectively quantify the effect of TEs on AD performance and provide an informed choice for industrial production. [ABSTRACT FROM AUTHOR]

Food waste (FW) is an impending issue, and its resource recovery and energy recycling have become a hotspot in the academic community. This paper presents an innovative integrated two-stage anaerobic digestion process that can enhance anaerobic digestion of food waste. The new technology is an attractive solution to resolve difficulties related to productivity and system optimization in traditional single and double-stage FW digestion processes. The study revealed that the oil extraction rate increased from 2% to 3%–4% after process improvement, and the specific biogas production of the integrated two-stage biogas plant (50.2 m3/t) was 10.54% higher than single-stage biogas plant. Metagenome data analysis indicated that aceticlastic methanogenesis was the main route for methane production in the integrated two-stage biogas plant. Considering the short payback time (1.5 years), high net present value (11.49 million) and internal rate of return (36.97%), this biogas project was economically viable. In this context, this innovative process got through the recycling bottleneck of food waste and promoted the industrialization of anaerobic treatment of food waste. Image 1 • This work compared performance of ITS and single-stage biogas plants. • The innovative two-stage process enhanced biogas yield and stability. • Dominate Methanothrix undergo aceticlastic methanogenic pathway in ITS digester. • Methanobacteriales can grow in syntrophy with Bacteroidetes. • Oil extraction rate was increased to 3–4% by continuous wet-heat steam technology. [ABSTRACT FROM AUTHOR]

• The AD of FW treatment improved with different biochars was studied. • Biochar significantly increased maximum production rates of biomethanation. • LBC was slightly superior to CBC at OLR of 6.0 gVS/L−d. • Methanothrix was the predominant methanogen in R1 and R2. Anaerobic digestion (AD) is a green technology that is widely applied to food waste (FW) treatment. It can harness resources from the FW and mitigate associated environmental pollution and sanitation related problems. Despite the AD high efficacy, at high organic loading rate and long-run time operations, low methane yield, and reactor instability often occurred. To overcome such associated problems and improve efficiency at a high organic loading rate (OLR) of 6.0 gVS/L−d and long-run operations of 350 days. The performance of different biochar as additives with food waste treatment in the AD was investigated. Both the local biochar (LBC) and commercial biochar (CBC) shows similar efficiency that enhanced high methane yield (5%) compared to the control. The further outcome from laboratory study revealed that biochar had significantly influenced alleviation of Ammonium–N concentrations above 2450 mg/L with bio-degradation of VFAs, thus stimulating reactor process stability and performance. Methanothrix was the most abundance methanogens in the biochar amended reactors, it out-strived Methanosarcina by the higher growth rate and tolerance against inhibition on long-run operations. Overall, the biochars had a positive effect on the digester stability at high OLR and promoted bio-methanation during the long run operations. [ABSTRACT FROM AUTHOR]

The application of low-cost magnetic industrial wastes as accelerants can significantly improve the performance of anaerobic co-digestion (AcoD), thereby enhancing the biogas yield. In this work, varying concentrations (1.0–4.0 wt.%) of magnetic flyash (MFA) were applied to the AcoD of cow manure (CM) and aloe peel waste (APW). All AcoD systems were operated under mesophilic condition (37 ᴼC) with a 5 mT magnetic field. The AcoD system with 2.0 wt.% of MFA showed the highest cumulative biogas yield (487 mL/g VS), methane content (65.17%), COD, TS and VS removal rates (36.45, 45.49 and 52.10%, respectively), and fertility (3.4%). However, the 1.0 wt.% of NMFA also showed higher cumulative biogas yield (432 mL/g VS), methane content (60.23%), COD, TS and VS (27.69, 18.24 and 43.64%, respectively), and fertility (3.31%) than other NMFA concentrations (1.5 & 2.0 wt.%). Kinetic models verified that MFA coupled with a magnetic field could increase biogas potential and production rate. A strategy for determining the role of MFA in microbial biofilm formation and improving biodegradation, which increases the biogas yield, is also suggested. This work demonstrates a cost-effective application of MFA in bioenergy production systems by improving the AD process. [Display omitted] • Magnetic-flyash allied WSMF increased biomethane by 18.88%. • Kinetic models (FOM, LM, and MGM) fit well with the experimental data (R2 > 0.98). • Magnetic-flyash allied with 5 mT can increase biogas production and its rate. • Magnetic-flyash encouraged the microbial biofilm. • Microbial biofilm enhance biodegradation in AcoD system. [ABSTRACT FROM AUTHOR]

[Display omitted] • CQDs and PC effectively promote biogas production in AcoD MF system. • Cumulative biogas yield of the CQDs/PC (1.2) group is 648.5 mL/g VS. • The digestate with CQDs/PC (1.2) show total nutrient content (N + P + K) of 49 g/kg. • Methanobacterium and Methanosarcina are enriched by adding CQDs and PC. • Mechanisms of magnetic field coupled CQDs/PC to improve AD performance is analysed. Carbon materials are widely used for direct interspecies electron transfer (DIET) to promote CH 4 yield in anaerobic digestion (AD). However, the addition of host–guest assembly carbon accelerant has not been reported. This work explores the facilitation of carbon quantum dots (CQDs) immobilized in porous carbon (PC) as a host–guest accelerant in anaerobic co-digestion (AcoD) under a magnetic field. The addition of CQDs and PC increased the biogas yield and TCOD removal efficiency by 30.1–38.6 % and 14.2–24.2 %, respectively, compared with control group (467.8 mL/g VS; 37.7 %). Fertilization efficiency of the optimal CQDs/PC group was 4.9 % and the excellent electronic exchange capability of CQDs (1.04 μmol e-/g) and PC (0.64 μmol e-/g) facilitated DIET. This approach helped in enriching anaerobic microorganisms and strengthened the thermal stability of the digestates. These findings provide new insights for improving AD performance using CQDs coupled PC. [ABSTRACT FROM AUTHOR]

[Display omitted] • MAX, ML-MXene, FL-MXene accelerants can improve the biogas yield of MEC-AD system. • ML-MXene 0.035 achieves the optimal CH 4 yield (69.8%) and CO 2 reduction (11.2%). • ML-MXene embodies superior excellent electron exchange capacity (2.89 μmol e-/g). • The abundance of Methanosarcina is increased in ML-MXene 0.035 group. • A strategy to elucidate synergistic effect of layered MXene and MEC is proposed. Accelerants can improve the anaerobic performance of a microbial electrolysis cell coupled anaerobic digestion (MEC-AD). MAX phase titanium aluminum carbide (MAX), multilayer Ti 3 C 2 T X MXene (ML-MXene) and few-layer Ti 3 C 2 T X MXene (FL-MXene) were utilized as accelerants for MEC-AD to promote CH 4 production and CO 2 reduction at a voltage of 0.6 V. The highest CH 4 yield (358.7 mL/g VS) and the lowest CO 2 yield (57.4 mL/g VS) relative to the control group (170.6 and 125.1 mL/g VS) were obtained in MEC-AD with ML-MXene (0.035 wt%). The digestates of MEC-AD with 0.035 wt% ML-MXene have superior thermal stability (40.9%) and total nutrient content (42.1 g/kg). The ML-MXene enhanced the abundances of Methanosarcina and Methanobacterium. This work highlights the possible role of MXene in promoting methanogenesis. These important findings provide a novel avenue for the development of MXene accelerants for MEC-AD systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • AP-CQDs as accelerants is used firstly in the AcoD systems. • Adding 0.36 wt.% AP-CQDs obtains the optimal cumulative CH 4 yield (339.64 mL/g VS). • The digestate with AP-CQDs shows considerable stability and fertility (46.65 g/kg). • AP-CQDs have abundant functional groups and excellent EEC (0.70 μmol e-/g AP-CQDs). • The underlying mechanism of AP-CQDs accelerants in the AcoD system is illustrated. Carbon materials have been widely used in anaerobic digestion (AD), but the role of zero-dimensional carbon quantum dots (CQDs) in anaerobic co-digestion (AcoD) has not yet been reported. In this work, the effect of aloe peel-derived CQDs (AP-CQDs) on the AcoD system of aloe peel and dairy manure was investigated. The addition of AP-CQDs accelerants increased the cumulative CH 4 yield from 201.14 to 266.92–339.64 mL/g VS and increased total chemical oxygen demand removal efficiency from 34.72 % to 48.77–57.87 %. The use of a digestate with 0.36 wt.% of AP-CQDs resulted in a thermogravimetric mass loss of 47.15 % and a promising total nutrient content of 46.65 g/kg. The excellent electron exchange capacity of AP-CQDs may facilitate direct interspecies electron transfer during the AD process. Moreover, the use of AP-CQDs can enrich methanogenic microorganisms (Methanosarcina and Methanobacterium). These findings provide a viable strategy for improving methane production and create awareness regarding the dual use of biomass waste. [ABSTRACT FROM AUTHOR]

Sustainable approaches for the anaerobic digestion treatment of food waste to minimize environmental challenges and recover energy are some economic goals receiving global attention. Meeting global bio-energy demand from food waste and associated waste residues requires exploring alternative optimization routes. Pyrolysis process for the treatment and recycling of difficult biodegradable fractions in food waste processing facility, and the subsequent utilization of real syngas in anaerobic digestion as a food waste treatment were investigated to evaluate their effects on biofuel production via bio-methanation. Different proportions of syngas that are transformed into methane show that the carbon monoxide content in the reactors (G21, G23, G61, and G63) was completely degraded on 195, 195, 95, and 145 h. The higher hydrogen concentration in the simulated syngas expedites the carbon monoxide degradation rate. Application of two-stage pyrolysis to difficult biodegradable fractions treatment generated real syngas (Hydrogen 60: Carbon monoxide 20 vol%) for improved bio-methanation (100% methane) compared to the blank. The simulated syngas from the anaerobic digestion treatment of food waste generated methane (75–80%) than the control (45%). Results from both the simulated and real syngas show that high volume percent of hydrogen in the syngas positively influenced the degradation and transformation of carbon monoxide and promoted a higher rate of bio-methanation. Further study showed that pH values in the range 7.21–7.78, and low concentrations of volatile fatty acids and ammonia nitrogen indicated no toxicity from syngas bio-methanation with anaerobic digestion. This route is beneficial for enhancing the value of resources recovered from difficult biodegradable fractions pyrolysis, achieving a higher bio-methanation rate, and improving sludge stabilization with anaerobic digestion treatment of food waste. • Difficult biodegradable fractions were pyrolyzed to produce hydrogen rich syngas. • Increase in carbon monoxide concentrations prolonged its degradation rate. • Sufficient hydrogen (60 vol%) in real syngas has no inhibitory effect. • Real syngas bio-methanation generates almost 100% methane. • Bio-methanation performance and sludge stabilization was enhanced. [ABSTRACT FROM AUTHOR]

Previous studies demonstrate anaerobic digestion of hydrothermal liquefaction wastewater (HTL-WW) is significant to the sustainability of algal biofuel development for nutrient reuse and residual energy recovery. HTL-WW contains substantial amounts of residual energy but is toxic to anaerobes. With 6% HTL-WW converted from cyanobacteria (e.g. Spirulina ), anaerobes were 50% inhibited. In this study, zeolite, granular activated carbon (GAC), and polyurethane matrices (PM) were used during a two-round anaerobic batch test with HTL-WW, and in the presence of each material, the total methane yields were 136 mL/g COD, 169 mL/g COD, and 168 mL/g COD, respectively, being 11%, 37% and 36% higher than the control. GAC was considered promising due to its highest methane yield of 124 mL/g COD at the second feeding, indicating a good recovery of adsorption capacity. The observed low methane production rates indicated the necessity for anaerobic process optimization. The physicochemical analysis of the digestates demonstrated that most of the compounds identified in the HTL-WW were degraded. [ABSTRACT FROM AUTHOR]

Syngas based co-digestion is not only more economically attractive than separate syngas methanation but also able to upgrade biogas and increase overall CH 4 amount simultaneously. However, high H 2 concentration in the syngas could inhibit syntrophic degradation of propionate, resulting in propionate accumulation and even failure of the co-digestion system. In an attempt to reduce propionate accumulation via enhancing both H 2 interspecies transfer (HIT) and direct interspecies electron transfer (DIET) pathways, layered granule-based biofilms induced by conductive carbon felt particles (CCFP) was employed. The results showed that propionate accumulation was effectively reduced with influent COD load up to 7 g L −1 d −1 . Two types of granule-based biofilms, namely biofilm adhered to CCFP (B-CCFP) and granules formed by self-immobilization (B-SI) were formed in the reactor. Clostridium , Syntrophobacter , Methanospirillum were possibly involved in HIT and Clostridium , Geobacter , Anaerolineaceae , Methanosaeta in DIET, both of which might be responsible for the high-rate propionate degradation. [ABSTRACT FROM AUTHOR]

A novel method of two-phase anaerobic digestion where the acid reactor is operated at low pH 4.0 was proposed and investigated. A completely stirred tank acid reactor and an up-flow anaerobic sludge bed methane reactor were operated to examine the possibility of efficient degradation of lactate and to identify their optimal operating conditions. Lactate with an average concentration of 14.8 g/L was the dominant fermentative product and Lactobacillus was the predominant microorganism in the acid reactor. The effluent from the acid reactor was efficiently degraded in the methane reactor and the average methane yield was 261.4 ml/g COD removed. Organisms of Methanosaeta were the predominant methanogen in granular sludge of methane reactor, however, after acclimation hydrogenotrophic methanogens enriched, which benefited for the conversion of lactate to acetate. The two-phase AD system exhibited a low hydraulic retention time of 3.56 days and high methane yield of 348.5 ml/g VS removed. [ABSTRACT FROM AUTHOR]

In order to investigate the oxygen tolerance capacity of upflow anaerobic solid-state (UASS) with anaerobic filter (AF) system, the effect of microaeration on thermophilic anaerobic digestion of maize straw was investigated under batch conditions and in the UASS with AF system. Aeration intensities of 0–431 mL O 2 /g vs were conducted as pretreatment under batch conditions. Aeration pretreatment obviously enhanced anaerobic digestion and an aeration intensity of 431 mL O 2 /g vs increased the methane yield by 82.2%. Aeration intensities of 0–355 mL O 2 /g vs were conducted in the process liquor circulation of the UASS with AF system. Dissolved oxygen (DO) of UASS and AF reactors kept around 1.39 ± 0.27 and 0.99 ± 0.38 mg/L, respectively. pH was relatively stable around 7.11 ± 0.04. Volatile fatty acids and soluble chemical oxygen demand concentration in UASS reactor were higher than those in AF reactor. Methane yield of the whole system was almost stable at 85 ± 7 mL/g vs as aeration intensity increased step by step. The UASS with AF system showed good oxygen tolerance capacity. [ABSTRACT FROM AUTHOR]

The feasibility of corn stalk anaerobic digestion was investigated in an upflow anaerobic solid-state (UASS) reactor with an additional anaerobic filter (AF) reactor. One single-stage (UASS) and two two-stage systems (UASS + AF) were compared at organic loading rates (OLR) of 2.5, 4.5, and 8.0 g vs L −1 d −1 . The single-stage system was operated under mesophilic conditions and the two-stage systems under both mesophilic and thermophilic conditions. Independently of OLR, the mesophilic two-stage system showed higher average methane production rates (0.50 ± 0.01, 0.63 ± 0.11, and 0.67 ± 0.12 L CH 4 L - 1 d - 1 ) than the single-stage (0.46 ± 0.02, 0.46 ± 0.06, and 0.31 ± 0.09 L CH 4 L - 1 d - 1 ) and thermophilic two-stage (0.30 ± 0.02, 0.42 ± 0.05, and 0.66 ± 0.12 L CH 4 L - 1 d - 1 ) systems. Respective methane yields were 84–201, 39–184, and 88–119 mL g vs −1 . The observed advantage of mesophilic digestion is of particular interest, as degradation of lignocellulosic biomass is usually reported to benefit from higher temperature. The results show the general feasibility of an additional AF reactor after the UASS digestion of corn stalk under mesophilic conditions. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility of varying the pH to enhance the accumulation of short-chain fatty acids (SCFAs) in the in vitro fermentation of maize straw. The corresponding hydrolysis rate and the net SCFA yield increased as inoculum ratio (VS inoculum /VS substrate ) increased from 0.09 to 0.79. The pH were maintained at 5.3, 5.8, 6.3, 6.8, 7.3, and 7.8, respectively. A neutral pH of approximately 6.8 was optimal for hydrolysis. The net SCFA yield decreased by 34.9% for a pH of less than 5.8, but remained constant at approximately 721 ± 5 mg/g vs for a pH between 5.8 and 7.8. In addition, results were obtained for variable and constant pH levels at initial substrate concentrations of 10, 30 and 50 g/L. A variable pH increased the net SCFA yield by 23.6%, 29.0%, and 36.6% for concentrations of 10, 30 and 50 g/L. Therefore, a variable pH enhanced SCFA accumulation in maize straw fermentation. [ABSTRACT FROM AUTHOR]

This work focused on the lactic acid production from acidogenic fermentation of fruit and vegetable wastes treatment. A long term completely stirred tank reactor (CSTR) lasting for 50 days was operated at organic loading rate (OLR) of 11 gVS/(L d) and sludge retention time (SRT) of 3 days with pH controlled at 4.0 (1–24 day) and 5.0 (25–50 day). The results indicated that high amount of approximately 10–20 g/L lactic acid was produced at pH of 4.0 and the fermentation type converted from coexistence of homofermentation and heterofermentation into heterofermentation. At pH of 5.0, the hydrolysis reaction was improved and the total concentration of fermentation products increased up to 29.5 gCOD/L. The heterofermentation was maintained, however, bifidus pathway by Bifidobacterium played an important role. [ABSTRACT FROM AUTHOR]

• A pilot-scale enhanced magnetic separation equipment (300 m3/d) was proposed for up-concentration. • Adsorption further enhanced the ability to capture soluble organics of magnetic separation. • Over 60% of organics were removed within 10 min with satisfactory energy consumption. • The energy potential of the produced sludge was competitive. The up-concentration process has been demonstrated as an attractive approach to carbon-neutral wastewater treatment. Innovation in the separation processes can help eliminate the current heavy dependence on gravity, and credible pilot-scale verification is crucial for application promotion. We hereby proposed a pilot-scale enhanced magnetic separation (EMS) system as an up-concentration step to maximize energy recovery from municipal wastewater. The design of EMS was based on the hypothesis that magnetic-driven separation could be a breakthrough in separation speed, and adsorption could further enhance the separation efficiency by capturing soluble substances. Jar tests confirmed the feasibility of activated carbon adsorption, which could also roughen the surface of aggregates. Further, over one-year operation of a 300 m3/d EMS equipment provided optimum operation strategies and evidence of system effectiveness. More than 80% of particulate organics and 60% of soluble organics were removed within 10 min at an energy consumption of only 0.036 kWh/m3. The characteristics of sludge were clarified in terms of organic concentration, extracellular polymeric substances composition, and micro-community analysis. The anaerobic experiments further demonstrated the potential value of the concentrated products. Surprisingly, the developed EMS system exhibited significant advantages in time consumption and space occupation, with competitive operating cost and energy consumption. Overall, the results of this study posed the EMS process for up-concentration as a potential approach to organics recovery from municipal wastewater. [Display omitted] [ABSTRACT FROM AUTHOR]

The concept of temperature staged and biological phased (TSBP) was proposed to enhance the performance of waste-activated sludge anaerobic digestion. Semi-continuous experiments were used to investigate the effect of temperature (35 to 70°C) as well as the hydraulic retention time (HRT) (2, 4 and 6 days) on the acidogenic phase. The results showed that the solubilization degree of waste-activated sludge increased from 14.7% to 30.1% with temperature increasing from 35 to 70°C, while the acidification degree was highest at 45°C (17.6%), and this was quite different from the temperature impact on hydrolysis. Compared with HRT of 2 and 6 days, 4 days was chosen as the appropriate HRT because of its relatively high solubilization degree (24.6%) and acidification degree (20.1%) at 45°C. The TSBP system combined the acidogenic reactor (45°C, 4 days) with the methanogenic reactor (35°C, 16 days) and the results showed 84.8% and 11.4% higher methane yield and volatile solid reduction, respectively, compared with that of the single-stage anaerobic digestion system with HRT of 20 days at 35°C. Moreover, different microbial morphologies were observed in the acidogenic- and methanogenic-phase reactors, which resulted from the temperature control and HRT adjustment. All the above results indicated that 45°C was the optimum temperature to inhibit the activity of methanogenic bacteria in the acidogenic phase, and temperature staging and phase separation was thus accomplished. The advantages of the TSBP process were also confirmed by a full-scale waste-activated sludge anaerobic digestion project which was an energy self-sufficient system. [ABSTRACT FROM AUTHOR]

[Display omitted] • MEC and CBC are combined to upgrade cow-manure-based anaerobic co-digestion. • MEC 0.6 CBC 0.15 improves the methane yield by 120.68% and COD removal rate by 58.33%. • MEC with CBC demonstrates an excellent electrochemical activity. • Digestates exhibit an acceptable thermal stability and fertilizer efficiency. • A general strategy to understand enhanced performance of MEC with CBC is proposed. Microbial electrolysis cells (MECs) and exogenous accelerants can augment anaerobic digestion performance. Herein, MECs and coconut-shell-derived bio-based carbon (CBC) accelerant are adopted to strengthen anaerobic co-digestion of cow manure and aloe peel waste. The MEC with the voltage of 0.6 V and CBC accelerant of 0.15 wt.% gained the highest cumulative biogas yield (444.20 NmL/g VS) and chemical oxygen demand removal rate (75.46%), which are 80.25% and 58.33% higher than those (246.44 NmL/g VS, 47.66%) of the blank group, respectively. The digestates embodied a utilization potential with thermogravimetric loss of 37.12%–50.67% and total nutrient content of 35.36–51.58 g/kg. These results benefited from excellent electrocatalytic activity of MECs and physicochemical properties of CBC accelerant. A general strategy for understanding improved methanogenesis was proposed based on integrated effects of MECs and CBC accelerant. This work will shed light on development of anaerobic co-digestion by combining MECs and bio-based carbon accelerants. [ABSTRACT FROM AUTHOR]

In recent years, the great interest in improving anaerobic digestion (AD) process resulted in the use of different types of additives or accelerants to exploit several profitable synergies, including improved CH 4 yield and digestate quality. However, the use of carbon-based materials also reduces operational instability and substrate-induced inhibition that hinder microbial breakdown activity of the organic matter. In this review, recent advances made by different research groups in order to enhance the performance of AD system are reviewed, emphasizing the utilization of low-cost carbon-based materials in the AD process, with a particular focus on the use of bio-based carbons such as biochar, activated carbon, and carbon cloth. The bio-based carbons in AD system support bacterial syntrophy and accelerate to direct interspecies electron transfer (DIET), and enhance methane yield. Moreover, this review gives emphasis on the fabrication of bio-based carbon materials and their applications as additives and their working mechanism in the AD system. Finally, this manuscript debates optimized AD technology to enhance biogas yield via bio-based carbons for energy production and sustainable environment for betterment of human health. • Fabrication methods of bio-based carbon materials are presented in detail. • Bio-based carbons enhance methanogenesis, improve the stability, stimulate syntrophy. • Enhanced AD performance by bio-based carbon as additive is illustrated. • Recent findings on the bio-based carbons mediating AD by DIET are summarized. • Future perspectives on use of bio-based carbon in AD are stressed. [ABSTRACT FROM AUTHOR]

• Long term pilot scale investigation for dry AD of manure, straw and sludge. • VFA/ALK (0.1 ~ 0.4) as effective dry AD system indicator for stability. • Dry method was better start-up strategies than wet method. • Organic loading rate of 4.8 kg/(m3·d) and temperature of 48 °C was optimized. • Co-digestion enhanced dry anaerobic digestion with better VSR and system stability. Dry anaerobic digestion (AD) with high total solid content might upgrade conventional wet AD by enhancing digestion and reducing liquid digestate generation, which was not so popular due to lack of adequate knowledge and perceived operational complexity. In this study long term (447 days) pilot scale investigation was performed for various feedstocks including pig manure, corn straw and sludge. It was found dry method was more suitable for reactor start-up than wet method with relieved inhibition. Volatile fatty acid (VFA)/alkalinity (0.1 ~ 0.4) was effective as dry AD system stability indicator. Organic loading rate of 4.8 kg/(m3·d) and temperature of 48 °C was optimized. Co-digestion achieved better volatile solid removal and system stability. Both hydrogenotrophic and acetoclastic methanogens stably existed in rector while hydrogenotrophic obtained higher abundance. This research contributed to understanding of reactor start-up, system stability indicator and optimized operational conditions (organic loading rate and temperature) during dry AD process. [ABSTRACT FROM AUTHOR]

• Magnetic field and Ti-sphere core–shell structured additives are firstly used in AD. • Optimized 5 mT magnetic field intensity exhibits a positive effect in AD systems. • The Ti-2 MF-5 increases the biogas yield by 65.53% as compared with the CK. • Enhanced performance is due to the synergistic effect of magnetic field and additive. • A general strategy for understanding enhanced methanogenesis pathway is proposed. Enhancing anaerobic digestion performance is highly desired for its large-scale application. In the present work, magnetic fields (0–30 mT) and Ti-sphere core–shell structured additives (Ti-1 and Ti-2) are simultaneously introduced in anaerobic mono-digestion and co-digestions. Compared with the control group, the Ti-sphere core–shell structured additives increase the biogas yield by 27.12%–65.53% for mono-digestion and 8.47%–35.89% for co-digestion systems under the optimized magnetic field intensity (5 mT), respectively. Meanwhile, the degradation rate of total chemical oxygen demand is 54.68%–69.14% for anaerobic mono-digestion and 53.03%–78.25% for anaerobic co-digestion with Ti-sphere core–shell structured additives, respectively. The digestate with Ti-sphere core–shell structured additives exhibits the remarkable stability (45.24%–53.17%) and fertility (4.85%–4.97%). This work clarifies the effect of magnetic field in AD system, and proposes a possible mechanism for understanding the enhanced methanogenesis pathways induced by Ti-sphere core–shell structured additives. [ABSTRACT FROM AUTHOR]

• Biomass-derived carbon-based composites are firstly used as accelerants in AD system. • Composite accelerants effectively enhance the biogas yield by 34.2% in AD system. • The digestate with accelerants shows the total nutrient content of 3.50–4.55%. • A general strategy for understanding the DIET mechanism of accelerants is proposed. • The first-principle DFT calculations provide the theoretical basis for the DIET. The performance of anaerobic digestion (AD) can be improved by the addition of accelerants. Three types of biomass-derived carbon-based composites (Co/C, CoO/C, and Co 3 O 4 /C) were used as accelerants to investigate the effect on AD systems in this work. These accelerants significantly improved the cumulative biogas yield (576–585 mL/g VS), and the total chemical oxygen demand degradation rate (68.48–71.11%) compared to the reference group (435.8 mL/g VS, 50.74%). The digestates with accelerants exhibited exceptional stability (59.24–63.67%) and superior fertilizer utilization (3.50–4.55%). In addition, first-principle density functional theory (DFT) calculations were conducted to provide the theoretical basis for the direct interspecies electron transfer (DIET), and a general strategy was proposed to help understand the enhanced methanogenesis pathway induced by the biomass-derived carbon-based composites. These important findings provide a novel avenue for the development of composite accelerants for AD systems. [ABSTRACT FROM AUTHOR]