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[Display omitted] • 102.1 mg/g-VS humic substances reduced the methane production rate by 33.8 % in AD. • 0.6 V MEC-AD maintained stable when 102.1 mg/g-VS humic substances were added. • Humic substances acted as carbon sources and electron shuttles in 0.6 V MEC-AD. • The newly formed humic substances have lower aromaticity and higher reducibility. • The abundance of hydrogenotrophic methanogens on the cathode reached 42.9 %. Humic substances as major components of waste activated sludge are refractory to degrade and have inhibition in traditional anaerobic digestion (AD). This study for the first time investigated the feasibility and mechanism of microbial electrolysis cell assisted anaerobic digestion (MEC-AD) to break the recalcitrance and inhibition of humic substances. The cumulative methane production of AD decreased from 134.7 to 117.6 mL/g-VS with the addition of humic acids and fulvic acids at 25.2–102.1 mg/g-VS. However, 0.6 V MEC-AD maintained stable methane production (155.5–158.2 mL/g-VS) under the effect of humic substances. 0.6 V MEC-AD formed electrical stimulation on microbial cells, provided anodic oxidation and cathodic reduction transformation pathways for humic substances (acting as carbon sources and electron shuttles), and aggregated functional microorganisms on electrodes, facilitating the degradation of humic substances and generation of methane. This study provides a theoretical basis for improving the energy recovery and system stability of sludge treatment. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • CFHP was applied to improve methane production from WAS for the first time. • Hydrolysis rate of WAS are improved through CFHP. • Biochemical methane potential of WAS are improved through CFHP. • CFHP is an attractive technology for the application in real-world situations. Abstract Anaerobic digestion of waste activated sludge (WAS) is often limited by low hydrolysis efficiencies and poor methane potentials. This work presents a novel pretreatment technology for WAS anaerobic digestion, i.e., combining free ammonia with heat pretreatment (CFHP). Experimental results showed that compared with control, solo free ammonia (135.4 mg NH 3 -N/L) and solo heat (70 °C) pretreatment, the combined free ammonia and heat (135.4 mg NH 3 -N/L with 70 °C) obtained 52.2%, 25.5% and 30.2% faster in hydrolysis rate and 25.2%, 17.9% and 16.5% higher in biochemical methane potential, respectively. Mechanism investigations showed that the combined pretreatment not only largely facilitated the disintegration of WAS but also increased the proportion of biodegradable organic matters, thereby providing better contract between biodegradable organics and the anaerobic microbes for methane production. Considering its effectiveness and renewability, the combined pretreatment is an attractive technology for the application in real-world situations. [ABSTRACT FROM AUTHOR]

• Triclosan had a tendency to restrain methane production from sludge. • Triclosan could be degraded by anaerobic microorganism. • Triclosan at higher levels had seriously negative effect on biological processes. • Triclosan exposure could greatly change the richness and diversity of populations. Triclosan (TCS), as an antimicrobial agent, is considered as a representative emerging contaminant and was frequently detected in excess sludge. This study investigated the effect of TCS on activate wastewater sludge (WAS) digestion through laboratory methane production experiment. It was concluded that TCS had a tendency to restrain methane production from sludge with its exposure level increasing. The results displayed that the yields of final maximum cumulative methane production were similar about 108.4 mL/g VSS at TCS level lower 200 mg TCS/kg TSS, while the values were approximately 95.2 mL/g VSS with TCS level over 550 mg TCS/kg TSS. Although TCS could be degraded, its intermediates in this study had no effect on sludge digestion. In addition, TCS at higher levels had seriously negative effect on the solubilization, hydrolysis, acidification, and methanogenesis processes. Microbial community was further analyzed to understand the TCS's effect on digestion system from a micro perspective. [ABSTRACT FROM AUTHOR]

• Microwave pretreatment (MP) benefited the degradation of PAM. • MP accelerated the release and hydrolysis of organics from PF-WAS. • MP facilitated the breaking of large firm "PAM-sludge" floccules. • Hydrolysis rate of PF-WAS was accelerated through MP. • Biochemical methane potential of PF-WAS was improved through MP. Deterioration of anaerobic digestion can occur with the presence of polyacrylamide (PAM) in waste activated sludge, but the information on alleviating this deterioration is still limited. In this study, the simultaneous alleviation of negative effect of PAM and improvement of methane production during anaerobic digestion was accomplished by microwave pretreatment. Experimental results showed that with the microwave pretreatment times increased from 0 to 12 min, the biochemical methane potential of PAM-flocculated sludge (12 g PAM/kg total solids) asymptotically increased from 123.1 to 242.5 mL/g volatile solids, hydrolysis rate increased from 0.06 to 0.13 d−1. Mechanism analysis indicated that the microwave pretreatment accelerated the release and hydrolysis of organic substrates from PAM-flocculated sludge, facilitated the breaking of large firm "PAM-sludge" floccules, and benefited the degradation of PAM, which alleviated the PAM inhibitory impacts on digestion and meanwhile provided better contact between the released organic substrates and anaerobic bacteria for methane production. [ABSTRACT FROM AUTHOR]

[Display omitted] • AITC was degraded by –N C S and C C–C– isomerization in anaerobic co-digestion. • AITC inhibited methane production from anaerobic co-digestion of KW and WAS. • AITC inhibited acetotrophic methanogenesis by reducing the activity of AK enzyme. • AITC enriched complex organic degradation microbes such as Bacillus. Producing methane from anaerobic co-digestion of kitchen waste and waste activated sludge has been widely implemented in real-world situations. However, the fate and impact of allyl isothiocyanate (AITC), a main active component in cruciferous vegetables, in the anaerobic co-digestion has never been documented. This study therefore aims to provide such supports. Experimental results exhibited that AITC was degraded completely by microorganisms and served as a substrate to produce methane. As AITC increased from 0 to 60 mg/L, the maximum methane production decreased from 285.1 to 35.8 mL/g VS, and the optimum digestion time was also prolonged. The mechanism study demonstrated that AITC induced cell apoptosis by modifying the physicochemical properties of cell membrane, which resulted in inhibitions to the procedure of anaerobic co-digestion. The high-throughput sequencing showed that AITC enriched the microorganism for degradation of complex organic compounds such as Bacillus , but lessened anaerobes involved in hydrolysis, acidogenesis, and methanogenesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sodium lauroyl sarcosinate improved methane yield in anaerobic digestion. • Methane can be produced during the degradation of sodium lauroyl sarcosinate. • Sodium lauroyl sarcosinate promoted the release of organic matters. • Sodium lauroyl sarcosinate improved the activities of hydrolytic enzymes. In this study, sodium lauroyl sarcosinate (SLS) was used to promote anaerobic digestion of waste activated sludge for producing methane. It was found maximum cumulative methane production increased from 98.1 ± 3.1 to 166.0 ± 4.3 mL/g Volatile Suspended Solids (VSS) with dosage increasing from 0 (control) to 40 mg SLS/g TSS. But the addition of SLS (>10 mg SLS/g Total Suspended Solids (TSS)) resulted in prolonged lag phase time. Microbiological analysis showed that Syntrophobacter and Syntrophomonas both got enriched in reactors fed with SLS. Furthermore, hydrogenotrophic methanogens genus got more enrichment in contrast to acetoclastic methanogens. Mechanism analysis indicated that addition SLS could decrease surface tension, and promote release of organic matters as well as improve activities of hydrolytic enzymes. Besides, SLS could be nearly degraded completely within 3 days, and its degradation intermediates could be further transformed into methane gradually, thus enhancing methane production eventually. [ABSTRACT FROM AUTHOR]

• The impact of S-mZVI on the anaerobic co-digestion of WAS and FW was evaluated. • The cumulative CH 4 yield within 15 days reached to 264.78 mL/g-VS at S-mZVI 10 g/L. • S-mZVI had significant influence on the methanogenesis stage of co-digestion. • The addition of S-mZVI improved the direct interspecies electron transfer (DIET). The enhancement of zerovalent iron (ZVI) on anaerobic digestion (AD) has been proved, but there are still some problems that constrain the large-scale application of ZVI, such as the destruction of cell membrane and the inhibition of methanogenesis led by rapid H 2 accumulation. Aiming at these problems, sulfidated microscale zerovalent iron (S-mZVI) was employed to evaluate its effect on anaerobic co-digestion (AcoD) of waste activated sludge (WAS) and food waste (FW). Experimental results showed that S-mZVI promoted the direct interspecies electron transfer (DIET) between specific bacteria and methanogens, resulting in higher methane yield. At S-mZVI 10 g/L, the cumulative methane yield and ETS activity reached 264.78 mL/g-VS and 24.62 mg INTF/(g-TS h), which was 1.33 and 1.83 times that of blank. Microbiological analysis demonstrated that the abundance of DIET-related microorganisms such as Syntrophomonas , Methanosarcina and Methanobacterium increased with the increasing dosage of S-mZVI. [ABSTRACT FROM AUTHOR]

• Biochar enhanced high-quality biomethane production from PS. • Biochar accelerated PS hydrolysis and enhanced methane production potential of PS. • Biochar incresed buffering capacity, conductivity and alleviated NH 3 inhibition. • Biochar enhanced sludge reduction and reduced sludge disposal costs. • Biochar could be applied to anaerobic digestion of the mixture of WAS and PS. This study conducted batch and continuous tests to reveal the feasibility of corn stover biochar on improving anaerobic digestion of primary sludge (PS). Dosing biochar (1.82, 2.55 and 3.06 g/g Total Solids (TS)) in digester improved methane content increasing from 67.5% to 81.3–87.3% and enhanced methane production by 8.6–17.8%. Model analysis indicated that biochar accelerated PS hydrolysis and enhanced methane potential of PS. The mechanistic studies showed that biochar enhanced process stability provided by strong buffering capacity and alleviated NH 3 inhibition. In continuous test over 116 days, the volatile solids (VS) destruction in the biochar-dosed digester increased by 14.9%, resulting in a 14% reduction in the volume of digestate for disposal. Biochar changed microbial community in an expected direction for anaerobic digestion. This work suggests that biochar technology would apply to co-digestion of WAS and PS to maximize the energy recovery and sludge reduction from the two sludge streams. [ABSTRACT FROM AUTHOR]

• Impact of pyrochar (PC) and hydrochar (HC) on the anaeribic digestion of WAS was compared. • The highest accumulative methane yield was observed at group HC180. • Pyrochar showed a slightly negative effect on methane production. • Specific DIET-based syntrophic microbes were enriched with HCs addition. This study compared the effects of sewage sludge-derived pyrochar (PC300, PC500, and PC700) and hydrochar (HC180, HC240, and HC300) on mesophilic anaerobic digestion of waste activated sludge (WAS). It was demonstrated that hydrochar can better promote the methane production compared with pyrochar. The highest accumulative methane yield of 132.04 ± 4.41 mL/g VS added was obtained with HC180 addition. In contrast, the PC500 and PC700 showed a slightly negative effect on methane production. Sludge-derived HC not only accelerated the solubilization and hydrolysis of sludge floc, but also improved the production of acetic acid and propionate, further resulting in improved methane production. Simultaneously, the syntrophic microbes facilitating direct interspecies electron transfer (DIET) such as Syntrophomonas, Peptococcaceae, Methanosaeta and Methanobacterium bred rapidly with the addition of HCs. These results indicated that the hydrochar is more ideal as the accelerant to promote the methane production from mesophilic anaerobic digestion of WAS than the pyrochar. [ABSTRACT FROM AUTHOR]