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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]

[Display omitted] • Refractory substances are primary but often ignored factor related to WAS biodegradability. • The presence and role of refractory substances in WAS biodegradability are reviewed. • Inhibition mechanisms of refractory substances in WAS are analyzed. • Mechanisms of pretreatment strategies to enhance WAS biodegradability are discussed. • Challenges of WAS enhanced biodegradability technology are prospected. Anaerobic digestion (AD) is a low-cost technology widely used to divert waste activated sludge (WAS) to renewable energy production, but is generally restricted by its poor biodegradability which mainly caused by the endogenous and exogenous refractory substances present in WAS. Several conventional methods such as thermal-, chemical-, and mechanical-based pretreatment have been demonstrated to be effective on organics release, but their functions on refractory substances conversion are overlooked. This paper firstly reviewed the presence and role of endogenous and exogenous refractory substances in anaerobic biodegradability of WAS, especially on their inhibition mechanisms. Then, the pretreatment strategies developed for enhancing WAS biodegradability by facilitating refractory substances conversion were comprehensively reviewed, with the conversion pathways and underlying mechanisms being emphasized. Finally, the future research needs were directed, which are supposed to improve the circular bioeconomy of WAS management from the point of removing the hindering barrier of refractory substances on WAS biodegradability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Non-antibiotic pharmaceutical also promoted the widespread enrichment of ARGs. • Low concentrations of carbamazepine enriched ARGs more than high concentrations. • Carbamazepine promoted the aggregation of microorganisms and conjugation of ARGs. • TCS, QS and T4SS played important roles in the horizontal transfer of ARGs. • Carbamazepine increased the potential for pathogens to acquire antibiotic resistance. Antimicrobial resistance is a global health security issue of widespread concern. Recent studies have unveiled the potential contribution of non-antibiotics to the emergence of antimicrobial resistance. This study investigated the effect of carbamazepine, a non-antibiotic pharmaceutical, on the fate of antibiotic resistance genes (ARGs) during anaerobic digestion. The results, as revealed by both metagenomic sequencing and absolute quantification, demonstrated that carbamazepine induced the enrichment of ARGs and increased the abundance of ARGs hosts by 1.2–2.1 times. Carbamazepine facilitated microbial aggregation and intercellular communication by upregulating functional genes associated with two-component systems, quorum sensing and type IV secretion systems, thereby increasing the frequency of ARGs conjugation. Furthermore, carbamazepine induced the acquisition of ARGs by pathogens and elevated the overall pathogenic abundance. This study revealed the mechanisms of microbial self-regulation and ARGs transmission under carbamazepine stress, highlighting the potential health risks posed by non-antibiotic pharmaceuticals during the safe disposal of sludge. [ABSTRACT FROM AUTHOR]

[Display omitted] • CaO effectively promoted kitchen waste dry anaerobic digestion, and the maximum biogas was 656.84 mL/g. • CaO facilitated the production of dissolved organic matter and the transformation of VFA, thereby avoiding its negative impact on biogas production. • Metagenomics revealed the microbial mechanism underlying the CaO enhanced kitchen waste dry anaerobic digestion. In light of the characteristics of excessive acidification and low biogas yield during kitchen waste (KW) dry digestion, the impact of the calcium oxide (CaO) on KW mesophilic dry digestion was investigated, and the enhanced mechanism was revealed through metagenomic approach. The results showed that CaO increased the biogas production, when the CaO dosage was 0.07 g/g (based on total solid), the biogas production reached 656.84 mL/g suspended solids (VS), approximately 8.38 times of that in the control. CaO promoted the leaching and hydrolysis of key organic matter in KW. CaO effectively promoted the conversion of volatile fatty acid (VFA) and mitigated over-acidification. Macrogenome analysis revealed that CaO increased the microbial diversity in KW dry digestion and upregulated the abundance of genes related to amino acid and carbohydrates metabolism. This study provides an effective strategy with potential economic benefits to improve the bioconversion efficiency of organic matter in KW. [ABSTRACT FROM AUTHOR]

[Display omitted] • UHP pretreatment enhanced the production of SCFAs in WAS anaerobic fermentation. • UHP pretreatment contributed to WAS disintegration significantly. • UHP pretreatment facilitated the generation and transformation of intermediates. • OH, O 2 and urea were the major contributors to the increased WAS disintegration. • Functional microbials and genes related with acetate production were upregulated. Improving the anaerobic treatment performance of waste activated sludge (WAS) to achieve resource recovery is an indispensable requirement to reduce carbon emissions, minimize and stabilize biosolids. In this study, a novel strategy by using urea hydrogen peroxide (UHP) to enhance SCFAs production through accelerating WAS disintegration, degrading recalcitrant substances and alleviating competitive suppression of methanogens. The SCFAs production and acetate proportion rose from 436.9 mg COD/L and 31.3% to 3102.6 mg COD/L and 54.1%, respectively, when UHP grew from 0 to 80 mg/g TSS. Mechanism investigation revealed that OH, O 2 and urea were the major contributors to accelerate WAS disintegration with the sequence of OH> O 2 > urea. Function microbes related to acidification and genes associated with acetate production ([EC:2.3.1.8] and [EC:2.7.2.1]) were upregulated while genes encoding propionic acid production ([EC:6.4.1.3] and [EC:6.2.1.1]) were downregulated. These results raised the application prospects of UHP in WAS resource utilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • Citric acid (CA) exhibits dose-dependent effects on the SCFAs promotion. • CA is mainly converted to acetic acid in the anaerobic fermentation system. • CA removes multivalent cations from extracellular polymeric substances (EPS). • CA facilitates WAS hydrolysis by disrupting EPS and microbial cells. • Microbial functional traits related to SCFAs production are regulated by CA. Numerous effective chemical strategies have been explored for short-chain fatty acids (SCFAs) production from waste activated sludge (WAS), but many technologies have been questioned due to the chemical residues. This study proposed a citric acid (CA) treatment strategy for improving SCFAs production from WAS. The optimum SCFAs yield reached 384.4 mg COD/g VSS with 0.08 g CA/g TSS addition. Meanwhile, CA biodegradation occurred and its contribution to the yield of total SCFAs, especially acetic acid, cannot be ignored. Intensive exploration indicated the sludge decomposition, the biodegradability of fermentation substrates, as well as the abundance of fermenting microorganisms were definitely enhanced in the existence of CA. The optimization of SCFAs production techniques based on this study deserved further study. This study comprehensively revealed the performance and mechanisms of CA enhancing biotransformation of WAS into SCFAs and the findings promotes the research of carbon resource recovery from sludge. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calcium hypochlorite-coupled aged refuse to enhance hydrogen production from sludge was reported. • Calcium hypochlorite-coupled aged refuse enhanced the soluble organic matter release in sludge. • Calcium hypochlorite-coupled aged refuse reduced the phosphate concentration in fermentation broth. • The prospect of calcium hypochlorite-coupled aged refuse in wastewater treatment plants is presented. This work investigated the effect of calcium hypochlorite (CH) coupled aged refuse (AR) treatment on the enhanced hydrogen generation from sludge anaerobic dark fermentation (SADF). The enhanced mechanism was systematically revealed through sludge disintegration, organic matter biotransformation, and microbial community characteristics, etc. The experimental data showed that CH coupled AR increased the hydrogen yield to 18.1 mL/g, significantly higher than that in the AR or CH group alone. Mechanistic analysis showed that CH-coupled AR significantly promoted sludge disintegration and hydrolysis processes, providing sufficient material for hydrogen-producing bacteria. Microbiological analysis showed that CH-coupled AR increased the relative abundance of responsible hydrogen-producing microorganisms. In addition, CH-coupled AR was very effective in reducing phosphate content in the fermentation liquid and fecal coliforms in the digestate, thus facilitating the subsequent treatment of fermentation broth and digestate. CH coupled AR is an alternative strategy to increase hydrogen production from sludge. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of PBDEs on hydrogen production from sludge has been explored. • PBDEs inhibited disintegration, hydrolysis, acidification and homoacetogenic processes. • PBDEs stimulated microorganisms to produce intracellular and extracellular ROS and reduced cellular activity. • PBDEs reduced the relative abundance of microorganisms associated with hydrogen production. Polybrominated diphenyl ethers (PBDEs), derived from electronics, furniture, etc., are detected with high level in excess sludge (ES). In this work, the influence of PBDEs on ES dark fermentation (ESDF) hydrogen production and the related key mechanisms were explored. The result shows PBDEs exposure reduced hydrogen production, and hydrogen accumulation decreased from 17.6 mL/g in blank to 12.3 mL/g with 12.0 mg/Kg PBDEs. PBDEs induced the reactive oxygen species production, which directly led to cell inactivation and reduced hydrogen production. Furthermore, PBDEs decreased ES disintegration, hydrolysis, acidification and homoacetogenic processes and inhibited the activities of enzymes related to hydrogen production. PBDEs also affected the diversity and richness of microbial communities in dark fermentation systems, especially high doses of PBDEs reduced the relative abundance of microorganisms associated with hydrogen production. In conclusion, PBDEs reduce hydrogen generation from ES. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfite-based pretreatment remarkably promoted VFAs production from microalgae. • Acetate proportion of 54.5% was obtained at 200 mg S/L with time of day 8. • More and relatively easy biodegradable organics were released into liquid phase. • Sulfite-induced sulfate-reducing bacteria facilitated the acetate generation pathway. • β-glucanase, β-glucosidase, and acetate kinase activities were accelerated. Volatile fatty acids (VFAs) production from anaerobic fermentation of microalgae is generally constrained by low organics solubilization and poor substrate-availability. In this study, sulfite-based pretreatment was developed to overcome such situation. Experimental results showed that the maximum concentration of VFAs (467.5 mg COD/g VSS) and corresponding acetate proportion (54.5%) was obtained at 200 mg sulfite-S/L with fermentation time of day 8, which was respectively 2.1- and 1.9-fold of control. It was found that after sulfite pretreatment, more and relatively easy biodegradable organics were released into liquid phase, providing available substrate for acid-producing bacteria. The rigid cell wall of microalgae was destroyed, evidenced by the decreased particle size and increased surface area, which made the microalgae more accessible for subsequent hydrolysis and acidification. Meanwhile, the sulfite-induced sulfate-reducing bacteria facilitated the acetate generation pathway. The accelerated activities of β-glucanase, β-glucosidase, and acetate kinase involved in anaerobic fermentation further validated the above results. [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] • DO partition was obtained in a single-stage PNA system. • A high TNRE of 82.6% was achieved, and the NRR reached 1.24 kg-N/m3/d. • The synergy between different functional microbes was enhanced via DO partition. • Sludge granulation enriched the functional microbes and promoted the synergy. The rapid start-up and stable operation of the single-stage partial nitritation-anammox (PNA) process remains a challenge in practical applications. An integrated investigation of nitrogen removal performance, sludge characteristics, activity and abundance, and microbial dynamics was implemented for 360 days via an airlift internal circulation reactor. During long-term operation, the reactor realized a stable dissolved oxygen (DO) partition and cultivated granular sludge. The nitrogen removal rate increased from 0.15 kg-N/m3/d to 1.24 kg-N/m3/d, and a high nitrogen removal efficiency of 82.6% was obtained. A stable DO partition further accelerated the bioreaction rates and enhanced the activity of functional microbes. The activities of ammonia oxidation and anammox reached 1.21 g-N/g-VSS/d and 1.43 g-N/g-VSS/d, respectively. Sludge granulation efficiently enriched the abundances of Candidatus Brocadia (7.4%) and Nitrosomonas (5.2%). These results demonstrated that efficient DO partition and stable culture of granular sludge could enhance the synergy of functional microbes for autotrophic nitrogen removal. [ABSTRACT FROM AUTHOR]

[Display omitted] • The intrinsic drawbacks of WAS for efficient AD process are disclosed. • The main inhibitory mechanisms of interfering pollutants for WAS AD were analyzed. • Potential strategies for mitigating the restrictions on WAS digestion are revealed. • The future directions for the improvement of WAS digestion are proposed. Anaerobic digestion (AD) is an effective approach for waste activated sludge (WAS) disposal with substantial recovery of valuable substrates. Previous studies have extensively explored the correlations of common operational parameters with AD efficiency, but the impacts of intrinsic characteristics of WAS on the AD processes are generally underestimated. This study focused on disclosing the association of intrinsic drawbacks in WAS with AD performance, and found that the cemented WAS structure, low fraction of biomass and various high levels of inhibitory pollutants (e.g. , organic pollutants and heavy metals), as the integral parts of WAS all greatly restricted the AD performance. The main potential strategies and underlying mechanisms to mitigate the restrictions for efficient WAS digestion, including the practical pretreatment methods, bioaugmentation and aided substances addition, were critically analyzed. Also, future directions for the improvement of WAS digestion were proposed from the perspectives of technical, management and economic aspects. [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]