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• The presence of 15% lignin promoted the SCFAs production to 1.7 times from WAS, and the proportion of acetic increased by 61.8%. • Lignin was beneficial to the solubilization process, which may be related to its hydrophobic properties. • Lignin enhanced the SCFAs production bio-processes and inhibited the SCFAs consumption bio-processes. • The abundance of microorganisms related to acid production in fermenter with lignin increased. Lignin, a biological resource with great potential, can be as high as ∼16% of the total organics in the waste activated sludge (WAS). This work therefore aims to fill the knowledge gap about the effect of lignin on short-chain fatty acids (SCFAs) production from anaerobic fermentation of sludge. Experimental results showed that lignin promoted rather than inhibited SCFAs production. Specifically, the presence of 15% lignin promoted the SCFAs production from 129.1 ± 6.5 to 223.14 ± 7.8 mg COD/g VSS compared with the control, and the proportion of acetic increased by 61.8%, while that of propionic decreased by 44.9%. Mechanism exploration revealed that lignin improved the solubilization of biodegradable substrates due to its hydrophobic characteristics. In addition, lignin enhanced the acidogenesis process, possibly by perfecting the electron transfer chain in the fermentation system, and the quinone structure in lignin may compete electrons with methanogens to inhibit the consumption of SCFAs. Microbiological analysis showed that the abundance of microorganisms related to acidogenesi, especially the acetogenesis, including Proteiniclasticum sp., Acetoanaerobium sp., in the fermenter with lignin increased, which caused the community to shift towards specialized and diverse SCFAs production. [Display omitted] [ABSTRACT FROM AUTHOR]

Tetracycline (TC), a widely used antibiotic, was enriched in waste activated sludge (WAS) at significant levels. However, the TC impact on WAS anaerobic fermentation are still poorly understood. This work aims to analyze the effect of TC to the WAS anaerobic fermentation by investigating the differences of sludge properties, short-chain fatty acids (SCFAs) production and microbial community abundance. The results showed that the environmental level of TC had no effect on the SCFAs production, but with the further increase of the content of TC to 60 mg/kg TSS, the maximum SCFAs yield decreased from 125.1 ± 3.2 to 90.8 ± 1.7 mg COD/g VSS. Mechanism exploration indicated that TC had no significant effect on solubilization, hydrolysis and homoacetogenesis processes, but severely inhibited acidogenesis, acetogenesis and methanogenesis processes. Microbial analysis showed that the presence of TC reduced the diversity of microbial communities and the abundance of functional microorganisms relevant to SCFAs production and complex organic degradation, such as Proteiniclasticun and Novosphingobium. This negative effect was persistent because only a small amount of TC can be degraded in the anaerobic fermentation process. Hence, CaO 2 was proposed and studied as a regulation strategy that can reduce the toxicity of TC on anaerobic fermentation. [Display omitted] • When the TC level were 5, 30 and 60 mg/kg TSS, the SCFAs production decreased by 11.0%, 18.2%, and 27.4%, respectively. • TC severely inhibited acidogenesis, acetogenesis and methanogenesis processes. • The most of TC was stuck after anaerobic fermentation of WAS. • CaO 2 improved the SCFAs production by degrading TC and disintegrating sludge. [ABSTRACT FROM AUTHOR]

Polyethylene (PE) microplastic, which is detected in various environmental media worldwide, also inevitably enters wastewater treatment plants, which may have an impact on anaerobic processes in wastewater treatment. In this work, the effect of PE microplastics on anaerobic sulfur transformation was explored. Experimental results showed that PE microplastics addition at 0.1%− 0.5% w/w promoted H 2 S production by 14.8%−27.4%. PE microplastics enhanced the release of soluble organic sulfur and inorganic sulfate, and promoted the bioprocesses of organosulfur compounds hydrolysis and sulfate reduction. Mechanism analysis showed that PE microplastics increased the content of electroactive components (e.g., protein and humic acids) contained in extracellular polymeric substances (EPS). In particular, PE microplastics increased the proportion and the dipole moment of α-helix, an important component involved in electron transfer contained in extracelluar protein, which provided more electron transfer sites and promoted the α-helix mediated electron transfer. These enhanced the direct electron transfer ability of EPSs, which might explain why PE microplastics facilitated the bioprocesses of organosulfur compounds hydrolysis and sulfate reduction. Correspondingly, metagenomic analysis revealed that PE microplastics increased the relative abundance of S2- producers (e.g., Desulfobacula and Desulfonema) and the relative abundance of functional genes involved in anaerobic sulfur transformation (e.g., PepD and cysD), which were beneficial to H 2 S production in anaerobic system. [Display omitted] • PE-MPs increased H 2 S production from WAS anaerobic treatment. • PE microplastics accelerate transformation of sulfur in gas-liquid and solid phases. • The presence of PE-MPs enhanced the direct electron transfer ability of EPSs. • PE-MPs increased the relative abundance of S2- producers and functional genes. [ABSTRACT FROM AUTHOR]

Due to the poor biodegradability of released organics and the rapid consumption of hydrogen, hydrogen production from the untreated waste activated sludge (WAS) and/or inocula is still limited. In this study, it was found that the dark fermentative hydrogen production was largely enhanced from WAS pretreated by freezing in the presence of nitrite. With an increase of nitrite addition from 100 to 400 mg NO 2 −-N/L during freezing pretreatment (−5 °C for 4 h), the maximal hydrogen yield increased from 7.96 to 19.40 mL/g VS (volatile solids), which was 5.5–13.4 times of that in the control (without freezing and nitrite addition). Mechanism explorations revealed that the proposed pretreatment not only accelerated the disintegration of sludge but also promoted the proportion of biodegradable organics released, thereby provided more bio-available substrates for subsequent hydrogen production. Proposed pretreatment severely suppressed the sludge microorganisms responding to homoacetogenesis (−32.1%), methanogenesis (−58.4%), and sulfate-reducing process (−51.5%), inhibited the consumption of hydrogen. Moreover, there was more acetic and butyric (76% versus 57.5%) but less propionic acid (22.6% versus 13.4%) in this pretreated fermenter, which was in correspondence with the theory of fermentation type affecting hydrogen production. Long-term fermentation experiments indicated that the proposed pretreatment boosted the [FeFe]-hydrogenase activities while suppressed the activities of carbon monoxide dehydrogenase, coenzyme F420, and adenylyl sulfate reductase. Image 1 • FNP enhanced dark fermentative hydrogen production from WAS by 5.5–13.4 times. • FNP accelerated sludge disintegration and promoted organics biodegradability. • FNP suppressed the hydrogen-consuming bacteria by 32.1–58.4%. • FNP induced the shift of fermentation to butyrate-type. [ABSTRACT FROM AUTHOR]

Recent investigations verified that calcium peroxide (CaO 2) could be used to pretreat waste activated sludge to promote methane yield from anaerobic digestion. However, the underlying mechanism of how CaO 2 pretreatment promotes methane production is unclear. This work therefore aims to provide insights into such systems. Experimental results showed that with an increase of CaO 2 dosage from 0 to 0.14 g/g VSS (volatile suspended solids) the methane yield increased linearly from 146.3 to 215.9 mL/g VSS. Further increases of CaO 2 resulted in decreases in methane yield. CaO 2 pretreatment promoted the disintegration of sludge and the degradation of sludge recalcitrant organics (especially humus and lignocellulose), thereby providing more substrates for subsequent methane production. Ultraviolet absorption spectroscopy indicated that CaO 2 enhanced the cleavage of unsaturated conjugated bonds and reduced the aromaticity of humus and lignocellulose. Fourier transform infrared spectroscopy showed that CaO 2 changed the structures and functional groups of humus and lignocellulose, making them transform to be biodegradable. GC/MS analyses exhibited that the degradation products of humus and lignocellulose included several types of small molecular organics such as ester-like, acid-like, and alcohol-like substances. Further investigation demonstrated that substantial methane could be produced from these degradation products. It was also found that the presence of recalcitrant organics was detrimental to anaerobes relevant to anaerobic digestion, and the degradation of such recalcitrant organics mitigated their inhibitions to the anaerobes. Model-based analysis suggested that CaO 2 pretreatment increased the maximum methane yield and methane production rate, which were consistent with the analysis above. Image 1 • Pretreatment with 0.14 g/g VSS CaO 2 increased methane yield to 1.3 times from WAS. • CaO 2 pretreatment promoted the degradation of humus and lignocellulose. • CaO 2 could mitigate inhibitions of recalcitrant organics to the anaerobes. • The CaO2 reaction residues inhibited all the microbes relevant to anaerobic digestion. [ABSTRACT FROM AUTHOR]

• Rhamnolipid significantly increased H 2 S production from sludge fermentation. • Rhamnolipid increased the release of organic sulfurs and inorganic sulfate. • The added and in situ generated rhamnolipid damaged the structure of organic sulfurs. • Rhamnolipid promoted H 2 S production from the hydrolysis of organic sulfurs. • Rhamnolipid facilitated H 2 S production from dissimilatory sulfate reduction. Rhamnolipid (RL), one representative biosurfactant, is widely regarded as an economically feasible and environmentally beneficial additive to improve fermentation efficiency and resource recovery from waste activated sludge (WAS). However, its potentially detrimental impact on WAS fermentation such as H 2 S generation was overlooked previously. This study therefore aims to fill the gap through exploring whether and how the presence of RL affects H 2 S generation from WAS anaerobic fermentation. Experimental results showed that when RL increased from 0 to 40 mg/g total suspended solids (TSS), the cumulative H 2 S yield enhanced from 323.6 × 10−4 to 620.3 × 10−4 mg/g volatile suspended solids (VSS). Mechanism analysis showed that RL reduced WAS surface tension, which benefited transformations of organic sulfurs (e.g., aliphatic-S and sulfoxide) and inorganic sulfate from solid to liquid phase. The presence of RL not only reduced the ratio of α-helix/(β-sheet + random coil) and damaged the hydrogen bonding networks of organic sulfurs but also promoted substrate surface charges and cell membrane permeability. These facilitated the contact between hydrolase and organic sulfurs, thereby increasing sulfide production from organic sulfurs hydrolysis. Further investigations showed that RL promoted the expression of key genes (e.g., aprA/B and dsrA/B) involved in the dissimilatory sulfate reduction, which accelerated the reaction of adenosine 5'-phosphosulfate (APS) → sulfite → sulfide. Meanwhile, RL inhibited the corresponding key genes such as CysH , and Sir , responsible for assimilatory sulfate reduction (APS → 3'-phosphoadenosine-5'phosphosulfate → organosulfur), which reduced substrate competition in favor of H 2 S production from dissimilatory sulfate reduction. Besides, RL decreased the fermentation pH, which benefited the transformation of H S − to H 2 S. [Display omitted] [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] • Pretreatment with 0.1 g/g TSS KMnO 4 reduced H 2 S yield from WAS to 67%. • KMnO 4 inhibited sulfur containing organics hydrolysis and sulfate reduction. • KMnO 4 addition changed the chemical equilibrium of sulfide species. • KMnO 4 decreased the related abundances of S2− producers and functional genes. Potassium permanganate, a versatile strong oxidant, has been applied as a highly effective additive to degrade pollutants and recover resources from Waste activated sludge (WAS). In addition to these benefits, it was observed in this study that KMnO 4 largely reduced H 2 S production from WAS anaerobic fermentation. With an increase of KMnO 4 dosage from 0 to 0.1 g/g TSS, the maximal H 2 S production reduced from 292.3 × 10−4 to 96.4 × 10−4 mg/g VSS while the maximal short-chain fatty acids production increased from 23 to 251 mg COD/g VSS. Model-based analysis showed that KMnO 4 decreased the maximal H 2 S yield potential and H 2 S production rate. The mechanism explorations revealed that several oxidative substances (e.g., •O 2 − and •OH), Mn2+, and O H - were substantially generated after KMnO 4 being added into the fermenters. The generated oxidative substances resulted in intracellular substance release even cell apoptosis. This inhibited the activities of two main S 2 - (H 2 S precursor) producers, i.e., Sulfate reducing bacteria (SRBs) and anaerobes responsible for hydrolysis of sulfur-containing organics, especially that of SRBs. Experimental results showed that 0.1 g/g TSS KMnO 4 inhibited sulfur-containing organics hydrolysis, amino acids degradation, and sulfate reducing process by 12.5%, 27.2%, and 61.2%, respectively. The Mn2+ released from KMnO 4 and other metal ions (e.g., Fe2+) originated from metal-binding functional groups owing to KMnO 4 addition caused substantial S-based precipitations, which also decreased S 2 - in the fermentation liquor. Besides, the generated O H - increased fermentation pH, which benefited the chemical equilibrium of sulfide species from H 2 S to H S - and S 2 - . Microbial community and PICRUSt2 analyses further revealed that KMnO 4 significantly decreased the abundances of S 2 - producers and functional genes responsible for sulfate reducing process. [ABSTRACT FROM AUTHOR]