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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]

• 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]

Free ammonia (FA), the unionized form of ammonium, is presented in anaerobic fermentation of waste activated sludge (WAS) at high levels. However, its potential role in sulfur transformation, especially H 2 S production, during WAS anaerobic fermentation process was unrecognized previously. This work aims to unveil how FA affects anaerobic sulfur transformation in WAS anaerobic fermentation. It was found that FA significantly inhibited H 2 S production. With an increase of FA from 0.04 to 159 mg/L, H 2 S production reduced by 69.9%. FA firstly attacked tyrosine-like proteins and aromatic-like proteins in sludge EPSs, with C O groups being responded first, which decreased the percentage of α-helix/(β-sheet + random coil) and destroyed hydrogen bonding networks. Cell membrane potential and physiological status analysis showed that FA destroyed membrane integrity and increased the ratio of apoptotic and necrotic cells. These destroyed sludge EPSs structure and caused cell lysis, thus strongly inhibited the activities of hydrolytic microorganisms and sulfate reducing bacteria. Microbial analysis showed that FA reduced the abundance of functional microbes (e.g., Desulfobulbus and Desulfovibrio) and genes (e.g., MPST , CysP , and CysN) involved in organic sulfur hydrolysis and inorganic sulfate reduction. These findings unveil an actually existed but previously overlooked contributor to H 2 S inhibition in WAS anaerobic fermentation. [Display omitted] • Free ammonia in situ reduced H 2 S production during sludge anaerobic treatment. • Free ammonia inhibited the activities of hydrolytic microorganisms and SRBs. • Free ammonia destroyed membrane integrity and led to apoptosis. • Free ammonia reduced the relative abundance of S2- producers. [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]

• CaO 2 effectively eliminated the inhibitory effect of grease on SCFAs production. • SCFAs yield from food waste fermentation was further promoted with CaO 2. • CaO 2 facilitated biodegradable organics release and improved grease degradation. • OH– and Ca2+ played a vital role in SCFAs production improvement. • O 2 – and OH radicals were the main contributors to grease degradation. Deterioration of anaerobic fermentation can occur with the presence of grease in food waste, but little information on eliminating this deterioration is currently available. In this study, it was found that the presence of 10 g/L grease decreased SCFAs production from 16.97 to 13.32 g COD/L and prolonged the optimal fermentation time to 7 days, but could be respectively recovered to 39.10 g COD/L and 4 days with 0.02 mg/g VS (volatile solids) calcium peroxide addition. Mechanism investigations indicated that calcium peroxide facilitated biodegradable organics release and improved grease degradation, thereby providing enough nutrients and better growth environments to microbes for SCFAs-producing, which could be further supported by the elevated enzymes activities responding to hydrolysis and acidification process. Further investigations revealed that among the main derivates of calcium peroxide, OH– and Ca2+ played vital role in SCFAs production promotion, O 2 – and OH radicals were the main contributors to grease degradation. [ABSTRACT FROM AUTHOR]