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Diclofenac (DCF), a nonsteroidal anti-inflammatory drug, is one of the most commonly detected pharmaceuticals in wastewater treatment plants. However, the fate of DCF in waste activated sludge (WAS) anaerobic fermentation has not been well-understood so far. This work therefore aims to comprehensively reveal whether and how DCF is transformed in WAS mesophilic anaerobic fermentation through both experimental investigation and density functional theory (DFT) calculation. Experimental results showed that ∼28.8% and 45.8% of DCF were respectively degraded during the batch and long-term fermentation processes. Based on the detected intermediates and DFT-predicted active sites, three metabolic pathways, i.e., chlorination, hydroxylation, and dichlorination, responsible for DCF transformation were proposed. DFT calculation also showed that the Gibbs free energy (ΔG) of the three transformation pathways was respectively 19.0, −4.3, and −19.3 kcal/mol, suggesting that the latter two reactions (i.e., hydroxylation and dichlorination) were thermodynamically favorable. Illumina MiSeq sequencing analyses revealed that DCF improved the populations of complex organic degradation microbes such as Proteiniclasticum and Tissierellales , which was in accord with the chemical analyses above. This work updates the fundamental understanding of the degradation of DCF in WAS anaerobic fermentation process and enlightens engineers to apply theoretical calculation to the field of sludge treatment or other complex microbial ecosystems. [Display omitted] • Approximately 28.8% of DCF was degraded during anaerobic fermentation system. • DCF reduced the diversity and complexity of microbial community. • Hydroxylation and dichlorination reactions were thermodynamically favorable. • Proteiniclasticum and Tissierellales may be microbes related to DCF degradation. [ABSTRACT FROM AUTHOR]

Hydrogen production from waste-activated sludge (WAS) anaerobic fermentation is considered to be an effective method of resource recovery. However, the presence of a large number of complex organic compounds in sludge will affect the biological hydrogen production process. As an extensively applied prevalent anti-inflammatory drug, diclofenac (DCF) is inevitably released into the environment. However, the effect of diclofenac on hydrogen production from WAS anaerobic fermentation has not been fully investigated. This work therefore aims to comprehensively investigate the removal efficiency of DCF in mesophilic anaerobic fermentation of WAS and its effect on hydrogen yield. Experiment results showed that 32.5%–38.3% of DCF was degraded in the fermentation process when DCF concentration was ranged from 6 to 100 mg/kg TSS (total suspended solids). DCF at environmental level inhibited hydrogen production, the maximal hydrogen yield decreased from 24.2 to 15.3 mL/g VSS (volatile suspended solids) with an increase of DCF addition from 6 to 100 mg/kg TSS. This is because the presence of DCF caused inhibitions to acetogenesis and acidogenesis, the processes responsible for hydrogen production, probably due to that the polar groups of DCF (i.e., carboxyl group) could readily bind to active sites of [FeFe]- Hydrogenase. Besides, the microbial analysis revealed that DCF increased the microbial diversity but had few influences on the microbial structure. [Display omitted] • Approximately 32.5%–38.3% of DCF was degraded during anaerobic fermentation system. • DCF reduced the hydrogen production from WAS anaerobic fermentation. • DCF led to inhibition to hydrolysis, acidogenesis, and acetogenesis. • DCF decreased the numbers of anaerobes relevant to hydrogen producers. [ABSTRACT FROM AUTHOR]

• BZC exhibited a dose-dependent effect on the production of SCFAs. • Novel methods revealed protein denaturation diversity between liquid-solid phases. • EPS secreted and the solubilization of sludge was enhanced with BZC. • The hydrolysis stage was promoted but the methanogenesis stage was inhibited. • Microbial structure changed and functional bacteria enriched with BZC. Benzethonium chloride (BZC) is viewed as a promising disinfectant and widely applied in daily life. While studies related to its effect on waste activated sludge (WAS) anaerobic fermentation (AF) were seldom mentioned before. To understand how BZC affects AF of WAS, production of short chain fatty acids (SCFAs), characteristics of WAS as well as microbial community were evaluated during AF. Results manifested a dose-specific relationship of dosages between BZC and SCFAs and the optimum yield arrived at 2441.01 mg COD/L with the addition of 0.030 g/g TSS BZC. Spectral results and protein secondary structure variation indicated that BZC denatured proteins in the solid phase into smaller proteins or amino acids with unstable structures. It was also found that BZC could stimulate the extracellular polymeric substances secretion and reduce the surface tension of WAS, leading to the enhancement of solubilization. Beside, BZC promoted the hydrolysis stage (increased by 7.09 % to 0.030 g/g TSS BZC), but inhibited acetogenesis and methanogenesis stages (decreased by 6.85 % and 14.75 % to 0.030 g/g TSS BZC). The microbial community was also regulated by BZC to facilitate the enrichment of hydrolytic and acidizing microorganisms (i.e. Firmicutes). All these variations caused by BZC were conducive to the accumulation of SCFAs. The findings contributed to investigating the effect of BZC on AF of WAS and provided a new idea for the future study of AF mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]

This study is the first to report a new free ammonia (FA) pretreatment technique to recover short-chain fatty acids (SCFAs) from primary sludge (PS). The results showed FA pretreatment (240 mg N/L) largely enhanced the SCFAs production from PS to 355.8 mg chemical oxygen demand (COD)/g VSS, which was about 4.5-fold that of control (i.e., 80 mg COD/g VSS). Mechanism investigations showed that FA pretreatment greatly accelerated the PS solubilization and destroyed the integrity of EPS, and the easily biodegradable substrates in the fermentation broth increased significantly, providing microorganisms with more organics to convert into SCFAs. Further analyses displayed that FA greatly inhibited the methane production during fermentation, resulting in further accumulation of SCFAs. Given that the NH 4 +-N released during the fermentation can be converted into FA in situ , this could facilitate the transition of wastewater treatment plants operation from linear to circular mode. [Display omitted] • FA greatly increased the production of SCFAs by about 4.5 times that of the control. • The optimum concentration of FA pretreatment was 240 mg/L with the SCFAs yield of 355.8 mg COD/g VSS. • FA facilitated the disintegration and biodegradability of PS and inhibited methane production. • FA pretreatment could be applied to PS alone and a mixture of WAS and PS. [ABSTRACT FROM AUTHOR]

[Display omitted] • CBZ at environmental levels slightly promoted the production of SCFAs. • The abundance of some functional traits changed in the presence of CBZ. • Persulfate-based treatment was effective for CBZ removal. • Hydroxylation and deamination reaction were the main pathways for CBZ degradation. The effects of pollutants on anaerobic fermentation of waste activated sludge (WAS) have been widely studied. Nevertheless, little attention was paid to how to mitigate the adverse effects of pollutants on anaerobic fermentation. In this work, representative pollutant carbamazepine (CBZ) was chosen to explore the potential effects of CBZ on WAS anaerobic fermentation. Experimental results showed that CBZ at environmental levels slightly promoted the production of short-chain fatty acids (SCFAs), which increased from 3858.2 to 4143.8 mg COD/L as the CBZ dose increased from 8 to 28 mg/kg VSS, but further increasing the CBZ dose to 88 mg/kg VSS decreased the production of SCFAs. Context of homologous group database revealed that the abundance of some functional traits changed, such as RNA processing and modification, energy production and conversion, and amino acid transport. This adverse effect was sustained because CBZ could not be degraded during anaerobic fermentation. Therefore, a regulation strategy was proposed, e.g., persulfate was used to attenuate the toxicity of CBZ to WAS anaerobic fermentation, and the results showed that the removal of CBZ reached 83.7 % in the persulfate-treated reactor. Based on density functional theory and metabolic intermediates determination, hydroxylation and deamination reactions were the two main metabolic pathways for CBZ degradation. [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]