Efficient electrosynthesis of HO2- from air for sulfide control in sewers.

Electrochemically in-situ generation of oxygen and caustic soda is promising for sulfide management while suffers from scaling, poor inactivating capacity, hydrogen release and ammonia escape. In this study, the four-compartment electrochemical cell efficiently captured oxygen molecules from the air chamber to produce HO2- without generating toxic by-products. Meanwhile, the catalyst layer surface of PTFE/CB-GDE maintained a relatively balanced gas-liquid micro-environment, enabling the formation of enduring solid-liquid-gas interfaces for efficient HO2- electrosynthesis. A dramatic increase in HO2- generation rate from 453.3 mg L-1 h-1 to 575.4 mg L-1 h-1 was attained by advancement in operation parameters design (flow channels, electrolyte types, flow rates and circulation types). Stability testing resulted in the HO2- generation rate over 15 g L-1 and the current efficiency (CE) exceeding 85%, indicating a robust stable operational capacity. Furthermore, after 120 mg L-1 HO2- treatment, an increase of 11.1% in necrotic and apoptotic cells in the sewer biofilm was observed, higher than that achieved with the addition of NaOH, H2O2 method. The in-situ electrosynthesis strategy for HO2- represents a significance toward the practical implementation of sulfide abatement in sewers, holding the potential to treat various sulfide-containing wastewater.

Sulfur-containing substances in sewers: Transformation, transportation, and remediation.

Sulfur-containing substances in sewers frequently incur unpleasant odors, corrosion-related economic loss, and potential human health concerns. These observations are principally attributed to microbial reactions, particularly the involvement of sulfate-reducing bacteria (SRB) in sulfur reduction process. As a multivalent element, sulfur engages in complex bioreactions in both aerobic and anaerobic environments. Organic sulfides are also present in sewage, and these compounds possess the potential to undergo transformation and volatilization. In this paper, a comprehensive review was conducted on the present status regarding sulfur transformation, transportation, and remediation in sewers, including both inorganic and organic sulfur components. The review extensively addressed reactions occurring in the liquid and gas phase, as well as examined detection methods for various types of sulfur compounds and factors affecting sulfur transformation. Current remediation measures based on corresponding mechanisms were presented. Additionally, the impacts of measures implemented in sewers on the subsequent wastewater treatment plants were also discussed, aiming to attain better management of the entire wastewater system. Finally, challenges and prospects related to the issue of sulfur-containing substances in sewers were proposed to facilitate improved management and development of the urban water system.

Peracetic acid (PAA)-based pretreatment effectively improves medium-chain fatty acids (MCFAs) production from sewage sludge.

Peracetic acid (PAA), known for its environmentally friendly properties as a oxidant and bactericide, is gaining prominence in decontamination and disinfection applications. The primary product of PAA oxidation is acetate that can serve as an electron acceptor (EA) for the biosynthesis of medium-chain fatty acids (MCFAs) via chain elongation (CE) reactions. Hence, PAA-based pretreatment is supposed to be beneficial for MCFAs production from anaerobic sludge fermentation, as it could enhance organic matter availability, suppress competing microorganisms and furnish EA by providing acetate. However, such a hypothesis has rarely been proved. Here we reveal that PAA-based pretreatment leads to significant exfoliation of extracellular polymeric substances (EPS) from sludge flocs and disruption of proteinic secondary structures, through inducing highly active free radicals and singlet oxygen. The production of MCFAs increases substantially to 11,265.6 mg COD L-1, while the undesired byproducts, specifically long-chain alcohols (LCAs), decrease to 723.5 mg COD L-1. Microbial activity tests further demonstrate that PAA pretreatment stimulates the CE process, attributed to the up-regulation of functional genes involved in fatty acid biosynthesis pathway. These comprehensive findings provide insights into the effectiveness and mechanisms behind enhanced MCFAs production through PAA-based technology, advancing our understanding of sustainable resource recovery from sewage sludge.

Polyvinyl Chloride Microplastics Facilitate Nitrous Oxide Production in Partial Nitritation Systems.

Partial nitritation (PN) is an important partner with anammox in the sidestream line treating high-strength wastewater and primarily contributes to nitrous oxide (N2O) emissions in such a hybrid system, which also suffers from ubiquitous microplastics because of the growing usage and disposal levels of plastics. In this study, the influences of polyvinyl chloride microplastics (PVC-MPs) on N2O-contributing pathways were experimentally revealed to fill the knowledge gap on N2O emission from the PN system under microplastics stress. The long-term results showed that the overall PN performance was hardly affected by the low-dose PVC-MPs (0.5 mg/L) while obviously deteriorated by the high dose (5 mg/L). According to the batch tests, PVC-MPs reduced biomass-specific ammonia oxidation rates (AORs) by 5.78-21.94% and stimulated aerobic N2O production by 9.22-88.36%. Further, upon increasing dissolved oxygen concentrations from 0.3 to 0.9 mg O2/L, the degree of AOR inhibition increased but that of N2O stimulation was lightened. Site preference analysis in combination with metabolic inhibitors demonstrated that the contributions of hydroxylamine oxidation and heterotrophic denitrification to N2O production at 0.3 mg O2/L were enhanced by 18.84 and 10.34%, respectively, accompanied by a corresponding decreased contribution of nitrifier denitrification. Finally, the underlying mechanisms proposed for negative influences of PVC-MPs were bisphenol A leaching and reactive oxygen species production, which led to more cell death, altered sludge properties, and reshaped microbial communities, further resulting in enhanced N2O emission. Overall, this work implied that the ubiquitous microplastics are a hidden danger that cannot be ignored in the PN system.

Permanganate (PM) pretreatment improves medium-chain fatty acids production from sewage sludge: The role of PM oxidation and in-situ formed manganese dioxide.

Medium-chain fatty acids (MCFAs) production from sewage sludge is mainly restricted by the complex substrate structure, competitive metabolism and low electron transfer rate. This study proposes a novel permanganate (PM)-based strategy to promote sludge degradation and MCFAs production. Results show that PM pretreatment significantly increases MCFAs production, i.e., attaining 12,036 mg COD/L, and decreases the carbon fluxes of electron acceptor (EA)/electron donor (ED) to byproducts. Further analysis reveals that PM oxidation enhances the release and biochemical conversion of organic components via disrupting extracellular polymers (EPS) structure and reducing viable cells ratio, providing directly available EA for chain elongation (CE). The microbial activity positively correlated with MCFAs generation are apparently heightened, while the competitive metabolism of CE (i.e., methanogensis) can be completely inhibited. Accordingly, the functional bacteria related to critical bio-steps and dissimilatory manganese reduction are largely enriched. Further mechanism exploration indicates that the main contributors for sludge solubilization are 1O2 (61.6 %) and reactive manganese species (RMnS), i.e., Mn(V)/Mn(VI) (22.3 %) and Mn(III) (∼16.1 %). As the main reducing product of PM reaction, manganese dioxide (MnO2) can enable the formation of microbial aggregates, and serve as electron shuttles to facilitate the carbon fluxes to MCFAs during CE process. Overall, this strategy can achieve simultaneous hydrogen recovery, weaken competitive metabolisms and provide electron transfer accelerator for CE reactions.

Percarbonate-strengthened ferrate pretreatment for enhancing short-chain fatty acids production from sewage sludge.

Sewage sludge management poses a pressing environmental challenge, demanding the implementation of sustainable solutions to facilitate resource recovery. Short-chain fatty acids (SCFAs) serve as valuable chemicals and renewable energy sources, underscoring the importance of maximizing their production to achieve sustainable waste management. Therefore, this study proposes a novel and green strategy, i.e., percarbonate-strengthened ferrate pretreatment to enhance SCFAs synthesis from sewage sludge, because percarbonate could activate ferrate oxidation through providing (bi) carbonate and hydrogen peroxide. Results show that percarbonate largely reduces the required ferrate dosage for fermentation improvement, and their combination exhibits obvious synergistic effects on SCFAs accumulation and sludge reduction. Under the optimal pretreatment conditions, SCFAs production is promoted to 3670.2 mg COD/L, representing a remarkable increase of 5512.4 %, 156.0 % or 395.1 % compared to the control, percarbonate alone or ferrate alone, respectively. Mechanism explorations demonstrate that percarbonate-strengthened ferrate pretreatment significantly enhances sludge solubilization, elevates substrate biodegradability, and alters the physiochemical properties of sludge to favor organics fermentation. The synergistic effects on solid organics release and sludge properties can be attributed to the combined mechanisms of enhanced oxidation and alkaline hydrolysis. Further investigations on metabolic pathways reveal that the combination substantially improves key enzyme activities associated with hydrolysis and SCFAs formation, while severely inhibits that of SCFAs consumption. These findings are further supported by the functional genes coding relevant enzymes. Moreover, the combination alters microbial structures and compositions, leading to the screening and enrichment of key microbes that facilitate SCFAs accumulation. This innovative strategy holds significant promise in advancing sewage sludge management towards a more circular and resource-efficient paradigm.

Impact of sertraline on biohydrogen production from alkaline anaerobic fermentation of waste activated sludge: Focusing on microbial community and metabolism.

Nowadays, antidepressants are massively consumed worldwide, inevitably bringing about the concern for their latent hazard to the natural environment. This research focused on exploring the effect of sertraline (SET, a typical antidepressant) on hydrogen yields from alkaline anaerobic fermentation of waste activated sludge (WAS). The hydrogen accumulation reached the peak of 14.73 mL/g VSS (volatile suspended solids) at a SET dosage of 50 mg/kg TSS (total suspended solids), i.e., 1.90 times of that in the control fermenter. The data of Illumina high-throughput sequencing demonstrated that SET promoted the expression of genes regulating the membrane transport. Microbial community analysis suggested that some species that could degrade refractory substances were enriched after SET exposure. Finally, metabolic pathways of hydrogen production and consumption were found to be significantly affected with SET addition. This study would deepen the concept of typical antidepressants influencing energy recovery from WAS.

Peracetic acid activated by ferrous ion mitigates sulfide and methane production in rising main sewers.

Iron-based peracetic acid (PAA) advanced oxidation process (AOP) is widely used in water purification because of its high efficiency and low toxicity. In this study, for the first time, ferrous iron (Fe2+) and PAA were dosed jointly into the rising main sewer reactor, to verify the feasibility of sulfide and methane control as well as investigate the comprehensive mechanism of Fe2+/PAA on sewer biofilm. Results demonstrated the superior biocidal effect of Fe2+/PAA dosing than that of PAA alone. Intermittent Fe2+/PAA dosing showed that the average inhibitory rate of sulfide production rate (SPR) and methane production rate (MPR) was 52.0% and 29.9%, respectively, at a Fe2+/PAA molar ratio of 1:1 and PAA concentration of 3 mmol/L (i.e., the mass-based concentrations of Fe2+ and PAA were 6.79 mg-Fe/L and 228 mg/L, respectively). Beside, sewer biofilm was found to be resistant to PAA during repeated dosing events. However, resistance could be alleviated by introducing sulfide in situ in the Fe2+/PAA process, and SPR and MPR were further reduced to 27.39% and 67.32% of the control, respectively. LIVE/DEAD Staining showed that Fe2+/PAA exhibited a strong destructive effect on microbial cells, with the proportion of viable cells being 26.34%. Electron paramagnetic resonance (EPR) and free radical quenching results indicated that the inhibitory order was R-O• > •OH > Fe(IV), which led to the disruption of cellular integrity (i.e., 17.24% increase in LDH) and intracellular enzyme system (i.e., cellular metabolic disorders). Microbial analysis revealed that long-term Fe2+/PAA dosing decreased the sulfate-reducing bacteria (SRB) abundance, and the dominant genus of methanogenic archaea (MA) shifted from Methanofastidiosum, Methanobacterium to Methanosaeta. The cost of Fe2+/PAA dosing on methane and sulfide control in rising main sewers was $1.81/kg-S, economically and environmental-friendly attractive for practical applications.

A novel free nitrous acid (FNA)-generation pathway via ferric salts hydrolysis to mitigate sulfide and methane production in sewer: Insights into the performance and microbial mechanisms.

Ferric chloride (FeCl3) served as a solid acid has attracted attention recently. However, the feasibility of FeCl3 combined with nitrite for free nitrous acid (FNA) generation in controlling sulfide and methane as well as the triggering mechanisms in the complex syntrophic consortium (i.e., sewer biofilm) remain largely unknown. This work disclosed FeCl3 as an alternative acid source could obtain comparable sulfide and methane mitigations at a low FNA dose (i.e., 0.26 mg N/L), compared to that of HCl acid source. Whereas, a faster recovery rate of sulfide production was observed using FeCl3 under a higher FNA dose (i.e., 0.81 mg N/L) despite the methane control still being comparable. The toxicological mechanisms revealed FNA reacted with proteins amide Ⅰ in extracellular polymeric substances and destroyed protein hydrogen bond. Enzymatic and genic analysis unveiled the overall suppression of hydrolysis, acidogenesis, acetogenesis, sulfidogenesis and methanogenesis steps due to the inactivation of viable cells by reactive nitrogen species. Economic and environmental assessments demonstrated that the ferric-based FNA strategy reduced chemical costs and N2O emission (ca. 26.5% decrease) compared to the traditional HCl-based FNA method. This work broadens the application of iron salt-based technology in urban water system, together with understanding the biological mechanisms of FNA-based technology.

Reduced sulfide and methane in rising main sewer via calcium peroxide dosing: Insights from microbial physiological characteristics, metabolisms and community traits.

Although the biocidal effect of calcium peroxide (CaO2) has attracted increasing attention in wastewater and sludge management, its potential in the reduction of sulfide and methane from sewer is not tapped. This study aims to fill this gap through the long-term operated sewer reactors. Results showed one-time dose of 0.2% (w/v) CaO2 with 12-h exposure decreased the average sulfide and methane production by 80% during one week. The electron paramagnetic resonance and free radical quenching tests indicated free radicals from CaO2 decomposing posed a major contribution on sewer biofilms (•OH>•O2->alkali). Mechanistic analysis revealed extracellular polymeric matrix breakdown (e.g., protein secondary structure) and cell membrane damage were caused by the increased lipid peroxidation of cells and exacerbated intracellular reactive oxygen species under CaO2 stress. Moreover, the intracellular metabolic pathways, such as electrons provision and transfer, as well as pivotal enzymatic activities (e.g., APS reductase, sulfite reductase and coenzymes F420) were significantly impaired. RT-qPCR analysis unveiled the absolute abundances of dsrA and mcrA were decreased by 7.53-40.37% and 67.00-74.85%, respectively. Although this study broadens the application scope of CaO2 and provides in-depth understanding of advanced oxidation-based technology in sewer management, the pipe scale risk due to the release of calcium ions warrants further investigation.

Enhanced anaerobic digestion of waste activated sludge with periodate-based pretreatment.

The potential of periodate (PI) in sludge anaerobic digestion is not tapped, although it has recently attracted great research interest in organic contaminants removal and pathogens inactivation in wastewater treatment. This is the first work to demonstrate significant improvement in methane generation from waste activated sludge (WAS) with PI pretreatment and to provide underlying mechanisms. Biochemical methane potential tests indicated that methane yield enhanced from 100.2 to 146.3 L per kg VS (VS, volatile solids) with PI dosages from 0 to 100 mg per g TS (TS, total solids). Electron spin resonance showed PI could be activated without extra activator addition, which might be attributed to the native transition metals (e.g., Fe2+) in WAS, thereby generating hydroxyl radical (•OH), superoxide radicals (•O2 -), and singlet oxygen (1O2). Further scavenging tests demonstrated all of them synergistically promoted WAS disintegration, and their contributions were in the order of •O2 - > •OH > 1O2, leading to the release of substantial biodegradable substances (i.e., proteins and polysaccharides) into the liquid phase for subsequent biotransformation. Moreover, fluorescence and ultraviolet spectroscopy analyses indicated the recalcitrant organics (especially lignocellulose and humus) could be degraded by reducing their aromaticity under oxidative stress of PI, thus readily for methanogenesis. Microbial community analysis revealed some microorganisms participating in hydrolysis, acidogenesis, and acetoclastic methanogenesis were enriched after PI pretreatment. The improved key enzyme activities and up-regulated metabolic pathways further provided direct evidence for enhanced methane production. This research was expected to broaden the application scope of PI and provide more diverse pretreatment choices for energy recovery through anaerobic digestion.

Unveiling the Mechanism of Urine Source Separation-Derived Pretreatment on Enhancing Short-Chain Fatty Acid Yields from Anaerobic Fermentation of Waste Activated Sludge.

A novel strategy employing urine wastewater derived from source separation technology, to pretreat waste activated sludge (WAS) for promoting yields of short-chain fatty acids (SCFAs), has been proposed in this study. It was found experimentally that SCFA production could ascend up to 305.4 mg COD/g VSS (volatile suspended solids) with a urine volumetric proportion of 1:2 to the whole reaction system, being 8.8 times that produced in the control. Exploration of the mechanism indicated that WAS disintegration was significantly enhanced due to the synergistic effect of urea and free ammonia (FA). Degradation rates of model organic substrates and measurements of critical enzymatic activities demonstrated that hydrolysis and acidogenesis were inhibited under high urine content (urine proportion of 1:2), while not significantly affected under low urine content (i.e., 1:4), which might be attributed to metal ions existing in urine wastes alleviating the inhibition induced by FA. In contrast, methanogenesis was negatively suppressed by any urine concentration owing to its higher sensitivity to the environmental variations. Shift of microbial population further elucidated the abundance of hydrolytic and acidogenic microbes were enriched in the fermenters with urine addition. The findings provide a new thought for recovering resources from wastes, potentially reducing the pressure of sewage and sludge treatment in wastewater treatment plants.

Ultrasound-sodium percarbonate effectively promotes short-chain carboxylic acids production from sewage sludge through anaerobic fermentation.

Short-chain carboxylic acids (SCCAs) production from sewage sludge via anaerobic fermentation is usually restricted by low substrates availability and rapid products consumption. Therefore, the ultrasound (US)-sodium percarbonate (SPC) technique was proposed to effectively break the bottlenecks. Results showed the total SCCAs yield, acetate yield and particulate organics reduction respectively attained 392.8 mg COD/g VSS, 204.6 mg COD/g VSS and 47.4 % under the optimal condition. Mechanistic explorations disclosed that US + SPC largely reduced biodegradation resistances of particulate organics and improved sludge biodegradability. The destruction of spatial structure was the inherent mechanisms for initial solubilization and further degradation of solid-phase sludge. Besides, US + SCP up-regulated hydrolytic and SCCAs-forming enzymes, but downregulated the key enzyme for methanation. Meanwhile, US + SPC altered the microbial structure and stimulated functional microorganism enrichment, well correlated with substrate biotransformation and products output. Overall, this strategy could effectively enhance SCCAs production from WAS and reduce the environmental risk for subsequent sludge disposal.

Potassium permanganate pretreatment effectively improves methane production from anaerobic digestion of waste activated sludge: Reaction kinetics and mechanisms.

As a powerful oxidizing agent, potassium permanganate (KMnO4) has attracted widespread interest in sludge treatment and contaminant removal. However, its effect on the anaerobic digestion of waste activated sludge (WAS) is ambiguous. This investigation was designed to provide perspectives into this problem. In comparison with the control, 0.3 g KMnO4/g TSS pretreatment enhanced the methane production by 78.82 %. Model analysis demonstrated that the KMnO4 pretreatment enhanced the biochemical methane potential (B0) of WAS. Mechanistic studies elucidated that the KMnO4 pretreatment process generated reactive radicals such as ·OH, ·O2- and 1O2, which contributed to sludge disintegration and biodegradation process of dissolved substances, thus resulting in more substances available for subsequent methane generation. Enzyme activity analysis indicated that KMnO4 pretreatment facilitated the activities of key enzymes associated with anaerobic digestion to various degrees. Microbial analysis illustrated that the relative abundance of functional microorganisms was significantly elevated after KMnO4 pretreatment, which was conducive to methane production.

New insight into mechanisms of ferroferric oxide enhancing medium-chain fatty acids production from waste activated sludge through anaerobic fermentation.

Medium chain fatty acids (MCFAs) production from waste activated sludge (WAS) is restricted by poor biodegradability of WAS and low electron transfer efficiency. Herein, a novel ferroferric oxide (Fe3O4) technique was proposed. Results indicated that the MCFAs yield and selectivity were respectively enhanced by 155.4% and 66.7% in the Fe3O4-mediated WAS. Mechanistic studies disclosed that Fe3O4 promoted substrates degradation through conducting dissimilatory iron reduction (DIR) and stimulating hydrolase activity, providing precursors for chain elongation (CE). Generally, Fe3O4 improved the key processes for MCFA production at different degrees, i.e., hydrolysis, acidification and CE. Interestingly, MCFAs yield enhancement was primarily ascribed to facilitated electron transfer rather than DIR or produced ferrous iron, which could be supported by the analyses of electrochemical properties, electron transfer system activity and morphology. Further, Fe3O4 shifted the key microorganisms in favor of MCFAs production. Overall, this strategy could improve MCFAs production, sludge dewatering and phosphorus removal, concurrently.

Insights into Fe(â ¡)-sulfite-based pretreatment strategy for enhancing short-chain fatty acids (SCFAs) production from waste activated sludge: Performance and mechanism.

This paper proposed a concept of "co-treating" waste activated sludge (WAS) with waste-derived sulfite and environmentally-friendly ferrous iron. The maximal short-chain fatty acids (SCFAs) production from WAS anaerobic fermentation ascended by 27.1 times after pretreated by Fe(Ⅱ) activated sulfite with a sulfite dosage of 500 mg S/L and a Fe(Ⅱ)/sulfite ratio of 1.25. Mechanism explorations elucidated that the production of SO4·- and ·OH induced by Fe(Ⅱ)-activated sulfite-auto-oxidation remarkably promoted the disintegration of WAS and the biodegradability of dissolved organic matter, leading to enrichment of substances available for SCFAs-producing microbes. Besides, activities of hydrolytic and acidogenic enzymes were stimulated, while enzymes related to SCFAs consumption were inhibited severely. Further microbial community investigation confirmed that the abundances of hydrolytic microorganisms and acidogens were enriched. In addition, sludge dewaterability and vivianite production was enhanced after Fe(Ⅱ)-sulfite pretreated WAS fermentation, thereby benefiting the subsequent sludge disposal and resource recovery.

Performance and mechanism of sodium percarbonate (SPC) enhancing short-chain fatty acids production from anaerobic waste activated sludge fermentation.

A novel pretreatment technique (i.e., using Sodium percarbonate, SPC) to improve the short-chain fatty acids (SCFA) production waste activated sludge (WAS) was proposed in this study. Results indicated that the maximum SCFA production of 1605.7 mg COD/L and acetic acid of 52.9% were attained at 0.2 g SPC/g TSS, being 8.4 and 2.8 times of the control (191.3 mg COD/L and 19%), respectively. Meanwhile, the optimal time for SCFA accumulation was decreased from 6d (control) to 4d (0.2 g/g TSS). Mechanism explorations unraveled that SPC largely accelerated WAS solubilization and enhanced the bioavailability of organics released from WAS. It improved enzymatic activities related to hydrolysis and acidogenesis, while suppressed the Coenzyme F420 responsible for SCFA consumption. Illumina MiSeq sequencing analysis showed that SPC substantially enhanced the relative abundances of hydrolytic and/or acid-forming microbes. Furthermore, CO3- and O2- were the key factors to production enhancement in SPC-involved sludge fermentation.

Unveiling the mechanisms of how vivianite affects anaerobic digestion of waste activated sludge.

Recently, phosphorus recovery as vivianite from sludge digestion system has attracted increasing attention because of its high recovery efficiency and economic value. However, the potential impact of vivianite on anaerobic digestion of waste activated sludge remains largely unknown. This study therefore aims to provide such support. Experimental results revealed that the maximal methane yield decreased from 103.55 to 76.55 mL/g volatile solids, with the vivianite level increasing from 0 to 500 mg P/L. Mechanism explorations showed that vivianite caused more substrates remaining in tightly-bound extracellular polymeric substances, and thus suppressed sludge solubilization. In addition, it was observed that hydrolysis, acidiogenesis, acetogenesis and methanogenesis bio-processes were all inhibited by vivianite. Microbial analysis revealed that vivianite significantly decreased the relative abundances of hydrolytic microbes, acidogens and methanogens. Further investigation showed that vivianite benefited sludge agglomeration and can enhance the mass transfer resistance of anaerobic digestion, further supporting the inhibitions on anaerobic digestion.

Unveiling the mechanisms of a novel polyoxometalates (POMs)-based pretreatment technology for enhancing methane production from waste activated sludge.

This study proposed a novel polyoxometalates (POMs)-based pretreatment technology to improve methane production from waste activated sludge (WAS) for the first time. Experimental results indicated methane production from WAS pretreated with 0.25 g POMs/g TSS increased by 43.7%. Mechanism analysis revealed POMs pretreatment promoted WAS disintegration and improved the biodegradability of the released organics. The declined oxidation-reduction potential of digestion system provided a more favorable situation for anaerobes, and hence had positive impacts on the activity of enzymes associated with hydrolysis/acidification/methanogenesis. Model-based analysis elucidated POMs pretreatment remarkably increased both biochemical methane potential and hydrolysis rate. Microbial community analysis showed microbial community was shifted toward increase hydrolytic and acidification-associated microbes and enriched the abundance of Methanosaeta sp. This work is expected to develop an innovative technology that will simultaneously enhance energy production from WAS in the sludge treatment line and improve biological nutrient removal in the wastewater treatment line of WWTPs.

Insight into the enhancing short-chain fatty acids (SCFAs) production from waste activated sludge via polyoxometalates pretreatment: Mechanisms and implications.

Polyoxometalates (POMs), a versatile and environmentally-friendly inorganic material, have been extensively studied and applied in chemical catalytic oxidation and biological nutrients removal processes. However, little is known about effects of POMs pretreatment on anaerobic sludge fermentation. This study thereby filled such knowledge gap and provided insights into the underlying mechanisms. Results demonstrated the maximal short-chain fatty acids (SCFAs) production increased by 6.18 times with POMs rising from 0 to 0.05 g/g TSS. Mechanistic investigations revealed that the oxidation stress of POMs as well as reactive oxygen species (ROS) activated by POMs were responsible for the disintegration of waste activated sludge (WAS). More importantly, POMs pretreatment improved the biodegradability of organics released, providing more biodegradable substrates for SCFAs generation. Furthermore, the inhibition of POMs to SCFAs producers was less severe than that to SCFAs consumers, leading to SCFAs accumulation. Microbial community analysis exhibited that increased the population of hydrolysis (i.e., Longilinea) and SCFAs generation microbes (i.e., Acinetobacter and Fusibacter). Further evaluation showed that the POMs-based technology is economically and environmentally attractive for the pretreatment of WAS. Finally, a "closed-loop" concept of the reutilization of renewable POMs may provide an important implication of WAS management in the future.