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Microaerobic sludge bed systems could align with low-energy, reasonable carbon-nitrogen (C/N) ratio, and synchronous removal objectives during wastewater treatment. However, its ability to treat municipal wastewater (MW) with varying low C/N ratio, low NH 4 + concentration, along with managing sludge bulking and loss are still unclear. Against this backdrop, this study investigated the performance of an Upflow Microaerobic Sludge Bed Reactor (UMSR) treating MW characterized by varying low C/N ratios and low NH 4 + concentrations. The study also thoroughly examined associated sludge bulking and loss, pollutant removal efficiencies, sludge settleability, microbial community structures, functional gene variations, and metabolic pathways. Findings revealed that the effluent NH 4 + -N concentration gradually decreased to 0 mg/L with a decrease in the C/N ratio, whereas the effluent COD was unaffected by the influent, maintaining a concentration below 50 mg/L. Notably, TN removal efficiency reached 90% when C/N ratio was 3. The decrease in the C/N ratio (C/N ratio was 1) increased microbial community diversity, with abundances of AOB, AnAOB, aerobic denitrifying bacteria, and anaerobic digestion bacteria reaching 8.34%, 0.96%, 5.07%, and 9.01%, respectively. Microorganisms' metabolic pathways significantly shifted, showing increased carbohydrate and cofactor/vitamin metabolism and decreased amino acid metabolism and xenobiotic biodegradation. This study not only provides a solution for the effluent of different pre-capture carbon processes but also demonstrates the UMSR's capability in managing low C/N ratio municipal wastewater and emphasizes the critical role of microbial community adjustments and functional gene variations in enhancing nitrogen removal efficiency., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Nitrate photolysis has become an efficient, low-cost and promising technology for emerging contaminants removal, while its performance and mechanism for waste activated sludge (WAS) treatment is still unknown. This study innovatively introduced nitrate photolysis for WAS disintegration, and investigated the effect of nitrate addition (150-375 mg N/L) for short-chain fatty acids (SCFAs) production during anaerobic fermentation (AF). The results showed that nitrate photolysis significantly promoted the SCFAs production from WAS, and peaked at 280.7 mg/g VSS with 7-d fermentation with 150 mg N/L addition (150N-UV), which increased by 8.8-35.0 % and 10.7-23.3 % compared with other photolysis groups and sole nitrate groups. Effective release of the soluble organics was observed in the nitrate photolysis groups during AF, especially soluble proteins, reaching 1505.4 mg COD/L at 9 d in 150N-UV group, promoted by 7.0∼15.7 % than nitrate/nitrate photolysis groups. The model compounds simulation experiment further demonstrated the positive effect of nitrate photolysis on organics hydrolysis and SCFAs accumulation. The result of the radical capture and quenching verified the reactive oxygen species contributed more compared with reactive nitrogen species. Functional group analysis confirmed the effective bioconversion of the macromolecular organics during the fermentation. Moreover, the nitrate photolysis enhanced the enrichment of the functional consortia, including anaerobic fermentation bacteria (AFB), e.g., Fnoticella, Romboutsia, Gracilibacter and Sedimentibacter, and nitrate reducing bacteria (NRB), e.g., Acinerobacter and Ahniella. The macrogenetic analysis further revealed that glycolysis, amino acid metabolism, acetate metabolism and nitrogen metabolism were the dominating metabolic pathways during fermentation, and the abundance of the relevant genes were enhanced in 150N-UV group., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Persulfate oxidation (PS) is widely employed as a promising alternative for waste activated sludge pretreatment due to the capability of generating free radicals. The product differences and microbiological mechanisms by which PS activation triggers WAS digestion through multiple modes need to be further investigated. This study comprehensively investigated the effects of persulfate oxidation activated through multiple modes, i.e., ferrous, zero-valent iron (ZVI), ultraviolet (UV) and heat, on the performance of sludge digestion. Results showed that PS_ZVI significantly accelerated the methane production rate to 12.02 mL/g VSS. By contrast, PS_Heat promoted the sludge acidification and gained the maximum short-chain fatty acids (SCFAs) yield (277.11 ± 7.81 mg COD/g VSS), which was 3.41-fold compared to that in PS_ZVI. Moreover, ferrous and ZVI activated PS achieved the oriented conversion of acetate, the proportions of which took 73% and 78%, respectively. MiSeq sequencing results revealed that PS_Heat and PS_UV evidently enriched anaerobic fermentation bacteria (AFB) (i.e., Macellibacteroides and Clostridium XlVa). However, PS_Ferrous and PS_ZVI facilitated the enrichment of Woesearchaeota and methanogens. Furthermore, molecular ecological network and mantel test revealed the intrinsic interactions among the multiple functional microbes and environmental variables. The homo-acetogens and sulfate-reducing bacterial had potential cooperative and symbiotic relationships with AFB, while the nitrate-reducing bacteria displayed distinguishing ecological niches. Suitable activation modes for PS pretreatments resulted in an upregulation of genes expression responsible for digestion. This study established a scientific foundation for the application of sulfate radical-based oxidation on energy or high value-added chemicals recovery from waste residues., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

The production of short-chain fatty acids (SCFAs) is constrained by substrate availability and the increased fractional pressure of H 2 emitted by acidogenic/fermentative bacteria during anaerobic fermentation of waste activated sludge (WAS). This study introduced a novel approach employing zero-valent iron (ZVI)-activated sulfite pretreatment combined with H 2 -consuming sulfate-reducing bacteria (SRB) mediation to improve SCFAs, especially acetate production from WAS fermentation. Experimental results showed that the combined ZVI-activated sulfite and incomplete-oxidative SRB (io-SRB) process achieved a peak SCFAs production of 868.11 mg COD/L, with acetate accounting for 80.55 %, which was 7.90- and 2.18-fold higher than that obtained from raw WAS fermentation, respectively. This could be firstly attributed to the SO 4 - and OH generated by ZVI-activated sulfite, which significantly promoted WAS decomposition, e.g., soluble proteins and carbohydrates increased 14.3- and 10.8-fold, respectively, over those in raw WAS. The biodegradation of dissolved organic matter was subsequently enhanced by the synergistic interaction and H 2 transfer between anaerobic fermentation bacteria (AFB) and io-SRB. The positive and negative correlations among AFB, nitrate-reducing bacteria (NRB) and the io-SRB consortia were revealed by molecular ecological network (MEN) and Mantel test. Moreover, the expression of functional genes was also improved, for instance, in relation to acetate formation, the relative abundances of phosphate acetyltransferase and acetate kinase was 0.002 % and 0.005 % higher than that in the control test, respectively. These findings emphasized the importance of sulfate radicals-based oxidation pretreatment and the collaborative relationships of multifunctional microbes on the value-added chemicals and energy recovery from sludge fermentation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Anaerobic fermentation is a crucial route to realize effective waste activated sludge (WAS) resource recovery and utilization, while the overall efficiency is commonly restrained by undesirable disruptors (i.e., chemical dewatering agents). This work unveiled the unexpectedly positive effects of biodewatering tannic acid (TA) on the volatile fatty acids (VFAs) biosynthesis during WAS anaerobic fermentation. The total VFAs yield was remarkably increased by 15.6 folds with enriched acetate and butyrate in TA-occurred systems. TA was capable to disintegrate extracellular polymeric substances to promote the overall organics release. However, TA further modulated the soluble proteins structure by hydrogen bonding and hydrophobic interactions, resulting in the decrease of proteins bioavailability and consequential alteration of metabolic substrate feature. These changes reshaped the microbial community and stimulated adaptive regulatory systems in hydrolytic-acidogenic bacteria. The keystone species for carbohydrate metabolism (i.e., Solobacterium and Erysipelotrichaceae ) were preferentially enriched. Also, the typical quorum sensing (i.e., enhancing substrate transport) and two-component systems (i.e., sustaining high metabolic activit y ) were activated to promote the microbial networks connectivity and ecological cooperative behaviors in response to TA stress. Additionally, the metabolic functions responsible for carbohydrate hydrolysis, transmembrane transport, and intracellular metabolism as well as VFA biosynthesis showed increased relative abundance, which maintained high microbial activities for VFAs biosynthesis. This study underscored the advantages of biodewatering TA for WAS treatment in the context of resource recovery and deciphered the interactive mechanisms.

Electro-fermentation (EF) has been extensively studied for recovering hydrogen and phosphorus from waste activated sludge (WAS), while was limited for the further application due to the low hydrogen yield and phosphorus recovery efficiency. This study proposed an efficient strategy for hydrogen and vivianite recovery from the simulated sludge fermentation liquid by sacrificial iron anode in EF. The optimum hydrogen productivity and the utilization efficiency of short chain fatty acids (SCFAs) reached 45.2 mmol/g COD and 77.6% at 5 d in pH 8. Phosphate removal efficiency achieved at 90.8% at 2 d and the high crystallinity and weight percentage of vivianite (84.8%) was obtained. The functional microbes, i.e., anaerobic fermentative bacteria, electrochemical active bacteria, homo-acetogens and iron-reducing bacteria were highly enriched and the inherent interaction between the microbial consortia and environmental variables was thoroughly explored. This work may provide a theoretical basis for energy/resource recovery from WAS in the further implementation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Boosting acetate production from waste activated sludge (WAS) fermentation is often hindered by the inefficient solubilization in the hydrolysis step and the high hydrogen pressure ( [Formula: see text] ) during the acidogenesis of C3-C5 short-chain fatty acid (SCFAs), i.e., propionate (HPr), butyrate (HBu) and valerate (HVa). Therefore, this study employed persulfate (PS) oxidation and C3-C5 incomplete-oxidative sulfate reducing bacteria (io-SRB) metabolizers to tailor SCFAs conversion from WAS fermentation. The decomposition efficiency, performance of SCFAs production was investigated. Results showed that the PS significantly promoted WAS decomposition, with a dissolution rate of 39.4%, which is 26.0% higher than the un-treated test. Furthermore, SCFAs yields were increased to 462.7 ± 42 mg COD/g VSS in PS-HBu-SRB, which was 7.4 and 2.2 times higher than that of un-treated and sole PS tests, respectively. In particular, the sum of acetate and HPr reached the peak value of 85%, indicating that HBu-SRB mediation promoted the biotransformation of HBu and macromolecular organics by reducing the [Formula: see text] restriction. Meanwhile, sulfate radical (SO 4 ∙ - )-based oxidation (SR-AOPs) was effective in the decomposition of WAS, the oxidative product, i.e., sulfate served the necessary electron acceptor for the metabolism of io-SRB. Further analysis of Mantel test revealed the cluster of the functional genus and their interaction with environmental variables. Additionally, molecular ecological network analysis explored the potential synergistic and competitive relationships between critical genera. Additionally, the potential synergistic and competitive relationships between critical genera was explored by molecular ecological network analysis. This study provides new insights into the integration of SR-AOPs with microbial mediation in accelerating SCFAs production from WAS fermentation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The influence of hydraulic retention time (HRT) on the granulation process, methane-producing capacity, microbial community structure, and pollutant removal efficiency of an up-flow anaerobic sludge blanket (UASB) with simulated municipal wastewater at a mesophilic temperature was investigated. The carbon recovery capacity of the anaerobic fermentation of municipal wastewater at mesophilic temperatures is one of the problems to be investigated for the realisation of carbon neutrality in municipal wastewater treatment plants. In this study, the HRT was gradually shortened (24-6 h), and the effluent chemical oxygen demand (COD), ammonia nitrogen, pH, volatile fatty acid concentration, and specific methanogenic activity (SMA) were investigated. The sludge morphology, the particle size distribution of the different HRT, and changes in the microbial community structure were determined by scanning electron microscopy, wet screening, and high-throughput sequencing. The results indicated that even if the COD concentration was only 300-550 mg/L, with a decrease in HRT, the proportion of granular sludge in the UASB still exceeded 78 %, and the COD removal efficiency reached 82.4 %. The SMA of granular sludge increased with an increase in the size of granules and was 0.289 g CH 4 -COD/(g VSS d) at an HRT of 6 h, but the proportion of dissolved methane in the effluent accounted for 38-45 % of the total methane production and the proportion of Methanothrix in UASB sludge was 82.44 %. In this study, dense granular sludge was obtained by gradually shortening the HRT to start the UASB, and the lower effluent COD reduced the load of subsequent treatment processes, which could be used as a low carbon/nitrogen ratio influent for activated carbon-activated sludge, activated sludge-microalgae, and partial nitrification-anaerobic ammonia oxidation processes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Persulfate has been applied extensively for waste activated sludge (WAS) decomposition due to the strong oxidizing sulfate radical generated as a product. However, the efficiency is not improved without activation to produce free radicals. In this study, a novel coupling strategy of heat-activated persulfate (Heat_PS) pretreatment and sulfate-reducing bacteria (SRB) triggering was explored to enhance short-chain fatty acids (SCFAs) produced by WAS fermentation. The remaining sulfate acts as an essential acceptor of electrons for the metabolism of synergistic SRB, thereby boosting WAS acidification by energetic cooperation with anaerobic fermenters. The results showed that SCFAs yield in the Heat_PS + SRB group peaked at 431.89 mg COD/gVSS, with the proportion of acetate reaching 57.8 %. This was 6.33 and 1.75 times higher than that in raw and single Heat_PS treated WAS, respectively. Carbon balance revealed a conversion rate of 26.1 % of carbon content in WAS to SCFAs, with 4.5 % lower CO 2 equivalents emitted than that in raw WAS fermentation by the assessments of environmental impacts. This was partially attributed to the strong decomposition of WAS by SO 4 •- and • OH oxidation from heat-activated PS and the SRB trigger. In addition, the synergistic relationship among acidogenic/fermentative bacteria and SRB consortia was further verified by the positive correlation among Desulfovibrio, the hydrolytic Escherichia-Shigella, Morganella and the fermetative Macellibacteroides and Bacteroides, as revealed by molecular ecological networks (MENs) analysis. The results of this study may highlight the cooperation of the synergistic micribial consortia as an additional perspective for the recovery of value-added biological metabolites from complex biotransformation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Peracetic acid (PAA) is an emerging oxidant for waste activated sludge (WAS) treatment due to its strong oxidization and few toxic byproducts. Nitrite which can be in-situ recovered from WAS fermentation liquor, its protonated form (free nitrous acid, FNA) is regarded as the cost-effective inactivator. The stubborn extracellular polymeric substance (EPS) is the rate-limiting step for energy/resource recovery from WAS. This work found that the co-pretreatment of PAA and FNA can effectively promote short-chain fatty acids (SCFAs) production during anaerobic fermentation. Higher PAA dosage (100 mg/g VSS, FP4WAS) in co-pretreatment was beneficial for organics release (1976.9 mg COD/L), remarkably increased by 10.3- 96.5 % than that of low PAA dosage (25- 75 mg/g VSS), and promoted by 105.1 % and 62.1 % than FNA (FWAS)/PAA (100 mg/g VSS, P4WAS)-pretreated WAS. Effective release of soluble organics contributed to the SCFAs accumulation (7679 ± 86 mg COD/L, 4 d), enhanced by 200.0 % and 19.0 % than FWAS and P4WAS, respectively. Acetic (HAc) and propionic acid (HPr) peaked at 6344.7 mg COD/L in FP4WAS (accounted for 82.6 %), which increased by 10.6- 899.0 % than other groups. Moreover, OH and O 2 - were detected in co-pretreatment, may play the synchronous effect with the crucial intermediates of NO, NO 2 and ONOO - /ONOOH on EPS decomposition., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In this study, a continuous stirred-tank reactor (CSTR) coupled with up-flow anaerobic sludge beds (UASBs) reactor was successfully developed for enhancing methane production and carbon recovery rate from cornstalks. Acetic acid production was higher in regions A than in B and C. The methane percentage achieved at 75.98% of total gas and methane production of cornstalks was up to 520.07 mL/g, during the stable operation period. The carbon of recovery rate, represented substrates converted to methane gas, reached 69.32% in stable stage. Microbial community structure analysis revealed that Paludibacter, Prevotella/Clostridium sensu stricto, and Caldisericum were the dominant bacteria for the degradation of cellulose, lignin, and other refractory macromolecules in regions A, B, and C, respectively. Methanobacterium and Methanolinea were the two major genera, accounting for methanogenesis generation.

Antibiotics in waste activated sludge (WAS) has drawn increasing attention because of their persistent and bioaccumulation characteristics. Most study illustrated the role of antibiotics in anaerobic fermentation from WAS, but lacking the analysis at microbial level as well as the possible interaction between them. This study investigated the effect of three sulfonamide antibiotics (sulfamethoxazole (SMX), sulfaquinoxaline (SQX), and sulfadiazine (SD)) on WAS fermentation and explored its microbiological mechanism. Results indicated that the production of short-chain fatty acids (SCFAs) was significantly improved by 1.9 folds with a peak value at 4626.1 mg COD L -1 in the existence of SD. This was attributed to the promoted release of soluble proteins and polysaccharides with the existence of sulfonamide antibiotics (SAs) as revealed by the excitation-emission matrix (EEM) spectrum. Analysis of microbial community structure showed that the total abundance of the fermenters in groups with SAs was1.2-1.6 times of that in Control. Specifically, the acid-forming genus Tissierella in SMX and SQX increased by 12.1%-15.0% compared with the Control, while the proteolytic genus Proteinivorax dominated in SD with 39.5%. Molecular ecological networks (MENs) analysis further revealed the potential cooperative relationships among different fermenters. This study was anticipated to provide some valuable information for the behavior of antibiotics in WAS fermentation., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Exploration of value-added products from wastewater treatment plants (WWTPs) was promising for its sustainable development. This study simultaneously addressed the possibility of volatile fatty acids (VFAs) production boost and cellulosic components recovery from fine-sieving fractions (FSF) under initial alkaline conditions. The step utilization of FSF was relatively untapped in similar literatures. The effect of different initial pH values with 8.5, 9.5 and 10.5 (defined as F-8.5, F-9.5 and F-10.5) on fermentation performance were investigated. Then, the fermentation residues were collected to evaluate the changes in chemical structure and thermodynamic properties by fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric (TG) analysis. Furthermore, analysis of the changes in microbial community structure and the interaction between functional genus and performance parameters were undertaken by high throughput sequencing and canonical correspondence analysis (CCA). Results showed that F-10.5 obtained the highest VFAs yields of 234 mg/g VSS, due to efficient polysaccharides release and inhibited methane production. However, high alkaline intensity caused proteins denaturation. Acidogenesis kinetics suggested that the fermentation rate was chemical-dominated. Although crystalline structure was more disordered with increasing alkalinity, the weight loss was lower than 2.5%, making it possible to recover cellulose from fermented residues. Interaction between functional genus and performance parameters revealed the microbial mechanism during the alkaline fermentation. Consequently, the initial-alkaline motivated fermentation was proved to be a promising technology in value-added products recovery to be cost economic, energy positive and environmental friendly., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The effects of anaerobic digestion (AD) on the abundance of antibiotic resistance genes (ARGs) are highly related to operational temperature. However, the removal performance of ARGs in psychrophilic AD and changed temperatures simulating variable seasonal temperatures is poorly understood. Herein, we investigated the fate of ARGs, correlated bacterial communities and physicochemical properties of AD operation at psychrophilic (15 ℃), mesophilic (35 ℃), and temperature changed conditions (15 to 35 ℃ and 35 to 15 ℃). The results indicated that ammonia release was positively correlated with temperature. The mesophilic AD facilitated phosphorous intake and ARGs proliferation and selection with oxytetracycline (OTC), while psychrophilic AD was conducive to the removal and control of ARGs if no OTC existed. The diversity and composition of AD bacterial communities were influenced more by temperature than OTC. The dominant genera like Candidatus_Microthrix and Acinetobacter had dramatical abundance discrepancies at different temperatures and were obviously positively correlated with ARGs (tet39, tetC and mexD), mobile genetic elements (MGEs) intI, insert sequences (IS) and plasmid. The physicochemical properties of AD influenced the bacterial richness, which in turn significantly correlated with the ARGs abundances. Therefore, ARGs removal could be potentially optimized by eliminating bacterial hosts with deteriorated living conditions and decreased nutrients. This study clarified the response of antibiotic resistome to different temperature variation and highlighted the potential strategies for improved ARGs removal in AD., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier Ltd.)

Extraction of short-chain fatty acids (SCFAs) from fermentation liquid of waste activated sludge (WAS) is the key bottleneck hindering its application as electron donor in denitrification. This study explores the feasibility of polyether-type polyurethane (PU)-modified layered double hydroxides (LDHs, prepared using eggshell waste as calcium source) in SCFAs adsorbing from WAS fermentation liquid (SFL). The adsorption parameters were first optimized by adsorption tests using artificial fermentation liquid (AFL). Then, adsorption kinetics, thermodynamic and isotherms were explored to further understand the adsorption mechanism. It revealed that SCFAs absorption by PU-LDHs from SFL was an endothermic and spontaneous process with positive enthalphy (ΔH ◦ ) values and negative Gibbs free energy (ΔG ◦ ) values. In addition, the maximum adsorption capacity of 208.0 mg SCFAs/g PU-LDHs was obtained from the Langmuir isotherm. Noting that both soluble carbohydrates and soluble proteins were simultaneously extracted, with efficiencies of 30.9%, 6.2%, respectively, compared with 62.9% SCFAs. The reuse tests confirmed that the prepared PU-LDHs can be used at least three times with high adsorptive capacity. With PU-LDHs-loaded SFL as external carbon source in the biodenitrification process, a denitrification rate of 0.014 mg NO 3 - -N/mg mixed liquid suspended solids (MLSS)·d was recorded. This study provided a sound basis for the preparation of cost-effective biodenitrification carbon source from SFL by a novel adsorbent., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Free nitrous acid (FNA) has been recently reported to be an effective and eco-friendly inactivator for waste activated sludge (WAS), while the limited decomposition of the extracellular polymeric substance (EPS) matrix hampers resource recovery from WAS. This work employed peracetic acid (PAA) to assist FNA and explored the contribution of co-pretreatment to hydrogen recovery in a prefermentation-bioelectrolysis cascading system. The results showed that co-pretreatment led to approximately 8.8% and 20.4% increases in the exfoliation of particulate proteins and carbohydrates, respectively, from tightly bound EPS (TB-EPS) over that of sole FNA pretreatment. Electron paramagnetic resonance analysis verified that the synergistic effect of FNA, PAA and various generated free radicals was the essential process. This effect further promoted the accumulation of volatile fatty acids (VFAs) after 96 h of prefermentation, and the peak concentration in co-pretreated WAS (AD-FPWAS) was approximately 2.5-fold that in sole FNA-pretreated WAS (AD-FWAS). Subsequently, the cascading utilization of organics in the bioelectrolysis step contributed to efficient hydrogen generation. A total of 10.8 ± 0.3 mg H 2 /g VSS was harvested in microbial electrolysis cells (MECs) fed with AD-FPWAS, while 6.2 ± 0.1 mg H 2 /g VSS was obtained from AD-FWAS. X-ray photoelectron spectroscopy (XPS) revealed the effective decomposition of the phospholipid bilayer in the cytomembrane and the transformation of macromolecular organics into VFAs and hydrogen in the cascading system. Further microbial community analysis demonstrated that co-pretreatment enhanced the accumulation of functional consortia, including anaerobic fermentative bacteria (AFB, 28.1%), e.g., Macellibacteroides (6.3%) and Sedimentibacter (6.9%), and electrochemically active bacteria (EAB, 57.0%), e.g., Geobacter (39.0%) and Pseudomonas (13.6%), in the prefermentation and MEC steps, respectively. The possible synergetic and competitive relationships among AFB, EAB, homo-acetogens, nitrate-reducing bacteria and methanogens were explored by molecular ecological network analysis. From an environmental and economic perspective, this promising FNA and PAA co-pretreatment approach provides new insight for energy recovery from WAS biorefineries., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, a novel upflow microaerobic sludge reactor (UMSR) was constructed to conduct anaerobic digestion of municipal wastewater with low carbon and nitrogen ratio (C/N). Oxygen in the UMSR was supplied by falling water and external recirculation. Excellent nitrogen removal performance was obtained in the UMSR for treating wastewater with low C/N ratio at a temperature of 25 °C and a hydraulic retention time of 24 h. Ammonium and total nitrogen removal efficiencies averaged 92.35% and 90.41%, respectively, and sludge granulation occurred during acclimation. The inferred metabolism of nitrogen removal and ecological positions of functional microbe were integrated into a granule model by scanning electron microscopy. Additionally, the analysis of microbial community indicated that aerobic nitrifying bacteria and heterotrophic bacteria survived on the surface of sludge floc and granules while the anaerobic autotrophic, heterotrophic denitrifying, and anaerobic ammonia oxidation bacteria were present in the inner layer., (Copyright © 2018. Published by Elsevier Ltd.)

The effects of three widely-used surfactants on waste activated sludge (WAS) fermentation and microbial community structures were investigated. Rhamnolipid bio-surfactants (RL) showed more positive effects on WAS hydrolysis and acidification compared to chemosynthetic surfactants, such as sodium dodecylsulphate (SDS) and sodium dodecyl benzene sulfonate (SDBS). The highest SCOD and VFAs concentrations obtained with RL were 1.15-fold and 1.16-fold that of SDS, and up to 1.73 and 3.63 times higher than those obtained with SDBS. Pyrosequencing analysis showed that an evident reduction in bacterial diversity in surfactant-treated WAS. Moreover, acid-producing bacteria (such as Megasphaera and Oscillibacter), detected with RL, were (6.8% and 6.4% in proportion) more abundant than with SDS, and were rarely found in SDBS and the control. The results also revealed that RL allowed efficient hydrolysis enhancement and was favorable to functional microorganisms for further acidification during WAS fermentation., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

A novel pretreatment method combining ultrasonic with thermophilic bacteria (Geobacillus sp. G1) was employed to pretreat waste-activated sludge (WAS) for enhancing the WAS hydrolysis and subsequent volatile fatty acids (VFAs) production. The soluble protein and carbohydrate were mostly released from intracellular ultrasonic-assisted Geobacillus sp. G1 pretreatment, and accumulated to 917 ± 70 and 772 ± 89 mg COD/L, respectively, which were 2.53- and 2.62-fold higher than that obtained in control test. Excitation emission matrix (EEM) fluorescence spectroscopy revealed the highest fluorescence intensity (FI) of protein-like substances, indicating the synergistic effect of ultrasonic and Geobacillus sp. G1 pretreatments on WAS hydrolysis. The maximum VFAs accumulation was 4437 ± 15 mg COD/L obtained in ultrasonic-assisted Geobacillus sp. G1 pretreatment test. High-throughput pyrosequencing analysis investigated that the microbial communities were substantial determined by the pretreatment used. The hydrolysis enhancement was caused by an increase in extracellular enzymes, which was produced by one of dominant species Caloramator sp. The positive effect was well explained to the enhancement of WAS hydrolysis and final VFAs accumulation.

Microbial electrolysis cell (MECs) were investigated as a promising technology to manage waste activated sludge (WAS) reduction and bio-methane generation. The effect of WAS concentration on the MECs performance was discussed. At the optimal concentration of 15gCOD/L, maximum methane yield of MECs fed with alkaline pretreated WAS (A-WAS) were achieved with the value of 77.13±2.52LCH4/kg-COD on Day 3, which had been improved by 1.5-fold compared with MECs fed with raw WAS (R-WAS), while that was negligible in open circuit controls. Efficient sludge reduction was also obtained in terms of TCOD, total protein, TSS and VSS removal. Pyrosequencing revealed the dominance of exoelectrogen Geobacter and hydrogen-producing bacteria Petrimonas in MECs fed with WAS. Methanocorpusculum with the capacity of methane generation using CO2 and H2 also showed overwhelming dominance (96.01%). The large proportions of Petrimonas and Methanocorpusculum indicated the occurrence of hydrogenotrophic methanogenesis in our methane-producing MECs., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

A novel pretreatment method combining freezing/thawing with Geobacillus sp. G1 was employed to pretreat waste activated sludge (WAS) for enhancing the WAS hydrolysis and subsequent short-chain fatty acids (SCFAs) production. Results showed that freezing/thawing combined with Geobacillus sp. G1 pretreatment achieved the maximal concentrations of soluble protein from 40±6mg COD/L (non-pretreated) to 1226±24mg COD/L (pretreated), and accumulated SCFAs concentration increased from 248±81mg COD/L to 3032±53mg COD/L. Excitation emission matrix (EEM) fluorescence spectroscopy revealed the highest fluorescence intensity (FI) of protein-like substances, which was the dominant fluorescent organic matters, indicating the synergistic effect of freezing/thawing and Geobacillus sp. G1 pretreatment on organics hydrolysis. High-throughput pyrosequencing analysis investigated that the abundance of bacteria responsible for WAS hydrolysis (such as Clostridium and Caloramator) and SCFAs production (such as Parabacteroides and Bacterodies) was greatly enhanced due to the novel pretreatment method used., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Alkaline pretreatment was studied to analyze the influence on waste activated sludge (WAS) reduction, methane production and microbial community structure during anaerobic digestion. Methane production from alkaline pretreated sludge (A-WAS) (pH = 12) increased from 251.2 mL/Ld to 362.2 mL/Ld with the methane content of 68.7% compared to raw sludge (R-WAS). Sludge reduction had been improved, and volatile suspended solids (VSS) removal rate and protein reduction had increased by ∼ 10% and ∼ 35%, respectively. The bacterial and methanogenic communities were analyzed using 454 pyrosequencing and clone libraries of 16S rRNA gene. Remarkable shifts were observed in microbial community structures after alkaline pretreatment, especially for Archaea. The dominant methanogenic population changed from Methanosaeta for R-WAS to Methanosarcina for A-WAS. In addition to the enhancement of solubilization and hydrolysis of anaerobic digestion of WAS, alkaline pretreatment showed significant impacts on the enrichment and syntrophic interactions between microbial communities., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Hydrolysis is known as the rate-limiting step during waste activated sludge (WAS) digestion. The optimization of the culture conditions of Geobacillus sp. G1 for enhancing WAS hydrolysis was conducted in this study with uniform design and response surface methodology. Taking the lysis rate of Escherichia coli as the response, the Plackett-Burman design was used to screen the most important variables. Experimental results showed that the maximum predicted lysis rate of E. coli was 50.9% for 4 h treatment time with concentrations of skim milk, NaCl and NH4SO4 at 10.78, 4.36 and 11.28 g/L, respectively. The optimized dosage ratio of Geobacillus sp. G1 to WAS was 35%:65% (VG1:VWAS). Under this condition, soluble protein was increased to 695 mg chemical oxygen demand (COD)/L, which was 5.0 times higher than that obtained in the control (140 mg COD/L). The corresponding protease activity reached 1.1 Eu/mL. Scanning electron microscopy showed that abundant cells were apparently lysed with treatment of Geobacillus sp. G1.

Volatile fatty acids (VFAs) are the most suitable and biodegradable carbon substrates for many bioprocesses. This study explored a new approach to improve the VFAs production from anaerobic co-digesting waste activated sludge (WAS) with corn straw (CS). The effect of feedstock proportion on the acidification efficiency was investigated. The maximum VFAs yield (corresponding fermentation time) was substantially increased 69% (96 h), 45% (72 h), 13% (120 h) and 12% (120 h) with 50%, 35%, 25% and 20% CS proportion of feedstock, respectively. HAc (acetic acid) was consistently the most abundant, followed by HPr (propionic acid) and n-HBu (butyric acid) in the co-digesting tests. The increase of CS in feedstock led to more production of HAc and HPr. Moreover, the consumption of protein and carbohydrate were also improved remarkably from 2955 and 249 mg COD/L (individual WAS fermentation) to 6575 and 815 mg COD/L (50%WAS:50%CS co-digestion) from 120 onward, respectively. The highest contribution of CS to additional VFAs production was1113 mg VFAs (as COD)/g CS/L in the 65%WAS:35%CS co-digesting test. Our study indicated a valuable method to improve VFAs production from anaerobic co-digesting WAS and CS., (Crown Copyright © 2013. Published by Elsevier B.V. All rights reserved.)

Short-chain fatty acids (SCFAs) are the most important intermediate in the waste activated sludge (WAS) fermentation process. This work explored a novel approach to improve the SCFAs production from WAS. Experimental results showed that the disintegration and acidification of WAS were enhanced markedly by using bi-frequency (28+40 kHz) ultrasonic pretreatment compared with monofrequency (28 kHz and 40 kHz) ultrasonic pretreatments. After 28 + 40 kHz ultrasonic pretreatment, the SCOD concentration increased from original 363 mg COD l(-1) to 10810 mg COD l(-1) which was 1.53-fold and 1.44-fold of the values obtained with 28kHz and 40kHz ultrasonic pretreatments, respectively. The maximum SCFAs production reached 7587 mg COD l(-1) in the 28 + 40 kHz test which was respectively 1.25-fold and 1.31-fold of that in the 28 kHz (6053 mg COD l(-1)) and 40 kHz (5809 mg COD I(-1)) tests. This was the highest SCFAs production obtained so far using WAS, pretreated by ultrasonic technology, as the renewable carbon source. SCFAs composition analysis revealed there was more acetic acid (3992 mg COD l(-1), accounted for 52.6% of the total SCFAs) for the 28+40 kHz ultrasonic pretreatment which was beneficial to many subsequent bioprocesses.

Constructed wetlands have been widely employed as a cost-effective and environmentally friendly alternative for treating primary and secondary sewage effluents. In this study, biochar and pyrite were utilized as electron donor substrates in intermittent-aerated vertical flow constructed wetlands to strengthen the nutrient and heavy metals removal simultaneously, and the response of nutrient reduction and microbial community to heavy metals stress was also explored. The results indicated that biochar addition exhibited a better nitrogen removal, while pyrite addition greatly promoted the phosphorus removal. Moreover, the high removal efficiencies of Cu2+, Pb2+ and Cd2+ (above 90%) except for Zn2+ were obtained in each system. However, the exposure of heavy metals decreased phosphorus removal while had little effect on nitrogen removal. The influent load and intermittent aeration implementation led to a significant shift in microbial community structures, but microbial biodiversity and abundance decreased under the exposure of heavy metals. Particularly, Thiobacillus and Ferritrophicum , associated with sulfur autotrophic denitrification and iron autotrophic denitrification, were more abundant in pyrite-based wetland systems. • Biochar and pyrite addition was beneficial to nitrogen and phosphorus removal. • Biochar-mediated heterotrophic denitrification played significant role in enhancing total nitrogen removal. • Exposure to heavy metals had little impact on denitrification but hindered phosphorus removal. [ABSTRACT FROM AUTHOR]

Photocatalytic removal of NH 3 –N is expected to be an alternative to the biological method that accompanied with high energy consumption and secondary pollution. However, NH 3 –N is always oxidized into nitrate and nitrite during the photocatalytic processes, which also need to be removed from the water. Herein, the g-C 3 N 4 /rGO/TiO 2 Z-scheme photocatalytic system was prepared and used for the NH 3 –N removal. The results showed the rate constant of NH 3 –N conversion on it was 0.705 h−1, 1.7 times as high as that on g-C 3 N 4 /TiO 2 , and most of the NH 3 –N were converted into gaseous products. And the experiment result indicated NH 3 –N and NO 3 − in water could enhance the removal of each other. According to the results, the main reaction mechanism is speculated as: ·OH radicals and ·O 2 − radicals were generated on TiO 2 and oxidized the NH 3 –N into NO 3 −, and the latter was reduced into non-toxic N 2 on the conduction band of g-C 3 N 4. Finally, NH 3 –N removal performance for actual coking wastewater was investigated, and the stability of the photocatalyst was tested. This work provides some theoretical basis for the two-step degradation of pollutants by Z-scheme photocatalytic system. • NH3–N removal was realized by photocatalytic nitrification-denitrification process. • g-C3N4/rGO/TiO2 was used for treatment of actual coking wastewater. • The stability of g-C3N4/rGO/TiO2 used in actual wastewater was tested. • Interaction of NH3–N and NO3 during the photocatalytic process was investigated. [ABSTRACT FROM AUTHOR]