Comparative metabolic modeling of multiple sulfate-reducing prokaryotes reveals versatile energy conservation mechanisms.

Sulfate-reducing prokaryotes (SRPs) are crucial participants in the cycling of sulfur, carbon, and various metals in the natural environment and in engineered systems. Despite recent advances in genetics and molecular biology bringing a huge amount of information about the energy metabolism of SRPs, little effort has been made to link this important information with their biotechnological studies. This study aims to construct multiple metabolic models of SRPs that systematically compile genomic, genetic, biochemical, and molecular information about SRPs to study their energy metabolism. Pan-genome analysis was conducted to compare the genomes of SRPs, from which a list of orthologous genes related to central and energy metabolism was obtained. Twenty-four SRP metabolic models via the inference of pan-genome analysis were efficiently constructed. The metabolic model of the well-studied model SRP Desulfovibrio vulgaris Hildenborough (DvH) was validated via flux balance analysis (FBA). The DvH model predictions matched reported experimental growth and energy yields, which demonstrated that the core metabolic model worked successfully. Further, steady-state simulation of SRP metabolic models under different growth conditions showed how the use of different electron transfer pathways leads to energy generation. Three energy conservation mechanisms were identified, including menaquinone-based redox loop, hydrogen cycling, and proton pumping. Flavin-based electron bifurcation (FBEB) was also demonstrated to be an essential mechanism for supporting energy conservation. The developed models can be easily extended to other species of SRPs not examined in this study. More importantly, the present work develops an accurate and efficient approach for constructing metabolic models of multiple organisms, which can be applied to other critical microbes in environmental and industrial systems, thereby enabling the quantitative prediction of their metabolic behaviors to benefit relevant applications.

Biological nitrogen removal from wastewater using sulphur-driven autotrophic denitrification.

Biological denitrification process in mainstream wastewater treatment often needs dosing supplemental electrons, consequently adding a remarkable operating cost. Organic carbon compounds are nowadays the most intensively used electron sources in full-scale wastewater treatment, corresponding with the well-understood carbon-nitrogen biogeochemistry for heterotrophic denitrification process. In the twenty-first century, the low-carbon technology is on calling to reduce the carbon footprint and relieve climate changing threatens. Autotrophic denitrification is highly recommended for mainstream wastewater treatment. The reduced-sulphur compounds (such as sulphide, elemental sulphur, and thiosulphate) could be utilised as electron donors, to drive sulphur cycle reactions to reduce nitrate and nitrite to dinitrogen gas. Based on the literature review and our own research experiences, this paper presents our perspectives on sulphur-driven autotrophic denitrification. It particularly focuses on the functional enzymes, sulphur bioreactors, and influential operating factors. Overall, this paper provides new insights on sulphur-nitrogen biogeochemistry and application as a low-carbon technology for nitrogen removal during municipal wastewater treatment.

Sludge flotation, its causes and control in granular sludge upflow reactors.

Sludge flotation is a commonly reported and long-standing issue hindering not only the widespread implementation of upflow anaerobic sludge bed (UASB)-type bioreactors in wastewater treatment but also the development of novel anaerobic/anoxic treatment processes such as anammox, partial denitrification, and biological sulfate reduction. This review attempts to address the instability of UASB-type bioreactors due to sludge flotation. Possible causes of sludge flotation are classified into intrinsic and extrinsic ones. Extrinsic causes include substrate overloading, inappropriate carbon source, overloading of proteins or oils, insufficient reactor mixing, a low temperature, and a low pH. These unfavorable extrinsic conditions can lead to unexpected intrinsic changes in sludge granules, including high gas production, formation of hollow space inside the granules, filamentous bacterial overgrowth, inappropriate production of extracellular polymeric substances, and development of an adhesive granule surface. These intrinsic changes can increase the flotation potential of sludge through reducing the granule density and promoting gas entrapment. To control the sludge flotation problem, both preventive and corrective strategies are summarized. Preventive strategies include maintaining a temperature of 30-35 °C and a pH of 7-9, preventing substrate overloading, providing sufficient nutrients and multiple carbon sources in the influent, applying pre-acidification, and enhancing reactor mixing. If the causes of a sludge flotation incident cannot be identified quickly, corrective strategies including breaking up floating granules and dosing with chemicals such as Fe2+ and surfactants can be applied to suppress the flotation problem.

Application of a moving-bed biofilm reactor for sulfur-oxidizing autotrophic denitrification.

Sulfur-oxidizing autotrophic denitrification (SO-AD) was investigated in a laboratory-scale moving-bed biofilm reactor (MBBR) at a sewage temperature of 22 °C. A synthetic wastewater with nitrate, sulfide and thiosulfate was fed into the MBBR. After 20 days' acclimation, the reduced sulfur compounds were completely oxidized and nitrogen removal efficiency achieved up to 82%. The operation proceeded to examine the denitrification by decreasing hydraulic retention time (HRT) from 12 to 4 h in stages. At steady state, this laboratory-scale SO-AD MBBR achieved the nitrogen removal efficiency of 94% at the volumetric loading rate of 0.18 kg N·(mreactor3·d)-1. The biofilm formation was examined periodically: the attached volatile solids (AVS) gradually increased corresponding to the decrease of HRT and stabilized at about 1,300 mg AVS·Lreactor-1 at steady state. This study demonstrated that without adding external organic carbon, SO-AD can be successfully applied in moving-bed carriers. The application of SO-AD MBBR has shown the potential for sulfur-containing industrial wastewater treatment, brackish wastewater treatment and the upgrading of the activated sludge system. Moreover, the study provides direct design information for the full-scale MBBR application of the sulfur-cycle based SANI process.

2.52 terahertz dual-axis reflection confocal scanning microscope.

We present a dual-axis reflection confocal scanning microscope operating at 2.52 terahertz with axial resolution of 0.67 mm. The spatial resolution of the system was evaluated by utilizing the resolution test chart. Lateral resolution exceeded 0.314 mm, and the lengthwise resolution was over 0.353 mm. We introduced a 0.3 mm pinhole to improve the resolution. Targets such as the Chinese character "TAI" written on paper with a pencil and the metal letter "G" were scanned to test the imaging quality. To verify the imaging ability of the axial sections, two pairs of metal straps and a combinatorial metal ring were scanned, further revealing the satisfying 3D imaging capability.

A novel nonwoven hybrid bioreactor (NWHBR) for enhancing simultaneous nitrification and denitrification.

This study proposed a nonwoven hybrid bioreactor (NWHBR) in which the nonwoven fabric played dual roles as a biofilm carrier and membrane-like separation of the flocculent sludge in the reactor. The results of long-term monitoring demonstrated that the NWHBR could achieve simultaneous nitrification and denitrification (SND), with nearly complete ammonium removal and 80% removal of total nitrogen. The biofilm attached to the nonwoven fabric removed 27% of the chemical oxygen demand (COD) and 36% of the nitrate in the reactor, an enhanced elimination of nutrients that was attributed to the increased mass transfer within the biofilm due to permeate drag. The results of batch experiments showed that the flocculent sludge played a more dominant role in nitrification and denitrification (79% and 61%, respectively) than the biofilm (21% and 36%, respectively). The batch experiments also revealed that the enforced mass transfer, with an effluent recirculation rate of 4.3 L/m(2)h (which was the same as the flux during the reactor's long-term operation), improved the denitrification rate by 58% (i.e., from 9.0 to 14.2 mg-NO(3)(-)-N/h). Pyrosequencing of the 16S rRNA gene amplification revealed a high microbial diversity in both the flocculent sludge and biofilm, with Proteobacteria, Bacteroidetes and Chloroflexi as the dominant groups. A phylogenetic (P) test indicated that the NWHBR contained phylogenetically distinct microbial communities: those in the biofilm differed from those in the flocculent sludge. However, the communities on the exterior and interior of the biofilm were more similar to each other. Due to its good SND performance, low physical back-washing frequency and low air-to-water ratio, the NWHBR represents an attractive alternative for the wider application of either low-cost membrane bioreactors or biofilm reactors.

A new oxic-settling-anaerobic (NOSA(®)) activated sludge process for minimizing excess sludge in secondary biological treatment plants: a pilot-scale evaluation of the absorption-biodegradation process.

This study compared the sludge reduction performance of a new oxic-settling-anaerobic (NOSA) process with that of a conventional adsorption-biodegradation process. A 50 m(3)/d pilot trial system with two different process configurations was operated for 6 months. The NOSA process functioned effectively in removing both chemical oxygen demand and nitrogen with the efficiencies of 86 and 92.5%, respectively, which reduced approximately 40% of the excess sludge. In this research, 0.77 kg volatile suspended solids/d sludge vanished in the anaerobic tank, which accounted for 58.9% of the total sludge loss in the NOSA process. Economic calculation suggests that the new process can dramatically upgrade the sludge reduction in wastewater treatment plants without a digestion device, and the investment for fundamental upgrading can be recovered in 5-6 years by cutting the costs of excess sludge dewatering and disposal treatment.

The impact of chlorine disinfection on biochemical oxygen demand levels in chemically enhanced primary treatment effluent.

The response trends of biochemical oxygen demand (BOD) and organic strength after the chlorination/dechlorination process were explored through a 2-year, 5-month chemically enhanced primary treatment (CEPT) effluent onsite monitoring program and a 2-month laboratory-scale study. The monitoring results showed that better instantaneous mixing at the chlorine injection point reduced the effect of chlorination/dechlorination on the 5-day BOD levels. The laboratory study results demonstrated that chlorination did not change the particle size distribution, dissolved organic carbon, or chemical oxygen demand of the organic content of the effluent. Nevertheless, chlorination/dechlorination strongly affected the BOD measurement when nitrification was inhibited by changing bioactivity/biodegradation rates.

Sulphate reduction, mixed sulphide- and thiosulphate-driven Autotrophic denitrification, NItrification, and Anammox (SANIA) integrated process for sustainable wastewater treatment.

This study proposes the Sulphate reduction, mixed sulphide- and thiosulphate-driven Autotrophic denitrification, Nitrification, and Anammox integrated (SANIA) process for sustainable treatment of mainstream wastewater after organics capture. Three moving-bed biofilm reactors (MBBRs) were applied for developing sulphate reduction (SR), mixed sulphide- and thiosulphate-driven partial denitrification and Anammox (MSPDA), and NItrification (N), respectively. Typical mainstream wastewater after organics capture (e.g., chemically enhanced primary treatment, CEPT) was synthesized with chemical oxygen demand (COD) of 110 mg/L, sulphate of 50 mg S/L, ammonium of 30 mgN/L. The feasibility of SANIA was investigated with mimic nitrifying effluent supplied in MSPDA-MBBR (Period I), followed by the examination of the applicability of SANIA process with N-MBBR integrated (Period II), under moderate temperatures (25-27 â„ƒ). In Period I, SANIA process was established with both SR- and MSPDA-MBBR continuously operated for over 300 days (no Anammox biomass inoculation). Specifically, in MSPDA-MBBR, high rates of denitratation (2.7 gN/(m2·d)) and Anammox (2.8 gN/(m2·d)) were achieved with Anammox contributing to 81 % of the total inorganic nitrogen removal. In Period II, the integrated SANIA system was continuously operated for over 130 days, achieving up to 90 % of COD, 93 % of ammonium, and 61 % of total inorganic nitrogen (TIN) removal, with effluent concentrations lower than 10 mg COD/L, 3 mg NH4+-N/L, and 13 mg TIN-N/L. The implementation of SANIA can ultimately reduce 75 % and 40 % of organics and aeration energy for biological nitrogen removal. Considering the combination of SANIA with CEPT for carbon capture and sludge digestion/incineration for energy recovery, the new integrated wastewater technology can be a promising strategy for sustainable wastewater treatment.

Physics-informed neural network-based serial hybrid model capturing the hidden kinetics for sulfur-driven autotrophic denitrification process.

Sulfur-driven autotrophic denitrification (SdAD) is a biological process that can remove nitrate from low carbon/nitrogen (C/N) ratio wastewater. Although this process has been intensively researched, the mechanism whereby its intermediates (i.e., elemental sulfur and nitrite ions) are generated and accumulated remains elusive. Existing mathematical models developed for SdAD cannot accurately predict the intermediates in SdAD because of the incomplete knowledge of process kinetic resulting from changes in the environmental conditions and electron competition during SdAD. To address this limitation, we proposed a novel serial hybrid model structure based on a physics-informed neural network (PINN) to capture the dynamics of the process kinetics and predict the substrate concentrations in SdAD. In this study, we evaluated the model through numerical experiments and applied it to real case studies involving batch and continuous-flow reactor scenarios. By leveraging the PINN approach, the hybrid model yielded accurate predictions at both the state (i.e. substrate concentration) and kinetic levels in the numerical experiments and performed better than both mechanistic and purely data-driven models in the case studies. Furthermore, we used the trained hybrid model to design control strategies for SdAD and a novel integrated process involving SdAD and anammox for energy-efficient nitrogen removal. Finally, we discuss the advantages and application scope of the PINN-based hybrid model.

Dosing with pyrite significantly increases anammox performance: Its role in the electron transfer enhancement and the functions of the Fe-N-S cycle.

Anaerobic ammonium oxidation (anammox) represents an energy-efficient process for biological nitrogen removal from ammonium-rich wastewater. However, there are mechanistic issues unsolved regarding the low microbial electron transfer and undesired accumulation of nitrate in treated water, limiting its widespread engineering applications. We found that the addition of pyrite (1 g L-1 reactor), an earth-abundant iron-bearing sulfide mineral, to the anammox system significantly improved the nitrogen removal rate by 52% in long-term operation at a high substrate shock loading (3.86 kg N m-3 d-1). Two lines of evidence were presented to unravel the underlying mechanisms of the pyrite-induced enhancement. Physiochemical evidence indicated that an increase of cytochromes c and Fe-S protein was responsible for the accelerated electron transfer among metabolic enzymes. Multi-omics evidence showed that the depletion of nitrate was attributed to the Fe-N-S cycle driven by nitrate-dependent Fe(II) oxidation and S-based denitrification. This study deepens our understanding of the roles of electron transfer and the Fe-N-S cycle in anammox systems, providing a fundamental basis for the development of mediators in the anammox process for practical implications.

The demonstration of a novel sulfur cycle-based wastewater treatment process: sulfate reduction, autotrophic denitrification, and nitrification integrated (SANI®) biological nitrogen removal process.

Saline water supply has been successfully practiced for toilet flushing in Hong Kong since 1950s, which saves 22% of freshwater in Hong Kong. In order to extend the benefits of saline water supply into saline sewage management, we have recently developed a novel biological organics and nitrogen removal process: the Sulfate reduction, Autotrophic denitrification, and Nitrification Integrated (SANI®) process. The key features of this novel process include elimination of oxygen demand in organic matter removal and production of minimal sludge. Following the success of a 500-day lab-scale trial, this study reports a pilot scale evaluation of this novel process treating 10 m(3) /day of 6-mm screened saline sewage in Hong Kong. The SANI® pilot plant consisted of a sulfate reduction up-flow sludge bed (SRUSB) reactor, an anoxic bioreactor for autotrophic denitrification and an aerobic bioreactor for nitrification. The plant was operated at a steady state for 225 days, during which the average removal efficiencies of both chemical oxygen demand (COD) and total suspended solids (TSS) at 87% and no excess sludge was purposefully withdrawn. Furthermore, a tracer test revealed 5% short circuit flow and a 34.6% dead zone in the SRUSB, indicating a good possibility to further optimize the treatment capacity of the process for full-scale application. Compared with conventional biological nitrogen removal processes, the SANI® process reduces 90% of waste sludge, which saves 35% of the energy and reduces 36% of fossil CO(2) emission. The SANI® process not only eliminates the major odor sources originating from primary treatment and subsequent sludge treatment and disposal during secondary saline sewage treatment, but also promotes saline water supply as an economic and sustainable solution for water scarcity and sewage treatment in water-scarce coastal areas.

Coupling sulfur-based denitrification with anammox for effective and stable nitrogen removal: A review.

Anoxic ammonium oxidation (anammox) is an energy-efficient nitrogen removal process for wastewater treatment. However, the unstable nitrite supply and residual nitrate in the anammox process have limited its wide application. Recent studies have proven coupling of sulfur-based denitrification with anammox (SDA) can achieve an effective nitrogen removal, owing to stable provision of substrate nitrite from the sulfur-based denitrification, thus making its process control more efficient in comparison with that of partial nitrification and anammox process. Meanwhile, the anammox-produced nitrate can be eliminated through sulfur-based denitrification, thereby enhancing SDA's overall nitrogen removal efficiency. Nonetheless, this process is governed by a complex microbial system that involves both complicated sulfur and nitrogen metabolisms as well as multiple interactions among sulfur-oxidising bacteria and anammox bacteria. A comprehensive understanding of the principles of the SDA process is the key to facilitating the development and application of this novel process. Hence, this review is conducted to systematically summarise various findings on the SDA process, including its associated biochemistry, biokinetic reactions, reactor performance, and application. The dominant functional bacteria and microbial interactions in the SDA process are further discussed. Finally, the advantages, challenges, and future research perspectives of SDA are outlined. Overall, this work gives an in-depth insight into the coupling mechanism of SDA and its potential application in biological nitrogen removal.

Microbial community of sulfate-reducing up-flow sludge bed in the SANI® process for saline sewage treatment.

This study investigated the microbial community of the sulfate-reducing up-flow sludge bed (SRUSB) of a novel sulfate reduction, autotrophic denitrification, and nitrification integrated (SANI®) process for saline sewage treatment. The investigation involved a lab-scale SANI® system treating synthetic saline sewage and a pilot-scale SANI® plant treating 10 m(3)/day of screened saline sewage. Sulfate-reducing bacteria (SRB) were the dominant population, responsible for more than 80% of the chemical oxygen demand removal, and no methane-producing archaea were detected in both SRUSBs. Thermotogales-like bacteria were the dominant SRB in the pilot-scale SRUSB while Desulforhopalus-like bacteria were the major species in the lab-scale SRUSB.

A real trial of a long-term non-fouling membrane bioreactor for saline sewage treatment.

This paper reports on a pilot trial of a novel MBR developed with coarse-pore membrane module by the authors. The plant was operated for 370 days with up to 7 m(3)/d raw saline sewage after 3-mm screening. The plant performed successfully without membrane fouling for 270 days except an accidental power source failure for 30 h, during which membrane was fouled under no aeration and mixing condition. EPS increases in both the reactor and the bio-cake on the membrane surface explained this fouling. The average TSS, COD and TKN removal efficiency were 92, 90, and 93%, respectively, under a high effective permeate flux of 4.8 m/d and a low air-to-water ratio of 15.

Shock effects of monovalent cationic salts on seawater cultivated granular sludge.

Saline wastewater is commonly encountered in various industries, posing challenges to biological treatments. The application of seawater as a seed source provides a media of diverse halophilic organisms for rapid startup. However, effects of transitioning from a mixed salt source to monovalent salt solutions prevalent in industry remains unexplored. Hence, seed sludge was cultivated using seawater and later granulated under a mixed-salt synthetic medium comprising a mixture of NaCl, KCl and Na2SO4 at a combined concentration of 0.8 M (0.27 M each). The stable, acclimated granules were then tested against single salt media of 0.8 M NaCl, KCl, or Na2SO4. Shift to single salt media resulted in granule disaggregation, poor settling, sludge washout and development of fluffy or slimy flocs. Changes in exopolysaccharides composition after the single salt shift was the predominant reason for the large changes in sludge morphology. The impacts of KCl and Na2SO4 were more significant than the shift to NaCl. The resulting impacts also had a major influence on the treatment performance. A complex mechanism involving monovalent cation stimulation of proteins; ionic strength impacts on exopolysaccharides and morphology; solution density influence on sludge density and settling; and tonicity impacts on cell viability and treatment is described.

The effectiveness of divalent cation addition for highly saline activated sludge cultures: Influence of monovalent/divalent ratio and specific cations.

Saline wastewaters are prevalent in various industries and pose challenges to stable biological treatment. Increasing monovalent cation concentrations are commonly reported to deteriorate treatment and settling performance, while divalent cations can enhance flocculation and settling. However, many previous studies were performed at relatively low salinities and reports conflict on whether concentrations of monovalent cations, divalent cations, or their ratio (M/D) are most critical. This study investigates whether addition of divalent cations shows the same benefits at high salinity (∼40 g NaCl.L-1) and whether divalent ion concentration or M/D is a better predictor of enhancement. Nine sequencing batch reactors were operated at 0.8 M NaCl or KCl monovalent salt concentration, and the concentration of divalent cations (Ca2+ and Mg2+) was varied. M/D was found to be the critical factor that consistently influenced sludge characteristics. It was particularly important in describing hydrophobicity, sludge volume index (SVI) and specific oxygen uptake rate (SOUR), with rpartial of -0.879, 0.971 and 0.966 respectively in models that had an r2adj greater than 0.93. Lower M/D also increased biomass concentrations and reduced extracellular polysaccharides, the latter which in turn correlated strongly with many shape and surface charge measures. The specific monovalent salt (Na+ or K+) influenced treatment performance, biomass concentrations, hydrophobicity, SOUR, extracellular protein and SVI. The specific divalent cation was only important in describing SVI, where Mg2+ was beneficial. Overall, this study shows that addition of divalent cations can greatly benefit high salinity activated sludge systems by improving the sludge structure, settling and organic removal.

Identifying the mechanisms of sludge reduction in the sulfidogenic oxic-settling anaerobic (SOSA) process: Side-stream sulfidogenesis-intensified sludge decay and mainstream extended aeration.

An energy-/cost-efficient and environment-friendly in-situ sludge reduction process, called the sulfidogenic oxic-settling anaerobic (SOSA) was developed recently. However, the underpinning mechanism of sludge reduction by the SOSA process remains elusive. This paper investigated the possible mechanisms of sludge reduction through biomass cultivation in three lab-scale experimental systems: one anoxic-oxic CAS process with a long sludge retention time (SRT) and extended aeration (EAO) process, and two EAO-based in-situ sludge reduction processes, i.e., the conventional oxic-settling anaerobic (COSA) process and the new SOSA process. These three comparative biosystems were operated with identical influent and reactor configurations as well as the same biomass concentrations and SRTs (approximately 5 g/L and 46 days, respectively), and the sludge interchange ratios (between the CAS and side-stream reactors) in COSA and SOSA were both 10% per day. Three systems all achieved high organic (>93%) and total nitrogen (TN) (>74%) removal efficiencies. SOSA produced 29% and 20% less sludge than EAO and COSA, respectively, simultaneously consumed 14% and 8% more oxygen than EAO and COSA, indicating that the sludge reduction in SOSA was not only caused by EAO-based aerobic digestion in the mainstream and conventional anaerobic reactions in the side-stream, but more importantly due to the bioaugmentation of sulfidogenesis. The roles of sulfidogenesis were further studied in batch tests, and the key findings were as follows: i) the SOSA biomass had a faster endogenous decay rate (0.097 d-1) than that of the COSA biomass (0.045 d-1), and ii) sulfidogenesis accelerated anaerobic solubilization, hydrolysis, acidogenesis and acetogenesis by 2.3 - 3.1 times, 6 - 22 %, 22 - 60% and 6 - 22%, respectively. Overall, the mechanisms of sludge reduction in SOSA were unraveled in this study which will help promote its full-scale application in future.

Development of a kinetic model to evaluate thiosulfate-driven denitrification and anammox (TDDA) process.

Recently, the integration of sulfur-driven denitrification and anammox process has been extensively studied as a promising alternative nitrogen removal technology. Most of these studies investigated the process feasibility and monitored the community dynamics. However, an in-depth understanding of this new sulfur-nitrogen cycle bioprocess based on mathematical modeling and elucidation of complex interactions among different microorganisms has not yet been achieved. To fill this gap, we developed a kinetic model (with 7 bioprocesses, 12 variables, and 19 parameters) to assess the sulfur(thiosulfate)-driven denitrification and anammox (TDDA) process in a single reactor. The parameters used in this process were separately estimated by fitting the data obtained from the experiments. Then, the model was further validated under different conditions, and the results demonstrated that the developed model could describe the dynamic behaviors of nitrogen and sulfur conversions in the TDDA system. The newly developed branched thiosulfate oxidation model was also verified by conducting a metagenomics analysis. Using the developed model, we i) examined the interactions between sulfur-oxidizing bacteria and anammox bacteria at steady-state conditions with varying substrates to demonstrate the reliability of TDDA, and ii) evaluated the feasibility and operation of the TDDA process in terms of practical implementation. Our results will benefit further exploration of the significance of this novel S-N cycle bioprocess and guide its future applications.

Electrochemical pretreatment (EPT) of waste activated sludge: Extracellular polymeric substances matrix destruction, sludge solubilisation and overall digestibility.

Anaerobic digestion (AD) of waste activated sludge (WAS) is widely used for stabilisation, mass reduction and resource recovery. However, AD performance is often hampered by the poor digestibility and slow degradation rate for WAS. A series of bench-scale tests was conducted using innovative electrochemical pretreatment (EPT) method to enhance the destruction of the extracellular polymeric substances (EPS) matrix and anaerobic digestibility. The results showed that the EPS matrix destruction was enhanced by 15-30% after EPT for 0.5 h at voltages of 8-15 V. The highest improvement in hydrolysis rate and overall digestibility was achieved at EPT of 15 V for 1.5 h, which was determined as 59% (from 0.27 to 0.43 d-1) and 28% (from 105 to 134 mL CH4/g VSSadded) respectively, compared with the WAS treatment without EPT. The economic analysis showed 1 h, 12 V EPT was more economically feasible.