Effect of extracellular polymeric substances (EPS) conditioned by combined lysozyme and cationic polyacrylamide on the dewatering performance of activated sludge

Phenacetin enhanced the inorganic nitrogen removal performance of anammox bacteria naturally in-situ enriched system

Among the earliest synthetic antipyretic drugs, phenacetin (PNCT) could be used as the novel partial nitrification (PN) inhibitor to effectively inhibit nitrite-oxidizing bacteria (NOB). In practical application, the rapidly starting of PN could provide stable source of nitrite for anaerobic ammonium oxidation (anammox) process. However, impact of PNCT on anaerobic ammonia oxidizing bacteria (AnAOB) and its underlying mechanisms were not clear. In this research, totally 14 times of PNCT aerobic soaking treatment were performed in the AnAOB naturally enrichment system to improve total inorganic nitrogen removal efficiency (TINRE). After once of PNCT treatment, TINRE rose from 61.89 % to 79.93 %. After 14 times of PNCT treatment, NOB Nitrospira relative abundance decreased from 9.82 % to 0.71 %, though Candidatus Brocadia relative abundance also declined, it might gradually adjust to PNCT by converting the leading oligotype species. The activity and relative abundances of NOB were reduced by PNCT via decreasing the abundances of genes amoA and nxrB, enzymes NxrA and NxrB. Moreover, Candidatus Jettenia and Ca. Brocadia might be the potential host of qacH-01 and they played the crucial role in the shaping profile of antibiotic resistance genes (ARGs). The explosive propagation or transmission of ARGs might not take place after PNCT treatment.

Comprehensive comparison of water quality risk and microbial ecology between new and old cast iron pipe distribution systems

The effects of cast iron pipe corrosion on water quality risk and microbial ecology in drinking water distribution systems (DWDSs) were investigated. It was found that trihalomethane (THMs) concentration and antibiotic resistance genes (ARGs) increased sharply in the old DWDSs. Under the same residual chlorine concentration conditions, the adenosine triphosphate concentration in the effluent of old DWDSs (Eff-old) was significantly higher than that in the effluent of new DWDSs. Moreover, stronger bioflocculation ability and weaker hydrophobicity coexisted in the extracellular polymeric substances of Eff-old, meanwhile, iron particles could be well inserted into the structure of the biofilms to enhance the mechanical strength and stability of the biofilms, hence enhancing the formation of THMs. Old DWDSs significantly influenced the microbial community of bulk water and triggered stronger microbial antioxidant systems response, resulting in higher ARGs abundance. Corroded cast iron pipes induced a unique interaction system of biofilms, chlorine, and corrosion products. Therefore, as the age of cast iron pipes increases, the fluctuation of water quality and microbial ecology should be paid more attention to maintain the safety of tap water.

Application of central composite design for commercial laundry wastewater treatment by packed bed electrocoagulation using sacrificial iron electrodes

This research paper deals with a novel method utilizing packed bed electrocoagulation (PBEC) comprising of sacrificial iron electrodes and coupled with extracellular polymeric substances (EPS) used as flocculent agents for the treatment of commercial laundry wastewater (LWW). The study employs stainless steel cathodes, graphite anodes, and scrap iron pieces as sacrificial electrodes, ensuring efficient treatment in dynamic batch mode operation with enhanced contact time facilitated by serpentine flow. The initial characteristics of LWW were COD 579 ± 30 mg/L, TSS of 60 ± 10 mg/L, TS of 622 ± 20 mg/L, turbidity of 110 ± 5 NTU, pH of 9 ± 0.5, NPEOs of 570 ± 150 μg/L and conductivity of 494 ± 20 mS/cm. The results demonstrate effective removal of turbidity (98 ± 2%), TS (95 ± 3%), COD (89 ± 5%), and NPEOs (53 ± 2%) under optimized current intensity: 2.99 A, treatment time: 58.8 min and enhanced EPS dose from 5.8 mg/L to 8.0 mg/L. The economic feasibility analysis reveals energy consumption as the primary expenditure, with a treatment cost of 1.20$CAN/m3. This research introduces sustainable treatment for commercial LWW, meeting Quebec's reuse standards, implying reuse potential and responsible wastewater management.

Unveiling the impacts of salts on halotolerant bacteria during filtration: A new perspective on membrane biofouling formation in MBR treating high-saline organic wastewater

In recent decades, membrane bioreactor (MBR) has been prevalently employed to treat high-saline organic wastewater, where the halotolerant microorganisms should be intensively utilized. However, limited works were devoted to investigating the biofouling characteristics from the perspective of the relationship between halotolerant bacteria and salts. This work filled the knowledge gap by exploring the biofouling formation mechanisms affected by high salinity. The results showed that the amount of negative charge on halotolerant bacteria surface was significantly reduced by high content of NaCl, probably leading to the obvious cell agglomeration. Despite the normal proliferation, the halotolerant bacteria still produced substantial EPS triggered by high salinity. Compared with the case of control without salt addition, the enhanced biofouling development was observed under high-saline conditions, with the fouling mechanism dramatically transformed from cake filtration to intermediate blocking. It was inferred that the halotolerant bacteria initially adhered on membrane created an extra filter layer, which contributed to the subsequent NaCl retention, resulting in the simultaneous occurrences of pore blockage and cake layer formation because of NaCl deposition both on membrane pores as well as on biofilm layer. Under high-saline environment, remarkable salt crystallization occurred on the biofilm layer, with more protein secreted by the attached halotolerant bacteria. Consequently, the potential mechanisms for the enhanced biofouling formation influenced by high salinity were proposed, which should provide new insights and enlightenments on fouling control strategies for MBR operation when treating high-saline organic wastewater.

Deciphering the molecular interaction of extracellular polymeric substances of a marine bacterium Pseudomonas furukawaii PPS-19 with petroleum hydrocarbons and development of bioadsorbent

Petroleum hydrocarbon contamination is a serious hazard to marine environments, affecting ecosystems and marine life. However, extracellular polymeric substances (EPS) of marine bacteria constituting various hydrophilic and hydrophobic functional groups sequester petroleum hydrocarbons (PHs). In this study, interaction of EPS of Pseudomonas furukawaii PPS-19 with PHs such as crude oil, n-dodecane, and pyrene and its impact on PHs adsorption was investigated. Protein component of EPS was increased after treatment with PHs. Red shift of UV-Vis spectra implied change in molecular structure of EPS. Functional groups of proteins (CO, NH2) and polysaccharides (C-C, C-OH, C-O-C) predominantly interacted with PHs. Interaction with PHs affected secondary structure of EPS. Change in binding energies of corresponding functionalities of C 1s, O 1s, and N 1s confirmed the interaction. Disruption of crystalline peaks led to increased pore size in EPS primarily due to the increase in surface electronegativity. Static quenching mechanism unveils formation of complex between fulvic acid of EPS and PHs. Relative expression of alg8 gene was significantly increased in the presence of n-dodecane (6.31 fold) (P < 0.05; One way ANOVA). n-dodecane and pyrene adsorption capacity of Immobilized EPS was significantly higher (356.5 and 338.2 mg g-1, respectively) (P < 0.001; One way ANOVA) than control. Adsorption rate fits into the pseudo-second-order kinetic model. This study establishes that interaction of PHs causes structural and physical changes in EPS and EPS could be used as an adsorbent material for the sequestration of PHs pollution.

Unleashing the power of acetylacetone: Effective control of harmful cyanobacterial blooms with ecological safety

Harmful algal blooms resulting from eutrophication pose a severe threat to human health. Acetylacetone (AA) has emerged as a potential chemical for combatting cyanobacterial blooms, but its real-world application remains limited. In this study, we conducted a 42-day evaluation of AA's effectiveness in controlling blooms in river water, with a focus on the interplay between ecological community structure, organism functional traits, and water quality. At a concentration of 0.2 mM, AA effectively suppressed the growth of Cyanobacteria (88 %), Bacteroidia (49 %), and Alphaproteobacteria (52 %), while promoting the abundance of Gammaproteobacteria (5.0 times) and Actinobacteria (7.2 times) that are associated with the degradation of organic matter. Notably, after dosing of AA, the OD680 (0.07 ± 0.02) and turbidity (8.6 ± 2.1) remained at a satisfactory level. AA induced significant disruptions in two photosynthesis and two biosynthesis pathways (P < 0.05), while simultaneously enriching eight pathways of xenobiotics biodegradation and metabolism. This enrichment facilitated the reduction of organic pollutants and supported improved water quality. Importantly, AA treatment decreased the abundance of two macrolide-related antibiotic resistance genes (ARGs), ereA and vatE, while slightly increased the abundance of two aminoglycoside-related ARGs, aacA and strB. Overall, our findings establish AA as an efficient and durable algicide with favorable ecological safety. Moreover, this work contributes to the development of effective strategies for maintaining and restoring the health and resilience of aquatic ecosystems impacted by harmful algal blooms.

Synergistic promotion of sludge reduction by surfactant-producing and lysozyme-producing bacteria: Optimization and effect of Na. BIORESOURCE TECHNOLOGY 2024;393:130065. [PMID: 37984671 DOI: 10.1016/j.biortech.2023.130065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

To improve the efficiency of aerobic digestion, this investigation utilized the synergistic effect of lysozyme-producing strain YH14 and surfactant-producing strain ZXY4 to promote sludge hydrolysis, and added NaCl to enhance this promoting effect. The best performance in promoting sludge hydrolysis was achieved when the inoculum of functional bacteria was 12 % (inoculum ratio of strain YH14: strain ZXY4 = 1:3) and the dosage of NaCl was 5 g L-1, which caused an increase of 19.25 % in the SS removal rate and 2588.21 mg L-1 in the SCOD release, as compared with the control. Fluorescence region integral analysis shows that the synergy of two functional bacteria and NaCl can enhance the biodegradability of sludge. Protein secondary structure analysis shows that strain ZXY4 and Na+ cause the EPS structure to loosen, increasing the chances of lysozyme lysis of bacteria. Nucleotide metabolism, metabolism of other amino acids and membrane transport enhanced in a co-processing system.

Enhanced dewaterability of sludge by Fe(II)-sludge biochar activate persulfate

Sludge biochar supported Fe(II) (Fe(II)-SBC) was successfully prepared using waste activated sludge as peroxydisulfate (PDS) activator to condition sludge for deep dewatering. The experimental results showed that Fe(II)-SBC with FeO on it could effectively active PDS to produce SO 4 - ⋅ and HO ⋅ . The radicals could destroy the structure of sludge cells and extracellular polymeric substance (EPS), transformed the hydrophilic and tightly bound EPS into soluble-EPS, degrade partial proteins and polysaccharides and released bound water. The negatively charged groups on sludge floc were dripped off by SO 4 - ⋅ /HO ⋅ or neutralized with Fe2+, Fe3+, H+, or Fe(II)-SBC, leading to an increase in zeta potential to -2.24 mV and sludge destabilization. The residual Fe(II)-SBC served as a skeleton builder that decreased the compression coefficient of the sludge cake to 0.75. Under the combined functions, the CST and SRF were reduced by 70% and 82.7%, respectively, and Wc was reduced to 72.4%. The byproducts of Fe3+ and SO42- finally remained in sludge cake in the form of NaFeSi2O6 and CaSO4.

Effect of ibuprofen (IBU) on the sulfur-based and calcined pyrite-based autotrophic denitrification (SCPAD) systems with two filling modes: Performance and toxic response mechanism

To investigate the effect of ibuprofen (IBU) on the sulfur-based and calcined pyrite-based autotrophic denitrification (SCPAD) systems, two individual reactors with the layered filling (L-SCPAD) and mixed filling (M-SCPAD) systems were established via sulfur and calcined pyrite. Effluent NO3--N concentration of the L-SCPAD and M-SCPAD systems was first increased to 6.44, 0.93 mg/L under 0.5 mg/L IBU exposure and gradually decreased to 1.66 mg/L, 0 mg/L under 4.0 mg/L IBU exposure, indicating that NO3--N removal performance of the M-SCPAD system was better than that of the L-SCPAD system. The variation of extracellular polymeric substances (EPS) characteristics demonstrated that more EPS was secreted in the M-SCPAD system compared to the L-SCPAD system, which contributed to forming a more stable biofilm structure and protecting microorganisms against the toxicity of IBU in the M-SCPAD system. Moreover, the increased electron transfer impedance and decreased cytochrome c implied that IBU inhibited the electron transfer efficiency of the L-SCPAD and M-SCPAD systems. The decreased adenosine triphosphate (ATP) and electron transfer system activity (ETSA) content showed that IBU inhibited metabolic activity, but the M-SCPAD system exhibited higher metabolic activity compared to the L-SCPAD system. In addition, the analysis of the bacterial community indicated a more stable abundance of nitrogen removal function bacteria (Bacillus) in the M-SCPAD system compared to the L-SCPAD system, which was conducive to maintaining a stable denitrification performance. The toxic response mechanism based on the biogeobattery effect was proposed in the SCPAD systems under IBU exposure. This study provided an important reference for the long-term toxic effect of IBU on the SCPAD systems.

Sludge biodrying coupled with photocatalysis improves the degradation of extracellular polymeric substances

The efficiency of sludge dewatering is limited by extracellular polymeric substances (EPS) during biodrying. This study investigated the effect of photocatalysis-mediated EPS degradation on sludge dewatering performance during the sludge biodrying process. The photocatalysis of municipal sludge was first carried out to choose a cost-efficient catalyst. Then sludge biodrying tests were performed using TiO2-coated amendment (TCA) and uncoated amendment (TUCA) as the control. Municipal sludge photocatalysis results showed that using TiO2 could efficiently degrade carbohydrates and proteins in the EPS within 60 min. After 20-day biodrying, photocatalysis significantly promoted a reduction in the moisture content and EPS by 17.64% and 6.88%, respectively. The surface-enhanced Raman scattering (SERS) intensities of the C-C-O symmetric stretching vibration peak of D-lactose and the C-S stretching vibration peak of cysteine were significantly decreased by approximately 33.19% and 44.76%, respectively, indicating that photocatalysis indeed promoted the reduction of polysaccharides and cysteine in the EPS, especially after the thermophilic phase. The hydrophilic amino acid content decreased by 23.02%, verifying that photocatalysis could improve EPS hydrophobicity. Consequently, municipal sludge biodrying coupled with photocatalysis promotes sludge EPS degradation and enhances sludge dewaterability, improving the efficiency of sludge biodrying.

Fast start-up of anammox process: Effects of extracellular polymeric substances addition on performance, granule properties, and bacterial community structure

The slow startup is the major obstacle to the application of anaerobic ammonium oxidation (anammox) process in mainstream wastewater treatment. Extracellular polymeric substances (EPS) are one potential resource for stable anammox reactor operation. Response surface analysis was used to optimize the specific anammox activity (SAA) with the addition of EPS; SAA was maximum at a temperature of 35 °C and the EPS concentration of 4 mg/L. By comparing the nitrogen removal of anammox reactors with no EPS (R0), immobilized EPS (EPS-alginate beads) (R1), and liquid EPS (R2), we found that EPS-alginate beads significantly speed up the startup of anammox process and enable the start time to be shortened from 31 to 19 days. As a result of the higher MLVSS content, higher zeta potential, and lower SVI₃₀, anammox granules of R1 exhibited a stronger capacity to aggregate. Moreover, EPS extracted from R1 had higher flocculation efficiencies than EPS derived from R0 and R2. Phylogenetic analysis of 16S rRNA genes revealed that the main anammox species in R1 is Kuenenia taxon. To clarify the relative significance of stochastic vs deterministic processes in the anammox community, neutral model and network analysis are employed. In R1, community assembly became more deterministic and stable than in other cultures. Our results show that EPS might inhibit heterotrophic denitrification and thereby promote anammox activity. This study suggested a quick start-up strategy for the anammox process based on resource recovery, which is helpful for environmentally sustainable and energy-efficient wastewater treatment.

Insights into the role of ·OH generated in Fe2+/CaO2/coal slime system for efficient extracellular polymeric substances degradation to improve dewaterability of sewage sludge

The disposal of massive sewage sludge and coal slime is a problem facing municipalities in China. A hypothesis for the co-disposal of sludge and coal slime is proposed to improve dewaterability by utilizing the beneficial role of coal slime as a filter assist and CaO₂ enhanced system in this research. Results showed that capillary suction time, specific resistance to filtration and water content decreased dramatically from 49.3 s, 13.2 × 10¹² m/kg and 84.85% to 19.1 s, 1.0 × 10¹² m/kg and 50.07%, respectively, under the optimal conditions with 0.3/0.1/0.3-Fe²⁺/CaO₂/coal slime g/g DS. The hydroxyl radicals generated in the Fe²⁺/CaO₂ process acted on extracellular polymeric substances (EPS), resulting in a drop in the ratio of α-helix/(β-sheet + random coil) in the secondary structure of EPS proteins and a reduction in the concentration of aromatic proteins and tryptophan-like substances in TB-EPS, thereby enhancing the sludge dewaterability. Furthermore, coal slime as the skeleton building material induced a rise in sludge particle size and contact angle, lowering the hydrophilicity, compressibility of sludge and providing more channels to facilitate water flow. This work verified the promising application prospect of the Fe²⁺/CaO₂/coal slime combined system in the enhancement of sludge dewaterability.

Impact of hydrophilic functional groups of macromolecular organic fractions on food waste digestate dewaterability

：Deterioration of dewaterability is one of challenges faced by anaerobic digestion (AD) of food waste (FW). The underlying mechanism of the effect of AD on digestate dewaterability remains unclear. Thus, the effect of hydrophilic functional groups of macromolecular organic on FW digestate dewaterability in different stages during AD was studied. Results showed that the dewaterability first improved at the acidification stage, and then worsened at the gasification and stabilization stages. The correlations between normalized capillary suction time (NCST), bound moisture (BM) and extracellular protein (extra-PN) were significant (R = 0.736, p < 0.05, R = 0.637, p < 0.05). Macromolecular extra-PN that enhance the bonding between organic fractions and moisture via peptide bonds. In addition, carbonyl, phenolic and amide groups increased after AD, resulting in the enhancement of the digestate hydrophilicity. Furthermore, the evolution of microbial community during AD resulting in the wrapping of BM by increased organic fractions. Therefore, higher organic fractions with hydrophilic functional groups in digestate strongly hinder moisture removal. The findings obtained deepen our understanding of hydrophilic functional groups of macromolecular organic affecting FW digestate dewaterability and provide strong supports to treatment and disposal of FW digestate.

Improving sludge dewaterability by free nitrous acid and lysozyme pretreatment: Performances and mechanisms

Reducing the water content of waste activated sludge (WAS) is critical for sludge treatment and disposal in wastewater treatment plants (WWTPs). In this study, a new combined conditioning processes by using lysozyme (LZM) and free nitrous acid (FNA) were proposed and demonstrated to enhance the dewaterability of WAS. The water content of sludge cake dropped from 82.82 % to 68.42 % (1 h FNA treatment + 1 h LZM treatment) and 69.52 % (6 h FNA treatment + 1 h LZM treatment) with the combined FNA and LZM treatment; and the corresponding capillary suction time (CST) reduction efficiency increased 49.29 % (1 h FNA treatment + 1 h LZM treatment) and 52.98 % (6 h FNA treatment + 1 h LZM treatment). A comprehensive investigation conducted in this study revealed the underlying mechanism of dewaterability improvement lies in the transformations of extracellular polymeric substances (EPS). The combined conditioning led to enhanced hydrophobicity in the sludge, as suggested by FTIR protein secondary structure and interfacial free energy. The reduced zeta potential and the potential barrier indicated the reduction of the repulsive force of sludge particles and the bound water content in the conditioned floc. The hydrophobicity, flow permeability and flocculability were enhanced after combined treatment, leading to the release of bound water.

Improved Dewaterability of Waste Activated Sludge by Fe(II)-Activated Potassium Periodate Oxidation

Fe(II)-activated potassium periodate (KIO₄) oxidation was used to improve the dewaterability of waste-activated sludge for the first time. Compared with those of raw sludge, the capillary suction time (CST), specific resistance filtration (SRF), and water content of filter cake (W_C) of sludge treated using the Fe(II)/KIO₄ process under the optimal conditions (i.e., the initial pH = 6.8, KIO₄ dose = 1.4 mmol/g volatile suspended solids, Fe(II)/KIO₄ molar ratio = 1.2) decreased by 64.34%, 84.13%, and 6.69%, respectively. For conditioned sludge flocs, the Zeta potential and particle size were increased, and hydrophilic proteins in extracellular polymeric substances (EPS) were partly degraded, accompanied by the transformation of tightly bound EPS into soluble EPS and the conversion of dense sludge flocs into loose and porous ones. During Fe(II)/KIO₄ oxidation, Fe(IV) and the accompanying ^•OH were determined as the predominant reactive species and the underlying mechanism of sludge EPS degradation was proposed. This work provides a prospective method for conditioning the sludge dewaterability.

The Performance and Mechanism of Sludge Reduction by the Bioaugmentation Approach

Simple Summary

Activated sludge-based wastewater treatment process is one of the most popular adopted systems in wastewater treatment plants around the world. Excess sludge is an inevitable byproduct of the process, and the enormous quantity has brought a significant burden on operational costs. Various physicochemical and biological methods have been developed. Biological-based methods are promising because of less chemical consumption and low operation cost comparing to physicochemical methods. Hence, the present study is aimed at searching for functional bacteria that could reduce sludge, enhance the performance of sludge reduction through optimization, and try to unveil the underlying mechanism during sludge reduction. A total of 19 strains that belong to Firmicutes, Proteobacteria, and Actinobacteria were successfully isolated and identified. Subsequently, the performance of sludge reduction by pure culture or mix-cultures was validated. In total, 21.2% and 13.9% of total suspended and volatile suspended solids were reduced within 48 h after optimization via response surface methodology. The three-dimensional excitation-emission matrix fluorescence spectrum and hydrolases test results revealed that the sludge reduction might be promoted by the strain mainly through hydrolysis via proteinase and amylase. The results obtained from the study could help us to find an effective and economical way to resolve the sludge issue.

Abstract

Millions of wastewater treatment plants (WWTPs) based on the activated sludge process have been established worldwide to help to purify wastewater. However, a vast amount of sludge is inevitably generated, and the cost of sludge disposal could reach over half of the total operation cost of a WWTP. Various sludge reduction techniques have been developed, including physicochemical, biological, and combinational methods. Micro-organisms that could reduce sludge by cryptic growth are vital to the biological approach. Currently, only limited functional bacteria have been isolated, and the lack of knowledge on the underlying mechanism hinders the technique development. Therefore, the present study is aimed at isolating sludge-reducing bacteria and optimizing the sludge reduction process through response surface methodology. Nineteen strains were obtained from sludge. The mix-cultures did not show a higher sludge reduction rate than the pure culture, which may be ascribed to the complicated interactions, such as competition and antagonistic effects. In total, 21.2% and 13.9% of total suspended and volatile suspended solids were reduced within 48 h after optimization. The three-dimensional excitation-emission matrix fluorescence spectrum and hydrolases test results revealed that the sludge reduction might be promoted by the strain mainly through hydrolysis via proteinase and amylase. The results obtained from the study demonstrate the potential of using micro-organisms for sludge reduction through cryptic growth.

Elucidating the role of extracellular polymeric substances (EPS) in dewaterability of fecal sludge from onsite sanitation systems, and changes during anaerobic storage

As the importance of fecal sludge management (FSM) is increasingly being realized, the need for adequately designed and functioning fecal sludge (FS) treatment plants is also increasing. Research to fill this gap is only emerging and dewatering is a key challenge for developing sustainable treatment solutions. This study evaluated the effect of extracellular polymeric substances (EPS) on dewaterability of FS, and how EPS and dewaterability change during anaerobic storage (as a proxy for time in onsite containment). EPS was extracted from FS and activated sludge using Na₂CO₃ and sonication and added to sludge samples to determine the effect on dewaterability. The results confirmed that an increase in EPS had a direct impact of decreasing FS dewaterability (as capillary suction time). In this context, we evaluated FS degradation during anaerobic storage, the effect of anaerobic storage time on EPS, EPS fractions and particle size distribution, and the effect of variations in these factors on FS dewaterability. Variations in EPS, EPS fraction and particle size distribution during anaerobic storage were less than expected and average VS reduction of 20% was recorded over 7 weeks. Although anaerobic digestion was verified (biogas production), the results indicate that kinetics of degradation of FS is different from wastewater sludges. Comparatively, EPS fractions in FS were 70 - 75% lower and with higher fractions of humic-like substances than wastewater sludges. Although EPS significantly affects FS dewaterability, anaerobic storage time is not a predictor of dewaterability.

An electro-peroxone oxidation-Fe(III) coagulation sequential conditioning process for the enhanced waste activated sludge dewatering: Bound water release and organics multivariate change

As a by-product of wastewater treatment, waste activated sludge (WAS) has complex composition, strong hydrophilic extracellular polymeric substance (EPS), which make it difficult to dewater. In this study, an electro-peroxone oxidation-Fe(III) coagulation (E-peroxone-Fe(III)) sequential conditioning approach was developed to improve WAS dewaterability. At E-peroxone oxidation stage, hydrogen peroxide was generated through 2-electron path on a carbon polytetrafluoroethylene cathode, and reacted with the sparged O₃ to produce hydroxyl radicals. At the subsequent coagulation stage, Fe(III) was dosed to coagulate the small WAS fragments and release water from WAS. Along E-peroxone-Fe(III) subsequent conditioning process, the physicochemical properties of WAS, main components, functional groups and evolution of protein secondary structure, and typical amino acids in EPS, as well as the type and semi-quantitative of elements in WAS, were investigated. The results indicated that under the optimal conditions, the reductions of specific resistance to filterability (SRF) and capillary suction time (CST) for WAS equalled 78.18% and 71.06%, respectively, and its bound water content decreased from 8.87 g/g TSS to 7.67 g/g TSS. After E-peroxone oxidation, part of protein and polysaccharide migrated outside from TB-EPS to slime, the ratio of α-helix/(β-sheet + random coil) declined, even some of organic-N disintegrated to inorganic-N. At Fe(III) coagulation stage, re-coagulation of the dispersed WAS fragments and easy extraction from inner EPS for protein and polysaccharide occurred. Furthermore, the protein secondary structure of β-sheet increased by 13.48%, the contents of hydrophobic and hydrophilic amino acids also increased. In addition, a strong negative correlation between the hydrophobic amino acid content of Met in slime and CST or SRF (R²_CST = -0.999, p < 0.05 or R²_SRF = -0.948, p < 0.05) occurred, while a strong positive correlation between the hydrophilic amino acid content of Cys in TB-EPS and CST or SRF (R²_CST = 0.992, p < 0.05 or R²_SRF = 0.921, p < 0.05) occurred, which could be related to the WAS dewaterability.

Upgradation of sludge deep dewatering conditioners through persulfate activated by ferrous: Compatibility with sludge incineration, dewatering mechanism, ecological risks elimination and carbon emission performance

Serious loss of organic substances and notable release of refractory intracellular organics and cell-free antibiotic resistance genes (ARGs) caused by cell lysis are found when quick lime, FeCl₃, and cationic polyacrylamide (CPAM) were used as sludge conditioners, which is not feasible to sludge separate incineration and increases ecological risks. Therefore, persulfate oxidation through ferrous (Fe²⁺-Na₂S₂O₈) activation was applied for the upgradation of sludge conditioner in China, the specific resistance to filtration (SRF) and capillary suction time (CST) significantly decreased and the removed water increased from 40% to 54%, implying that the persulfate activated by ferrous (PAF) conditioner presents good performance in sludge dewatering. Organic matter content and heating value of sludge merely decreased, and Cl^- content in sludge simultaneously decreased with the use of the PAF conditioner, thereby effectively reducing the corrosion risk to the incinerator and showing good compatibility with sludge separate incineration. In accordance with ferrous activation, sulfate radical plays an important role in sludge dewatering process because remarkable decrease in polysaccharides and protein contents from tightly bound extracellular polymeric substances (TB-EPS) was discovered. Based on flow cytometry analysis, slight cell lysis presented better filtrate quality by the use of PAF conditioner, 49.3% of refractory intracellular organics was removed and the respective ermB, tetW and blaTEM decreased by factors of 37.3%, 54.5% and 63.6% due to the strong oxidizing property of sulfate radical. The intensive decrease in refractory intracellular organics and cell-free ARGs will reduce the ecological risks. The total carbon emission significantly decreases to 1771.1 kgCO₂/tDS when PAF conditioner was employed, which is beneficial to the upgradation of sludge deep dewatering conditioners.

Newly isolated lysozyme-producing strain Proteus mirabilis sp. SJ25 reduced the waste activated sludge: Performance and mechanism

To promote aerobic digestion of sludge, a lysozyme-producing strain was screened and identified as Proteus mirabilis sp. SJ25. The results of response surface methodology (RSM) showed that at the temperature of 30.8 °C, pH of 6.69, and the inoculum amount of 2.81%, the sludge reduced by 26.58%. Compared with the control group, the removal efficiency of suspended solids (SS) from sludge in the experimental group increased by 14.60%, the release of soluble chemical oxygen demand (SCOD) increased by 2.21 times, and the release of intracellular substances increased significantly. Actinobacteriota, Chloroflexi, Proteobacteria, Bacteroidota, and Firmicutes were the main phyla involved in the sludge reduction process. Strain SJ25 enhanced the degradation rate of sludge by releasing lysozyme lysis to lyse bacteria, enhancing the metabolism and membrane transport of carbohydrates and amino acids. This study provides a new perspective in the field of efficient degradation of waste sludge.

Stress responses of sulfate-reducing bacteria sludge upon exposure to polyethylene microplastics

The stress responses of sulfate-reducing bacteria (SRB) sludge to polyethylene (PE) microplastic exposure were revealed for the first time. In this study, a lab-scale sulfate-reducing up-flow sludge bed reactor was continuously operated with different concentrations of PE microplastics in the feed (20, 100, and 500 microplastic particles (MPs)/L). Exposure to low levels of PE microplastics (i.e., 20 MPs/L) had a limited effect on SRB consortia, whereas higher levels of PE microplastics imposed apparent physiological stresses on SRB consortia. Despite this, the overall reactor performance, i.e., chemical oxygen demand removal and sulfate conversion, was less affected by prolonged exposure to PE microplastics. Moreover, as the concentration of PE microplastics increased, the SRB consortia promoted the production of extracellular polymeric substances to a greater extent, especially the secretion of proteins. As a result, protective effects against the cytotoxicity of PE microplastics were provided. Batch experiments further demonstrated that leaching additives from PE microplastics (including acetyl tri-n‑butyl citrate and bisphenol A, concentrations up to 5 μg/g sludge) exerted only a minor effect on the activity of SRB consortia. Additionally, microbial community analysis revealed active and potentially efficient sulfate reducers at different operational stages. Our results provide insight into the stress responses of SRB sludge under PE microplastic exposure and suggested that SRB consortia can gradually adapt to and resist high levels of PE microplastics. These findings may promote a better understanding of the stable operation of SRB sludge systems under specific environmental stimuli for practical applications.

Changes of network structure and water distribution in sludge with the stratified extraction of extracellular polymeric substances

The water in sludge is trapped within the extracellular polymeric substance (EPS) with gelatinous structure, greatly challenging the sludge deep dewatering. In this paper, the effect of the EPS viscoelasticity and the structural characteristics of sludge flocs on water distribution was revealed to provide a highly efficient approach in research on sludge dewatering. After biological, and physical method conditioning, the change of viscoelasticity and sludge network structure before/after EPS extraction was comprehensively explored, together with the sludge dewaterability and water distribution. The results suggested the proportion of capillary water and adsorption water carried in soluble EPS (S-EPS) was 59.17% and 40.83%, and that in tightly bound EPS (TB-EPS) was 54.77% and 45.23%, respectively. By contrast, the capillary water in loosely bound EPS (LB-EPS) accounted for as high as 99.99%. In comparison with raw sludge, adsorption water proportion in TB-EPS and S-EPS was reduced after lysozyme (LZM) or freezing-thaw conditioning, which was ascribed to reduction of EPS viscosity and the weakness of water adsorption capacity. Additionally, the sludge yield stress (τ_y) value first reduced and then increased with the extraction of EPS. Meanwhile, the consistency coefficient (k) also decreased from 4.23 Pa·sⁿ to 0.006 Pa·sⁿ and then slightly increased after LZM conditioning. This observation indicated the sludge system became sensitive to shearing, and its network structural strength as well as colloid elasticity first weakened and then slightly strengthened. In addition, after LZM or freezing-thaw conditioning, the sludge particle size significantly increased after TB-EPS extraction, while the sludge particle more easily absorbed water molecules, thereby increasing adsorption water and capillary water within the sludge flocs. This phenomenon also resulted in an increasing trend of capillary suction time (CST) after TB-EPS extraction, indicating the deterioration of sludge filtration performance.

A review of flocculants as an efficient method for increasing the efficiency of municipal sludge dewatering: Mechanisms, performances, influencing factors and perspectives

Mechanical sludge dewatering is one of the stages of the municipal wastewater treatment process, which allows the amount of generated sludge and the cost of its transport and management to be reduced. Achieving a high degree of dewatering is possible thanks to the use of flocculation technology. The article presents issues related to the theory of flocculation, sewage sludge, and its dewatering. The main mechanisms of flocculation, the kinetics of the process, the division of flocculants, and flocculation in dual systems are discussed. The influence of particular parameters on the efficiency of flocculation and the dewatering of sewage sludge was analyed. The assessed parameters are: pH, the presence of salt, the mixing process, the structure and ionicity of chains, and the dose. The results of experimental studies on the dewatering of various types of sludge were compared. The literature review included in the paper helps to better understand the process of flocculation and sludge dewatering, and presents the progress to date and the possible directions for further development in this field.

Lysozyme regulates the extracellular polymer of activated sludge and promotes the formation of electroactive biofilm

The formation of electroactive biofilm from activated sludge on electrode surface is a key step to construct a bio-electrochemical system, yet it is greatly limited by the poor affinity between the bacteria and the electrode interface. Herein, we report a new method to promote the formation of electroactive biofilm by regulating the extracellular polymeric substance (EPS) content in activated sludge with lysozyme. The investigation of the effect of lysozyme treatment on the content of extracellular polymers and the biofilm formation of electroactive bacteria suggests that lysozyme can improve the permeability of the positive bacterial cell membrane and thus increase the EPS content in the activated sludge. The characterizations of electrochemical activity, surface morphology and community structure of the anode biofilm indicate that increasing EPS content promotes the adhesion of the mixed bacteria in the activated sludge on the electrode and results in denser biofilms with better conductivities. The microbial fuel cell (MFC) inoculated with the sludge of high EPS content exhibits the power density up to 2.195 W/m², much higher than that inoculated with the untreated sludge (1.545 W/m²). The strategy of adjusting EPS content in activated sludge with a biological enzyme can effectively enhance the ability of the bacterial community to form biofilms and exhibits great application potentials in the construction of high efficiency bio-electrochemical systems.

Cationic polyacrylamide (CPAM) enhanced pressurized vertical electro-osmotic dewatering of activated sludge

Pressurized vertical electro-osmotic dewatering (PVEOD) has been regarded as a feasible method to achieve sludge deep-dewatering, but the dewatering efficiency is still challenged by high electric resistance. This study employed cationic polyacrylamide (CPAM) as a skeleton builder to enhance electro-osmotic flow in PVEOD. The sludge dewatering efficiency and synergistic effect of CPAM and PVEOD were elucidated. The sludge morphology, surface property, extracellular polymeric substances (EPS) destruction and migration, spatial distributions of proteins and polysaccharides, and current changes were investigated. After the addition of optimal CPAM dose, the sludge formed a uniform and porous structure that provided water channels and enhanced electric transport, thus promoting EPS destruction. The sludge moisture content (MC) analysis indicated the more liberation of bound water due to EPS destruction. Besides, the re-flocculation of disintegrated sludge flocs improved the sludge filtration and thus dewaterability. Instantaneous energy consumption (E_t,0.5) was optimized and two-step synergistic mechanism was thus proposed. These findings indicated that the combination of CPAM and PVEOD is a promising strategy to broaden the scope of industrial application of sludge deep-dewatering.

Insights into the minimization of excess sludge production in micro-aerobic reactors coupled with a membrane bioreactor: Characteristics of extracellular polymeric substances

The production of excess sludge by the activated sludge system of wastewater treatment plants is a problem. In this study, the EPS characteristics on production and degradation were investigated in the real-scale food processing wastewater treatment system (i.e., a micro-aerobic reactor coupled with a membrane bioreactor (MAR-MBR)) with a treatment capacity of 150 t d^-1, which could cater for the low production of excess sludge (i.e., 9 t·a^-1; 76% moisture content). The total organic carbon concentrations in the different EPS fractions were in the following order: soluble EPS (S-EPS) < loosely bound EPS (LB-EPS) < tightly bound EPS (TB-EPS). Although the components (e.g., protein and humic acid-like substances) of each EPS fraction changed significantly throughout the MAR-MBR process owing to the low production of excess sludge, the degrees of change in S-EPS, LB-EPS, and TB-EPS were significantly different from the corresponding change in their relative molecular weights. Furthermore, the microbial community composition was beneficial for the release and degradation of EPS, and the regulation of gene functions via the MAR-MBR enhanced this process.

Effects of cast iron pipe corrosion on nitrogenous disinfection by-products formation in drinking water distribution systems via interaction among iron particles, biofilms, and chlorine

The effects of cast iron pipe corrosion on nitrogenous disinfection by-products formation (N-DBPs) in drinking water distribution systems (DWDSs) were investigated. The results verified that in the effluent of corroded DWDSs simulated by annular reactors with corroded cast iron coupons, typical N-DBPs, including haloacetamides, halonitromethanes, and haloacetonitriles, increased significantly compared with the influent of DWDSs. In addition, more dissolved organic carbon, adenosine triphosphate, and iron particles were simultaneously detected in the bulk water of corroded DWDSs, thereby indicating that abundant iron particles acted as a "protective umbrella" for microorganisms. Under the condition of corroded DWDSs, the extracellular polymeric substances gradually exhibited distinct characteristics, including a higher content and lower flocculation efficiency, thereby resulting in a large supply of N-DBPs precursors. Corroded cast iron pipes, equivalent to a unique microbial interface, induced completely distinct microbial community structures and metabolic functions in DWDSs, thereby enhancing the formation of N-DBPs. This is the first study to successfully reveal the interactions among iron particles, biofilms, and chlorine in DWDSs, which may help to fully understand the biofilm transformation and microbial community succession in DWDSs.

The combination of aerobic digestion and bioleaching for heavy metal removal from excess sludge

In this study, bioleaching is employed for removing heavy metals from excess sludge generated during municipal wastewater treatment. To avoid organic matter impact on bioleaching, aerobic digestion was performed as pretreatment of the bioleaching or accompanied with the bioleaching. The results showed that the leaching amounts of heavy metals from the process of aerobic digestion accompanied with bioleaching was 2.3 times more than that of the process of aerobic digestion followed by bioleaching. The stable-state proportions of Zn, Cu, Ni and Mn increased by 83%, 94%, 96% and 91%, respectively, in the process of aerobic digestion accompanied with bioleaching, and moreover, the reduction rate of MLSS increased by 22.7%. Although the content of ammonia nitrogen and total phosphorus in sludge decreased after bioleaching treatment, they were still much higher than the soil background value. It indicates that the treated sludge still has agricultural value. High throughput sequencing analysis showed that the relative abundance of acid-producing bacteria (Romboutsia, Clostridium, Tricibacter, and Intestinibacter) significantly increased from 0% to 28.6%, 6.9%, 3.9%, and 2.4%. The enrichment of these acidogenic bacteria was the main reason for the pH decrease, which was conducive to the removal of heavy metals from sludge.

Enhanced dewaterability of waste activated sludge by UV assisted ZVI-PDS oxidation

Ultraviolet (UV) assisted zero-valent iron (ZVI)-activated sodium persulfate (PDS) oxidation (UV-ZVI-PDS) was used to treat waste activated sludge (WAS) in this study. The dewaterability performance and mechanism of WAS dewatering were analyzed. The results showed that UV-ZVI-PDS can obtain better sludge dewatering performance in a wide pH range (2.0-8.0). When the molar ratio of ZVI/PDS was 0.6, UV was 254nm, PDS dosage was 200 mg/g TS (total solid), pH was 6.54, reaction time was 20 min, the CST (capillary suction time) and SRF (specific resistance to filtration) were decreased by 64.0% and 78.2%, respectively. The molar ratio of ZVI/PDS used in this paper is much lower than that of literatures, and the contents of total Fe and Fe²⁺ in sludge supernatant remained at a low level, as 3.7 mg/L and 0.0 mg/L. The analysis of extracellular polymeric substances (EPS), scanning electron microscope (SEM) and particle size distribution showed that the EPS could be effectively destroyed by UV-ZVI-PDS, the sludge flocs broken down into smaller particles, cracks and holes appeared, and then the bound water was released. At the same time, the highly hydrophilic tightly bound-EPS (TB-EPS) were converted into loosely bound EPS (LB-EPS) and soluble EPS (S-EPS). During sludge pretreated by UV-ZVI-PDS, positively charged ions, such as Fe²⁺, Fe³⁺ and H⁺, produced in the reaction system could reduce the electronegativity of sludge surface, promote sludge particles aggregation, and then enhanced the sludge dewaterability.

Two-stage microbial fuel cell (MFC) and membrane bioreactor (MBR) system for enhancing wastewater treatment and resource recovery based on MFC as a biosensor

Lack of process control between the two stages of a combined microbial fuel cell-membrane bioreactor (MFC-MBR) system limits its application in wastewater treatment due to membrane fouling and high energy consumption. In this study, a two-stage MFC-MBR integrated system was established to investigate the impact of incorporating process control on petroleum refinery wastewater treatment. The results showed that chemical oxygen demand (COD) removal exhibits a linear relationship with the MFC voltage output (R² = 0.9821); therefore, the MFC was used as a biosensor to control the combined system. The removal efficiencies of COD, ammonium nitrogen (NH₄⁺-N), and total nitrogen (TN) were 96.3%, 92.4%, and 86.6%, respectively, in the MFC-MBR biosensor, whereas those in the control system were 74.7%, 71.2%, and 64.7% respectively. Furthermore，using the biosensor control system yielded a 50% reduction in the transmembrane pressure (1.01 kPa day^-1) and decreased membrane fouling in wastewater treatment. The maximum energy recovery of the biosensor system (0.00258 kWh m^-3) was five times higher than that of the control system, as determined by calculating the mass balance of the system. Thus, this study indicates that using the MFC as a biosensor for process control in an MFC-MBR system can improve overall system performance.

Understanding the synergistic mechanism of PAM-FeCl3 for improved sludge dewaterability

Hybrid flocculant polyacrylamide-ferric chloride (PAM-FeCl₃) was developed to improve the dewaterability of sewage sludge and the dewatering performance, properties of treated sludge, composition and morphology distribution of extracellular polymeric substance (EPS) were investigated. The physicochemical properties of the PAM-FeCl₃ were characterized, and its effectiveness as a sludge conditioner was evaluated. The results indicated that PAM-FeCl₃ conditioning was able to promote sludge dewaterability. Simultaneously, PAM-FeCl₃ neutralized the negative charges on the surface of sludge particles and increased the sludge floc size. Besides, PAM-FeCl₃ also formed a rough and porous floc structure that reduced sludge compressibility. Meanwhile, the exciting emission matrix analysis suggested that PAM-FeCl₃ can effectively disintegrate of EPS fraction in sludge and decompose the aromatic protein-like substances as well as the humic acid-like substances in EPS. Additionally, the larger sludge floc formation, electrostatic interaction and adsorption bridging effect resulted in compression of sludge structure and the decomposition of EPS fractions and improved sludge dewatering performance.

Comprehensive insights into the organic fractions on solid-liquid separation performance of anaerobic digestates from food waste

Anaerobic digestion (AD) is an effective approach for food waste treatment and valorization. However, AD is limited by proper disposal of the food waste digestates in megacities. The objective of this study was to elucidate the dominant factors on solid-liquid separation performance of the digestates from food wastes. Results indicated that the composition differences in organic fractions showed significant impacts on solid-liquid separation performance by comparing the digestates from different cities in China. Dissolved organic matter (DOM), especially for proteins and carbohydrates, varied between the digestates in various cities, which may lead to the difference in solid-liquid separation performance. Digestate with lowest proteins (33.86 mg/L) from Shanghai's food waste AD plant had the best dewatering performance. In contrast, digestate from Nanjing's food waste AD plant showed the worst dewatering performance. Pearson's correlation analysis indicated that there is a significant correlation between soluble protein and the dewaterability of digestates (R² > 0.9573, p < 0.03), the lower soluble protein achieved higher dewaterability of digestates.

Effects of dissolved oxygen on the sludge dewaterability and extracellular polymeric substances distribution by bioleaching

Bioleaching is a biological conditioning technology for sludge, which not only improves sludge dewatering performance but also removes heavy metals from sludge. As the bioleaching process is a comprehensive biological and chemical process, it is necessary to explore the effects of dissolved oxygen (DO) concentrations on bioleaching efficiency. Three bioleaching experiments with different DO concentrations (T1: 0.8-3.1 mg/L, T2: 3.1-5.5 mg/L, T3: 5.5-7.5 mg/L) were conducted for five days. The sludge dewatering efficiency was evaluated using capillary suction time (CST) and specific resistance to filtration (SRF). The relationship between sludge dewaterability and extracellular polymeric substance (EPS) fraction distribution was investigated. In the treatment with the highest DO concentration, the minimum values of SRF and CST were 4.31 × 10¹¹ m/kg and 13.5 s, which occurred earlier than the treatment with the lower DO concentrations by approximately 24-48 h. A significant decrease (83.4-93.2%) in tightly bound EPS (TB-EPS) protein (PN) was observed in all treatments, while a positive correlation (r = 0.924, P < 0.01) was observed between SRF and PN content in TB-EPS. A relatively higher abundance of Acidithiobacillus was found with the increase in DO concentration. Additionally, other genera including Metallibacterium, Alicyclobacillus, Acidibacter, Acidocella, and Luteococcus also played important roles in EPS biodegradation. These results revealed that increasing the DO concentration could improve sludge dewatering performance and heavy metal removal by enhancing bioleaching microbial activity, the degradation of PN in TB-EPS, and sludge floc fragmentation, but only if sufficient energy sources were provided.

Coupling electro-dewatering and low-temperature air-drying for efficient dewatering of sludge

This study investigated the effects of electro-dewatering on subsequent low-temperature drying at various potentials and the characteristics of low-temperature air-drying sludge were explored through experiments and multi-physical modeling. Experimental results showed that the extracellular polymeric substance (EPS) content in the sludge was reduced during electro-dewatering process, even the species of organic matter was changed, as well as the dewatered cake tend to form many seepage channels, crack and a certain number of holes. These changes in the properties and structure were conducive to the subsequent low-temperature drying process. For air-drying process, the mass of the sludge cake variation was simulated and results were consistent with the experimental phenomenon. Firstly, the weight of the sludge cake was decreased approximately linearly with time, then tended to stable and reached the dewatering limitation finally. The applied higher electric field intensity (25 V cm⁻¹) in the front-end electro-dewatering were conducive to promote water vapor diffusion activity in air-drying stage. Energy consumption and yield analysis results indicated that the combined technology has lower energy consumption and higher yield than that of directly low-temperature drying.

Improving waste activated sludge dewaterability with sodium periodate pre-oxidation on extracellular polymeric substances

The efficiency of sludge dewatering is affected by the structure and composition of hydrated extracellular polymeric substances (EPS). Degrading EPS can improve the sludge dewatering performance. As an oxidizing agent, sodium periodate (NaIO₄ ) has ability to oxidize organics, which is expected to decompose the protein and polysaccharide in EPS and improve the efficiency of sludge dewaterability. This study adopted NaIO₄ , for the first time, as an advanced oxidation agent to regulate EPS of waste activated sludge and was combined with anionic polyacrylamide (APAM) as a flocculant to subsequently enhance sludge dewatering. Response surface methodology (RSM) was used to determine the optimal conditions of pH, NaIO₄ , and APAM. The results showed that the composite conditioner's specific resistance of filtration (SRF) and the water content of the vacuum-filtered cake (Wc) were highly enhanced compared with those of the raw sludge (RS) under pH 6.5, a NaIO₄ concentration of 50 mg/g dry solids (DS), and an APAM concentration of 5 mg/g DS. Owing to the pre-oxidation achieved by NaIO₄ under a mildly acid environment, sludge flocs were broken. Subsequently, chemical coagulation (APAM) agglomerated the smaller particles into larger flocs of sludge by adsorption and bridging, thus improving sludge dewaterability. PRACTITIONER POINTS: A novel conditioner, pH/NaIO₄ /APAM, was explored for sludge dewatering. IO³ • and HO• oxidized extracellular polymeric substances (EPS). Degradation of the protein content of EPS released bound water. Highly enhanced sludge dewaterability was achieved under optimal conditions.

Fluorescent Characteristics and Metal Binding Properties of Different Molecular Weight Fractions in Stratified Extracellular Polymeric Substances of Activated Sludge

The combination of heavy metals and extracellular polymeric substances (EPSs) affects the distribution of heavy metals in microbial aggregates, soil, and aquatic systems. This paper aimed to explore the binding mechanisms of EPSs of different molecular weights in activated sludge with heavy metals. We extracted the stratification components of activated sludge EPSs and divided the components into five fractions of different molecular weight ranges. In the three-dimensional fluorescence analysis of each fraction, the EPSs of activated sludge had two peaks, peak A (representing low-excitation tryptophan) and peak B (representing high-excitation tryptophan), and static quenching was the main reason for the fluorescence quenching between the compounds attributable to peak A in activated sludge EPSs and Pb2+ and Cu2+. Further exploration suggested that the EPSs of activated sludge interacted with Cd2+, Pb2+, Cu2+, and Zn2+ to form new substances. The quenching effect of the EPSs with the highest molecular weight (100 kDa–0.7 μm) was more significant, and the binding ability was more stable. This study implies that the application of EPSs from activated sludge is promising. While effectively binding heavy metals, it can also reduce the volume of the excess activated sludge.

Enhancement of sludge dewaterability by a magnetic field combined with coagulation/flocculation: a comparative study on municipal and citric acid-processing waste-activated sludge

The difficulties in dewatering waste-activated sludge (WAS) using mechanical devices have caused great problems in sludge transportation and disposal. Herein, coagulation and flocculation are combined with the use of a magnetic field as a clean and low-energy physical treatment method to enhance the dewaterability of municipal and citric acid-processing WAS. It is shown that the use of the magnetic field had a significant effect on the capillary suction time (CST) of municipal WAS but not on the specific resistance filtration (SRF) and CST of the citric acid WAS. The differences in the magnetic field effects were due to differences in the sludge properties. For municipal WAS, the particle size decreased, the zeta potential remained unchanged, and the viscosity decreased, whereas in the citric acid WAS, the particle size increased, the absolute value of the zeta potential decreased, and the viscosity increased. In addition, these effects were also confirmed with studies of the water state and micro-morphology analyses. It is shown that the acidification of the municipal WAS and coagulation of citric acid WAS were likely the reasons for the enhancement of their dewaterability, respectively. This study confirmed that the use of a magnetic field combined with coagulation/flocculation may serve as an effective sludge conditioning method; however, the treatment conditions may vary with the sludge type.

Solidification effect of river bottom sediments after flocculation via different composite flocculants

The main problem in the reduction of river bottom sediments is to solve the dewatering of the rive sediments. The reduction of river bottom sediments is usually dehydrated by natural air drying and requires more time and economic costs. Different proportions of composite flocculants and curing agents have been developed to the reduction of river bottom sediments according to the requirements of the project. Two or more flocculants were mixed with the rive sediments. Therefore, anionic polyacrylamide (PAM), polyaluminum chloride (PAC), polysilicate aluminum ferric (PSAF), and iron perchloride (IC) were selected for flocculation of river sediments. Through the sedimentation column test, the relationship between sedimentation amount and time was plotted, the turbidity value and pH value of the supernatant filtration supernatant were detected, and the flocculation effect of different flocculants was evaluated to obtain suitable groups of composite flocculants. The optimum ratio of two types of polyacrylamide with a molecular weight of 18 million and 23 million was 3:7. The turbidity of the supernatant of water could well be reduced by adding polysilicate aluminum ferric. Finally, the 6 groups of composite flocculants were determined according to the sedimentation and the turbidity value of the supernatant. The relative water content was maintained at about 60% before and after flocculation. At the same curing age, the compressive strength increased as the amount of curing agent increased after flocculation. At the same curing agent dosage, the overall solidification effect was reduced with increase of curing time after flocculation.

Insight to peroxone-Fe(III) joint conditioning-horizontal electro-dewatering process on water reduction in activated sludge: Performance and mechanisms

Peroxone disintegration-Fe(III) coagulation (peroxone-Fe(III)) joint conditioning was proposed to enhance the horizontal electro-dewatering (HED) effect of activated sludge (AS). Operating parameters were optimized and the evolutions of AS physicochemical properties, water fractions distribution, organic matter, extracellular polymeric substance (EPS) key components, functional groups, and protein secondary structures during the process were identified. Under the optimized joint conditioning parameters, dewatered AS achieved a final water content of 84.88 ± 0.17% and its bound water content (BWC) was decreased by 1.88 ± 0.28 g/g dry solid. During peroxone pretreatment, the yielded HO decreased the AS floc size, disintegrated the EPS network structure and cell wall, released the bound water, and extracted proteins, polysaccharides, and humic acid-like materials. Furthermore, soluble microbial byproduct-like materials (SMBP) in the EPS layers and tyrosine in tightly bound EPS significantly increased. Protein structures were destroyed, decreasing their water affinity. Subsequent Fe(III) addition re-coagulated broken flocs fragments and EPS fractions, built water flow channels, removed tyrosine and SMBP, and reduced α-helix percentage in slime, facilitating AS dewatering. After joint conditioning, the bound water and intracellular substances were further released by HED. Therefore, the peroxone-Fe(III)-HED process exhibited an excellent performance in AS water reduction.

Changes in the characteristics of dissolved organic matter during sludge treatment: A critical review

Dissolved organic matter (DOM) of sludge is a heterogeneous mixture of high to low molecular weight organic substances which is including proteinaceous compounds, carbohydrates, humic substances, lipids, lignins, organic acids, organic micropollutants and other biological derived substances generated during wastewater treatment. This paper reviews definition, composition, quantification, and transformation of DOM during different sludge treatments, and the complex interplay of DOM with microbial communities. In anaerobic digestion, anaerobic digestion-refractory organic matter, particularly compounds showing polycyclic steroid-like, alkane and aromatic structures can be generated after pretreatment. During dewatering, the DOM fraction of low molecular weight proteins (< 20,000 Dalton) is the key parameter deteriorating sludge dewaterability. During composting, decomposition and polymerization of DOM occur, followed by the formation of humic substances. During landfill treatment, the composition of DOM, particularly humic substances, are related with leachate quality. Finally, suggestions are proposed for a better understanding of the transformation and degradation of DOM during sludge treatment. Future work in sludge studies needs the establishment and implementation of definitions for sample handling and the standardization of DOM methods for analysis, including sample preparation and fractionation, and data integration. A more detailed knowledge of DOM in sludge facilitates the operation and optimization of sludge treatment technologies.

New insights into the effect of extracellular polymeric substance on the sludge dewaterability based on interaction energy and viscoelastic acoustic response analysis

To elucidate the effects of extracellular polymeric substance (EPS) on the sludge dewaterability, this study comparatively investigated the changes in EPS composition and spatial distribution, together with the sludge dewaterability after lysozyme (LZM) conditioning. The protein concentration in the tightly bound EPS (TB-EPS) increased from 3.47 mg g^-1 DS to 4.99 mg g^-1 DS within the first 2 min, then gradually decreased, which could be described by a piecewise linear function. Unlike TB-EPS, the protein content variation trend in both soluble EPS (S-EPS) and loosely bound EPS (LB-EPS) followed the typical first-order kinetics. Additionally, the extended DLVO theory was employed in combination with viscoelastic acoustic response analysis to further explore the impact of EPS composition on water adhesion and microbial cell. After the extraction of S-EPS from the conditioned sludge, the adsorption free energy (ΔG_adh) of EPS ascended to -61.05 mJ m^-2, indicating the weakened microbial hydrophobicity. By contrast, the ΔG_adh value declined after the subsequent extraction of LB-EPS and TB-EPS. Meanwhile, the adsorption potential energy between S-EPS and microbial cells showed an increasing trend, whereas the repulsion potential energy between TB-EPS and microbial cells fell to 1.40 × 10⁴ kT, signifying a weakened adsorption capacity to water. Accordingly, the viscosity and shear modulus of each EPS layer were reduced after conditioning, which contributed to the transformation of bound water into free water. These changes reasonably explained the results that the water content in the dewatered sludge after conditioning was reduced to 58.54%, and the bound water content decreased by 15.06%.

Applying organic polymer flocculants in conditioning and advanced dewatering of landfill sludge as a substitution of ferric trichloride and lime: Mechanism, optimization and pilot-scale study

In this study, poly dimethyl diallyl ammonium chloride (PDADMAC) and polyacrylamide (PAM) were applied to substitute ferric trichloride (FeCl₃) and lime conditioning for advanced dewatering of landfill sludge (LS). Four response surface methodology (RSM) models were constructed for FeCl₃-lime, FeCl₃-PAM, PDADMAC-lime and PDADMAC-PAM, and identical dosages, namely 29.86, 57.91, 5.73 and 2.99 mg/g dry solids (DS) for FeCl₃, lime, PDADMAC and PAM, were obtained by solving the system of four RSM equations at water content of 60% to investigate conditioning mechanisms. Compared to FeCl₃-lime, PDADMAC-PAM conditioning had strong charge neutralization and bridging performance, and obtained conditioned LS with large flocs size, strong network structure and rapid dewatering rate. By integrating RSM with nonlinear programming for optimization, the total cost of PDADMAC-PAM route was saved by 7.9% and close to FeCl₃-lime, and the optimized condition with dosages of 1.93 and 3.47 kg/t DS was further confirmed by pilot-scale experiments. The results indicated that PDADMAC-PAM was a feasible substitute for FeCl₃-lime in sludge conditioning, and showed more advantage if dewatered sludge was further treated by incineration.

Profiling of amino acids and their interactions with proteinaceous compounds for sewage sludge dewatering by Fenton oxidation treatment

During advanced oxidation treatment for enhancing sludge dewaterability, the peptide chains of protein can be decomposed into amino acids. Protein exhibits a great impact on sewage sludge dewaterability. However, the role of amino acids in sludge dewatering remains unclear. In this study, among the 23 types of amino acids investigated, tryptophane (Trp) and lysine (Lys) were identified as the key amino acids affecting sludge dewaterability during Fenton oxidation treatment. The content of lysine showed positive correlations with capillary suction time (CST), specific resistance to filtration (SRF), and bound water content, and the concentrations of total protein, low molecular weight protein, amines and amides, and 3-turn helix of proteinaceous compounds in bound extracellular polymeric substances (EPS), while the content of tryptophane showed negative correlations with the above parameters. The amino acids may be sourced from damage of the membrane and ribosomal proteins by hydroxyl radicals, and the peptide bonds connected with tryptophane were more inclined to be decomposed than other amino acids. Particularly, more amino acids of tryptophane can result in more hydrophobic interaction, and less necessary energy barrier for aggregation of particles. As such, regulating protein degradation towards production of tryptophane may be related with enhanced sludge dewaterability by Fenton oxidation treatment.

An evaluation of lysozyme enzyme and thermal pretreatments on dairy sludge digestion and gas production

Anaerobic digestion is one of the common methods of managing and stabilizing sludge. However, due to the limitations of the biological sludge hydrolysis stage, anaerobic decomposition is slow and requires a long time. This study evaluated the effects of thermal (80 °C) (TH-PRE) and a combination of thermal with the lysozyme enzyme (LTH-PRE) pretreatments on the enhancement of anaerobic activated sludge digestion. Response surface methodology was implemented to optimize enzyme pretreatment conditions (enzyme and mixed liquid suspended solids concentration). The results showed that both pretreatment methods increase soluble chemical oxygen demand (COD) and reduces total and volatile suspended solids (VSS), and phosphate concentration. The COD removal rate in LTH-PRE and TH-PRE was 95% and 81%, respectively. The value of VSS reduction in LTH-PRE and TH-PRE was 41% and 31%, more than the control operation, respectively. The biogas production in LTH-PRE and in TH-PRE also increased by 124% and 96%, respectively.

Performance and mechanisms of wastewater sludge conditioning with slag-based hydrotalcite-like minerals (Ca/Mg/Al-LDH)

Extracellular polymeric substances (EPS) in wastewater sludge form a network structure that is highly hydrophilic and compressible. Thus chemical conditioning is always required to improve sludge dewaterability by changing the gelatinous structure of sludge flocs. Layered double hydroxides (LDH) are generally characterized by large surface area and high anion exchange capacity, so we prepared three types of hydrotalcite-like compounds (Ca/Mg/Al-LDHs) from a typical solid waste, blast furnace slag, using NaOH precipitation (giving LDH_a), a hydrothermal method (LDH_b), and NaOH-Na₂CO₃ precipitation (LDH_c). The physicochemical properties of the three LDH were comprehensively characterized, and their effectiveness as sludge conditioners was evaluated. The results showed that LDH conditioning was able to promote sludge dewaterability, and conditioning efficiency was strongly dependent on LDH structural properties. LDH neutralized the negative charges onto sludge particles and interacted with EPS to increase floc strength. LDH also formed a skeletal structure that reduced sludge compressibility. In addition, there were interactions between the LDH surfaces and the OC-OH in EPS proteins, which altered the secondary structure of protein molecules, consequently increasing sludge dewaterability. The biomolecules of low-molecular-weight fractions (such as peptides and humic acids) in soluble EPS intercalated LDH. Both the surface complexation of organic matter containing carboxyl groups and the intercalation of small molecules in soluble EPS were responsible for EPS-LDH interactions. The combination of skeleton formation, electrostatic interaction, and EPS-LDH interactions resulted in compression of gel-like structure and improved sludge dewatering performance. We finally suggested a novel sludge treatment process that increases sludge dewaterability using slag-derived Ca/Mg/Al-LDH to condition the sludge, and it could be combined with pyrolysis to prepare multi-functional materials or bio-oil.