In situ generation of zero valent iron for enhanced hydroxyl radical oxidation in an electrooxidation system for sewage sludge dewatering

Enhanced dewaterability and triclosan removal of waste activated sludge with iron-rich mineral-activated peroxymonosulfate

High water and pharmaceutical and care products (PPCPs) bounded in sludge flocs limit its utilization and disposal. The advanced oxidation process of perxymonosulfate (PMS) catalyzed by iron salts has been widely used in sludge conditioning. In this study, two iron-rich minerals pyrite and siderite were proposed to enhance sludge dewatering performance and remove the target contaminant of triclosan (TCS). The permanent release of Fe2+ in the activation of PMS made siderite more effective in enhancing sludge dewater with capillary suction time (CST) diminishing by 60.5 %, specific resistance to filtration (SRF) decreasing by 79.2 %, and bound water content (BWC) dropping from 37.1 % to 2.6 % at siderite/PMS dosages of 0.36/0.20 mmol/g-TSS after 20 min of pretreatment. Pyrite/PMS performed slightly inferior under the same conditions and the corresponding CST and SRF decreased by 51.5 % and 71.8 % while the BWC only declined to 17.8 %. Rheological characterization was employed to elucidate the changes in sludge dewatering performance, with siderite/PMS treated sludge showing a 48.3 % reduction in thixotropy, higher than 28.4 % of pyrite/PMS. Oscillation and creep tests further demonstrated the significantly weakened viscoelastic behavior of the sludge by siderite/PMS pretreatment. For TCS mineralization removal, siderite/PMS achieved a high removal efficiency of 43.9 %, in comparison with 39.9 % for pyrite/PMS. The reduction in the sludge solids phase contributed the most to the TCS removal. Free radical quenching assays and EPR spectroscopy showed that both siderite/PMS and pyrite/PMS produced SO4-·  and ·OH, with the latter acting as the major radicals. Besides, the dosage of free radicals generated from siderite/PMS exhibited a lower time-dependence, which also allowed it to outperform in destroying EPS matrix, neutralizing the negative Zeta potential of sludge flocs, and mineralizing macromolecular organic matter.

Formation mechanism of persistent free radicals during pyrolysis of Fenton-conditioned sewage sludge: Influence of NOM and iron

The present study provided an innovative insight into the formation mechanism of persistent free radicals (PFRs) during the pyrolysis of Fenton-conditioned sludge. Fenton conditioners simultaneously improve the dewatering performance of sewage sludge and catalyze the pyrolysis of sewage sludge for the formation of PFRs. In this process, PFRs with a total number of spins of 9.533×1019 spins/g DS could be generated by pyrolysis of Fenton-conditioned sludge at 400°C. The direct thermal decomposition of natural organic matter (NOM) fractions contributed to the formation of carbon-centered radicals, while the Maillard reaction produced phenols precursors. Additionally, the reaction between aromatic proteins and iron played a crucial role in the formation of phenoxyl or semiquinone-type radicals. Kinetics analysis using discrete distributed activation energy model (DAEM) demonstrated that the average activation energy for pyrolysis was reduced from 178.28 kJ/mol for raw sludge to 164.53 KJ/mol for Fenton conditioned sludge. The reaction factor (fi) indicated that the primary reaction in Fenton-conditioned sludge comprised of 27 parallel first-order reactions, resulting from pyrolysis cleavage of the NOM fractions, the Maillard reaction, and iron catalysis. These findings are significant for understanding the formation process of PFRs from NOM in Fenton-conditioned sludge and provide valuable insight for controlling PFRs formation in practical applications.

Hybrid conditioning of ionic liquid coupling with H2SO4 to improve the dewatering performance of municipal sludge

Municipal sludge generated from wastewater treatment plants can cause a serious environmental and economic burden. A novel hybrid conditioning strategy was developed to enhance the dewatering performance of sludge, employing 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4mim][CF3SO3]) treatment combined with H2SO4 acidification. Following conditioning, the capillary suction time ( CST normalized ), the specific resistance of filtration (SRF), and moisture content of the treated sludge were decreased to 1.99 ± 0.24 (s·L/g TSS), 1.33 ± 0.05 (1012 m/kg), and 72.01 ± 0.94%, respectively. The results were superior to those achieved with sludge treated solely by H2SO4 acidification or [C4mim][CF3SO3] alone. The biomacromolecules within the sludge flocs were dissolved by [C4mim][CF3SO3], while simultaneously, the microorganisms were inactivated. Consequently, the colloidal-like structures of the sludge flocs were destroyed. Additionally, the ionizable functional groups of the biomacromolecules were instantly protonated by the introduced H+ ions, and their negative charges were neutralized during the H2SO4 acidification process. The presence of H+ ions promoted the weakening of electrostatic repulsion between the sludge flocs. As a result, an enhancement of sludge dewaterability was obtained after treatment with [C4mim][CF3SO3] and H2SO4 acidification. The finding of the intensification mechanism of sludge dewaterability brought by hybrid treatment of acidification and [C4mim][CF3SO3] provides novel insights into the field of sludge disposal.

Enhanced molecular oxygen activation via K/O interfacial modification for boosted electrocatalytic degradation over a broad pH range

Molecular oxygen activation plays an important role in the electrocatalytic degradation of recalcitrant pollutants. And the key lies in the tailoring of electronic structures over catalysts. Herein, carbon nitride with K/O interfacial modification (KOCN) was designed and fabricated for efficient molecular oxygen activation. Theoretical screening results revealed the possible substitution of peripheral N atoms by O atoms and the location of K atoms in the six-fold cavities of g-C3N4 framework. Spectroscopic and experimental results reveal that the existence of K/O promotes charge redistribution over as-prepared catalysts, leading to optimized electronic structures. Therefore, optimized oxygen adsorption was realized over 8 % KOCN, which was further converted into superoxide and singlet oxygen effectively. The rate constant of 8 % KOCN (1.8 × 10-2 min-1) reached 2.2 folds of pristine g-C3N4 (8.1 × 10-3 min-1) counterpart during tetracycline degradation. Moreover, the high electron mobility and excellent structural stability endow the catalyst with remarkable catalytic performance in a broad pH range of 3-11.

Molecular oxygen activation: Innovative techniques for environmental remediation

Molecular oxygen as a green, non-toxic, and inexpensive oxidant has displayed numerous advantages compared with other oxidants for more sustainable and environmentally benign pollutant degradation. Molecular oxygen activation stands as a groundbreaking approach in advanced oxidation processes, offering efficient environmental remediation with minimal environmental impact with the production of high-oxidation reactive oxygen species (ROS). The adaptability and energy efficiency of molecular oxygen activation significantly contribute to the progression of sustainable water remediation technologies. This review meticulously explores the principles and mechanisms of molecular oxygen activation, shedding light on the diverse ROS production pathways. Subsequently, this review comprehensively details contemporary activation approaches, including photocatalytic activation, electrocatalytic activation, piezoelectric activation, and photothermal activation, explicating their distinct activation mechanisms. Additionally, it delves into the promising applications of molecular oxygen activation in the degradation of water pollutants, primary air pollutants, and volatile organic compounds, providing an in-depth analysis of the associated degradation pathways and mechanisms. Moreover, this review also addresses the imminent challenges and emerging opportunities in environmental remediation. It is envisioned that this comprehensive analysis will spur ongoing exploration and innovation in the use of molecular oxygen activation for environmental remediation and beyond.

Conditioning fecal sludge of public toilets with coupled zero-valent iron and persulfate: Efficiency and mechanism

This study investigated the efficiency of fecal sludge conditioning using peroxydisulfate (PDS) activated by zero-valent iron (ZVI). For fecal sludge obtained from public toilets in a densely-populated rural area in China, the ZVI/PDS coupling greatly improved its dewaterability as well as the supernatant quality in terms of organic matter and nutrient contents. The capillary suction time (CST) and supernatant turbidity of fecal sludge can be reduced up to 97% and 73% respectively in 10 min by the combination of 0.15 g/g TS ZVI and 0.2 g/g TS PDS. Protein removal, especially for tightly and loosely bound extracellular-polymeric-substance (EPS), is more linearly correlated to CST reduction than polysaccharide removal. Fecal sludge dewatering was improved by the hybrid functions of radical oxidation and iron coagulation. The ZVI/PDS treatment produced larger and looser flocs, probably because 1) surface ionic and hydrophilic groups of fecal sludge were reduced, 2) surface charge was neutralized, and 3) secondary structures of EPS proteins were altered by the radicals. The excellent fecal sludge dewatering was related to strengthened particle hydrophobicity and reduced sludge viscosity and compressibility. The results highlight that the ZVI/PDS combination is potentially an effective conditioning approach for fecal sludge from public toilets.

Effect of KMnO4/pH adjustment of extracellular polymeric substances under waste activated sludge on sludge dewatering

In this study, we examine the dewaterability of sludge after treatment by KMnO4 at various pH levels, with the goal of understanding the dewaterability of strong oxidizers to waste activated sludge. Good dewatering performance is observed, with capillary suction times (CST) reduced from 263.4 to 30.1 s, and specific resistance to filtration (SRF) falling by 19.6%. Proteins and polysaccharides in tightly bound extracellular polymeric substances (EPS) were also significantly reduced. Based on spectroscopic and electrochemical analysis, we propose mechanisms for the improved dewatering in terms of changes to the sludge's physicochemical properties and EPS. Under strong oxidation, the structure surrounding the bound water is oxidized and bound water is released, so the dewaterability of the sludge is improved.Weiliang Pan and Jiaoni Li contributed equally to this work.

Co-treatment of municipal solid waste incineration fly ash (MSWI FA) and municipal sludge: A innovative method to improve sludge dewatering with fly ash dechlorination

The complexity of municipal sludge dewatering is a bottleneck problem limiting resource utilization. In this paper, adding municipal solid waste incineration fly ash (MSWI FA) to municipal sludge for enhanced dewatering was applied, while the chlorine salt in MSWI FA was simultaneously removed using water in municipal sludge. The effects of different dosages and chemical components of MSWI FA on municipal sludge dewatering, and the removal effect of municipal sludge washing on Cl element were investigated. The results showed that the municipal sludge's specific resistance to filtration after co-treatment was significantly reduced, and more hydrophobic channels were formed in the vacuum suction filtration of the treated municipal sludge, conducive to efficient water removal. The moisture content of municipal sludge was reduced from 96.0% to 48.3%, and the moisture reduction rate increased from 17.7% to 32.1%. The chemical composition of MSWI FA could effectively promote the dewatering of municipal sludge, among which CaO was the best, followed by CaCl₂ and NaCl, and KCl was the worst. Simultaneously, the municipal sludge showed a good effect on removing Cl from MSWI FA. The minimum Cl content in the mixture after Co-treatment is 1.5%. These results could provide a new way to dispose of MSWI FA and municipal sludge.

Iron boride boosted Fenton oxidation: Boron species induced sustainable FeIII/FeII redox couple

The regeneration of Fe(II) is the rate-limiting step in the Fenton/Fenton-like chain reactions that seriously hinder their scientific progress towards practical application. In this study, we proposed iron boride (FeB) for the first time as a new material to sustainably decompose H₂O₂ to generate hydroxyl radicals, which can non-selectively degrade a wide array of refractory organic pollutants. Fe(II) can be steadily released by the stepwise oxidation of FeB to stimulate Fenton reaction, meanwhile, B-B bonds as electron donors on the surface of FeB effectively promote the regeneration of Fe(II) from Fe(III) species and significantly accelerate the production of hydroxyl radicals. The low generation of toxic by-products and the high utilization rate of iron species validly avoid the secondary organic/metal pollution in the FeB/H₂O₂ system. Therefore, FeB mediated Fenton oxidation provides a novel strategy to realize a green and long-lasting environmental remediation.

State-of-the-art review and bibliometric analysis on electro-Fenton process

The electro-Fenton (EF) process was first proposed in 1996 and, since then, considerable development has been achieved for its application in wastewater treatment, especially at lab and pilot scale. After more than 25 years, the high efficiency, versatility and environmental compatibility of EF process has been demonstrated. In this review, bibliometrics has been adopted as a tool that allows quantifying the development of EF as well as introducing some useful correlations. As a result, information is summarized in a more visual manner that can be easily analyzed and interpreted as compared to conventional reviewing. During the recent decades under review, 83 countries have contributed to the dramatic growth of EF publications, with China, Spain and France leading the publication output. The top 12 most cited articles, along with the top 32 most productive authors in the EF field, have been screened. Four stages have been identified as main descriptors of the development of EF throughout these years, being each stage characterized by relevant breakthroughs. To conclude, a general cognitive model for the EF process is proposed, including atomic, microscopic and macroscopic views, and future perspectives are discussed.

Effect of Pharmaceutical Sludge Pre-Treatment with Fenton/Fenton-like Reagents on Toxicity and Anaerobic Digestion Efficiency

Sewage sludge is successfully used in anaerobic digestion (AD). Although AD is a well-known, universal and widely recognized technology, there are factors that limit its widespread use, such as the presence of substances that are resistant to biodegradation, inhibit the fermentation process or are toxic to anaerobic microorganisms. Sewage sludge generated by the pharmaceutical sector is one such substance. Pharmaceutical sewage sludge (PSS) is characterized by high concentrations of biocides, including antibiotics and other compounds that have a negative effect on the anaerobic environment. The aim of the present research was to determine the feasibility of applying Advanced Oxidation Processes (AOP) harnessing Fenton's (Fe²⁺/H₂O₂) and Fenton-like (Fe³⁺/H₂O₂) reaction to PSS pre-treatment prior to AD. The method was analyzed in terms of its impact on limiting PSS toxicity and improving methane fermentation. The use of AOP led to a significant reduction of PSS toxicity from 53.3 ± 5.1% to 35.7 ± 3.2%, which had a direct impact on the taxonomic structure of anaerobic bacteria, and thus influenced biogas production efficiency and methane content. Correlations were found between PSS toxicity and the presence of Archaea and biogas yields in the Fe²⁺/H₂O₂ group. CH₄ production ranged from 363.2 ± 11.9 cm³ CH₄/g VS in the control PSS to approximately 450 cm³/g VS. This was 445.7 ± 21.6 cm³ CH₄/g VS (1.5 g Fe²⁺/dm³ and 6.0 g H₂O₂/dm³) and 453.6 ± 22.4 cm³ CH₄/g VS (2.0 g Fe²⁺/dm³ and 8.0 g H₂O₂/dm³). The differences between these variants were not statistically significant. Therefore, due to the economical use of chemical reagents, the optimal tested dose was 1.5 g Fe²⁺/6.0 g H₂O₂. The use of a Fenton-like reagent (Fe³⁺/H₂O₂) resulted in lower AD efficiency (max. 393.7 ± 12.1 cm³ CH₄/g VS), and no strong linear relationships between the analyzed variables were found. It is, therefore, a more difficult method to estimate the final effects. Research has proven that AOP can be used to improve the efficiency of AD of PSS.

Influence of alternating electric field on deep dewatering of municipal sludge and changes of extracellular polymeric substance during dewatering

A self-prepared experimental device made of plexiglass with alternating power supply system was used to study the deep dewatering of municipal dewatered sludge. Considering the reduction rate of sludge water content (W_r) as the index, factors affecting enhanced electric settlement of sludge such as exchange electrode method, voltage gradient, sludge thickness, and mechanical pressure were studied, and the dewatering mechanism was elucidated. The single-factor experiment combined with the surface response method based on the Box-Behnken central experimental design was performed. With W_r as the response value, the voltage gradient conditions, time ratio, and sludge thickness were optimized. Pearson correlation analysis showed that the reduction of proteins/polysaccharides was beneficial to improving the sludge dewatering effect. Tightly bound extracellular polymeric substances (TB-EPSs) showed a significant influence on the sludge dewatering effect. Under the action of the external electric field, particles with negative charge moved toward the anode sludge, water with partial positive charge flowed to the cathode, and the sludge cellular structure was damaged. This resulted in the dissolution of a large number of EPSs and the release of bound water. The anode sludge cake got thickened due to the accumulation of the sludge particles, leading to the increase in resistance. The TB-EPS was deconstructed by the ohmic heating to improve the sludge dewatering effect and achieve deep dewatering. Scanning electron microscopy results showed that the drying problem of anode sludge was alleviated during the dewatering process.

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.

Insights into the dewatering of excavated landfill sludge conditioned by polyferric silicate sulfate

Large quantities of landfill sludge (LS) with higher water content (WC) were stored underground, and excavation and re-dewatering of LS is a sustainable and economic strategy to save landfill space and reduce the leaching of contaminants. In this study, polyferric silicate sulfate (PFSS) was first applied in the conditioning of excavated LS, and the effects of the Si/Fe mass ratio and PFSS dosage on physicochemical properties, dewaterability and rheological properties were investigated. At the best Si/Fe of 0.18, PFSS conditioning obtained compact aggregates with the strongest internal structure, thus achieving the lowest WC. Large sludge flocs were formed, and slime and loosely-bound extracellular polymeric substances were effectively removed with the PFSS dosage above 100 mg/g dried solids, which made the WC to be lower than 51.4%. The whole mechanical compression process of conditioned LS can be described by the modified Terzaghi-Voigt model, and increasing the PFSS dosage induced the release of bound water and migration of the consolidation stage from ternary to secondary. PFSS is an economically sustainable conditioner for LS, integrating multiple functions such as charge neutralization, particle aggregation, interparticle bridging and skeleton building in one chemical.

A novel conditioning approach for amelioration of sludge dewaterability using activated carbon strengthening electrochemical oxidation and realized mechanism

Sludge dewatering is an essential process for reduction of sludge volume to decrease cost of ultimate disposal. In this study, a novel method using activated carbon (AC) strengthening electrochemical (EC) treatment (EC/AC) was adopted to improve greatly sludge dewaterability. It was shown that capillary suction time (CST) and water content of dewatered sludge cake (Wc) were reduced to 55.9 ± 1.24 s and 64.3 ± 1.23%, respectively, under the optimal conditions of EC voltage 20 V, EC time 30 min and 0.2 g/g dry solid (DS) AC. AC with rich functional groups as "the third electrode" intensified electrooxidation by forming multiple microelectrodes and electron transfer capacity and conductivity of sludge were strengthened by AC in EC system, which were illustrated by electrochemical analysis. It could be found that zeta potential and particle size were increased and surface roughness was reduced after EC/AC treatment intensifying sludge hydrophobicity. Form the results of rheological behaviors of sludge, flowability was strengthened and viscosity was weakened under the conditioning of EC/AC. Besides, colloidal force and gel-like network strength were lessened, which was also verified by organic matters and percentage of inviable cells. At the same time, intracellular matters were released and degraded and bound water was released converting into free water. In addition, sludge compressibility and structural strength were increased and porous structure was formed facilitating water outflow via addition of mesoporous AC as skeleton builder, which eventually led to an improved separation efficiency of solid-water and sludge dewaterability. The results of heavy metals suggested that sludge cake after EC/AC treatment was favorable for land application.

Iron-based advanced oxidation processes for enhancing sludge dewaterability: State of the art, challenges, and sludge reuse

The increasing amount of sewage sludge produced in wastewater treatment plants (WWTPs) poses a great challenge to both environment and economy globally. As a requisite process during sludge treatment, sludge dewatering can significantly minimize the sludge volume and lower the operational cost for downstream transportation and disposal. Iron-based advanced oxidation process (AOP), a robust and cost-effective technique with relatively low technical barriers for high-level sludge dewatering, has been widely explored in the past 20 years. The development was mainly driven by the demands of efficient and sustainable sludge conditioning technology and the flexible sludge management approaches. The application of iron-based AOPs in sludge dewatering process attracts more and more attention. In this work, we discussed the current application of iron-based AOPs technology in the sludge dewatering processes in a holistic manner, summarized the factors affecting the sludge dewaterability in the treatment processes, and analyzed the mechanisms of iron-based AOPs to improve dewatering processes. Furthermore, we elaborated potential advantages, limitations, and challenges associated with implementing iron-based AOPs in the full-scale plants and shared the opportunities for sludge reutilization. This review aims to contribute to the development of highly efficient iron-based AOPs for sludge dewatering and offer perspectives and directions towards the new-generation of WWTPs with the sustainable and eco-friendly benefits.

Improvement of sludge dewaterability by energy uncoupling combined with chemical re-flocculation: Reconstruction of floc, distribution of extracellular polymeric substances, and structure change of proteins

This study innovatively combines energy uncoupling and chemical re-flocculation helped to accelerate residual sludge dewatering. Ferric chloride (FeCl₃) and 3, 3', 4', 5-tetrachlor-osalicylanilide (TCS) were employed as the flocculant and uncoupler, respectively. The results showed that the specific resistance to filtration (SRF) and the water content of sludge filtered cake fell dramatically from 11 × 10¹² m/kg and 80.2% to 1.1 × 10¹² m/kg and 77.1% respectively, when the addition of TCS ranged from 0 to 0.12 g/g VSS with flocculation conditioning. The distribution of sludge extracellular polymeric substance (EPS) was altered radically after adding TCS, leading to the collapse and fragmentation of EPS, causing the reduction and formation of fragmentized sludge flocs. Meanwhile, the stretching and deformation vibrations of CO and NH bonds suggested the strong attack between TCS and EPS proteins, while variations of the main secondary structures of protein (i.e. α-helix, β-sheet and random coil) indicated the loose structure of proteins and enhanced hydrophobicity. Consequently, the cracked and loose structure of residual sludge resulted in the release of bound water. After TCS addition combined with chemical re-flocculation, the channels of sludge water discharge were widened, guaranteeing the discharge of sludge water. Therefore, the sludge dewaterability was elevated under the energy uncoupling combined with chemical re-flocculation. As well, the application of TCS would not destroy sludge cells, in which bioenergy (sludge carbon source) could be retained and effectively utilized in the subsequent disposal process. The findings reported here not only widen our perception of the energy uncoupling technology, but also encourage researchers to explore both effective and economic methods on the basis of energy uncoupling, aiming to achieve high-efficiency of reduction and dewatering in the future.

In-depth research on percarbonate expediting zero-valent iron corrosion for conditioning anaerobically digested sludge

Anaerobically digested sludge (ADS) is commonly hard to dewater for the presence of extracellular polymeric substances (EPS) and the liberation of glutinous soluble microbic products during anaerobic digestion. Sodium percarbonate (SPC) expediting zero-valent iron (ZVI) corrosion (SPC/ZVI) process firstly conditioned ADS to amend its dewaterability. Results showed that SPC/ZVI conditioning decreased moisture content of dewatered cake from 90.5% (control) to 69.9% with addition of 0.10 g/g TS SPC and 0.20 g/g TS ZVI. Mechanistic research indicated that the enhanced ADS dewaterability mainly resulted from •OH and Fe(III)/iron polymers yielded in SPC/ZVI. •OH disrupted EPS, damaged cytoderm & cytomembrane, and lysed intracellular substances, unbinding the bound water. Meanwhile, the breakage and inactivation of microbe by •OH prompted the production of macro-pores in ADS. •OH adjusted the conformation of extracellular/intracellular proteins by intervening in the H-bonds and S-S bonds, availing the hydrophobicity and slight flocculation of ADS. •OH further facilitated the despiralization of α-helical to β-sheet structure in ADS pellets, benefiting cell-to-cell aggregation. Additionally, Fe(III)/iron polymers from ZVI corrosion accelerated to gather ADS and maintained its floc structure. Consequently, SPC/ZVI conditioning not only adjusted the natures of ADS and its EPS but also the features of residual pellets, which further induced the advancement of ADS dewaterability. In addition, SPC/ZVI conditioning possibly surmounts some limitations existing in ZVI/Peroxide or ZVI/Persulfate technique.

Enhanced dewatering of activated sludge by acid assisted Heat-CaO2 treatment: Simultaneously removing heavy metals and mitigating antibiotic resistance genes

High water content and accumulation of heavy metals and antibiotic resistance genes (ARGs) in sewage sludge limit its application. Fenton process has been widely used in sludge dewatering, but the use of hydrogen peroxide (H₂O₂) and generation of acid sludge are the main drawbacks. Here, a novel method of heat-CaO₂ treatment was proposed to enhance sludge dewatering. Results showed that CaO₂ (12.5 mg/g dry solids (DS)) combined with heat at 60 °C significantly improved the sludge dewaterability, e.g. the water content decreased from 79.9% to 69.2% and the specific resistance to filtration (SRF) decreased from 9.21 × 10¹³ to 1.51 × 10¹³ m/kg. At 62.5 mg CaO₂/g DS, the final pH of filtrate was close to neutral and the good dewatering performance was still achieved. The improvement of sludge dewaterability was closely correlated with the decomposition of tightly-bound extracellular polymeric substances (EPS), lysis of the sludge cells, and increased particle size of the flocs. The distribution of bacterial community in the sludge has changed, leading to the decreases in the percentage of some ARGs. The concentrations of typical heavy metals wrapped in the sludge colloid network dramatically reduced. Economic analyses showed that the heat-CaO₂ treatment was a promising method for sludge disposal.

Simultaneous implementation of sludge dewatering and solid biofuel production by microwave torrefaction

Sludge dewatering is a matter of great concern to reduce the volume of sludge, stabilize its organic components, and achieve resource utilization. This study investigates sludge dewatering by microwave torrefaction along with the production of sludge solid biofuel at 480-800 W combined with durations of 5-25 min. Proximate analysis, calorific value analysis, thermogravimetric analysis, and scanning electron microscopy observations are employed to evaluate the dewatering degree, fuel properties, and energy efficiency of the torrefaction process. The independent parallel reaction (IPR) model and particle swarm optimization (PSO) analysis are also adopted for sludge pyrolysis kinetics calculation. The results show that microwave torrefaction is efficient for sludge dewatering with a short duration. The produced sludge solid biofuel is similar to stone-like coal, and can be used for civil or industrial boilers after flotation or just co-firing with briquette. The ash content of sludge solid biofuel shows a declining trend and the surface characteristics change from smooth to rough and fluffy with increasing the torrefaction severity. The bio-oil is mainly composed of phenols, siloxanes, and cholesterol. In addition, hydrogen is detected in the torgas. Furthermore, it is found that lower torrefaction power with a shorter duration yields a higher energy efficiency of the torrefaction process.

Simultaneous heavy metal removal and sludge deep dewatering with Fe(II) assisted electrooxidation technology

A hybrid sludge conditioning strategy with electrooxidation and Fe(II) addition was used for heavy metal removal from sewage sludge and industrial sludge, with simultaneous sludge dewatering and stabilization. With the addition of 82 mg/g DS Fe(II) and treatment time of 4.5 h, heavy metal removals of 72.95% and 78.49% for Cu, 66.29% and 84.26% for Zn, and 36.52% and 36.99% for Pb were achieved from sewage sludge and industrial sludge samples respectively. The system pH decreased to 2.33 and 2.98 and the oxidation-reduction potential (ORP) values increased to 435.90 mV and 480.60 mV in sewage sludge and industrial sludge samples, respectively, which was conducive to the desorption and dissolution of heavy metals from sludge structures and the degradation of the organic compounds that complexed with heavy metals. In addition, the hybrid conditioning process demonstrated excellent dewatering performance due to the efficient electrochemical disintegration of sludge flocs together with the coagulation of sludge particles by Fe(III) generated via electrooxidation. The strong acidic and oxidative environment produced by the enhanced electrooxidation process was also responsible for pathogen inactivation.

Improving dewaterability of waste activated sludge by thermally-activated persulfate oxidation at mild temperature

The mass production of waste activated sludge in wastewater treatment plants may lead to environmental pollution and sludge dewatering is an essential process during its treatment. The oxidation of extracellular polymeric substances (EPS) was the core step to achieve deep sludge dewatering. In this study, thermally-activated sodium persulfate (SPS) process was managed to improve the dewaterability of waste activated sludge (WAS) and its internal mechanism was systematically elaborated. Experimental results showed that with 2.0 mmol/g VSS SPS at 80 °C, capillary suction time (CST) was roughly 59.74% of that in raw sludge. Under this condition, 14.66 ± 0.10 × 10¹¹ kg/m of specific resistance to filtration (SRF) and 61.8% ± 0.1% of water content (W_C) was determined, respectively. A solubilization/oxidation process was proposed to unravel the mechanism of the enhanced dewaterability of WAS in thermally-activated SPS process. Mild temperature efficiently disrupted the sludge flocs and broke cell walls, releasing large amounts of EPS into bulk phase. Meanwhile, mild temperature accelerated the decomposition of SPS to generate sulfate radicals (SO₄^-) and hydroxyl radicals (OH) for oxidizing EPS, facilitating the conversion of bound hydrated water into free water and achieving solid-water separation. The higher reaction temperature favored sludge dewatering, whereas overdosing SPS posed no significant impact. Further analysis illustrated that tyrosine protein-like, tryptophan protein-like, fulvic acid-like and humic acid-like substances in various EPS fractions together exerted the influence on sludge dewatering. Furthermore, the synergy process could alter the secondary structure of protein, which caused a loose structure of EPS and the exposure of hydrophobic sites, facilitating the dehydration of sludge flocs. The details of how thermally-activated SPS process enhanced sludge dewaterability provided the theoretical and technical basis for the application of the process under a real-world situation.

Understanding synergistic mechanisms of ferrous iron activated sulfite oxidation and organic polymer flocculation for enhancing wastewater sludge dewaterability

The bound water in waste activated sludge (WAS) is trapped in extracellular polymeric substances (EPS) in the form of gel-like structure, leading to a great challenge in the sludge deep dewatering. Traditional flocculation conditioning is unable to destroy EPS and ineffective to remove the bound water in WAS. In this study, we employed integration of Fe(II)-sulfite oxidation and polyacrylamide flocculation (F/S-PAM) treatment for removing the bound water and improving sludge dewaterability under aerobic conditions. Meanwhile, the floc microstructure and EPS properties were examined to understand the mechanisms of F/S-PAM conditioning. F/S produced SO₃^·- radicals which could decompose the EPS in sludge, releasing bound water into free water. In addition, the formed Fe(III) from F/S led to re-coagulation of decomposed EPS, and C=O groups of tryptophan played the leading role in Fe-EPS association binding, causing transformation of the secondary structure of proteins (especially β-sheets and α-helices). Then, the introduction of PAM caused re-flocculation of disintegrated sludge flocs, enhancing the sludge filterability. This work provides a novel and cost-effective method for efficient removal of bound water in sludge, and subsequence improvement in sludge dewaterability.

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.

Integration of electrochemical and calcium hypochlorite oxidation for simultaneous sludge deep dewatering, stabilization and phosphorus fixation

A hybrid electrochemical process with Ca(ClO)₂ addition for simultaneous sludge dewaterability, stabilization and phosphorus fixation was proposed. Under optimal conditions (150 mg/g VS Ca(ClO)₂, 15 V), the capillary suction time (CST) and specific resistance to filtration (SRF) were decreased by 88% and 92%, respectively. Efficient sludge stabilization with E. coli colonies of less than 1000 MPN/g TS was achieved. Phosphorus of 99% was removed from the filtrate and successfully fixed in the sludge cake and on the electrode surface. The integration of electrochemical and hypochlorite oxidation could effectively degrade the tightly bound extracellular polymeric substances (TB-EPS) structure with a total organic carbon (TOC) reduction of 52%. Besides, the disintegration of microbial cell envelopes was also achieved, with a reduction of living cell fraction of 98%. Furthermore, system pH could be maintained at near neutral (7.45) and the conversion of Fe(II) to Fe(III) was also facilitated with the addition of Ca(ClO)₂, resulting in improved electrocoagulation process for enhanced sludge dewatering and phosphorus fixation. The multifunctional effects were achieved with the cooperated extracellular electrooxidation for EPS destruction and the active chlorine for intracellular microbial cell disintegration. This research provides a promising strategy for integrated sludge treatment and recycling for possible land utilization.

Peroxide/Zero-valent iron (Fe0) pretreatment for promoting dewaterability of anaerobically digested sludge: A mechanistic study

Peroxide/Zero-valent iron (Fe⁰) was reported to promote dewaterability of anaerobically digested sludge (ADS), but the mechanism of how Peroxide/Fe⁰ facilitates ADS dewatering is unknown. This study therefore aims to uncover the details of how Peroxide/Fe° elevates ADS dewaterability. Experimental results showed that with 0.6 g Fe⁰/g TSS and 0.08 g peroxide/g TSS, capillary suction time, specific resistance to filtration, and time to filtration of ADS was 50.7 %, 41.4 %, and 54.4 % of that in the control, respectively. In this condition, water content of sludge cake decreased from 91.2 % ± 0.5 % (the control) to 68.6 % ± 1.3 %. The mechanism explorations revealed that the elevated dewaterability was mainly caused by role of OH and Fe(II)/Fe(III) species during Peroxide/Fe° pretreatment. OH decreased the polysaccharides and proteins in extracellular polymeric substance (EPS), then injured the cytoderm & cytomembrane through the releases of lactate dehydrogenase and N-acetylglucosamine, and further facilitated the decrease of intracellular substances, which disengaged the water trapped in ADS. In addition, the cell lysis caused by OH facilitated forming macro-pores. Moreover, OH converted the conformational structure of extracellular proteins, which may strengthen the ADS hydrophobicity, promoting the discharge of unbound water and ADS flocculation. Meanwhile, Fe(II)/Fe(III) benefited aggregating the denatured ADS particulates.

Extracellular polymeric substances trigger an increase in redox mediators for enhanced sludge methanogenesis

Artificial redox mediators can be employed to improve the electron transfer efficiency during sludge methanogenesis, whereas these artificial redox mediators have possible deficiencies, such as high cost and non-biodegradability. For large-scale commercial applications, more cost-effective and environmentally friendly alternatives should be developed. Herein, the potential of extracellular polymeric substances (EPS) as natural redox mediators to improve methanogenesis was investigated. Compared to the control test without EPS addition, the methane (CH₄) production yield was increased by 83.5 ± 2.4% with an EPS dosage of 0.50 g/L and the lag phase duration was shortened by 45.6 ± 7.0%, along with the enhanced sludge dewaterability. Spectroelectrochemical measurements implied that EPS addition notably changed the intensities of different redox-active groups, which decreased the charge transfer resistance and enhanced the extracellular electron transfer efficiency. These redox-active groups were mainly from the solubilization and hydrolysis of sludge protein due to increased protease activities, thereby leading to a higher acetate concentration during the acidification step. Further investigation showed that EPS addition also improved the activities of both acetotrophic and hydrogenotrophic methanogens, as indicated by a higher abundance of alpha subunit of methyl coenzyme M reductase (mcrA) genes, enhancing CH₄ production. This work provides an innovative strategy for improving sludge anaerobic digestion with efficient additives.

Dewaterability enhancement and sulfide mitigation of CEPT sludge by electrochemical pretreatment

Dewatering and sulfide control are the key challenges in treating chemically enhanced primary treatment (CEPT) sludge. In this study, an electrochemical pretreatment (EPT) approach with the input of 10 V/800 mA was explored for simultaneously improving the dewaterability of CEPT sludge and eliminating its sulfide production. The effects of different electrode materials (carbon and titanium) and EPT durations (from 5 to 15 min) were documented to reveal the underlying EPT mechanism. EPT with titanium electrodes (titanium-EPT) led to limited improvement in dewaterability and sulfide control. EPT with carbon electrodes (carbon-EPT) for 15 min, however, led to decreases in capillary suction time and specific resistance in filtration of over 80% and the suppression of about 99% of hydrogen sulfide (H₂S_(g)) production over 5 days of anaerobic storage. Analysis of the characteristics of treated CEPT sludge revealed that carbon-EPT disintegrated sludge flocs with ∼70% reduction in sludge particle sizes and release of aromatic and tyrosine protein-like substances, thus enhancing sludge dewaterability. The sulfur balance in the liquid and gaseous phases showed that most of the sulfur-containing compounds remained in the solid phase as aliphatic sulfur and sulfonic acid after carbon-EPT, thereby mitigating sulfide emission. While the pattern of sulfur distribution in sludge with titanium-EPT was dominated by sulfide, it was similar to the control sample. Reduction in bacteria associated with sulfide production (i.e., Lachnospiraceae) in CEPT sludge after carbon-EPT also contributed to sulfide elimination. This study demonstrates that EPT can be a superior option for simultaneously enhancing the dewaterability of CEPT sludge and mitigating its sulfide production.

Fe(II) catalyzing sodium percarbonate facilitates the dewaterability of waste activated sludge: Performance, mechanism, and implication

In this work, Fe(II) catalyzing sodium percarbonate (Fe(II)/SPC) was managed to facilitate waste activated sludge (WAS) dewatering for the first time. The results showed that after WAS was treated by 20 mg/g total suspended solids (TSS) Fe(II) and 50 mg/g TSS SPC, the water content of sludge cake (WC_SC) by press filtration and capillary suction time (CST) dropped from 90.8% ± 1.6% and 96.1 ± 4.0 s (the control) to 55.6% ± 1.4% and 30.1 ± 2.5 s, respectively. The mechanism investigations indicated that four intermediates or products (i.e., •OH, H₂O₂, Fe(II), and Fe(III)) generated in the Fe(II)/SPC process were responsible for the improved WAS dewaterability, and •OH and Fe(III) were the two major contributors. It was found that •OH collapsed and fragmented extracellular polymeric substances, damaged cell wall and permeabilized cytoplasmic membrane, and transformed conformation of the extracellular proteins secondary structure via both affecting the hydrogen bond maintaining α-helix and cracking disulfide bond in cysteine residues while Fe(III), the oxidization product of Fe(II), decreased the surface electronegativity and water-affinity surface areas of WAS flocs. As a result, the bound water release, flocculability, surface hydrophobicity, drain capability, and flowability of WAS flocs were strengthened whereas the compact surface structure, colloidal forces, network strength, gel-like structure, and apparent viscosity of WAS flocs were weakened. In addition, Fe(II)/SPC process also reduced the recalcitrant organics and fecal coliforms in sludge, which facilitated land application of dewatered sludge. The findings acquired in this work not only deepens our understanding of Fe(II)/SPC-involved WAS treatment process but also may guide engineers to develop both effective and promising strategies to better condition WAS for dewatering in the future.

Mechanism of zero valent iron and anaerobic mesophilic digestion combined with hydrogen peroxide pretreatment to enhance sludge dewaterability: Relationship between soluble EPS and rheological behavior

This study proposed a novel two-step conditioning strategy to enhance activated sludge (AS) dewatering performance. The method involved a zero valent iron (ZVI), anaerobic mesophilic digestion (AMD) process, and hydrogen peroxide (H₂O₂) oxidation. Response surface methodology (RSM) was applied to achieve optimum dewatering conditions. After the combined conditioning, dewatering was significantly better in the treated sludge compared to the raw AS. The specific resistance of filtration (SRF) of the treated sludge decreased to 2.48 × 10¹¹ m/kg; this SRF level was 93.60% lower compared to the raw AS. The bound water content (BWC) decreased to 1.19 g/g dry solid (DS); this BWC level was 15.2% lower compared to the raw AS. The water content of the treated sludge cake decreased to 44.18 ± 0.46%. An economic analysis shows that ZVI-AMD-H₂O₂ can be used in real-world settings. Investigations of the underlying mechanisms showed that small block structures were formed after conditioning; viscosity and the colloidal forces of the sludge decreased; and organic matter and BWC were released from inner extracellular polymeric substances (EPS) layers to form soluble (SB)-EPS. This study illuminated the relationship between SB-EPS and the rheological behavior of AS. There is a high correlation coefficient between rheological parameter τ_y and N-containing substances in SB-EPS (R = -0.993, p < 0.05). The ZVI-AMD-H₂O₂ process effectively changed the EPS content, especially protein materials. This led to a decrease in AS viscosity and an increase in sludge dewaterability.

Ultrasonic coupled bioleaching pretreatment for enhancing sewage sludge dewatering: Simultaneously mitigating antibiotic resistant genes and changing microbial communities

In this study, ultrasonic as a pretreatment coupled with bioleaching was used to enhance sludge dewaterability. Changes in microbial diversity and antibiotic resistant genes (ARGs) were studied during the combined treatment process. The results show that under optimal conditions, combined ultrasonic and bioleaching treatment led to decreases in the specific resistance of filtration and bioleaching time by 7.59% and 12.5%, respectively, compared with single bioleaching process. Using high pressure filtration system, the water content of sludge cake treated by the combined treatment was decreased to 58.04%, which was 10.04% lower than bioleaching sludge. After combined treatment, the microbial diversity and the total number of bacteria in the sludge decreased significantly, which caused the decreases in the absolute abundance of sulfonamide and tetracycline ARGs by 1.56-1.58 and 0.34-1.23 log units, respectively. However, the decrease in the total bacterial biomass was greater than the decrease in the number of potential hosts carrying the tetracycline ARG, resulting in an increase in the relative abundance of tetracycline gene. Furthermore, this study proposed a mechanism of the dewatering and ARGs, involving the combined ultrasonic and bioleaching treatment: Firstly, ultrasonic cavitation causes extracellular polymeric substances (EPS) to fall off the surface of sludge; Secondly, this faster and directly makes bacteria cells affected by bio-acidification and bio-oxidation. In this case, the cells could be more easily destroyed by the combined ultrasonic and bioleaching treatment, compared with individual bioleaching treatment; As a result, stronger dewaterability and more removal rates of ARGs were achieved under the combined treatment. The economic analyses showed that the combined ultrasonic and bioleaching treatment is a more practical and economical technique for achieving deep dewatering of sludge.

Effect of citric acid on extracellular polymeric substances disruption and cell lysis in the waste activated sludge by pH regulation

This paper investigated the effects of citric acid (CA) on extracellular polymer destruction and cell lysis in sludge at different initial pH by measuring capillary suction time (CST), extracellular polymeric substances (EPS) and intracellular bound water. The results indicated that under CA concentration at 0.05 g/g suspended solids (SS) and initial pH 4, the CST value decreased from 175.5 s to 112.3 s, slime extracellular polymeric substances (S-EPS) and loosely bound EPS (LB-EPS) content respectively to increase from 4.92 to 41.43, 2.27 to 5.49 mg/g volatile suspended solids (Vss), while tightly bound EPS (TB-EPS) content to decrease from 12.35 to 5.01 mg/g (Vss), which suggested CA could disrupt outer EPS effectively. Intracellular bound water content decreased from 1.23 g/g to 0.41 g/g dry solid (DS). As a result, CA could release intracellular bound water effectively, thereby improving sludge dewatering degree.

Efficient degradation of refractory organic contaminants by zero-valent copper/hydroxylamine/peroxymonosulfate process

Degradation of naproxen, bisphenol S and ibuprofen in a hydroxylamine enhanced zero-valent copper (Cu⁰) catalyzed peroxymonosulfate system was investigated for the first time. We found that hydroxylamine addition accelerated the reduction of Cu²⁺ to Cu⁺ as well as the corrosion of Cu⁰, and environmental friendly gas nitrogen was the main product of hydroxylamine. Additionally, hydroxyl radical and sulfate radical were identified to be the dominant reaction species by competitive experiments. The degradation of naproxen, bisphenol S and ibuprofen kept highly efficient in the pH range of 3.0-7.0 in Cu⁰/hydroxylamine/peroxymonosulfate process, with their degradation products identified by HPLC-MS, which showed that Cu⁰/hydroxylamine/peroxymonosulfate system could be an alternative to remove non-steroidal antiinflammatory drugs or plasticizers in wastewater. Furthermore, the effects of Cu⁰, hydroxylamine and peroxymonosulfate dosage were studied and optimized by a BBD based response surface model. This study provided a method to solve the disadvantages of Cu⁰/peroxymonosulfate systems, and gave a promising method to enhance the efficiencies of ZVMs activated system such as iron, cobalt and copper.

Electrocoagulation as a Pretreatment for Electroxidation of E. coli

Insufficient funding and operator training, logistics of chemical transport, and variable source water quality can pose challenges for small drinking water treatment systems. Portable, robust electrochemical processes may offer a strategy to address these challenges. In this study, electrocoagulation (EC) and electrooxidation (EO) were investigated using two model surface waters and two model groundwaters to determine the efficacy of sequential EC-EO for mitigating Escherichia coli. EO alone (1.67 mA/cm2, 1 min) provided 0.03 to 3.9 logs mitigation in the four model waters. EC alone (10 mA/cm2, 5 min) achieved ≥1 log E. coli mitigation in all model waters. Sequential EC-EO did not achieve greater mitigation than EC alone. To enhance removal of natural organic matter, the initial pH was decreased. Lower initial pH (pH 5–6) improved E. coli mitigation during both stages of EC-EO. EC-EO also had slightly greater E. coli mitigation than EC alone at lower pH. However, EO alone provided more energy efficient E. coli mitigation than either EC or EC-EO.

Improved sludge dewaterability by tannic acid conditioning: Temperature, thermodynamics and mechanism studies

Waste activated sludge (WAS), containing biological pathogens, chemical elements and high moisture (>99%), was generated continually from municipal sewage treatment plants. Sludge dewatering could diminish the volume of WAS and control the diffusion of environmental pollution efficiently. In this study, tannic acid (TA), as a plant-derived phenolic compound, was investigated for improving WAS dewaterability at different temperatures. Apparently, the WAS dewaterability was enhanced by TA conditioning in the range of 25-55 °C, but further increase in temperature did not significantly affect the dewatering. With the TA addition of 0.15 mmol/gTS (total solid) at 55 °C, the WAS dewaterability was improved by 84.5% decrease in capillary suction time (CST), 96.5% decrease in specific resistance of filtration (SRF), and 19.9% decrease in water content (Wc) of dewatered sludge cake. TA facilitated removing supernatant viscosity and protein of sludge EPS (extracellular polymeric substances), specifically with 88.9% and 75.0% protein removal of slime EPS (S-EPS) and loosely bound EPS (LB-EPS). Thermodynamics modeling revealed that the improved dewaterability was dominantly attributed to the hydrophobic bonding between TA and EPS proteins, which was strengthened with the increase in temperature. However, when the conditioning temperature exceeded 55 °C, thermal effect took place and accelerated the release of biopolymers into EPS and hence, counteracted the beneficial effect of TA conditioning to further improve WAS dewatering. The results offered not only the dewatering effectiveness and mechanism of TA conditioning, but also a potential approach of applying plant waste to treat WAS for the high dewaterability.

Anaerobically-digested sludge conditioning by activated peroxymonosulfate: Significance of EDTA chelated-Fe2

This study investigates the efficiency of anaerobically-digested sludge (ADS) conditioning using peroxymonosulfate (PMS) activated by EDTA chelated-Fe²⁺ process (PMS-EDTA-Fe²⁺), and the roles and mechanism of EDTA are explored by investigating the capillary suction time (CST), specific resistance to filtration (SRF), bound water content (BWC), extracellular polymeric substances (EPS), iron species transformation, sludge morphology, and active radicals formation. PMS-EDTA-Fe²⁺ process exhibits better performance in sludge dewatering than PMS-Fe²⁺ process. Upon the introduction of EDTA at optimum molar ratio of EDTA to Fe²⁺ [Formula: see text] of 1 : 3, CST, SRF, and BWC are decreased by 60.0%, 70.6%, and 1.5%, and the cell viability is decreased from 75.4% to as low as 24.7%. EDTA introduction significantly enhances the yield of active radicals (i.e., SO₄^-· and O⋅H) by nearly 50% as compared to PMS-Fe²⁺ process. This effect contributes to stronger cells lysis as indicated by SEM and CLSM, and the contents of polysaccharide and protein in total EPS fractions are increased by 19.2% and 37.4% accordingly. Additionally, EDTA increases the iron mobility by forming Fe^II/III-EDTA complexes and potentially inhibits ADS coagulation at high doses. The total dissolved iron (Fe_{Tot_dis}) concentration increases from 203.4 mg/L to 601.4 mg/L due to the introduction of EDTA at 0.4 mmol/g VSS, and the dominant iron species in supernatant transformed from Fe²⁺ to Fe³⁺ accordingly. The optimization of EDTA doses is significant to balance oxidation and coagulation effects and to achieve better dewatering performance.

Preparation of Biomass Activated Carbon Supported Nanoscale Zero-Valent Iron (Nzvi) and Its Application in Decolorization of Methyl Orange from Aqueous Solution

The nanoscale zero-valent iron (nZVI) has great potential to degrade organic polluted wastewater. In this study, the nZVI particles were obtained by the pulse electrodeposition and were loaded on the biomass activated carbon (BC) for synthesizing the composite material of BC-nZVI. The composite material was characterized by SEM-EDS and XRD and was also used for the decolorization of methyl orange (MO) test. The results showed that the 97.94% removal percentage demonstrated its promise in the remediation of dye wastewater for 60 min. The rate of MO matched well with the pseudo-second-order model, and the rate-limiting step may be a chemical sorption between the MO and BC-nZVI. The removal percentage of MO can be effectively improved with higher temperature, larger BC-nZVI dosage, and lower initial concentration of MO at the pH of 7 condition.

Variations in macro and micro physicochemical properties of activated sludge under a moderate oxidation-in situ coagulation conditioning: Relationship between molecular structure and dewaterability

A moderate Mn(Ⅶ) oxidation-in situ Fe(Ⅲ) coagulation (Mn(Ⅶ)-Fe(Ⅱ)) conditioning strategy was proposed to improve sludge filterability and release the water bound in extracellular polymeric substances (EPS). During Mn(Ⅶ)-Fe(Ⅱ) conditioning, flocs disintegration and cell disruption, macro and micro physicochemical properties of activated sludge, especially of EPS, were investigated. Relationships between protein molecular structures in EPS fractions of three layers and sludge dewaterability were also determined. Besides, factor analysis was used to explain the variances of "functional" protein secondary structures, which may have an important effect on sludge dewaterability. Results showed that sludge filterability (CST₀/CST) increased by 2.40 times and partial bound water was released at 2 min oxidation of 120 mg/g KMnO₄ with subsequent FeCl₂ termination at equivalent molar ratio of 1:3. During this strategy, EPS wrapping on cells surface was disintegrated, and a limited influence occurred on cells. It was also found that CST and bound water content were strongly correlated with aggregated strands, random coil and β-turn percentages in slime (R² >-0.82, p < 0.05). Moreover, the dewaterability also presented strong negative correlations with aggregated strands, β-sheet and β-turn in TB-EPS (R² >-0.78, p < 0.05). This suggested that unfolding and despiralization of slime protein and moderate weakening rigidity of tightly bound EPS (TB-EPS) protein were beneficial for improvement of sludge dewaterability. In addition, the strong correlation between percentages of "functional" protein secondary structures and factor 1 score (R² > 0.85, p < 0.05) demonstrated that EPS migration, rather than only EPS disintegration, may have a key impact on the formation of some protein secondary structures in slime and TB-EPS. The observed protein secondary structures, which may affect sludge dewaterability, were probably derived from inner EPS.