Conditioning of aluminium-based water treatment sludge with Fenton's reagent: effectiveness and optimising study to improve dewaterability

Enhancement of sludge dewaterability using combined technology of bioleaching and Fenton: Microscopic structure and hydrophilic/hydrophobic properties of sludge particles

Bioleaching and Fenton technology are commonly used preconditioning techniques for sludge dewatering. This study compared the dewatering mechanisms of different conditioning technologies. The results showed that bound water, specific resistance to filtration (SRF), and capillary suction time decreased from 3.95 g/g, 6.16 × 1012 m/kg, and 130.6 s to 3.15 g/g, 2.81 × 1011 m/kg, and 33 s, respectively, under combined treatment condition. Moreover, the free radicals, including ·OH, O2-·and Fe (Ⅳ), further damaged the cell structure, thus increasing the concentration of DNA in the S-EPS layer. This intense degradation sludge particle size decreased by 15.6% and significantly increased zeta potential. Under the combined technology, the α-helix and β-sheet decreased by 42.2% and 56.5%, respectively, destabilizing the spatial structure of proteins and promoting the release of bound water. In addition, the combined technology decreased (Ala/Lys) ratio in the TB-EPS layer by 67.6%, indicating the weakening of protein water-holding capacity. Moreover, the conversion of oxygen-containing compounds to nonpolar hydrocarbons increased the hydrophobicity of the sludge under a combined treatment, thus enhancing dewatering performance.

Effect of microwaves combined with peracetic acid to improve the dewatering performance of residual sludge

The activated sludge process plays a crucial role in modern wastewater treatment plants. During the treatment of daily sewage, a large amount of residual sludge is generated, which, if improperly managed, can pose burdens on the environment and human health. Additionally, the highly hydrated colloidal structure of biopolymers limits the rate and degree of dewatering, making mechanical dewatering challenging. This study investigates the impact and mechanism of microwave irradiation (MW) in conjunction with peracetic acid (PAA) on the dewatering efficiency of sludge. Sludge dewatering effectiveness was assessed through capillary suction time (CST) and specific resistance to filtration (SRF). Examination of the impact of MW-PAA treatment on sludge dewatering performance involved assessing the levels of extracellular polymeric substances (EPS), employing three-dimensional excitation-emission matrix (3D-EEM), Fourier transform-infrared spectroscopy (FT-IR), and scanning electron microscopy. Findings reveal that optimal dewatering performance, with respective reductions of 91.22% for SRF and 84.22% for CST, was attained under the following conditions: microwave power of 600 W, reaction time of 120 s, and PAA dosage of 0.25 g/g MLSS. Additionally, alterations in both sludge EPS composition and floc morphology pre- and post-MW-PAA treatment underwent examination. The findings demonstrate that microwaves additionally boost the breakdown of PAA into •OH radicals, suggesting a synergistic effect upon combining MW-PAA treatment. These pertinent research findings offer insights into employing MW-PAA technology for residual sludge treatment.

Sustained oxidation of Tea-Fe(III)/H2O2 simultaneously achieves sludge reduction and carbamazepine removal: The crucial role of EPS regulation

Establishing an economic and sustained Fenton oxidation system to enhance sludge dewaterability and carbamazepine (CBZ) removal rate is a crucial path to simultaneously achieve sludge reduction and harmless. Leveraging the principles akin to "tea making", we harnessed tea waste to continually release tea polyphenols (TP), thus effectively maintaining high level of oxidation efficiency through the sustained Fenton reaction. The results illustrated that the incorporation of tea waste yielded more favorable outcomes in terms of water content reduction and CBZ removal compared to direct TP addition within the Fe(III)/hydrogen peroxide (H2O2) system. Concomitantly, this process mainly generated hydroxyl radical (•OH) via three oxidation pathways, effectively altering the properties of extracellular polymeric substances (EPS) and promoting the degradation of CBZ from the sludge mixture. The interval addition of Fe(III) and H2O2 heightened extracellular oxidation efficacy, promoting the desorption and removal of CBZ. The degradation of EPS prompted the transformation of bound water to free water, while the formation of larger channels drove the discharge of water. This work achieved the concept of treating waste with waste through using tea waste to treat sludge, meanwhile, can provide ideas for subsequent sludge harmless disposal.

Enhanced dewatering extent of sludge by Fe3O4-driven heterogeneous Fenton

Homogeneous Fenton (Fe2+/H2O2) serves as a high-efficiency conditioning method for sludge dewatering due to the generation of strong oxidizing hydroxyl radicals (OH). However, high dose of ferric salts produces iron-rich dewatered sludge and decrease sludge organic matters, which will not be conducive to the subsequent disposal and reutilization. Considering advantages of Fe3O4 as heterogeneous Fenton catalyst, Fe3O4-activated H2O2 (Fe3O4 + H2O2) in this study was adopted to improve sludge deep-dewatering. Reduction efficiency of the bound water (71.3 %) after Fe3O4 + H2O2 treatment (after a reaction time of 30 min) were much higher than those in the Fe2++H2O2 treatment. Especially, the moisture content of treated sludge cake by Fe3O4 + H2O2 remarkably decreased from 86.4 % to 61.3 %. Improvement mechanism of sludge dewatering after Fe3O4 + H2O2 treatment mainly included electrostatic neutralization, reactive radical oxidation, and skeleton building by analysis of contribution factors. The generation of H+ in acidification could neutralize the negatively charged compounds to promote sludge hydrophobicity. Meanwhile reactive radicals generated from Fe3O4 + H2O2 destroyed sludge extracellular polymeric substances and cell structure to release intracellular water. Furthermore, Fe3O4 as a skeleton builder could reconstruct destructive sludge flocs and form new dewatering channels. Finally, low Fe leaching content and recoverability of Fe3O4 effectively will decrease environmental implication.

Optimizing waste activated sludge disintegration by investigating multiple electrochemical pretreatment conditions: Performance, mechanism and modeling

The complex and rigid floc structure often limits the reutilization of waste activated sludge (WAS). Electrochemical pretreatment (EPT) is one of the most effective technologies that can enhance WAS disintegration. But a comprehensive investigation into how multiple EPT conditions work was rarely reported. The study evaluated the effects of multiple EPT conditions, i.e., different electrolytes (NaCl, Na₂SO₄, and CaCl₂), electrolytes dosage (0 g/L, 0.5 g/L, 1.0 g/L, and 3.0 g/L), EPT current (0 A, 0.5 A, 1.0 A, and 3.0 A) and EPT time (0 min, 30 min, 60 min, and 90 min) on WAS disintegration. The results showed that NaCl was outstanding from other electrolytes in promoting more WAS disintegration. Besides, a relatively higher NaCl dosage, a higher EPT current, and a longer EPT time promoted more reactive chlorine species (RCS), thus enhancing WAS disintegration in terms of extracellular polymeric substances (EPS) structure destruction and biodegradable organic matter release. After EPT for 60 min at NaCl dosage of 1.0 g/L and current of 1.0 A, the EPS multilayer structure destruction, biodegradable organic matters release, and soluble chemical oxygen demand (SCOD) increase in the supernatant were enhanced by 17.2 %, 130.5 %, and 238.7 %, respectively. Then a predictive quadratic model was established and the impact significance of the above EPT factors for enhancing WAS disintegration followed dosage of NaCl > current > EPT time. Furthermore, response surface methodology (RSM) suggested NaCl dosage of 2.75 g/L, current of 2.0 A, and EPT time of 30 min were the optimal EPT conditions, bringing a 42.0 % increase in the net economic benefit of WAS treatment compared to without EPT.

Multiple environmental risk assessments of heavy metals and optimization of sludge dewatering: Red mud-reed straw biochar combined with Fe2+ activated H2O2

In this study, Fe-rich biochar (RMRS-BC) was prepared from red mud and reed straw to improve sludge dewatering and transformation of heavy metals (HMs, including Cd, Cr, Cu, Pb, and Zn). The optimal concentrations of RMRS-BC, Fe²⁺, and H₂O₂ to promote sludge dewaterability were identified by response surface methodology (RSM). The optimal dosages of RMRS-BC, Fe²⁺, and H₂O₂ were 74.0, 104.9, and 75.7 mg/g dry solids (DS), respectively. The corresponding capillary suction time (CST) and water content of sludge cake were 14.3 s and 51.25 wt%. For the improvement mechanism, heterogeneous and homogeneous Fenton reactions occurred due to RMRS-BC and Fe²⁺ activating H₂O₂. The extracellular polymeric substances (EPS) decomposed into dissolved organic matter (proteins and polysaccharides), thereby promoting the transformation of bound water to free water and further reducing the water content of the sludge cake. The research quantitatively assessed the environmental risk of heavy metals in the conditioned sludge cake based on bioavailability and ecotoxicity, pollution levels and potential ecological risks. Compound conditioning using RMRS-BC, Fe²⁺, and H₂O₂ could significantly improve the solubility and reduce the leaching toxicity of HMs. In general, RMRS-BC combined with Fe²⁺ to activate H₂O₂ provided an effective method to enhance sludge dewaterability and reduce HMs risk.

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.

Supplementation of tea polyphenols in sludge Fenton oxidation improves sludge dewaterability and reduces chemicals consumption

The Fenton oxidation improves sludge dewatering but faces notable technical and economic challenges, including a narrow acidic pH range, slow reduction of Fe(III), and the use of high doses of chemicals. Herein, we used a natural polyhydroxyphenol tea polyphenols (TP), as an iron redox conversion enhancer, to mitigate these issues. Compared with the classical Fenton process at pH 3.0, the process with TP (33.8 mg/g dry solids (DS)) improved sludge dewaterability at pH 7.5 in a Fenton-like system with faster Fe(II)/Fe(III) cycling and two times lower consumption of the Fenton reagent. Sludge capillary suction time and specific resistance to filtration decreased from 70 s to 22 s and from 2.7 × 10¹³ m/kg to 5.2 × 10¹¹ m/kg, respectively, while the required doses of Fe(II) and H₂O₂ were cut to 25 mg/g DS and 31.2 mg/g DS. Mechanistically, TP could bond readily with Fe(II)/Fe(III) at neutral pH to form stable complexes with complexation constants of 34 ± 161 M^-1 and 52 ± 70 M^-1, respectively, and reduce part of the Fe(III) to Fe(II) simultaneously. This maintained sufficient soluble Fe in the sludge and boosted efficient conversion of Fe(II)/Fe(III) to yield more hydroxyl radicals (•OH). Subsequently, •OH oxidation resulted in the decomposition of biopolymers with a molecular weight of 10⁸ Da (e.g., 58.2% of polysaccharides and 31.6% of proteins in tightly bound extracellular polymeric substances) into small molecules and disintegration of bioflocs into smaller particles with increased porosity, contact angle, and cell lysis; these changes helped reduce bound water content and improved sludge dewaterability. In addition, the TP-mediated Fenton process disinfected fecal coliforms in the sludge and preserved the sludge organic matters. This work proposes a new paradigm for developing cost-effective sludge dewatering technologies that relies on the synergistic effects of plant polyphenols and advanced oxidation processes.

Mechanistic insights into enhanced waste activated sludge dewaterability with Cu(II) and Cu(II)/H2O2 treatment: Radical and non-radical pathway

Without extra adjustment of pH, the effects of cupric ions (Cu(II)) and hydrogen peroxide (H₂O₂) alone or in combination on sludge dewatering were studied. It showed good dewatering capability after treated by Cu(II) and Cu(II)/H₂O₂, which indicated by the capillary suction times (CST) decreased from 120.8 ± 4.7 s (control) to about 40 s, and the water content (Wc) of sludge cake dropped by about 10%. The results showed that the extracellular polymeric substances (EPS) were destroyed, which characterized by a significant decrease in the biopolymers' concentrations in tightly-bound EPS. Meanwhile, more rough and porous microstructures and higher zeta potentials were obtained after conditioned. Based on the changes of physicochemical properties of sludge, the variations of EPS, and the identification of reactive species, two distinct mechanisms of improved sludge dewatering were postulated. As for Cu(II) treatment, it was mainly due to the surface charge neutralization, strong cytotoxicity of Cu(I) produced by intracellular reduction of Cu(II), and pH decline caused by Cu(II) hydrolysis that improved sludge dewatering performance, which could be noted as a "non-radical pathway". When in combination with H₂O₂, hydroxyl radicals (·OH) produced by Cu(II)-catalyzed Fenton-like process played a dominant role in degrading sludge flocs and EPS, which could be regarded as a "radical pathway".

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.

Improving solid-liquid separation performance of anaerobic digestate from food waste by thermally activated persulfate oxidation

Anaerobic digestion is a promising ecofriendly technology for the management of the continuous increasing food waste (FW). However, the large amount of resulting anaerobic digestate are very difficult to be purified due to high concentration of suspended colloids. Solid-liquid separation is a pivotal step for the subsequent biological treatment of the digestate by activated sludge process. The dewaterability of digestate could directly reflect the solid-liquid separation performance. In this study, a thermally-activated persulfate (PDS) conditioning method was utilized to enhance the digestate dewaterability. Results revealed that PDS thermally conditioning significantly improved the dewaterability by decreasing digestate pH and decomposing organic substances in digestate. The decline of pH, which was resulted from PDS thermally activation reaction, facilitated filterability improvement via reducing the surface negative charges and prompting the oxidizing ability of PDS-relevant radicals. Protein, the main organic component in digestate, was most closely correlated with digestate dewaterability. Fortunately, they were also the most vulnerable constituent under the oxidation attack. PDS thermal conditioning at 80°C was proven to be the most suitable for improving the solid-liquid separation performance of anaerobic. For practical application in conditioning the anaerobic digestate from FW, the conditions should be further optimized according to the digestate characteristic.

Optimized Pretreatment of Non-Thermal Plasma for Advanced Sewage Oxidation

This study investigates how the non-thermal plasma (NTP) process leads to advanced oxidation of sewage using response surface methodology. For environmentally viable and efficient operation of the NTP process, temperature and contact time were selected as two important independent variables. Their impacts on the performance were tested following an experimental design to figure out optimal operating conditions. Based on obtained treatment efficiency, statistically optimized conditions were derived by using an approach adapting the central composite design. Results show that coupling 40 °C of temperature and 4 h of contact time demonstrate optimal performance for total chemical oxygen demand (TCOD, 59%) and total suspended solids (85%), respectively. This implies that NTP may present efficient particulate destruction leading to organic solids dissolution. Statistical analysis reveals that the contact time shows more significant dependency than the temperature on the advanced oxidation of TCOD, possibly due to dissolved organic material. For total nitrogen removal, on the contrary, the optimal efficiency was strongly related to the higher temperature (~68 °C). This work provides an inroad to considering how NTP can optimally contribute to better oxidation of multiple pollutants.

Optimisation of Fe2+/H2O2 ratio in Fenton process to increase dewaterability and solubilisation of sludge

Fenton is one of the advanced oxidation processes that can oxide organic compounds efficiently increasing the dewaterability of sludge. This study reports the optimisation of two reagents, Fe²⁺ and H₂O₂, involved in the Fenton process in order to increase sludge dewaterability and solubilisation, which were evaluated in terms of SRF, CST and DS. The study was divided into two sets of tests. First the optimal ratio Fe²⁺/H₂O₂ was set varying from 0.5-2.0. Results showed that the best Fe²⁺/H₂O₂ was equal to 0.8 corresponding to 2.1 s of CST, 2.1·10¹³ m kg^-1 of SRF and 3.1% of DS. In the second set of tests, the Fe²⁺/H₂O₂ ratio was maintained fixed to 0.8 while the concentration of reagents was decreased up to 98% in order to verify the efficiency of the process. Results showed that performing Fenton process with a concentration of H₂O₂ and Fe²⁺ of, respectively, 6000 and 5000 mg L^-1 the SRF and CST could be reduced up to 88% and 76%, respectively, and a DS equal to 3.1% could be obtained. A reduction in the Fenton reagents down to 300 and 250 mg L^-1, respectively, for H₂O₂ and Fe²⁺ showed a little decrease in efficiency of the process. However, the Fenton process could be still performed thus obtaining an economic saving.

Insight into conditioning landfill sludge with ferric chloride and a Fenton reagent: Effects on the consolidation properties and advanced dewatering

The landfill sludge in storage reservoirs needs to be dewatered and disposed of for environmental and engineering purposes. The key factors are the high organic matter content and low permeability. Chemical conditioning is considered an efficient method for adjusting the properties of sludge. In this paper, two typical chemical agents, FeCl₃ and a Fenton reagent with different additive amounts, are studied and compared for dewatering and consolidation purposes. Compression experiments and consolidation experiments are compared, and the coefficient of compressibility and compression index are obtained and compared. Then, the sludge permeability, grain size distribution variations, specific resistance to filtration (SRF) and morphology observations are considered to analyse the treatment mechanism. The results indicate that the properties of landfill sludge will change as the curing time increases. FeCl₃ and Fenton are both effective in improving the consolidation and permeability properties of sludge. For the conditioning process, the optimum FeCl₃ content is 20%, and the process is dominated by coagulation if FeCl₃ is less than 20%; otherwise, it is dominated by hydrolysis. For the Fenton reagent, the optimum Fe²⁺ content and H₂O₂ content are 4% and 12%, respectively. The depolymerization effect of the Fenton reagent leads to the oxidation and recombination of the polar group on extracellular polymeric substances (EPSs). The results can be used to explain the conditioning mechanism of the effective agents of FeCl₃ and Fenton and compare the corresponding consolidation properties. The consolidation characteristics provide a reference for further application of vacuum preloading in the sludge disposal process.

Key factor on improving secondary advanced dewatering performance of municipal dewatered sludge: Selective oxidative decomposition of polysaccharides

Advanced dewatering technologies with moisture content from nearly 80% to below 60% have attracted widespread attention in the field of municipal dewatered sludge disposal. The usage of the correct types of oxidants and the degradation of key component on the effect of secondary advanced dewatering performance is a rising focus. In this study, three types of typical oxidants (Fenton's reagent, H₂O₂, and KMnO₄) were used to pre-treat dewatered sludge directly, then advanced dewatering performance, conversion rate of bio-bound water and decomposition trend of various organic biomass were analysed. Results showed that final moisture content of Fenton's reagent group reduced to below 50% with exposure to the compression of 1000 kPa for 30 min. Different oxidants that were characterized by selective oxidizability and, compared with other oxidants, mainly decomposed proteins, lipids and humic substances, the key component of polysaccharides, which may combine with the most water were primarily decomposed by Fenton's reagent. This promoted the conversion from bio-bound water to free water and advanced dewatering performance significantly. From a morphological perspective, the ratio of dissolved polysaccharides from three layers showed Pellets: tightly bound EPS (T-EPS): loosely bound EPS (L-EPS) = 52.28%-66.56%: 8.37%-12.75%: 23.15%-39.08%, and due to the cell-breaking capacity, Fenton's reagent could mainly promote the release of intracellular polysaccharides-bound water.

Optimizing sludge dewatering with a combined conditioner of Fenton's reagent and cationic surfactant

Enhancing sludge dewatering is of importance in reducing environmental burden and disposal costs. In this work, a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), was combined with Fenton's reagent for sludge dewatering. Results show that the Fenton-CTAB conditioning significantly promotes the sludge dewatering. Using combined techniques of response surface methodology and uniform design, dosages of Fe²⁺, H₂O₂, and CTAB for water content response were optimized to be 89, 276, and 233 mg/g dry solids (DS), respectively. The water content of sludge decreased from 79.0% to 66.8% under the optimal conditions. Compared with cationic polyacrylamide, the Fenton-CTAB system exhibited superior sludge dewatering performance. To gain insights into the mechanisms involved in sludge dewatering, the effects of Fenton-CTAB conditioning on the composition of extracellular polymeric substances (EPS) and the morphology of the sludge flocs were investigated. The decomposition of EPS into some dissolved organics and the release of proteins in tightly bound EPS facilitated the conversion of bound water to free water and further reduced the water content of sludge cake. After conditioning, morphology of sludge showed aggregation. Overall, the enhanced sludge dewatering by Fenton-CTAB treatment provides an efficient way for management of sewage sludge.

A novel sewage sludge biochar and ferrate synergetic conditioning for enhancing sludge dewaterability

A great prospect of sewage sludge self-recycling as a conditioner supports the research. A synergetic conditioning effect and mechanism were reflected after the synergistic conditioning experiment, and the corresponding separated experiment of biochar, K₂FeO₄ or acid treatment on WAS. All of the biochar, K₂FeO₄ and acid treatment could reduce the water content of sludge cake. Biochar had good effect on WAS settleability, although the influence of the biochar dosage was weak. Similar to K₂FeO_4, acid treatment also could reinforce the disintegration degree effectively, but it deteriorated the filter property of WAS. In the situation of synergistic condition, owing to the strong oxidation of K₂FeO₄, most of the sludge flocs was disintegrated, thus the settleability and filter property of WAS were still bad, even the biochar worked as a skeleton builder. It is encouraging to find that, even without acid treatment, there is a great decline of water content of sludge cake in the situation of synergistic condition.

Investigating the photo-Fenton process for treating soil washing wastewater

PURPOSE

Petroleum hydrocarbons have created numerous problems for water resources. The main objective of this study was focused on the application of advanced oxidation processes (AOPs) in treatment of effluent of petroleum contaminated soil washing operation.

METHODS

The AOP process in the present study was run with Fe²⁺/H₂O₂ (Fenton's reagent), Fe²⁺/H₂O₂/UV (photo-Fenton's reagent) and UV lamp (medium pressure mercury lamp, 400 W) in the batch-mode reactor at laboratory-scale.

RESULTS

Various parameters and optimized values which could maximize the removal efficiency of COD were: Fe²⁺ = 0.1 g/L, H₂O₂ = 1 g/L, pH = 3 and irradiation time of 120 min. Under the optimal conditions, the removal efficiency of COD and TOC were achieved 86.3% and 68% respectively. The results showed that the reaction of the oxidation of diesel fuel by Fenton and photo-Fenton systems followed second-order kinetic model with reaction rate constants (k) of 7 × 10^-6 and 3 × 10^-6 l/mg min^-1 respectively.

CONCLUSIONS

The photo-Fenton process can be used as an effective and environmental friendly method in the degradation of petroleum organic compounds.

Valorization of alum sludge via a pyrolysis platform using CO2 as reactive gas medium

In an effort to seek a new technical platform for disposal of drinking water treatment sludge (DWTS: alum sludge), pyrolysis of DWTS was mainly investigated in this study. To establish a more sustainable thermolytic platform for DWTS, this study particularly employed CO₂ as reactive gas medium. Thus, this study laid great emphasis on elucidating the mechanistic roles of CO₂ during the thermolysis of DWTS. A series of the TGA tests of DWTS in CO₂ in reference to N₂ revealed no occurrence of the heterogeneous reaction between CO₂ and the sample surface of DWTS. As such, at the temperature regime before initiating the Boudouard reaction (i.e., ≥700 °C), the mass decay patterns of DWTS in N₂ and CO₂ were nearly identical. However, the gaseous effluents from lab-scale pyrolysis of DWTS in CO₂ in reference to N₂ were different. In sum, the homogeneous reactions between CO₂ and volatile matters (VMs) evolved from the thermolysis of DWTS led to the enhanced generation of CO. Also, CO₂ suppressed dehydrogenation of VMs. Such the genuine mechanistic roles of CO₂ in the thermolysis of DWTS subsequently led to the compositional modifications of the chemical species in pyrolytic oil. Furthermore, the biochar composite was obtained as byproduct of pyrolysis of DWTS. Considering that the high content of Al₂O₃ and Fe-species in the biochar composite imparts a strong affinity for As(V), the practical use of the biochar composite as a sorptive material for arsenic (V) was evaluated at the fundamental levels. This work reported that adsorption of As(V) onto the biochar composite followed the pseudo-second order model and the Freundlich isotherm model.

The Effects of Aluminium- and Ferric-Based Chemical Phosphorus Removal on Activated Sludge Digestibility and Dewaterability

The uses of Al3+ and Fe3+ salts in chemical phosphorus removal (CPR) in activated sludge plants have increased considerably in recent years and their full impacts on downstream processes such as dewaterability and digestibility are not fully understood. In this research, the effects of CPR on sludge digestibility and dewaterability were investigated in laboratory-scale experiments using sludge samples from a full-scale wastewater treatment plant. The results of the digestibility tests showed a 21% and 36% reduction in the biogas volume generated during anaerobic digestion of surplus activated sludge at 0.1 g/L doses of Al3+ and Fe3+ salts, respectively. This demonstrates that Al3+ dosing for CPR has less of a reduction effect compared with Fe3+ salts on biogas generation during anaerobic digestion of sludge. The dewaterability tests showed that primary sludge dewaterability was improved by up to 25% by Fe3+ and 16% by Al3+, while that of surplus activated sludge was reduced by 64% and 73%, respectively, at a metal salt dose of 50 mg/L. Consequently, a pre-precipitation process during CPR where phosphorus is removed in the primary tank would, therefore, enhance sludge dewaterability.

Unraveling oxidation behaviors for intracellular and extracellular from different oxidants (HOCl vs. H2O2) catalyzed by ferrous iron in waste activated sludge dewatering

Cell lysis in sludge pretreatment by advanced oxidation process (AOP) has a great effect on sludge dewaterability. Cell lysis caused by reactive radicals (e.g. hydroxyl radical) was dependent on the reaction site of AOP. However, little is known about the accurate radical generation site of AOP in sludge pretreatment. In this study, two kinds of oxidation behaviors from different oxidants (HOCl vs. H₂O₂) catalyzed by ferrous iron were comparatively investigated. Higher amount of living cells (84.3%) and hydroxyl radicals (9.86 × 10^-5 M), and more fragmentized sludge flocs (particle sizes of D50 was 50.1 vs. 57.3 μm of RS) were detected in sludge conditioned by Fe²⁺/H₂O₂, which implied that Fenton reaction mainly happened at surface and outside of sludge flocs (such as EPS layer and liquid phase). Thus, it could be regarded as "extracellular oxidation". Fewer living cells (undetectable), fewer amount of hydroxyl radicals (undetectable in sludge), and more integrated sludge flocs (particle size of D50 was 56.1 vs. 57.3 μm of RS) were determined in sludge conditioned by Fe²⁺/Ca(ClO)₂. Hence, it could be regarded as "Intracellular oxidation". In addition, sludge pretreatment based on Fe²⁺/Ca(ClO)₂ could achieve simultaneous deep-dewatering performance and total coliforms inactivation. Based on response surface methodology, the optimal dosages of Fe²⁺ and Ca(ClO)₂ were proposed as 106.1 and 234.5 mg/g volatile solids respectively, without any acidification of sludge. Under these optimal dosages, the water content of dewatered sludge cake was 51.9 ± 0.1 wt% and the pH of the final filtrate was 5.8 ± 0.2. Total coliforms of sludge could be inactivated in 10 s after Fe²⁺/Ca(ClO)₂ addition.

Employing Electrochemical-Fenton process for conditioning and dewatering of anaerobically digested sludge: A novel approach

In this study, for the first time, the occurrence mechanism of anaerobically digested sludge conditioning for dewatering process based on Electrochemical-Fenton technology was investigated and the optimum condition has been determined to employ a lab-scale reactor. Due to the results of current studies using electrochemical and Fenton methods, a comparative economic-technical investigation has been provided accordingly. The results showed that under optimum operational condition by utilizing Electrochemical-Fenton process e.g. H₂O₂ = 25 mg/g DS (dry solid), Fe²⁺ = 15 mg/g DS, retention time = 20 min, electrolysis voltage = 11 V, the specific resistance to filterability (SRF) and time to filter (TTF) parameters reduction equal to 93.8% and 75.9% respectively. The occurrence mechanism of the sludge conditioning was determined by evaluation of extracellular polymeric substances (EPS), particle size distribution, zeta potential and bound water tests. The dry solids concentration of the conditioned sludge by Electrochemical-Fenton process was increased from 2.3% to 41% by dewatering employing filter press system. Furthermore, the estimated cost of conditioning using this method is 41.82 USD$/t DS, which is less than other investigated methods e.g. traditional Fenton process. It can be concluded that the results reached in this comprehensive and comparative study could be a suitable basis for further investigations regarding utilization of novel electrochemical advanced oxidation technologies for efficient sludge conditioning and dewatering purposes.

Pretreatment technologies for industrial effluents: Critical review on bioenergy production and environmental concerns

The implementation of different pretreatment techniques and technologies prior to effluent discharge is a direct result of the inefficiency of several existing wastewater treatment methods. A majority of the industrial sectors have known to cause severe negative effects on the environment. The five major polluting industries are the paper and pulp mills, coal manufacturing facilities, petrochemical, textile and the pharmaceutical sectors. Pretreatment methods have been widely used in order to lower the toxicity levels of effluents and comply with environmental standards. In this review, the possible environmental benefits and concerns of adopting different pretreatment technologies for renewable energy production and product/resource recovery has been reviewed and discussed.

Combined zero valent iron and hydrogen peroxide conditioning significantly enhances the dewaterability of anaerobic digestate

The importance of enhancing sludge dewaterability is increasing due to the considerable impact of excess sludge volume on disposal costs and on overall sludge management. This study presents an innovative approach to enhance dewaterability of anaerobic digestate (AD) harvested from a wastewater treatment plant. The combination of zero valent iron (ZVI, 0-4.0g/g total solids (TS)) and hydrogen peroxide (HP, 0-90mg/g TS) under pH3.0 significantly enhanced the AD dewaterability. The largest enhancement of AD dewaterability was achieved at 18mg HP/g TS and 2.0g ZVI/g TS, with the capillary suction time reduced by up to 90%. Economic analysis suggested that the proposed HP and ZVI treatment has more economic benefits in comparison with the classical Fenton reaction process. The destruction of extracellular polymeric substances and cells as well as the decrease of particle size were supposed to contribute to the enhanced AD dewaterability by HP+ZVI conditioning.

Dewatering of drilling sludge by ultrasound assisted Fe(ii)-activated persulfate oxidation

An ultrasound assisted Fe(ii)-activated persulfate oxidation method was put forward to improve the dewaterability of drilling sludge in this research. The water content in the filter cake and specific resistance to filtration (SRF) were measured to evaluate the sludge dewaterability. Volatile suspended solids (VSS), transmittance of supernatant, microstructure, particle size distribution and zeta potential were tested to justify the proposed mechanism. The results showed that appropriate ultrasound assisted Fe(ii)-activated persulfate oxidation could not only further enhance the sludge dewaterability but also reduce the reaction time as well. The optimal conditions for this method were 1.6% sodium persulfate, 0.8% ferrous sulfate, 40 W ultrasonic power and 45 min reaction time. Reduction of VSS and an increase of transmittance were further achieved compared to oxidation alone. SEM results and the decrease of particle size after the treatment confirmed the disintegration of sludge flocs, which promoted the release of bound water. A synergistic effect mechanism of ultrasound and chemical oxidation was proposed, with ultrasonic cavitation disintegrating the flocs, exposing the interior organics and persulfate further oxidizing the released organics.

An ultrasound assisted Fe(ii)-activated persulfate oxidation method was put forward to improve the dewaterability of drilling sludge in this research.

Improved sludge dewaterability and hydrolysis performance after pretreatment with Fenton's reagent

The dewaterability of excess sludge significantly improved upon pretreatment with Fenton's reagent in this study. After 0.9 g/L of Fe²⁺ and 5.0 g/L of H₂O₂ were added to the sludge, and reacted for 2 h at pH = 4, the specific resistance to filtration (SRF) of the excess sludge decreased from an initial value of 29.74 × 10¹² m/kg to 6.49 × 10¹² m/kg. The factors that affected this improvement in sludge dewaterability as evaluated by SRF reduction showed the following order: H₂O₂ > pH > Fe²⁺ > reaction time. Furthermore, the hydrolysis performance of the sludge under the optimal reaction conditions was investigated. The results indicated that the concentration of soluble chemical oxygen demand in the supernatant increased almost 14 times compared to raw sludge, and the contents of soluble protein and soluble polysaccharide were more than 8 and 17 times higher, respectively, than for the untreated situation. However, the amounts of ammonia nitrogen (NH₄⁺-N) and phosphate (PO₄^3--P) released from the sludge showed different trends: NH₄⁺-N increased by 200%, while PO₄^3--P decreased by 82%. The production of volatile fatty acids (VFAs) from the treated sludge showed that total VFAs increased by 66%, and iso-butylacetic acid was the dominant product among the total VFAs.

A comparatively optimization of dosages of oxidation agents based on volatile solids and dry solids content in dewatering of sewage sludge

Organic content of sludge is a major factor influencing its dewaterability. Conditioning sewage sludge with oxidation reagents (Fenton's reagent or Fe²⁺/persulfate) can effectively improve sludge dewaterability. In traditional conditioning process of sewage sludge, the optimization of conditioner dosage were commonly based on volume of sludge (referred as mg/L) or mass of dry solid (DS) of sludge (referred as mg/g DS). However, inconsistency of the oxidation dose mode existed for different sewage sludge sources. In this study, sludge samples of different volatile solids (VS) contents were used to derive optimal dosages of Fenton's reagent and Fe²⁺/persulfate, using the response surface methodology (RSM). For the case of Fenton's reagent, the optimal dosages of Fe²⁺ and H₂O₂ were 107-110 mg/g VS and 86-88 mg/g VS, respectively. For Fe²⁺/persulfate, the optimal dosages of Fe²⁺ and persulfate were 49 mg/g VS and 269-271 mg/g VS, respectively. The optimal dosages of the oxidation reagents based on VS contents were proved to be consistent and effective for different sewage sludge with different organic matter contents from different wastewater treatment plants (WWTPs). In contrast, the optimal dosages of oxidation reagents, based on DS, fluctuated significantly for different sludge sources. Furthermore, sewage sludge dewaterability was significantly related to the degradation and the content of loosely bound extracellular polymeric substances (LB-EPS) in the organic matters of conditioned sludge (R² > 0.9, p < 0.01). Thus, the improvement of sludge dewaterability could be related with the destruction of the VS in sludge with the conditioners of oxidant reagent. It indicated that optimization of oxidation reagent based on VS content is more plausible than that of based on DS content for different sewage sludge with different organic matter contents.

Changing profiles of bound water content and distribution in the activated sludge treatment by NaCl addition and pH modification

Currently the dewatering of activated sludge from wastewater treatment plants is a problem not well solved. Extracellular polymeric substances (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), are highly hydrated biopolymers and play important roles in sludge dewatering. In the present work, two types of treatments, i.e., salt addition and pH modification, were proposed to evaluate the effects of bound water content and its distribution on the dewatering performance of activated sludge. Results show that the bound water content in activated sludge was deeply related to the floc structures and EPS compositions. Both salt addition and acid treatment altered the flocculated matrix and increased the contents of LB-EPS, resulting in the release of trapped water and reduction in sludge volume. In addition, the chemical treatments also affected the distribution of bound water. The internal water content increased upon the dose of NaCl, leading to a decreased water content trapped in EPS. Hence, salt addition caused a slower filtration rate, but did not effectively decrease the total water content, although the EPS were decomposed. Under acidic conditions, cell lysis helped to release the intracellular water and further enhance the sludge dewatering performance. In contrast, conditioning with low-dosage alkali increased the bound water content and deteriorated the sludge dewaterability. Therefore, an in-depth investigation into the mechanisms is useful to optimize the activated sludge dewatering process.

Enhancing dewaterability of waste activated sludge by combined oxidative conditioning process with zero-valent iron and peroxymonosulfate

The enhancement of sludge dewaterability is of great importance for facilitating the sludge disposal during the operation of wastewater treatment plants. In this study, a novel oxidative conditioning approach was applied to enhance the dewaterability of waste activated sludge by the combination of zero-valent iron (ZVI) and peroxymonosulfate (PMS). It was found that the dewaterability of sludge was significantly improved after the addition of ZVI (0-4 g/g TSS) (TSS: total suspended solids) and PMS (0-1 g/g TSS). The optimal addition amount of ZVI and PMS was 0.25 g/g TSS and 0.1 g/g TSS, respectively, under which the capillary suction time of the sludge was reduced by approximately 50%. The decomposition of sludge flocs could contribute to the improved sludge dewaterability. Economic analysis demonstrated that the proposed conditioning process with ZVI and PMS was more economical than the ZVI + peroxydisulfate and the traditional Fenton conditioning processes.

Exploring the potential of iTRAQ proteomics for tracking the transformation of extracellular proteins from enzyme-disintegrated waste activated sludge

To characterize the transformation of extracellular proteins extracted from raw and enzyme-disintegrated waste activated sludge (WAS), extracts of extracellular polymeric substances (EPS) were subject to isobaric tags for relative and absolute quantitation (iTRAQ) proteomics analysis. 209 proteins were identified and categorized into three Gene Ontology classifications: "cellular components", "molecular function", and "biological processes". Most identified proteins originated from intracellular components, organelles, or cytoplasm, suggesting that cell decline and lysis represent the main sources of extracellular proteins in WAS. The major protein functions comprised "transporter binding activity", "macromolecule metabolic process", and "biosynthesis enzyme catalytic activity". In total, 15 proteins categorized as "membrane part" and "biological adhesion" and 10 as "organelle" were down- or up-regulated, respectively, implying that the enzyme-disintegration mainly induced WAS floc-structure disintegration via membrane structure and corresponding biological adhesion disruption. The proteomics study will provide valuable clues to better understand EPS changes associated with enzymatic treatment at molecular levels.

Mechanism and Parameter Optimization of Fenton's Reagent Integrated with Surfactant Pretreatment to Improve Sludge Dewaterability

Sludge dewatering can effectively reduce the volume and mass of sludge for subsequent treatment and disposal. The work validated the potential of Fenton's reagent combined with dodecyl dimethyl benzyl ammonium chloride (DDBAC) in improving sludge dewaterability and proposed the mechanism of joint conditioning. The composite conditioner dosage was optimized using response surface methodology. Results indicated the good conditioning capability of the composite conditioners. The optimum dosages for H2O2, Fe2+, and DDBAC were 44.6, 39.6, and 71.0 mg/g, respectively, at which a sludge cake water content of 59.67% could be achieved. Moreover, a second-order polynomial equation was developed to describe the behavior of joint conditioning. Analysis of the reaction mechanism showed that Fenton oxidation effectively decomposed extracellular polymeric substance (EPS), including loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS), into dissolved organics, such as proteins and polysaccharides. The process facilitated the conversion of the bound water into free water. Furthermore, DDBAC further released the bound water through solubilization of TB-EPS and LB-EPS after the Fenton reaction. The bound water content of the sludge conditioned with Fenton's reagent decreased from 3.15 to 1.36 g/g and further decreased to 1.08 g/g with the addition of DDBAC. High-performance liquid chromatography analysis verified that the composite conditioning could oxidize and hydrolyze EPS into low-molecular-mass organics (e.g., formic and acetic acid), thereby facilitating the release of bound water.

Novel insights into enhanced dewatering of waste activated sludge based on the durable and efficacious radical generating

This study aims to develop a high-efficiency radical oxidation process for enhancing the dewaterability of waste activated sludge (WAS). Radical scavenging studies combined with electron paramagnetic resonance (EPR) were carried out for the direct radical identification and effectiveness evaluation of radical oxidation. The results indicated that Fe(II)-activated CaO₂ can pose a superior effect on dewatering WAS due to its distinctive capacity of stable •OH production and the high reaction efficiency of regulated-released •OH with water-holding organics. The mechanism for the enhanced dewatering performance was also explored. The rupture of sludge colloidal flocs and the reduction of hydrophilic functional groups in loosely bound extracellular polymeric substances (LB-EPS) were found to be mainly responsible for the release of interstitial water and improved dewaterability, respectively. In addition, an inference about the relationship between interfacial water and zeta potential of different EPS fractions was established by the simultaneous measurement of the binding affinities of Ca²⁺ and Fe²⁺/Fe³⁺ for EPS and bound water content. All these results provide the direct evidence that Fe(II)-activated CaO₂ is a promising pretreatment reagent for sludge disposal.

IMPLICATIONS

Fe(II)-activated CaO₂ was first proposed to be highly effective in enhancing the dewaterability of waste activated sludge. Electron paramagnetic resonance (EPR) spectroscopy provided the direct evidence for the specific advantages of CaO₂, especially the capacity of durable and efficacious •OH production leading to the excellent conditioning performance.

Treatment of laundrette wastewater using Starbon and Fenton's reagent

The use of grey water for a variety of purposes is gaining increased popularity as a means of preserving scarce freshwater resources. In this work, catalytic oxidation over Fenton's reagent and adsorption techniques using Starbon (mesoporous material derived from polysaccharides) has been applied. These novel techniques are used as an alternative to already studied treatments of grey water such as filtration and/or biological processes. In this study, grey water, collected from a commercial laundrette, has been used. Treatment efficiency was determined by changes in the chemical oxygen demand (COD) of the grey water. Experiments using Fenton's reagent at optimum conditions of Fe(3+) = 40 mg L(-1); H2O2 = 400 mg L(-1) and pH 3 were very successful, resulting in a 95% COD removal after 15 min. Treatment with Starbon adsorption was also effective, reaching up to 81% COD removal at pH 3 within 1 h. The combined treatment with Fenton's reagent and Starbon resulted in a 93% COD removal at a significantly reduced concentration of Fenton's reagent compared to the treatment with solo Fenton's reagent. This lower chemical dose has the advantage of reducing costs and lowering sludge generation.

Roles of iron species and pH optimization on sewage sludge conditioning with Fenton's reagent and lime

Conditioning sewage sludge with Fenton's reagent could effectively improve its dewaterability. However, drawbacks of conditioning with Fenton's reagent are requirement of acidic conditions to prevent iron precipitation and subsequent neutralization with alkaline additive to obtain the pH of the filtrate close to neutrality. In this study, roles of pH were thoroughly investigated in the acidification pretreatment, Fenton reaction, and the final filtrate after conditioning. Through the response surface methodology (RSM), the optimal dosages of H2SO4, Fe(2+), H2O2, and lime acted as a neutralizer were found to be 0 (no acidification), 47.9, 34.3 and 43.2 mg/g DS (dry solids). With those optimal doses, water content of the dewatered sludge cakes could be reduced to 55.8 ± 0.6 wt%, and pH of the final filtrate was 6.6 ± 0.2. Fenton conditioning without initial acidification can simplify the conditioning process and reduce the usage of lime. The Fe(3+) content in the sludge cakes showed a close correlation with the dewaterability of conditioned sludge, i.e., the water content of sludge cakes, SRF (specific resistance to filtration), CST (capillary suction time), bound water content, and specific surface area. It indicated that the coagulation by Fe(3+) species in Fenton reaction could play an important role, compared to traditional Fenton oxidation effect on sludge conditioning. Thus, a two-step mechanism of Fenton oxidation and Fe(III) coagulation was proposed in sewage sludge conditioning. The mechanisms include the following: (1) extracellular polymeric substances (EPS) were firstly degraded into dissolved organics by Fenton oxidation; (2) bound water was converted to free water due to degradation of EPS; (3) the sludge particles were disintegrated into small ones by oxidation; (4) Fe(3+) generated from Fenton reaction acted as a coagulant to agglomerate smaller sludge particles into larger dense particles with less bond water; (5) finally, the dewatered sludge cakes were obtained, with less small pores (1-10 nm) that contributed to water affinity, but with more large pores (>10 nm) that contributed to a permeable, rigid lattice structure. Morphology of the Fenton-conditioned sludge cake exhibited a porous structure. The estimated cost of the composite conditioner, Fenton's reagent and lime, is USD$ 43.8/t DS, which is less than that of ferric chloride and lime (USD$ 54/t DS). Furthermore, pH of the final filtrate using this composite conditioner is about 6.6. Comparatively, that using ferric chloride and lime is as high as 12.4.

Aluminum chloride induces neuroinflammation, loss of neuronal dendritic spine and cognition impairment in developing rat

Aluminum (Al) is present in the daily life of humans, and the incidence of Al contamination increased in recent years. Long-term excessive Al intake induces neuroinflammation and cognition impairment. Neuroinflammation alter density of dendritic spine, which, in turn, influence cognition function. However, it is unknown whether increased neuroinflammation is associated with altered density of dendritic spine in Al-treated rats. In the present study, AlCl3 was orally administrated to rat at 50, 150 and 450 mg/kg for 90d. We examined the effects of AlCl3 on the cognition function, density of dendritic spine in hippocampus of CA1 and DG region and the mRNA levels of IL-1β, IL-6, TNF-α, MHC II, CX3CL1 and BNDF in developing rat. These results showed exposure to AlCl3 lead to increased mRNA levels of IL-1β, IL-6, TNF-α and MCH II, decreased mRNA levels of CX3CL1 and BDNF, decreased density of dendritic spine and impaired learning and memory in developing rat. Our results suggest AlCl3 can induce neuroinflammation that may result in loss of spine, and thereby leads to learning and memory deficits.

Dewaterability of five sewage sludges in Guangzhou conditioned with Fenton's reagent/lime and pilot-scale experiments using ultrahigh pressure filtration system

Sludge conditioning with Fenton's reagent and lime is a valid method for sludge dewatering. This study investigated the influence of different organic matter content sludge on sludge dewatering and discussed the main mechanism of sludge conditioning by combined Fenton's reagent and lime. The results indicated that the specific resistance to filterability (SRF) of sludge was reduced efficiently by approximately 90%, when conditioned with Fenton's reagent and lime. Through single factor experiments, the optimal conditioning combinations were found. In addition, the relationship between VSS% and consumption of the reagents was detected. Furthermore, it was also demonstrated that the SRF and filtrate TOC values had a significant correlation with VSS% of sludge (including raw and conditioned). The main mechanism of sludge dewatering was also investigated. Firstly, it revealed that the dewaterability of sludge was closely correlated to extracellular polymeric substances (EPS) and bound water contents. Secondly, the results of scanning electron microscopy (SEM) stated that sludge particles were to be smaller and thinner after conditioning. And this structure could easily form outflow channels for releasing free water. Additionally, with the ultrahigh pressure filtration system, the water content of sludge cake conditioned with Fenton's reagent and lime could be reduced to below 50%. Moreover, the economic assessment shows that Fenton's reagent and lime combined with ultrahigh pressure filtration system can be an economical and viable technology for sewage sludge dewatering. Finally, three types of sludge were classified: (1) Fast to dewater; (2) Moderately fast to dewater; (3) Slow to dewater sludge.

Enhanced dewaterability of textile dyeing sludge using micro-electrolysis pretreatment

The effects of micro-electrolysis treatment on textile dyeing sludge dewatering and its mechanisms were investigated in this study. Capillary suction time (CST) and settling velocity (SV) were used to evaluate sludge dewaterability. Extracellular polymeric substances (EPS) concentration and sludge disintegration degree (DDSCOD) were determined to explain the observed changes in sludge dewaterability. The results demonstrated that the micro-electrolysis could significantly improve sludge dewaterability by disrupting the sludge floc structure. The optimal conditions of sludge dewatering were the reaction time of 20 min, initial pH of 2.5, Fe/C mass ratio of 1/1, and the iron powder dosage of 2.50 g/L, which achieved good CST (from 34.1 to 27.8 s) and SV (from 75 to 60%) reduction efficiency. In addition, the scanning electron microscope (SEM) images revealed that the treated sludge floc clusters are broken up and that the dispersion degree is better than that of a raw sludge sample. The optimal EPS concentration and DDSCOD to obtain maximum sludge dewaterability was 43-46 mg/L and 4.2-4.9%, respectively. The destruction of EPS was one of the primary reasons for the improvement of sludge dewaterability during micro-electrolysis treatment.