Sludge Dewatering Research Articles

Sludge dewaterability improvement in microbial fuel cell powered electro-Fenton system (MFCⓅEFs) coupled with chitosan quaternary ammonium salt

As improved and expanded wastewater treatment facilities, sludge dewatering is the essential process and major challenge due to the complex and abundant organic matter. Microbial fuel cell powered electro-Fenton system (MFCⓅEFs) has been demonstrated to generate •OH and destroy hydrophilic extracellular polymeric substances (EPS) as an improved method of high efficiency and low energy consumption. Nevertheless, the smaller particle size of the treated sludge and the release of partial organic matter into the supernatant can affect the sludge-water separation process. Chitosan quaternary ammonium salt (CQAS) as a renewable and biodegradability cationic coagulant can be involved in the follow-up treatment. The sludge after combined treatment exhibited better dewaterability, where the water content of sludge cake (WCSC), capillary suction time (CST), and specific resistance filtration (SRF) were 61.21%, 15.6 s, and 1.02×1012 m/kg (26.47%, 80.72% and 84.28% reduction), respectively. The oxidation of the MFCⓅEFs destroyed the cellular and EPS structure and the bridging flocculation and charge neutralization of CQAS caused the fine particles to squeeze each other. The combined treatment fully reduced the content of negative charge and hydrophilic substances on the surface, which affected the intensity change of N-H bond and altered the protein secondary structure to make it looser, thus releasing more bound water while improving aggregation characteristics. Overall, combined treatment can significantly improve sludge dewaterability and owns operational advantages of high efficiency, low energy and consumption, safety, and non-toxicity.

A pilot-scale evaluation of residual sludge quality in a worm-sludge treatment reed bed in the Mediterranean region

A pilot-scale study on sludge treatment reed beds investigated the combined effects of earthworms and Arundo donax on sewage sludge dewatering and residual sludge quality. Four units were tested: one planted with earthworms, one planted without earthworms, one unplanted with earthworms, and one control, each unit replicated. Over a year, 24 cycles of sludge (dry and volatile solid contents of 24.71 g.L−1, and 19.14 g.L−1) were fed onto the units at a sludge loading rate: 43.59 kg.DS.m−2.year−1. Afterward, the units experienced 132 days of resting period, increasing dry solids from 21 to 70 % and decreasing volatile solids from 81 to 69 % on average (40 % sludge volume reduction). The bottom layers of the planted unit with earthworms showed a 30 % reduction in volatile solids, indicating improved sludge stabilization. Macronutrient abundance in the residual sludge followed the sequence N > Ca > P > K > S > Mg. The planted unit with earthworms reduced micronutrient concentrations by 22 % compared to the control unit (Fe > Na > Mn > B > Mo). Earthworms also played a key role in reducing heavy metal concentrations by 11 % compared to the planted unit without earthworms (Zn > Cr > Pb > Ni > Cd). Heavy metal levels in the residual sludge met EU and Portugal standards, with a 99.9 % reduction in Escherichia coli and fecal coliforms. Cost estimation showed centrifugation and W-STRB scenarios cost 167 and 183 €.PE−1 for a ten-year operation, with O&M costs of 7 and 3 €.PE−1.year−1, respectively.

Persistence evaluation of fecal pollution indicators in dewatered sludge and dewatering filtrate of municipal sewage sludge: The impacts of ambient temperature and conditioning treatments

Sludge resource utilization is one of the important routines for transmitting fecal pollution to water and soil, and sludge dewatering is a crucial step for sludge resource utilization. However, it remains unclear the decay characteristics and persistence of fecal pollution indicators after sludge dewatering. In this study, the persistence of six fecal pollution indicators, namely E. coli (EC), human-specific HF183 Bacteroides (HF183), human adenovirus (HAdV), human JC and BK polyomavirus (JCPyV and BKPyV), and crAssphage, in dewatered sludge cake and dewatering filtrate deriving from raw sewage sludge, as well as three types of sludge conditioned with polyacrylamide (PAM), Fenton's reagent, or Fe[III] and CaO were analyzed. The quantitative polymerase chain reaction (qPCR) and viability-qPCR methods were used to analyze the variation in abundances and infectivity of fecal pollution indicators in dewatered sludge cake or dewatering filtrate over the storage time, respectively. Decay predications of fecal pollution indicators over time were modeled using either the first-order or the biphasic decay model. The qPCR results revealed that fecal pollution indicators in dewatered sludge cake persisted longer than those in dewatering filtrate at the same temperature. Increasing temperature can accelerate the decay of fecal pollution indicators in both dewatered sludge cake and dewatering filtrate. Notably, sludge conditioning treatment may prolong the persistence of fecal pollution indicators in both dewatered sludge cake and dewatering filtrate. Viability-qPCR results indicated that the fecal pollution indicators (except HAdV) in dewatered sludge cakes deriving from both raw sewage sludge and conditioned sludges remained infectious for up to 30 days. After a storage period of 40 days, the abundances of fecal pollution indicators (except for EC) in sludge conditioned with Fenton's reagent were effectively decreased and meanwhile the infectivity of EC was reduced, exhibiting the lowest levels of fecal pollution. Therefore, both ambient temperature and conditioning treatment greatly impacted the decay characteristics and persistence of fecal pollution indicators in dewatered sludge cake and dewatering filtrate, and selecting suitable conditioning method can minimize environmental risks associated with fecal pollution in sewage sludge.

Plant-Based Flocculants as Sustainable Conditioners for Enhanced Sewage Sludge Dewatering

With the aim to establish clean and sustainable sludge treatment, green conditioning using natural flocculants has recently gained a growing interest. In this study, a variety of plant materials, namely Moringa (Moringa oleifera) seeds, Fenugreek (Trigonella foenum-graecum) seeds, Potato (Solanum tuberosum) peels, Aloe (Aloe vera) leaves, Cactus (Opuntia ficus indica) cladodes, and Phragmites (Phragmites australis) stems, were evaluated for their potential bioflocculant activity in conditioning sewage sludge. They were thoroughly characterized to determine their active flocculating compounds. Sludge dewaterability was evaluated by assessing various sludge parameters, including specific resistance to filtration (SRF), dryness of filtration cake (DC), and total suspended solid removal (TSS) from sludge filtrate. The collected results from various physicochemical characterizations of plant materials suggest that the main flocculating agents are carbohydrates in Cactus and Fenugreek and proteins in Moringa, Potato, and Phragmites. Additionally, all tested plant-based flocculants demonstrated effective dewatering performance. Interestingly, compared to the chemical flocculant polyaluminum chloride, Moringa and Cactus showed superior conditioning effects, yielding the lowest SRF values and the highest DC. As a result, the use of these natural flocculants improved sewage sludge filterability, leading to a significant removal of total suspended solids from the filtrate. The conditioning properties of Moringa and Cactus can be attributed to their high protein and sugar content, which facilitates the effective separation of bound water from solids through charge neutralization and bridging mechanisms. Thus, green conditioning using plant-based flocculants, particularly Moringa and Cactus materials, presents a promising and eco-friendly approach to enhance sewage sludge dewatering for safer disposal and valorization.

Sludge carbon quantum dots-activated peroxymonosulfate oxidation for sludge conditioning

Large amounts of waste activated sludge (WAS) are produced from biological treatment processes in wastewater treatment plants, and its effective disposal and reutilization are considered to be inevitable challenges in the world. In this work, carbon quantum dots derived from WAS (SCQDs) were successfully synthesized via hydrothermal method, which had a significant photoluminescence effect, excellent water solubility, and graphite structures with main elements of C, N, and O. Subsequently, its potential for peroxymonosulfate (PMS) activation under visible light for WAS conditioning was investigated. The results showed that SCQDs-activated PMS (SCQDs-PMS) system could effectively improve sludge dewaterability. Under experimental conditions, capillary suction time reduction and water content of sludge cake after conditioning were 81.2% and 72.6%, respectively. Reactive oxygen species including SO4·-, ·OH, and 1O2 produced in SCQDs-PMS system could effectively degrade extracellular polymeric substances (EPS) (especially tyrosine-like and tryptophan-like substances in tightly bound-EPS), inactivate microbial cells, and destruct α-helix structure of protein molecule, which resulted in the desirable release of EPS-bound water, consequently improving sludge dewaterability. This result was well supported by the variations in the transverse relaxation time of protons at low field nuclear magnetic resonance. Thus, this work explored a potential pathway of reutilizing sludge and a new activator for PMS activation. However, it should be noticeable that this work was the first attempt using SCQDs-PMS system for sludge conditioning, the future studies about system optimization and its wider application scenarios should be further investigated.

Correlation between sewage sludge pore structure evolution and water filtration performance: Effect of thermal hydrolysis with or without carbonaceous skeleton-assisted

Municipal sewage sludge contains a high water content and strong hydrophilicity, making mechanical dewatering a critical step in sludge treatment and disposal. To clarify the collapse of filtration channels within the sludge cake under high pressure and to develop more precise targeted conditioning methods, this study focused on the direct correlation between pore structure evolution and sludge dewatering performance. A self-designed online system was used to compare the dewatering processes of raw sludge, thermal hydrolyzed (TH) sludge, and carbonaceous skeleton-assisted thermal hydrolyzed (CSkel-TH) sludge. In-depth analysis was conducted on the structure scanning data of the filter cake at different time intervals and the corresponding filtrate mass data. The results showed that during the press filtration process, the raw sludge gradually transformed into a filter cake, with larger pores trapping the water. In the upper and bottom layers, regions with a porosity higher than 10 % appeared, forming a “water-locking layer” even with continued pressure, it became impossible to remove additional water. After separate hydrolysis, the porosity and pore connectivity of the sludge decreased, and the thickness of the “water-locking layer” increased as press filtration progressed, inhibiting water discharge and making cake formation difficult. Following CSkel-TH treatment, the number of pores with diameters ranging from tens to over a hundred micrometers increased, and the connectivity between pores was enhanced. In this case, the channels formed by interconnected small pores continuously transported the water trapped in the large pores outward, facilitating water discharge. This work provided a basis for further targeted regulation of pore structures to enhance the effectiveness of high-pressure dewatering of sludge.

Effect of conditioners used for sludge dewatering on the adsorption performance of sludge-derived adsorbent

Converting waste activated sludge into adsorbent is a promising alternative for sludge valorization. While various conditioners are widely employed in sludge conditioning and dewatering processes, the influence of these conditioners on the properties of sludge derived adsorbents remains largely unexplored. Four conditioners, including FeCl3, CaO, polyacrylamide, FeSO4·7 H2O/Na2S2O8, were used for sludge conditioning, and the sludge dewaterability and the adsorption performance of the resultant adsorbents were evaluated. The sludge dewaterability was markedly improved by the conditioners in a descending order as polyacrylamide, FeCl3, FeSO4·7 H2O/Na2S2O8, and CaO. The type of conditioner highly influenced the adsorption ability of the sludge adsorbent: FeSO4·7 H2O/Na2S2O8 enhanced the adsorption ability, while others deteriorated it. Infrared spectra, pore size distribution, and micromorphology analysis of the adsorbents suggest that: FeCl3 reduced mesopores through strong electrostatic interactions; CaO acted as a physical barrier for adsorption; polyacrylamide reduced the adsorbent surface area through hydrogen bond-driven bridging and potentially forming polymeric barrier; FeSO4·7 H2O/Na2S2O8 disrupted the sludge flocs and exposed abundant adsorption sites, promoting the adsorbent performance markedly. FeSO4·7 H2O/Na2S2O8 conditioning was thus beneficial to both sludge dewatering and adsorption. Adsorption of methylene blue by FeSO4·7 H2O/Na2S2O8-conditioned sludge adsorbent was best described by the pseudo-second-order model and Langmuir model, indicating the dominance of monolayer chemisorption. The adsorption mainly occurred in the mesopores of the adsorbent, with hydroxyl group and carbonyl in carboxyl group as the main binding sites. Both film and pore diffusion contributed to the adsorption rate, with pore diffusion serving as the main rate limiting step. Results highlight the beneficial effect of destructive conditioning method on sludge adsorbent performance.

A life cycle-based comparison study of sludge recycling technology incorporating subjective and objective evaluations

Inadequate land capacity and low sludge recycling rates have become a major global environmental challenge. Low organic sludge content and inadequate waste management policy mean that there is an urgent need to improve sludge solutions in China, which has the world's largest WWT capacity. Decision-makers face difficulties in selecting sustainable sludge-to-resource technologies given the existence of multiple social, environmental and economic objectives, and also in optimizing the allocation of sludge between different available technologies. In this paper we used a combined analytic hierarchic process (AHP) and entropy weight (EW) method to evaluate four recycling technologies: aerobic composting (AC), dry-incineration (DI), hydrothermal carbonization (HTC) and pyrolysis (PY), in terms of five economic, environmental and land resource indicators. The results showed that human toxicity was viewed as the most important indicator, while economic value of sludge product was the least important. HTC had the best overall performance of the evaluated technologies while PY was the least attractive. However, all four sludge recycling technologies showed greater potential for reducing carbon emissions and human toxicity than landfilling when sludge dewatering was included. Sensitivity analysis showed that adjustments to AHP weights only had a limited impact on the technical ranking. Finally, the result was further verified by a particle swarm optimization algorithm. Considering capacity constraints, the optimal proportion of the four technologies was found to be 44.9%, 42.7%, 0 and 12.4% for HTC, DI, PY and AC respectively. The paper demonstrates the effectiveness of combining subjective and objective methods to evaluate multiple indicators, providing decision-makers with a practical analysis framework for waste technology selection.

Conversion of waste paper sludge into magnetic biochar for activation of peroxydisulfate for tetracycline removal

ABSTRACT The Fe2+-peroxydisulfate (PDS) process is an effective method to enhance paper sludge dewaterability. However, the generated waste of iron-rich sludge cake needs to be disposed of properly. Converting sludge cake into magnetic biochar catalysts can help to shorten its environmental risks, recover resources, and reduce catalyst costs. In this work, the magnetic sludge biochar (Fe-SBC) was prepared and applied as a PDS activator to remove tetracycline (TC). Results showed that the Fe-SBC pyrolyzed at 600 °C presented excellent catalytic activity for PDS to degrade TC (rate of 74.89%) under the optimum conditions (intrinsic pH, 10 mM PDS, 0.5 g/L Fe-SBC, and 50 mg/L TC). It was found for the first time that the addition sequences of the biochar catalyst and PDS were insignificant on TC removal. Furthermore, the TC removal mechanism was proposed to be free radicals (·OH, SO4·−, and O2−·) and non-radical (1O2) pathways working together for TC removal, for which 1O2 was dominated. In addition, coexisting ions (Cl− and CO32−) had an inhibitory effect on TC degradation. This work will provide a new recycling approach for waste paper sludge in wastewater treatment.

Pilot Study on the Possibility of Improving Water Treatment Sludge Management in Almaty

This article presents the results of a pilot study on the treatment of sludge from a water treatment plant in the city of Almaty, Republic of Kazakhstan, to ensure further disposal. The main objective of the study was to compare the efficiency of sludge drying by natural and artificial methods. The qualitative characteristics of the leachate from the dewatering unit, the chemical composition of the dried sludge and the granulometric analysis of the dried sludge were also studied. The greatest reduction in moisture content was recorded for drying in natural conditions (2.1%), but this process required the longest drying time. The leachate obtained from sludge dewatering was characterized by significant contamination (e.g., turbidity—55.65 on average, color—67.7, total Fe—5.15 mg/L, total N—79.6 mg/L, COD—311 mg/L, BOD—336.15 mg/L), which indicates the need for its pretreatment before further management in the technological system of the treatment station. The content of chemical substances contained in the dry residue of the sludge was also determined, of which aluminum was 0.94–13.8 mg/kg, silicon was 50.24–146.3 mg/kg, potassium was 1.72–5.51. mg/kg, calcium was 71.8–79.1 mg/kg, iron was 2.0–7.54 mg/kg and nickel was 0.9–4.4 mg/kg. A particle size analysis of the dried sludge showed that the majority fractions were fine and very fine sand, with a total of 20.2%, and silt and clay, with a total of 78.3%. Such properties justify the rationality of considering the reuse of dried sludge as a raw material for making, for example, construction materials or soil remediation material.

USE OF GEOSYNTHETICS FOR DEWATERING, CONTAINEMENT AND DISPOSAL OF MINING SLUDGE

Whether it is sludge produced by the technological process of flotation, sludge tailings or sludge produced in another process, which contains pollutants such as heavy metals, it is necessary to dispose it in a controlled manner to reduce the risk for contamination of environment. Mining sludge has been disposed in open basins for decades, recently with measures taken to reduce the possibility of leakage or spillage of toxic contents into the environment. Reduction of the space for permanent disposal of sludge and significant reduction of the risk of spreading contamination is achieved using geosynthetics. In this paper, we will present the concept of dewatering and permanent storage of mining sludge in woven geotextile tubes, as well as the concept of using geosynthetic materials for the safe closure of mining sludge lagoons. Both concepts presented in the paper are accompanied by one case study.

The impairment of joint tetracycline and copper oxide nanoparticle exposure on activated sludge

The increasing usage of two emerging contaminants (i.e., tetracycline (TET) and copper oxide nanoparticles (CuO-NPs)) has raised wide concerns about their potential impacts on the efficiency of wastewater treatment. However, the joint effects of TET and CuO-NPs on activated sludge processes have rarely been documented. This study investigated the sludge characteristics and bioactivities under both individual and joint exposure to TET (1 mg/L) and CuO-NPs (2 mg/L) for 60 days. The results demonstrated that both individual and joint exposures of TET and CuO-NPs deteriorated the flocculation ability and dewatering of sludge by inducing non-filamentous bacteria. The joint exposure showed higher effects on sludge when compared with individual exposure. Sludge characterization analysis attributed this deterioration partly to the increased extracellular polymeric substance (EPS) secretion (especially loose-bound EPS). In addition, exposure to CuO-NPs would result in an inhibition of total nitrogen removal due to impairment of the denitrification process (i.e., nitrate reductase, nitrous reductase, and electron-transfer associated enzyme), but not for TET. The inhibition of nitrogen removal could be exacerbated when simultaneously exposed to CuO-NPs and TET. 16S rRNA analysis further revealed that the long-term joint exposure to TET and CuO-NPs resulted in a significant decrease in microbial community richness, diversity, and associated functional bacteria abundance. The results of this study suggest that joint exposure to TET and CuO-NPs results in the deterioration of sludge function efficiency.

Impact of Hydroxy-Aluminum and Extracellular polymeric substances interactions on waste activated sludge Dewatering: A molecular perspective

Al13 and Al30 are the dominant aluminum (Al) species in polyaluminium chloride commonly used for sludge dewatering. However, the presence of extracellular polymeric substances (EPS) in the waste activated sludge hinders the coagulation effectiveness of Al-based coagulants. This study focused on the effects and mechanisms of Al13 and Al30 on treating sludge EPS. From a bulk perspective, the dosing of two coagulants significantly reduced the dissolved organic carbon and various organic compounds, reflecting their efficacy in removing organic substances in EPS. Further molecular characterization was revealed by FT-ICR MS. Al13 was more effective in removing lipids, lignins, and sulfur-containing compounds compared to Al30. Al13 also demonstrated a pronounced removal in components enriched in oxygen atoms (10–20) and KMD(COO) (0.5–0.7), suggesting its ability to remove molecules across a broader range of unsaturation. After coagulation with Al13, the areas corresponding to Al2p1/2 and Al2p2/3 in the Al2p spectra were more prominent compared to those in the Al30-coagulated EPS. Therefore, Al13 can both remove complex and low molecule weight compounds through abound forms of adsorption sites, making it more efficient in releasing bound water compared to Al30.

Clarifying the mechanism of peroxydisulfate and sulfite activated by Fe2+ for waste activated sludge pretreatment: Enhancement of dewaterabiliy, removal of antibiotic resistance genes and pathogenic microorganisms

The remarkable performance of SO4•— based advanced oxidation processes in improving waste activated sludge (WAS) dewatering has recently received considerable attention. However, its potential effect on the removal of emerging pollutants is often overlooked. In this study, two types of pretreatment methods (S2O82-/Fe2+ and SO32-/Fe2+) were employed to comprehensively evaluate their performance in improving the dewatering of WAS and the removal of antibiotic resistance genes (ARGs) and pathogenic microorganisms. At the optimal dosage of 1.2/1.5 mmol-S2O82-/Fe2+/g-VS, the capillary suction time reduction rate of WAS after S2O82-/Fe2+ was 1.8 times than that of SO32-/Fe2+. Notably, both S2O82-/Fe2+ and SO32-/Fe2+ could remove the 12 types of ARGs identified in WAS. Nonetheless, S2O82-/Fe2+ was more effective in removing ARGs, with a range of removal rate (0.96–2.17 log-units), and reduced the propagation and proliferation potential of residual ARGs. Furthermore, the coliforms content in WAS after S2O82-/Fe2+ decreased significantly with a minimum of 1.84 ± 0.24 log (MPN/g-TS) compared to SO32-/Fe2+. Further analysis indicated that the redistribution of bound extracellular polymeric substances (EPS) in WAS, especially the variations in protein, was the key factor affecting the dewaterability. In contrast to SO32-/Fe2+, the S2O82-/Fe2+ could quickly destroy the EPS structure to release bound water, accelerate the dissociation of WAS flocs, and cause cell lysis and DNA dissolution because of the continuous production and accumulation of SO4•— in the hostile conditions inside. Therefore, S2O82-/Fe2+ is an efficient, economical, and green method to improve WAS dewatering and the removal of pollutants.

A Novel Approach for Rapid Dewatering of Water-Based Ink Wastewater Sludge under Low Temperature and Its Mechanism

A Novel Approach for Rapid Dewatering of Water-Based Ink Wastewater Sludge under Low Temperature and Its Mechanism

Multifaceted Impact of Lipid Extraction on the Characteristics of Polymer-Based Sewage Sludge towards Sustainable Sludge Management.

Dewatered sludge (DS) is a sewage sludge with a unique property due to extracellular polymeric substances (EPSs) and polymer flocculants. These components form a stable 3D polymer network to increase dewatering efficiency, leaving behind valuable materials such as lipids. This article explored the influences of DS particle size on lipid yield and the effects of extraction on the chemical, morphological, and thermal properties of the residual dewatered sludge (RDS). Lipid yields with unimodal distribution were observed across the particle size ranges (<0.5, 0.5-1.0, 1.0-2.0, 2.0-4.0, and 4.0 mm). The highest lipid yield of 1.95% was extracted from 1.0-2.0 mm after 4 h at 70 °C and 0.1 g/mL sludge-to-solvent ratio. Efficiency was influenced by the DS's morphology, facilitating solvent infiltration and pore diffusion. The extraction process reduced water and organic fractions, resulting in higher thermal stability. Bibliometric analysis of "extraction*" and "sewage sludge" shows increasing research interest from 1973 to 2024. Five research clusters were observed: heavy metal speciation and stabilization, sludge and its bioavailability, extraction techniques and resource recovery, contaminants remediation, as well as phosphorus recovery and agricultural applications. These clusters highlight the diverse approaches to researching DS and RDS while promoting sustainable waste management.

Influential mechanism of water occurrence states of waste-activated sludge: Specifically focusing on the pore characteristics dominated by cation-organic interactions

The solid pore characteristics are commonly considered as the important influential factors on waste-activated sludge (WAS) dewaterability, and should be related to the cohesive force of bio-flocs dominated by cation-organic interactions at solid-water interface. This study aimed to establish an approach for regulating the solid pore structure of WAS by cationic regulation. The influential mechanism of WAS dewaterability was accordingly explored from the perspective of the pore characteristics dominated by cation-organic interactions. Primarily, with the gradient removal or addition of bivalent cations, the varying pore structure of WAS flocs was tracked by in-situ synchrotron X-ray computed microtomography imaging technique (CMT). The three-dimensional visual model was established to quantify the pore structure parameters of WAS flocs. Following the visualization analysis, the artificial intelligence means, the gradient-weighted class activation mapping (Grad CAM) of three-dimensional convolutional neural network (3D-CNN), was applied for the first time to explore the linkages among solid surface properties, solid pore structure, water occurrence states and sludge dewaterability. It was found that the number and volume of isolated pores jointly determined the mobility and the fractions of vicinal water and interstitial water (p-value ≤ 0.02); also, the decreasing polar or acid-based interfacial free energy with the cationic addition was accompanied with the decreasing isolated pore mean-volume (Pearson coefficient=-0.77, p-value < 0.01). These results indicated that the pore structure characteristics determined the water occurrence states, but the solid porosity strongly depended on the interfacial properties. Accordingly, the molecular docking was applied to explore the interfacial reaction mechanism between Ca2+/Mg2+ and solid compositions in terms of complexation sites, molecular dynamics and free energy calculations. As a result, how the cation-organic interactions affected the pore characteristics through solid surface modification could be clarified, which is expected to serve as theoretical foundation for the development of novel sludge conditioning technologies, i.e., more efforts should be devoted to increasing the dense degree of sludge particles through weakening the hydration repulsion of solid surface.

Leaching behavior of microplastics during sludge mechanical dewatering and its effect on activated sludge

Dewatering is an indispensable link in sludge treatment, but its effect on the microplastics (MPs) remains inadequately understood. This study investigated the physicochemical changes and leaching behavior of MPs during the mechanical dewatering of sludge, as well as the impact of MP leachates on activated sludge (AS). After sludge dewatering, MPs exhibit rougher surfaces, decreased sizes and altered functional groups due to the addition of dewatering agents and the application of mechanical force. Meanwhile, plastic additives, depolymerization products, and derivatives of their interactions are leached from MPs during sludge dewatering process. The concentration of MP-based leachates in sludge is 2–25 times higher than that in water. The enhancement of pH and ionic strength caused by dewatering agents induces the release of MP leachates enriched with protein-like, fulvic acid-like, and soluble microbial by-product-like substances. The reflux of MP leachates in sludge dewatering liquor to the wastewater treatment system negatively impacts AS, leading to a decrease in COD removal rate and inhibition of the extracellular polymeric substances secretion. More importantly, MP leachates cause oxidative stress to microbial cells and alter the microbial community structure of AS at the phylum and genus levels. These findings confirm that MPs undergo aging and leaching during sludge dewatering process, and MP leachates may negatively affect the wastewater treatment system.

A synergistic method using ferrous sulfate and cementitious materials to solidify landfilled municipal sludge

The filling of landfilled municipal sludge (LMS), which is typical of high water content and low strength, poses great challenges for the landfill expansion and its mechanical stability. This study proposed a synergistic method to treat the LMS using ferrous sulfate (FS)-conditioning and cementitious materials (e.g., lime, fly ash, and cement) solidification. A series of water content, unconfined compressive strength (UCS), pH, and toxicity leaching tests were conducted to evaluate the dewatering/solidification performance of this synergistic method. The results showed that this synergistic method was effective in LMS dewatering and solidification. For the LMS tested, the proposed optimum dosage was 7 % FS, 4 % lime, 5 % fly ash, and 10 % cement, which is a much lower usage than similar studies in the literature. At this dosage, the treated LMS after 28 days of curing exhibited water content of 57.8 %, UCS of 279.1 kPa, pH value below 10.0, and no leaching toxicity, which satisfied the landfill disposal requirement by Chinese standard GB/T 23485–2009. Microscopic analyses (e.g., optical microscope, bound water measurement, scanning electron microscopy, and X-ray diffraction) revealed that FS-conditioning destroyed the colloidal agglomerate in the sludge and released the bound water to become free water; then, the cementitious materials reacted with the free water and generated cementation products (e.g., ettringite, and calcium silicate/aluminate hydrate), which significantly improved the sludge strength. The novelty of this work is that the proposed synergistic use of FS and cementitious materials, relative to the traditional method, is more effective in sludge dewatering and solidification and yet has a lower cost.

Promotion of aromatic amino acids of extracellular polymeric substance targeted transformation via sulfite mediated iron redox cycling in sludge solid-liquid separation

Highly hydrophilic extracellular polymeric substance (EPS) with gel-like structure seriously plagues the development of sludge deep dewatering. Oxysulfur radicals-based oxidation driven by iron-bearing mineral proposes a promising strategy for effective EPS decomposition. However, the transformation and involved interaction mechanisms of aromatic proteins are still controversial due to the complex EPS structure. Herein, sulfite mediated siderite (denoted as Fe(II)/S(IV)) was developed for targeted transformation aromatic amino acids in EPS oxidation to strengthen sludge solid-liquid separation. The enhanced sludge dewaterability were benefited from the Fe(II)/S(IV) bonded interaction assisted by Fe3+/Fe2+ as redox interface that facilitating the release of intracellular bound water via diminish the hydrophily and bind strength with solid protons. The amide region nitrogen of aromatic amino acids (especially tyrosine and tryptophan) originating from EPS presented looser structure and lower spatial site resistance, which were attributed to the exposure of hydrophobic sites in amino groups after Fe(II)/S(IV) treatment. Furthermore, the effective decline of aromatic amino acids in inner layer-EPS (loosely bound EPS and tightly bound EPS) was directed from Fe-N targeted interaction by triggering a series of sulfate-based radical chain reactions. The good correlation between electron transfer amount (R2 = 0.926) and Fe-N (R2 = 0.925) with bonding interaction demonstrated that the complexation of aromatic amino acids with Fe sites on siderite/sulfite via Fe-N bonds, accounting for efficient sludge solid-liquid separation. This study deepens the understanding of sludge organic matter targeted transformation and provides a tactic for iron-based conditioning of sludge.