Enhancement Of Sludge Dewaterability Research Articles

Mutual-benefit modification of the coagulant solution and fly ash for enhanced sludge dewatering

Faced with the escalating volume of municipal sludge from wastewater treatment plants, urgent measures are required to enhance the sludge dewatering efficiency. This study introduces an innovative and cost-effective approach for mutual modifications of AlCl3 coagulant solution (AC) and fly ash (FA) powder as additives to significantly enhance sludge dewaterability. Unlike the traditional method that modifies agents alone, our technique achieves dual functionalities via blending FA with AC at room temperature. The modified FA (MFA) exhibits a 60 % increase in specific surface area to 2.176 m2/g and ζ-potential shift from –22.2 to +2.0 mV, meanwhile enhances the metal ions content in the modified AC (MAC) by dissolving 96.5 % of Ca, 70.3 % of Mg, 10.6 % of Fe, and 6.1 % of Al ions from FA. When sludge is treated with 5 % MAC and 10 % MFA, the water content in the filter cake is reduced from 84.9 % originally to 52.9 % through plate-frame pressure filtration (PFPF), a significant improvement over 65.4 % for that with unmodified AC and FA treatment, corresponding to the decreased specific resistance to filtration (SRF) and increased the filtration flux during the draining phase. The notable dewaterability enhancement through AC and FA modification is due to the enhanced flocculation and charge neutralization by the abundant metal ions in MAC, coupled with the MFA-facilitated water adsorption and drainage channel maintenance. This one-step, double-benefit modification not only surpasses traditional methods in dewatering efficiency but also reduces sludge treatment costs by 42.4 %, offering a sustainable solution to the increasing challenges of municipal sludge management.

Advanced application of tea residue extracts rich in polyphenols for enhancing sludge dewaterability: Unraveling the role of pH regulation

Tea polyphenols (TPs), as a kind of derivatives from tea waste, were employed as a novel environmentally friendly bio-based sludge conditioner in this study. The findings showed that when TPs were applied at a dosage of 300 mg g−1 DS, the sludge CST0/CST ratio significantly increased to 1.90. pH regulation was found to markedly affect the dewatering efficiency of sludge. At pH 4, the CST0/CST rose to 2.86, coupled with a reduction in the specific resistance to filtration (SRF) from 6.69 × 1013 m kg−1 to 1.43 × 1013 m kg−1 and a decrease in the moisture content (MC) from 90.57% to 68.75%. TPs formed complexes and precipitated sludge proteins, as demonstrated by changes in the extracellular polymeric substances (EPS), viscosity, zeta potential, and particles size distribution. The optimization significance of acidification treatment on sludge structure disintegration, the interaction of TPs with EPS, and the removal of sludge proteins were elucidated. The research provided an ideal approach for the integrated utilization of biomass resources from tea waste and highlighted the potential application of TPs as an environmentally friendly conditioner in sludge dewatering.

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.

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

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

Visualization of water transfer channel in sludge dewatering conditioned with skeleton builders by X-ray micro-computed tomography

Skeleton builders were normally deemed to improve the high porosity and newly-generated permeability of sludge cakes by building water transfer channel during high pressure filtration, thus enhancing sludge dewaterability. However, currently a direct visualization proof of water transfer channel was still lacking. This study provided the direct proof for visualizing water transfer channel in dewatered sludge cakes conditioned with a typical skeleton builder (i.e., phosphogypsum (PG)) by X-ray micro-computed tomography (micro-CT) for the first time. After the addition of PG, the pixel value and image luminance increased significantly, indicating the presence of high density substances from both two-dimensional (2D) cross section and three-dimensional (3D) reconstruction CT images. Moreover, the CT numbers showed strong and negative correlations with specific resistance to filtration (SRF) (R = − 0.99, p < 0.05), capillary suction time (CST) (regression coefficient (R) = − 0.87, probability (p) < 0.05), and water content of the dewatered sludge cake (R = − 0.99, p < 0.05), respectively. These results indicated that the X-ray micro-CT could be a potential technique for analyzing the water distribution in sludge samples conditioned with skeleton builders.

Pivotal role of intracellular oxidation by HOCl in simultaneously removing antibiotic resistance genes and enhancing dewaterability during conditioning of sewage sludge using Fe2+/Ca(ClO)2

Pre-acidification has been shown to be crucial in attenuating antibiotic resistance genes (ARGs) during the conditioning of sewage sludge. However, it is of great significance to develop alternative conditioning approaches that can effectively eliminate sludge-borne ARGs without relying on pre-acidification. This is due to the high investment costs and operational complexities associated with sludge pre-acidification. In this study, the effects of Fe2+/Ca(ClO)2 conditioning treatment on the enhancement of sludge dewaterability and the removal of ARGs were compared with other conditioning technologies. The dose effect and the associated mechanisms were also investigated. The findings revealed that Fe2+/Ca(ClO)2 conditioning treatment had the highest potential, even surpassing Fenton treatment with pre-acidification, in terms of eliminating the total ARGs. Moreover, the effectiveness of the treatment was found to be dose-dependent. This study also identified that the •OH radical reacted with extracellular polymeric substance (EPS) and extracellular ARGs, and the HOCl, the production of which was positively correlated with the dose of Fe2+/Ca(ClO)2, could infiltrate the EPS layer and diffuse into the cell of sludge flocs, inducing the oxidation of intracellular ARGs. Furthermore, this study observed a significant decrease in the predicted hosts of ARGs and MGEs in sludge conditioned with Fe2+/Ca(ClO)2, accompanied by a significant downregulation of metabolic pathways associated with ARG propagation, thereby contributing to the attenuation of sludge-borne ARGs. Based on these findings, it can be concluded that Fe2+/Ca(ClO)2 conditioning treatment holds great potential for the removal of sludge-borne ARGs while also enhancing sludge dewaterability, which mainly relies on the intracellular oxidation by HOCl.

In-situ generation of iron activated percarbonate for sustainable sludge dewatering

Effective dewatering of sewage sludge could potentially address the issues of high energy consumption and large carbon footprint inherent in the sludge treatment process, advancing toward carbon neutrality in environmental remediation. Yet, the surface hydrophilic characteristics and water-holding interfacial affinity in sludge led to dwindled sludge-water separation performance. Here, the integration of in-situ generation of iron from zero-valent scrap iron (ZVSI) and sodium percarbonate (SPC) was attempted to attenuate the water-retaining interfacial affinity within sludge, thus achieving superior sludge dewatering performance. Results showed that under the optimal conditions, the ZVSI + SPC system led to a remarkable decline of 76.09 % in the specific resistance to filtration of the sludge, accompanied by a notable decline of 34.96 % in the water content. Moreover, the utilization of ZVSI + SPC system could be a viable alternative to the traditional strategies in terms of enhanced sludge dewaterability, offering application potential with stable operating performance, economic feasibility, and reduced carbon emissions. Investigation into dewatering mechanism revealed that ZVSI could maintain the Fe3+/Fe2+ in a stable dynamic cycle and continuously in-situ generate Fe2+, thereby efficaciously fostering the SPC activation for the ceaseless yield of reactive oxygen species. The predominant •OH and 1O2 efficiently decomposed the hydrophilic biopolymers, therefore minimizing the hydrophilic protein secondary structures, along with the hydrogen and disulfide bonds within proteins. Subsequently, the water-holding interfacial affinity was profoundly diminished, leading to intensified hydrophobicity, self-flocculation, and dewaterability. These findings have important implications for the advancement of efficacious ZVSI + SPC conditioning techniques toward sustainable energy and low-carbon prospects.

Effect of electrolytic zero-valent iron activated sodium hypochlorite on sludge dewatering performance.

Using electrolytic zero-valent iron-activated sodium hypochlorite (EZVI-NaClO) to pretreat sludge, the capillary suction time (CST) was utilized to evaluate sludge dewaterability. Ammonia nitrogen (NH4-N), dissolved phosphorus, and total phosphorus in the supernatant were used to analyze sludge disintegration. This approach aimed to evaluate the effectiveness of the pretreatment process and its impact on the sludge composition. The migration and transformation of extracellular polymeric substances (EPS), including dissolved EPS (S-EPS), loosely boundEPS, and tightly bound-EPS (TB-EPS), were analyzed by detecting protein and polysaccharide concentrations and three-dimensional fluorescence excitation-emission spectroscopy (3D-EEM). The sludge particle properties, including sludge viscosity and particle size, were also analyzed. The results suggested that the optimal pH value, NaClO dosage, current, and reaction time were 2, 100 mg/gDS (dry sludge), 0.2A, and 30 min, respectively, with a CST reduction of 43%. Protein and polysaccharide contents in TB-EPS were significantly reduced in the EZVI-NaClO group. Conversely, protein and polysaccharides contents in S-EPS increased, suggesting that EZVI-NaClO treatment could disrupt the EPS. Besides, the viscosity of the treated sludge decreased from 195.4 to 54.9 mPa·S, indicating that sludge fluidity became better. ZEVI-NaClO could enhance sludge dewaterability by destructing protein and polysaccharide structure and improving sludge hydrophobicity.

Enhancing sludge dewaterability in sequential bioleaching: Degradation of dissolved organic matter (DOM) by filamentous fungus Mucor sp. ZG-3 and the influence of energy source.

This study aimed to enhance sludge dewatering through sequential bioleaching, employing the filamentous fungus Mucor sp. ZG-3 and the iron-oxidizing bacterium Acidithiobacillus ferrooxidans LX5. The mechanism by which Mucor sp. ZG-3 alleviates sludge dissolved organic matter (DOM) inhibition of A. ferrooxidans LX5 was investigated, and the optimal addition of energy source for enhanced sludge dewaterability during sequential bioleaching was determined. Sludge dissolved organic carbon (DOC) decreased to 272 mg/L with a 65.2% reduction by Mucor sp. ZG-3 in 3 days, and the degraded fraction of sludge DOM was mainly low-molecular-weight DOM (L-DOM) which inhibited the oxidization of Fe2+ by A. ferrooxidans LX5. By degrading significant inhibitory low-molecular-weight organic acids, Mucor sp. ZG-3 alleviated DOM inhibition of A. ferrooxidans LX5. In the sequential bioleaching process, the optimal concentration of FeSO4·7H2O for A. ferrooxidans LX5 was 4 g/L, resulting in the minimum specific resistance to filtration (SRF) of 2.60×1011 m/kg, 40.0% lower than that in the conventional bioleaching process with 10 g/L energy source. Moreover, the sequential bioleaching process increased the sludge zeta potential (from -31.8 to -9.47 mV) and median particle size (d50) of the sludge particle (from 17.90 to 27.44 μm), contributing to enhanced sludge dewaterability. Inoculation of Mucor sp. ZG-3 during the bioleaching process reduced the demand for energy sources by A. ferrooxidans LX5 while improving sludge dewaterability performance.

Possibility of utilizing waste activated sludge as a renewable energy source

This paper gives results of a study of biofuel granules made from a waste activated sludge of wastewater treatment. A novel method to enhance waste activated sludge dewaterability with untreated and calcined water treatment sludge of thermal power plants is proposed, and the potential reuse of dewatered sludge as biofuel is evaluated. The water treatment sludge destroyed membrane, resulting in the release of intracellular water by converting bound water into free water, thus enhancing sludge dewaterability. Biofuel granules can be used for technological needs, electricity generation and in heating and hot water supply systems at industrial and domestic facilities. Biofuel granule is a renewable energy that can substituted low grade coal from biomass sources.

The role of microstructure of extracellular proteins in dewaterability of alkaline pretreatment sludge during bioleaching

Alkaline pre-treatment is known to enhance the acid production efficiency of sludge but adversely affects its dewatering performance. In this study, the improvement of sludge dewaterability by a novel bioleaching system with inoculating domesticated acidified sludge (AS) and its underlying mechanism were investigated. The results showed that although the addition of Fe2+ and the reduction of pH improved the dewatering performance of sludge, their effects were inferior to that of AS + Fe. The addition of AS and Fe2+ significantly reduced the specific resistance to filtration and capillary suction time of the sludge by 98.6 % and 95.5 %, respectively. This improvement in dewatering performance was achieved through the combined actions of bio-acidification, bio-oxidation, and bio-flocculation. Remarkably, under alkaline pH, microorganisms in AS remained active, leading to the formation of iron-based bioflocculants, along with a rapid pH decrease. These bioflocculants, in combination with protein (PN) in tightly bound extracellular polymeric substances (TB-EPS) through amide bonding, transformed TB-EPS from extractable to non-extractable form, reducing PN content from 12.1 mg g−1DS to 5.09 mg g−1DS and altering the protein's secondary structure. Consequently, the gel-like TB-EPS matrix effectively broke down, releasing cellular water and significantly enhancing sludge dewaterability.

Optimization of Fe(II)/SPC Sludge Conditioning and Dewatering Process Based on Response Surface Methodology: Full-Scale Application

Sludge conditioning is a crucial step in sludge dewatering aimed at minimizing excessive sludge production. The Fenton process, which harnesses oxidative radicals to dismantle extracellular polymeric substances (EPS) and microorganisms, has been unequivocally proven to enhance sludge dewaterability. However, the widespread adoption of the Fenton process is hampered by its high costs and logistical challenges in transportation. In contrast, the Fe(II)-activated sodium percarbonate (Fe(II)/SPC) process has emerged as a promising technology for sludge conditioning due to its remarkable performance and safe operation. However, limited information is available regarding the optimization of Fe(II)/SPC for sludge conditioning and dewatering at full scale. This study conducted the sludge conditioning and dewatering process within a full-scale wastewater treatment plant, utilizing the response surface methodology (RSM) to optimize the Fe(II)/SPC process. Furthermore, this study investigated its impact on sludge structure and compared the economic benefits of the Fe(II)/SPC process with other full-scale conditioning processes. The results of bound water and LDH analysis revealed that the Fe(II)/SPC process not only degraded EPS but also disrupted microbial cells, thereby releasing intracellular water. Based on the RSM results, we successfully established a polynomial prediction model to determine the optimal capillary suction time (CST) and moisture content. The optimal parameters determined through RSM were an initial pH of 3.02, Fe(II) dosage of 0.05 g/g TSS, and SPC dosage of 0.07 g/g TSS. The validation test confirmed the accuracy of the prediction results, with the conditioned sludge exhibiting a CST of 31.6 s and a moisture content of 51.47%. Furthermore, when compared to the PFS and Fenton processes, the Fe(II)/SPC process demonstrated higher economic efficiency and safety, while maintaining good dewatering performance. Overall, the Fe(II)/SPC treatment shows promise as a prospective sludge dewatering and conditioning process.

A three-stage process of Mn(VII)-Fe(III)/PDS system for enhancing sludge dewaterability: Effective driving of Fe(II)/Fe(III) cycle and adequate assurance of ROS

Sludge dewatering helps to reduce the cost of sewage treatment plants and environmental impact. Hence, we used a type of permanganate (Mn(IV)) activated ferric chloride (Fe(III))/ peroxydisulfate (PDS) system to enhance sludge dewaterability. At optimal dose, the simultaneous addition of Mn(IV), Fe(III) and PDS (MFP treatment) reduced the value of specific resistance to filtration (SRF) from 6.76 × 108 s2/g to 2.01 × 108 s2/g. There is a three-stage process during MFP conditioning: oxidation/flocculation, adsorption/oxidation, and reflocculation. X-ray photoelectron spectroscopy (XPS) and Electron spin resonance (ESR) analyses were employed to investigate the oxidation mechanism. Meanwhile, the analysis of Mn valence was improved by considering metal leaching rates. The cycles of Mn(II)/Mn(III)/Mn(IV) were initiated under the reaction between Mn(VII) and extracellular polymeric substances (EPS)/PDS. This process sustained the cycle of Fe(II)/Fe(III) to promote activation of PDS, which continuously promoted to generate OH•, SO4-•, •O2–, 1O2 and Fe(IV). Additionally, sludge EPS was proven to be the primary electron donor of Fe(II)/Fe(III) cycle, resulting in the increasing of Fe(II) proportion. Notably, the hydrophilicity and water-holding capacity of EPS declined significantly following excellent oxidation, which promoted the conversion of bound water. The effective destruction of hydrogen bonds and protein secondary structures explained the outstanding effects. Meanwhile, XDLVO calculation revealed that sludge coagulation performance enhanced through Fe(III) flocculation, MnO2 adsorption and hydrophobic flocculation. Raw and converted free water would be effectively removed through the more hydrophobic surface of large and tough drain pores formed after the reflocculation process. The efficient drainage of sludge water created strong sludge dewaterability. This study verified the practicality of MFP treatment by exploring the oxidation and coagulation mechanisms to clarify the dewatering mechanism.

Enhanced sludge dewaterability using a bifunctional hybrid coagulant

The combination of coagulation and addition of skeleton builder is a popular pretreatment method to improve the dewaterability of sludge. In this study, a novel bifunctional inorganic/organic hybrid coagulant (CS–Si@ATP) was designed and obtained by chemically coupling a cationic starch (CS) with a popular clay, that is, attapulgite (ATP), via a silane coupling agent (APTES) for one-step conditioning of sludge. CS-Si@ATP can evidently enhance the sludge dewatering performance compared with CS, ATP, and their simple combination due to the distinct dual functions of this hybrid coagulant. The tentacle-like cationic CS in CS-Si@ATP shows efficient charge neutralization effect to aggregate and precipitate the suspended solids for further formation of compact sludge cakes. Meanwhile, the internal ATP with a stable and rigid structure acts as the skeleton builder to notably improve the filterability and permeability of the sludge cakes. The synergistic effects of CS and ATP in CS-Si@ATP, i.e., the charge neutralization of CS and the skeleton construction of ATP, cause the evidently enhanced sludge dewaterability, with a filter cake moisture content approximately 78.30% after the mechanical dewatering at 0.05 MPa. In comparison with the traditional two-step combination process by separated addition of CS and ATP, the one-step addition of CS-Si@ATP can reduce the required ATP dose nearly an order of magnitude. Thus, CS-Si@ATP has the notable advantages of simple operation, efficient utilization of ATP and evident reduction of disposal cost. This study provides an environmentally friendly and cost-effective coagulant to further improve the dewaterability of sludge.

In-situ utilization of EPS improves the directional oxidation ability of Fe(III)/H2O2 and enhances sludge dewaterability

Inefficient sludge dewatering can result in high costs for sludge treatment and disposal, as well as increased pollution of the environment. In this study, we constructed a double oxidation–reduction (Redox) cycle system of Fe(II)/Fe(III) and Fe(II)-extracellular polymeric substance (EPS)/Fe(III)-EPS by utilizing EPS in situ and collaborating with Fe (III) and H2O2 so as to regulate the performance of Fenton oxidation for efficiently enhancing the dewaterability. Results displayed the specific resistance to filtration (SRF) reduced from 34.1 ± 2.4 × 1012 m/kg to 16.2 ± 1.5 × 1012 m/kg with only 0.15 mmol Fe(III)/g VSS and 1.46 mmol H2O2/g VSS. Notably, the formation of relative stable Fe(III)-EPS complex was found under the interval addition of Fe(III) and H2O2. Four types of reactive species (hydroxyl radical (•OH), singlet oxygen (1O2), superoxide radical (O2•-) and Fe(IV)) which could effective destroy EPS structure during conditioning process, were generated after the addition of H2O2. It effectively promoted the transition from intracellular oxidation to extracellular oxidation under Fenton oxidation conditions, which reduced negative effects of cell lysis under excessive oxidation during sludge conditioning. The structure of EPS damaged significantly during the oxidation process, leading to the effective conversion of bound water to free water. Meanwhile, the existence of dissociative Fe(III) promoted the aggregation of sludge flocs, generating large channels or pores for sludge water to discharge, and then improving the dewaterability. Overall, [Fe(III)-EPS]/H2O2 treatment as an efficient sludge conditioning method can provide guidance for sludge dewaterability enhancement in urban sludge treatment and disposal.

Enhanced sludge dewatering by PDMDAAC coupled with Fenton-like reaction initiated by Fe-rich sludge biochar with in-situ generation of H2O2: Fe/C structure as an electron shuttle

Fenton-like reaction has been used to enhance sludge dewaterability effectively. However, the unstable characteristic, ignitability, and corrosivity of H2O2 make it difficult for application. To address this challenge, a novel process of in-situ H2O2 generation by Fe-rich sludge biochar under aeration condition combined with poly-diallyldimethylammonium chloride (PDMDAAC) was proposed to enhance sludge dewaterability. Under optimized conditions, the capillary suction time and specific resistance to filterability of the conditioned sludge were reduced significantly compared with raw sludge (54.2 vs. 351 s, 0.249×1013 vs. 2.68×1013 m/kg, respectively). The carbon skeleton in Fe-rich sludge biochar can reduce the charge transfer impedance between Fe and O2, promoting in-situ generation of H2O2. The degradation of hydrophilic organics in extracellular polymeric substances of sludge floc and the PDMDAAC coagulation effect promoted the release of bound water. This study provides a strategy to enhance sludge dewaterability by Fenton-like reaction initiated by Fe-rich biochar with no H2O2 addition.

Behavior of organic components and the migration of heavy metals during sludge dewatering by different advanced oxidation processes via optical spectroscopy and molecular fingerprint analysis.

A comparative study of the different advanced oxidation processes (Fe(II)-Oxone, Fe(II)-H2O2, and Fe(II)-NaClO) was carried out herein to analyze the characteristics of organic components and the migration of heavy metals in waste activated sludge. With the Fe(II)-Oxone and Fe(II)-H2O2 treatments, sludge dewaterability was significantly improved, however, sludge dewaterability was deteriorated by the Fe(II)-NaClO treatment. The enhanced sludge dewaterability by the Fe(II)-Oxone and Fe(II)-H2O2 treatments was strongly correlated with the shifted organic components, particularly proteins, in soluble extracellular polymeric substances (S-EPS), while the deteriorated sludge dewaterability by the Fe(II)-NaClO treatment was strongly correlated with the over release of organic components from bound EPS (B-EPS) to S-EPS. For both the Fe(II)-Oxone and Fe(II)-H2O2 treatments, the radicals preferentially attacked humic acid-like organic components over the protein-like organic components in S-EPS, while for the Fe(II)-NaClO treatment, interestingly, the radicals preferentially attacked the protein-like organic components in both S-EPS and B-EPS. The hydrophilic functional groups like phenolic OH and CO of polysaccharides may be more preferentially migrated to S-EPS of sludge by the Fe(II)-NaClO treatment compared to the other two treatments. With the Fe(II)-Oxone and Fe(II)-H2O2 treatments, the proportion of aliphatic compounds as well as the much oxygenated organic components with a low desaturation and a low molecular weight increased. While with the Fe(II)-NaClO treatment, the proportion of low oxygenated organic components with a high desaturation and a high molecular weight increased. The concentration of total organic carbon, particularly the concentration of proteins, may be the key factor determining the shift of Zn and Cu from sludge solid to liquid phase, along with the high oxidation extent of organic components and close binding to CHOS and CHON compounds as indicated by density functional theory (DFT) calculation. This study systematically revealed the simultaneous sludge dewatering and migration of heavy metals when the role of organic components was factored into herein.

Schwertmannite-based heterogeneous Fenton for enhancing sludge dewaterability over a wide pH range

Fe-based Fenton technology is commonly used to enhance sludge dewaterability, but it requires subsequent neutralization, resulting in excessive chemical consumption. In this study, we investigated the feasibility of using schwertmannite-composited Fe3O4 (Sch/Fe3O4) as a heterogeneous Fenton catalyst to enhance sludge dewaterability without the need for pH adjustment. A high reduction efficiency of sludge specific resistance to filtration (94.4%), moisture content (11.4%) and bound water (45.5%) after Sch/Fe3O4 +H2O2 treatment at initial pH 7.5 were obtained, suggesting that Sch/Fe3O4 +H2O2 posed good dehydration performance without any acidification. SO42- and H+ generation in Sch/Fe3O4 system played an important role in sludge pH decrease, which facilitated sludge cell lysis, intracellular water release, and provided a suitable pH for Fenton reaction. Reactive species (•OH, •O2-, and 1O2) from Sch/Fe3O4 +H2O2 could effectively destroy sludge EPS, releasing more bound water. Additionally, the negatively charged compounds were neutralized by dissolved Fe2+/Fe3+. Sch/Fe3O4, as a skeleton builder, rearranged the dissociative sludge flocs to improve the incompressibility and permeability of sludge cake. Finally, sludge treated with Sch/Fe3O4 +H2O2 achieved organic matters reserve, heavy metals reduction, further benefiting the final disposal.

Enhancement of sludge dewaterability by repeated inoculation of acidified sludge: Extracellular polymeric substances molecular structure and microbial community succession

Improving the dewatering performance of sewage sludge is of great scientific and engineering significance in the context of accelerated urbanization and increasingly strict environmental regulations. Acidified sludge (AS) can improve sludge dewatering performance, but the dewatering effect of repeated inoculation is unclear. The effects of long-term repeated inoculation of AS on the sludge dewaterability were investigated. The molecular structure and microbial community succession of extracellular polymeric substances (EPS) are emphasized. The results revealed that increasing the inoculation ratio of AS reduced the pH, absolute value of sludge zeta potential, and sludge particle size, and the decreasing trend was more evident with prolonging treatment time. Under the conditions of 30% and 50% AS inoculation, the dewatering performance of the sludge was significantly improved (p < 0.05). Compared with the raw sludge, the specific resistance of filtration (SRF) and capillary suction time of 30% inoculation were reduced by 64.3% and 50.1% after 30 cycles, respectively. Excluding loosely bound (LB)-EPS, soluble (S)-EPS and tightly bound (TB)-EPS exhibited a visible decrease, the protein in TB-EPS was significantly related to sludge dewaterability (p < 0.05). The fluorescent components of aromatic protein and fulvic acid-like substances in TB-EPS were significantly associated with SRF, with a correlation coefficient 0.99 (p < 0.05). Both the increase in the percentages of random coil and decrease in α-helix in TB-EPS contributed to improving dewaterability. Increasing Firmicutes and decreasing Chloroflexi levels improved the sludge dewatering capacity. Repeated inoculation did not disrupt the dewatering effect of AS rather increased the feasibility of the engineering application of AS. Considering the dewatering performance and cost synthetically, 30% AS inoculated ratio is feasible for practical applications.

The novel application of polyoxometalates in sludge dewatering: Cells lysis and re-flocculation

Polyoxometalates (POMs) coupled with FeCl3 was tested as an efficient and eco-friendly sludge dewatering conditioning in this study. The results indicated that the water content of the sludge cake and capillary suction time were reduced from 86.61 % and 51.15 s to 67.68 % and 16.7 s under the optimum POMs and FeCl3 dosages of 1.20 mM/g volatile suspended solids (VSS) and 300 mg/g VSS, respectively. The underlying mechanism of the enhanced sludge dewaterability was elucidated based on the variation of physicochemical properties and extracellular polymeric substances (EPS) fractions of the conditioned sludge. The strong acidity of POMs and its interaction with proteins contributed to tightly bound EPS leaching and cell lysis during POMs/FeCl3 conditioning, which disrupted the sludge flocs structure. POMs denatured the released proteins and exposed the internal hydrophobic groups, enhancing the hydrophobicity of the sludge samples. Likewise, the engagement of POMs with sludge cells promoted the lysis of sludge cells by triggering the inactivation of specific functional enzymes, releasing capillary water, surface bound water, and a portion of the intracellular water. Fe3+ re-flocculated the free EPS with the crushed sludge particles through electrical neutralization to form a rigid porous structure. The cells crushing and re-flocculation effects synergistically enhanced the release efficiency of internal bound water, thus achieving sludge deep dewatering. Moreover, POMs/FeCl3 conditioning decreased the absolute abundance of antibiotic resistance genes (ARGs) and intI1 by disrupting the bacterial hosts, resulting in the removal and oxidation of ARGs and intI1 from the solid phase.