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

Enhanced deep-dewatering of high EPS-Containing sludge waste using PDMDAAC-PFS and H2O2

Large quantities of sludge from wastewater treatment plants require dewatering before final disposal, with extracellular polymeric substance (EPS) significantly impacting sludge dewatering performance. This study achieved deep-dewatering of sludge with high EPS content (164.36-181.62 mg/g VSS) by reducing moisture content to 57.2% using a combination of polydimethyldiallylammonium chloride-ferric sulphate (PDMDAAC-PFS) and hydrogen peroxide (H2O2). Using PDMDAAC-PFS alone decreased tightly bound EPS (TB-EPS) from 152.7 to 135.3 mg/g VSS while increasing EPS by 77.2%, indicating that the reagent solubilised TB-EPS and disrupted the cell wall, releasing intracellular bound water. Further addition of H2O2 reduced total EPS by 34.2-55.1%, primarily affecting extracellular protein (PN) in TB-EPS. Three-dimensional fluorescence and Fourier transform infrared spectrometry revealed that the reduced PN in TB-EPS consisted mainly of tyrosine proteins, with the destruction of hydrophilic groups (amino group and carbonyl group) contributing to the release of bound water. Quenching tests demonstrated that hydroxyl radicals generated by H2O2 were crucial for EPS oxidation, contributing to 21.9% of sludge dewatering. Additionally, PDMDAAC-PFS re-flocculated the structurally damaged sludge into larger, more porous particles, enhancing the dewatering process. Thus, this study presents a novel method of deep-dewatering for waste sludge containing high EPS content.

A synergistic approach integrating potassium ferrate oxidation with polyacrylamide flocculation to enhance sludge dewatering and its mechanisms

Sludge dewatering is a critical phase in sludge treatment and disposal, significantly impacting storage, transportation, and subsequent handling. This study introduces an innovative approach combining potassium ferrate (PF) oxidation and polyacrylamide (PAM) flocculation to synergistically enhance sludge dewatering efficiency. PF disrupts EPS and releases bound water, while PAM restores floc structure, addressing the limitations of standalone oxidation. Initial PF conditioning significantly reduced sludge water content (Wc) to 75.18 %, attributed to the oxidative breakdown of extracellular polymeric substances (EPS) and the release of bound water. However, higher PF doses increased specific filtration resistance (SFR) and capillary suction time (CST), indicating deteriorated filterability. The subsequent addition of PAM mitigated these issues, further reducing Wc to 73.64 %, SFR from 12.75 × 1012 m/kg to 3.62 × 1012 m/kg, and reduced CST from 88.95 s to 32.3 s, demonstrating marked improvements in dewatering performance. Characterization studies revealed the underlying mechanisms: PF-induced sludge fragmentation and EPS degradation, followed by PAM-mediated re-flocculation and structural reorganization. Further, applying XDLVO theory and Flory-Huggins lattice theory revealed changes in the sludge's surface hydrophilicity and the system's chemical potential, improving SFR and enhancing dewatering efficiency while reducing moisture content. This investigation not only offers an innovative dewatering approach but also underpins the mechanism of improved dewaterability.

The impact of radicals on physicochemical properties of waste activated sludge during hydrodynamic cavitation treatment

In this study, laboratory-scale Pinned Disc Rotary Generator of Hydrodynamic Cavitation was used to treat waste-activated sludge with a Total Solids concentration of 0.7 %. Five different rotor-stator arrangements were tested, focusing on waste-activated sludge physicochemical and rheological parameters of industrial relevance: general chemical analysis, rheometry, dewaterability, interfacial tension, UV-Vis and FTIR spectroscopy. Radical formation in all five arrangements was confirmed using salicylic acid dosimetry before sample testing. Three of the arrangements generated twice the radical concentration of the other two and achieved a disintegration degree three times higher (17 % compared to 5 %). Capillary Suction Time tests demonstrated a 14-fold reduction in filterability across all arrangements, accompanied by an increase in interfacial tension exceeding 10 %. Statistically significant changes in the UV-Vis spectra indicated alterations in dissolved organic matter humification, aromaticity, and molecular size of colorimetric dissolved organic matter, DNA, and RNA. FTIR analysis revealed characteristic peaks at 1537 cm-1 and 1648 cm-1, signifying microbial cell wall damage. Rheological analysis showed a reduction in apparent viscosity within the low shear stress zone (τ < 5 Pa) and a shift in the yield stress point to lower shear stresses (τ < 0.14 Pa compared to τ = 0.17 Pa for the untreated samples). Pearson's correlation test revealed strong, statistically significant correlations between cell wall damage (as identified by FTIR) and hydrodynamic conditions in the reactor, while the correlation with radical formation was not statistically significant. This suggests that hydrodynamic forces were the primary drivers of cell wall damage, with potential synergetic effects from radicals.

Deep dewatering of oily sludge: Mechanism, characterization, and pretreatment technology

Oily sludge, characterized by its high organic pollution, poses significant challenges for treatment and disposal due to its high proportion of bound water and elevated viscosity from petroleum hydrocarbons. This study focuses on the deep dewatering of oily sludge, examining the role of internal bound water and the pretreatment mechanisms involved. The deep dewatering process is categorized into two main areas: liberation of bound water and modification of physicochemical properties. (1) Bound water is primarily found in two major categories: water bound within proteins, EPS, and cells through hydrophilic interactions, and water within an oil-water emulsion structure facilitated by inorganic particles. (2) Physicochemical properties: The formation of flocs in oily sludge is crucial for effective dewatering, while creating dewatering channels in later stages enhances efficiency. Advanced oxidation and emerging demulsification technologies are also discussed, summarizing the latest research. The significant potential of electric fields in the deep dewatering of oily sludge is emphasized, offering valuable insights for future advancements.

New insights into extracellular polymeric substance degradation during dewaterability of sludge by UV-driven advanced reduction processes: Role of hydrated electron and spectroscopic profiling of dissolved organic components in sludge filtrate

Currently, Advanced Reduction Process (ARP) is gaining popularity as an alternative to Advanced Oxidation Process (AOP). Though UV/Sulfite process is effective in degrading organic compounds, no investigation has been done using ARP to improve sludge dewaterability. Here, effect of two different ARP's (UV/Sulfite; UV/Sulfide) that generates hydrated electron (eaq-) and hydrogen atom (H•) in enhancing sludge dewatering was explored. Based on findings, alkaline pH was favourable for ARP's to improve sludge dewatering. At optimal conditions, CST value was 18 and 23.3 s for UV/Sulfite and UV/Sulfide with raw sludge exhibiting 100 s at pH-7.7 respectively. The mechanism revealed that eaq- was the dominant reducing radical along with H•, based on EPR spectra and quenching experiments. UV-Vis, Gaussian fitting, 3D EEM Fluorescence and Synchronous Fluorescence Spectroscopy exhibited higher release of organic matter and aromaticity which agrees with FTIR analysis. Emission peak around 330-380 nm in all samples exhibited Microbial Soluble Products and aromatic protein II.

Enhancing methane production in anaerobic digestion of waste activated sludge by combined thermal hydrolysis and photocatalysis pretreatment

Thermal hydrolysis (TH) is promising for sludge pretreatment, but the refractory substances generated at high temperatures inhibit anaerobic digestion. In this study, a novel combined TH and photocatalytic pretreatment method was proposed to improve the anaerobic digestion performance of waste activated sludge. The results showed that the combined pretreatment (170 °C, 0.5 g/L TiO2) increased methane yield by 66 % from 111 ± 5 m L/g VS to 185 ± 5 m L/g VS. After TH pretreatment, photocatalysis further promoted sludge solubilization by destroying extracellular polymeric substances, resulting in an increase in released soluble organic matter from 292 ± 16 mg/L to 4,091 ± 85 mg/L. In addition, photocatalysis improved the biodegradability of sludge by reducing the melanoidin and humic acid contents by 26 % and 20 %, respectively. The proposed novel pretreatment method effectively overcomes the bottleneck of TH technology and provides an alternative pretreatment technology for improving sludge resource recovery.

Characteristics and aging of microplastics in waste activated sludge under persulfate and hydrothermal co-treatment: Impact of solid content and temperature

Activated persulfate and hydrothermal treatment (HTT) are often employed to treat waste activated sludge, which can improve the efficiency of subsequent sludge treatment and change the distribution of pollutants in the sludge. However, the impact of sludge solid content and temperature on the occurrence and aging of microplastics (MPs) during HTT remains poorly understood. This study investigated the effects of persulfate-HTT (SPS-HTT) co-treatment on the migration, occurrence, and aging of MPs in sludge with different solid contents (2% and 5% solid content). The results indicated that SPS-HTT co-treatment triggers both the disruption of sludge flocs and the melting deformation of MPs at high temperatures, leading to variations in the increasing trend of MP concentration in the solid-liquid phase at different solid contents. 5% solid content sludge showed a weak release of MPs from the solid phase. The proportion of fiber MPs first increased and then decreased with increasing temperature, while no significant changes were observed in the color and type of MPs. Higher temperature and solid content induced the melting deformation of MPs, exacerbated the aging of polypropylene MPs, and resulted in rough surfaces, higher carbonyl index, and variations in crystallinity. Moreover, the correlation between the carbonyl index and aging indicators increased with increasing solid content. The MP-derived dissolved organic matter under HTT primarily comprised soluble microbial by-products and humic acid-like substances. These findings underscore the significance of sludge solid content in affecting the migration and aging of MPs during HTT, and offer novel insights into the application of HTT to MP management in sludge treatment.

Synergetic conditioning via oxalic acid enhanced Fe2+/CaO2 and skeleton construct to achieve deep dewatering of sewage sludge

Extracellular polymeric substance (EPS) with highly hydrophilic groups and sludge with high compressibility are determined sludge dewaterability. Herein, Fe2+ catalyzed calcium peroxide (CaO2) assisted by oxalic acid (OA) Fenton-like process combined with coal slime was applied to improve sludge dewaterability. Results demonstrated that the sludge treated by 0.45/1/1.1-OA/Fe2+/CaO2 mM/g DS, the water content (WC), specific resistance to filtration and capillary suction time dropped to 53.01%, 24.3 s and 1.2 × 1012 m/kg, respectively. Under coal slime ratio as 0.6, WC and compressibility were further reduced to 42.72% and 0.66, respectively. The hydroxyl radicals generated by OA/Fe2+/CaO2 under near-neutral pH layer by layer collapsed EPS, resulting in the degradation and migration of inner releasing components and the exposure of inner sludge flocs skeleton. The hydrophilic tryptophan-like protein of TB-EPS were degraded into aromatic protein of S-EPS and exposed inner hydrophobic sites. The protein secondary structures were transformed by destroying hydrophilic functional groups, which were attributed to the reducing α-helix ratio and reconstructing β-sheet. Moreover, coal slime as the skeleton builder lowered compressibility and formed more macropores to increase the filterability of pre-oxidized sludge for the higher intensity of rigid substances. This study deepened the understanding of OA enhanced Fenton-like system effects on sludge dewaterability and proposed a cost-effective and synergistic waste treatment strategy in sludge dewatering.

Physical conditioning methods for sludge deep dewatering: A critical review

Sludge is an inevitable waste product of sewage treatment with a high water content and large volume, it poses a significant threat of secondary pollution to both water and the atmosphere without proper disposal. In this regard, dewatering has emerged as an attractive method in sludge treatment, as it can reduce the sludge volume, enhance its transportability and calorific value, and even decrease the production of landfill leachate. In recent years, physical conditioning methods including non-chemical conditioners or energy input alone, have been extensively researched for their potential to enhance sludge dewatering efficiency, such as thermal treatment, freeze-thaw, microwave, ultrasonic, skeleton builders addition, and electro-dewatering, as well as combined methods. The main objective of this paper is to comprehensively evaluate the dewatering capacity of various physical conditioning methods, and identify key factors affecting sludge dewatering efficiency. In addition, future research anticipated directions and outlooks are proposed. This work is expected to provide valuable insights for developing efficient, eco-friendly, and low-energy consumption techniques for deep sludge dewatering.

Excess secondary sludge reuse by H2O2 thermal dehydration

The excess of activated sludge generated in municipal wastewater treatment plants constitutes one of the challenging problems facing modern society. The high-water content of this waste makes difficult the transport, disposal, and management of these solids. In this work, activated sludge excess from a secondary clarifier has been dehydrated by means of a combination of temperature and hydrogen peroxide treatment. Three main operating variables have been considered to affect sludge dewaterability and filterability. Temperature (120-180 °C), hydrogen peroxide dose (0.01-0.03 M), and treatment time (20-60 min) influence have been assessed by completing a 15-run Box Behnken experimental design. Different output variables (water content, resistance to filtration, sedimentation volumetric index, extracellular polymeric substances, etc.) have been monitored. Generally, temperature seems to be the most influencing parameter to obtain a dehydrated sludge with acceptable management/disposal characteristics (sludge volume reduction and filterability). In line with the concept of circular economy, an attempt has been conducted to obtain a sustainable biosorbent from the dehydrated sludge generated in the previous stage. Optimum conditions of carbonization and activation revealed that the solid obtained at 400 °C by using ammonium nitrate as activation agent was the most efficient absorbent to eliminate some model compounds from water (namely, phenol, ofloxacin, and diuron); however, a clear improvement margin in the synthesis is foreseen.

Insight into sludge dewatering by periodate driven directly with Fe(Ⅱ): Extracellular polymeric substances solubilization and mineralization

The production of waste activated sludge is expanding in tandem with the significant growth in the global population. It is important to explore sludge pretreatment technology to achieve sludge reduction. In this study, deep sludge dewatering was achieved by using Fe2+-catalyzed periodate (Fe2+/PI) conditioning. The result showed that capillary suction time was reduced by 48.27% under the optimum Fe2+ and PI dosages. ·OH, FeⅣ, O2·-, 1O2, and IO3· generated from the reaction between Fe2+ and PI, while ·OH (49.79%) and FeⅣ (47.76%) contributed significantly to sludge dewatering. Investigations of the mechanism revealed that the synergistic action of radical species oxidation and iron species flocculation in Fe2+/PI conditioning led to the mineralization and aggregation of hydrophilic substances in extracellular polymeric substances. The hydrophobic groups on the protein surface were more exposed to soluble extracellular polymeric substances and reduced protein-water interaction. The variations in zeta potential and particle size also verified the presence of a synergistic effect of oxidation and flocculation. The morphology observations revealed that the increased frictional forces generated when water flowed over the raw sludge (RS) surface prevented the rapid passage of internal water. In addition, the hydrophobic and electrostatic interactions in the sludge samples were essential influences that promoted flocculation and sedimentation of the sludge. This research aids engineers by providing a new option to better optimize sludge management while also deepening understanding of the Fe2+/PI conditioning involved in sludge dewatering.

Enhanced disintegration mechanism of surplus activated sludge to improve dewatering by thermally activated persulfate oxidation under mild temperature

The dewatering treatment is an essential process for the treatment and disposal of surplus activated sludge (SAS), and improving sludge dewatering performance is still a challenge and has become a research hotspot in recent years. The oxidation and disintegration of bacterial cells and extracellular polymeric substances (EPS) by active radicals produced by advanced oxidation processes (AOPs) were extremely promising to achieve deep sludge dewatering. This paper systematically studied the efficiency and mechanism of thermally activated persulfate (TAP) oxidation technology to the improvement of SAS dewatering performance. The results showed that the relative filterability (CST0/CST) was increased 2.52 times with 2.0 mmol/g VSS potassium peroxydisulfate (PDS) at 80 °C in 90 min. Under this condition, the Zeta potential of SAS significantly decreased from - 14.8 to - 1.44 mV, while the average particle size (dp50) decreased from 52.981 to 48.259 μm. Thermal treatment disrupted the sludge structure to release large amounts of EPS including polysaccharides and protein. Meanwhile, the results of three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectra showed that the TAP treatment could expedite the disintegration of sludge, facilitating the decrease of total EPS content and conversion of tightly bound EPS (TB-EPS) to loosely bound EPS (LB-EPS) and soluble EPS (S-EPS). The mechanism of TAP process to improve SAS dewatering performance was revealed, which could contribute to breaking the bottleneck of sludge depth dewatering and provide a theoretical and technical basis for its practical application.

Improving sewage sludge dewaterability via heterogeneous activation of persulfate by Fe-Al layered double hydroxide: Role of generated SO4-•

In this study, Fe-Al layered double hydroxide (Fe-Al LDH) was prepared and applied to activate persulfate to condition sewage sludge and improve its dewaterability. The results showed that Fe-Al LDH activated persulfate to generate a large amount of free radicals, which attacked extracellular polymeric substances and reduced their content, disrupted microbial cells, released bound water, decreased sludge particle size, increased sludge zeta potential, and improved sludge dewaterability. After sewage sludge was conditioned with Fe-Al LDH (0.20 g/g total solids (TS)) and persulfate (0.10 g/g TS) for 30 min, the capillary suction time of the sludge dropped from 52.0 s to 16.3 s, while the moisture content of the sludge cake decreased from 93.2% to 68.5%. The dominant active free radical produced by the Fe-Al LDH-activated persulfate was SO₄^-•. The maximum Fe³⁺ leaching of the conditioned sludge was only 102.67 ± 4.45 mg/L, thus effectively alleviating the secondary pollution of Fe³⁺. The leaching rate of 2.37% was significantly lower than that of the sludge homogeneously activated with Fe²⁺ (738.4 ± 26.07 mg/L and 71.00%).

Effects of persulfate-assisted hydrothermal treatment of municipal sludge on aqueous phase characteristics and phytotoxicity

Hydrothermal technology (HT) has received much attention in recent years as a process to convert wet organic waste into hydrochar. The aqueous phase (HTAP) produced by this process is still a burden and has become a bottleneck issue for HT process development. In this study, we provide the first investigation of the HTAP characteristics, phytotoxicity, and their correlation with persulfate (PS) (PS, 2.0 mmol/g TS)-assisted municipal sludge HT. The results showed that PS accelerated the hydrolysis of protein substances and increased the concentration of NH₄⁺ by 13.4% to 190.5% and that of PO₄^3- by 24.2% to 1103.7% in HTAP at hydrothermal temperatures of 120 to 240 °C. PS can reduce the phytotoxicity of HTAP by reducing aldehydes, ketones, N heterocyclic compounds, and particle size and by increasing its humification index. The maximum values of the root length and biomass of pakchoi (Brassica chinensis L.) seedlings occurred when electrical conductivity was 0.2 mS/cm of HTAP. This work provided a new strategy for the selection and design of HTAP management strategies.

A comparison of oxidation and re-flocculation behaviors of Fe2+/PAA and Fe2+/H2O2 treatments for enhancing sludge dewatering: A mechanism study

In this study, Fe²⁺ activated-PAA was developed as a novel technology to enhance sludge dewatering. The result showed that the filterability (CST₀/CST) enhanced by 4.20 ± 0.14 times more than the control, and the SRF and bound water content decreased from 4.58 ± 0.07 × 10¹³ m/kg and 2.11 ± 0.28 g/g dry sludge to 9.47 ± 0.05 × 10¹² m/kg and 1.27 ± 0.18 g/g dry sludge, respectively after the sludge was conditioned by 1.20 mM/g VSS Fe²⁺ and 1.20 mM/g VSS PAA. The dewatering performance, physicochemical properties, aggregation behaviors, and EPS fractions of sludge were compared before and after Fe²⁺/PAA and Fe²⁺/H₂O₂ conditionings. The results showed that Fe²⁺/PAA treatment was more competitive in enhancing dewaterability under neutral and alkaline conditions than Fe²⁺/H₂O₂ treatment but slightly weaker under acid conditions. Besides, it was found that the oxidation and re-flocculation behaviors were different in those two enhanced dewatering technologies due to the difference in the generated ROS. R-O was the primary radical in the Fe²⁺/PAA system, while OH was the major one in the Fe²⁺/H₂O₂ system. The mechanism analysis found that the Fe²⁺/PAA process caused harsher disintegration of sludge flocs, meaning more generation of fine particles. However, it exhibited less effect on reducing the energy barrier between sludge particles. Therefore, the Fe²⁺/PAA treated sludge presented weaker aggregation behaviors. The weaker aggregation was unfavorable for sludge dewatering because the weaker aggregated flocs were more easily fragmented, which hampered the consolidation of sludge cakes and removal of bound water. Moreover, loosely-bound extracellular polymeric substances, particularly tightly-bound extracellular polymeric substances, governed the sludge dewaterability.

A novel pre-magnetized ZVI/PS pretreatment for improving sludge dewaterability: The role of EPS fractions

The dewaterability of waste-activated sludge (WAS) has been extensively examined using zero-valent iron (ZVI)-based advanced oxidation processes (AOPs). However, the high dosage and low utilization efficiencies of ZVI cast doubt on the dependability and viability of ZVI-based AOPs. In this study, we successfully demonstrated pre-magnetization as an efficient, chemical-free, and ecological method for improving the efficiency of sludge dewatering by ZVI/persulfate (PS) process, in which the reduction ratios of capillary suction time (CST) and specific resistance to filtration (SRF) increased by 8.67% and 11.06% under optimal conditions, respectively. The highly active Fe²⁺ released during ZVI corrosion may be more essential than ZVI itself during PS activation, which could be strengthened by pre-magnetization. Both homogeneous and heterogeneous Fe²⁺ could react with PS to produce aqueous hydroxyl radicals (∙OH) and sulfate radicals (SO₄^-∙) as well as surface-bound ∙OH and SO₄^-∙, further decomposing bound-extracellular polymeric substances fractions, broking hydrophilic functional groups and compounds, altering protein secondary structure to expose more hydrophobic sites, and releasing abundant EPS-bound water. Due to the protection of tightly-bound extracellular polymeric substances (TB-EPS) and the competitive oxidation of organics released during the early disintegration stage, radical oxidation primarily occurs at extracellular levels, releasing a bit of intracellular water. Besides, polysaccharides in TB-EPS may function a more significant role in flocculation than proteins, and a porous structure favorable to drainage will be formed after the pre-magnetized ZVI/PS treatment. The cost-benefit analysis further reveals that the Pre-ZVI/PS process presents high reusability and utilization, making it potential for particle application in sludge dewatering.

The application of sulfate radical-based advanced oxidation processes in hydrothermal treatment of activated sludge at different stages: A comparative study

Integrating hydrothermal treatment (HT) and advanced oxidation processes (AOP) was proved to be a promising approach for improving sludge dewaterability. In this study, the EPS valorization under elevated temperature and sulfate radical-based AOP were investigated to clarify the valorization of organic matter in different EPS layers and its effects on the sludge dewaterability. Results indicated that the organic matters in the inner layer of EPS decreased sharply with the elevated temperature, and released into the soluble EPS. Sulfate radical-based AOP significantly accelerated the degradation of organics and microbial cells lysis, especially in the presence of ZVI. The protein with the higher hydrophobicity was detected under the AOP enhanced HT. A better synergistic effect on sludge dewaterability was obtained by integrated the AOP at the initial hydrothermal stage. 3D-EEM and parallel factor analysis indicated that the protein and microbial by-product like substances in tightly bound EPS significantly affected the dewaterability.

Activation of Peroxydisulfate by Bimetallic Nano Zero-Valent Iron for Waste-Activated Sludge Disintegration

Waste-activated sludge (WAS) disintegration using peroxydisulfate (PDS) has attracted scientific attention over the past few years. Despite several advantages offered by a sulfate radical-advanced oxidation process, there are still too many downsides of this treatment that limit its facile large-scale application. This study investigated whether modifying nano zero-valent iron (nZVI) with a second metal such as Ag and Cu enhanced the disruption of WAS. The disintegration efficiency was assessed using standard techniques, i.e., soluble chemical oxygen demand, Fourier-transform infrared spectroscopy and a scanning electron microscope. The bimetallics were shown to have an improved disintegration efficiency of > 2.5-fold compared with the untreated sample. Furthermore, nZVI/Ag was found to be more efficient than nZVI/Cu for PDS activation, which was validated by the higher ratio (3 and 2.5 for nZVI/Ag and nZVI/Cu, respectively) between the soluble extracellular polymeric substances and the bound extracellular polymeric substances (S-EPS/B-EPS). Similar conclusions were derived from a SEM analysis. The improved disintegration efficiency could be related to the enhanced electron transfer from nZVI to PDS or the intrinsic properties of silver, which was found to be one of the best activators for PDS under homogeneous conditions. We believe that this study deepens the understanding of PDS heterogeneous activation processes.

Insights into vacuum preloading consolidation of landfill sludge based on Fe2+-activated sodium persulfate

To further reduce the in-situ sludge from landfill, Fe²⁺-activated sodium persulfate combined with vacuum preloading was first proposed. Firstly, the effects of optimal Na₂S₂O₈ dosage on the landfill sludge (LS) were investigated by the vacuum filtration experiments. Then, vacuum preloading experiments were conducted on the sludge with different Na₂S₂O₈ dosages to study the water content, water discharge, and settlement. Besides, sludge particle size diversification was carried out by particle size distribution and scanning electron microscopy (SEM) tests. The results were summarized as follows: the specific resistance of filtration (SRF) of LS could be reduced by 98.5% mostly when the Na₂S₂O₈ dosage was 30%; the particle size became significantly smaller, and large particles were converted to small particles; the water content dropped from 86.9 to 58.3%; and the SEM test manifested the oxidation of sodium persulfate caused the destruction of the glial structure of the sludge and the recombination of partial particles.

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

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

Enhanced waste activated sludge dewaterability by the ozone-peroxymonosulfate oxidation process: Performance, sludge characteristics, and implication

Dewatering treatment is an essential step to diminish sludge volume, cut down transportation costs, and improve subsequent disposal efficiency. In this study, ozone-peroxymonosulfate (O₃/PMS) oxidation process was employed to ameliorate sludge dewaterability. Sludge capillary suction time (CST) and water content (Wc) of dewatered sludge cake could reduce from 70.5 s and 81.93% to 26.7 s and 65.65%, respectively, under the optimal dosage of 30 mg/g TS O₃ and 0.4 mmol/g TS PMS. The increased sludge zeta potential, particle size, and fluidity promoted sludge dewatering performance apparently. The decreased hydrophilic, fluorescent EPS components and proteins/peptides-like + Lipids percentage in EPS as well as the ratio of α-helix/(β-sheet + random coil) of treated EPS protein secondary structure was greatly responsible for the enhanced sludge dewaterability. SO₄^- and OH were detected in ozone-peroxymonosulfate process to crack sludge flocs, eliminate hydrophilic substances and liberate bound water. Moreover, the concentrations of both heavy metals and polycyclic aromatic hydrocarbons (PAHs) of sludge after O₃/PMS conditioning were decreased, and the stability and toxicity of heavy metals were also reduced, except Zn. In conclusion, this work offered a comprehensive insight based on ozone-peroxymonosulfate (O₃/PMS) advanced oxidation for improving the sludge dewaterability and environmental implication.

Fe(II)-activated sodium percarbonate for improving sludge dewaterability: Experimental and theoretical investigation combined with the evaluation of subsequent utilization

Fe(II)-activated sodium percarbonate (SPC) was an emerging technology for enhancing the dewaterability of waste activated sludge, and its operational parameters were systematically explored. The results showed that after the treatment by 1.20 mmol/g VSS SPC and 1.44 mmol/g VSS Fe(II) at initial pH 3.0, the water content and specific resistance to filtration remained at 76.05 ± 0.36% and 2.57 ± 0.08 × 10¹² m·kg^-1, respectively. The acid condition was instrumental in sludge dewatering, whereas overdosing Fe(II) or SPC imposed adverse effect. The conversion of EPS fractions was examined to elucidate the underlying mechanism, which indicated that a coexisting oxidation/flocculation process accounted for the improvement of sludge dewaterability. The stronger oxidative ·OH degraded the hydrophilic compounds (proteins and carbohydrates) of tightly-bound extracellular polymeric substance and the dissolved multivalence iron promoted solid-liquid separation. Additionally, the theoretical analysis (DFT calculation) demonstrated that the oxygen- and nitrogen-containing groups of EPS resulted in high-water holding capacity of sludge. The difficulty of destroying hydrophilic functional groups followed C=O > C-N > C-O during oxidation process. Moreover, Fe(II)/SPC treatment performed well in coliforms inactivation and phytotoxicity reduction compared with different ·OH-based advanced oxidation processes for sludge conditioning.

Degradation of TBBPA by nZVI activated persulfate in soil systems

Tetrabromobisphenol A (TBBPA) greatly impacts on ecosystems and human health due to its high environmental toxicity and persistence. Persulfate (PS) advanced oxidation technology to remove organic pollutants in soils has received intense attention. In this study, nanoscale zero-valent iron (nZVI) was synthesized through the borohydride reduction method to explore its activating potential towards PS to accelerate the degradation of TBBPA in soils. The degradation behaviors of TBBPA in soils were investigated by batch experiments. The degradation efficiency of TBBPA (5 mg kg^-1) was 78.32% within 12 h under the following reaction conditions: 3 g kg^-1 nZVI, 25 mM PS, and pH 5.5 at 25 °C. Notably, PS can be used effectively, and the pH changed slightly in the reaction system. Oxidative degradation of TBBPA is favored at higher temperatures and lower pH values, while it is inhibited when the amount of catalyst increases significantly. The coexisting heavy metal ions such as Zn(II) and Ni(II) inhibit TBBPA degradation, while Cu(II) accelerates the degradation. Radical scavenging and electron spin resonance (ESR) tests further confirmed the generation of SO₄^·-, ·OH, and O₂^·- in nZVI activated PS. The intermediates identified by gas chromatograph-mass spectrometry analysis indicated that TBBPA via debromination and the cleavage between the isopropyl group and one of the benzene rings complete degradation. These findings provide new insight into the mechanism of nZVI activation of PS and will promote its application in the degradation of refractory organic compounds.

Efficient decomposition of lignocellulose and improved composting performances driven by thermally activated persulfate based on metagenomics analysis

In this study, fresh dairy manure and bagasse pith were used as raw materials to study the effect of potassium persulfate in the aerobic composting process. The influence of sulfate radical anion (SO₄^-·) generated by thermally activated persulfate on physicochemical parameters, lignocellulose degradation, humic substance (HS) formation, microbial community succession, and carbohydrate-active enzymes (CAZymes) composition were assessed during composting. Experimental results showed that the degradation rates of cellulose, hemicellulose and lignin in the treatment group with potassium persulfate (PS) (61.47%, 74.63%, 73.1%) were higher than that in blank control group (CK) (59.98%, 71.47%, 70.89%), respectively. Additionally, persulfate additive promoted dynamic variation of dissolved organic matter (DOM) and accelerated the formation of HS. Furthermore, metagenomics analysis revealed that persulfate changed the structure of the microbial community, and the relative abundances of Actinobacteria and Proteobacteria increased by 17.64% and 34.09% in PS, whereas 12.09% and 29.96% in CK. Glycoside hydrolases (GHs) and auxiliary activities (AAs) families were crucial to degrade lignocellulose, and their abundances were more in PS. Redundancy analysis (RDA) manifested that Actinobacteria and Proteobacteria were closely associated with lignocellulosic degradation. In brief, persulfate could accelerate the degradation of organic components, promote the formation of HS, optimize the structure of microbial community, and improve the compost quality.

Insight into the roles of electrolysis-activated persulfate oxidation in the waste activated sludge dewaterability: Effects and mechanism

Sludge dewatering, as one of the most important steps of sludge treatment, can facilitate transportation and improve disposal efficiency by reducing the volume of sludge. This study investigated the effects of electrolysis-activated persulfate oxidation on improving sludge dewaterability. The results indicated that the sludge capillary suction time (CST) and water content of dewatered sludge cake (Wc) reduced from 93.7 s and 87.8% to 9.7 s and 68.3% respectively at the optimized process parameters: electrolysis voltage of 40 V, electrolysis time of 20 min, and 1.2 mmol/g TS S₂O₈^2-. Correlation analysis revealed that the enhancement of sludge dewaterability was closely associated with the increased floc size and zeta potential, decreased protein content in three-layers extracellular polymeric substances (EPS) and viscosity (R = -0.868, p = 0.002; R = -0.703, p = 0.035; R ≥ 0.961, p < 0.001; R = 0.949, p < 0.001). Four protein fluorescence regions in EPS were analyzed by three-dimensional excitation-emission matrix parallel factor (3D-EEM-PARAFAC). The protein secondary structure was changed after the treatment, and the reduction of α-helix/(β-sheet + random coil) indicated that more hydrophobic sites were exposed. Analysis by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and rheological test demonstrated that the hydrophilic functional groups of the sludge were decreased and the sludge mobility was significantly enhanced after the treatment with electrolysis-activated persulfate oxidation. Moreover, bound water was converted to free water during SO₄·^- and ·OH generated by electrolysis-activated persulfate degraded EPS and attacked sludge cells. Meanwhile, scanning electron microscopy (SEM) images revealed that the treated sludge formed porous channel structures, which promoted the flowability of the water. These findings provide a new insight based on electrolysis-activated persulfate oxidation in sludge treatment for enhancing sludge dewaterability.

Novel insights into enhanced dewaterability and consolidation characteristics of landfill sludge and fresh sludge conditioned by Fe2+ activated sodium persulfate

Considering the reduction and resource utilization of landfill sludge (LS) and fresh sludge (FS), Fe²⁺ activated Na₂S₂O₈ is proposed. The effects of the molar ratio of Fe²⁺/S₂O₈^2- and the addition of Na₂S₂O₈ on the dewatering performance of sludge were studied by vacuum filtration experiments. Consolidation tests were conducted on the sludge with different Na₂S₂O₈ dosage, and the compression, consolidation, and permeability characteristics of the sludge were researched. Besides, via particle size distribution (PSD) and scanning electron microscope (SEM) test, the variation of particle size of sludge was studied from the microscopic perspective. The results are as follows: the specific resistance of filtration (SRF) of LS and FS decreases by 99.3%, 95.2% at an optimal dosage (the molar ratio of (Fe²⁺/S₂O₈^2-) = 1, 30% Na₂S₂O₈); the particle size of LS and FS is significantly smaller; the consolidation and permeability coefficients are increased by 1-2 orders of magnitude compared with non-conditioned sludge; the water content of LS and FS drops from 86.5% to 58.4%, 82.4%-59.7%. The research results have certain guiding significance for the in-situ treatment of sludge deep dewatering.

Identifying the key sludge properties characteristics in Fe2+-activated persulfate conditioning for dewaterability amelioration and engineering implementation

Fe²⁺-activated persulfate process has been introduced into sludge conditioning currently, however the key sludge properties characteristics are worthwhile comprehensively considering for the engineering implementation and management. The results indicated that both the optimal dosages of persulfate and Fe²⁺ were 0.6 mmol/gTS for sludge dewaterability amelioration, and the reduction efficiencies of capillary suction time (CST), specific resistance of filtration (SRF), and water content (Wc) of dewatered sludge cake reached to 90.5%, 97.2%, and 22.4%, respectively. Significantly, the persulfate and Fe²⁺ exerted distinctive roles in the conditioning process. The increased persulfate could promote the oxidatively disintegrated effect on sludge flocs, rendering the decrease of particle size. With the oxidative decomposition of the negatively charged biopolymers, sludge zeta potential rose gradually. However, Fe²⁺ contributed to more persulfate activation to generate free radicals, and the produced Fe³⁺ could further electrically neutralize the broken sludge fragments. The core mechanism of Fe²⁺-activated persulfate conditioning is "destroying and re-building" of sludge flocs. Noteworthily, EPS protein was oxidatively degraded more preferentially than EPS polysaccharide, and the decrease of the α-helix content of EPS protein was conducive to the enhancement of sludge dewaterability. Furthermore, the hydrophilic functional groups reduced clearly and element chemical states on sludge flocs altered pronouncedly, also the destroyed structure and microchannel facilitated the flowability of water. These findings provide theoretical and technical support for the practical engineering implementation of the Fe²⁺-activated persulfate conditioning process.