Interfacial electron transfer (IET) between aqueous Fe(II) (Fe(II)(aq)) and iron (oxyhydr)oxides is a widespread process that generates highly reactive Fe(III) species (Fe(III)(labile)), facilitating rapid mineral recrystallization into stable crystalline phases. These systems are known to be more reducing towards a wide variety of electron accepting species. However, these same systems show anomalous redox reactivity toward arsenic, in that they favor oxidation of As(III) rather than reduction of As(V). We hypothesized this reactivity arises from a direct quantitative connection between Fe(III)(labile) production and As(III) oxidation. Here we tested this hypothesis by employing magnetite nanoparticles with varying stoichiometries (Fe(II)/Fe(III) ratios), denoted Mt(0.48), Mt(0.37), and Mt(0.24), as representative minerals that, along with varying Fe(II)(aq) amendment, were used to manipulate Fe(III)(labile) generation and establish its role in reactions with As(III) and As(V). Magnetite could generate Fe(III)(labile) through dual pathways of Fe(II)(aq) release and adsorption, driven by reversible electron redistribution across the magnetite-solution interface. At pH 7.0 and 20-100 & micro;M arsenic, the adsorption rates and capacities for both As(III) and As(V), as well as As(III) oxidation extents, followed the order Mt(0.48) > Mt(0.37) > Mt(0.24), despite the lower apparent redox potentials of more stoichiometric particles. These reactions were accompanied by extensive depletion of Fe(III)(labile), showing a strong global linear correlation between Fe(III)(labile) consumption and As(III) oxidation across all systems. DFT calculations further revealed the strong electronic interactions and substantial Bader charge transfer (1.943-2.212 e) from As(III) to Fe(III)(labile). Our results identify Fe(III)(labile) as the critical redox-active species controlling arsenic adsorption and As(III) oxidation on magnetite nanoparticles, providing new mechanistic insights into the role of this important species and coupled arsenic-iron cycling in subsurface environments.

Pentachlorophenol (PCP) is a persistent chlorinated organic pollutant with high toxicity, strong environmental stability, and resistance to biodegradation. Although persulfate-based oxidation is promising for PCP remediation, its performance in contaminated soil is often limited by complex soil matrices and unclear activation mechanisms. In this study, CaO-activated persulfate was applied to PCP degradation in actual contaminated soil, with emphasis on synergistic alkaline–thermal activation and calcium-associated PCP transformation. CaO significantly enhanced PCP degradation, achieving 86.0% removal after 7 d, whereas persulfate alone showed limited oxidation capability. Mechanistic analysis showed that CaO promoted PCP degradation through Ca(OH)2-induced alkaline activation, hydration-induced transient thermal activation, and Ca2+-mediated formation of calcium-associated pentachlorophenolate species (PCP-Ca). PCP-Ca formation reduced the apparent degradation activation energy from 112.8 to 92.3 kJ mol−1 and increased the apparent pseudo-first-order rate constant by 62.7% at 30 °C, indicating enhanced oxidative susceptibility. SO4•- and •OH were identified as the main reactive species. LC-MS analysis suggested that PCP degradation proceeded through hydroxylation, dechlorination, and ring-cleavage pathways, generating intermediates with lower predicted toxicity. This study reveals the multifunctional role of CaO in persulfate activation and provides mechanistic insight into PCP degradation in contaminated soil.

Propionate is a key intermediate in anaerobic digestion (AD), and its accumulation may lead to over-acidification and process failure. This study assessed methanogenic tolerance to increased propionate concentrations. The specific methane yield ranged from 238.0 to 277.3 mL/g COD at the initial propionate concentration of 2 to 10 g COD/L, and slightly decreased to 260.6 and 233.3 mL/g COD at 13 and 16 g COD/L, respectively. Kinetic analysis indicates lower inoculum-to-substrate ratio primarily negatively affected digestion time rather than accumulated methane yield. No clear inhibition occurred, even at 16 g COD/L, indicating a substantial propionate tolerance in AD. 16S rRNA gene analysis revealed that Desulfobacterota, particularly the family Syntrophobacteraceae was positively associated with propionate degradation, showing a linear correlation (p < 0.01) with both initial propionate concentration and digestion duration. Genome-centric metagenomic analysis further identified Bin.002 (Syntrophobacteraceae JABUEY01) and Bin.012 (Syntrophobacteraceae sp.) as dominant syntrophic populations, exhibiting high RPKM abundance and encoding the complete methylmalonyl-CoA (mmc) pathway. A metabolically diverse methanogenic community was also enriched, including aceticlastic Methanosarcina mazei (Bin.006), Methanothrix spp. (Bin.009 and Bin.014), and hydrogenotrophic Methanobacterium spp. (Bin.011 and Bin.026), which rapidly consumed metabolic intermediates, thereby avoiding inhibition at high propionate concentrations. Overall, the batch experiments demonstrated strong propionate tolerance under stable anaerobic conditions, supporting the conclusion that propionate accumulation is more likely a consequence rather than a primary cause of anaerobic reactor imbalance.

Poor sludge properties and weak hydrodynamics severely limit mass transfer and solid-liquid separation in anaerobic membrane bioreactors (AnMBRs) treating food waste. This study developed a synergistic foulingmitigation strategy that couples moderate biogas sparging with a self-antifouling reciprocating membrane module. Compared with reciprocation alone, the integrated operation extended the stable filtration period from 19 to 60 days, and enabled an in-situ recovery step that sustained operation for a further 35 days, accompanied by a 14.5% increase in methane production rate. The integrated mode reduced sludge viscosity and particle size, indicating a higher mixing efficiency. Particle-image velocimetry showed higher near-membrane shear and stronger bulk circulation attributable to gas scouring and inertial effects. Scanning electron microscopy showed reduced gel-like coverage on the cake layer under the integrated strategy. Microbial sequencing identified filamentous Anaerolineae (SBR1031) as dominant in sludge and cakes, with sparging reshaping community structure. Genome-resolved metagenomics reconstructed key genomes and suggested higher representation of acetogenic and methanogenic potential under the integrated strategy. Overall, this study demonstrates a promising fouling control strategy for high-solids, viscous organic waste treatment.

The application of polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes in drinking water treatment plants (DWTPs) is increasing rapidly. However, as a class of fluoropolymer materials, PVDF membranes might be a source of per- and polyfluoroalkyl substances (PFAS) in drinking water systems. In this work, we identified the occurrence of PFAS in commercial PVDF UF membranes, with PFOA as the dominant species (82-97% of & sum;PFAS). Subsequently, we explored their release behavior during chemical cleaning and membrane aging. NaOH/NaClO solutions induced sustained and enhanced release of C-4-C-6 and C-8 perfluorocarboxylic acids (PFCAs) (up to 104 ng/L), significantly higher than the leached levels from virgin membranes. Apart from short-term release of leachable PFCA residues, structural degradation of PVDF led to long-term release of PFCAs that were previously nonleachable from virgin membranes. In the chemical-cleaning wastewater from PVDF UF units at a full-scale DWTP, PFAS levels were much higher (up to 371 ng/L) than those observed in laboratory experiments, with similar dominant PFAS species. This study provides evidence that PVDF membrane aging by chemical cleaning induces persistent PFAS release, highlighting these membranes as an overlooked source of PFAS in DWTPs.

Radio-frequency heating (RFH) coupled with peroxydisulfate (PDS) represents a promising approach for the remediation of polycyclic aromatic hydrocarbons (PAHs)-contaminated soil, however, its performance and enhancement mechanisms remain unclear. Here, an RFH-PDS system was systematically evaluated using benz[a]anthracene (BaA) as a representative PAH, and its applicability was further assessed in field-contaminated soils. Under temperature-matched conditions, RFH outperformed conventional heating (CH) with increasing BaA degradation rate constant by 57% and reducing the apparent activation energy by 8.72 kJ mol-1 at 50 W RF power. RFH accelerated PDS decomposition with a 1.80-fold higher rate constant and enhanced SO4•- and •OH generation, consistent with density functional theory (DFT) calculations showing RF-induced weakening of the O-O bond in PDS. The BaA desorption rate from soil was increased by 59% under RFH relative to CH, which was potentially promoted by RFH-induced dissolved organic matter release, whereas metal dissolution showed a negligible contribution. DFT and GC-MS analyses indicated that RF exposure could modify the electrostatic potential distribution of BaA and alter its degradation pathways. Overall, the temperature-matched kinetic comparison, enhanced PDS activation, and altered BaA degradation pathways suggest an RF-associated enhancement beyond bulk thermal activation. For field-contaminated soil containing eight PAHs at 402.88 mg kg-1, RFH-PDS achieved 97.15% removal and reduced the total PAHs concentration to 11.49 mg kg-1, with residual PAHs below regulatory limits. These findings demonstrate that the RFH-PDS system is an effective and potentially scalable technology for the remediation of PAHs-contaminated soils.

Abstract Permanganate (KMnO4) is widely recognized as a green and efficient oxidant for water purification. During the oxidation of phenolic contaminants, however, soluble coupling products and Mn-containing species (e.g., MnOx colloids and dissolved Mn ions) may remain in the aqueous phase, increasing the burden of downstream separation. Herein, we demonstrate that commercial polyferric sulfate (PFS) can simultaneously serve as a KMnO4 activator and an in situ coagulant, establishing a one-step synergistic polymerization-coagulation strategy for efficient 4-chlorophenol (4-CP) removal with minimal soluble oligomers and leachable metal species. Mechanistic studies reveal that PFS forms a positively charged Fe-(hydr)oxide interface that facilitates KMnO4 activation via electrostatic interactions. Meanwhile, PFS serves as a solid scaffold that stabilizes the critical 4-chlorophenoxyl radical intermediate via bis(4-chlorocatecholato)iron(III) complex formation, thereby driving polymer chain growth. Leveraging its inherent coagulation property, PFS effectively captures organic polymers, increasing chemical oxygen demand (COD) removal from 35.4% to 56.2% within 10 min, while efficiently sequestering MnOx colloids and reducing residual Fe and Mn concentrations in the treated supernatant by 99.2% and 99.4%, respectively. This work addresses limitations of conventional KMnO4 oxidation through in situ polymerization-coagulation, offering a strategy for phenolic pollutant remediation with reduced soluble oligomer accumulation and metal residuals.

The stabilization of realgar tailings is extensively employed to reduce the contamination from arsenic (As) leaching to the environment. The high efficiency of realgar oxidation and the formation of stable As-bearing minerals are crucial for the long-term stability of realgar tailings. Herein, the mineralogical transformation of labile As-bearing minerals, i.e., realgar and stabilization mechanisms of realgar tailings with microwave (MW) and FeSO4 treatment were studied. Firstly, the activation of O2 by FeSO4 was enhanced and the generation of reactive oxygen species (ROS) was accelerated through MW treatment. Additionally, the mineralogical transformation to pararealgar due to "hot spots" on FeSO4 under MW irradiation enhanced the oxidation of realgar. Pararealgar exhibited higher electrons delocalization and electron-donating ability compared than realgar based on density functional theory (DFT) calculations. Furthermore, the formation of stable As-bearing minerals in tailings was promoted after MW and FeSO4 treatment, including crystalline Fe-As minerals and amorphous Ca-Fe-As minerals. Consequently, successful stabilization of realgar tailings was achieved with the As leachability <0.1 mg L-1, which was below the Chinese standard limit (1.2 mg L-1) for pollution control on the hazardous waste landfill. With 365 days of curing, the leachability of As in tailings furtherly decreased, demonstrating the long-term effectiveness of MW and FeSO4 treatment. The long-term stability of realgar tailings was attributed to the increased proportions of crystalline Fe-As minerals and amorphous Ca-Fe-As minerals. Overall, this study provided a novel stabilization strategy toward realgar tailings as well as As-bearing mining wastes by using MW and FeSO4 treatment.

Calcite plays a significant role in regulating As speciation in natural and engineering systems. However, known processes, including surface adsorption and probable structural incorporation, likely underestimate the effect of calcite-induced surface reactions on the As fate. This study reveals the epitaxial crystallization of calcium arsenite (CaHAsO3) on calcite surfaces, which is responsible for the enhanced As(III) stability caused by calcite during lime interaction with As(III). SEM images showed that Ca arsenite grew in a "standing" geometry on the calcite (104) face and appeared in order as micrometer-sized, well-crystallized platy crystals, rather than poorly crystallized nanosheets formed in the absence of calcite. The higher crystallinity/order and larger size of the epitaxial Ca arsenite led to its lower As(III) solubility. By electron diffraction analyses, lattice matching between calcite and Ca arsenite was evidenced. Despite the lack of Ca arsenite's crystallographic data, the epitaxial relationship was determined as (hkl)d=3.05Å// (104)calcite; [uvw]Ca-As-Ca PBC// [-441]calcite, where PBC stands for periodic bond chain. In contrast, no epitaxial crystallization of Ca arsenate minerals was observed on calcite surfaces; thus, the presence of calcite had little effect on As(V) stability. Our findings improve the understanding of calcite's role in affecting As speciation and broaden the application of calcite-containing materials in environmental remediation.

Alginate-modified ferrous sulfide (FeS) has received much attention in heavy metals (HMs) adsorption. However, whether calcium alginate (CA) could hinder FeS oxidation and promote HMs immobilization in Pb/Zn smelter soil, remains unclear. Herein, CA prolonged half-lives of S(-II) in CA-coated FeS (FeS-CA) by 92.2 % and 46.9 % when coexisting with O2 and MnO2, resulting in that S(-II) content in soil treated by FeS-CA was 38.7 % higher than bare FeS. The Pb, Zn, and Cd immobilization efficiencies by FeS within FeS-CA (FeSFeS-CA) were 79.1 %, 70.2 %, and 80.1 %, 3.3 %-17.6 % higher than that by bare FeS. The enhancement was mainly attributed to that labile HMs reduced by FeSFeS-CA were 20.6 %-32.2 % higher than bare FeS due to 19.5 %-30.5 % more SOM-bound labile HMs captured by FeSFeS-CA. The labile Pb was converted into Fe/Mn (hydr)oxides-bound and residual fractions, while labile Zn and Cd were converted into Fe/Mn (hydr)oxides-bound fractions. The CA was stable during soil incubation and leaching. It could immobilize 10.8 %-28.2 % of HMs and promote 12.8 %-16.6 % of the labile HMs conversion due to competitively adsorbing the SOM-bound HMs. The HM-bridging configurations of CA-HM-DOM were responsible for DOM adsorption, accompanied by HMs stabilization with high adsorption energies (>7 eV). The CA-bound HMs were stable under the rainfall conditions. Furthermore, CA could recapture more than 82.2 % of HMs released from solid phases via carboxyl complexation when H+ is input, alleviating HM leaching. The results indicate that FeS-CA is an effective and applicable stabilizer for HM immobilization in Pb/Zn smelter soil.

Anaerobic membrane bioreactors (AnMBRs) offer a promising solution for high-solid organic waste digestion, but their widespread application is limited by severe membrane fouling. This study investigates the fouling mechanisms in a novel reciprocating AnMBR (rAnMBR) compared to a conventional biogas sparging AnMBR (sAnMBR) under increasing organic loading rates (OLR) from 2 to 6 g COD/L/d, with a corresponding reduction in hydraulic retention time to 11.7 days. Both systems exhibited similar methanogenic performance; however, the rAnMBR demonstrated significantly better fouling resistance, maintaining filtration for 33 and 20 days at low and high OLRs, respectively, whereas the sAnMBR fouled within 11 and 4 days. Sludge characterization revealed that the rAnMBR retained a higher fraction of microparticles (1.5-10 mu m), which reduced sludge filterability. Particle image velocimetry showed improved hydrodynamics in the rAnMBR, leading to slower and more uniform cake layer formation. Microbial analysis indicated distinct communities between the systems, with the rAnMBR favouring filamentous and helix-shaped bacteria, potentially contributing to its observed fouling behaviour. These findings suggest that reciprocation, as a self-antifouling strategy, is a viable alternative for mitigating membrane fouling in high-solid food waste digestion, offering improved operational stability and lower maintenance costs. This study provides valuable insights for optimizing AnMBR design and advancing sustainable waste-to-energy technologies.

The excellent adsorption performance of layered double hydroxides (LDHs) toward heavy metals (HMs) had been demonstrated. The carbonate contamination was one of the inherent problems for LDHs whether during the synthesis or application procedure, which significantly affected the adsorption performance of LDHs toward HMs. However, a few studies investigated the mutual effect and mechanism between HMs on LDHs with carbonate interference, especially for the coexistence system of cationic and anionic HMs. In this study, cadmium (Cd) and arsenate (As) were selected as typical cationic and anionic HMs to study the influences of carbonates on their adsorption performance on LDHs. The carbonate intercalated LDHs (CLDH) promoted Cd adsorption but inhibited As adsorption in single system. The adsorption capacity of Cd increased by similar to 50 % while As adsorption decreased by half. CdCO3 precipitation contributed to similar to 40 % of the adsorbed Cd whereas weaker electrostatic adsorption inhibited As adsorption due to lower surface zeta potentials of CLDH than LDH. In contrast, both adsorption capacities and rates of Cd and As on CLDH were promoted in binary system (the co-existence of Cd and As) compared with single system. The surface potentials of CLDH turned from positive to negative with As rapid occupation, facilitating Cd entrance into the interlayers. And then the opening of the interlayer space and rearrangement of CLDH enhanced CdCO3 precipitation and isomorphic substitution. With the increase of surface zeta potentials and rearrangement of CLDH, in turn, the adsorption of As was promoted via electrostatic adsorption (similar to 65 %) and surface complexation (similar to 35 %). The adsorption capacity of Cd increased by similar to 15 % whereas As adsorption decreased by half with increasing pH from 4 to 9 in binary system. In contrast, temperature (15-35 degree celsius) had negligible influence on the adsorption of CLDH toward Cd and As. Herein, this study illustrated the influence mechanism of carbonate intercalation on the simultaneous immobilization of Cd and As on LDHs, providing an understanding for fates of Cd and As with LDHs in more realistic scenes.

Calcium alginate (CA)-modification could suppress aggregation and oxidation of ferrous sulfide (FeS), thereby altering its surface properties and heavy metal (HM) adsorption performance. However, effects of CA on HM adsorption routes and stabilities of adsorption products remain unclear. Herein, systematic research on the impacts was conducted. Boundary diffusion of HMs was accelerated due to the rapid HMs uptake by surface FeSFeS-CA on FeS-CA composite. Maximum adsorption capacities of Pb, Zn, and Cd on FeSFeS-CA were 6.51, 5.57, and 6.44 mmol g(-1), 2.04-fold to 4.13-fold higher than those on bare FeS due to the 74.7% smaller size of FeSFeS-CA and more adsorption sites. Affinities of FeSFeS-CA toward HMs increased by similar to 35% due to more chemisorption sites than bare FeS. Ion exchange was the predominant route for HM adsorption on FeSFeS-CA, accounting for 72.0%-87.0% of total adsorbed HMs, while its contribution on bare FeS was 35.4% - 66.7% due to less exchangeable Fe and more surface -OH. Thus, fractions of HM sulfides formed on FeSFeS-CA were 26.9%-40.2% more than bare FeS. HM adsorption energies in sulfides were 0.938-fold to 30.4-fold higher than those in HM complexes formed via surface complexation, thereby HM stabilities on FeSFeS-CA were 21.1% - 56.4% higher than on bare FeS. Moreover, HM amounts simultaneously adsorbed on FeSFeS-CA were enhanced by 4.35-fold to 8.67-fold compared to bare FeS due to the larger adsorption sites. Stabilities of Pb and Zn were further enhanced in multi-HM systems due to their higher adsorption energies on CdS or PbS. This study highlights mechanisms of CA modification enhancing the HM adsorption performance and stabilities on FeS, thereby producing high-performance FeS for HMs immobilization in soil.

Accurate quantification of per- and polyfluoroalkyl substances (PFAS) in complex matrices, such as sewage sludge, is an ongoing challenge. To address this issue, a rigorously validated, robust, and efficient method for a wide range of PFAS (48 different species) extraction in sludge was developed. By optimizing liquid-solid ratio (30 mL/g), extracting solvent (methanol ammonia hydroxide (99.5 : 0.5, v/v)), oscillation time (60 min, 300 rpm), and pH of extraction solution (pH = 3) before solid phase extraction, an acceptable recovery (50 %-125 %) of the majority target PFAS (45 of 48) with low relative standard deviation (≤ 16.84 %) was achieved. Compared to currently widely used extraction methods, such as ASTM D2216, a Chinese standard (HJ 1334-2023) and the U.S. EPA method 1633A, the proposed method achieves a 17.3 %-27.6 % increase in the extracted total PFAS concentration for target analysis. Furthermore, it enables the identification of 3 additional PFAS types, thereby enhancing the scope and accuracy of PFAS analysis. During the investigation of matrix effects, despite the higher organic matter content in anaerobically digested sludge (71.8 %) compared to waste activated sludge (46.3 %), the matrix effect in the former was significantly lower during PFAS extraction and detection. This result suggests that unstable organic matter in sludge may primarily contribute to the observed matrix effects. Furthermore, reducing the injection volume during mass spectrometry analysis, diluting samples prior to detection, and applying internal standards correction can effectively mitigate matrix effects. When this method was applied to the analysis of different sludge samples (n = 10), all samples exhibited satisfied recoveries of internal standards within the range of 50 %-150 % except for long-chain 13C2-PFDoA in a sludge sample. Long-chain PFAS, such as PFOA and PFOS, remained the predominant compounds in different sludge. These findings highlight the method's reliability for complex matrices and its potential for broader environmental monitoring.

Natural and synthetic ferrous sulfide (FeS) is commonly used in simultaneous stabilization of multi-heavy metal-contaminated soil due to its high selectivity. The coating of alginate on FeS (FeS@A) can enhance the activity and availability toward heavy metals (HMs). However, the quantified contributions of alginate and inner FeS to the adsorption/stabilization of HMs are still limited, which can provide the key information to stabilizer regulation. Two types of FeS@A with different coating of alginate were synthesized by using co-precipitation method. The enhanced dispersity, antioxidant performance, and activity could be obtained with appropriate coating of alginate on FeS, i.e. FeS@A0.5. The activity of FeS in FeS@A0.5 was accordingly enhanced, leading to higher adsorption capacities of inner FeS in FeS@A0.5 toward cadmium (Cd, 436 mg g-1) and lead (Pb, 951 mg g-1) than FeS (378 and 617 mg g-1). Nearly 85 % of adsorbed Cd on FeS@A0.5 was in the form of (Fe,Cd)S sulfides and the chelation of Cd with alginate groups contributed to another 15 %. In comparison, 98.1 % of adsorbed Pb was existed in PbS sulfides rather than chelation with alginate. The activity of inner FeS in FeS@A could also be achieved in real soil scenario due to high resistance against MnIV. Up to 85 % of Cd and Pb could be stabilized in soil treated with 3 % FeS@A0.5 even under air-sufficient condition whereas the corresponding values were less than 40 % for FeS-treated soil. In addition, some adsorbed Pb and Cd were gradually fixed by the secondary ferric minerals, ensuring the long-term stabilities of Cd and Pb in soil. Thus, FeS@A could be used as suitable alternative to simultaneous stabilization of multi-HMs-contaminated soil through optimizing coating thickness of alginate. The feasibility of FeS@A on the remediation of actual long-term Pb/Cd-contaminated soil to reveal the application potential was testified in this study.

Harmless treatment of waste activated sludge (WAS) is the primary goal for sludge management while bioresource recovery is raising wide scholarly and industrial interest due to the abundant resource potential in WAS. This study employed sulfite and freezing/thawing to pretreat WAS for its versatility in simultaneously enhancing methane production, improving dewaterability, and inactivating pathogenic microorganisms. The addition of 100 mg S/L of sulfite and subsequent freezing/thawing significantly promoted the release of organics from a low organic-contained WAS (volatile solid/total solid = 0.4), leading to a substantial increase in methane production by 10.99 %. The combined pretreatment significantly reduced the capillary suction time of sludge by 77.24 % and effectively inactivated pathogenic microorganisms to below detectable levels. From a micro level, sulfur aggregation was observed around sludge particles, which can be attributed to the process of ice formation. During this process, sulfite was continuously transferred to the aqueous phase surrounding the particles where were froze even slower. Moreover, the formation of capillary water ice crystals further compromised the protective function of extracellular polymeric substances (EPS) on sludge cells. Economic, and environmental analyses suggest this combined sulfite and freezing/thawing pretreatment has a potential for efficient sludge treatment towards energy recovery and safe disposal with high environmental and economic value.

Employing chemical pretreatment for waste activated sludge (WAS) fermentation is crucial to achieving sustainable sludge management. This study investigated the feasibility of metabisulfite (MS) pretreatment for enhancing volatile fatty acids (VFAs) production from WAS. The results show that after 24-h MS pretreatment, the content of soluble organic matter and loosely bound extracellular polymeric substances (LB-EPS), especially proteins, increased significantly. During the fermentation, MS pretreatment under alkaline conditions was more efficient, with VFA peaking on the fifth day, showing a 140 % increase compared to the alkaline control group. Correlation analysis suggests that the dosage of MS, rather than pH, is closely related to the levels of soluble protein, polysaccharides, LB-EPS, and subsequential VFAs production, while alkaline conditions facilitate the dissolution of total organic carbon. Furthermore, sulfite radicals (SO3 center dot- ) are attributed to cell inactivation and lysis, while alkaline conditions initially reduce the size of the flocs, further promoting MS for attacking flocs, thereby improving the performance of fermentation. The study also found that MS pretreatment reduced microbial community diversity, enriched hydrolytic and fermentation bacteria (Actinobacteriota and Firmicutes), and suppressed methanogens (Methanobacteriaceae and Methanosaetaceae), making it a safe, viable, and costeffective chemical agent for sustainable sludge management.

The flowing-water remediation of contaminated soil was investigated. Urease combined with biochar (UCB) technology was used to handle the Pb2+-contaminated sand column. The results showed that with the continuous increase of pore volume, the concentration of Pb2+ in the leachate undergoes three stages: slow growth, rapid growth, and steady state. With increasing seepage velocity, the concentration of Pb2+ in leachate increased slightly. The residual amount of each section of the sand column gradually decreased with increasing migration distance. The comparative results indicated that the UCB technology had a good solidification effect on Pb2+. This was due to urease-induced CaCO3 precipitation, cementation, and adsorption of Pb2+. Biochar provided more nucleation sites for urease, and some Pb2+ was adsorbed on its surface or diffused into the pores of biochar, or ions exchanged with functional groups on the surface of biochar, which effectively stabilized the free Pb2+.