Efficient elimination of antibiotics and antibiotic resistance genes in hyperthermophilic sludge composting.

Composting is widely applied in recycling ever-increasing sewage sludge. However, the insufficient elimination of antibiotics and antibiotic resistance genes (ARGs) in conventional compost fertilizer poses considerable threat to agriculture safety and human health. Here we investigated the efficacy and potential mechanisms in the removal of antibiotics and ARGs from sludge in hyperthermophilic composting (HTC) plant. Our results demonstrated that the HTC product was of high maturity. HTC led to complete elimination of antibiotics and potential pathogens, as well as removal of 98.8 % of ARGs and 88.1 % of mobile genetic elements (MGEs). The enrichment of antibiotic-degrading candidates and related metabolic functions during HTC suggested that biodegradation played a crucial role in antibiotic removal. Redundancy analysis (RDA) and structural equation modelling (SEM) revealed that the reduction of ARGs was attributed to the decline of ARG-associated bacteria, mainly due to the high-temperature selection. These findings highlight the feasibility of HTC in sludge recycling and provide a deeper understanding of its mechanism in simultaneous removal of antibiotics and ARGs.

Succession from acetoclastic to hydrogenotrophic microbial community during sewage sludge anaerobic digestion for bioenergy production.

To assess microbial dynamics during anaerobic digestion (AD) of sewage sludge (SWS) from a municipal Wastewater Treatment Plant (WWTP), a Biochemical Methane Potential (BMP) assay at 37 °C under mono-digestion conditions was conducted. Utilizing the Illumina MiSeq platform, 16S ribosomal RNA (rRNA) gene sequencing unveiled a core bacterial community in the solid material, showcasing notable variations in profiles. The research investigates changes in microbial communities and metabolic pathways to understand their impact on the efficiency of the digestion process. Prior to AD, the relative abundance in SWS was as follows: Proteobacteria > Bacteroidota > Actinobacteriota. Post-AD, the relative abundance shifted to Firmicutes > Synergistota > Proteobacteria, with Sporanaerobacter and Clostridium emerging as dominant genera. Notably, the methanogenic community underwent a metabolic pathway shift from acetoclastic to hydrogenotrophic in the lab-scale reactors. At the genus level, Methanosaeta, Methanolinea, and Methanofastidiosum predominated initially, while post-AD, Methanobacterium, Methanosaeta, and Methanospirillum took precedence. This metabolic transition may be linked to the increased abundance of Firmicutes, particularly Clostridia, which harbor acetate-oxidizing bacteria facilitating the conversion of acetate to hydrogen.

Acid leaching of vivianite separated from sewage sludge for recovering phosphorus and iron.

This paper examines the acid leaching efficiencies of Fe and P from vivianite slurry (VS, Fe3(PO4)2·8H2O), which is magnetically separated from anaerobic digested sludge, and elaborates on Fe and P reuse routes. The characteristics and dissolution behavior of raw VS in hydrochloric, sulfuric, phosphoric, oxalic, and citric acids are investigated. Results reveal that the primary impurities in VS are organic matter, other phosphate compounds, and Mg present in the vivianite crystal structure. Hydrochloric and sulfuric acids could effectively extract P (90%) from VS at an optimal hydrogen-to-phosphorus (H⁺/P) ratio of 2.5, compared with sewage sludge ash (SSA) that normally needs an H⁺/P ratio greater than 3. Hence, VS can be employed as an alternative P resource following a similar recovery route used with SSA. However, in comparison to SSA, VS use can decrease acid consumption in P extraction and the requirement for the extensive purification of cationic impurities. Furthermore, oxalic acid effectively facilitates the separation of P and Fe in VS by precipitating Fe as insoluble ferrous oxalate in acidic conditions, leading to a high Fe recovery rate of 95%. The recovery and reuse of Fe through the oxalic acid route further improves the feasibility of VS as an alternate resource.

Effect of anaerobic digestion on pathogens and antimicrobial resistance in the sewage sludge.

Antimicrobial resistance (AMR) is recognized as a global threat. AMR bacteria accumulate in sewage sludge however, knowledge on the persistence of human pathogens and AMR in the sludge line of the wastewater treatment is limited. Sludge can be used, with or without additional treatment, as fertilizer in agricultural fields. The aim of this study is to obtain knowledge about presence of human pathogens and AMR in the sewage sludge, before and after the anaerobic digestion (AD) applying innovative combinations of methods. Fifty sludge samples were collected. Cultivation methods combined with matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and Antibiotic Susceptibility Test (AST) were used obtaining knowledge about the microbial community, pathogens, and antibiotic resistant bacteria while the droplet digital Polymerase Chain Reaction (ddPCR) was performed to detect most common AMR genes. In total, 231 different bacterial species were identified in the samples. The most abundant species were spore-forming facultative anaerobic bacteria belonging to Bacillus and Clostridium genera. The AD causes a shift in the microbial composition of the sludge (p = 0.04). Seven pathogenic bacterial species constituting 188 colonies were isolated and tested for susceptibility to Clindamycin, Meropenem, Norfloxacin, Penicillin G, and Tigecycline. Of the Clostridium perfringens and Bacillus cereus isolates 67 and 50 %, respectively, were resistant to Clindamycin. Two B. cereus and two C. perfringens isolates were also resistant to other antibiotics showing multidrug resistance. ARGs (blaOXA, blaTEM, ermB, qnrB, tet(A)-(W), sulI-II) were present at 7-8 Log gene copies/kg of sludge. AD is the main driver of a reduction of some ARGs (1 Log) but resistant bacteria were still present. The results showed the usefulness of the integration of the proposed analytical methods and suggest a decrease in the risk of presence of cultivable pathogens including resistant isolates after AD but a persistent risk of ARGs' horizontal transmission.

Nano Fe3O4 improved the electron donating capacity of dissolved organic matter during sludge composting.

The effect of Fe3O4 nanoparticles (Fe3O4 NPs) on the electron transfer process in aerobic composting systems remains unexplored. In this study, we compared the electron transfer characteristics of DOM in sludge composting without additives (group CK) and with the addition of 50 mg/kg Fe3O4 NPs additive (group Fe). It was demonstrated that the electron transfer capacity (ETC) and electron donating capacity (EDC) of compost-derived DOM increased by 13%-29% and 40%-47%, respectively, with the addition of Fe3O4 NPs during sludge composting. Analyzing the composition and structure of DOM revealed that Fe3O4 NPs promoted the formation of humic acid-like substances and enhanced the aromatic condensation degree of DOM. Correlation analysis indicated that the increase in EDC of DOM was closely associated with the phenolic group in DOM and influenced by quinone groups and the degree of aromatization of DOM. The higher EDC and the structural evolution of DOM in group Fe reduced the bioaccessibility of Cu, Cr, Ni, Zn. This study contributes to a deeper understanding of the redox evolutionary mechanism of DOM in sludge composting and broadens the application of iron oxides additives.

Use of aqueous liquor from digested sludge pyrolysis for biogas production: characterization, toxicity assessment, and rate-limiting step determination.

This study assessed the characteristics and toxicity of aqueous pyrolytic liquid (APL) derived from digested sewage sludge on anaerobic digestion (AD) and determined its rate-limiting step. Digested sewage sludge was pyrolyzed at multiple temperatures (350-650 °C) and moisture levels (0-40.4 %), resulting in APLs with varying AD toxicities. APL 350 °C-0 % showed the least toxicity, whereas APL 650 °C-40.4 % exhibited the greatest toxicity. Glucose (GL) and sodium acetate (SA) were introduced to elucidate the rate-limiting steps. SA, but not GL, enhanced APL conversion to CH4. And volatile fatty acid lack was observed in treatments without SA addition. This suggested that acidification was the primary rate-limiting step. This finding was confirmed using the modified Gompertz model: SA considerably improved the maximum methane production rate, whereas GL did not. Insights gained from this research clarified the feasibility and potential of AD for APL utilization and conversion.

Multi-criteria optimisation of subcritical wet oxidation for sludge treatment.

Subcritical wet oxidation (SWO) is an environmentally-friendly solution for sewage sludge volume reduction. However, little study has comprehensively optimised SWO conditions across various aspects. This study developed a multi-objective model using genetic algorithms (GAs) to optimise SWO conditions, considering sludge deconstruction, emissions, energy balance, and resource recovery. The multi-criteria optimisation approach highlights the significant environmental benefits of SWO, including substantial sludge volume reduction and effective pollutant removal. An in-depth analysis of temperature, reaction time, and severity factor revealed their critical roles in enhancing sludge deconstruction and resource recovery efficiency. GAs predicted optimal conditions at 271 ± 2 °C and 51 ± 1 min, with confirmation experiments showing only 12% discrepancy between predicted and actual outcomes. This study provides practical insights for efficient sewage sludge treatment and sustainable wastewater management.

Pyrolysis-induced migration and transformation of heavy metals in sewage sludge containing microplastics.

Stabilizing heavy metals (HMs) in sewage sludge is urgently needed to facilitate its recycling and reuse. Pyrolysis stands out as a promising method for not only stabilizing these metals but also producing biochar. Our research delves into the migration and transformation of specific HMs (Cr, Mn, Ni, Cu, Zn, As, and Pb) during co-pyrolysis under various conditions, including the presence and absence of microplastics (PVC and PET). We examined different concentrations of these plastics (1 %, 5 %, 10 %, and 15 %) and temperatures (300 °C, 500 °C, and 700 °C). Findings reveal that microplastics, particularly PVC, enhance the migration of Zn and Mn, leading to significant volatilization of Zn and Pb at higher temperatures, peaking at 700 °C. The increase in temperature also markedly influences HM migration, with As showcasing notable loss rates that climbed by 18.0 % and 16.3 % in systems with PET and PVC, respectively, as temperatures soared from 300 °C to 700 °C. Moreover, our speciation analysis indicates that microplastics aid in transforming certain HMs from unstable to more stable forms, suggesting their beneficial role in HM stabilization during pyrolysis. This study significantly enriches our understanding of microplastics' impact on HM behavior in sewage sludge pyrolysis, offering new avenues for pollution control and environmental management strategies.

Occurrence and risk assessment of p-phenylenediamines and their quinones in aquatic environment: From city wastewater to deep sea.

p-Phenylenediamines (PPDs) and PPD-derived quinones (PPD-Qs) have been considered emerging pollutants recently. Their available data on sediment and sewage sludge are limited, especially the ecological risks. Here, typical PPDs and PPD-Qs were measured in the sludge of wastewater treatment plants and surface sediment of a developed river basin (including reservoirs, estuaries, and rivers) and deep-sea troughs. The total concentrations of PPDs (∑PPD) were highest in sludge (range: 9.06-248 ng g-1), followed by surface sediment of the Dongjiang River basin, China (3.33-85.3 ng g-1), and lowest in sediment of the Okinawa Trough (0.01-7.46 ng g-1). The median value of ∑PPD in surface sediment of rivers (9.54 ng g-1) was higher than those in reservoirs (4.28 ng g-1) and estuaries (5.26 ng g-1). N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) was the major congener in all samples, accounting for over 60 % of ∑PPD. For quinones, 6PPD-Q and IPPD-Q were frequently detected in sludge, only trace 6PPD-Q was detected in the sediment of estuaries (nd-0.62 ng g-1) and rivers (nd-5.24 ng g-1), and both of them were absent from the sediment of the Okinawa Trough. The occurrence of PPDs in the trough may be the in-situ release of microplastics, and due to the low-light and weak alkaline conditions of deep-sea water, quinones may hardly photodegrade from PPDs. The PPD concentrations in sludge were positively correlated with local GDP, and the annual PPD emission from sludge will exceed 1370 kg in China. The results of ecological risk assessments indicated low risks for PPDs in sludge-amended soil, median risks for several PPDs in river sediment, but median to high risks for 6PPD-Q contamination sludge-amended soil. For the first time, we reported the occurrence of PPDs and related quinones in the sludge of WWTPs and found a potential environmental risk from 6PPD-Q in sludge used as a soil conditioner.

Effect of thermochemical treatment of sewage sludge on its phosphorus leaching efficiency: Insights into leaching behavior and mechanism.

Thermochemical conversion, including hydrothermal processing, pyrolysis and incineration, has become a promising technology for sewage sludge (SS) treatment and disposal. Furthermore, acid leaching is considered as an effective method to recover phosphorus (P) from SS and its thermochemical treatment products. This study has investigated the potential of P reclamation from SS and its thermochemical derivatives, including hydrochar (HC), biochar (BC), and SS incinerated ash (SA). Comparative analyses of physicochemical properties of these derivatives revealed a decrease in hydroxyl and aromatic groups and an increase in aliphatic and oxygen-containing functional groups in HC and BC. Leaching experiments using 1 M sulfuric acid (H2SO4) and 1 M oxalic acid (C2H2O4) suggested that H2SO4 slightly outperformed C2H2O4 in terms of P leaching efficiency. HC achieved 79.1 % optimal leaching efficiency in 60 min using H2SO4, while BC, SS, and SA required 360 min to achieve comparable efficiency. SS and BC reached optimal leaching efficiency at 74.1 % and 76.2 % in H2SO4, while SA achieved 80.9 % in C2H2O4. Importantly, HC and SA are more favorable for P extraction using acid leaching, whereas BC tends to be a potential P carrier. Time-dependent kinetics revealed a two-stage leaching process, i.e., fast and slow reaction stages. Shrinking core model indicates product layer diffusion as the primary rate-limiting step in both stages. Overall, these fundamental insights play an important role in practical P recovery through acid leaching of SS derived residues after thermochemical treatment.

Three birds with one stone: Sewage sludge deep-drying in 1 hour using secondary aluminum ash to fabricate bricks.

Due to the high moisture, strong hydrophilicity, and hard compressibility of sewage sludge (SS), it is difficult to realize the high-efficiency drying. Herein, a novel SS drying technology was developed to quickly and deeply reduce the moisture of SS from 75.6% to 38.5% in 1 h. During the process, secondary aluminum ash (SAA), a solid waste, was added to SS and acted as skeletons to form plenty of channels. Subsequently, NaOH was added and reacted with SAA to produce a lot of heat, resulting in a rapid temperature rise of the system from 20 to 105°C in 60 s. The heat could effectively remove water from these channels, which could be proved by the T1-T2 maps of in-site Low-Field 1H nuclear magnetic resonance. In addition, the extracellular polymeric substances were decomposed by SAA/NaOH successfully, and thus the SS became hydrophobic, favoring the drying. Finally, the dried SS could be used to fabricate unburned bricks. Thus, this work provides a promising method to realize the rapid SS deep drying and high-efficiency utilization of SAA and dried SS.

Enhanced Cu2+ and Cd2+ removal by a novel co-pyrolysis biochar derived from sewage sludge and phosphorus tailings: adsorption performance and mechanisms.

The reutilization of municipal wastes has always been one of the hottest subjects of sustainable development study. In this study, a novel biochar co-pyrolyzed from municipal sewage sludge and phosphorus tailings was produced to enhance the adsorption performance of the composite on Cu2+ and Cd2+. The maximum Cu2+ and Cd2+ adsorption capacity of SSB-PT were 44.34 and 45.91 mg/g, respectively, which were much higher than that of sewage sludge biochar (5.21 and 4.58 mg/g). Chemisorption dominated the whole adsorption process while multilayer adsorption and indirect interaction were also involved. According to the result of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectrum (XPS), the load of CO32-, Mg2+, and Ca2+ on the surface of SSB-PT enhanced the precipitation and ion exchange effect. Posnjakite and CdCO3 were formed after the adsorption of Cu2+ and Cd2+, respectively. Besides, complexation, and metal-π interaction were also involved during the adsorption process. Therefore, this study offered a promising method to reuse sewage sludge and phosphorus tailings as an effective adsorbent.

Study on the effect of conditioner on NOx precursor control behavior from sewage sludge pyrolysis: Focusing on conditioner assessments and in-situ fixation mechanism.

The nitrogen transformation during sludge pyrolysis is affected by the dewater conditioner. However, the comparative analysis of the conditioner under identical pyrolysis conditions has been previously absent. In this study, Ca-, Fe- and Al-based conditioners were selected as the representatives. A comprehensive evaluation considering the cost of the conditioners and the product characteristics was conducted. Additionally, the in-situ fixation mechanism of the conditioner on nitrogen-containing gas was concurrently revealed. Among the six conditioners, CaO and AlCl3 were identified as the top performers, ranking first and second, respectively. Furthermore, Fe/Ca-based conditioners reduced NH3 and HCN release by 1.5 âˆ¼ 5.53 % and 0 âˆ¼ 1.55 %, respectively, by facilitating the conversion of amine-N to a more stable form in condensable fraction. Fe promoted volatile amine-N cyclization, while Ca encouraged its dehydrogenation. Both Fe/Ca-based conditioners increased 7.5 âˆ¼ 14.8 % nitrogen retention in char, by inhibiting the decomposition of protein-N. Al-based conditioners had little effect on NH3 and HCN, but contributed to 2.3 âˆ¼ 2.8 % production of stabilized nitrogen in char. The introduction of Cl in Fe/Ca/Al chloride conditioners would promote the decomposition of inorganic ammonium salts to produce NH3 at 30 âˆ¼ 185 °C. And Cl also reacted with volatiles through electrophilic substitution reaction, leading to the formation of halogenated hydrocarbons in condensable fraction and the release of more NH3, HCN, and HNCO at 30 âˆ¼ 465 °C. The findings of this study provide a detailed comparative analysis of various conditioners under uniform conditions and reveal the in-situ fixation mechanism of nitrogen-containing gas. This will provide guidance for the sludge conditioning-dewatering-drying integrated treatment and disposal.

Effect of hydrochar from sludge mixed with coffee grounds on the immobilization of Cu, Cr and Ni in soil.

In this study, hydrochars were prepared at varying temperatures with distinct mixing ratio, and then the hydrochars were characterized and evaluated for heavy metals to ascertain its potential as a soil conditioner. The application of elevated temperatures resulted in a reduction in the yield of hydrochars, whereas the incorporation of coffee grounds led to an increase in the yield. The blended hydrochar displays elevated ash, fixed carbon, and diminished H/C, O/C, and (O + N)/C ratios, indicating enhanced stability in soil treatment and potential for enhanced soil fertility. The application of hydrothermal carbonization facilitated the stabilization of heavy metals within the sewage sludge, with the stabilizing effect being enhanced by the addition of coffee grounds. Following the application of SCC as a soil conditioner to the heavy metal-contaminated soil for a period of 90 days, it was observed that the heavy metals Cu, Cr, and Ni present in the contaminated soil underwent a transition from an unstable to a stable speciation. Of the treatments tested, AK15 was identified as the most effective, demonstrating a significant reduction in the risk of leaching and biotoxicity associated with Cu, Cr, and Ni in the contaminated soil.

Biochar from Co-Pyrolyzed Municipal Sewage Sludge (MSS): Part 2: Biochar Characterization and Application in the Remediation of Heavy Metal-Contaminated Soils.

The disposal of municipal sewage sludge (MSS) from wastewater treatment plants poses a major environmental challenge due to the presence of inorganic and organic pollutants. Co-pyrolysis, in which MSS is thermally decomposed in combination with biomass feedstocks, has proven to be a promising method to immobilize inorganic pollutants, reduce the content of organic pollutants, reduce the toxicity of biochar and improve biochar's physical and chemical properties. This part of the review systematically examines the effects of various co-substrates on the physical and chemical properties of MSS biochar. This review also addresses the effects of the pyrolysis conditions (temperature and mixing ratio) on the content and stability of the emerging pollutants in biochar. Finally, this review summarizes the results of recent studies to provide an overview of the current status of the application of MSS biochar from pyrolysis and co-pyrolysis for the remediation of HM-contaminated soils. This includes consideration of the soil and heavy metal types, experimental conditions, and the efficiency of HM immobilization. This review provides a comprehensive analysis of the potential of MSS biochar for environmental sustainability and offers insights into future research directions for optimizing biochar applications in soil remediation.

Enhancing proton-coupled electron transfer drives efficient methanogenesis in anaerobic digestion.

The enhancement of electron or proton transfer between syntrophic microbes has been widely recognised as a means for improving methane generation. However, the uncoupled supplementation of electrons and protons in multiphase anaerobic environment hinders the balanced uptake of electrons and protons in the cytoplasm of methanogens, limiting methanogenesis efficiency. Herein, the cooperative effect of a proton-conductive material (PM) and an electron-conductive material (EM) in enhancing proton-coupled electron transfer (PCET) and driving efficient methanogenesis in anaerobic digestion was investigated. The cooperation of the PM and EM significantly increased methane production and the maximum methane generation rate by 78.9 % and 103.5 %, respectively, indicating enhanced methanogenesis efficiency. Analysis of the physicochemical properties, biochemical components, and microbial dynamics revealed that the cooperation of the PM and EM improved the metabolism of syntrophic microbes, which was critically dependent on electron and proton transfer. This enhancement was primarily due to the improvement in PCET, as mainly supported by hydrogen/deuterium kinetic isotope effect measurements, multi-omics integration analyses and reaction thermodynamics and kinetics analyses. Our findings suggest that the PCET enhancement stimulated efficient membrane-bound enzymatic reactions related to electron-driven proton translocation and facilitated electron and proton supply for CO2 reduction to realise highly efficient methane generation. These findings are expected to provide a new insight into effective electron and proton coupling transfer for methanogenic metabolism in multiphase anaerobic environments.

Regulation of Antibiotic Resistance Genes on Agricultural Land Is Dependent on Both Choice of Organic Amendment and Prevalence of Predatory Bacteria.

Antibiotic resistance genes (ARGs) are widespread in the environment, and soils, specifically, are hotspots for microorganisms with inherent antibiotic resistance. Manure and sludge used as fertilizers in agricultural production have been shown to contain vast amounts of ARGs, and due to continued applications, ARGs accumulate in agricultural soils. Some soils, however, harbor a resilience capacity that could depend on specific soil properties, as well as the presence of predatory bacteria that are able to hydrolyse living bacteria, including bacteria of clinical importance. The objectives of this study were to (i) investigate if the antibiotic resistance profile of the soil microbiota could be differently affected by the addition of cow manure, chicken manure, and sludge, and (ii) investigate if the amendments had an effect on the presence of predatory bacteria. The three organic amendments were mixed separately with a field soil, divided into pots, and incubated in a greenhouse for 28 days. Droplet digital PCR (ddPCR) was used to quantify three ARGs, two predatory bacteria, and total number of bacteria. In this study, we demonstrated that the choice of organic amendment significantly affected the antibiotic resistance profile of soil, and promoted the growth of predatory bacteria, while the total number of bacteria was unaffected.

Synchrotron induced X-ray fluorescence spectroscopy reveals heavy metal translocation in sludge amended soil-plant systems: assessment of ecological and health risks.

The use of composted sludge from sewage treatment plants as a soil amendment is a common practice of recycling nutrients like organic carbon, nitrogen, and phosphorus. The sewage generated in larger cities of developing countries is often contaminated with various heavy metals (HMs) that ultimately end up in composted sludge. Thus, using such composted sludge is likely to pose ecological and human health risks. Hence, the knowledge of HM translocation in sludge-soil-plant systems is of vital importance. The present study was aimed at investigating the HM translocation in sludge-soil-plant system. The HM translocation was measured using synchrotron radiation-induced x-ray fluorescence spectrometry and atomic absorption spectroscopic techniques. The results indicated high HM mobility (up to 2628.5 mg kg-1) from sludge to spinach plant. The metal accumulation (mg kg-1) ranged in the order-Fe (950.55-2628.5) > Zn (20.11-172.13) > Cu (13.86-136.17) > Mn (2.13-34.67) > Cd (0.11-31.17) > Pb (1.50-30.16) > Co (0.18-9.85) As (0.02-7.80) > Cr (0.01-5.69). This observed accumulation depended on the volume of sewage being treated in the sewage treatment plant (STP) and varied in the order control < (8 MLD Bhagwanpur, STP 1) < (80 MLD Dinapur, STP2) < (140 MLD Dinapur, STP3) hence the HM load coming into STPs. The metal transfer factor, bioconcentration factor, and translocation factor values also correlated with the abundance of Fe, Cu, Pb, Cd, and Zn in spinach root and shoot compartments. The carcinogenic risk for heavy metal carcinogens like As, Cd, Cr, and Pb revealed children being more prone to cancer upon spinach consumption. Hence, it is necessary to assess the heavy metals present in the sludge prior to its application in agricultural fields.

Multiple drivers and mechanisms of solid-water interfacial interactions in sludge dewatering: Roles of polarity and molecular structure of extracellular polymeric substances.

Water occurrence states in sewage sludge, influenced by sludge physicochemical properties, are crucial for sludge dewaterability and have recently been regarded as a research hotspot. Here, the multifold characteristics of sludge flocs during hydrothermal treatment, including rheological properties, solid-water interfacial interactions, and the polarity distribution and molecular structure of extracellular polymeric substances (EPS), were systematically investigated, and the impact of these characteristics on sludge dewaterability was explored in depth. Hydrothermal treatment at 80 °C and 100 °C induced the conversion of free water into bound water, while an increase in temperature to 180 °C resulted in a significant decrease in bound water content, approximately 4-fold lower than at 100 °C. In addition to the conventional view of decreased sludge surface hydrophilicity at high temperatures, the decline in bound water was associated with the reduction in sludge apparent viscosity. XAD resin fractionation identified the hydrophobic/hydrophilic EPS (HPO-/HPI) ratio as an important factor determining water occurrence states. Especially, hydrolysis of HPI-related hydrophilic proteins and subsequent increase in HPO-related tryptophan-like substances played a dominant role in reducing sludge viscosity and facilitating the release of bound water. Protein conformational analysis revealed that the disruption of α-helix structures and disulfide bonds significantly reduced EPS water-holding capacity, providing strong evidence for the potential of targeting these dense structure units to enhance sludge dewaterability. These findings provide a holistic understanding of multidimensional drivers of water occurrence states in sludge, and guide directions for optimizing sludge treatment efficiency through EPS modification.

Valorization of sewage sludge incineration ash as a novel soilless growing medium for urban agriculture and greenery.

Limited open areas for urban agriculture and greenery have led to the search for innovative, sustainable growing media to strengthen the food supply and improve atmospheric quality for a resilient city. Rampant land developments have caused soil to become increasingly scarce. Sewage sludge incineration ash (SSIA), the by-product of waste-to-energy (WtE) incineration of sewage sludge, is a major municipal waste containing phosphorus-fertilizing nutrients. For the first time, we investigated the novel application of SSIA as a soilless plant-growing medium with built-in fertilizer. SSIA outperformed topsoil in bulk density, water-holding capacity, porosity, and nutrient content. However, it was found that SSIA has a high salinity and should be treated first. Wheatgrass (Triticum aestivum L.), a fast-growing glycophyte, thrived in the desalinated SSIA, showing growth and nutrient content comparable to the topsoil case. Simultaneously, it demonstrated phytoremediation. The SSIA residue was then recycled into cementitious materials, using desalinating water for mixing. SSIA upcycle into a growing medium facilitates urban resource management by utilizing nutrients in sewage waste for eco-friendly plant cultivation, benefiting urban agriculture and greenery. It is also a prudent valorization step before further recycling SSIA to reduce landfill requirements.