Changes in molecular structure of extracellular polymeric substances (EPS) with temperature in relation to sludge macro-physical properties

Overlooked role of extracellular polymeric substances in antibiotic-resistance gene transfer within microalgae-bacteria system

Controlling the spread of antibiotic-resistance genes (ARGs) under antibiotic stress has become an increasingly urgent issue. Microalgae possess the capability to remove antibiotics while concurrently inhibiting ARGs. Microalgae-bacteria systems can produce significant quantities of extracellular polymeric substances (EPS). However, the roles of EPS in the spread of ARGs have not been sufficiently explored, resulting in an insufficient understanding of the contribution of each EPS component and a lack of analysis on the complex interactions between EPS and ARGs. This study systematically explored the overlooked role of EPS in the transmission of ARGs within microalgae-bacteria systems. The current results showed that the potential of the microalgae-bacteria system for treating antibiotic wastewater. The tightly bound-EPS (TB-EPS) can acquire the higher absolute abundances of ARGs compared with the loosely bound-EPS (LB-EPS). The correlation coefficient between polysaccharides and TB-EPS ARGs was higher than that between polysaccharides and LB-EPS ARGs. The gene patterns of LB-EPS closely clustered with those of TB-EPS, while intracellular ARG gene patterns differed from both TB-EPS and LB-EPS. Metagenomic analyses indicated that the relative abundances of sul1 and sul2 were considerably higher at the beginning stage compared to the end stage. The abundance of Achromobacter, increased by the end stage, aligning with its potential to produce exopolysaccharide. Additionally, the absolute abundance of genes encoding exopolysaccharides (nagB and galE) and conjugative transfer transcription regulator (traF), increased over time. These findings enhanced our comprehension of the significance of EPS on the fate of ARGs in microalgae-bacteria systems during the treatment of antibiotic-contaminated wastewater.

Adhesion behavior of dewatered sewage sludge during indirect thermal drying

We comprehensively investigated the factors influencing sludge adhesion during indirect thermal drying. We analyzed sludge properties and assessed adhesion during thermal drying using peel and shear tests at temperatures ranging from 100 to 180 °C. We conducted a comparative analysis of sludge properties and adhesion, exploring their correlations. Additionally, we examined the relationship between sludge adhesion and changes in extracellular polymeric substances (EPSs) throughout the drying process. The results indicate that factors leading to increased sludge adhesiveness include higher drying temperatures and the initial soluble EPS (S-EPS) concentration (R > 0.88). Only the S-EPS concentration showed an initial increase during thermal drying, followed by a decrease. Sludge with higher initial S-EPS concentrations released more S-EPS during the early stages of thermal drying. Sludge adhesion tended to increase after the S-EPS concentration began to decline. These observations suggest that the adhesive properties of sludge are not directly related to S-EPS but rather to the heat-induced release and transformation of organic content into substances that enhance adhesion. Potential technical solutions to mitigate sludge adhesion include lowering the drying temperature or reducing the S-EPS concentration through anaerobic digestion.

Characterisation of polysaccharide from anammox granular sludge and potential application in hydrogel preparation

Microorganisms capable of anaerobic ammonia oxidation (anammox), or the conversion of nitrite and ammonium to dinitrogen, tend to aggregate and form a granular sludge in anammox reactors. This anammox granular sludge is a potential source of polysaccharides due to its richly diverse microbial community and abundant polymers. In this study, anammox polysaccharide (APS) was extracted from anammox granular sludge, and its potential to form hydrogels with alginate was investigated. The yield of APS was 9.91 % ± 0.12 %. The three main monosaccharides in APS were glucose (60.63 % ± 3.45 %), glucuronic acid (13.81 % ± 0.31 %), and rhamnose (18.88 % ± 0.22 %). The antioxidant potential of APS was evaluated through three antioxidant assays, which revealed significant antioxidant benefits at APS concentrations between 100 and 500 mg/L. Furthermore, L929 mouse fibroblasts exhibited high survival rates (>85 %) under different APS concentrations (1-50 μg/mL), indicating the good biological compatibility of APS. A series of hydrogels were prepared by mixing alginate with APS in different ratios (10:0, 9:1, 8:2, 7:3, and 6:4). The swelling ability of the prepared hydrogels in simulated gastric fluid varied between 1.4 and 2.0. In contrast, the swelling ability increased significantly to 10.37 ± 0.01 in simulated intestinal fluid when the ratio of alginate to APS in the hydrogel was 8:2. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were also used to analyse the functional groups and specific chemical bonds in the hydrogels. Subsequent loading experiments using bovine serum albumin (BSA) demonstrated that an alginate:APS ratio of 8:2 exhibited the highest loading efficiency for BSA, reaching 80.59 % ± 1.46 %. As the quantity of APS was increased, the release of BSA into simulated gastric fluid was effectively inhibited, with an alginate:APS ratio of 6:4 resulting in the lowest release amount (0.023 % in dry state, 0.11 % in wet state). Overall, this study highlights the derivation of a valuable resource from anammox sludge and offers insights into its potential applications in drug delivery.

Coupled effects of initial water content with refrigeration temperature and freeze-thaw cycles on dewatering of sludge

Many studies have displayed that freeze-thaw (F/T) conditioning is an environmentally friendly approach of improving sludge dewaterability. However, Initial water content (IWC) has a strong influence on the efficiency of the F/T method in conditioning sludge dewatering performance. Finding the most suitable F/T parameters for sludge with different IWCs is a critical issue that needs to be solved. Therefore, the coupled effects of different IWCs, refrigeration temperatures and the number of F/T cycles on sludge dewatering characteristics were explored. Single and multiple F/T cycles were performed on sludge from each group of IWCs at the same temperature. The coupling mechanism was analyzed by comparing the changes in sludge dewatering capacity before and after conditioning. The outcomes show that the F/T method is more suitable for sludge with a higher IWC. At -28 °C, the specific resistance to filtration of sludge with 87.5% IWC was reduced to 65.8 × 1012 m/kg, and the post-filtration water content was only 63.1%. After repeated F/T cycles, the water content of the sludge gradually decreased, and the post-filtration water content of sludge with 87.5% IWC dropped to 58.8% after 7 cycles. Appropriate refrigeration temperatures can improve the effectiveness of ice crystal cracking, especially for sludge with a water content of less than 82.5%. The results of research provide a guide for the selection of F/T parameters in the operation of deep dewatering of sludge with different IWCs.

Hydrogel inspired by "adobe" with antibacterial and antioxidant properties for diabetic wound healing

With the aging population, the incidence of diabetes is increasing. Diabetes often leads to restricted neovascularization, antibiotic-resistant bacterial infections, reduced wound perfusion, and elevated reactive oxygen species, resulting in impaired microenvironments and prolonged wound healing. Hydrogels are important tissue engineering materials for wound healing, known for their high water content and good biocompatibility. However, most hydrogels suffer from poor mechanical properties and difficulty in achieving sustained drug release, hindering their clinical application. Inspired by the incorporation of fibers to enhance the mechanical properties of "adobe," core-shell fibers were introduced into the hydrogel. This not only improves the mechanical strength of the hydrogel but also enables the possibility of sustained drug release. In this study, we first prepared core-shell fibers with PLGA (poly(lactic-co-glycolic acid)) and PCL (polycaprolactone). PLGA was loaded with P2 (Parathyroid hormone-related peptides-2), developed by our group, which promotes angiogenesis and cell proliferation. We then designed a QTG (QCS/TA/Gel, quaternary ammonium chitosan/tannic acid/gelatin) hydrogel, incorporating the core-shell fibers and the anti-inflammatory drug celecoxib into the QTG hydrogel. This hydrogel exhibits excellent antibacterial properties and biocompatibility, along with good mechanical performance. This hydrogel demonstrates excellent water absorption and swelling capabilities. In the early stages of wound healing, the hydrogel can absorb the wound exudate, maintaining the stability of the wound microenvironment. This hydrogel promotes neovascularization and collagen deposition, accelerating the healing of diabetic wounds, with a healing rate exceeding 95 % by day 14. Overall, this study provides a promising strategy for developing tissue engineering scaffolds for diabetic wound healing.

Effect of pre-chlorination on bioelectricity production and stabilization of excess sludge by microbial fuel cell

Microbial fuel cell (MFC) is a technology that can generate electricity while degrading excess sludge. However, the complex components, intricate biological structures, and inhibitory compounds in sludge limit the application of MFC. Therefore, this study utilized chlorination as a sludge pretreatment method to improve the comprehensive performance of MFC in sludge treatment. Results showed that pre-chlorination at a dose of 0.2 mg/L increased output voltage of MFC by 500 % from approximately 100 mV to around 600 mV, and power density by 15.60 % from 3.15 W/m³ to 3.64 W/m³, and simultaneously increased the degradation of sludge MLSS (mixed liquor suspended solids), MLVSS (mixed liquor volatile suspended solids), EPS (extracellular polymeric substances) polysaccharide and protein by 9.64 %, 47.07 %, 18.63 % and 16.26 %, respectively. Molecular composition analysis of EPS in sludge by three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM), Fourier transform infrared spectroscopy (FTIR) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) indicated pre-chlorination significantly promoted the molecular transformation in MFC. The microbiome analysis of anode biofilm in MFC by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), metagenomics and metametabolomics revealed that pre-chlorination facilitated the development of biomass, enrichment of electricity-producing bacteria (EPB), enhancement of electricity-producing activity and metabolic activity. Moreover, the sludge EPS was the importance source for the microbial metabolites in MFC was validated by the joint analysis of FT-ICR-MS and metametabolomics.

A critical review of in-situ moisture distribution detection and characterization techniques utilizing deep dewatering for organic waste

Deep dewatering is crucial for effectively reducing the volume of organic waste and facilitating its downstream transportation and disposal. An in-depth understanding of the occurrence states, composition, and morphological characteristics of moisture in organic waste is the basis for optimizing the dewatering process, improving dewatering efficiency, and reducing energy consumption. Given the common problems of time-consuming, low sensitivity, and poor parallelism of traditional methods, this work reviews the advanced in-situ analysis methods for moisture distribution of organic waste. The Raman microscopy imaging technique is highlighted to provide a new approach for visualizing the spatial distribution of moisture with different binding strengths in solid flocs. Various physical, chemical, and biological characteristics and characterization methods of organic waste related to deep dewatering are introduced, and they are correlated with conditioning methods. Almost all conditioning will cause changes in the physical characteristics of organic waste, while the improvement of dewatering performance is actually caused by changes in the chemical composition and biological characteristics of the matrix, and these characteristics are intrinsically related to the moisture distribution. The characterization and in-situ moisture detection methods presented in this work aim to support future studies in understanding changes in material composition related to improving dewatering performance and further clarifying the mechanisms of deep dewatering of organic wastes.

Enhanced sludge solid-liquid separation based on Fe2+/periodate conditioning coupled with polyoxometalates: Cell destruction and protein adsorption

Dewatering of waste activated sludge is a necessary step for achieving subsequent reduction, stabilization, and resource utilization. In this study, Fe2+/periodate (PI) coupled with polyoxometalates (POMs) conditioning was tested for realizing sludge deep dewatering. After the addition of POMs (0.20 mmol g-1 VSS), Fe2+/PI/POMs conditioning enhanced the efficiency of sludge dewatering by 42.93% compared to Fe2+/PI conditioning. It was found that the electrostatic repulsion posed a significant influence on the interaction between POMs and proteins. The reduction of electrostatic repulsion facilitated the proximity of POMs to the sludge flocs and promoted its reaction. The strong acidity and interaction with cells of POMs could induce the damage or apoptosis in sludge cells, resulting in the release of intracellular substances. The active radicals generated by Fe2+/PI process attacked TB-EPS, causing the dissolution of EPS and the decomposition of hydrophilic substances. With the assistance of Fe2+/PI process, POMs exhibited an enhanced cell-disruptive effect, thereby inducing the liberation of a greater quantity of intracellular substances. Moreover, Fe2+/PI/POMs conditioning effectively lowered the zeta potential of sludge system, facilitating the interaction between negatively charged POMs anions and the positively charged regions of proteins. This interaction tended to favor adsorption and precipitation rather than destruction. The adsorption and sedimentation of proteins by POMs further reduced the hydrophilicity of sludge system, thereby enhancing sludge dewaterability. Furthermore, POMs could enhance the electron transfer capacity of sludge system, which was beneficial for subsequent filtrate denitrification treatment.

Coupling Fe3O4 and micro-hydrogen for enhancing the anaerobic bio-conversion of phenol: Methanogenesis pathway and interspecies electron transfer

Low anaerobic biological conversion rate is a challenge in the anaerobic biological treatment of phenol wastewater. The dominant syntrophic acetate oxidation and hydrogenotrophic methanogenesis (SAO-HM) pathway is expected to solve the problem. However, there are raw studies on artificially simulating a dominant SAO-HM pathway for enhancing the anaerobic bio-conversion of phenol. In this study, Fe3O4 and micro-hydrogen (Fe3O4/H2) was used to strengthen the anaerobic bio-conversion of phenol by simulating the dominant SAO-HM pathway. The results suggested Fe3O4 and H2 had a coupling promotion on the anaerobic bio-conversion of phenol and Fe3O4/H2 increased the relative abundance of Syntrophus (29.35%), Syntrophorhabdu (3.27%), Clostridium (3.01%) and Methanobacterium (65.74%), indicating Fe3O4/H2 formed a dominant SAO-HM pathway. However, Fe3O4/H2 obviously reduced the conductivity of sludge, the extracellular protein and the functional gens pilA, pilB and OmcS, implying direct interspecies electron transfer (DIET) generated by Fe3O4 was interfered by micro hydrogen in extracellular electron transport process which reduced the efficiency of extracellular electron transport. This study remind that extracellular electron transport cannot be ignored in the dominate SAO-HM pathway for the anaerobic bio-conversion of phenol.

Surface engineering-based S, N co-doped biochar for improved anaerobic digestion: Enhancing microbial-pollutant and inter-microbial electron transfer synergistic EPS protection

Enhancing extracellular electron transfer (EET) efficiency is crucial for improving the anaerobic digestion (AD) system's capability to treat recalcitrant wastewater. In this study, a novel S, N co-doped biochar (S-N-BC) was prepared through surface engineering to optimize EET within AD systems. The addition of S-N-BC significantly enhanced the performance of a mesophilic AD system treating Congo red wastewater, increasing the decolorization rate by 78 %, COD degradation rate by 82 %, and methane yield by 87 % compared to the control. Additionally, the shock resistance of anaerobic granular sludge was improved, as evidenced by the formation of the protective extracellular polymeric substances (EPS) barrier and the enhanced activities of the electron transport system. Mechanistic analysis revealed that adding S-N-BC did not alter the Congo red decolorization pathway but significantly enriched various electrochemically active bacteria and established EET pathways between microbial-pollutant and inter-microbial. This significantly accelerated EET efficiency within the AD system, ensuring stable and efficient operation under challenging conditions. This study proposed a novel approach using S-N-BC to simultaneously enhance "dual-pathway EET" between microbial-pollutant and inter-microbial while constructing an EPS protective barrier, addressing the issues of low efficiency and fragile stability of AD systems for treating recalcitrant wastewater.

Uncovering the toxic effects and adaptive mechanisms of aminated polystyrene nanoplastics on microbes in sludge anaerobic digestion system: Insight from extracellular to intracellular

The impacts of polystyrene nanoplastics (PS NPs) with amino functional groups on sludge anaerobic digestion process and the underlying microbial feedbacks remains unclear. Herein, PS NPs coated with and without amino functional groups were employed to explore their impacts on the sludge digestion performance. Experimental results showed that aminated PS NPs (PS-NH2) deteriorated the methane yield and hydrolysis rate. The Derjaguin-Landau-Verwey-Overbeek theory analysis suggested that the PS-NH2 decreased the interaction energy barrier, making it easier to contact with sludge and disrupting the structure of extracellular polymeric substances. Metagenomic analysis showed that the abundance of functional microbes (e.g., Longilinea, Leptolinea, and Methanosarcina) decreased, accompanied with lower network complexity and fewer keystone taxa. Molecular docking revealed that PS-NH2 occupy the antioxidant enzyme active binding sites through hydrogen bonding and hydrophobic interactions, impairing degradation of reactive oxygen species. The severe intracellular oxidative stress up-regulated genes associated with quorum sensing (e.g., luxI and luxR) and protein biosynthesis (e.g., algA, trpG and trpE), and further inducing compact tryptophan-like proteins as a defense against NPs. These findings provide new understanding of the toxic effects from PS-NH2 in biological systems and offer valuable insights into the regulation strategies aimed at alleviating NPs inhibition.

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.

Co-stabilization effects of gluten/carrageenan to the over-heated myofibrillar protein: Inhibit the undesirable gel weakening and protein over-aggregations

High-temperature (120 °C) sterilization is an indispensable process for manufacturing ready-to-eat surimi products, yet risking the denaturation of their myofibrillar proteins (MP), thus significantly reducing the gelling properties. To resolve this problem, herein, a synergistic co-strengthening strategy was designed. The negatively charged polysaccharide carrageenan (CG) was introduced into MP simultaneously with wheat gluten, followed by 120 °C thermal treatment for 30 min. A substantial enhancement in mechanical strength, up to four times greater (from 9.86 to 42.38 g·cm), was observed for MP gels, which even surpassed that subjected to conventional gelation processes at 90 °C (36.53 g·cm). Gels that were concurrently added with gluten and CG exhibited porous networks, uniform water distribution, and improved water holding capacity. Accordingly, over-aggregation behaviors of MP were restricted, as evidenced by their reduced particle sizes and polymer dispersity index. Other heat-induced protein deteriorations at 120 °C, i.e., changes of secondary structures and disulfide bonding conformations, were also alleviated. By varying the CG types, it was shown that the κ-CG/gluten-added MP achieved highest gel strength, while the ι-CG/gluten combination may better stabilize the moisture in gel networks. This study introduces a co-reinforcement paradigm and scientific insights to the quality improvement of ready-to-eat meat products.

Manganese(IV) reduction coupled with ammonium oxidation mediated by a single strain Aromatoleum evansii MAY27: Performance, metabolomics, and mechanism

Manganese(IV) (Mn(IV)) reduction coupled to anaerobic ammonium (NH4+-N) oxidation (Mnammox) is a recently identified metal oxide-mediated nitrogen (N) loss pathway, holding potential value for the efficient removal of NH4+-N from wastewater. However, little is known about the application of Mnammox in wastewater treatment. Here, a novel Mnammox bacterium Aromatoleum evansii (strain MAY27) was screened. Strain MAY27 can utilize MnO2 as an electron acceptor to achieve NH4+-N removal under a low C/N condition (C/N = 0.5). The influencing factors in the Mnammox process and the Mn(IV) reduction driving effect on NH4+-N oxidation were investigated. The physiological characteristics of strain MAY27 and differential metabolic pathways were identified through whole-genome sequencing and metabolomic analyses. A significant up-regulation of several key pathways upon the addition of MnO2, including glycolysis/gluconeogenesis, transmembrane transporter activity, and oxidoreductase activity. This study contributes to the advancement of biotechnological approaches for treating N-containing wastewater.

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.

Comprehensive analysis of the relationship between yield stress and dewatering performance in sludge conditioning: Insights from various treatment methods

Understanding the relationship between sludge yield stress (σy) and dewatering performance is essential for optimizing sludge conditioning processes. This study systematically investigates the effects of various conditioning methods-including thermal hydrolysis (TH), freezing/thawing (FT), anaerobic digestion (AD), polyaluminum chloride (PAC), polyacrylamide (PAM), and Fenton treatment (Fenton)-on sludge yield stress and its correlation with dewatering efficiency. Using linear regression, partial least squares regression (PLSR), and correlation heatmap analyses, we reveal significant variations in the correlation between σy and dewatering indexes, including moisture content (Mc), capillary suction time (CST), and bound water proportion (Wb/Wt), depending on the conditioning method and intensity. Under FT and PAM conditioning, σy shows a strong negative linear correlation with dewatering performance, with Pearson's r values exceeding -0.880, indicating that a decrease in σy corresponds to improved dewatering efficiency. Conversely, AD conditioning exhibits a positive linear correlation, with r values up to 0.993, suggesting that an increase in σy correlates with reduced dewatering efficiency. For TH, PAC, and Fenton treatments, the correlation between σy and dewatering metrics is highly sensitive to changes in treatment intensity. In the PLSR analysis, the VIP values, which quantify the importance of each predictor variable, indicate that Wb/Wt in TH conditioning (VIP = 1.649) and CST in PAC (VIP = 1.309) and Fenton (VIP = 1.299) conditioning strongly influence σy. This study highlights the significant impact of conditioning methods and intensities on the correlation between σy and dewatering performance. While σy provides valuable insights as a predictive indicator, its predictive power is limited in more complex conditioning scenarios. Therefore, optimizing conditioning intensity and incorporating multiple rheological parameters are essential for achieving superior sludge dewatering outcomes.

Enhancement of sludge dewaterability using combined technology of bioleaching and Fenton: Microscopic structure and hydrophilic/hydrophobic properties of sludge particles

Bioleaching and Fenton technology are commonly used preconditioning techniques for sludge dewatering. This study compared the dewatering mechanisms of different conditioning technologies. The results showed that bound water, specific resistance to filtration (SRF), and capillary suction time decreased from 3.95 g/g, 6.16 × 1012 m/kg, and 130.6 s to 3.15 g/g, 2.81 × 1011 m/kg, and 33 s, respectively, under combined treatment condition. Moreover, the free radicals, including ·OH, O2-·and Fe (Ⅳ), further damaged the cell structure, thus increasing the concentration of DNA in the S-EPS layer. This intense degradation sludge particle size decreased by 15.6% and significantly increased zeta potential. Under the combined technology, the α-helix and β-sheet decreased by 42.2% and 56.5%, respectively, destabilizing the spatial structure of proteins and promoting the release of bound water. In addition, the combined technology decreased (Ala/Lys) ratio in the TB-EPS layer by 67.6%, indicating the weakening of protein water-holding capacity. Moreover, the conversion of oxygen-containing compounds to nonpolar hydrocarbons increased the hydrophobicity of the sludge under a combined treatment, thus enhancing dewatering performance.

Untangling the interplay of dissolved organic matters variation with microbial symbiotic network in sludge anaerobic fermentation triggered by various pretreatments

Various pretreatments are commonly adopted to facilitate dissolved organic matter (DOM) release from waste activated sludge (WAS) for high-valued volatile fatty acids (VFAs) promotion, while the interplay impact of DOM dynamics transformation on microbial population and metabolic function traits is poorly understood. This work constructed "DOM-microorganisms-metabolism-VFAs" symbiotic ecologic networks to disclose how DOM dynamics variation intricately interacts with bacterial community networks, assembly processes, and microbial traits during WAS fermentation. The distribution of DOM was altered by different pretreatments, triggering the release of easily biodegradable compounds (O/C ratio > 0.3) and protein-like substance. This alteration greatly improved the substrates biodegradability (higher biological index) and upregulated microbial metabolism capacity (e.g., hydrolysis and fatty acid synthesis). In turn, microbial activity modifications augment substance metabolism level and expedite the conversion of highly reactive compounds (proteins-like DOM) to VFAs, leading to 1.6-4.2 fold rise in VFAs generation. Strong correlations were found between proteins-like DOM and topological properties of DOM-bacteria associations, suggesting that high DOM availability leads to more intricate ecological networks. A change in the way communities assemble, shifting from stronger uniform selection in pH10 and USp reactors to increased randomness in heat reactor, was linked to DOM composition alterations. The ecologic networks further revealed metabolic synergy between hydrolytic-acidogenic bacteria (e.g., Bacteroidota and Firmicutes) and biodegradable DOM (e.g., proteins and amino sugars) leading to higher VFAs generation. This study provides a deeper knowledge of the inherent connections between DOM and microbial traits for efficient VFAs biosynthesis during WAS anaerobic fermentation, offering valuable insights for effective WAS pretreatment strategies.

Development of oriented multi-enzyme strengthens waste activated sludge disintegration and anaerobic digestion: Performance, components transformation and microbial communities

Low methane production and long retention time are the main dilemmas in current anaerobic digestion (AD) of waste activated sludge (WAS). This work used WAS as only substrate to prepare oriented multi-enzyme (ME) that directly used for WAS pretreatment. Under the optimal parameters, the highest activities of protease and amylase in ME could respectively reach 16.5 U/g and 580 U/g, and the corresponding methane production attained 197 mLCH4/g VS, which was increased by 70.4% compared to blank group. It was found that ME pretreatment could strengthen WAS disintegration and organic matters dissolution, lead to the soluble chemical oxygen demand (SCOD) was increased from the initial 486 mg/L to 2583 mg/L, and the corresponding volatile suspended solid (VSS) and extracellular polymeric substances (EPS) were reduced by 27% and 73.8%, respectively. The results of three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform infrared spectroscopy (FTIR) indicated that protein disintegration may be the critical step during the process of WAS hydrolysis with ME, of which the release of tyrosine-like proteins achieved the better biodegradability of WAS, while the results of X-ray photoelectron spectroscopy (XPS) showed that the formation of protein derivatives was the main harmful factor that could extend the lag phase of AD process. Microbial communities analysis further suggested that ME pretreatment facilitated the enrichment of acetogenic bacteria and acetotrophic methanogens, which caused the transition of the methanogenesis pathway from hydrogenotrophic to acetotrophic. This study is expected to furnish valuable insight for ME pretreatment on enhancing WAS disintegration and methane production.

Deep dewatering of sludge and resource recovery of hydroxyapatite: A recyclable approach via ionic liquid biphasic system and hydrogen bonds reformation

Deep dewatering of Waste Activated Sludge (WAS) through mechanical processes remains inefficient, primarily due to the formation of a stable hydrogen bonding network between the biopolymers and water, which consequently leads to significant water trapped by Extracellular Polymeric Substances (EPS). In this study, a novel and recyclable treatment for WAS based on Ionic Liquids (ILs) was established, named IL-biphasic aqueous system (IL-ABS) treatment. Specifically, the IL-ABS formed in WAS facilitated rapid and efficient in-situ deep dewatering while concurrently recovering hydroxyapatite. The water content decreased from an initial 98.27 % to 65.35 % with IL-ABS, formed by 1-Butyl-3-methylimidazolium bromide (BmimBr) and K3PO4 synthesized from waste H3PO4. Moreover, the recycled BmimBr maintaining the water content of the dewatered sludge consistently between 65.61 % and 67.25 % across five cycles, exhibited remarkable reproducibility. Through three-dimensional excitation-emission matrix, lactate dehydrogenase analyses and confocal laser scanning microscopy, the high concentration of BmimBr in the upper phase effectively disrupted the cells and EPS, which exposed protein and polysaccharide on the EPS surface. Subsequently, the K3PO4 in the lower phase led to an enhanced salting-out effect in WAS. Furthermore, FT-IR analysis revealed that K3PO4 disrupted the original hydrogen bonds between EPS and water. Then, BmimBr formed numerous hydrogen bonds with the sludge flocs, leading to deep dewatering and agglomeration of the sludge flocs during the unique phase separation process of IL-ABS. Notably, sludge-derived hydroxyapatite product exhibited remarkable adsorption capacity for prevalent heavy metal contaminants such as Pb2+, Cd2+ and Cu2+, with efficiencies comparable to those of commercial hydroxyapatite, thereby achieving the resource utilization of waste H3PO4. Moreover, economic calculations demonstrated the suitability of this novel treatment. This innovative treatment exhibits potential for practical applications in the non-mechanical deep dewatering of WAS.

Feasibility of sludge deep dewaterability improvement for incineration disposal by combined conditioning of freeze-thaw and sawdust

Sludge incineration is the main strategy for sludge reduction in China. The combined conditioning of lime and chemical agents has been proven to achieve sludge dewatering by disrupting the extracellular polymeric substances (EPS) of sludge and reducing its compressibility. However, when incineration is the intended disposal purpose, this method poses challenges such as incomplete combustion, equipment corrosion, secondary pollution, and decreased calorific value of sludge cake. In contrast, freeze-thaw conditioning, coupled with sawdust as a high-calorific-value bio-waste, emerges as an efficient and clean alternative. The research investigates the synergistic effects of freeze-thaw and sawdust co-conditioning on various sludge properties, including dewaterability, compressibility, consolidation, permeability, microscopicity, and calorific value. The study reveals that the combined conditioning significantly reduces water content and compressibility while increasing void ratio, consolidation, permeability, and enhancing the calorific value of the sludge cake. Specifically, sludge cake conditioned with 60% dried solids (DS) sawdust and freeze-thaw achieved a water content (Wc) of 49.07% and a calorific value of 1422.3 kcal/kg, meeting standards for self-sustained incineration. With heat recovery, the combined conditioning generates an economic revenue of 25.1 $/t DS after deducting costs, thereby reducing the overall cost of sludge reduction treatment. This research offers a clean and practical solution for sludge incineration and reduction, demonstrating great economic value and application potential.

Solid-liquid redistribution and degradation of antibiotics during hydrothermal treatment of sewage sludge: Interaction between biopolymers and antibiotics

Waste activated sludge serves an important reservoir for antibiotics within wastewater treatment plants, and understanding the occurrence and evolution of antibiotics during sludge treatment is crucial to mitigate the potential risks of subsequent resource utilization of sludge. This study explores the degradation and transformation mechanisms of three typical antibiotics, oxytetracycline (OTC), ofloxacin (OFL), and azithromycin (AZI) during sludge hydrothermal treatment (HT), and investigates the influence of biopolymers transformation on the fate of these antibiotics. The findings indicate that HT induces a shift of antibiotics from solid-phase adsorption to liquid-phase dissolution in the initial temperature range of 25-90 °C, underscoring this phase's critical role in preparing antibiotics for subsequent degradation phases. Proteins (PN) and humic acids emerge as crucial for antibiotic binding, facilitating their redistribution within sludge. Specifically, the binding capacity sequence of biopolymers to antibiotics is as follows: OFL>OTC>AZI, highlighting that OFL-biopolymers display stronger electrostatic attraction, more available adsorption sites, and more stable binding strength. Furthermore, antibiotic degradation mainly occurs above 90 °C, with AZI being the most temperature-sensitive, degrading 92.97% at 180 °C, followed by OTC (91.26%) and OFL (52.51%). Concurrently, the degradation products of biopolymers compete for active sites to form novel amino acid-antibiotic conjugates, which inhibits the further degradation of antibiotics. These findings illuminate the effects of biopolymers evolution on intricate dynamics of antibiotics fate in sludge HT and are helpful to optimize the sludge HT process for effective antibiotics abatement.

Chemical Dynamics of Selenium Nanoparticles in Archaeal Systems

Methanogenic archaea, characterized by their cell membrane lipid molecules consisting of isoprenoid chains linked to glycerol-1-phosphate via ether bonds, exhibit exceptional adaptability to extreme environments. However, this distinct lipid architecture also complicates the interactions between methanogenic archaea and nanoparticles. This study addresses this challenge by exploring the interaction and transformation of selenium nanoparticles (SeNPs) within archaeal Methanosarcina acetivorans C2A. We demonstrated that the effects of SeNPs are highly concentration-dependent, with chemical stimulation of cellular processes at lower SeNPs concentrations as well as oxidative stress and metabolic disruption at higher concentrations. Notably, we observed the formation of a protein corona on SeNPs, characterized by the selective adsorption of enzymes critical for methylotrophic methanogenesis and those involved in selenium methylation, suggesting potential alterations in protein function and metabolic pathways. Furthermore, the intracellular transformation of SeNPs into both inorganic and organic selenium species highlighted their bioavailability and dynamic transformation within archaea. These findings provide vital insights into the nano-bio interface in archaeal systems, contributing to our understanding of archaeal catalysis and its broader applications.

A novel approach for sludge deep-dewatering via flowing-out enhancement but not relying on cell lysis and bound water release

Effective deep-dewatering is crucial for wastewater sludge management. Currently, the dominant methods focus on promoting cell lysis to release intracellular water, but these techniques often lead to secondary pollution and require stringent conditions, limiting their practical use. This study explores an innovative method using a commercially available complex quaternary ammonium salt surfactant, known as G-agent. This agent remarkably reduces the sludge water content from 98.6 % to 56.8 % with a low dosage (50 mg/g DS) and under neutral pH conditions. This approach surpasses Fenton oxidation in terms of dewatering efficiency and avoids the necessity for cell lysis and bound water release, thereby reducing the risk of secondary pollution in the filtrate, including heavy metals, nitrogen, phosphorus, and other contaminants. The G-agent plays a significant role in destabilizing flocs and enhancing flocculation during the conditioning and initial dewatering stages, effectively reducing the solid-liquid interfacial affinity of the sludge. In the compression filtration stage, the agent's solidification effect is crucial in forming a robust skeleton that improves pore connectivity within the filter cake, leading to increased water permeability, drainage performance and water flow-out efficiency. This facilitates deep dewatering of sludge without cell lysis. The study reveals that the G-agent primarily improves water flow-out efficiency rather than water flowability, indicating that cell lysis and bound water release are not indispensable prerequisites for sludge deep-dewatering. Furthermore, it presents an encouraging prospect for overcoming the limitations associated with conventional sludge deep-dewatering processes.

Novel Developments and Progress in Two-Dimensional Correlation Spectroscopy (2D-COS)

This first of the two-part series of the comprehensive survey review on the progress of the two-dimensional correlation spectroscopy (2D-COS) field during the period 2021-2022, covers books, reviews, tutorials, novel concepts and theories, and patent applications that appeared in the last two years, as well as some inappropriate use or citations of 2D-COS. The overall trend clearly shows that 2D-COS is continually growing and evolving with notable new developments. The technique is well recognized as a powerful analytical tool that provides deep insights into systems in many science fields.

Diverse Applications of Two-Dimensional Correlation Spectroscopy (2D-COS)

This second of the two-part series of a comprehensive survey review provides the diverse applications of two-dimensional correlation spectroscopy (2D-COS) covering different probes, perturbations, and systems in the last two years. Infrared spectroscopy has maintained its top popularity in 2D-COS over the past two years. Fluorescence spectroscopy is the second most frequently used analytical method, which has been heavily applied to the analysis of heavy metal binding, environmental, and solution systems. Various other analytical methods including laser-induced breakdown spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, capillary electrophoresis, seismologic, and so on, have also been reported. In the last two years, concentration, composition, and pH are the main effects of perturbation used in the 2D-COS fields, as well as temperature. Environmental science is especially heavily studied using 2D-COS. This comprehensive survey review shows that 2D-COS undergoes continuous evolution and growth, marked by novel developments and successful applications across diverse scientific fields.

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.

Mechanism insights into hydrothermal-activated tannic acid (TA) for simultaneously sewage sludge deep dewatering and antibiotics removal

Tannic acid (TA) aided hydrothermal treatment (HT) can decrease effective HT temperatures for sludge deep dewatering by chelator protein, but faces notable and economic challenges including the failure to remove antibiotics and the limited protein binding capacity. Herein, hydrothermally activated TA (in situ TA + HT) was conducted to simultaneously improve sludge dewaterability and antibiotic (tetracycline (TC), oxytetracycline (OTC), norfloxacin (NOR), ofloxacin (OFL)) removal. Compared to traditional HT and HT + TA treatment, the in-situ TA + HT process could further strengthen the TA-aided HT efficacy in enhancing sludge and reducing the protein content in the filtrate simultaneously; in which the optimal HT temperature for the dewatering of the sludge was reduced from 180 °C to 140 °C. Furthermore, the total removal efficiency of target antibiotics was achieved at more than 71.0-94.7% for TC and OTC, and 72.0-84.8% for NOR and OFL. The highly reactive species (·OH) generation and the electron transfer efficiency from the hydrothermal-activated TA process were responsible for the elimination of antibiotics and promoted the hydrolyzation and mineralization of HMW protein in sludge during the HT process. Meanwhile, the degradation of HMW proteins and the destruction of the secondary structure of these proteins resulted in improved hydrophobicity and dewaterability of sludge. Hydrothermally activated TA induces covalent binding with the protein. As a result, hydrothermal-activated TA could promote the removal of antibiotics and proteinaceous compounds from the sludge samples, improving the hydrophobicity of sludge and releasing bound water from the sludge flocs during HT. Finally, the cost of hydrothermal-activated TA was 66.51% lower than that of thermal drying treatment. This study not only proposed an effective method to improve traditional HT for sludge thermal dry-free treatment, but also provided new information on the catalysis roles of polyphenols in the hydrothermal conversion of sludge.

New insights on destruction mechanisms of waste activated sludge during simultaneous thickening and digestion process via forward osmosis membrane

This study delved into the efficacy of sludge digestion and the mechanisms involved in sludge destruction during the implementation of forward osmosis process for sludge thickening and digestion (FO-MSTD). Utilizing a lab-scale FO membrane reactor for the thickening and digestion of waste activated sludge (WAS), the investigation explored the effects of sludge thickening and digestion in FO-MSTD processes using draw solutions of varying concentrations. The findings underscored the significance of hydraulic retention time (HRT) as a pivotal parameter influencing the swift thickening or profound digestion of sludge. Consequently, tailoring the HRT to specific processing objectives emerged as a key strategy for achieving desired treatment outcomes. In the investigation, the use of a 1 M NaCl draw solution in the FO-MSTD process showcased enhanced thickening and digestion capabilities. This specific setup raised the concentration of mixed liquor suspended solids (MLSS) to over 30 g/L and achieved a 42.7% digestion efficiency of mixed liquor volatile suspended solids (MLVSS) within an operational timeframe of 18 days. Furthermore, the research unveiled distinct stages in the sludge digestion process of the FO-MSTD system, characterized by fully aerobic digestion and aerobic-local anaerobic co-existing digestion. In the fully aerobic digestion stage, the sludge digestion rate exhibited a steady increase, leading to the breakdown of sludge floc structures and the release of a substantial amount of nutrients into the sludge supernatant. The predominant microorganisms during this stage were typical functional microorganisms found in wastewater treatment systems. Transitioning into the aerobic-local anaerobic co-existing digestion stage, both MLSS concentration and MLVSS digestion efficiency continued to rise, accompanied by a decreasing dissolved oxygen (DO) concentration. More organic matter was released into the supernatant, and sludge microbial flocs tended to reaggregate. The localized anaerobic environment within the FO-MSTD reactor fostered an increase in the relative abundance of bacteria with nitrogen and phosphorus removal functions, thereby positively impacting the mitigation of total nitrogen (TN) and total phosphorus (TP) concentrations in the sludge supernatant. The results of this research enhance comprehension of the advanced FO-MSTD technology in the treatment of WAS.

Cellulose nanofibers embedded chitosan/tannin hydrogel with high antibacterial activity and hemostatic ability for drug-resistant bacterial infected wound healing

Millions of patients annually suffer life-threatening illnesses caused by bacterial infections of skin wounds. However, the treatment of wounds infected with bacteria is a thorny issue in clinical medicine, especially with drug-resistant bacteria infections. Therefore, there is an increasing interest in developing wound dressings that can efficiently fight against drug-resistant bacterial infections and promote wound healing. In this work, an anti-drug-resistant bacterial chitosan/cellulose nanofiber/tannic acid (CS/CNF/TA) hydrogel with excellent wound management ability was developed by electrospinning and fiber breakage-recombination. The hydrogel exhibited an outstanding antibacterial property exceeding 99.9 %, even for drug-resistant bacteria. This hydrogel could adhere to the tissue surface due to its abundant catechol groups, which avoided the shedding of hydrogel during the movement. Besides, it exhibited extraordinary hemostatic ability during the bleeding phase of the wound and then regulated the wound microenvironment by absorbing water and moisturizing. Moreover, the CS/CNF/TA also promoted the regrowth of vessels and follicles, accelerating the healing of infected wound tissue, with a healing rate exceeding 95 % within a 14-day timeframe. Therefore, the CS/CNF/TA hydrogel opens a new approach for the healing of drug-resistant bacterial infected wounds.

Novel multiplexed alkali enzyme lysis coupled with EDTA pretreatment for RNA virus extraction from wastewater sludge: Optimization, recovery, and detection

RNA viruses are readily enriched in wastewater sludge owing to adsorption by extracellular polymeric substances (EPS) during wastewater treatment, causing pathogenicity. However, conventional wastewater extraction methods often fail to fully extract these viruses from sludge. In this study, three methods: enzymatic (ENP), alkaline (ALP), and ethylenediaminetetraacetic acid (EDTA) pretreatments were applied to sludges and promote the RNA virus extraction from sludge. Our results show that the total recovery rate of RNA viruses increased by 87.73% after ENP pretreatment, whereas ALP pretreatment inhibited virus extraction. The highest recovery rate of viruses from sludge, reaching 296.80%, was achieved with EDTA pretreatment (EDP) coupled with ENP. Notably, the most significant increase was observed in the abundance of Astroviruses, which increased from 7.60 × 107 to 7.86 × 108 copies/g TSS after EDP + ENP treatment. Our investigations revealed that virus extraction was affected by a class of short-wavelength protein substances, as opposed to tryptophan or tyrosine, which were eluted by proteins with beef paste buffer by substitution after EDP + ENP treatment. The results of this study provide essential insights for sludge-based epidemiology with the required sensitivity for managing the extraction of RNA epidemic viruses to control viral transmission.

In-situ sewer sediment self-cleaning by plant ash-driven hydrolysis: Impairing adhesion and hydraulic erosion resistance from gelatinous biopolymer molecule deconstruction

The gelatinous structure and adhesion of sediments induced strong hydraulic erosion resistance and bottom siltation, which brought about serious challenges in sewer management. The in-situ sediment self-cleaning technology with low energy and labor consumption has become urgent demand. This study proposed an innovative plant ash-triggered molecule hydrolysis strategy for driving sewer sediment self-cleaning. Plant ash treatment at the optimal dosage of 0.10 g/g SS promoted molecular deconstruction and dissolution of aromatic proteins (tryptophan-like and tyrosine-like proteins), humic acids (fulvic acid-like and humic acid-like substances) and carbohydrates with secondary structure deflocculation (α-helix to β-turn), meanwhile numerous microbial cells were lysed, contributing to linkage breakage in extracellular polymeric substance (EPS). The gelatinous EPS disruption and outward migration with cohesion reduction were achievable. Sediment adhesion was vulnerable to EPS structural damage, which was degenerated by 91.14 %. Correspondingly, the sediment matrix structure was observably disintegrated into dispersive and small fragments, with increased surface electronegativity and eliminated adhesive bio-agglomeration. Thereby, the sensitivity of sediments to hydraulic erosion was greatly improved. In this case, substantial organic and inorganic sediment particles were solubilized and downstream transported by gravity sewage flow. Such plant ash-triggered hydrolysis provided a sustainable strategy for sediment self-cleaning in "waste control by waste" pattern, which improved sediment floating by 7.25-9.57 times. Considerable economic benefits of 35.56-123.46 CNY/(sewer meter length) were obtained compared with traditional mechanical flushing approaches. The findings might provide theoretical and engineering inspirations for solving sewer sediment issues.

Roles of extracellular polymeric substances in the adsorption and removal of norfloxacin during hydrothermal treatment of sewage sludge

Hydrothermal treatment (HT) is promising to remove antimicrobials from sewage sludge (SS); however, the mechanism of antimicrobial degradation during the HT of SS is not fully understood. In this study, the roles of extracellular polymeric substances (EPS) in the removal and transformation of norfloxacin (NOR) during the HT of SS at temperatures of 100 and 160 °C were investigated. The results indicated that the degradation of NOR increased with increasing HT temperature, with maximum NOR removal (52%) achieved at 160 °C. Furthermore, the NOR in sludge showed higher degradation efficiencies than the control as HT temperature was higher than 120 °C. Evident promotion effects of bound-EPS (B-EPS) in sludge were observed on the NOR degradation as HT temperature was higher than 120 °C, leading to the mineralization and deamination of protein-like components in EPS during HT. Beside, the adsorption capacity of NOR during the HT of SS decreased at temperatures higher than 120 °C. The evolution of the spatial structure of B-EPS was predominantly responsible for the adsorption of antimicrobials, a spontaneous process driven mainly by hydrophilic interactions. With the hydrothermal conversion of B-EPS, the electron transfer, and reactive species (3EPS* and ·OH) derived from B-EPS could facilitate the degradation of NOR. In particular, hydrogen bonds between B-EPS and NOR increased the apparent yield of ·OH and accelerated the decarboxylation of NOR during HT at temperatures higher than 120 °C. A toxicity evaluation suggested that HT for NOR degradation could attenuate toxicity, whereas deep oxidation or mineralization would be needed to promote ecosystem safety. These findings provide new insights into the hydrothermal activation of EPS and the interrelated hydrothermal fate of antimicrobials and other toxic pollutants in sludge.

Molecular dynamic modeling of EPS and inorganic/organic flocculants during sludge dual conditioning

Extracellular polymeric substances (EPS) are the key components determining the dewatering behavior of wastewater sludge. However, current technical optimization of sludge conditioning for dewatering is limited by the poor understanding of the conditioner-EPS interactions at molecular levels. Herein, a combination of molecular dynamic (MD) simulations, dewaterability assessment and EPS characterization was used to reveal the sludge dewatering mechanisms using dual conditioning processes (prevalent inorganic (poly aluminum chloride (PAC)) and organic (poly dimethyl diallyl ammonium chloride (PDDA)). Results suggested that PAC and PDDA bridged the biopolymers mainly through electrostatic interactions, promoting the agglomeration of biopolymers and reducing their contact probability with water molecules. Water molecules were tightly bound to EPS mainly through hydrogen bonding with polar oxygen-containing functional groups. The adsorption of PAC and PDDA on hydrophilic components reduced the molecular polarity of biopolymers and altered the conformation of water molecules in the hydration shell, resulting in a decreased hydration capacity of EPS and the release of bound water, and sludge dewaterability was improved. PAC was found to be more effective than PDDA in disrupting the hydrogen bonding between water molecules and EPS, especially the protein β-sheet structure inside the molecular clusters with its high charge strength and diffusivity. Sludge bound water decreased by 73.16 % after PAC conditioning. In addition, PDDA exhibited superior agglomeration ability to biopolymers and promoted the electrostatic interaction between PAC and polar groups during dual conditioning. The strength and hydrophobicity of EPS molecular clusters were thus enhanced, and the conditioning efficiency was improved. This study offers molecular-level insights into the coagulation treatment process of sludge and provides theoretical references for process optimization and new conditioner development.

Characterization of melanoidins in thermal hydrolysis sludge and effects on dewatering performance

Thermal hydrolysis pretreatment (THP) of sludge can form the refractory brown melanoidins due to the occurrence of the Maillard reaction, which adversely involves the subsequent sludge anaerobic digestion (AD) process. However, details of the generation pattern of melanoidins and how they affect the sludge dewaterability remain largely unknown. This work aims to determine an approach to characterize and quantify the melanoidins created by THP of sludge. On this basis, the effect of melanoidins on sludge dewatering performance was revealed by adding synthetic melanoidins to the mixed sludge. Experimental results showed that three-dimensional fluorescence-region integration (3DEEM-FRI) could effectively distinguish melanoidins from other organic substances and achieve semi-quantitative characterization in sludge. The melanoidins significantly deteriorated the sludge dewaterability, and the lowest solids content of the filter cake (TS) was only 17.78% at the addition of 480 mg (g TS)-1, which was a drop of about 20% compared to the control group. The mechanism investigations indicated that the internal structure of sludge becoming particularly complicated and the opportunities for molecules to collide with each other enlarged because of the contribution of melanoidins, resulting in the increment of the sludge apparent viscosity and consistency coefficient (k), a decline of the flow behavior index (n) and a weakening of flowability. Melanoidins could capture massive water molecules and carry negative charges with the decrease of sludge particle size and zeta potential value, which enhanced the electrostatic repulsion between sludge particles and abated the flocculation ability, thus further aggravating the sludge dewatering performance.

High-performance biochar-loaded MgAl-layered double oxide adsorbents derived from sewage sludge towards nanoplastics removal: Mechanism elucidation and QSAR modeling

Utilization of sewage sludge for the fabrication of environmental functional materials is highly desirable to achieve pollution mitigation and resource recovery. In the present work, we introduced a novel MgAl-layered double oxide (LDO)@biochar composite adsorbent in-situ fabricated from Al-rich sewage sludge, and its excellent application in nanoplastics adsorption. Initially, fifteen model contaminants with varied conjugate structures, hydrogen bonding and ionic properties were selected for an investigation of adsorption behavior and adsorption selectivity on LDO@biochar. Structural variation of LDO@biochar suggested reconstruction of the layered double hydroxide (LDH) during the adsorption process due to the "memory effect". Under the synergy of LDH and biochar, the contaminants were adsorbed via multiple adsorbent-adsorbate interactions, including anion exchange, electrostatic interaction, hydrogen bonding and π-π conjugation. Then, a quantitative structure-activity relationship (QSAR) model was constructed by integrating the number of hydrogen bond acceptors, polarity surface area, number of aromatic rings, and Fukui index f(-)x together to reflect the affinity of each contaminant to the adsorbent. Guided by the QSAR model, the negatively charged polystyrene nanoplastics with continuously conjugated aromatic rings were predicted to be effectively adsorbed on LDO@biochar. Experimental tests confirmed a great capacity of LDO@biochar towards the polystyrene nanoplastics, given the equilibrium adsorption capacity as high as 360 mg g-1 at 30-50 °C. This work not only opened up a new avenue for sustainable utilization of sewage sludge towards high-performance environmental functional materials, but also demonstrated the potential of the QSAR analysis as a rapid and accurate approach for guiding the application of an adsorbent to new emerging containments.

Two birds with one stone: The multiple roles of hydrothermal treatment in dewatering municipal sludge and producing value-added products

Sludge dewatering and resource recovery are key steps in the sustainable treatment of municipal sludge (MS) owing to the high levels of moisture and nutrients. Among the treatment options available, hydrothermal treatment (HT) is promising to efficiently improve dewaterability and recover biofuels, nutrients, and materials from MS. However, hydrothermal conversion at different HT conditions generates multiple products. Integrating the characteristics of dewaterability and value-added products under different HT conditions facilitates the application of HT for the sustainable management of MS. Therefore, a comprehensive review of HT for its multiple roles in MS dewatering and value-added resource recovery is conducted. First, the impact of HT temperature on sludge dewaterability and key mechanisms are summarized. Then, this study elucidates the characteristics of biofuels produced (combustible gases, hydrochars, biocrudes, and H2-rich gases), nutrient recovery (proteins and phosphorus), and value-added materials under a wide range of HT conditions. Importantly, along with the integration and evaluation of HT product characteristics under different HT temperatures, this work proposes a conceptual sludge treatment system that integrates the different value-added products in different HT stages. Furthermore, a critical evaluation of the knowledge gaps in the HT for sludge deep dewatering, biofuels, nutrients, and materials recovery is provided along with recommendations for further research.

Volatile fatty acids bio-production using extracellular polymeric substances disengaged from sludge for carbon source recycling

Excessive waste-activated sludge (WAS) and insufficient carbon source (CS) for biological nitrogen removal (BNR) often coexist in municipal sewage treatment. Although the production of volatile fatty acids (VFAs) from WAS has been recognized as a promising solution, the development is limited by low VFAs production efficiency and dewatering deterioration of sludge. This study extracted the extracellular polymeric substances (EPS) from sludge by low-temperature thermal-hydrolysis (LTH) and high-speed hydro-cyclone (HSHC) pretreatment and recovered it for high-quality VFAs bio-production in thermophilic fermentation. Microbial mechanism analysis disclosed that interspecific interaction networks composed of functional flora, which accumulate VFAs by bio-converting EPS primarily and supplemented by EPS synthesis, guaranteed the efficient bio-production of VFAs. This process scheme shows promise in providing alternative denitrification CSs and avoiding deterioration of sludge dewaterability.

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

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

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

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

Trace elements' deficiency in energy production through methanogenesis process: Focus on the characteristics of organic solid wastes

Excessive or insufficient supplementation of trace elements (TEs) limits the progression of anaerobic digestion. The main reason for this is the lack of sufficient understanding of digestion substrate characteristics, which significantly affects the demand for TEs. In this review, the relationship between TEs requirements and substrate characteristics is discussed. We mainly focus on three aspects. 1) The basis for TE optimization and existing problems: The optimization of TEs often based on the total solids (TS) or volatile solids (VS) of substrates, does not fully consider substrate characteristics. 2) TE deficiency mechanisms for different types of substrates: nitrogen-rich, sulfur-rich, TE-poor, and easily hydrolyzed substrates are the four main types of substrates. The mechanisms underlying TEs deficiency in the different substrates are investigated. 3) Regulation of TE bioavailability: characteristics of substrates affect digestion parameters, which disturb the bioavailability TE. Therefore, methods for regulating bioavailability of TEs are discussed.

Aggregation and construction mechanisms of microbial extracellular polymeric substances with the presence of different multivalent cations: Molecular dynamic simulation and experimental verification

Interactions between cations and extracellular polymeric substances (EPS) play an important role in the formation of microbial aggregates and have key effects on the physical properties of activated sludge across wastewater and sludge treatment process. Here, a molecular model of EPS cluster in activated sludge was constructed and simulated by molecular dynamics (MD) to probe the structural properties of EPS and the interaction between EPS and prevalent multivalent cations (Ca²⁺, Mg²⁺, Al³⁺). Then the predicted changes in physical properties were validated against the dynamic light scattering, XAD resin fractionation and rheology test. The binding dynamics and interactions mechanisms between multivalent cations and EPS functional groups were further investigated using MD in combination with spectroscopic analysis. Results suggest that biopolymers are originally aggregated by electrostatic and intermolecular interactions forming dynamic clusters with negatively charged surface functional groups, which induced electrostatic repulsion preventing further agglomeration of biopolymer clusters. In the presence of multivalent cations, surface polar functional groups in biopolymers are connected, causing the rearrangement of EPS molecular conformation that forms larger and denser agglomerates. Reduced solvent accessible surface area, enhanced hydrophobicity, and increased binding free energy lead to a strong gel-like network of EPS. Ca²⁺ and Al³⁺ predominantly interact with functional groups in polysaccharides, promoting agglomeration of macromolecules. In contrast, Mg²⁺ and Al³⁺ disrupted the secondary structure of proteins, exposing hydrophobic interaction sites. Al³⁺ can better agglomerate biopolymers with its higher positive charge and shorter coordination distance as compared to Ca²⁺ and Mg²⁺, but compromised by the effect of hydration. This work offers a novel approach to explore the construction and molecular aggregation of EPS, enriching the theoretical basis for optimization of wastewater and sludge treatment.

Metagenomic insight of fluorene-boosted sludge acidogenic fermentation: Metabolic transformation of amino acids and monosaccharides

Fluorene (Flu) occurs widely in various environments and its toxicity to organisms is well-known. However, the impact of Flu on complicated biochemical processes involving functional microbial community has been reported rarely. In this study, the facilitation of Flu on the volatile fatty acids (VFAs) generation executed by acidogenic microbial population during sludge acidogenic fermentation (37 °C, SRT = 8 d, pH = 10.0) was investigated. The accumulation of VFAs (particularly acetic acid) increased initially and then declined with the increasing of Flu concentration (0-500 mg/kg dry sludge), which reached a maximum (3211.1 mg COD/L) as Flu content was 200 mg/kg dry sludge. The Flu-enhanced VFAs production was primarily attributed to the shift of hydrolysis/acidification, as well as the corresponding functional microbial community and the activity of enzymes. Based on the metagenomics analysis, the conversion of organic substrates, i.e. amino acid and monosaccharide, into VFAs embraced in hydrolysis/acidification shaped by Flu was constructed at the genetic level. The relative abundances of genes included in aminotransfer and deamination process of amino acid and glycolysis of monosaccharide into VFA-precursors (pyruvate, acetyl-CoA and propionyl-CoA), and the further formation of VFAs were improved due to the Flu presence. This study shed light on the Flu-affected microbial processes at the molecular biology level during acidogenic fermentation and was of great significance in resource recovery of sludge containing persistent organic pollutants.

Calcium hypochlorite-coupled aged refuse promotes hydrogen production from sludge anaerobic fermentation

This work investigated the effect of calcium hypochlorite (CH) coupled aged refuse (AR) treatment on the enhanced hydrogen generation from sludge anaerobic dark fermentation (SADF). The enhanced mechanism was systematically revealed through sludge disintegration, organic matter biotransformation, and microbial community characteristics, etc. The experimental data showed that CH coupled AR increased the hydrogen yield to 18.1 mL/g, significantly higher than that in the AR or CH group alone. Mechanistic analysis showed that CH-coupled AR significantly promoted sludge disintegration and hydrolysis processes, providing sufficient material for hydrogen-producing bacteria. Microbiological analysis showed that CH-coupled AR increased the relative abundance of responsible hydrogen-producing microorganisms. In addition, CH-coupled AR was very effective in reducing phosphate content in the fermentation liquid and fecal coliforms in the digestate, thus facilitating the subsequent treatment of fermentation broth and digestate. CH coupled AR is an alternative strategy to increase hydrogen production from sludge.

Continuing progress in the field of two-dimensional correlation spectroscopy (2D-COS): Part III. Versatile applications

In this review, the comprehensive summary of two-dimensional correlation spectroscopy (2D-COS) for the last two years is covered. The remarkable applications of 2D-COS in diverse fields using many types of probes and perturbations for the last two years are highlighted. IR spectroscopy is still the most popular probe in 2D-COS during the last two years. Applications in fluorescence and Raman spectroscopy are also very popularly used. In the external perturbations applied in 2D-COS, variations in concentration, pH, and relative compositions are dramatically increased during the last two years. Temperature is still the most used effect, but it is slightly decreased compared to two years ago. 2D-COS has been applied to diverse systems, such as environments, natural products, polymers, food, proteins and peptides, solutions, mixtures, nano materials, pharmaceuticals, and others. Especially, biological and environmental applications have significantly emerged. This survey review paper shows that 2D-COS is an actively evolving and expanding field.

Roles of zero-valent iron in anaerobic digestion: Mechanisms, advances and perspectives

With the rapid growth of population and urbanization, more and more bio-wastes have been produced. Considering organics contained in bio-wastes, to recover resource from bio-wastes is of great significance, which can not only achieve the resource recycle, but also protect the environment. Anaerobic digestion (AD) has been proved as one of the most promising strategies to recover bio-energy from bio-wastes, as well as to realize the reduction of bio-wastes. However, the conventional interspecies electron transfer is sensitive to environmental shocks, such as high ammonia, organic pollutants, metal ions, etc., which lead to instability or failure of AD. The recent findings have proved that the introduction of zero-valent iron (ZVI) in AD system can significantly enhance methane production from bio-wastes. This review systematically highlighted the recent advances on the roles of ZVI in AD, including underlying mechanisms of ZVI on AD, performance enhancement of AD contributed by ZVI, and impact factors of AD regulated by ZVI. Furthermore, current limitations and outlooks have been analyzed and concluded. The roles of ZVI on underlying mechanisms in AD include regulating reaction conditions, electron transfer mode and function of microbial communities. The addition of ZVI in AD can not only enhance bio-energy recovery and toxic contaminants removal from bio-wastes, but also have the potential to buffer adverse effect caused by inhibitors. Moreover, the electron transfer modes induced by ZVI include both interspecies hydrogen transfer and direct interspecies electron transfer pathways. How to comprehensively evaluate the effects of ZVI on AD and further improve the roles of ZVI in AD is urgently needed for practical application of ZVI in AD. This review aims to provide some references for the introduction of ZVI in AD for enhancing bio-energy recovery from bio-wastes.

Intracellular and extracellular sources, transformation process and resource recovery value of proteins extracted from wastewater treatment sludge via alkaline thermal hydrolysis and enzymatic hydrolysis

Excess sludge contains a large amount of protein and can be recycled to prepare industrial foaming agents, foliar fertilizers and other high value-added products. The optimization and effects of sludge protein extraction using the common processes of alkaline thermal hydrolysis (ATH) and enzymatic hydrolysis (EH) have been widely studied. This study focused on the protein extraction mechanisms of ATH and EH by comparing the ratio of intracellular to extracellular proteins extracted and the transformation of protein during the hydrolysis process. The extracellular protein content was 82.6 ± 5.07 mg/g VSS, and the content of intracellular protein extracted using ATH and EH was 376.9 mg/g VSS and 127.9 mg/g VSS, respectively. The ratio of intracellular to extracellular proteins extracted by ATH and EH was 4.5 and 1.5, respectively, indicating that ATH had a much better wall-breaking effect that allowed it to extract abundant intracellular proteins. The protein content obtained from ATH continuously increased over time, and approximately 38 % of proteins were further hydrolyzed to polypeptides. In contrast, the relatively low protein content extracted by EH possibly limited subsequent polypeptide hydrolysis, but subsequent hydrolysis to amino acids was not noticeably affected and was linearly correlated with the amount of protein extracted. An analysis of the recycling convenience and value of extracted proteins showed that the sludge dewatering performance increased by 86.7 % and 45.5 % after ATH and EH treatment, respectively, which was conducive to the subsequent separation of the protein solution. The protein extracted by ATH, with a large amount of peptides, would be beneficial to prepare industrial foaming agents, while the protein extracted by EH was rich in free amino acids and could be used to prepare foliar fertilizer.

Phage Predation Promotes Filamentous Bacterium Piscinibacter Colonization and Improves Structural and Hydraulic Stability of Microbial Aggregates

Although bacteria-phage interactions have broad environmental applications and ecological implications, the influence of phage predation on bacterial aggregation and structural stability remains largely unexplored. Herein, we demonstrate that inefficient lytic phage predation can promote host filamentous bacterium Piscinibacter colonization onto non-host Thauera aggregates, improving the structural and hydraulic stability of the dual-species aggregates. Specifically, phage predation at 10³-10⁴ PFU/mL (i.e., multiplication of infection at 0.01-0.1) promoted initial Piscinibacter colonization by 10-15 folds and resulted in 29-31% higher abundance of Piscinibacter in the stabilized aggregates than that in the control aggregates without phage predation. Transcriptomic analysis revealed upregulated genes related to quorum sensing (by 15-92 folds) and polysaccharide secretion (by 10-90 folds) within the treated aggregates, which was consistent with 120-172% higher content of polysaccharides for the treated dual-species aggregates. Confocal laser scanning microscopic images further confirmed the increase of filamentous bacteria and polysaccharides (both with wider distribution) within the dual-species aggregates. Accordlingly, the aggregates' structural strength (via atomic force microscopes) and shear resistance (via hydraulic stress tests) increased by 77 and 42%, respectively, relative to the control group. In the long-term experiments, the enhanced hydraulic stability of the treated aggregates could facilitate dwelling bacteria propagation in flow-through conditions. Overall, our study demonstrates that phage predation can promote bacterial aggregation and enhance aggregate structural stability, revealing the beneficial role of lytic phage predation on bacterial symbiosis and environmental adaptivity.

Comprehensive insights into the impact of pretreatment on anaerobic digestion of waste active sludge from perspectives of organic matter composition, thermodynamics, and multi-omics

Although various pretreatments have been applied to promote the anaerobic digestion of waste active sludge (WAS), the mechanisms regarding the impact of pretreatment on anaerobic digestion have not been well addressed. In this study, the effects of acid, alkali, and thermal pretreatments on anaerobic digestion of WAS were comprehensively investigated from the perspectives of organic matter composition, thermodynamics, and multi-omics. Results showed acid, alkali, and thermal pretreatments increased the methane production potential of WAS by 53.7%, 98.2%, and 101.8%, respectively, compared with the control. The protein secondary structure was disrupted after pretreatment, with a shift from α-helix and β-sheet to random coil and antiparallel β-sheet/aggregated strands. Thermodynamically, the WAS flocculation process was controlled by the short-range interfacial interactions described by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, which was positively correlated (R = 0.97, p < 0.05) with the organic matter solubilization of the WAS. After pretreatment, the flocculation energy barrier of pretreated WAS was 4.1 (acid), 7.0 (alkali) and 7.1 (thermal) times higher than that of the control group, respectively. Multi-omics analysis confirmed that pretreatment promoted amino acids (tryptophan, tyrosine, phenylalanine, aspartate, glutamate) metabolism, energy metabolism (ABC transporters) and vitamin metabolism. Moreover, the comparison of upregulated differentially expressed proteins (DEPs) revealed that for amino acid metabolism, thermal treatment had the best promotion effect; for carbohydrate metabolism, alkali treatment had the best promotion effect; and for lipid metabolism, acid treatment was more advantageous, resulting in different anaerobic digestion efficiencies. This study provides an in-depth understanding of the impact of different pretreatments on WAS anaerobic digestion and has practical implication for the choice of proper pretreatment technology for biosolids.