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Currently, headspace gas chromatography-mass spectrometry is a widely used method to identify the key odorants of sludge. However, the effect of incubation temperature on the generation and emission of key odorants from sludge was still uncertain. Thus, in this paper, headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) and headspace gas chromatography-coupled ion mobility spectrometry (HS-GC-IMS) were carried out to analyze the volatiles emitted from the sludge incubated at different temperatures (30 °C, 50 °C, 60 °C, and 80 °C). The results indicated that the total volatile concentration of the sludge increased with temperatures, which affected the identified proportion of sludge key odorants to a certain extent. Differently from the aqueous solutions, the variation of volatile emission from the sludge was inconsistent with temperature changes, suggesting a multifactorial influence of incubation temperature on the identification of sludge odorants. The microbial community structure and adenosine triphosphate (ATP) metabolic activity of the sludge samples were analyzed at the initial state, 30 °C, and 80 °C. Although no significant effect of incubation temperature on the microbial community structure of the sludge, the incubation at 80 °C led to a noticeable decrease in microbial ATP metabolic activity, accompanied by a significant change in the proportion of odor-related microorganisms with low relative abundances. Changes in the composition and activity of these communities jointly contributed to the differences in odor emission from sludge at different temperatures. In summary, the incubation temperature affects the production and emission of volatiles from sludge through physicochemical and biochemical mechanisms, by which the microbial metabolism playing a crucial role. Therefore, when analyzing the key odorants of sludge, these factors should be considered. [Display omitted] • Incubation temperature affected the composition of sludge key odorants. • Incubation temperature effects on odorants emission varied with sludge properties. • Incubation temperature influences sludge odor formation through multiple-mechanisms. [ABSTRACT FROM AUTHOR]

• The sustainability of sludge treatment and disposal routes in different regions of China were evaluated. • Co-incineration and thermal hydrolysis-anaerobic digestion were preferred sludge treatment processes in China. • A framework integrates carbon emissions, economic cost and environmental risk to assess sustainability was created. • Technical selection was proposed based on sludge characteristics and economic/environmental level for each region. • Developing high-value resource utilization technologies for sludge will be the core of future sludge treatment. In various regions of China, the sludge characteristics, available sludge treatment and disposal routes, and economic and environmental concerns exhibit significant variations. This makes it challenging for regions to select appropriate technologies for sustainable sludge management. This study proposed a universal framework that integrates carbon emissions, economic cost, and environmental risk potential to assess sustainability of diverse sludge treatment and disposal routes in different regions of China. An up-to-date database of sludge characteristics in different regions of China has also been created. Depending on sludge characteristics, co-incineration in coal-fired plants or cement kilns and thermal hydrolysis-anaerobic digestion routes demonstrate outstanding sustainability for most regions in China. Moreover, the current carbon trading price in China is low and does not significantly influence the technical selection. The created sludge characteristics database and the sustainability assessment framework could help sludge managers make better in process selection, technological improvement, and future policy formulation. [Display omitted] [ABSTRACT FROM AUTHOR]

l Al3+ and Al 13 were converted into amorphous Al(OH) 3 at high alkalinity. l Different mechanisms governed sludge conditioning at different alkalinity. l Binding strength of aluminum hydroxyl to EPS affected sludge conditioning efficiency. l Al 13 and Al 30 caused significant change of the secondary structure of protein molecule. Extracellular polymeric substances (EPS) form a stable gel-like structure to combine with water molecules through steric hindrance, making the mechanical dewatering of wastewater sludge considerably difficult. Coagulation/flocculation has been widely applied in improving the sludge dewatering performance, while sludge properties (organic fraction and solution chemistry conditions) are highly changeable and have important effects on sludge flocculation process. In this work, the alkalinity effects on sludge conditioning with hydroxy-aluminum were comprehensively investigated, and the interaction mechanisms between EPS and hydroxy-aluminum with different speciation were unraveled. The results showed that the effectiveness of hydroxy-aluminum conditioning gradually deteriorated with increase in alkalinity. Meanwhile, the polymeric hydroxy-aluminum (Al 13) and highly polymerized hydroxy-aluminum (Al 30) were hydrolysed and converted into amorphous aluminum hydroxide (Al(OH) 3), which changed the flocculation mechanism from charge neutralization and complexing adsorption to hydrogen bond interaction. Additionally, both Al 13 and Al 30 showed higher binding capacity for proteins and polysaccharides in EPS than monomeric aluminum and Al(OH) 3. Al 13 and Al 30 coagulation changed the secondary structure of proteins in EPS, which caused a gelation reaction to increase molecular hydrophobicity of proteins and consequently sludge dewaterability. This study provided a guidance for optimizing the hydroxy-aluminum flocculation conditioning of sludge with high solution alkalinity. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Sewage sludge, the major by-product during the primary treatment and subsequent biotreatment of wastewater, is increasingly generated around the world. KMnO 4 Fe(II) consists both oxidation properties of KMnO 4 and flocculation ability by in-situ formed Fe(III) and is widely used in water treatment. In this study, KMnO 4 Fe(II) was used as chemical conditioners to synchronously improve sludge dewatering performance and catalyze the biomass pyrolysis of waste activated sludge for preparing multi-functional material to remedy arsenic containing groundwater. The results showed that the sludge dewaterability was significantly improved due to the moderate pre-oxidation of extracellular polymeric substances by KMnO 4 , and then the sludge particles were re-flocculated by Fe(III) generated from KMnO 4 Fe(II). The conditioned sludge cake was then utilized for preparing sludge-based carbon (Fe-Mn-SBC) which was systematically characterized. The surface area of Fe-Mn-SBC was characteristic of high surface area (100.08 m2/g) which had a great adsorption capacity on arsenic. Besides, Fe-Mn-SBC could effectively oxidize As(III) to As(V), and addition of low dose of H 2 O 2 can further improve total arsenic removal due to catalytic peroxidation of Fe-Mn-SBC. Besides, it was found that the presence of humic acid could inhibit the hydroxy iron formation and compete for the active adsorption sites and then resulted in the decrease in arsenic removal, and the co-existing humic acid could also be removed by adsorption of Fe-Mn-SBC. This work proposed a novel sludge treatment process by combining enhanced sludge dewatering with catalytic pyrolysis for preparing multi-functional materials, and they are promising in treatment of water containing combined pollutants. Image 1 • KMnO 4 Fe(II) was effective in improving the sludge dewaterability. • Both oxidation and coagulation were responsible for KMnO 4 Fe(II) conditioning. • Fe-Mn-SBC performed well in combined pollutants (arsenic and HA) removal in groundwater. • Oxidation and adsorption showed synergetic effects in arsenic removal under Fe-Mn-SBC treatment. • HA inhibited the arsenic removal by competing adsorption sites and slowing down the hydrolysis of ferric ions. [ABSTRACT FROM AUTHOR]

In this study, the effects of chemical conditioning using titanium salt coagulants (TSCs) of different hydrolysis speciation in combination with magnetic nano-particles on dewatering performance of waste activated sludge were evaluated by means of specific resistance to filtration (SRF) and capillary suction time (CST). The morphological and extracellular polymeric substances (EPS) properties under chemical conditioning were investigated in detail to understand the reaction mechanisms involved. The results showed that the TSC with basicity of 0.5 performed better in improving sludge dewatering performance than other TSCs. Sludge floc formed by TSC 0.5 treatment was characterized by larger floc size and higher floc strength than that conditioned by other TSCs. EPS compression and densification were the major mechanisms of sludge conditioning, and TSC 0.5 had better performance in compressing EPS structure. In addition, reduction of soluble EPS concentration, especially protein-like substances contributed to improvement of sludge filterability under conditioning. Furthermore, addition of Fe 2 O 3 nanoparticles could further improve dewatering performance and decrease compressibility of sludge system by acting as skeleton builders and enhancing floc strength. The sludge particles aggregation efficiency was effectively improved with addition of nano-Fe 2 O 3 . They also were able to bind with protein-like substance in EPS component, which might contribute to promotion of sludge filterability. [ABSTRACT FROM AUTHOR]

The effect of pH on chemical conditioning with potassium ferrate (K 2 FeO 4 ) for improving sludge filtration dewatering performance has been studied. The variation of extracellular polymeric substances (EPS) in conditioning process was investigated in detail to unravel the reaction mechanism. The results indicated that sludge dewaterability was improved by decreasing solution pH in terms of filtration rate and cake solids content. At acid conditions, protonation of EPS resulted in reduction of negative charge and densification of sludge floc. Sludge conditioning efficiency was improved with decrease in pH. Ferrate can solubilize EPS through oxidation process and also remove a portion of soluble EPS (SEPS) by charge neutralization and interfacial adsorption of hydrolyzed ferric ions, consequently compressing EPS and decreasing total extractable EPS content. In addition, when pH and potassium ferrate were 3 and 0.1 g/gTSS, the sludge filtration dewatering rate and extent reached the maximum. Deterioration of sludge dewaterability was observed as the ferrate was overdosed (>0.2 g/gTSS). This could be attributed to the release of a large amount of bound EPS (BEPS) as a result of ferrate oxidation, consequently increasing the sludge filtration resistance. [ABSTRACT FROM AUTHOR]

Extracellular polymeric substances (EPS) are highly hydrated biopolymers and play important roles in bioflocculation, floc stability, and solid-water separation processes. Destroying EPS structure will result in sludge reduction and release of trapped water. In this study, the effects of combined process of peracetic acid (PAA) pre-oxidation and chemical re-flocculation on morphological properties and distribution and composition of EPS of the resultant sludge flocs were investigated in detail to gain insights into the mechanism involved in sludge treatment. It was found that sludge particles were effectively solubilized and protein-like substances were degraded into small molecules after PAA oxidation. A higher degradation of protein-like substances was observed at acid environments under PAA oxidation. Microscopic analysis revealed that no integral sludge floc was observed after oxidation with PAA at high doses. The floc was reconstructed with addition of inorganic coagulants (polyaluminium chloride (PACl) and ferric chloride (FeCl 3 )) and PACl performed better in flocculation due to its higher charge neutralization and bridging ability. Combined oxidative lysis and chemical re-flocculation provide a novel solution for sludge treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • The microorganism E. coli in sludge was effectively inactivated by NaClO treatment. • Lignin and N-compounds in sludge were major precursors for Cl-DBPs generation. • N-compounds played the leading role in the generation of Cl-DBPs. • Acidic condition prevented Cl-DBPs generation by lowering the N-compounds production. Chlorination disinfection has been widely used to kill the pathogenic microorganisms in wastewater sludge during the special Covid-19 period, but sludge chlorination might cause the generation of harmful disinfection byproducts (DBPs). In this work, the transformation of extracellular polymeric substance (EPS) and mechanisms of Cl-DBPs generation during sludge disinfection by sodium hypochlorite (NaClO) were investigated using multispectral analysis in combination with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The microorganism Escherichia coli (E. coli) was effectively inactivated by active chlorine generated from NaClO. However, a high diversity of Cl-DBPs were produced with the addition of NaClO into sludge, causing the increase of acute toxicity on Q67 luminous bacteria of chlorinated EPS. A variety of N-containing molecular formulas were produced after chlorination, but N-containing DBPs were not detected, which might be the indicative of the dissociation of –NH 2 groups after Cl-DBPs generated. Additionally, the release of N-containing compounds was increased in alkaline environment caused by NaClO addition, resulted in more Cl-DBPs generation via nucleophilic substitutions. Whereas, less N-compounds and Cl-DBPs were detected after EPS chlorination under acidic environment, leading to lower cell cytotoxicity. Therefore, N-containing compounds of lignin derivatives in sludge were the major Cl-DBPs precursors, and acidic environment could control the release of N-compounds by eliminating the dissociation of functional groups in lignin derivatives, consequently reducing the generation and cytotoxicity of Cl-DBPs. This study highlights the importance to control the alkalinity of sludge to reduce Cl-DBPs generation prior to chlorination disinfection process, and ensure the safety of subsequential disposal for wastewater sludge. [ABSTRACT FROM AUTHOR]

Biosolid–liquid separation performance plays an important role in suspended solids removal and sludge thickening and dewatering process. Since the sludge is a highly complex colloidal system, the key factors affecting sludge dewatering and settling performance were not well understood. In this study, the dynamic variation in distribution and chemical composition of extracellular polymeric substances (EPS), floc size distribution, charge property and settling and dewatering performance was investigated at four full scale WWTPs over 100 days. It was found that the change in EPS distribution and composition from different WWTPs showed a very similar pattern with operating time. The temperature rather than wastewater composition had more significant influence on content and chemical constituents of different EPS fractions. Additionally, more EPS was extracted from activated sludge at lower temperature (<15 °C), indicating that the binding strength of EPS with microbial cells was weak. According to Pearson's correlation analysis, sludge dewatering property correlated well with content of protein-like substances in soluble EPS, while there was a strong correlation between sludge settleability (measured by sludge volume index) and floc size and volatile suspended solid/total suspended solid ratio (VSS/TSS). [ABSTRACT FROM AUTHOR]

Extracellular polymeric substances (EPS) in wastewater sludge form a network structure that is highly hydrophilic and compressible. Thus chemical conditioning is always required to improve sludge dewaterability by changing the gelatinous structure of sludge flocs. Layered double hydroxides (LDH) are generally characterized by large surface area and high anion exchange capacity, so we prepared three types of hydrotalcite-like compounds (Ca/Mg/Al-LDHs) from a typical solid waste, blast furnace slag, using NaOH precipitation (giving LDH a), a hydrothermal method (LDH b), and NaOH–Na 2 CO 3 precipitation (LDH c). The physicochemical properties of the three LDH were comprehensively characterized, and their effectiveness as sludge conditioners was evaluated. The results showed that LDH conditioning was able to promote sludge dewaterability, and conditioning efficiency was strongly dependent on LDH structural properties. LDH neutralized the negative charges onto sludge particles and interacted with EPS to increase floc strength. LDH also formed a skeletal structure that reduced sludge compressibility. In addition, there were interactions between the LDH surfaces and the O C–OH in EPS proteins, which altered the secondary structure of protein molecules, consequently increasing sludge dewaterability. The biomolecules of low-molecular-weight fractions (such as peptides and humic acids) in soluble EPS intercalated LDH. Both the surface complexation of organic matter containing carboxyl groups and the intercalation of small molecules in soluble EPS were responsible for EPS–LDH interactions. The combination of skeleton formation, electrostatic interaction, and EPS–LDH interactions resulted in compression of gel-like structure and improved sludge dewatering performance. We finally suggested a novel sludge treatment process that increases sludge dewaterability using slag-derived Ca/Mg/Al-LDH to condition the sludge, and it could be combined with pyrolysis to prepare multi-functional materials or bio-oil. Image 1 • Slag based LDH were used as chemical conditioners to improve sludge dewaterability. • LDH structural properties had important effects on sludge conditioning efficiency. • LDH conditioning reduced sludge cake compressibility by functioning as skeleton builders. • Charge neutralization and EPS-LDH interaction were responsible for sludge conditioning. • LDH interacted with EPS through surface complexation and intercalation. [ABSTRACT FROM AUTHOR]

Activated sludge is a heterogeneous colloidal system in which small sludge particles form a stable suspension in water and are very difficult to separate from water phase. Chemical conditioning is an indispensable step in sludge treatment for dewatering performance enhancement. Organic flocculants were always used in low-pressure dewatering process and inorganic coagulants were always used in high-pressure dewatering process. In this study, the effects of PAC, and PASiC of different Al/Si ratio (PASiCs) on sludge dewatering performance in term of capillary suction time (CST), specific resistance to filtration (SRF) and compressiability coefficient were comparatively investigated. Also, the changes of extracellular polymeric substances (EPS) and the morphological properties of flocs and sludge cakes under chemical conditioning were examined to unravel the interaction mechanisms between inorganic flocculants and sludge particles. It was found that PASiC 5 exhibited better in improving dewatering improvement and reducing compressibility of sludge due to it higher adsorption and bridging abilities than other inorganic coagulants. Sludge flocs formed by PASiC 5 conditioning was characterized by smaller floc size but higher fractal dimension. The sludge flocs conditioned by PASiC 5 was more compact and resistant to compress than that formed by PAC and other PASiCs, and the volume of pore of sludge conditioned by PASiC 5 is larger than PAC and other PASiCs, the atomic percentage of C element in the sludge cake conditioned by PASiC 5 was higher at 73.09% than that of other sludges. PASiC 5 was more effective remove the SEPS content than other inorganic coagulants, which contributed to improvement of sludge filterability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimal conditions for sulfide treatment of sludge to establish PN were determined. • High NAR and NRR were achieved in long-term treating wastewater. • amoA and soxB abundance increased and positively correlated in stable phase of PN. • Nitromonas and Sulfuritalea enriched with Nitrospira reduction in long-term reactor. This study proposes an innovative strategy for achieving PN in synthetic domestic wastewater by side-stream sludge treatment using sulfide as the sole control factor. By conducting controllable batch experiments and response surface analysis, optimal sulfide treatment conditions were firstly determined as 90 mg/L of sulfide, 7.5 of pH, 100 rpm of rotation and 12 h of treatment time. After treatment, half of ammonia oxidizing bacteria (AOB) activity remained, but nitrite oxidizing bacteria (NOB) activity was barely detected. Nitrite accumulation rate of long-term running PN steadily reached 83.9 % with 99.1 % of ammonia removal efficiency. Sulfide treatment increased community diversity and facilitated stability of microbiota functioning with PN phenotype, which might be sustained by the positive correlation between ammonia oxidation gene (amoA) and sulfur oxidation gene (soxB). Correspondingly, the network analysis identified the keystone microbial taxa of persistent PN microbiota as Nitrosomonas , Thauera , Truepera , Defluviimonas and Sulitalea in the later stage of long-term reactor. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biopolymers transformation of sludge drying was elucidated by FT-ICR MS technique. • Hydrophobic groups exposure increased with drying temperature increased below 150 °C. • Maillard products trapped water molecules made difficulty in sludge drying at 180 °C. • Eliminating the hydrophilic groups exposing is crucial to sludge drying efficiency. The biopolymers are regarded as the leading role on the water evaporation in thermal drying process for sludges. Herein, the relationships between molecular transformation and water-holding capacities of biopolymers in sludge drying was investigated by multispectral methods coupled with FT-ICR MS technique. Our results showed that the exposure of hydrophobic groups in biopolymers was affected by drying temperature, causing significant differences upon water molecules binding and evaporation. In particular, below 120 °C, there was no obvious changes on the structural compositions of hydrophilia and hydrophobic compounds in sludge. Between 120 °C and 150 °C, the macromolecules were broken into smaller molecules with abundant hydrophobic groups exposing, resulted in efficient water evaporation with lower moisture in sludge. However, organics containing –NH and –C=O groups were aggregated via Maillard reaction at higher temperature (＞150 oC), the water molecules were trapped inside the Maillard products, and more energy was required to destroy the structure of organics for water evaporation, ended with higher moisture of dried sludges. In addition, a strong correlation between the hydrophilic index and CHON/CHONS distributions of extracted proteins in dried-sludge (DS) indicated that the water holding capacity and evaporation relied more on the spatial exposure of hydrophilic groups rather than their content. These implied that preventing the aggregation of hydrophilic functional groups (–NH and –C=O) in proteins was the key to eliminating the inhibitory of hydrophilic compounds in the biopolymers-bound water evaporation, and drying temperature below 150 °C was recommended. This study provides a mechanistic basis for better understanding of the biopolymer transformation (especially hydrophilic compounds) in drying process, and enable development of a more efficient and energy-saving drying procedure for sludges. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermally activated persulfate (TAP) oxidation enhanced sludge dewaterability. • Thermal hydrolysis and oxidation had a synergistic effect in biopolymer hydrolysis. • Proteins were decomposed into polypeptides, amino acids, and ammonia nitrogen. • TAP oxidation increased bioavailable phosphorus content of sludge. • TAP oxidation reduced antibiotic content and ecotoxicological risk of sludge. Wastewater sludge is mainly comprised of microorganisms and extracellular polymeric substances (EPS). The gel-like network structure of EPS traps bound water, resulting in poor dewaterability of sludge. In this work, the thermally activated persulfate (TAP) oxidation was used in sludge treatment to improve dewaterability. The transformation of proteins and phosphorus were systematically investigated to understand the mechanisms of sludge conditioning with TAP at molecular levels. The results showed that TAP oxidation produced SO 4 - and OH radicals which decomposed the macromolecular proteins, causing uncoiling of protein secondary structures and exposure of inner hydrophobic sites. The polypeptide, amino acid, and ammonia nitrogen were generated, and sludge dewaterability was enhanced. A mechanism was proposed to explain the synergistic effects of thermal hydrolysis and TAP oxidation on the transformations of nitrogen and phosphorus containing biopolymers. Furthermore, 30%-100% of antibiotics were degraded in TAP treatment. TAP performed well in macrolide and tetracycline degradation (>80%), while most of quinolone antibiotics were more refractory to oxidation. [ABSTRACT FROM AUTHOR]

• During sludge AHT treatment, leaching of MP-DOM hindered HA formation. • The inhibition of Maillard reaction was vital for the reduction of HA content. • Amino reactant consumption was the main way for inhibition of Maillard reaction. • MPs released organic acids that reduce pH, causing protonation of amino groups. • Oxidation of lipid-like compounds yielded fatty aldehydes, reducing amino reactants. Alkali-hydrothermal treatment (AHT) of sewage sludge is often used to recover value-added dissolved organic matters (DOM) enriched with artificial humic acids (HA). Microplastics (MPs), as emerging contaminants in sewage sludge, can leach organic compounds (MP-DOM) during AHT, which potentially impact the characteristics of thermally treated sludge's DOM. This study employed spectroscopy and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS) to explore the impacts of MPs on DOM composition and transformation during AHT. The biological effects of DOM were also investigated by hydroponic experiments. The results showed that the leaching of MP-DOM led to a substantial increase in DOC content of DOM of thermally treated sludge. Conversely, the HA content significantly decreased in the presence of MPs, resulting in a decline of plant growth facilitation degree. FT-ICR-MS analysis revealed that the reduction in HA content was characterized by a notable decline in the abundance of O 6–7 and N 1–3 O 6–7 molecules. Reactomics results indicated that the leaching of MP-DOM inhibited the Maillard reaction but bolstered oxidation reactions. The inhibition of Maillard reaction, resulting in a decrease in crucial precursors (dicarbonyl compounds, ketoses, and deoxyglucosone), was responsible for the decrease of HA content. The primary mechanism responsible for inhibiting the Maillard reaction was the consumption of reactive amino reactants through two pathways. Firstly, the leaching of organic acids in MP-DOM caused decrease of sludge pH, leading to the protonation of amino groups. Secondly, the lipid-like compounds in MP-DOM underwent oxidation (-2H+O), producing fatty aldehydes that consumed the reactive amino reactants. These discoveries offer enhanced insights into the specific contribution of MPs to the composition, transformation, bioactivity of DOM during AHT process. [Display omitted] [ABSTRACT FROM AUTHOR]

• Sludge enhanced dewatering technologies are comprehensively reviewed. • Mechanisms of different sludge enhanced dewatering technologies are discussed. • Process adaptability of different sludge conditioning methods are analysed. • Sludge electro-dewatering and its coupled processes are discussed. • Sludge enhanced dewatering technology and its coupled processes are prospected. Sludge is an inevitable by product of sewage treatment, and it includes pathogens, heavy metals, organic pollutants and other toxic substances. The components of sludge are complex and variable with extracellular polymeric substances (EPS) being one. EPS are highly hydrophilic and compressible, and make sludge dewatering difficult. Therefore, the development of efficient sludge-dewatering technology is an important means of mitigating rapid sludge growth. At present, the main methods used for sludge deep-dewatering technology are chemical preconditioning with high-pressure filtration and electrical mechanical dewatering. The selection of chemical preconditioning directly determines the final efficiency of the sludge-dewatering process. In this paper, we conduct a comprehensive review of the problems related to sludge dewatering and systematically summarise the impact of different chemical conditioning technologies on the efficiency of sludge dewatering. Furthermore, the characteristics of different enhanced dewatering technologies are evaluated and analysed for their adaptability and final disposal methods. We believe that this review can clarify the chemical conditioner mechanism to improve sludge dewatering, provide reference debugging information for the sludge-dewatering process and promote the development of efficient and environmentally friendly sludge-dewatering technology. [ABSTRACT FROM AUTHOR]

This study aimed to explore the adsorption performance of sludge-based activated carbon (SBC) towards dissolved organic matters (DOMs) removal from sewage, and investigated the modification effect of different types of chemicals on the structure of synthesized SBC. Waste activated sludge (WAS) was used as a carbon source, and HCl, HNO 3 , and NaOH were used as different types of chemicals to modify the SBC. With the aid of chemical activation, the modified SBC showed higher adsorption performances on DOMs removal with maximum adsorption of 29.05 mg/g and second-order constant (k) of 0.1367 (L/mol/sec) due to the surface elution of ash and minerals by chemicals. The surface elemental composition of MSBC suggested that the content of C-C and C-O functional groups on the surface of modified sludge-based activated carbon (MSBC) played an important role on the adsorption capacities of MSBC towards DOMs removal in sewage. Additionally, the residual molecular weight of DOMs in sewage was investigated using a 3-dimension fluorescence excitation-emission matrix (3D-EEM) and high-performance size exclusion chromatography (HP-SEC). Results showed that the chemical modification significantly improved the adsorption capacity of MSBC on humic acids (HA) and aromatic proteins (APN), and both of NaOH-MSBC and HCl-MSBC were effective for a wide range of different AMW DOMs removal from sewage, while the HNO 3 -MSBC exhibited poorly on AMW organics of 2,617 Da and 409 Da due to the reducing content of macropore. In brief, this study provides reference values for the impact of the chemicals of the activation stage before the SBCs application. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• CHON is the most reactive component in DOM under sludge AHT process. • Deamination is the most frequent reaction in the whole sludge AHT process. • Reactive fragments (-C2H2O2, -C3H4O2, -C4H6O2) were potential precursors of humic acids. • DOM12h could stimulate energy metabolism and carbohydrate storage in rice seedlings. • Byproducts (pyrrole, pyridine, etc.) formed in AHT > 12 h displayed phytotoxicity. Understanding the composition, transformation and bioactivity of dissolved organic matter (DOM) at the molecular level is crucial for investigating the hydrothermal humification process of wastewater sludge and producing ecological fertilizers. In this study, DOM transformation pathways under alkali–thermal humification treatment (AHT) were characterized by Fourier transform–ion cyclotron resonance mass spectrometry (FT–ICR MS) in conjunction with molecular reaction network analysis. The effects of DOM on plant growth were examined using hydroponics and transcriptomic analysis. In the wastewater sludge humification process, AHT produced maximum amounts of protein (3260.56 mg/L) and humic acid (5788.24 mg/L) after 12 h. FT–ICR MS results indicated that protein-like structures were prone to continuous oxidation and were ultimately transformed into aromatic N-containing compounds resembling humic substances. Several reactive fragments (such as –C 2 H 2 O 2 , –C 3 H 4 O 2 , and –C 4 H 6 O 2) formed by the Maillard reaction (MR) were identified as potential precursors to humic acid (HA). In terms of biological effects, DOM 12h showed the highest rice germination and growth activity, whereas that produced by AHT for a longer period (> 12 h) displayed phytotoxicity owing to the accumulation of toxic substances. Plant biostimulants (such as amino acids and HAs) in DOM improved energy metabolism and carbohydrate storage in rice seedlings by upregulating the "starch and sucrose metabolism" pathways. Toxic substances (such as pyrrole, pyridine, and melanoidin) in DOM can activate cell walls formation to inhibit abiotic stimuli in rice seedlings through the biosynthesis of phenylpropanoid pathway. These findings provide a theoretical basis for optimizing sludge hydrothermal humification and recovering high-quality liquid fertilizers. [Display omitted] [ABSTRACT FROM AUTHOR]

Previous knowledge of dissolved organic matter leached from microplastics (MP-DOM) was mainly based on the aquatic environment. The molecular characteristics and biological effects of MP-DOM in other environments have rarely been examined. In this work, FT-ICR-MS was applied to identify MP-DOM leached from sludge hydrothermal treatment (HTT) at different temperatures, and the plant effects and acute toxicity were investigated. The results showed that the molecular richness and diversity of MP-DOM increased with rising temperature, accompanied by molecular transformation in the meantime. The oxidation was crucial whereas the amide reactions mainly occurred at 180–220 oC. MP-DOM promoted root development of Brassica rapa (field mustard) by affecting the expression of genes and the effect was enhanced with rising temperature. Specifically, the lignin-like compounds in MP-DOM down-regulated Phenylpropanoids biosynthesis, while CHNO compounds up-regulated the nitrogen metabolism. Correlation analysis presented that alcohols/esters leached at 120–160 oC were responsible for the promotion of root, while glucopyranoside leached at 180–220 oC was vital for root development. However, MP-DOM produced at 220 oC showed the acute toxicity to luminous bacteria. Considering the further-treatment of sludge, the optimum HTT temperature could be controlled at 180 oC. This work provides novel insight into the environmental fate and eco-environmental effects of MP-DOM in sewage sludge. [Display omitted] • MPs is a non-negligible source of DOM in sewage sludge during HTT. • Oxidation reaction is key to MP-DOM transformation while amide reaction mainly occurred at relatively high-temperature stage. • MP-DOM could promote plant growth by affecting gene expression. • Alcohol, esters and glucopyranoside compounds in MP-DOM are key to promote plant growth. • 180oC is the optimum HTT temperature to remove MPs and convert it into harmless active MP-DOM. [ABSTRACT FROM AUTHOR]

• Electrodialysis pretreatment showed high recovery efficiency for sludge-derived DOM. • Molecular number in DOM identified with dual ESI modes was increased by 200%. • DOM WAS mainly contained proteins/aliphatic and lipid-like compounds. • DOM ADS was composed of lipids, proteins/aliphatic, and lignins/CRAM-like compounds. • Two ESI analysis modes can recognize different emerging contaminants. High-resolution mass spectrometry was extensively applied in molecular composition and transformation pathways of dissolved organic matter (DOM) in wastewater sludge treatments. Sample pretreatment methods and electrospray ionization (ESI) modes significant affect the accuracy of molecular characterization for DOM. This study investigated the effects of pretreatment methods (styrene divinyl benzene polymer (PPL), octadecyl (C18), and electrodialysis (ED)) on molecular characteristics of DOM in two typical wastewater sludges (waste activated sludge (WAS) and anaerobic digestion sludge (ADS)) analyzed by FT-ICR MS in both positive ESI (ESI (+)) and negative ESI (ESI (−)) modes. The results indicated that ED pretreatment exhibited the highest recovery rate of 70% ‒ 95% for sludge-derived DOM. ED and PPL performed well in recovering the different sludge-derived DOM with a high similarity of molecular characteristics (e.g., lipids, proteins/aliphatic, and lignins/CRAM-like), and the C18 method was ineffective in extracting carbohydrates, unsaturated hydrocarbons, and amino sugars. In addition, compared with single ESI (−) analysis mode, the molecular number identified by ESI (+) analysis mode was increased by 200%, especially, more unsaturated hydrocarbons and N-containing compounds were detected. Except for biogenic DOM, plenty of emerging containments (ECs) in sludge-derived DOM were identified; ESI (−) mode was more effectively in recognizing the alkyl benzene sulfonic acids (e.g., anionic surfactants); and ESI (+) mode was more effectively for plasticizers identification, for example, dioctyl terephthalate and dibutyl phthalate. This study illustrated that ED pretreatment coupled with FT-ICR MS in dual ESI modes could give more insights in complexed molecular information for DOM in wastewater sludge, and provides a theoretical basis for subsequent sludge treatments and disposals. [Display omitted] [ABSTRACT FROM AUTHOR]

• A molecular model was built to reveal the arrangements and dynamic characteristics of biopolymers in EPS. • Biopolymers form agglomerates spontaneously through electrostatic and hydrophobic interactions. • Rearrangement of EPS molecular conformation reduced the exposure of hydrophilic groups. • Contact of biopolymers promoted by multivalent cations enhancing the intermolecular forces and compactness of EPS. • The hydration of Al3+ and Mg2+ affect the stability of association with biopolymers. 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. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Non-targeted mass difference analysis was used to clarify DON transformation pathways. • Nucleic acid (mainly RNA) contributed to deamidization and deamination at 30 °C–70 °C. • Aspartyl, serine, histidine, and glutamyl units were representative precursors at 160 °C–200 °C. • HT liquor at 70–120 °C showed the highest DON bioavailability (∼57.6 %). Hydrothermal (HT) treatment has been considered effectively to recover nitrogen-containing organic nutrients from wastewater activated sludge (WAS), and understanding the fate and distribution of dissolved organic nitrogen (DON) during HT process is of great importance to process optimization. Thus, this study aims to investigate molecular transformation pathway of DON during HT process using non-targeted mass difference network analysis and evaluate the bioavailability of DON with chlorella. Results suggested that HT treatment was superior in N -containing organic matter solubilization (DON /TN > 60 %), and DON in WAS underwent extensive transformation processes at various HT temperatures. From room temperature to 70 °C, nucleic acids were solubilized to HT liquor, accomplishing with deamidation (–CONH + H 2 /H 2 O). And a representative ribose nucleic acid with a 'PA–pentose (ribose)–uracil (U)' structure was identified. With temperature rising to 120 °C, large amounts of stable protein were solubilized and hydrolyzed into HT liquor. The non-targeted mass difference network analysis suggested that, from 160 °C to 200 °C, aspartyl, serine, histidine, and glutamyl units were representative precursors for a variety of reactions including Maillard reactions, deamidation, deamination and so on. Amino acids were deaminated (–NH) to produce organic acids and ammonia (ammonium) or decarboxylated (–COO) to produce amines and CO 2. Dicarbonyl compounds (–C 2 H 2 O 2) were identified as the most abundant fragments which could either form humic substances or Maillard reaction products. Chlorella growth bioassay indicated that org-N in HT liquor produced at 120 °C showed the highest bioavailability for Chlorella , while that generated in HT liquor above 160 °C inhibited the growth of Chlorella. This study provided molecular insights for DON transformation following HT process and promoted high-quality resource utilization of WAS. [ABSTRACT FROM AUTHOR]

Non-renewable phosphorus (P) largely converges into waste activated sludge (WAS) during sewage treatment, thus P reclamation from WAS is essential for sustainable utilization of P resource. Hydrothermal (HT) process is a promising and widely used sanitation technique for improving WAS recycling efficiency, whilst the transformation and bioavailability of dissolved organic P (DOP) in WAS following HT treatment are unclear. Therefore, this work unveiled the transformation pathway of DOP during HT process using Fourier transform-ion cyclotron resonance mass spectrometry coupled with molecular reaction network analysis, and its bioavailability was determined by enzymatic hydrolysis. In summary, DOP underwent a two-stage transformation following HT treatment. In stage I (50 °C–120 °C), adenosine triphosphate and ribonucleic acid were initially solubilized at 50 °C, followed by P-diesters (ribonucleic and deoxyribonucleic acid) and P-monoesters (mononucleotides, phospholipids) at 70 °C. Meanwhile, the release of P-monoesters is highly parallel to the solubilization of protein (R2 = 0.81–0.96, p < 0.05). Then, these DOP compounds were decomposed into DOP hydrolysates with high bioavailability including phosphoenolpyruvic acid, dihydroxyacetone phosphate, and 1-phosphono butanedioate, etc. DOP enzymatic hydrolysis test also revealed a maximum bioactive concentration of 41.69 mg L−1 at 120 °C. During stage II (120 °C–200 °C), the DOP hydrolysates reacted with nitrogenous heterocyclic compounds (e.g., pyrimidine, pyridine, and pyrazine) generated in Maillard reactions, and caused formation of CNON compounds with low bioavailability (8.23 mg L−1 at 200 °C). In addition, reduction, decarbonization, decarboxylation, and nitration played significant roles in DOP transformation. And toxic phosphonates were dissolved into aqueous phase above 160 °C and progressively increased with temperature. This study provided a theoretic basis for sludge P recovery and efficient utilization based on HT treatment. [Display omitted] • A two-stage DOP transformation process in WAS following HT treatment was identified. • Decarboxylation, nitration, and reduction are superior in DOP transformation process. • DOP hydrolysates generated at 120 °C was the main bioactive DOP. • Maillard reaction products (e.g., pyridine) bonded to DOP hydrolysates above 160 °C. • 160 °C is a suitable HT temperature for WAS reclamation from the perspective of OP. [ABSTRACT FROM AUTHOR]

[Display omitted] • A BOM-extraction process for resource utilization of bio-stabilized WAS is proposed. • Amino acid, amino sugar, fatty acid, carboxylic acid, and humic substance are the main BOM extracted from WAS. • BOM increased the root length and enzymatic indicators of Brssica rapa (Chiifu-401 – 42). • BOM promote plant growth through carbohydrate, lipid, and amino acid metabolism. • Alkali extraction can recycle abundant BOM with low environmental risks from WAS. Bioactive organic compounds (BOCs) contained in bio-stabilized products of waste activated sludge (WAS) have attracted considerable attention, as they can enhance the fertilizing effect of WAS in land applications. This study investigated the molecular composition and plant-growth-promoting mechanisms of various BOCs in the bio-stabilized products of WAS. After stepwise fractionation, aerobic composting sludge (ACS) and anaerobic digestion sludge (ADS) were chemically fractioned into five subcomponents, namely dissolved organic matter (DOM) (C1), weakly interacted organic matter (OM) (C2), metal-bonded OM (C3), NaOH-extracted OM (C4), and strongly interacted OM (C5), in sequence. The results showed that fatty acids and carboxylic acid (CAs) present in ACS C2 promoted plant growth and enhanced the ability of plants against stresses by upregulating pathways related to "carbohydrate metabolism," "lipid metabolism," "amino acid metabolism," and "phenylpropanoid biosynthesis." However, in ACS C4, plenty of amino acids could promote plant growth via upregulating "carbohydrate metabolism" and "amino acid metabolism" pathways. As an important precursor, aromatic amino acids inside ACS C4 also stimulated the production of indoleacetic acids. In ADS C1, amino sugar and phytohormone were the major BOCs causing the up-regulation of "carbohydrate metabolism" and AAA catabolism in "amino acid metabolism" pathways. CAs enriched in ADS C2 stimulated plant growth through "amino acid metabolism" pathway. In summary, alkali extraction can recycle a large proportion of BOCs with low environmental risk from the bio-stabilization products of WAS. The results from this study provide scientific guidance for safe and value-added resource utilization of bio-stabilization products of WAS in land applications. [ABSTRACT FROM AUTHOR]

• F/S produced SO3•− which decomposed the biopolymers and released bound water. • F/S oxidation and PAM flocculation showed a synergistic effect in sludge conditioning. • C=O groups of tryptophan played the leading role in Fe-EPS association binding. • The formed β-sheets and destructed α-helices structure promoted sludge dewatering. The bound water in waste activated sludge (WAS) is trapped in extracellular polymeric substances (EPS) in the form of gel-like structure, leading to a great challenge in the sludge deep dewatering. Traditional flocculation conditioning is unable to destroy EPS and ineffective to remove the bound water in WAS. In this study, we employed integration of Fe(II)-sulfite oxidation and polyacrylamide flocculation (F/S-PAM) treatment for removing the bound water and improving sludge dewaterability under aerobic conditions. Meanwhile, the floc microstructure and EPS properties were examined to understand the mechanisms of F/S-PAM conditioning. F/S produced SO 3 · − radicals which could decompose the EPS in sludge, releasing bound water into free water. In addition, the formed Fe(III) from F/S led to re-coagulation of decomposed EPS, and C=O groups of tryptophan played the leading role in Fe-EPS association binding, causing transformation of the secondary structure of proteins (especially β-sheets and α-helices). Then, the introduction of PAM caused re-flocculation of disintegrated sludge flocs, enhancing the sludge filterability. This work provides a novel and cost-effective method for efficient removal of bound water in sludge, and subsequence improvement in sludge dewaterability. Image, graphical abstract [ABSTRACT FROM AUTHOR]