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The presence of organic matter in sludge plays a significant role in sludge dewatering, anaerobic sludge digestion, resource (i.e., protein) recovery and pollutants removal (i.e., heavy metals) from sludge, as well as post-application of sludge liquid and solid digestate. This study summarized the current knowledge on using liquid chromatography organic carbon detection and organic nitrogen detection (LC-OCD-OND) for characterization and quantification of organic matter in sludge samples related with sludge treatment processes by fractionating organic matter into biopolymers, building blocks, humic substances, low molecular weight (LMW) acids, low LMW neutrals, and inorganic colloids. In addition, the fate, interaction, removal, and degradation of these fractions in different sludge treatment processes were summarized. A standardized extraction procedure for organic components in different extracellular polymeric substances (EPS) layers prior to the LC-OCD-OND analysis is highly recommended for future studies. The analysis of humic substances using the LC-OCD-OND analysis in sludge samples should be carefully conducted. In conclusion, this study not only provides a theoretical foundation and technical guidance for future experiments and practices in characterizing sludge organic matter using LC-OCD-OND, but also serves as a valuable resource for consulting engineers and other professionals involved in sludge treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

This study investigated degradation kinetics of five selected organic micropollutants (OMPs) present in poultry litter (namely: sulfadiazine, tetracycline, and doxycycline hyclate (antibiotics); estrone and 17-β-estradiol (hormones)) during hydrothermal carbonization (HTC) treatment as the temperature stepwise increased to 250 °C. All five pure OMPs were completely degraded before 250 °C was reached during the HTC process. Nevertheless, presence of poultry litter slowed down the degradation of OMPs. Through elemental mass balance calculation, it is noted that after 15 min (temperature less than 137 °C), 69-82% of organic carbon and 50-66% of organic nitrogen initially consisting part of the target antibiotics were fully mineralized. Both HTC filtrates and hydrochars obtained from poultry litter inhibited Escherichia coli and Bacillus subtilis growth. A combination of high salinity, high nutrients, dissolved organic carbon, and other ions in the filtrate as well as the adsorption of OMPs on hydrochars were probably the reason for the high toxicity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

The impact of ciprofloxacin (CIP) in the partial nitrification and anammox biofilm system was investigated by multivariate analysis, focusing on size-fractionated organic components. The CIP dose of 10 μg/L did not inhibit the total nitrogen (TN) removal efficiency, even though the abundance of antibiotic resistant genes (ARGs) (i.e., qnrD, qnrB, qnrA, qnrS, and arcA) was elevated. However, a gradual higher CIP dosing up to 100 μg/L inhibited the TN removal efficiency, while the abundance of ARGs was still increased. Moreover, both the TN removal efficiency and the abundant ARGs were dwindled at 470 μg/L of CIP. As the CIP dose increased from 0 to 100 μg/L, the abundance of high molecular weight (MW) fractions (14,000 to 87,000 Da; 1000 to 14,000 Da) and humic/fulvic acid-like components in the soluble extracellular polymeric substances (HSS) decreased, with more increases of low MW (84-1000 Da; less than 84 Da) fractions and soluble microbial by-products in soluble extracellular polymeric substances (SMPS). Continuously increasing the CIP dose till 470 μg/L, an inverse trend of the changes of these organic components was noted, along with clear reductions of the microbial diversity and richness, and the abundance of key functional genes responsible for nitrogen removal. The predominance of functional gene amoA (related with ammonia oxidizing bacteria) was more significantly with more distribution of SMPS with relatively low MW and less distribution of HSS with relatively high MW, as well as polymer decomposing microorganisms such as Bryobacteraceae and the unclassified Saprospirales., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Skeleton builders were normally deemed to improve the high porosity and newly-generated permeability of sludge cakes by building water transfer channel during high pressure filtration, thus enhancing sludge dewaterability. However, currently a direct visualization proof of water transfer channel was still lacking. This study provided the direct proof for visualizing water transfer channel in dewatered sludge cakes conditioned with a typical skeleton builder (i.e., phosphogypsum (PG)) by X-ray micro-computed tomography (micro-CT) for the first time. After the addition of PG, the pixel value and image luminance increased significantly, indicating the presence of high density substances from both two-dimensional (2D) cross section and three-dimensional (3D) reconstruction CT images. Moreover, the CT numbers showed strong and negative correlations with specific resistance to filtration (SRF) (R = - 0.99, p < 0.05), capillary suction time (CST) (regression coefficient (R) = - 0.87, probability (p) < 0.05), and water content of the dewatered sludge cake (R = - 0.99, p < 0.05), respectively. These results indicated that the X-ray micro-CT could be a potential technique for analyzing the water distribution in sludge samples conditioned with skeleton builders., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

A comparative study of the different advanced oxidation processes (Fe(II)-Oxone, Fe(II)-H 2 O 2 , 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)-H 2 O 2 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)-H 2 O 2 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)-H 2 O 2 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)-H 2 O 2 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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

A sustainable strategy for P recovery from sewage sludge via alkali-activated pyrolysis, water leaching and crystallization was proposed, and a high value-added product of vivianite was recovered. Effects of the type and dose of alkali activator on P transformation during sludge pyrolysis were investigated. 50 wt% dose of KHCO 3 was determined as the alkali-activated pyrolysis condition. The content of water-soluble P (referred to as Water-P) in biochar derived from raw sludge (referred to as RS) and ferric sludge (Fenton's reagent conditioned sludge, referred to as FS) by KHCO 3 -activated pyrolysis at different temperatures was compared. The Fe element in the Fenton's reagent enhanced the content of Fe-bound P in the dewatered sludge, which was readily transformed into potassium phosphate during KHCO 3 -activated pyrolysis, thus increasing the Water-P content in the biochar derived from FS. The proportions of Water-P to total P in the biochar samples obtained by KHCO 3 -activated pyrolysis of RS and FS at 600 °C were 72.5% and 96.2%, respectively, which were notably higher than those in the biochar samples obtained by direct pyrolysis of RS and FS (3.5% and 0.5%), respectively. The water leaching solution of biochar obtained by KHCO 3 -activated pyrolysis of FS at 600 °C was purified to remove impurity elements, and vivianite with high purity was finally recovered by crystallization. A total P recovery efficiency of 88.08% was achieved throughout the process from sewage sludge to the final vivianite product. This study proposes a promising and sustainable approach for realizing the recovery of high value-added product vivianite from sewage sludge., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Ventilation is an efficient approach employed for accelerating stabilization and reducing aftercare of landfill, but its effect on leachate reduction is still elusive. To fill this knowledge gap, five lab-scale landfill reactors with different ventilation rates were established in this study. Suitable ventilation (e.g. 0.25-0.5 L·min -1 ·kg -1 dry solid of waste (DS)) was beneficial to promoting the stabilization of landfill, which effectively accelerated the degradation of organic matter and reduced water content of landfilled waste. Based on the mass balance of water, the dominant input water was initial water of landfilled waste (more than 94 %), which was partially converted to leachate and evaporated water. Ventilation enhanced the intensity of biochemical reactions heat to increase evaporated water content from 0 to 0.29 t/t DS while reducing the leachate generation significantly from 0.69 to 0.49 t/t DS with the increase of ventilation rate. Besides, the hydrophilic substances, such as humic acid-like substances, in landfilled waste increased, and the surface of the landfilled waste converted from smooth to rough. The reduction of the bound water content has a significant correlation with the degradation of organic matter content (p less than 0.05), which reduced the water-holding capacity of waste. Actinobacteriota and Firmicutes were the key bacterial phyla in the degradation of organic matter to promote bio-heat and evaporation of water, thus reducing leachate production under suitable ventilation conditions. Carbohydrates and amino acids were the main energy metabolism sources of bacteria during the landfill process. This study deepens our understanding of the leachate reduction mechanism in the micro-aerobic landfill., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This study investigated the effects of electrical signaling disruption induced by adding tetraethylammonium (TEA, a potassium channel blocker) on the formation of mixed-cultured electroactive biofilms, especially the relative abundance of Geobacter over time. Results showed that TEA addition decelerated the biofilm formation, but selectively enriched Geobacter over time (45.8% on Day 32, 67.7% on Day 60 and 78.1% on Day 90), thus resulting in higher final extracellular electron transfer (EET) efficiency. Redundancy analysis (RDA) confirmed that TEA and operation time were significant factors for the selective enrichment of Geobacter. Moreover, increase in cellular processes and signal processing by PICRUSt analysis indicated adaptive responses of electrogenic biofilms to electrical signaling disruption. Furthermore, qRT-PCR indicated the compensatory roles of key cytochromes and pilA in electrochemical communication, which induced Geobacter enrichment. This work provided a broader understanding of electroactive biofilm regulation and potential applications for electricity generation and biosensor in the future., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

A novel mechanochemically assisted persulfate activation method was proposed in this study to enhance the leaching of valuable metals from lithium-ion batteries by combining ball-milling, advanced oxidation processes and sucrose reduction. By optimizing leaching parameters including temperature, pH, milling time and solid-to-liquid ratio, high leaching efficiencies of 97.1%, 94.0%, 87.6% and 93.8% can be achieved for Li, Ni, Co and Mn respectively. In the mechanochemical process, the breakage of covalent bonds in cathode material is facilitated by free radicals generated from zero valent iron activated ammonia persulfate as well as mechanochemical activation. To further explore the role of free radicals, the mechanism of ammonia persulfate activation by zero valent iron was elucidated, and SO 4 •- was identified as the dominant reactive oxygen species in the mechanochemical process. Meanwhile, the synergistic effect of mechanochemically driven crystal dissolution and sulfate radical facilitated bond cleavage was revealed by ab initio molecular dynamics simulation. Moreover, the released metal was reduced by sucrose to a lower valent state of high solubility to promote transfer to the aqueous phase during the subsequent leaching process with dilute sulfuric acid. In this work, the insight on the mechanism of mechanochemical processes strengthened by free radicals may provide an inspiration for the recovery of valuable metals from LIBs., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The role of humic substances (HS) during sludge treatment has been the focus in recent years. Quantification of HS in sludge dissolved organic matter (DOM) and the chemical and structural characterization of HS data are the prerequisite for understanding their role during different sludge treatment processes. Currently, a number of published articles inadequately acknowledge fundamental principles of analysis methods both in terms of experimental approach and data analysis. Therefore, a more comprehensive and detailed description of the experimental methods and the data analysis are needed. In this study, the current used methods for HS quantification in DOM of sludge had been tested for different calibration and sludge DOM samples. The results indicated that the current methods showed overestimated and contradictory results for HS quantification in sludge DOM. To be specific, using the modified Lowry method, different values were obtained depending on the humic acids used for calibration, and false negative results were observed for some sludge samples. By using the relative amount of HS (based on dissolved organic carbon (DOC)) to total sludge DOM (based on DOC), variations among the results of different analysis methods for the same sample were high. According to the calculated Bray-Curtis dissimilarity indexes, the results for HS quantification obtained by three-dimensional excitation emission matrix (3D-EEM), either with spectra analysis methods by peak picking, fluorescence region integration (both region volume and area integration), or PARAllel FACtor analysis showed higher degrees of dissimilarity to those quantified by size exclusion liquid chromatography or XAD-8 method. The selection of fluorescence regions for HS seemed to be the determining factor for overestimation obtained by the 3D-EEM technique. In future work, strategies, like a consistent terminology of HS, the use of an internal standard sample, and the related standardized operation for HS quantification in sludge DOM need to be established., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

This study investigated a novel sodium iron chlorophyllin-H 2 O 2 (SIC-H 2 O 2 ) sludge pretreatment strategy before anaerobic digestion to enhance methane production. The efficiencies and mechanism of the proposed strategy to enhance sludge biodegradability were explored. The SIC-H 2 O 2 pretreatment could enhance the oxidation performance for sludge floc disintegration to dissociate TB-EPS into S-EPS increased SCOD to 521.38 mg/L. The increase of solubilization and release of EPS with the pretreatment facilitate the biogas production at 702 L kg -1 VS, which was 3-folds of the control and significantly higher than other pretreatments. The result of excitation-emission matrix and parallel factor (EEM-PARAFAC) analysis showed that the SIC-H 2 O 2 pretreatment enhanced the dissociation of TB-EPS fractions, especially the protein-like and soluble microbial by-product-like substances. Electron paramagnetic resonance (EPR) results provided evidence for homolytic catalysis H 2 O 2 for the generation OH and the production of high-valent (Por)Fe IV (O) intermediates. Synergistic effects of reactive oxygen species (OH, H 2 O 2 and /HO 2 ) and (Por)Fe IV (O) enhanced the EPS disintegration during SIC-H 2 O 2 pretreatment. The mixed-acid type fermentation provided continuous VFAs supply under the enrichment of Chloroflexi and Actinobacteria and multiplication Methanosaeta also promoted methane production. This research provides a feasible pretreatment strategy increase sludge biodegradability and enhance biogas production in the anaerobic digestion process., (Copyright © 2021. Published by Elsevier Inc.)

Microplastic accumulation in agricultural soils can stress plants and affects quality of the products. Current research on the effects of microplastics on plants is not consistent and the underlying mechanisms are yet unknown. Here, the molecular mechanisms of the stress response were investigated via metabolomic and transcriptomic analyses of rice Oryza sativa L. II Y900 and XS123 under the exposure of polystyrene microplastics (PS-MPs) in a field study. Distinct responses were obtained in these two rice subspecies, showing decreased head rice yield by 10.62% in Y900 and increase by 6.35% in XS123. The metabolomics results showed that PS-MPs exposure inhibited 29.63% of the substance accumulation-related metabolic pathways and 43.25% of the energy expenditure-related metabolic pathways in the Y900 grains; however, these related pathways were promoted in the XS123 grains. The transcriptomics results indicated that the expression of genes encoding proteins involved in the tricarboxylic acid cycle in the Y900 grains was inhibited, but it was enhanced in the XS123 grains. The XS123 subspecies could response against microplastic exposure stress through the metabolite accumulation and energy expenditure pathways, while the Y900 could not. The results provide insight into the perturbation of rice grains in farmlands with microplastics contamination., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The evaluation of ecological risks of contaminant mixtures to organisms is very challenging due to the non-linear response of organisms to each component, especially under the co-existence of both stimulators and inhibitors. Whether the stimulatory effect can reduce or even offset the inhibitory effect would be critical to the risk assessment and the treatment measures of mixed pollutants. Here, the combined toxicity of sodium fluoride (NaF), a stimulator with stimulation rate >100%, and six compounds that cannot induce hormesis (four ionic liquids (ILs) and two pesticides) were studied. The time-dependent toxicity of each toxicant on Vibrio qinghaiensis sp.-Q67 was investigated at 0.25, 2, 4, 6, 8, 10 and 12 h. Results showed that four ILs and two pesticides failed to induce hormesis, while NaF induced hormesis from 2 to 6 h and induced stimulation only after 6 h and reached its maximum (650%) at 12 h. All mixture rays with NaF induced hormesis at different times. In the four NaF-IL mixture systems, the absolute value of maximum stimulation demonstrated an upwards and then a downwards trend with the increasing of mixture ratio of IL. In two NaF-pesticide systems, the maximum stimulation effect declined with the increasing of the mixture ratio of pesticide. The toxicities of the mixture were successfully predicted by the improved inverse distance weighted interpolation, which are not able to be predicted by the commonly used concentration addition or independent action models. This paper shed lights on evaluating the hormesis of mixtures and the ecological risk of fluoride., (Copyright © 2021. Published by Elsevier Ltd.)

Deep dewatering of sewage sludge pretreated with advanced oxidation processes (AOPs) is a strategy for efficient sludge reduction and subsequent disposal. The pretreatment and dewatering performance of sludge conditioned with three types of AOPs (Fe 2+ /H 2 O 2 , Fe 2+ /Ca(ClO) 2 , and Fe 2+ /Na 2 S 2 O 8 ), compared with sludge conditioned with traditional conditioner (Fe 3+ /CaO), were investigated in both bench and pilot-scale tests. All of those conditioner systems could reduce the water content of dewatered sludge cake to below 60 wt% in bench-scale (about 16 kg raw sludge per round) and pilot-scale (approximate 800 kg raw sludge per round) diaphragm filter press dewatering. Compared with raw sludge, the deep-dewatering filtrate after different conditioning and dewatering processes had higher ammonia nitrogen (NH 4 + -N) and chemical oxygen demand (COD) contents due to the degradation of organic matter, and much lower total phosphorus (TP) content due to the formation of iron phosphate precipitate. A better biodegradability (i.e. higher BOD 5 /COD ratio) was found in the deep-dewatering filtrate of sludge conditioned with Fe 2+ /H 2 O 2 (25.2 %) and Fe 2+ /Ca(ClO) 2 (17.4 %). Most of the heavy metals (Cr, Cu, Ni, and Pb) (>79 wt%) have remained in the dewatered sludge cake, and most of the Cl element (>90 wt%) in the sludge pretreated by Fe 2+ /Ca(ClO) 2 and Fe 3+ /CaO was kept in the filtrate, rather than the dewatered sludge cake. Based on the pilot-scale experimental results, if all the filtrate in the deep-dewatering process returned to the influent of WWTP, the loading ratios of TP, NH 4 + -N, COD in the four conditioner systems were less than 3 wt%. The above results proved that the AOPs conditioned sludge could achieve deep-dewatering in pilot-scale and the direct recirculation of deep-dewatering filtrate to the influent of wastewater treatment plant was feasible., (Copyright © 2021 Elsevier Inc. All rights reserved.)

A microbial fuel cell-photocatalysis system with a novel photocatalytic air-cathode (MFC-PhotoCat) was proposed for synergistic degradation of 2,4,6-trichlorophenol (TCP) with simultaneous electricity generation. Stable electricity generation of 350 mV was achieved during 130 days of operation. Besides, 50 mg L -1 TCP was completely degraded within 72 h, and the rate constant of 0.050 h -1 was 1.8-fold higher than MFC with air-cathode without N-TiO 2 photocatalyst. Degradation pathway was proposed based on the intermediates detected and density functional theory (DFT) calculation, with two open-chain intermediates (2-chloro-4-keto-2-hexenedioic acid and hexanoic acid) detected. Furthermore, hierarchical cluster and PCoA revealed significant shifts of microbial community structures, with enriched exoelectrogen (55.2% of Geobacter) and TCP-degrading microbe (7.1% of Thauera) on the cathode biofilm as well as 61.8% of Pseudomonas in the culture solution. This study provides a promising strategy for synergic degradation of recalcitrant contaminants by intimate-coupling of MFC and photocatalysis., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The electrogeneration of H 2 O 2 and electro-regeneration of ferrous are conflicting matters in electro-Fenton system. In this research, the degradation of Rhodamine B, methyl orange (MO) and 4-chlorophenol (4-CP) was investigated using a novel dual-cathode microbial fuel cell (MFC) electro-Fenton (EF) hybrid system. An air-cathode of an EF system was used for H 2 O 2 electrogeneration and a carbon felt cathode of a MFC was used to accelerate Fe 2+ regeneration. Synergistic improvement of MFC power generation and the degradation of the above refractory organics through EF reaction was achieved. The EF air-cathode was fabricated by adopting activated carbon/graphite powder mixture and PVDF binder, which showed higher H 2 O 2 generation but slower Fe 3+ reduction rate than MFC carbon felt cathode. The Rhodamine B removal rate constant and mineralization current efficiency of the MFC coupled EF were 64% and 42% higher than that of uncoupled EF, respectively. The MFC-EF coupled system also exhibited significantly higher removal efficiency for MO and 4-CP than that of un-coupled EF system. Moreover, the power density of MFC was greatly enhanced by coupling EF due to higher Fe 3+ /Fe 2+ redox potential than oxygen reduction., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Oxidation ditches (ODs) are often used for wastewater treatment. However, limitations of ODs like high energy expenditure and increased sludge sedimentation hinder its wide application. In this study, the computational fluid dynamics (CFD) model integrated with Activated Sludge Model No. 2 (ASM2) was proposed and applied in a full-scale OD. The integrated model provided heterogeneous information on the characteristics of hydrodynamics and biokinetics of OD, especially with respect to the simulation of total phosphorus removal by CFD-ASM2 integration model for the first time. The simulated values of flow velocities, suspended solids (SS), dissolved oxygen, chemical oxygen demand, total nitrogen, ammonium nitrogen, and total phosphorus concentrations were well validated with the measured results, with the standard deviation errors of less than 5.56%, 0.28%, 0.74%, 7.39%, 3.17%, 5.27%, and 7.40%, respectively. Based on the integrated model, four different operational strategies were simulated. The proposed operational strategy of operating 7 surface aerators and 10 submerged impellers not only met the standard discharge requirements (GB 18918-2002) but also consumed less energy by 22.3%, compared with the original strategy of operating 9 surface aerators and 13 submerged impellers. Meanwhile, this proposed operational strategy also reduced the SS concentrations in the second and fourth channels, which was beneficial to elimination of sludge sedimentation. Moreover, the proposed operational strategy was successfully applied and validated in full-scale OD. The foregoing results collectively suggest that the CFD-AMS2 integration model is numerically capable to optimize the operational strategy of ODs., Competing Interests: Declaration of Competing Interest We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Dissolved organic matter (DOM) of sludge is a heterogeneous mixture of high to low molecular weight organic substances which is including proteinaceous compounds, carbohydrates, humic substances, lipids, lignins, organic acids, organic micropollutants and other biological derived substances generated during wastewater treatment. This paper reviews definition, composition, quantification, and transformation of DOM during different sludge treatments, and the complex interplay of DOM with microbial communities. In anaerobic digestion, anaerobic digestion-refractory organic matter, particularly compounds showing polycyclic steroid-like, alkane and aromatic structures can be generated after pretreatment. During dewatering, the DOM fraction of low molecular weight proteins (< 20,000 Dalton) is the key parameter deteriorating sludge dewaterability. During composting, decomposition and polymerization of DOM occur, followed by the formation of humic substances. During landfill treatment, the composition of DOM, particularly humic substances, are related with leachate quality. Finally, suggestions are proposed for a better understanding of the transformation and degradation of DOM during sludge treatment. Future work in sludge studies needs the establishment and implementation of definitions for sample handling and the standardization of DOM methods for analysis, including sample preparation and fractionation, and data integration. A more detailed knowledge of DOM in sludge facilitates the operation and optimization of sludge treatment technologies., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Reuse of sludge-derived Fe-rich biochar as sludge conditioner is an attractive route for management of waste activated sludge at source. Homogeneous and heterogeneous Fenton reactions have been proved in sludge conditioning with Fe-rich biochar activating H 2 O 2 to enhance sludge dewaterability. The FeAl 2 O 4 phase in Fe-rich biochar was first identified during pyrolysis of sewage sludge after adding both Fe 2 O 3 and Al 2 O 3 , since Fe and Al elements are two of major metal elements in Fe-rich sludge. Compared with the Fe-rich biochar that did not comprise FeAl 2 O 4 phase, the capillary suction time (CST) and specific resistance to filterability (SRF) of the sludge conditioned with the Fe-rich biochar comprising FeAl 2 O 4 phase could be efficiently decreased by 23% and 44%, respectively. The results indicated that FeAl 2 O 4 phase in Fe-rich biochar could improve sludge dewaterability by enhancing heterogeneous Fenton reaction. Synergistic effect between Fe and Al in FeAl 2 O 4 contributed to weak the O-O bond in H 2 O 2 and reduce the activation energy of H 2 O 2 decomposition for enhancing ·OH generation, which could be explained by density functional theory (DFT) calculations for the first time. Thus, the decomposition rate of H 2 O 2 and the amount of ·OH generation were obviously promoted by FeAl 2 O 4 phase in sludge-derived biochar during sludge conditioning, attributing to the destruction of sludge flocs, the release of bound water, and the improvement of sludge dewaterability., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

An innovative cathodic algal biofilm microbial fuel cell equipped with a bioactive oxygen consuming unit (AB-OCU-MFC) was proposed for enhancing the leachate treatment containing biorefractory organic matters and high strength of ammonium nitrogen. The proposed AB-OCU-MFC performed better with regard to COD, NH 4 + -N, TN removals and algal biomass yield than standalone algal biofilm-MFC and control reactors. AB-OCU-MFC with OCU of 2 cm thickness removed more than 86% of COD, 89.4% of NH 4 + -N, 76.7% of TN and produced a maximum voltage of 0.39 V and biomass productivity of 1.23 g·L -1 ·d -1 . The High-throughput sequencing of DNA showed a significant change in microbial community of reactors implemented with OCU, in which the ratio of exoelectrogenic bacteria of anode and denitrifying bacteria on cathode were significantly increased. The results obtained by cathodic algal biofilm MFC with low cost and bioactive barrier of OCU, would provide a new sight for practical application of MFC., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

During advanced oxidation treatment for enhancing sludge dewaterability, the peptide chains of protein can be decomposed into amino acids. Protein exhibits a great impact on sewage sludge dewaterability. However, the role of amino acids in sludge dewatering remains unclear. In this study, among the 23 types of amino acids investigated, tryptophane (Trp) and lysine (Lys) were identified as the key amino acids affecting sludge dewaterability during Fenton oxidation treatment. The content of lysine showed positive correlations with capillary suction time (CST), specific resistance to filtration (SRF), and bound water content, and the concentrations of total protein, low molecular weight protein, amines and amides, and 3-turn helix of proteinaceous compounds in bound extracellular polymeric substances (EPS), while the content of tryptophane showed negative correlations with the above parameters. The amino acids may be sourced from damage of the membrane and ribosomal proteins by hydroxyl radicals, and the peptide bonds connected with tryptophane were more inclined to be decomposed than other amino acids. Particularly, more amino acids of tryptophane can result in more hydrophobic interaction, and less necessary energy barrier for aggregation of particles. As such, regulating protein degradation towards production of tryptophane may be related with enhanced sludge dewaterability by Fenton oxidation treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The novel catalyst LaCu 0.5 Fe 0.5 O 3-δ with oxygen vacancies (OVs) was prepared and demonstrated excellent stability and activity for the degradation of bisphenol A. The removal rate of 92.1 % and H 2 O 2 utilization efficiency of 70.4 % were obtained due to the efficient hydroxyl radical generation mediated by OVs. The density functional theory calculation showed that the substitution of Cu and formation of OVs significantly increases the charge density near the active sites. Bader charge analysis revealed that the charge offset accelerated the reduction of Fe. The elevation of electron transfer efficiency also promotes the valence transition of copper and iron atoms. The reversible electronic transition between Fe 2+ ⇆ Fe 3+ , Cu + ⇆ Cu 2+ and Cu 2+ ⇆ Fe 2+ involved in this reaction were considered to be enhanced and the homolytic bond clearage of H 2 O 2 was simultaneously promoted, facilitated by the electron-rich region combined with OVs on the surface of LaCu 0.5 Fe 0.5 O 3-δ ., Competing Interests: Declaration of Competing Interest The authors declare no competing financial interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A novel technique for phosphorus recovery from the liquid phase of anaerobic digestate was developed using biochar derived from iron-rich sludge (dewatered sludge conditioned with Fenton's reagent). The biochar pyrolyzed from iron-rich sludge at a low temperature of 300 °C (referred to as Fe-300 biochar) showed a better phosphorus (P) adsorption capacity (most of orthophosphate and pyrophosphate) than biochars pyrolyzed at other higher temperatures of 500-900 °C, with the maximum P adsorption capacity of up to 1.843 mg g -1 for the liquid phase of anaerobic digestate. Adsorption isotherms study indicated that 70% P was precipitated through chemical reaction with Fe elements, i.e., Fe(II) and Fe(III) existed on the surface of the Fe-300 biochar, and other 30% was through surface physical adsorption as simulated by a dual Langmuir-Langmuir model using the potassium dihydrogen orthophosphate (KH 2 PO 4 ) as a model solution. The seed germination rate was increased up to 92% with the addition of Fe-300 biochar after adsorbing most of P, compared with 66% without the addition of biochar. Moreover, P adsorbed by the chemical reaction in form of iron hydrogen phosphate can be solubilized by a phosphate-solubilizing microorganism of Pseudomonas aeruginosa, with the total solubilized P amount of 3.045 mg g -1  at the end of an incubation of 20 days. This study indicated that the iron-rich sludge-derived biochar could be used as a novel and beneficial functional material for P recovery from the liquid phase of anaerobic digestate. The recovered P with biochar can be re-utilized in garden soil as an efficient P-fertilizer, thus increasing the added values of both the liquid phase of anaerobic digestate and the iron-rich sludge., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

A coupled microbial electrolysis cell - anaerobic granular sludge system (MEC-AGS) was established to explore the degradation efficiency of 2,4,6-trichlorophenol (TCP) with synchronous biogas production. Results showed that MEC-AGS yielded a higher proportion of CH 4 than MEC (83.8 ± 0.4% vs 82.0 ± 1.0%, P < 0.05) with sodium acetate (NaAc) as the only carbon source. Moreover, MEC-AGS had higher tolerance to the addition of TCP, with the highest TCP degradation efficiency of 45.5 ± 0.5% under 5 mg L -1 of TCP addition in 24 h. Furthermore, microbial community structures were significantly changed based on community composition, hierarchical cluster and PCoA analysis, which proved that MEC-AGS favored the enrichment of dechlorination-related microbes such as Pseudomonas, Desulfovibrio and Longilinea, as well as their syntrophic bacteria of Anaerolineacea, Syntrophobacter, Arcobacter, etc. The coupled system provides a promising strategy for biogas production from wastewater with recalcitrant organics., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Most previous studies of phosphorus (P) removal focused on investigation of the soluble, and particulate P, but ignoring the difference between organic and inorganic P. In this study, the effects of various flocculants, namely polyacrylamide (PAM) and polyaluminum chloride (PAC), on flocculation efficiency in different P speciations (organic and inorganic P) were investigated. A modified method to differentiate between organic and inorganic P content in secondary effluent samples was developed. The results showed that P speciation based on organic/inorganic P (Pearson's correlation R = 0.915, p < 0.05) was more effective than those based on soluble/particulate P (p > 0.05) in evaluating the P content in secondary effluents. The liquid 31 P nuclear magnetic resonance measurements results indicated that PAM was more effective in removing organic P (phosphonates and orthophosphate monoesters) rather than inorganic P. However, PAC was more effective in removing inorganic P (particularly orthophosphate) rather than organic P. Based on the modeled results of a response surface methodology (RSM), doses of PAM and PAC were optimized for secondary effluent containing different amounts of organic and inorganic P from the two typical wastewater treatment plants (WWTPs) in Wuhan city, China.

Sludge pyrolysis is a complex process including complicated reaction chemistry, phase transition, and transportation phenomena. To better evaluate the use of syngas, the monitoring and prediction of a higher heating value (HHV) is necessary. This study developed an artificial neural network (ANN) model to predict the HHV of syngas, with the process variables (i.e., sludge type, catalyst type, catalyst amount, pyrolysis temperature, and moisture content) as the inputs. In the first step, through optimizing various sets of parameters, a three-layer network including 8 input neurons, 15 hidden neurons, and 1 output neuron was established. Then, in the second step, an ANN model has been successfully used to predict the HHV of syngas, with a fitting correlation coefficient of 0.97 and a root mean square error (MSE) value of 14.62. The relative influence of input variables showed that the pyrolysis temperature and moisture content were the determining factors that affected the HHV of syngas. The results of optimization experiments showed that when temperature was 895 °C and the moisture content was 45.63 wt%, the highest HHV can be obtained as 438.22 kcal/m 3 -N. Moreover, the ANN model showed a higher prediction accuracy than other models like multiple linear regression and principal component regression. The model developed in this work may be used to predict the HHV of syngas using conventional operational parameters measured from in situ experiments, thus further providing predictive information for the use of syngas as energy and fuel.

Wet chemical approach is widely applied for P extraction from incinerated sewage sludge ash (ISSA) due to the relatively simple process and low lost. In this study, H 2 SO 4 and H 2 C 2 O 4 were compared to recover P from ISSA through three steps of acid leaching, cation exchange resin (CER) purification and precipitation. Transformations of P speciation and mineral phases in ISSA from 600 to 900 °C were studied. The results showed that the ISSA samples were mainly composed of inorganic P (IP), and part of non-apatite IP (NAIP, mainly AlPO 4 ) would transform to apatite P (AP, Ca 3 (PO 4 ) 2 ) with the increase in temperature. The ratio of NAIP to IP dropped from 71.9% at 600 °C to 53.7% at 900 °C. Effect of acid concentration on the leaching efficiency of P from the ISSA samples incinerated at different temperatures by H 2 SO 4 and H 2 C 2 O 4 was investigated, and the leaching behaviors of key elements of P, Ca, Al and Fe were compared. H 2 C 2 O 4 exhibited a better performance than H 2 SO 4 for the leaching efficiency of P. Severe sintering of ash particles occurred at temperature >800 °C inhibited the P leaching by H 2 SO 4 . During CER purification, the impurity elements in the H 2 SO 4 leachate were easily removed by CER, whereas the Al and Fe elements in the H 2 C 2 O 4 leachate were hardly removed due to the formation of anionic complexes between Al 3+ /Fe 3+ and oxalic ions. Finally, high-purity struvite product was synthesized from the purified H 2 SO 4 leachate, which could be directly utilized as a fertilizer with negligible environmental risk. Amorphous aluminum and iron hydroxyphosphates were obtained from the H 2 C 2 O 4 leachate. This study provides insights for P recovery from ISSA samples by different acid leaching systems., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

In this study, a method to reduce the emission of NO x precursors (e.g., hydrogen cyanide (HCN) and ammonia (NH 3 )) while simultaneously reclaim more plant-available P was proposed through pyrolyzing ferric sludge (sludge conditioned by Fenton's reagents) rather than raw sludge. The nitrogen and phosphorus transformation at different pyrolysis temperatures was investigated. The results indicated that in comparison with the pyrolysis of raw sludge, the remaining iron compounds in ferric sludge can fix char-N in more stable forms (e.g., appearance of pyrrole-N at 900 °C). The secondary cracking of amine-N compounds in tar-N (e.g., 81.67% increase of amine-N at 900 °C) can be inhibited. Hence, more amine-N was remained and less heterocyclic-N and nitrile-N compounds were generated in tarN. Less generation of NH 3 -N and HCN-N was also observed in NO x precursors (e.g., 5.46% decrease of NH 3 -N and 6.91% decrease of HCN-N at 900 °C). Moreover, the results of X-ray diffractometry, liquid 31 P nuclear magnetic resonance spectroscopic, X-ray photoelectron spectroscopic, and chemical analyses collectively indicated that iron present in ferric sludge also favored reclamation of more plant-available P. In comparison with the pyrolysis of raw sludge, an increase in the total phosphorus pool was noted (18.06-36.26 versus 15.54-30.59 mg g -1 dry solids). A decrease in mobility with the predominant P as sodium hydroxide (NaOH)-P, and an increase in plant-available P can be also obtained. This study indicated that pyrolysis of ferric sludge was a feasible way to simultaneously reduce emission of NO x precursors, reclaim plant-available P, and reuse ferric sludge., (Copyright © 2019 Elsevier B.V. All rights reserved.)

A liquid-gas two-phase computational fluid dynamics (CFD) model was developed to simulate flow field and gas hold-up in a pilot-scale oxidation ditch (OD). The volume of fluid (VOF) model and the mass flow inlet boundary condition for gas injection were introduced in this model. The simulated values of the flow velocities and the gas hold-up were verified by experimental measurements in the pilot-scale OD. The results showed that the gas hold-up at test-site 3, immediately downstream of the surface aerator, was the highest among all three test-sites. Most of the gas existed in the upper portion of the ditch and was close to the inner side of the channel. Based on the liquid-gas two-phase CFD model, three operating conditions with different setting height ratios of the submerged impellers were simulated. The simulated results suggested that the setting heights of the submerged impellers have significant impacts on the flow velocity distribution. Lowering the setting height could increase the flow velocity in the pilot-scale OD. An optimal setting height ratio of 0.273 was proposed, which would be beneficial for minimizing sludge sedimentation, especially near the inner side of the curve bend.

Fe 3 O 4 @SiO 2 -NH 2 magnetic particles with core-shell structure were attached on carboxylated biochar derived from phoenix tree leaves to synthesize a novel magnetic biochar for removing Cr(VI) ions from acidic solutions. FSEM, FTEM, XRD characterizations of the synthesized magnetic biochar revealed that the Fe 3 O 4 @SiO 2 -NH 2 magnetic particles distributed uniformly on the surface or macrospores of carboxylated biochar by strong chemical bonding. The Cr(VI) ions adsorption capacity of magnetic biochar was 27.2mg·g -1 , surpassing original carboxylated biochar (18.2mg·g -1 ). VSM and XPS characterizations demonstrated that the attached Fe 3 O 4 @SiO 2 -NH 2 magnetic particles not only endowed biochar with perfect magnetic property (23emu·g -1 ) but also provided complexing sites for binding Cr(III) cations reduced from Cr(VI) anions. The Cr(VI) ions removal by magnetic biochar contained three steps: (1) adsorption of Cr(VI) anions by protonated functional groups; (2) reduction of Cr(VI) anions to Cr(III) cations by electron-donor groups; and (3) chelation of Cr(III) cations by amine groups. The adsorption recycling test showed that magnetic biochar kept 85% of its initial Cr(VI) adsorption capacity at the sixth cycle, and the Fe leakage under pH1.0 was smaller than 0.25mg·L -1 . The results indicated that this novel magnetic biochar was applicable for the practical treatment of Cr(VI)-containing wastewater., (Copyright © 2018 Elsevier B.V. All rights reserved.)