Impact of co-substrate molecular weight on methane production potential, microbial community dynamics, and metabolic pathways in waste activated sludge anaerobic co-digestion.

Proteins and carbohydrates are important organics in waste activated sludge, and greatly affect methane production and microbial community composition in anaerobic digestion systems. Here, a series of co-substrates with different molecular weight were applied to investigate the interactions between microbial dynamics and the molecular weight of co-substrates. Biochemical methane production assays conducted in batch co-digesters showed that feeding high molecular weight protein and carbohydrate substrates resulted in higher methane yield and production rates. Moreover, high-molecular weight co-substrates increased the microbial diversity, enriched specific microbes including Longilinea, Anaerolineaceae, Syner-01, Methanothrix, promoted acidogenic and acetoclastic methanogenic pathways. Low-molecular weight co-substrates favored the growth of JGI-0000079-D21, Armatimonadota, Methanosarcina, Methanolinea, and improved hydrogenotrophic methanogenic pathway. Besides, Methanoregulaceae and Methanolinea were indicators of methane yield. This study firstly revealed the complex interactions between co-substrate molecular weight and microbial communities, and demonstrated the feasibility of adjusting co-substrate molecular weight to improve methane production process.

Mechanistic insight into the aggregation ability of anammox microorganisms: Roles of polarity, composition and molecular structure of extracellular polymeric substances.

The chemical characteristics of extracellular polymeric substances (EPS) of anammox bacteria (AnAOB) play a crucial role in the rapid enrichment of AnAOB and the stable operation of wastewater anammox processes. To clarify the influential mechanisms of sludge EPS on AnAOB aggregation, multiple parameters, including the polarity distribution, composition, and molecular structure of EPS, were selected, and their quantitative relationship with AnAOB aggregation was analyzed. Compared to typical anaerobic sludge (anaerobic floc and granular sludge), the anammox sludge EPS exhibited higher levels of tryptophan-like substances (44.82-56.52 % vs. 2.57-39.81 %), polysaccharides (40.02-53.49 mg/g VSS vs. 30.22-41.69 mg/g VSS), and protein structural units including α-helices (20.70-23.98 % vs. 16.48-19.32 %), ß-sheets (37.43-42.98 % vs. 25.78-36.72 %), and protonated nitrogen (Npr) (0.065-0.122 vs. 0.017-0.061). In contrast, it had lower contents of ß-turns (20.95-27.39 % vs. 28.17-39.04 %). These biopolymers were found to originate from different genera of AnAOB. Specifically, the α-helix-rich proteins were mainly derived from Candidatus Kuenenia, whereas the extracellular proteins related to tryptophan and Npr were closely associated with Candidatus Brocadia. Critically, these EPS components could drive anammox aggregation through interactions. Substantial amounts of tryptophan-like substances facilitated the formation of ß-sheet structures and the exposure of internal hydrophobic clusters, which benefited the anammox aggregation. Meanwhile, extracellular proteins with high Npr content played a pivotal role in the formation of mixed protein-polysaccharide gel networks with the electronegative regions of polysaccharides, which could be regarded as the key component in the maintenance of anammox sludge stability. These findings provide a comprehensive understanding of the multifaceted roles of EPS in driving anammox aggregation and offer valuable insights into the development of EPS regulation strategies aimed at optimizing the anammox process.

Sludge dewaterability improvement with microbial fuel cell powered electro-Fenton system (MFCⓠEFs): Performance and mechanisms.

Throughout the entire process of sludge treatment and disposal, it is crucial to explore stable and efficient techniques to improve sludge dewaterability, which can facilitate subsequent resource utilization and space and cost savings. Traditional Fenton oxidation has been widely researched to enhance the performance of sludge dewaterability, which was limited by the additional energy input and the instabilities of Fe2+ and H2O2. To reduce the consumption of energy and chemicals and further break the rate-limiting step of the iron cycle, a novel and feasible method that constructed microbial fuel cell powered electro-Fenton systems (MFCⓅEFs) with ferrite and biochar electrode (MgFe2O4@BC/CF) was successfully demonstrated. The MFCⓅEFs with MgFe2O4@BC/CF electrode achieved specific resistance filtration and sludge cake water content of 2.52 × 1012 m/kg and 66.54 %. Cellular structure and extracellular polymeric substances (EPS) were disrupted, releasing partially bound water and destroying hydrophilic structures to facilitate sludge flocs aggregation, which was attributed to the oxidation of hydroxyl radicals. The consistent electron supply supplied by MFCⓅEFs and catalytically active sites on the surface of the multifunctional functional group electrode was responsible for producing more hydroxyl radicals and possessing a better oxidizing ability. The study provided an innovative process for sludge dewaterability improvement with high efficiency and low energy consumption, which presented new insights into the green treatment of sludge.

Enhanced dewaterability of food waste digestate by biochar/potassium ferrate treatments: Performance and mechanisms.

The combined process of biochar (BC) and potassium ferrate (PF) offers a fascinating technique for efficient dewatering of digestate. However, the effects of BC/PF treatment on the dewaterability and mechanisms of FWD are still unknown. This study aimed to reveal the impact mechanisms of BC/PF treatment on digestate dewatering performance. Experimental results indicated that BC/PF treatment significantly enhanced the dewaterability of digestate, with the minimum specific resistance to filtration of (1.05 ± 0.02) × 1015 m·kg-1 and water content of 57.52 ± 0.51% being obtained at the concentrations of 0.018 g·g-1 total solid (TS) BC300 and 0.20 g·g-1 TS PF, which were 8.60% and 13.59% lower than PF treatment, respectively. BC/PF treatment proficiently reduced the fractal dimension, bound water content, apparent viscosity, and gel-like network structure strength of digestate, as well as increased the floc size and zeta potential of digestate. BC/PF treatment promoted the conversion of extracellular polymeric substances (EPS) fractions from inner EPS to soluble EPS, increased the fluorescence intensity of the dissolved compounds, and enhanced the hydrophobicity of proteins. Mechanisms investigations showed that BC/PF enhanced dewatering through non-reactive oxygen species pathways, i.e., via strong oxidative intermediate irons species Fe(V)/Fe(IV). BC/PF treatment enhanced the solubilization of nutrients, the inactivation of fecal coliforms, and the mitigation of heavy metal toxicity. The results suggested that BC/PF treatment is an effective digestate dewatering technology which can provide technological supports to the closed-loop treatment of FWD.

Effect and potential mechanisms of sludge-derived chromium, nickel, and lead on soil nitrification: Implications for sustainable land utilization of digested sludge.

Increasing occurrence of heavy metals (HMs) in sewage sludge threatens its widespread land utilization in China due to its potential impact on nutrient cycling in soil, requiring a better understanding of HM-induced impacts on nitrification. Herein, lab-scale experiments were conducted over 185-day, evaluating the effect of sludge-derived chromium (Cr3+), nickel (Ni2+), and lead (Pb2+) on soil nitrification at different concentrations. Quantitative polymerase chain reaction and linear regression results revealed an inhibitory sequence of gene abundance by HMs' labile fraction: ammonia-oxidizing bacteria (AOB)-ammonia monooxygenase (amoA)> nitrite oxidoreductase subunit alpha (nxrA)> nitrite oxidoreductase subunit beta (nxrB). The toxicity of HMs' incremental labile fraction decreased in the order of Ni2+>Cr3+>Pb2+, with respective threshold values of 5.01, 24.03 and 38.42 mg·kg-1. Furthermore, extending incubation time reduced HMs inhibition on ammonia oxidation, mainly related to their fraction bound to carbonate minerals. Random Forest analysis, variation partitioning analysis, and Mantel test indicated that soil physicochemical properties primarily affected nitrification genes, especially in the test of Cr3+ on AOB-amoA, nxrA, nxrB, Ni2+ for complete ammonia-oxidizing bacteria-amoA, and Pb2+ for nxrA and nxrB. These findings underline the importance of labile HMs fractions and soil physicochemical properties to nitrification, guiding the establishment of HM control standards for sludge utilization.

Electro-oxidation and UV irradiation coupled method for in-site removing pollutants from human body fluids in swimming pool.

A comprehensive study was conducted to investigate how ultraviolet (UV) irradiation combined with electrochemistry (EC) can efficiently remove human body fluids (HBFs) related pollutants, such as urea/creatinine/hippuric acid, from swimming pool water (SPW). In comparison with the chlorination, UV, EC, and UV/chlorine treatments, the EC/UV treatment exhibited the highest removal rates for these typical pollutants (TPs) from HBFs in synthetic SPW. Specifically, increasing the operating current of the EC/UV process from 20 to 60 mA, as well as NaCl content from 0.5 to 3.0 g/L, improved urea and creatinine degradation while having no influence on hippuric acid. In contrast, EC/UV process was resilient to changes in water parameters (pH, HCO3-, and actual water matrix). Urea removal was primarily attributable to reactive chlorine species (RCS), whereas creatinine and hippuric acid removal were primarily related to hydroxyl radical, UV photolysis, and RCS. In addition, the EC/UV procedure can lessen the propensity for creatinine and hippuric acid to generate disinfection by-products. We can therefore draw the conclusion that the EC/UV process is a green and efficient in-situ technology for removing HBFs related TPs from SPW with the benefits of needless chlorine-based chemical additive, easy operation, continuous disinfection efficiency, and fewer byproducts production.

Mediating oxidative stress through the Palbociclib/miR-141-3p/STAT4 axis in osteoporosis: a bioinformatics and experimental validation study.

Osteoporosis is a common bone disease characterized by loss of bone mass, reduced bone strength, and deterioration of bone microstructure. ROS-induced oxidative stress plays an important role in osteoporosis. However, the biomarkers and molecular mechanisms of oxidative stress are still unclear. We obtained the datasets from the Gene Expression Omnibus (GEO) database, and performed differential analysis, Venn analysis, and weighted correlation network analysis (WGCNA) analysis out the hub genes. Then, the correlation between inflammatory factors and hub genes was analyzed, and a Mendelian randomization (MR) analysis was performed on cytokines and osteoporosis outcomes. In addition, "CIBERSORT" was used to analyze the infiltration of immune cells and single-cell RNA-seq data was used to analyze the expression distribution of hub genes and cell-cell communications. Finally, we collected human blood samples for RT-qPCR and Elisa experiments, the miRNA-mRNA network was constructed using the miRBase database, the 3D structure was predicted using the RNAfold, Vfold3D database, and the drug sensitivity analysis was performed using the RNAactDrug database. We obtained three differentially expressed genes associated with oxidative stress: DBH, TAF15, and STAT4 by differential, WGCNA clustering, and Venn screening analyses, and further analyzed the correlation of these 3 genes with inflammatory factors and immune cell infiltration and found that STAT4 was significantly and positively correlated with IL-2. Single-cell data analysis showed that the STAT4 gene was highly expressed mainly in dendritic cells and monocytes. In addition, the results of RT-qPCR and Elisa experiments verified that the expression of STAT4 was consistent with the previous analysis, and a significant causal relationship between IL-2 and STAT4 SNPs and osteoporosis was found by Mendelian randomization. Finally, through miRNA-mRNA network and drug sensitivity analysis, we analyzed to get Palbociclib/miR-141-3p/STAT4 axis, which can be used for the prevention and treatment of osteoporosis. In this study, we proposed the Palbociclib/miR-141-3p/STAT4 axis for the first time and provided new insights into the mechanism of oxidative stress in osteoporosis.

Deciphering the role of polystyrene microplastics in waste activated sludge anaerobic digestion: Changes of organics transformation, microbial community and metabolic pathway.

Microplastics are ubiquitous in the natural environment, which inevitably affect the relevant biochemical process. Nevertheless, the knowledge about the impacts of microplastics on organics transformation and corresponding microbial metabolism response in anaerobic environment is limited. Here, polystyrene (PS) microplastics were selected as model microplastics to explore their potential impacts on organics transformation, microbial community and metabolic pathway during sludge anaerobic digestion system operation. The results indicated that the PS microplastics exhibited the dose-dependent effects on methane production, i.e., the additive of 20-40 particles/g TS of PS microplastics improved the maximum methane yield by 3.38 %-8.22 %, whereas 80-160 particles/g TS additive led to a 4.78 %-11.04 % declining. Overall, PS microplastics facilitated the solubilization and hydrolysis of sludge, but inhibited the acidogenesis process. Key functional enzyme activities were stimulated under low PS microplastics exposure, whereas were almost severely inhibited due to the increased oxidative stress induced from excess PS microplastics. Microbial community and further metabolic analysis indicated that low PS microplastics improved the acetotrophic and hydrogenotrophic methanogenesis, while a high level of PS microplastics shifted methanogenesis from acetotrophic to hydrogenotrophic pathway. Further analysis showed that the reacted PS microplastics exhibited greater toxicity and ecological than the raw PS microplastics due to that they are more likely to adsorb contaminants. These findings revealed the dosage-dependent relationships between microplastics and organics transformation process in anaerobic environments, providing new insights for assessing the impact of PS microplastics on sludge anaerobic digestion.

A systemic evaluation of aerobic granular sludge among granulation, operation, storage, and reactivation processes in an SBR.

As a biological promising wastewater treatment technology, aerobic granular sludge (AGS) technology had been widely studied in sequencing batch reactors (SBRs) for the decades. Presently, the whole processes of its granulation, long-term operation, storage, and reactivation have not been thoroughly evaluated, and also the relationships among microbial diversity, granular size, and characteristics were still not that clear. Hence, they were systematically evaluated in an AGS-SBR in this work. The results demonstrated that Proteobacteria and Bacteroidetes were the dominant phyla, Flavobacterium, Acinetobacter, Azoarcus, and Chryseobacterium were the core genera with discrepant abundances in diverse stages or granular size. Microbial immigration was significant in various stages due to microbial diversity had a line relationship with COD/MLVSS ratio (R2 = 0.367). However, microbial diversity had no line relationship with granular size (R2 = 0.001), indicating the microbial diversity in different-sized AGS was similar, although granular size had a line relationship with settleability (R2 = 0.978). Overall, compared to sludge traits (e.g., sludge size, settleability), COD/MLVSS played a key role on microbial evolution. This study revealed the relationships between granule characteristics and microbial community, and contributed to the future AGS-related studies.

A review of application of combined biochar and iron-based materials in anaerobic digestion for enhancing biogas productivity: Mechanisms, approaches and performance.

Strengthening direct interspecies electron transfer (DIET), via adding conductive materials, is regarded as an effective way for improving methane productivity of anaerobic digestion (AD). Therein, the supplementation of combined materials (composition of biochar and iron-based materials) has attracted increasing attention in recent years, because of their advantages of promoting organics reduction and accelerating biomass activity. However, as far as we known, there is no study comprehensively summarizing the application of this kind combined materials. Here, the combined methods of biochar and iron-based materials in AD system were introduced, and then the overall performance, potential mechanisms, and microbial contribution were summarized. Furthermore, a comparation of the combinated materials and single material (biochar, zero valent iron, or magnetite) in methane production was also evaluated to highlight the functions of combined materials. Based on these, the challenges and perspectives were proposed to point the development direction of combined materials utilization in AD field, which was hoped to provide a deep insight in engineering application.

Stable photodegradation of antibiotics by the functionalized 3D-Bi2MoO6@MoO3/PU composite sponge: High efficiency pathways, optical properties and Z-scheme heterojunction mechanism.

The designation and fabrication of heterogeneous photocatalyst with superior redox capability is an important technique for emerging pollutants treatment. In this study, we designed the Z-scheme heterojunction of stable 3D-Bi2MoO6@MoO3/PU, which could not only accelerate the migration and separation in photogenerated carriers, but also stabilize the separation rate of photo-generation carriers. In the Bi2MoO6@MoO3/PU photocatalytic system, 88.89% of oxytetracycline (OTC, 10 mg L-1) and 78.25%-84.59% of multiple antibiotics (SDZ, NOR, AMX and CFX, 10 mg L-1) could be decomposed within 20 min under the optimized reaction condition, revealing the superior performance and potential application value. Specifically, the morphology, chemical structure and optical properties detection of Bi2MoO6@MoO3/PU greatly affected the direct Z-scheme electron transferring mode in the p-n type heterojunction. Besides, the ·OH, h+, ·O2- dominated the photoactivation process through ring-opening, dihydroxylation, deamination, decarbonization and demethylation in OTC decomposition. Expectantly, the stability and universality of Bi2MoO6@MoO3/PU composite photocatalyst would further broaden the practical application and demonstrated that the potential of photocatalytic technique in antibiotics pollutants for wastewater remediation.

Towards the carbon neutrality of sludge treatment and disposal in China: A nationwide analysis based on life cycle assessment and scenario discovery.

Motivated by the carbon neutrality target, strategic planning for a low-carbon transition of sludge treatment and disposal in China is challenging due to the unpredictability of technical, regional, socioeconomic, and political factors affecting greenhouse gas (GHG) emissions. This study combines the use of a Life Cycle Assessment and the Patient Rule Induction Method, accounting for possibilities that could achieve net-zero carbon emissions by exploring multiple plausible future profiles of sludge treatment and disposal. Results show that reducing sludge landfill and increasing anaerobic digestion are effective methods to facilitate GHG reduction. Achieving carbon neutrality is closely linked to developing a cleaner electricity mix. Based on a cascaded scenario analysis considering regional differences for 31 Chinese provinces, results demonstrated a maximum cumulative reduction potential of 371 Mt CO2 equivalents from 2020 to 2050, equal to 59.84% of the business-as-usual scenario. Together with GHG reductions, terrestrial acidification and ecotoxicity as well as freshwater ecotoxicity are synergistically reduced. However, the shifting environmental burden results in freshwater eutrophication, human toxicity, marine ecotoxicity, marine eutrophication, and photochemical oxidant formation. This study presents a novel method for systematically identifying possible future development paths toward carbon neutrality. The findings may support policy designs for achieving target carbon reduction effects for sludge disposal.

Carbonate-bound Pb percentage distribution in agricultural soil and its toxicity: Impact on plant growth, nutrient cycling, soil enzymes, and functional genes.

Metals pollution of lead in agricultural soils is a serious problem for food safety. Therefore, we investigated the toxic effects of carbonate-bound fraction Pb on agricultural soil from various aspects. The results revealed that a higher carbonate-bound fraction of Pb had more toxic effects on wheat growth, as evidenced by higher malondialdehyde (3.17 µmol g-1 FW) and lower catalase levels (9.77 µg-1 FW min-1). In terms of nutrient cycling, soil nutrients including carbon, nitrogen, and phosphorus would slow down transformation rates in high concentrations. Compared to carbon, nitrogen and phosphorus were more likely to be affected by the initial carbonate-bound fraction at the earlier stage. Increased Pb dosage may reduce the soil enzymes activity such as urease (119-50 U g-1) and phosphatase (3191-967 U g-1), as well as the functional genes of nitrogen degradation related nirK, nisS, and carbon related pmoA. Correlation analysis and structural equation modeling indicated that carbonate bound Pb could regulate nutrients cycle via functional genes inhibition, soil enzyme activity reduction and wheat growth suppression in agricultural soil. Our findings will help with polluted agricultural soil monitoring and regulation through microbial activity to ensure food safety.

Effect of Dietetic Obesity on Testicular Transcriptome in Cynomolgus Monkeys.

Obesity is a metabolic disorder resulting from behavioral, environmental and heritable causes, and can have a negative impact on male reproduction. There have been few experiments in mice, rats, and rabbits on the effects of obesity on reproduction, which has inhibited the development of better treatments for male subfertility caused by obesity. Nonhuman primates are most similar to human beings in anatomy, physiology, metabolism, and biochemistry and are appropriate subjects for obesity studies. In this investigation, we conducted a transcriptome analysis of the testes of cynomolgus monkeys on high-fat, high-fructose, and cholesterol-rich diets to determine the effect of obesity on gene expression in testes. The results showed that the testes of obese monkeys had abnormal morphology, and their testes transcriptome was significantly different from that of non-obese animals. We identified 507 differentially abundant genes (adjusted p value < 0.01, log2 [FC] > 2) including 163 up-regulated and 344 down-regulated genes. Among the differentially abundant genes were ten regulatory genes, including IRF1, IRF6, HERC5, HERC6, IFIH1, IFIT2, IFIT5, IFI35, RSAD2, and UBQLNL. Gene ontology (GO) and KEGG pathway analysis was conducted, and we found that processes and pathways associated with the blood testes barrier (BTB), immunity, inflammation, and DNA methylation in gametes were preferentially enriched. We also found abnormal expression of genes related to infertility (TDRD5, CLCN2, MORC1, RFX8, SOHLH1, IL2RB, MCIDAS, ZPBP, NFIA, PTPN11, TSC22D3, MAPK6, PLCB1, DCUN1D1, LPIN1, and GATM) and down-regulation of testosterone in monkeys with dietetic obesity. This work not only provides an important reference for research and treatment on male infertility caused by obesity, but also valuable insights into the effects of diet on gene expression in testes.

Heavy metals in influent and effluent from 146 drinking water treatment plants across China: Occurrence, explanatory factors, probabilistic health risk, and removal efficiency.

Heavy metals (HMs) in drinking water have drawn worldwide attention due to their risks to public health; however, a systematic assessment of the occurrence of HMs in drinking water treatment plants (DWTPs) at a large geographical scale across China and the removal efficiency, human health risks, and the correlation with environmental factors have yet to be established. Therefore, this study characterised the occurrence patterns of nine conventional dissolved HMs in the influent and effluent water samples from 146 typical DWTPs in seven major river basins across China (which consist of the Yangtze River, the Yellow River, the Songhua River, the Pearl River, the Huaihe River, the Liaohe River and the Haihe River) for the first time and removal efficiency, probabilistic health risks, and the correlation with water quality. According to the findings, a total of eight HMs (beryllium (Be), antimony (Sb), barium (Ba), molybdenum (Mo), nickel (Ni), vanadium (V), cobalt (Co) and titanium (Ti)) were detected, with detection frequencies in influent and effluent water ranging from 2.90 (Mo) to 99.30% (Ba) and 1.40 (Ti) to 97.90% (Ba), respectively. The average concentration range was 0.41 (Be)- 77.36 (Sb) µg/L. Among them, Sb (exceeding standard rate 8%), Ba (2.89%), Ni (21.43%), and V (1.33%) were exceeded the national standard (GB5749-2022). By combining Spearman's results and redundancy analysis, our results revealed a close correlation among pH, turbidity (TURB), potassium permanganate index (CODMn), and total nitrogen (TN) along with the concentration and composition of HMs. In addition, the concentration of HMs in finished water was strongly affected by the concentration of HMs in raw water, as evidenced by the fact that HMs in surface water poses a risk to the quality of finished water. Metal concentration was the primary factor in assessing the health risk of a single metal, and the carcinogenic risk of Ba, Mo, Ni, and Sb should be paid attention to. In DWTPs, the removal efficiencies of various HMs also vary greatly, with an average removal rate ranging from 16.30% to 95.64%. In summary, our findings provide insights into the water quality and health risks caused by HMs in drinking water.

Extracellular polymeric substances-antibiotics interaction in activated sludge: A review.

Antibiotics, the most frequently prescribed drugs, have been widely applied to prevent or cure human and veterinary diseases and have undoubtedly led to massive releases into sewer networks and wastewater treatment systems, a hotspot where the occurrence and transformation of antibiotic resistance take place. Extracellular polymeric substances (EPS), biopolymers secreted via microbial activity, play an important role in cell adhesion, nutrient retention, and toxicity resistance. However, the potential roles of sludge EPS related to the resistance and removal of antibiotics are still unclear. This work summarizes the composition and physicochemical characteristics of state-of-the-art microbial EPS, highlights the critical role of EPS in antibiotics removal, evaluates their defense performances under different antibiotics exposures, and analyzes the typical factors that could affect the sorption and biotransformation behavior of antibiotics. Next, interactions between microbial EPS and antibiotic resistance genes are analyzed. Future perspectives, especially the engineering application of microbial EPS for antibiotics toxicity detection and defense, are also emphatically stressed.

Investigation of electrochemical properties, leachate purification, organic matter characteristics, and microbial diversity in a sludge treatment wetland- microbial fuel cell.

Sludge treatment wetland-microbial fuel cell (STW-MFC) is a unique sludge treatment process that produces bioelectricity, but its technology is still in its infancy. This study investigated the electrochemical properties, organic matter characteristics, leachate purification, and microbial community structure of STW-MFCs as affected by electrode location. When electrodes were placed in the filler layer, the STW-MFC system presented a higher power generation capacity (maximum output power density: 0.498 W/m3; peak cell voltage: 0.879 V) and organic matter degradation efficiency. The hydrophilic fraction was the main dissolved organic carbon fraction in sludge extracellular biological organic matter (EBOM) and leachate dissolved organic matter (DOM). Aromatics were mainly concentrated in the hydrophobic acid fraction. The UV-254 content of sludge EBOM decreased mainly in the hydrophilic and transphilic acid fractions. The excitation-emission matrix analysis showed that tryptophan-like protein was more easily eliminated than tyrosine-like protein. In addition, there was a strong correlation between voltage and NH4+ removal efficiency; a negative correlation between total chemical oxygen demand (TCOD), total nitrogen (TN), and total phosphorus (TP) removal efficiency, and a negative correlation between pH and TN, TP, and NH4+ removal efficiencies. High-throughput sequencing showed that the system was most abundant in Thermomonas, Geothrix and Geobacter when the electrodes were placed in the filled layer, while the levels of genes for membrane transport, carbohydrate metabolism and energy metabolism functions were higher than in other systems. This work will support STW- MFC widespread implementation by illuminating the underlying mechanics of different anode positions.

Mechanisms, performance, and the impact on microbial structure of direct interspecies electron transfer for enhancing anaerobic digestion-A review.

Direct interspecies electron transfer (DIET) has been received tremendous attention, recently, due to the advantages of accelerating methane production via organics reduction during anaerobic digestion (AD) process. DIET-based syntrophic relationships not only occurred with the existence of pili and some proteins in the microorganism, but also can be conducted by conductive materials. Therefore, more researches into understanding and strengthening DIET-based syntrophy have been conducted with the aim of improving methanogenesis kinetics and further enhance methane productivity in AD systems. This study summarized the mechanisms, application and microbial structures of typical conductive materials (carbon-based materials and iron-based materials) during AD reactors operation. Meanwhile, detail analysis of studies on DIET (from substrates, dosage and effectiveness) via conductive materials was also presented in the study. Moreover, the challenges of applying conductive materials in boosting methane production were also proposed, which was supposed to provide a deep insight in DIET for full scale application.

Calcium peroxide and freezing co-pretreatment enhancing short-chain fatty acids production from waste activated sludge towards carbon-neutral sludge treatment.

Short-chain fatty acids (SCFAs) recovery through anaerobic fermentation is a promising technology to achieve carbon-neutral in waste activated sludge (WAS) management. After 0.15 g CaO2/g volatile suspended solids (VSS) addition and three-cycle freezing co-pretreatments, the maximal SCFAs production of 438.5 mg COD/g VSS was achieved within 4 days fermentation, and more than 70 % of SCFAs was composed of acetate and propionate, which achieved a higher level than reported in previous studies. Mechanism explorations elucidated that co-pretreatment triggered sludge solubilization, promoting the release of biodegradable organics, providing more biodegradable substrates for SCFAs generation. Further microbial community analysis indicated that the abundances of hydrolytic microorganisms and acidogens were enriched, whereas methanogens were inhibited. Besides, environmental analysis suggested that co-pretreatment could achieve carbon reduction benefits of 0.116-0.291 ton CO2/ton WAS, demonstrating its huge carbon-neutral potential benefits.

Environmental impacts and optimizing strategies of municipal sludge treatment and disposal routes in China based on life cycle analysis.

The management and utilization of sludge in a sustainable approach require a systematic analysis of the environmental impacts generated from diverse sludge treatment and disposal processes. This study systematically assessed 12 common sludge treatment and disposal routes based on the existing operating and construction conditions of representative sludge disposal projects in China. We evaluated their environmental impacts using a life cycle assessment following the International Organization for Standardization (ISO 14040 and ISO 14044), and found that the routes of co-incineration, mono-incineration, and anaerobic digestion with or without thermal hydrolysis may be useful in terms of simultaneously controlling environmental pollution and carbon emissions in China. Therein, the route of co-incineration was recommended as the best one because its human toxicity potential (-152.31 kg dichlorobenzene (1,4-DB) eq/ton dry solid (t DS)), freshwater ecotoxicity potential (FEP, -127.40 kg 1,4-DB eq/t DS), terrestrial ecotoxicity potential (TEP, -0.81 kg 1,4-DB eq/t DS), and global warming potential (-27.26 kg CO2 eq/t DS) were all negative (environmental benefits). Furthermore, the toxicity impacts of the mono-incineration route were also negative, but it still needed to further enhance energy recovery to reduce carbon emissions. Despite the routes of anaerobic digestion and thermal hydrolysis in combination with anaerobic digestion had the excellent negative carbon emission attributes (-572.44 kg CO2 eq/t DS, -474.92 kg CO2 eq/t DS), they showed serious FEP and TEP owing to the heavy metals pollution caused by subsequent land use of anaerobic digested sludge. Overall, this study selected the most suitable sludge treatment and disposal routes to simultaneously satisfy the requirements of carbon emission reduction and pollution control in China and proposed optimizing suggestions for future technical improvement and development.