Ferroheme/Ferriheme Directly Involved in the Synthesis and Decomposition of Hydrazine as an Electron Carrier during Anammox.

Anammox bacteria performed the reaction of NH4+ and NO with hydrazine synthase to produce N2H4, followed by the decomposition of N2H4 with hydrazine dehydrogenase to generate N2. Ferroheme/ferriheme, which serves as the active center of both hydrazine synthase and hydrazine dehydrogenase, is thought to play a crucial role in the synthesis and decomposition of N2H4 during Anammox due to its high redox activity. However, this has yet to be proven and the exact mechanisms by which ferroheme/ferriheme is involved in the Anammox process remain unclear. In this study, abiotic and biological assays confirmed that ferroheme participated in NH4+ and NO reactions to generate N2H4 and ferriheme, and the produced N2H4 reacted with ferriheme to generate N2 and ferroheme. In other words, the ferroheme/ferriheme cycle drove the continuous reaction between NH4+ and NO. Raman, ultraviolet-visible spectroscopy, and X-ray absorption fine structure spectroscopy confirmed that ferroheme/ferriheme is involved in the synthesis and decomposition of N2H4 via the core FeII/FeIII cycle. The mechanism of ferroheme/ferriheme participation in the synthesis and decomposition of N2H4 was proposed by density functional theory calculations. These findings revealed for the first time the heme electron transfer mechanisms, which are of great significance for deepening the understanding of Anammox.

Enhanced Extracellular Electron Transfer in Magnetite-Mediated Anaerobic Oxidation of Methane Coupled to Humic Substances Reduction: The Pivotal Role of Membrane-Bound Electron Transfer Proteins.

Humic substances are organic substances prevalent in various natural environments, such as wetlands, which are globally important sources of methane (CH4) emissions. Extracellular electron transfer (EET)-mediated anaerobic oxidation of methane (AOM)-coupled with humic substances reduction plays an important role in the reduction of methane emissions from wetlands, where magnetite is prevalent. However, little is known about the magnetite-mediated EET mechanisms in AOM-coupled humic substances reduction. This study shows that magnetite promotes the reduction of the AOM-coupled humic substances model compound, anthraquinone-2,6-disulfonate (AQDS). 13CH4 labeling experiments further indicated that AOM-coupled AQDS reduction occurred, and acetate was an intermediate product of AOM. Moreover, 13CH313COONa labeling experiments showed that AOM-generated acetate can be continuously reduced to methane in a state of dynamic equilibrium. In the presence of magnetite, the EET capacity of the microbial community increased, and Methanosarcina played a key role in the AOM-coupled AQDS reduction. Pure culture experiments showed that Methanosarcina barkeri can independently perform AOM-coupled AQDS reduction and that magnetite increased its surface protein redox activity. The metatranscriptomic results indicated that magnetite increased the expression of membrane-bound proteins involved in energy metabolism and electron transfer in M. barkeri, thereby increasing the EET capacity. This phenomenon potentially elucidates the rationale as to why magnetite promoted AOM-coupled AQDS reduction.

Metagenomic evidence of a novel anammox community in a cold aquifer with high nitrogen pollution.

The process of anaerobic ammonium oxidation by nitrite (anammox) is a globally essential part of N cycle. To date, 8 Candidatus genera and more than 22 species of anammox bacteria have been discovered in various anthropogenic and natural habitats, including nitrogen-polluted aquifers. In this work, anammox bacteria were detected for the first time in the groundwater ecosystem with high anthropogenic nitrogen pollution (up to 1760 mg NO3--N/L and 280 mg NH4+-N/L) and low year-round temperature (7-8 °C) in the zone of a uranium sludge repository. Further metagenomic analysis resulted in retrieval of metagenome-assembled genomes of 4 distinct anammox bacteria: a new genus named Ca. Frigussubterria, new species in Ca. Kuenenia, and two strains of a new species in Ca. Scalindua. Analysis of the genomes revealed essential genes involved in anammox metabolism. Both strains of Ca. Scalindua chemeplantae had a high copy number of genes encoding the cold shock proteins CspA/B, which can also function as an antifreeze protein (CspB). Ca. Kuenenia glazoviensis and Ca. Frigussubterria udmurtiae were abundant in less N-polluted site, while Ca. Scalindua chemeplantae inhabited both sites. Genes for urea utilization, reduction of insoluble Fe2O3 or MnO2, assimilatory sulfate reduction, reactive oxygen detoxification, nitrate reduction to ammonium, and putatively arsenate respiration were found. These findings enrich knowledge of the functional and phylogenetic diversity of anammox bacteria and improve understanding of the nitrogen cycle in polluted aquifers.

Stress Granule Core Protein-Derived Peptides Inhibit Assembly of Stress Granules and Improve Sorafenib Sensitivity in Cancer Cells.

Upon a variety of environmental stresses, eukaryotic cells usually recruit translational stalled mRNAs and RNA-binding proteins to form cytoplasmic condensates known as stress granules (SGs), which minimize stress-induced damage and promote stress adaptation and cell survival. SGs are hijacked by cancer cells to promote cell survival and are consequently involved in the development of anticancer drug resistance. However, the design and application of chemical compounds targeting SGs to improve anticancer drug efficacy have rarely been studied. Here, we developed two types of SG inhibitory peptides (SIPs) derived from SG core proteins Caprin1 and USP10 and fused with cell-penetrating peptides to generate TAT-SIP-C1/2 and SIP-U1-Antp, respectively. We obtained 11 SG-inducing anticancer compounds from cell-based screens and explored the potential application of SIPs in overcoming resistance to the SG-inducing anticancer drug sorafenib. We found that SIPs increased the sensitivity of HeLa cells to sorafenib via the disruption of SGs. Therefore, anticancer drugs which are competent to induce SGs could be combined with SIPs to sensitize cancer cells, which might provide a novel therapeutic strategy to alleviate anticancer drug resistance.

Applying Dynamic Magnetic Field To Promote Anaerobic Digestion via Enhancing the Electron Transfer of a Microbial Respiration Chain.

Electrochemical methods have been reported to strengthen anaerobic digestion, but the continuous electrical power supply and the complicated electrode installed inside the digester have restricted it from practical use. In this study, a dynamic magnetic field (DMF) was placed outside a digester to induce an electromotive force to electrically promote anaerobic digestion. With the applied DMF, an electromotive force of 0.14 mV was generated in the anaerobic sludge, and a 65.02% methane increment was obtained from the anaerobic digestion of waste-activated sludge. Experiments on each stage of anaerobic digestion showed that acidification and methanogenesis that involve electron transfer of respiration chains were promoted with the DMF, while solubilization and hydrolysis less related to respiration chains were not enhanced. Further analysis indicated that the induced electromotive force polarized the protein-like substances in the sludge to increase the conductivity and capacitance of the sludge. Electrotrophic methanogens (Methanothrix) and exoelectrogens (Exiguobacterium) were enriched with DMF. The kinetic isotope effect test confirmed that electron transfer was accelerated with DMF. Consistently, the concentration ratio of co-enzymes (NADH/NAD+ and F420H2/F420) that reflects the electron exchange with respiration chains significantly increased. Applying the DMF seemed a more accessible strategy to electrically strengthen anaerobic digestion.

Focus on Co-digestion of waste activated sludge and food waste via yeast pre-fermentation and biochar supplementation: The optimization and mechanism.

Anaerobic digestion is a promising method to recover energy from waste, but the slow rate of fermentation hinders its application. Yeast pre-fermentation has been reported to enhance organic matter solubilization and ethanol production to promote syntrophic metabolism and methanogenesis. However, the pre-fermentation with yeast has not been optimized so far. In this study, the lab-scale experiment was conducted to optimize operational conditions, and a pilot-scale study was conducted to evaluate the combined strategy of yeast pre-fermentation and biochar supplementation. Results demonstrated that at a fermentation time of 6 h, temperature of 30 °C, and dry yeast dosage of 2‰, the highest ethanol production was achieved, which accounted for 6.2% of the total COD of pre-fermentation effluent of a mixture of waste-activated sludge and food waste. The methane yield of the pre-fermented waste averaged 161.3 mL/g VS/d, which was 18.7% higher than that of the control group without the yeast inoculation (135.8 mL/g VS/d). With supplementing biochar of 0.5 and 1 g/L, the average methane production was 27.8% and 36.4% higher than the control group, respectively. The volatile solid removal rate was over 10% higher than the control (58.2 ± 3.12%). Consistently, the electrochemical properties of sludge with biochar were significantly improved. A pilot-scale experiment further showed that the methane production with the yeast pre-fermentation and biochar supplementation reached 227 mL/g VS/d, 54.3% higher than that without yeast pre-fermentation and biochar. This study provided a feasible method to combine yeast pre-fermentation and biochar supplementation under optimal conditions, which effectively increased methane production during anaerobic digestion of organic waste.

Alleviating acid inhibition in anaerobic digestion of food waste: Coupling ethanol-type fermentation with biochar addition.

In this study, ethanol-type fermentation pretreatment and adding two types of biochar prepared at 600 °C and 1000 °C (referred to as SS600 and SS1000) were combined to alleviate acid accumulation via strengthening direct interspecies electron transfer (DIET) during anaerobic digestion of food waste. Results demonstrated that ethanol production was about 11 g/L after the ethanol-type fermentation at pH of 4-5 for 4 days, accounting for 8.9% of the influent COD of the subsequent methanogenesis. After the ethanol-type fermentation pretreatment, average methane productions of digesters with SS600 and SS1000 addition increased by 86.3% and 64.9% to 618.1 ± 30.1 and 527.3 ± 25.4 mL/g VS under solid retention time (SRT) of 25 d respectively, and the conductivity of sludge increased by 95.3% and 65.3% compared to digester without biochar addition. Furthermore, adding biochar also could accelerate the recovery of acidification digester. The relative abundance of Methanothrix performing DIET were enriched with SS600. These results suggested that coupling ethanol-type fermentation with biochar addition could strengthen DIET to resist the shocks of high organic loading rate.

Anaerobic Ammonium Removal Pathway Driven by the Fe(II)/Fe(III) Cycle through Intermittent Aeration.

Feammox, that is, Fe(III) reduction coupled to anaerobic ammonium oxidation, has been reported to play an important role in the nitrogen cycle in natural environments. However, the application of Feammox in wastewater treatment is limited because continuous Fe(III) supplementation is required for achieving continuous nitrogen removal, which is not feasible in practice. In this study, air was aerated intermittently into the Feammox system containing iron and high-content ammonium for oxidizing Fe(II) generated from Feammox to Fe(III), then, the produced Fe(III) participated in the next round of Feammox, leading to continuous nitrogen removal through the Fe(II)/Fe(III) cycle. The results showed that after each 10 min of aeration (150 mL/min), every 6-7 days, dissolved oxygen (DO) increased from 0 to about 0.4 mg/L, accompanied by a decrease in Fe(II) and an increase in Fe(III). One day after the aeration, DO was undetectable, and then, Fe(II) content increased and Fe(III) content decreased. On day 90, NH4+-N content in the aerated reactor was only 10.2 mg/L, while it remained at around 288.3 mg/L in the aeration-free group. X-ray diffraction showed that the generated Fe(III) through air aeration was Fe(OH)3. Microbial analysis showed that anammox and nitrification/denitrification could be excluded in the system. This NH4+ removal process, driven by the Fe(II)/Fe(III) cycle with O2 as the terminal electron acceptor, might be used as an in situ remediation method for treating high-content NH4+.

Effects of dissimilatory iron reduction on acetate production from the anaerobic fermentation of waste activated sludge under alkaline conditions.

Anaerobic digestion of waste activated sludge (WAS) to produce acetate has recently attracted growing interest, while the slow hydrolytic acidification of sludge and the consumption of acetate by methanogens both decrease the yield of acetate. In this study, Fe3O4 was added to a WAS anaerobic digester under alkaline conditions (pH = 10). The concentration of short-chain fatty acids (SCFA) during WAS anaerobic fermentation was found to be affected positively by Fe3O4. The maximal SCFA production of the Fe3O4-added digester was 3619.4 mg/L, while the maximal SCFA production in the control was 2899.7 mg/L. The increase of SCFA with Fe3O4 was mainly resulted from the increase in acetate accumulation (accounting for 90%), because Fe3O4 stimulated dissimilatory iron reduction (DIR) that participated in the decomposition of complex organics and the transformation of pronionate and butyrate into acetate. Further investigation showed that each step of hydrolytic-acidification process was promoted except the homoacetogenesis. The activity of enzymes and abundance of microbes relevant to hydrolysis and acidification were in agreement with the above results.

Biochar stimulates growth of novel species capable of direct interspecies electron transfer in anaerobic digestion via ethanol-type fermentation.

The study presented here was to evaluate the effects of combining biological ethanol-type fermentation pretreatment (BEFP) with biochar on the growth of novel species capable of direct interspecies electron transfer (DIET) and methanogenesis in anaerobic co-digestion (AcoD) of kitchen wastes (KWs) and waste activated sludge (WAS). The results showed that, after BEFP, the genera capable of extracellular electron transfer to Fe(III) oxides or the elemental sulfur, such as Geobacter, Sphaerochaeta and Sporanaerobacter species, were detected, which however were not detected in the seed sludge. In the presence of biochar, their abundance was further increased, suggesting that biochar stimulated their growth. With biochar, methane production rate increased by about 44% and the effluent concentration of total organic substrates further declined, compared with that without biochar. With biochar, methane production efficiency reached 241.6 mL/g-COD, more than 30% higher than that without biochar (185.0 mL/g-COD), suggesting that more energy from the oxidation of organic substrates was converted into methane. Analysis of Fourier transform infrared spectroscopy (FT-IR) and three-dimensional excitation emission matrix (3D-EEM) showed that decomposition of complex organic compounds in KWs and WAS was enhanced, since the novel species might proceed DIET with methanogens and participate in the metabolism of complex organic compounds.

A strategy for enhancing anaerobic digestion of waste activated sludge: Driving anodic oxidation by adding nitrate into microbial electrolysis cell.

Cathodic reduction of CO2 and anodic oxidation of organic matters are crucial to methane-producing microbial electrolysis cell (MEC) applied in anaerobic digestion of waste activated sludge. However, cathodic CO2 reduction is usually restrained by slow metabolism rates of H2-utilizing methanogens and low electron-capturing capacity of CO2, which consequently slows down the anodic oxidation that participates to sludge disintegration. Herein, a strategy with adding nitrate as electron acceptor to foster electronic transfer between the anode and cathode was proposed to improve anodic oxidation. Results showed that the average efficiency of anodic oxidation in the nitrate-added MEC increased by 55.9%. Accordingly, volatile suspended solid removal efficiency in the nitrate-added MEC was 21.9% higher than that of control MEC. Although the initial cumulative methane production in the nitrate-added MEC was lower than that of control MEC, the cumulative methane production in 24 days was 8.9% higher. Fourier transform infrared spectroscopy analysis indicated that anodic oxidation of MEC with nitrate accelerated the disintegration of sludge flocs and cell walls. Calculation on current signal further revealed that anodic oxidation driven by cathodic nitrate reduction was the main mechanism responsible for the improved sludge digestion.

Enhancing nitrogen removal efficiency in a dyestuff wastewater treatment plant with the IFFAS process: the pilot-scale and full-scale studies.

The activated sludge (AS) process is widely applied in dyestuff wastewater treatment plants (WWTPs); however, the nitrogen removal efficiency is relatively low and the effluent does not meet the indirect discharge standards before being discharged into the industrial park's WWTP. Hence it is necessary to upgrade the WWTP with more advanced technologies. Moving bed biofilm processes with suspended carriers in an aerobic tank are promising methods due to enhanced nitrification and denitrification. Herein, a pilot-scale integrated free-floating biofilm and activated sludge (IFFAS) process was employed to investigate the feasibility of enhancing nitrogen removal efficiency at different hydraulic retention times (HRTs). The results showed that the effluent chemical oxygen demand (COD), ammonium nitrate (NH4+-N) and total nitrogen (TN) concentrations of the IFFAS process were significantly lower than those of the AS process, and could meet the indirect discharge standards. PCR-DGGE and FISH results indicated that more nitrifiers and denitrifiers co-existed in the IFFAS system, promoting simultaneous nitrification and denitrification. Based on the pilot results, the IFFAS process was used to upgrade the full-scale AS process, and the effluent COD, NH4+-N and TN of the IFFAS process were 91-291 mg/L, 10.6-28.7 mg/L and 18.9-48.6 mg/L, stably meeting the indirect discharge standards and demonstrating the advantages of IFFAS in dyestuff wastewater treatment.

A colorimetric aptasensor for sulfadimethoxine detection based on peroxidase-like activity of graphene/nickel@palladium hybrids.

A sensitive, rapid and label-free colorimetric aptasensor for sulfadimethoxine (SDM) detection was developed based on the tunable peroxidase-like activity of graphene/nickel@palladium nanoparticle (Gr/Ni@Pd) hybrids. The addition of the SDM aptamer could inhibit the peroxidase-like catalytic activity of the hybrids. However, the target SDM and aptamer could be triggered tightly and recover the catalytic activity of the Gr/Ni@Pd hybrids. Due to the peroxidase-like catalytic activity, Gr/Ni@Pd could catalyze the decomposition of H2O2 with releasing hydroxyl radicals which further oxidized reagent 3, 3', 5, 5'-Tetramethylbenzidine (TMB) to oxTMB accompanied with a colorless-to-blue color change. The original color change could be applied to obtain quantitative detection of SDM, due to the relationship between the concentration of the target and the color difference. As a result, this approach performed a linear response for SDM from 1 to 500 ng/mL with a limit detection of 0.7 ng/mL (S/N = 3) under the optimized conditions and realized the detection of SDM in spiked lake water samples. Therefore, this colorimetric aptasensor was an alternative assay for SDM detection in real water. Moreover, with its design principle, this work might be applied to detecting other small molecule by employing appropriate aptamer.

Scaling-up of a zero valent iron packed anaerobic reactor for textile dye wastewater treatment: a potential technology for on-site upgrading and rebuilding of traditional anaerobic wastewater treatment plant.

Anaerobic digestion (AD) is a cost-effective technology for the treatment of textile dye wastewater with clear environmental benefits. However, the need to improve process feasibility of high treatment efficiency as well as to shorten hydraulic retention time has raised interest on several intensification techniques. Zero valent iron (ZVI) packed anaerobic digesters have the potential to become an on-site upgrading wastewater treatment technology through building a ZVI bed in a traditional AD plant. However, the experiences and knowledge of scale-up are limited. In this study, a pilot-scale ZVI packed upflow anaerobic sludge bed (ZVI-UASB) was built up and operated for actual dye wastewater treatment in a textile dye industrial park. Results showed that the treatment performance of this digester is higher than that of a traditional AD plant in terms of chemical oxygen demand (COD) removal and color removal. During 90 days of operation, the average COD removal and color removal in ZVI-UASB was maintained at around 19% and 40%, respectively, while it was only 10% and 20%, respectively, in the traditional AD plant.

Selective Electrochemical Reduction of Carbon Dioxide to Ethanol on a Boron- and Nitrogen-Co-doped Nanodiamond.

Electrochemical reduction of CO2 to ethanol, a clean and renewable liquid fuel with high heating value, is an attractive strategy for global warming mitigation and resource utilization. However, converting CO2 to ethanol remains great challenge due to the low activity, poor product selectivity and stability of electrocatalysts. Here, the B- and N-co-doped nanodiamond (BND) was reported as an efficient and stable electrode for selective reduction of CO2 to ethanol. Good ethanol selectivity was achieved on the BND with high Faradaic efficiency of 93.2 % (-1.0 V vs. RHE), which overcame the limitation of low selectivity for multicarbon or high heating value fuels. Its superior performance was mainly originated from the synergistic effect of B and N co-doping, high N content and overpotential for hydrogen evolution. The possible pathway for CO2 reduction revealed by DFT computation was CO2 →*COOH→*CO→*COCO→*COCH2 OH→*CH2 OCH2 OH→CH3 CH2 OH.

Enhancement of sludge granulation in hydrolytic acidogenesis by denitrification.

Acidogenesis is an important pretreatment process for various industrial wastewater treatments. Granular sludge is an efficient form of a microbial community in anaerobic methanogenic reactors, such as upflow anaerobic sludge blanket (UASB), but it is hard to develop in the acidogenic process due to the short hydraulic retention times (HRTs) of acidogenesis. In this study, nitrate was added into an acidogenic reactor as an electron acceptor to enhance electron exchange between acidogenic and denitrifying bacteria to accelerate sludge growth in the acidogenesis process. The results showed that it developed solid and mature granular sludge with a mean size of 410 ± 35 µm over 84 days of operation. Comparatively, the sludge in a no-nitrate acidogenic reactor showed a flocculent appearance with a mean size of 110 ± 18 µm. Analysis of the microbial community indicated that denitrifying bacteria interwoven with propionate-oxidizing bacteria were distributed in the outer granule layer, which provided an ideal shield for susceptible microorganisms inside the granules. This microbial structure was favorable for the development of granular sludge and made the system possible to respond well to shocks in the operation.

Enhancing nitrogen removal efficiency and reducing nitrate liquor recirculation ratio by improving simultaneous nitrification and denitrification in integrated fixed-film activated sludge (IFAS) process.

An integrated fixed-film activated sludge (IFAS) process (G1) and an activated sludge anoxic-oxic process (G2) were operated at nitrate liquor recirculation ratio (R) of 100, 200 and 300% to investigate the feasibility of enhancing nitrogen removal efficiency (RTN) and reducing R by improving simultaneous nitrification and denitrification (SND) in the IFAS process. The results showed that the effluent NH4(+)-N and total nitrogen (TN) of G1 at R of 200% were less than 1.5 and 14.5 mg/L, satisfying the Chinese discharge standard (NH4(+)-N < 5 mg/L; TN < 15 mg/L). However, the effluent NH4(+)-N and TN of G2 at R of 300% were higher than 8.5 and 15.3 mg/L. It indicated that better RTN could be achieved at a lower R in the IFAS process. The polymerase chain reaction-denaturing gradient gel electrophoresis results implied that nitrifiers and denitrifiers co-existed in one microbial community, facilitating the occurrence of SND in the aerobic reactor of G1, and the contribution of SND to TN removal efficiency ranged 15-19%, which was the main reason that the RTN was improved in the IFAS process. Therefore, the IFAS process was an effective method for improving RTN and reducing R. In practical application, this advantage of the IFAS process can decrease the electricity consumption for nitrate liquor recirculation flow, thereby saving operational costs.

Nutrient removal performance and microbial characteristics of a full-scale IFAS-EBPR process treating municipal wastewater.

This work describes the nutrient removal performance and microbial characteristics of a full-scale integrated fixed-film activated sludge-enhanced biological phosphorus removal (IFAS-EBPR) process for municipal wastewater treatment. The polymerase chain reaction-denaturing gradient gel electrophoresis results showed that the presence of bacteria in this process, including Nitrosomonas sp., Nitrospira sp., Nitrobacter sp., Pseudomonas sp. and Acinetobacter sp., clusters. The fluorescence in situ hybridization results implied that there were more nitrifiers and denitrifiers on the biofilm carriers than in the suspended sludge, whereas more phosphorus-accumulating organisms (PAOs) resided in the suspended sludge. With the cooperation of these functional microbial populations both on the biofilm carriers and in the suspended sludge, the chemical oxygen demand (COD), NH4(+)-N, total nitrogen (TN) and total phosphorus (TP) removal efficiencies were maintained at 84, 97, 70 and 81%, and the effluent concentrations of them averaged 30, 1.0, 11.5 and 0.6 mg/L, which all satisfy the Chinese discharge standard (COD <50 mg/L, NH4(+)-N <5 mg/L, TN <15 mg/L and TP <1 mg/L), respectively. Therefore, the IFAS-EBPR process is a reliable and effective process for nutrient removal.

Evaluating enhanced sulfate reduction and optimized volatile fatty acids (VFA) composition in anaerobic reactor by Fe (III) addition.

Anaerobic reactors with ferric iron addition have been experimentally demonstrated to be able to simultaneously improve sulfate reduction and organic matter degradation during sulfate-containing wastewater treatment. In this work, a mathematical model is developed to evaluate the impact of ferric iron addition on sulfate reduction and organic carbon removal as well as the volatile fatty acids (VFA) composition in anaerobic reactor. The model is successfully calibrated and validated using independent long-term experimental data sets from the anaerobic reactor with Fe (III) addition under different operational conditions. The model satisfactorily describes the sulfate reduction, organic carbon removal and VFA production. Results show Fe (III) addition induces the microbial reduction of Fe (III) by iron reducing bacteria (IRB), which significantly enhances sulfate reduction by sulfate reducing bacteria (SRB) and subsequently changes the VFA composition to acetate-dominating effluent. Simultaneously, the produced Fe (II) from IRB can alleviate the inhibition of undissociated H2S on microorganisms through iron sulfide precipitation, resulting in further improvement of the performance. In addition, the enhancement on reactor performance by Fe (III) is found to be more significantly favored at relatively low organic carbon/SO4(2-) ratio (e.g., 1.0) than at high organic carbon/SO4(2-) ratio (e.g., 4.5). The Fe (III)-based process of this work can be easily integrated with a commonly used strategy for phosphorus recovery, with the produced sulfide being recovered and then deposited into conventional chemical phosphorus removal sludge (FePO4) to achieve FeS precipitation for phosphorus recovery while the required Fe (III) being acquired from the waste ferric sludge of drinking water treatment process, to enable maximum resource recovery/reuse while achieving high-rate sulfate removal.

Efficient Mineralization of Perfluorooctanoate by Electro-Fenton with H2O2 Electro-generated on Hierarchically Porous Carbon.

Perfluorochemicals are environmentally persistent, bioaccumulative, and globally distributed contaminants, which present potential toxicity to both humans and ecosystems. However, rapid mineralization of perfluorochemicals with cost-effective method remains great challenges. Here, an electro-Fenton system was reported for efficient mineralization of perfluorooctanoate (PFOA), where H2O2 was electro-generated in situ from O2 reduction on hierarchically porous carbon (HPC). Benefited from the high H2O2 production rate (41.2-14.0 mM/h) of HPC, PFOA (50 mg/L) was rapidly degraded by electro-Fenton with first-order kinetic constants of 1.15-0.69 h(-1) at low potential (-0.4 V) in a wide range of pH (2-6). Meanwhile, PFOA was effectively mineralized, as revealed by a total organic carbon removal efficiency of 90.7-70.4% (-0.4 V, pH 2-6, 4 h). Moreover, the current efficiency of this electro-Fenton system for PFOA degradation was 1 order of magnitude higher than those of electrochemical oxidation. On the basis of the intermediate analysis, we proposed a possible mechanism for PFOA degradation: PFOA lost one electron to the anode and got decarboxylated. The formed perfluoroalkyl radical was mainly oxidized by hydroxyl radical, resulting in the formation of shorter chain perfluorocarboxylic acid, which followed the same reaction cycle as PFOA until it was mineralized.