Feb 2021, Volume 15 Issue 1

Cover illustration

  • Demand for water is expanding with increases in population, particularly in urban areas in developing countries. Moreover, urban water system needs a novel perspective for upgradation with urbanization. We present a novel 5R approach for managing urban water resources: Recover (storm water), Reduce (toilet flushing water), Recycle (gray water), Resource (black water), and  Reuse (

    Download cover Download table of contents

  • Select all
    Jinjin Fu, Quan Zhang, Baocheng Huang, Niansi Fan, Rencun Jin

    • Anammox is promising for nitrogen removal from antibiotic-containing wastewater.

    • Most antibiotics could inhibit the anammox performance and activity.

    • Antibiotic pressure promoted the increase in antibiotic resistance genes (ARGs).

    • Antibiotic-resistance mechanisms of anammox bacteria are speculated.

    Antibiotic is widely present in the effluent from livestock husbandry and the pharmaceutical industry. Antibiotics in wastewater usually have high biological toxicity and even promote the occurrence and transmission of antibiotic resistant bacteria and antibiotic resistance genes. Moreover, most antibiotic-containing wastewater contains high concentration of ammonia nitrogen. Improper treatment will lead to high risk to the surrounding environment and even human health. The anaerobic ammonium oxidation (anammox) with great economic benefit and good treatment effect is a promising process to remove nitrogen from antibiotic-containing wastewater. However, antibiotic inhibition has been observed in anammox applications. Therefore, a comprehensive overview of the single and combined effects of various antibiotics on the anammox system is conducted in this review with a focus on nitrogen removal performance, sludge properties, microbial community, antibiotic resistance genes and anammox-involved functional genes. Additionally, the influencing mechanism of antibiotics on anammox consortia is summarized. Remaining problems and future research needs are also proposed based on the presented summary. This review provides a better understanding of the influences of antibiotics on anammox and offers a direction to remove nitrogen from antibiotic-containing wastewater by the anammox process.

    Lijie Zhou, Hongwu Wang, Zhiqiang Zhang, Jian Zhang, Hongbin Chen, Xuejun Bi, Xiaohu Dai, Siqing Xia, Lisa Alvarez-Cohen, Bruce E. Rittmann

    5R (Recover, Reduce, Recycle, Resource and Reuse) approaches to manage urban water.

    5R harvests storm water, gray water and black water in several forms.

    5R offers promise for moving solutions for urban water scarcity in practice.

    Demand for water is expanding with increases in population, particularly in urban areas in developing countries. Additionally, urban water system needs a novel perspective for upgradation with urbanization. This perspective presents a novel 5R approach for managing urban water resources: Recover (storm water), Reduce (toilet flushing water), Recycle (gray water), Resource (black water), and Reuse (advanced-treated wastewater). The 5R generation incorporates the latest ideas for harvesting storm water, gray water, and black water in its several forms. This paper has briefly demonstrated each R of 5R generation for water treatment and reuse. China has the chance to upgrade its urban water systems according to 5R principles. Already, a demonstration project of 5R generation has been installed in Qingdao International Horticultural Exposition, and Dalian International Convention Center (China) has applied 5R, achieving over 70% water saving. The 5R offers promise for moving solutions for urban water scarcity from “hoped for in the future” to “realistic today”.

    Ragini Pirarath, Palani Shivashanmugam, Asad Syed, Abdallah M. Elgorban, Sambandam Anandan, Muthupandian Ashokkumar

    • Synthesized few-layered MoS2 nanosheets via surfactant-assisted hydrothermal method.

    • Synthesized MoS2 nanosheets show petal-like morphology.

    • Adsorbent showed 93% of mercury removal efficiency.

    • The adsorption of mercury is attributed to negative zeta potential (-21.8 mV).

    Recently, different nanomaterial-based adsorbents have received greater attention for the removal of environmental pollutants, specifically heavy metals from aqueous media. In this work, we synthesized few-layered MoS2 nanosheets via a surfactant-assisted hydrothermal method and utilized them as an efficient adsorbent for the removal of mercury from aqueous media. The synthesized MoS2 nanosheets showed petal-like morphology as confirmed by scanning electron microscope and high-resolution transmission electron microscopic analysis. The average thickness of the nanosheets is found to be about 57 nm. Possessing high stability and negative zeta potential makes this material suitable for efficient adsorption of mercury from aqueous media. The adsorption efficiency of the adsorbent was investigated as a function of pH, contact time and adsorbent dose. The kinetics of adsorption and reusability potential of the adsorbent were also performed. A pseudo-second-order kinetics for mercury adsorption was observed. As prepared MoS2 nanosheets showed 93% mercury removal efficiency, whereas regenerated adsorbent showed 91% and 79% removal efficiency in the respective 2nd and 3rd cycles. The adsorption capacity of the adsorbent was found to be 289 mg/g at room temperature.

    Rencheng Zhu, Jingnan Hu, Liqiang He, Lei Zu, Xiaofeng Bao, Yitu Lai, Sheng Su

    • Emissions from two sedans were tested with gasoline, E10 and M15 at 30°C and -7°C.

    • As the temperature decreased, the PM, PN and BC emissions increased with all fuels.

    • Particulate emissions with E10 and M15 were more sensitive to the temperature.

    • The PN and BC generated during cold start-up dominated those over the WLTC.

    Ambient temperature has substantial impacts on vehicle emissions, but the impacts may differ between traditional and alcohol gasolines. The objective of this study was to investigate the effects of temperature on gaseous and particulate emissions with both traditional and alcohol gasoline. Regulated gaseous, particle mass (PM), particle number (PN) and black carbon (BC) emissions from typical passenger vehicles were separately quantified with gasoline, E10 (10% ethanol and 90% gasoline by volume) and M15 (15% methanol and 85% gasoline by volume) at both 30°C and -7°C. The particulate emissions with all fuels increased significantly with decreased temperature. The PM emissions with E10 were only 48.0%–50.7% of those with gasoline at 30°C but increased to 59.2%-79.4% at -7°C. The PM emissions with M15 were comparable to those with gasoline at 30°C, but at -7°C, the average PM emissions were higher than those with gasoline. The variation trend of PN emissions was similar to that of PM emissions with changes in the fuel and temperature. At 30°C, the BC emissions were lower with E10 and M15 than with gasoline in most cases, but E10 and M15 might emit more BC than gasoline at -7°C, especially M15. The results of the transient PN and BC emission rates show that particulate emissions were dominated mainly by those emitted during the cold-start moment. Overall, the particulate emissions with E10 and M15 were more easily affected by ambient temperature, and the advantages of E10 and M15 in controlling particulate emissions declined as the ambient temperature decreased.

    Milan Malhotra, Anurag Garg

    • Hydrothermal treatment can greatly improve resource recovery from sewage sludge.

    • tCOD removal during WO was ~55% compared with ~23% after TH.

    • TOC solubilization during hydrothermal treatment followed first-order kinetics.

    • Solids and carbon balance confirmed loss of organics during thermal hydrolysis.

    • Reaction pathways for thermal hydrolysis and wet oxidation are proposed.

    We evaluated the effect of hydrothermal pretreatments, i.e., thermal hydrolysis (TH) and wet oxidation (WO) on sewage sludge to promote resource recovery. The hydrothermal processes were performed under mild temperature conditions (140°C–180°C) in a high pressure reactor. The reaction in acidic environment (pH= 3.3) suppressed the formation of the color imparting undesirable Maillard’s compounds. The oxidative conditions resulted in higher volatile suspended solids (VSS) reduction (~90%) and chemical oxygen demand (COD) removal (~55%) whereas TH caused VSS and COD removals of ~65% and ~27%, respectively at a temperature of 180°C. During TH, the concentrations of carbohydrates and proteins in treated sludge were 400–1000 mg/L and 1500–2500 mg/L, respectively. Whereas, WO resulted in solids solubilization followed by oxidative degradation of organics into smaller molecular weight carboxylic acids such as acetic acid (~400–500 mg/L). Based on sludge transformation products generated during the hydrothermal pretreatments, simplified reaction pathways are predicted. Finally, the application of macromolecules (such as proteins), VFAs and nutrients present in the treated sludge are also discussed. The future study should focus on the development of economic recovery methods for various value-added compounds.

    Yanqing Duan, Aijuan Zhou, Xiuping Yue, Zhichun Zhang, Yanjuan Gao, Yanhong Luo, Xiao Zhang

    • Carbon availability was partially solved by POM recovery and fermentation.

    • 12% carbon sources were regenerated by fermentation of the entrapped 35% TCOD.

    • The unique microbial communities facilitated the efficient hydrolysis of the POM.

    • Considerable economic benefits in aeration power and ECS dosage were anticipated.

    To address the availability of carbon sources for denitrification, the accelerated hydrolysis of the most abundant but low-availability fraction of particulate organic matter (POM) was investigated. Mesh sieves with different pore sizes were used as primary pretreatment at the start-up-stage of the biological process to separate some POM from the liquid system. The changes in soluble carbohydrates and proteins were monitored to investigate the hydrolysis performance of the sieved POM, with waste activated sludge (WAS) as the control test. The results showed that an average of 35% POM could be entrapped before filtrate mat development. In addition, benefiting from the high polysaccharides concentration, as well as the high availability due to the relatively loose physical structure, a 23% hydrolysis efficiency of POM was obtained, in contrast to that of WAS (3.4%), with a hydrolysis constant of 0.39 h1. The prominent performance was also attributed to the unique microbial communities having been domesticated at a lower temperature, especially the cellulose-degrading bacteria Paraclostridium and psychrophile Psychrobacter, making up 6.94% and 2.56%, respectively. Furthermore, the potential benefits and application of improved POM hydrolysis by start-up stage recovery via mesh sieves combined with anaerobic fermentation were evaluated, including selective POM entrapment, alleviation of blockage and wear, and a reduction in aeration energy. By the proposed strategy, carbon availability for biological nutrient removal (BNR) processes is anticipated to be improved more economically than that can be achieved by primary clarifier elimination.

    Shuo Wei, Lei Du, Shuo Chen, Hongtao Yu, Xie Quan

    • A stable and electroconductive CNTs/ceramic membrane was fabricated.

    • The membrane with the electro-assistance exhibited optimal fouling mitigation.

    • The removal efficiency was improved by the -2.0 V electro-assistance.

    • Electro-assisted filtration is energy-saving than that of commercial membrane.

    Ultrafiltration is employed as an important process for water treatment and reuse, which is of great significance to alleviate the shortage of water resources. However, it suffers from severe membrane fouling and the trade-off between selectivity and permeability. In this work, a CNTs/ceramic flat sheet ultrafiltration membrane coupled with electro-assistance was developed for improving the antifouling and separation performance. The CNTs/ceramic flat sheet membrane was fabricated by coating cross-linked CNTs on ceramic membrane, featuring a good electroconductivity of 764.75 S/m. In the filtration of natural water, the permeate flux of the membrane with the cell voltage of -2.0 V was 1.8 times higher than that of the membrane without electro-assistance and 5.7-fold greater than that of the PVDF commercial membrane. Benefiting from the electro-assistance, the removal efficiency of the typical antibiotics was improved by 50%. Furthermore, the electro-assisted membrane filtration process showed 70% reduction in energy consumption compared with the filtration process of the commercial membrane. This work offers a feasible approach for membrane fouling mitigation and effluent quality improvement and suggests that the electro-assisted CNTs/ceramic membrane filtration process has great potential in the application of water treatment.

    Hanli Wan, Jianmin Bian, Han Zhang, Yihan Li

    • A model coupling water-heat-salt of unsaturated frozen soil was established.

    • Future temperature, precipitation, and evaporation increase in freeze–thaw period.

    • Soil water, heat, and salt transport are closely coupled during freeze–thaw period.

    • Freeze–thaw cycles and future climate change can exacerbate salinization.

    The transport mechanisms of water, heat, and salt in unsaturated frozen soil, as well as its response to future climate change are in urgent need of study. In this study, western Jilin Province in north-eastern China was studied to produce a model of coupled water-heat-salt in unsaturated frozen soil using CoupModel. The water, heat, and salt dynamics of unsaturated frozen soil under three representative concentration pathway (RCP) scenarios were simulated to analyze the effects of future climate change on unsaturated frozen soil. The results show that water, heat, and salt migration are tightly coupled, and the soil salt concentration in the surface layer (10 cm) exhibits explosive growth after freezing and thawing. The future (2020–2099) meteorological factors in the study area were predicted using the Statistical Downscaling Model (SDSM). For RCP2.6, RCP4.5, and RCP8.5 scenarios, future temperatures during the freeze–thaw period increased by 2.68°C, 3.18°C, and 4.28°C, respectively; precipitation increased by 30.28 mm, 28.41 mm, and 32.17 mm, respectively; and evaporation increased by 93.57 mm, 106.95 mm, and 130.57 mm, respectively. Climate change will shorten the freeze–thaw period, advance the soil melting time from April to March, and enhance water and salt transport. Compared to the baseline period (1961–2005), future soil salt concentrations at 10 cm increased by 1547.54 mg/L, 1762.86 mg/L, and 1713.66 mg/L under RCP2.6, RCP4.5, and RCP8.5, respectively. The explosive salt accumulation is more obvious. Effective measures should be taken to prevent the salinization of unsaturated frozen soils and address climate change.

    Jiandong Lu, Shijie You, Xiuheng Wang

    • Forward osmosis (FO) coupled with chemical softening for CCI ROC minimization

    • Effective removal of scale precursor ions by lime-soda ash softening

    • Enhanced water recovery from 54% to 86% by mitigation of FO membrane scaling

    • High-purity CaCO3 was recovered from the softening sludge

    • Membrane cleaning efficiency of 88.5% was obtained by EDTA for softened ROC

    Reverse osmosis (RO) is frequently used for water reclamation from treated wastewater or desalination plants. The RO concentrate (ROC) produced from the coal chemical industry (CCI) generally contains refractory organic pollutants and extremely high-concentration inorganic salts with a dissolved solids content of more than 20 g/L contributed by inorganic ions, such as Na+, Ca2+, Mg2+, Cl, and SO42. To address this issue, in this study, we focused on coupling forward osmosis (FO) with chemical softening (FO-CS) for the volume minimization of CCI ROC and the recovery of valuable resources in the form of CaCO3. In the case of the real raw CCI ROC, softening treatment by lime-soda ash was shown to effectively remove Ca2+/Ba2+ (>98.5%) and Mg2+/Sr2+/Si (>80%), as well as significantly mitigate membrane scaling during FO. The softened ROC and raw ROC corresponded to a maximum water recovery of 86% and 54%, respectively. During cyclic FO tests (4 × 10 h), a 27% decline in the water flux was observed for raw ROC, whereas only 4% was observed for softened ROC. The cleaning efficiency using EDTA was also found to be considerably higher for softened ROC (88.5%) than that for raw ROC (49.0%). In addition, CaCO3 (92.2% purity) was recovered from the softening sludge with an average yield of 5.6 kg/m3 treated ROC. This study provides a proof-of-concept demonstration of the FO-CS coupling process for ROC volume minimization and valuable resources recovery, which makes the treatment of CCI ROC more efficient and more economical.

    Kuo Fang, Fei Peng, Hui Gong, Huanzhen Zhang, Kaijun Wang

    • Powdered resin was employed for ammonia recovery from municipal wastewater.

    • Powdered resin achievedefficient ammonia removal under various working conditions.

    • Co-existing cations indicated competitive adsorption of ammonia.

    • Ammonia was recoveredby two-stage crystallization coupled with ion exchange.

    Low-strength municipal wastewater is considered to be a recoverable nutrient resource with economic and environmental benefits. Thus, various technologies for nutrient removal and recovery have been developed. In this paper, powdered ion exchange resin was employed for ammonia removal and recovery from imitated low-strength municipal wastewater. The effects of various working conditions (powdered resin dosage, initial concentration, and pH value) were studied in batch experiments to investigate the feasibility of the approach and to achieve performance optimization. The maximum adsorption capacity determined by the Langmuir model was 44.39 mg/g, which is comparable to traditional ion exchange resin. Further, the effects of co-existing cations (Ca2+, Mg2+, K+) were studied. Based on the above experiments, recovery of ammonia as struvite was successfully achieved by a proposed two-stage crystallization process coupled with a powdered resin ion exchange process. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) results revealed that struvite crystals were successfully gained in alkaline conditions (pH= 10). This research demonstrates that a powdered resin and two-stage crystallization process provide an innovative and promising means for highly efficient and easy recovery from low-strength municipal wastewater.

    Jing Ding, Wanyi Seow, Jizhong Zhou, Raymond Jianxiong Zeng, Jun Gu, Yan Zhou

    • 0.12 mmol/L Fe(II) enhanced the total anammox activity and bacterial abundance best.

    • 0.09 mmol/L Fe(II) led to the best performance on relative anammox activity.

    • 0.75 mmol/L Fe(II) had an immediate but recoverable inhibition on anammox activity.

    • More genes but not relative level were expressed at higher Fe(II) concentration.

    Though there are many literatures studying the effects of iron on anammox process, these studies only focus on the reactor performance and/or the microbial community changes, the detailed effects and mechanisms of Fe(II) on anammox bacterial activity and physiology have not been explored. In this study, four Fe(II) concentrations (0.03, 0.09, 0.12 and 0.75 mmol/L) were employed into the enriched anammox culture. The enhancement and inhibition effects of Fe(II) on anammox process and bacterial physiology were investigated. It was discovered that the anammox process and bacterial growth were enhanced by 0.09 and 0.12 mmol/L Fe(II), in which the 0.12 mmol/L Fe(II) had advantage in stimulating the total anammox activity and bacterial abundance, while 0.09 mmol/L Fe(II) enhanced the relative anammox activity better. The anammox activity could be inhibited by 0.75 mmol/L Fe(II) immediately, while the inhibition was recoverable. Both 0.09 and 0.12 mmol/L Fe(II) induced more genes being expressed, while didn’t show a stimulation on the relative expression level of functional genes. And anammox bacteria showed a stress response to detoxify the Fe inhibition once inhibited by 0.75 mmol/L Fe(II). This study provides more information about physiologic response of anammox bacteria to external influence (enhancement and inhibition), and may also instruct the future application of anammox process in treating various sources of wastewater (containing external disturbances such as heavy metals) and/or different treatment strategies (e.g. from side-stream to main-stream).

    Barsha Roy, Khushboo Kadam, Suresh Palamadai Krishnan, Chandrasekaran Natarajan, Amitava Mukherjee

    • UVA pre-irradiation to TiO2 NPs enhanced its toxicity toward plant A. cepa.

    • UVA TiO2 NPs increased intracellular ROS, resulting in more cell damage.

    • Cell death enhanced cell permeability and increased uptake of NPs.

    • Being highly toxic (EC50 = 0.097 µmol/L), TC did not increase ROS generation.

    • Even at a low dose, TC enhanced the toxic potential of TiO2 NPs significantly.

    Usage of titanium dioxide nanoparticles (TiO2 NPs) and tetracycline (TC) has increased significantly in the present era. This leads to their release and accumulation in the environment. Both the compounds, individually, can have adverse toxic effects on the plants. Their binary mixtures can increase this degree of damage. The present study aimed to evaluate the toxicity of both the contaminants in individual and binary mixtures in Allium cepa. Further, the toxicity of TiO2 NPs upon UVA pre-irradiation was also measured. Results showed that UVA pre-irradiated NPs (UVA-TiO2 NPs) had a significant decrease in cell viability than their non-irradiated counterparts (NI-TiO2), denoting an increase in photocatalytic activity upon UVA pre-irradiation. Very low concentrations of TC (EC10 = 0.016 µmol/L) mixed with TiO2 NPs significantly increased the toxicity for both UVA-TiO2 and NI-TiO2 NPs. Intracellular ROS generation was significantly high for UVA-TiO2 NPs. However, TC did not have any effects on ROS production. Both the compounds exhibited genotoxic potential in A. cepa. Different chromosomal abnormalities like anaphase bridges, telophase bridges, laggard chromosomes, binucleate cells, etc. were observed. The binary mixture of UVA-TiO2 NPs and TC showed the highest chromosomal aberrations (64.0%±1.26%) than the mixture with NI-TiO2 or the individual contaminants. This decreased significantly after recovery (46.8%±1.92%), denoting the self-repair processes. This study proved that UVA-TiO2 NPs were more toxic and could be enhanced further when mixed with a sub-lethal concentration of TC. This work will help to assess the risk of both compounds in the environment.

    Jianmei Zou, Jianzhi Huang, Huichun Zhang, Dongbei Yue

    • Humification evolution was identified with non-destructive characterization method.

    • Humification process from precursors to fulvic and humic acid was confirmed.

    • MnO2 alone had limited oxidation ability to form HA.

    • MnO2 played a key role as a catalyst to transform FA to HA in the presence of O2.

    • MnO2 could affect the structure of the humification products.

    Abiotic humification is important in the formation and evolution of organic matter in soil and compost maturing processes. However, the roles of metal oxides in abiotic humification reactions under micro-aerobic remain ambiguous. The aim of this study was to use non-destructive measurement methods to investigate the role of MnO2 in the evolution of humic substances (HSs) during oxidative polymerization of polyphenol-amino acid. Our results suggested a synergistic effect between MnO2 and O2 in promoting the polymerization reaction and identified that MnO2 alone had a limited ability in accelerating the transformation of fulvic acid (FA) to humic acid (HA), whereas O2 was the key factor in the process. Two-dimensional correlation spectroscopy (2D-COS) showed that the evolution in the UV-vis spectra followed the order of 475–525 nm>300–400 nm>240–280 nm in the humification process, indicating the formation of simple organic matter followed by FA and then HA. 13C nuclear magnetic resonance (13C NMR) analysis revealed that the products under both air and N2 conditions in the presence of MnO2 had greater amounts of aromatic-C than in the absence of MnO2, demonstrating that MnO2 affected the structure of the humification products. The results of this study provided new insights into the theory of abiotic humification.

    Pol Masclans Abelló, Vicente Medina Iglesias, M. Antonia de los Santos López, Jesús Álvarez-Flórez

    • New method named CAbOP is presented based on ordering data according to power.

    • Three emission models are used and their emission results compared.

    • Emissions data are analyzed in real driving cycles under CAbOP criteria.

    • Methodology to collect data and reconstruct lost data in real urban driving cycles.

    In this work three fuel consumption and exhaust emission models, ADVISOR, VT-MICRO and the European Environmental Agency Emission factors, have been used to obtain fuel consumption (FC) and exhaust emissions. These models have been used at micro-scale, using the two signal treatment methods presented. The manuscript presents: 1) a methodology to collect data in real urban driving cycles, 2) an estimation of FC and tailpipe emissions using some available models in literature, and 3) a novel analysis of the results based on delivered wheel power. The results include Fuel Consumption (FC), CO2, NOx and PM10 emissions, which are derived from the three simulators. In the first part of the paper we present a new procedure for incomplete drive cycle data treatment, which is necessary for real drive cycle acquisition in high density cities. Then the models are used to obtain second by second FC and exhaust emissions. Finally, a new methodology named Cycle Analysis by Ordered Power (CAbOP) is presented and used to compare the results. This method consists in the re-ordering of time dependant data, considering the wheel mechanical power domain instead of the standard time domain. This new strategy allows the 5 situations in drive cycles to be clearly visualized: hard breaking zone, slowdowns, idle or stop zone, sustained speed zone and acceleration zone. The complete methodology is applied in two real drive cycles surveyed in Barcelona (Spain) and the results are compared with a standardized WLTC urban cycle.

    Xiling Li, Tianwei Hao, Yuxin Tang, Guanghao Chen

    • Capacitive biochar was produced from sewage sludge.

    • Seawater was proved to be an alternative activation agent.

    • Minerals vaporization increased the surface area of biochar.

    • Molten salts acted as natural templates for the development of porous structure.

    Sewage sludge is a potential precursor for biochar production, but its effective utilization involves costly activation steps. To modify biochar properties while ensuring cost-effectiveness, we examined the feasibility of using seawater as an agent to activate biochar produced from sewage sludge. In our proof-of-concept study, seawater was proven to be an effective activation agent for biochar production, achieving a surface area of 480.3 m2/g with hierarchical porosity distribution. Benefited from our design, the catalytic effect of seawater increased not only the surface area but also the graphitization degree of biochar when comparing the pyrolysis of sewage sludge without seawater. This leads to seawater activated biochar electrodes with lower resistance, higher capacitance of 113.9 F/g comparing with control groups without seawater. Leveraging the global increase in the salinity of groundwater, especially in coastal areas, these findings provide an opportunity for recovering a valuable carbon resource from sludge.

    Senem Yazici Guvenc, Gamze Varank

    • 90% total COD, 95.3% inert COD and 97.2% UV254 were removed.

    • High R2 values (over 95%) for all responses were obtained with CCD.

    • Operational cost was calculated to be 0.238 €/g CODremoved for total COD removal.

    • Fenton oxidation was highly-efficient method for inert COD removal.

    • BOD5/COD ratio of leachate concentrate raised from 0.04 to 0.4.

    The primary aim of this study is inert COD removal from leachate nanofiltration concentrate because of its high concentration of resistant organic pollutants. Within this framework, this study focuses on the treatability of leachate nanofiltration concentrate through Fenton oxidation and optimization of process parameters to reach the maximum pollutant removal by using response surface methodology (RSM). Initial pH, Fe2+ concentration, H2O2/Fe2+ molar ratio and oxidation time are selected as the independent variables, whereas total COD, color, inert COD and UV254 removal are selected as the responses. According to the ANOVA results, the R2 values of all responses are found to be over 95%. Under the optimum conditions determined by the model (pH: 3.99, Fe2+: 150 mmol/L, H2O2/Fe2+: 3.27 and oxidation time: 84.8 min), the maximum COD removal efficiency is determined as 91.4% by the model. The color, inert COD and UV254 removal efficiencies are determined to be 99.9%, 97.2% and 99.5%, respectively, by the model, whereas the total COD, color, inert COD and UV254 removal efficiencies are found respectively to be 90%, 96.5%, 95.3% and 97.2%, experimentally under the optimum operating conditions. The Fenton process improves the biodegradability of the leachate NF concentrate, increasing the BOD5/COD ratio from the value of 0.04 to the value of 0.4. The operational cost of the process is calculated to be 0.238 €/g CODremoved. The results indicate that the Fenton oxidation process is an efficient and economical technology in improvement of the biological degradability of leachate nanofiltration concentrate and in removal of resistant organic pollutants.

    Yang Li, Yixin Zhang, Guangshen Xia, Juhong Zhan, Gang Yu, Yujue Wang

    • Gas diffusion electrode (GDE) is a suitable setup for practical water treatment.

    • Electrochemical H2O2 production is an economically competitive technology.

    • High current efficiency of H2O2 production was obtained with GDE at 5–400 mA/cm2.

    • GDE maintained high stability for H2O2 production for ~1000 h.

    • Electro-generation of H2O2 enhances ibuprofen removal in an E-peroxone process.

    This study evaluated the feasibility of electrochemical hydrogen peroxide (H2O2) production with gas diffusion electrode (GDE) for decentralized water treatment. Carbon black-polytetrafluoroethylene GDEs were prepared and tested in a continuous flow electrochemical cell for H2O2 production from oxygen reduction. Results showed that because of the effective oxygen transfer in GDEs, the electrode maintained high apparent current efficiencies (ACEs,>80%) for H2O2 production over a wide current density range of 5–400 mA/cm2, and H2O2 production rates as high as ~202 mg/h/cm2 could be obtained. Long-term stability test showed that the GDE maintained high ACEs (>85%) and low energy consumption (<10 kWh/kg H2O2) for H2O2 production for 42 d (~1000 h). However, the ACEs then decreased to ~70% in the following 4 days because water flooding of GDE pores considerably impeded oxygen transport at the late stage of the trial. Based on an electrode lifetime of 46 days, the overall cost for H2O2 production was estimated to be ~0.88 $/kg H2O2, including an electricity cost of 0.61 $/kg and an electrode capital cost of 0.27 $/kg. With a 9 cm2 GDE and 40 mA/cm2 current density, ~2–4 mg/L of H2O2 could be produced on site for the electro-peroxone treatment of a 1.2 m3/d groundwater flow, which considerably enhanced ibuprofen abatement compared with ozonation alone (~43%–59% vs. 7%). These findings suggest that electrochemical H2O2 production with GDEs holds great promise for the development of compact treatment technologies for decentralized water treatment at a household and community level.