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Frontiers of Environmental Science & Engineering

  • Cover Illustration

    2018, Vol.12  No.3

    The world is facing several challenges in the future. Due to world over-population and intensive use of the world’s resources, severe threats have been recognized. Threats such as climate changes, depletion of the planet resources has drawn immense attention on renewable energy. Biogas process has been recognized as a reliable and sustainable way of helping out these challenges. The biogas process has been known and applied for hundreds of years mainly for [Detail] ...

    Table of Contents

ISSN 2095-2201 (Print)
ISSN 2095-221X (Online)
Formerly Known as Frontiers of Environmental Science & Engineering in China
2017 Impact Factor: 1.961

, Volume 12 Issue 3

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FESE’s Best Papers of 2017
Front. Environ. Sci. Eng.. 2018, 12 (3): 17 .
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Erratum to: Electrochemical removal of nitrate in industrial wastewater
Dong Xu, Yang Li, Lifeng Yin, Yangyuan Ji, Junfeng Niu, Yanxin Yu
Front. Environ. Sci. Eng.. 2018, 12 (3): 16 .
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Hydrophilic/underwater superoleophobic graphene oxide membrane intercalated by TiO2 nanotubes for oil/water separation
Zhichao Wu, Chang Zhang, Kaiming Peng, Qiaoying Wang, Zhiwei Wang
Front. Environ. Sci. Eng.. 2018, 12 (3): 15 .
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GO/TiO2 membrane was prepared by assembling GO nanosheets and TiO2 nanotubes.

The intercalation of TiO2 nanotubes enlarged the space of GO interlayers and modified the surface morphology.

Hydrophilic/underwater superoleophobic property of GO/TiO2 membrane was obtained.

Water permeability, hydrophilicity, oleophobicity and antifouling ability of GO-based membrane were all enhanced by intercalating TiO2 nontubes.

Membrane technology for oil/water separation has received increasing attention in recent years. In this study, the hydrophilic/underwater superoleophobic membrane with enhanced water permeability and antifouling ability were fabricated by synergistically assembling graphene oxide(GO) nanosheets and titanium dioxide (TiO2) nanotubes for oil/water separation. GO/TiO2 membrane exhibits hydrophilic and underwater superoleophobic properties with water contact angle of 62° and under water oil contact angle of 162.8°. GO/TiO2 membrane shows greater water permeability with the water flux up to 531 L/(m2·h·bar), which was more than 5 times that of the pristine GO membrane. Moreover, GO/TiO2membrane had excellent oil/water separation efficiency and anti-oil-fouling capability, as oil residual in filtrate after separation was below 5 mg/L and flux recovery ratios were over 80%.The results indicate that the intercalation of TiO2 nanotubes into adjacent GO nanosheets enlarged the channel structure and modified surface topography of the obtained GO/TiO2 membranes, which improved the hydrophilicity, permeability and anti-oil-fouling ability of the membranes, enlightening the great prospects of GO/TiO2 membrane in oil-water treatment.

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Biogas and its opportunities—A review
Panagiotis G. Kougias, Irini Angelidaki
Front. Environ. Sci. Eng.. 2018, 12 (3): 14 .
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A comprehensive description of the biogas process is presented.

Main operational parameters influencing the biogas process are reviewed.

A historical overview of the biogas development is extensively presented.

The current status of anaerobic digestion for biogas production is discussed.

New horizons for exploitation and utilisation of biogas are proposed.

Biogas production is a well-established technology primarily for the generation of renewable energy and also for the valorization of organic residues. Biogas is the end product of a biological mediated process, the so called anaerobic digestion, in which different microorganisms, follow diverse metabolic pathways to decompose the organic matter. The process has been known since ancient times and was widely applied at domestic households providing heat and power for hundreds of years. Nowadays, the biogas sector is rapidly growing and novel achievements create the foundation for constituting biogas plants as advanced bioenergy factories. In this context, the biogas plants are the basis of a circular economy concept targeting nutrients recycling, reduction of greenhouse gas emissions and biorefinery purposes. This review summarizes the current state-of-the-art and presents future perspectives related to the anaerobic digestion process for biogas production. Moreover, a historical retrospective of biogas sector from the early years of its development till its recent advancements gives an outlook of the opportunities that are opening up for process optimisation.

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How aerosol direct effects influence the source contributions to PM2.5 concentrations over Southern Hebei, China in severe winter haze episodes
Litao Wang, Joshua S. Fu, Wei Wei, Zhe Wei, Chenchen Meng, Simeng Ma, Jiandong Wang
Front. Environ. Sci. Eng.. 2018, 12 (3): 13 .
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The aerosol direct effects result in a 3%–9% increase in PM2.5 concentrations over Southern Hebei.

These impacts are substantially different under different PM2.5 loadings.

Industrial and domestic contributions will be underestimated if ignoring the feedbacks.

Beijing-Tianjin-Hebei area is the most air polluted region in China and the three neighborhood southern Hebei cities, Shijiazhuang, Xingtai, and Handan, are listed in the top ten polluted cities with severe PM2.5 pollution. The objective of this paper is to evaluate the impacts of aerosol direct effects on air quality over the southern Hebei cities, as well as the impacts when considering those effects on source apportionment using three dimensional air quality models. The WRF/Chem model was applied over the East Asia and northern China at 36 and 12 km horizontal grid resolutions, respectively, for the period of January 2013, with two sets of simulations with or without aerosol-meteorology feedbacks. The source contributions of power plants, industrial, domestic, transportation, and agriculture are evaluated using the Brute-Force Method (BFM) under the two simulation configurations. Our results indicate that, although the increases in PM2.5 concentrations due to those effects over the three southern Hebei cities are only 3%–9% on montly average, they are much more significant under high PM2.5 loadings (~50 μg·m−3 when PM2.5 concentrations are higher than 400 μg m−3). When considering the aerosol feedbacks, the contributions of industrial and domestic sources assessed using the BFM will obviously increase (e.g., from 30%–34% to 32%–37% for industrial), especially under high PM2.5 loadings (e.g., from 36%–44% to 43%–47% for domestic when PM2.5>400 μg·m−3). Our results imply that the aerosol direct effects should not be ignored during severe pollution episodes, especially in short-term source apportionment using the BFM.

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Oxidation and biotoxicity assessment of microcystin-LR using different AOPs based on UV, O3 and H2O2
Siyi Lu, Naiyu Wang, Can Wang
Front. Environ. Sci. Eng.. 2018, 12 (3): 12 .
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MC-LR removal performances under different AOPs were compared systematically.

Higher removal efficiency and synergistic effects were obtained by combined process.

The acute biotoxicity raised in different degrees after oxidation.

Microcystin-LR attracts attention due to its high toxicity, high concentration and high frequency. The removal characteristics of UV/H2O2 and O3/H2O2 advanced oxidation processes and their individual process for MC-LR were investigated and compared in this study. Both the removal efficiencies and rates of MC-LR as well as the biotoxicity of degradation products was analyzed. Results showed that the UV/H2O2 process and O3/H2O2 were effective methods to remove MC-LR from water, and they two performed better than UV-, O3-, H2O2-alone processes under the same conditions. The effects of UV intensity, H2O2 concentration and O3 concentration on the removal performance were explored. The synergistic effects between UV and H2O2, O3 and H2O2 were observed. UV dosage of 1800 mJ·cm2 was required to remove 90% of 100 mg·L1 MC-LR, which amount significantly decreased to 500 mJ·cm2 when 1.7 mg·L1 H2O2 was added. 0.25 mg·L1 O3, or 0.125 mg·L1 O3 with 1.7 mg·L1 H2O2 was needed to reach 90% removal efficiency. Furthermore, the biotoxicity results about these UV/H2O2, O3/H2O2 and O3-alone processes all present rising trends with oxidation degree of MC-LR. Biotoxicity of solution, equivalent to 0.01 mg·L1 Zn2+, raised to 0.05 mg·L1 Zn2+ after UV/H2O2 or O3/H2O2 reaction. This phenomenon may be attributed to the aldehydes and ketones with small molecular weight generated during reaction. Advice about the selection of MC-LR removal methods in real cases was provided.

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Application and mechanism of polysaccharide extracted from Enteromorpha to remove nano-ZnO and humic acid in coagulation process
Jianzhang Sun, Baoyu Gao, Yuanxia Luo, Moxi Xue, Xing Xu, Qinyan Yue, Yan Wang
Front. Environ. Sci. Eng.. 2018, 12 (3): 11 .
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Green source Ep was extracted from marine alga waste.

The molecule model structure of Ep was studied and constructed.

PAC-Ep coagulation system improves the efficiency of removal efficiency.

Synergistic effects between NPs and HA make a big difference to enhance efficiency.

Mechanism is charge neutralization, hydrogen bonding and adsorbing-complexing

Enteromorpha polysaccharide (Ep) extracted from alga a novel green coagulant aid for nanoparticles (NPs) and heavy metal ions removal and the structure of EP was intensively studied in this study. The integration of Ep with polyaluminum chloride (PAC-Ep) coagulants exhibited higher coagulation performance than that of the polyaluminum chloride (PAC) because of the negatively charged NPs suspension and humic aid (HA) solution. Significant high removal efficiencies of dissolved organic matter (94.1%), turbidity (99.3%) and Zn ions (69.3%) were achieved by the PAC-Ep coagulants. The dual-coagulation properties of PAC-Ep for different pollutants was based on multiple mechanisms, including (i) Al3+ charge neutralization; (ii) hydroxy aluminum hydroxyl bridging formed polynuclearhydroxy complexes bridge and sweep colloidal particles; (iii) adsorption and bridging of Ep chain for the NPs and heavy metal ions. Results indicated that the destabilization of colloid was induced by the coexisting HA and higher removal was achieved as ions adsorption was enhance in the presence of HA complexation. On the basis of that, the extraction of polysaccharide is a promising candidate for its high coagulation performance in water treatment.

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Anaerobic ammonia oxidizing bacteria: ecological distribution, metabolism, and microbial interactions
Dawen Gao, Xiaolong Wang, Hong Liang, Qihang Wei, Yuan Dou, Longwei Li
Front. Environ. Sci. Eng.. 2018, 12 (3): 10 .
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The unique characteristics of anammox bacteria were reviewed.

Ecological distribution and nitrogen loss contributions were well documented.

Ecological interactions between anammox bacteria and other organisms were discussed.

Anammox (ANaerobic AMMonia OXidation) is a newly discovered pathway in the nitrogen cycle. This discovery has increased our knowledge of the global nitrogen cycle and triggered intense interest for anammox-based applications. Anammox bacteria are almost ubiquitous in the suboxic zones of almost all types of natural ecosystems and contribute significant to the global total nitrogen loss. In this paper, their ecological distributions and contributions to the nitrogen loss in marine, wetland, terrestrial ecosystems, and even extreme environments were reviewed. The unique metabolic mechanism of anammox bacteria was well described, including the particular cellular structures and genome compositions, which indicate the special evolutionary status of anammox bacteria. Finally, the ecological interactions among anammox bacteria and other organisms were discussed based on substrate availability and spatial organizations. This review attempts to summarize the fundamental understanding of anammox, provide an up-to-date summary of the knowledge of the overall anammox status, and propose future prospects for anammox. Based on novel findings, the metagenome has become a powerful tool for the genomic analysis of communities containing anammox bacteria; the metabolic diversity and biogeochemistry in the global nitrogen budget require more comprehensive studies.

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Effect of placement angles on wireless electrocoagulation for bipolar aluminum electrodes
Zhenlian Qi, Jinna Zhang, Shijie You
Front. Environ. Sci. Eng.. 2018, 12 (3): 9 .
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A new electrocoagulation process based on bipolar aluminum electrode is proposed.

The placement angles of bipolar electrode are key parameter.

The numerical simulations support the experimental results.

We in our previous study reported the wireless electrocoagulation (WEC) based on bipolar electrochemistry for water purification. One of the most important advantages of WEC is the omission of ohmic connection between bipolar electrode (BPE) and power supply, and thus the electrochemical reactions on BPE are driven by electric field in solution induced by driving electrodes. In this study, the impact of placement angle of bipolar aluminum electrode on WEC was investigated to provide a detailed analysis on the correlations between the bipolar electrode placement angle and bipolar electrocoagulation reactions. The results showed that the WEC cell with a horizontal BPE placed at 0° produced the maximum dissolved aluminum coagulant, accounting for 71.6 % higher than that with a vertical one placed at 90°. Moreover, the finite element simulations of current and potential distribution were carried out along the surface of BPE at different placement angles, revealing the mechanism of different BPE placement angles on aluminum dissolution rates in WEC system.

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Photolysis and photooxidation of typical gaseous VOCs by UV Irradiation: Removal performance and mechanisms
In-Sun Kang, Jinying Xi, Hong-Ying Hu
Front. Environ. Sci. Eng.. 2018, 12 (3): 8 .
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UV photodegradation of 27 typical VOCs was systematically investigated.

Contribution of photolysis and photooxidation to VOCs removal was identified.

Gaseous VOC could be partially converted to particles by 185/254 nm UV irradiation.

The mineralization and conversion of 27 VOCs by UV irradiation were reported.

Photodegradation by ultraviolet irradiation (UV) is increasingly applied in volatile organic compound (VOC) and odor gas treatments. In this study, 27 typical VOCs, including 11 hydrocarbons and 16 hydrocarbon derivatives, at 150–200 ppm in air and nitrogen gas were treated by a laboratory-scale UV reactor with 185/254 nm irradiation to systematically investigate their removal and conversion by UV irradiation. For the tested 27 VOCs, the VOC removal efficiencies in air were within the range of 13%–97% (with an average of 80%) at a retention time of 53 s, which showed a moderate positive correlation with the molecular weight of the VOCs (R = 0.53). The respective contributions of photolysis and photooxidation to VOC removal were identified for each VOC. According to the CO2 results, the mineralization rate of the tested VOCs was within the range of 9%–90%, with an average of 41% and were negatively correlated to the molecular weight (R = -0.63). Many of the tested VOCs exhibited high concentration particulate matters in the off-gases with a 3–283 mg/m3 PM10 range and a 2–40 mg/m3 PM2.5 range. The carbon balance of each VOC during UV irradiation was analyzed based on the VOC, CO2 and PM10 concentrations. Certain organic intermediates and 23–218 ppm ozone were also identified in the off-gases. Although the UV technique exhibited a high VOC removal efficiency, its drawbacks, specifically low mineralization, particulate matters production, and ozone emission, must be considered prior to its application in VOC gas treatments.

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Occurrence of veterinary antibiotics in struvite recovery from swine wastewater by using a fluidized bed
Zhi-Long Ye, Yujun Deng, Yaoyin Lou, Xin Ye, Shaohua Chen
Front. Environ. Sci. Eng.. 2018, 12 (3): 7 .
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Antibiotics in wastewater pose pharmacological threats to phosphorous recovery.

Recovered struvite particles possessed significantly antibiotic residues.

Smaller granules contained much more antibiotics than the larger ones.

Organic matters and struvite granulation process exerted significant impacts.

Recovering phosphorus from livestock wastewater has gained extensive attention. The residue of veterinary antibiotics in the wastewater may be present in the recovered products, thereby posing pharmacological threats to the agricultural planting and human health. This study investigated antibiotic occurrence in the struvite particles recovered from swine wastewater by using a fluidized bed. Results revealed that tetracyclines possessed significant residues in the struvite granules, with the values ranging from 195.2 mg·kg1 to 1995.0 mg·kg1. As for fluoroquinolones, their concentrations varied from 0.4 mg·kg1 to 1104.0 mg·kg1. Struvite particles were of various sizes and shapes and displayed different antibiotic adsorption capacities. The data also showed that the smaller granules contained much more antibiotics than the larger ones, indicating that the fluidized granulation process of struvite crystals plays an important role on the accumulation of antibiotics. For tetracyclines, organic matters and struvite adsorption exerted significant impacts on tetracyclines migration. The outcomes underscore the need to consider the residues of antibiotics in resource recovery from wastewater because they exert pharmacological impacts on the utilization of recovered products.

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Molecular analysis of bacterial community in the tap water with different water ages of a drinking water distribution system
Feng Wang, Weiying Li, Yue Li, Junpeng Zhang, Jiping Chen, Wei Zhang, Xuan Wu
Front. Environ. Sci. Eng.. 2018, 12 (3): 6 .
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The increase of water ages drove the deterioration of drinking water quality.

The relative abundance of Rhizobiales uniquely increase during distributing process.

Rhizobiales order was helpful for inhibiting corrosion under high chlorine level.

New disinfecting strategies should be developed to ensure drinking water safety.

Bacterial community in the drinking water distribution system (DWDS) was regulated by multiple environmental factors, many of which varied as a function of water age. In this study, four water samples with different water ages, including finished water (FW, 0 d) and tap water (TW) [TW1 (1 d), TW2(2 d) and TW3(3 d)], were collected along with the mains of a practical DWDS, and the bacterial community was investigated by high-throughput sequencing technique. Results indicated that the residual chlorine declined with the increase of water age, accompanied by the increase of dissolved organic matter, total bacteria counts and bacterial diversity (Shannon). For bacterial community composition, although Proteobacteria phylum (84.12%-97.6%) and Alphaproteobacteria class (67.42%-93.09%) kept dominate, an evident regular was observed at the order level. In detail, the relative abundance of most of other residual orders increased with different degrees from the start to the end of the DWDS, while a downward trend was uniquely observed in terms of Rhizobiales, who was inferred to be chlorine-resistant and be helpful for inhibiting pipes corrosion. Moreover, some OTUs were found to be closely related with species possessing pathogenicity and chlorine-resistant ability, so it was recommended that the use of agents other than chlorine or agents that can act synergically with chlorine should be developed for drinking water disinfection. This paper revealed bacterial community variations along the mains of the DWDS and the result was helpful for understanding bacterial ecology in the DWDS.

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Effectiveness of aerobic pretreatment of municipal solid waste for accelerating biogas generation during simulated landfilling
Munawar Ali, Junli Zhang, Roberto Raga, Maria Cristina Lavagnolo, Alberto Pivato, Xu Wang, Yuanyuan Zhang, Raffaello Cossu, Dongbei Yue
Front. Environ. Sci. Eng.. 2018, 12 (3): 5 .
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Effect of aerobic pretreatment of MSW on landfill gas generation was investigated.

Volatile solid (VS) loss of MSW is an effective and comparable indicator.

Chinese MSW requires at least a reduction of VS about 27% (w/w) prior to disposal.

Aerobic pretreatment of MSW reduced lag phase more than 90% before methanogenesis.

Aerobic pretreatment degree influences quantity of gas generation.

This study evaluates the effectiveness of aerobic pretreatment of municipal solid waste (MSW) on reducing lag phase and accelerating biogas generation. Aerobic pretreatment degree (APD) was determined on the basis of reduction in volatile solids (VS) on a wet weight basis. In this study, intermittent aeration (IA) was applied to three reactors as a main aeration mode; since a single reactor was operated under continuous aeration mode. However, the purpose of the experiment was to reduce VS content of waste, irrespective of the comparison between aeration modes. Fresh MSW was first pretreated aerobically with different aeration rates (10, 40, 60 and 85 L/min/m3) for the period of 30–50 days, resulting in VS-loss equivalent to 20%, 27%, 38% and 53% on w/w basis for the wastes A1, A2, A3 and A4, respectively. The cumulative biogas production, calculated based on the modified Gompertz model were 384, 195, 353, 215, and 114 L/kg VS for the wastes A0, A1, A2, A3 and A4, respectively. Untreated waste (A0) showed a long lag phase; whereas the lag phases of pretreated MSW were reduced by more than 90%. Aerobically pretreated wastes reached stable methanogenic phase within 41 days compared to 418 days for untreated waste. The waste mass decreased by about 8% to 27% compared to untreated MSW, indicative that even more MSW could be placed in the same landfill. The study confirmed the effectiveness of aerobic pretreatment of MSW prior to landfilling on reducing lag phase and accelerating biogas generation.

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Effects of eggshell addition on calcium-deficient acid soils contaminated with heavy metals
Weiqi Luo, Yanping Ji, Lu Qu, Zhi Dang, Yingying Xie, Chengfang Yang, Xueqin Tao, Jianmin Zhou, Guining Lu
Front. Environ. Sci. Eng.. 2018, 12 (3): 4 .
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The eggshell was used to remediate the contaminated soil by heavy metals.

The eggshell addition decreased the available state of the heavy metals.

The available calcium in the soil increased due to eggshell addition.

The efficiency was investigated in different moisture conditions.

In this study, effects of water conditions (flooded, wet, or dry) and eggshell dosages (0, 0.1, 1.0, and 10.0 g/kg soil, respectively) on pH variation, content of unavailable state of heavy metals, form of heavy metals, and available nutritious element calcium (Ca) in acid soils contaminated with heavy metals were investigated, respectively. The soil samples were continuously cultivated indoors and analyzed by toxicity characteristic leaching procedure and community bureau of reference (BCR) sequential extraction procedure. The results showed that the addition of eggshell could effectively improve the pH of acid soil and increase it to neutral level. Moreover, the contents of unavailable state of heavy metals Cu, Zn, and Cd increased significantly. Furthermore, when the soil was cultivated under the flooded condition with 1.0 g/kg eggshell, the unavailable state of Cu, Zn, and Cd increased the most, and these heavy metals were transformed into residual state. On the other hand, the amount of available state of Ca increased to 432.19 from 73.34 mg/kg with the addition of 1.0 g/kg eggshell, which indicated that the addition of eggshell dramatically improved the available state of Ca. Therefore, eggshell could ameliorate the soil environment as it led to the decrease of available heavy metals and improvement of fertilization effectively. In a word, this study indicates that the addition of eggshell would be a new potential method for remediation of acid field soils contaminated with heavy metals.

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End-of-life batteries management and material flow analysis in South Korea Collection
Hyunhee Kim, Yong-Chul Jang, Yeonjung Hwang, Youngjae Ko, Hyunmyeong Yun
Front. Environ. Sci. Eng.. 2018, 12 (3): 3 .
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Analysis of collection and recycling system of end-of-life batteries was examined.

Relatively limited fractions of portable batteries were collected by EPR system.

More effective and diverse collection pathways should be developed.

Consumers increasingly have worn-out batteries as electrical and electronic equipment with new technical developments are introduced into the market and quickly replace older models. As a result, large amounts of end-of-life (EOL) or waste batteries are generated. Such batteries may contain a variety of materials that includes valuable resources as well as toxic elements. Thus, the proper recycling and management of batteries is very important from the perspective of resource conservation and environmental effect. The collection and recycling of EOL batteries is relatively low in South Korea compared to other countries, although an extended producer responsibility (EPR) policy was adopted for battery recycling in 2003. In this study, the management and material flow of EOL batteries is presented to determine potential problems and quantitative flow, based on literature review, site visits to battery recycling facilities, and interviews with experts in the Korea Battery Recycling Association (KBRA), manufacturers, and regulators in government. The results show that approximately 558 tons of manganese-alkaline batteries, the largest fraction among recycling target items, was disposed in landfills or incinerators in 2015, while approximately 2,000 tons of batteries were recovered at a recycling facility by simple sorting and crushing processes. By raising environmental awareness, more diverse and effective collection systems could be established for consumers to easily dispose of EOL batteries in many places. Producers, retailers and distributors in South Korea should also play an important role in the collection of EOL batteries from consumers. Lithium-ion batteries from many electronic devices must be included in the EPR system for resource recovery.

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Current state and future perspectives of sewer networks in urban China
Dong Huang, Xiuhong Liu, Songzhu Jiang, Hongchen Wang, Junyan Wang, Yuankai Zhang
Front. Environ. Sci. Eng.. 2018, 12 (3): 2 .
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Sewer network construction is insufficient in China currently.

The management for sewer network is very disordered in China.

Maintenance is far from enough for current sewer networks in China.

China’s top priority for sewer networks is to elevate its overall performance.

The new technical route is an optimal option for sewer maintenance in China.

Chinese authorities and the public have largely ignored sewer networks; however, various problems are emerging nationwide with the increase construction of new sewers. The current state of sewer network construction, administration, and maintenance in China is comprehensively reviewed in this study. Serving about 444 million people, 511,200 km of sewer lines are located in urban areas. In 2014, $7 billion was invested in sewer network construction. However, both the sewer pervasion rate and the per capita sewer length were significantly lower than those in developed countries. Sewer administrative agencies in local governments are uncoordinated. Laws, regulations, and standards are incomplete, and some practices are unscientific. The future situation of sewer maintenance is extremely grim because sewer corrosion control measures have not been launched. Moreover, inspection and rehabilitation chiefly rely on traditional approaches. In contrast, the overall market share of innovative technologies is very low owing to high cost, funds shortage, and technical limitations. Approaches such as liner inversion cured-in-place pipe, pull-in ultraviolet light cured liners, and spiral wound lining are applied mostly in economically developed regions. According to status and problem analyses, China’s top priority will be to conduct aggressive maintenance work in sewer networks in the future. New technical route, corrosion control - periodic visualized inspection - trenchless rehabilitation, could be the best option for future sewer maintenance in China. Instructions and opportunities for applying this technical route are discussed in detail in this study. Finally, additional factors in the development of sewer networks in China are suggested.

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Energy reduction of a submerged membrane bioreactor using a polytetrafluoroethylene (PTFE) hollow-fiber membrane
Taro Miyoshi, Thanh Phong Nguyen, Terumi Tsumuraya, Hiromu Tanaka, Toru Morita, Hiroki Itokawa, Toshikazu Hashimoto
Front. Environ. Sci. Eng.. 2018, 12 (3): 1 .
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The fiber length and packing density of the PTFE membrane element were increased.

The MBR was stably operated under an SADm of 0.13 m3·m-2·hr-1.

Specific energy consumption was estimated to be less than 0.4 kWh·m-3.

In this study, we modified a polytetrafluoroethylene (PTFE) hollow-fiber membrane element used for submerged membrane bioreactors (MBRs) to reduce the energy consumption during MBR processes. The high mechanical strength of the PTFE membrane made it possible to increase the effective length of the membrane fiber from 2 to 3 m. In addition, the packing density was increased by 20% by optimizing the membrane element configuration. These modifications improve the efficiency of membrane cleaning associated with aeration. The target of specific energy consumption was less than 0.4 kWh·m-3 in this study. The continuous operation of a pilot MBR treating real municipal wastewater revealed that the MBR utilizing the modified membrane element can be stably operated under a specific air demand per membrane surface area (SADm) of 0.13 m3·m-2·hr-1 when the daily-averaged membrane fluxes for the constant flow rate and flow rate fluctuating modes of operation were set to 0.6 and 0.5 m3·m-2·d-1, respectively. The specific energy consumption under these operating conditions was estimated to be less than 0.37 kWh·m-3. These results strongly suggest that operating an MBR equipped with the modified membrane element with a specific energy consumption of less than 0.4 kWh·m-3 is highly possible.

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