Frontiers of Environmental Science & Engineering

ISSN 2095-2201

ISSN 2095-221X(Online)

CN 10-1013/X

2018 Impact Factor: 3.883

Cover Story   2019, Volume 13 Issue 6
The unprecedented double pressures of environmental pollution and resource deficiency and the growing innovation ability in China together are now driving a fundamental change in the wastewater treatment paradigm in this country. Despite of rapid development over the past 40 years, China’s wastewater sector has been following the development mode o [Detail] ...
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, Volume 13 Issue 6

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G-CNTs/PVDF mixed matrix membranes with improved antifouling properties and filtration performance
Xiaoyan Guo, Chunyu Li, Chenghao Li, Tingting Wei, Lin Tong, Huaiqi Shao, Qixing Zhou, Lan Wang, Yuan Liao
Front. Environ. Sci. Eng.. 2019, 13 (6): 81-.

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A novel nanocomposite OMWCNT-A-GO was synthesized by conjugating OMWCNT and GO.

The P-OMWCNT-A-GO membrane was fabricated by non-solvent induced phase inversion.

The P-OMWCNT-A-GO exhibits the best water flux, BSA rejection and flux recovery.

It should be due to the enhanced membrane pore size, porosity and hydrophilicity.

Although carbon nanomaterials have been widely used as effective nanofillers for fabrication of mixed matrix membranes (MMMs) with outstanding performances, the reproducibility of the fabricated MMMs is still hindered by the non-homogenous dispersion of these carbon nanofillers in membrane substrate. Herein, we report an effective way to improve the compatibility of carbon-based nanomaterials with membrane matrixes. By chemically conjugating the oxidized CNTs (o-CNTs) and GO using hexanediamine as cross-linker, a novel carbon nanohybrid material (G-CNTs) was synthesized, which inherited both the advanced properties of multi-walled carbon nanotubes (CNTs) and graphene oxide (GO). The G-CNTs incorporated polyvinylidene fluoride (PVDF) MMMs (G-CNTs/PVDF) were fabricated via a non-solvent induced phase separation (NIPS) method. The filtration and antifouling performances of G-CNTs/PVDF were evaluated using distillate water and a 1 g/L bovine serum albumin (BSA) aqueous solution under 0.10 MPa. Compared to the MMMs prepared with o-CNTs, GO, the physical mixture of o-CNTs and GO and pure PVDF membrane, the G-CNTs/PVDF membrane exhibited the highest water flux up to 220 L/m2/h and a flux recovery ratio as high as 90%, as well as the best BSA rejection rate. The excellent performances should be attributed to the increased membrane pore size, porosity and hydrophilicity of the resulted membrane. The successful synthesis of the novel nanohybrid G-CNTs provides a new type of nanofillers for MMMs fabrication.

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The impact of ultrasonic treatment on activity of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria in activated sludge
Siqi Li, Min Zheng, Shuang Wu, Yu Xue, Yanchen Liu, Chengwen Wang, Xia Huang
Front. Environ. Sci. Eng.. 2019, 13 (6): 82-.

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Conditions for ultrasonic treatment to achieve partial nitritation are optimized.

Ultrasound reduces metabolic activity and releases intracellular metabolites.

Mechanical shearing is essential to inhibit nitrite oxidation.

The ultrasonic treatment of sludge has been considered as an effective method to facilitate the partial nitritation of municipal sewage. This study aims to reveal the effects of ultrasound on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). The impact factors including ultrasonic irradiation time and intensity, sludge concentration, thermal effect and released free radicals were studied. The maximized difference between the changes in AOB and NOB activities were obtained with 10 g mixed liquor suspended solids (MLSS)/L, using 0.9 kJ/mL ultrasonic energy density and 12 h interval time. The increased ultrasonic intensity destroyed the floc structure of activated sludge, increased the microbial death, and decreased the cellular ATP level. Further, the mechanism exploration indicated that the mechanical shearing could be a critical factor in achieving the nitritation with inhibitory effect on nitrite oxidation.

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Characteristic and correlation analysis of influent and energy consumption of wastewater treatment plants in Taihu Basin
Luxi Zou, Huaibo Li, Shuo Wang, Kaikai Zheng, Yan Wang, Guocheng Du, Ji Li
Front. Environ. Sci. Eng.. 2019, 13 (6): 83-.

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Poor biodegradability and insufficient carbon source are discovered from influent.

Influent indices presented positively normal distribution or skewed distribution.

Average energy consumption of WWTPs in Taihu Basin was as high as 0.458 kWh/m3.

Energy consumption increases with the increase in influent volume and COD reduction.

The total energy consumption decreases with the NH3-N reduction.

The water quality and energy consumption of wastewater treatment plants (WWTPs) in Taihu Basin were evaluated on the basis of the operation data from 204 municipal WWTPs in the basin by using various statistical methods. The influent ammonia nitrogen (NH3-N) and total nitrogen (TN) of WWTPs in Taihu Basin showed normal distribution, whereas chemical oxygen demand (COD), biochemical oxygen demand (BOD5), suspended solid (SS), and total phosphorus (TP) showed positively skewed distribution. The influent BOD5/COD was 0.4%–0.6%, only 39.2% SS/BOD5 exceeded the standard by 36.3%, the average BOD5/TN was 3.82, and the probability of influent BOD5/TP>20 was 82.8%. The average energy consumption of WWTPs in Taihu Basin in 2017 was 0.458 kWh/m3. The specific energy consumption of WWTPs with a daily treatment capacity of more than 5 × 104 m3 in Taihu Basin was stable at 0.33 kWh/m3. A power function relationship was observed between the reduction in COD and NH3-N and the specific energy consumption of pollutant reduction, and the higher the pollutant reduction is, the lower the specific energy consumption of pollutant reduction presents. In addition, a linear relationship existed between the energy consumption of WWTPs and the specific energy consumption of influent volume and pollutant reduction. Therefore, upgrading and operation with less energy consumption of WWTPs is imperative and the suggestions for Taihu WWTPs based on stringent discharge standard are proposed in detail.

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Anaerobic biodegradation of trimethoprim with sulfate as an electron acceptor
Bin Liang, Deyong Kong, Mengyuan Qi, Hui Yun, Zhiling Li, Ke Shi, E Chen, Alisa S. Vangnai, Aijie Wang
Front. Environ. Sci. Eng.. 2019, 13 (6): 84-.

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Anaerobic biodegradation of trimethoprim (TMP) coupled with sulfate reduction.

Demethylation of TMP is the first step in the acclimated microbial consortia.

The potential degraders and fermenters were enriched in the acclimated consortia.

Activated sludge and river sediment had similar core microbiomes.

Trimethoprim (TMP) is an antibiotic frequently detected in various environments. Microorganisms are the main drivers of emerging antibiotic contaminant degradation in the environment. However, the feasibility and stability of the anaerobic biodegradation of TMP with sulfate as an electron acceptor remain poorly understood. Here, TMP-degrading microbial consortia were successfully enriched from municipal activated sludge (AS) and river sediment (RS) as the initial inoculums. The acclimated consortia were capable of transforming TMP through demethylation, and the hydroxyl-substituted demethylated product (4-desmethyl-TMP) was further degraded. The biodegradation of TMP followed a 3-parameter sigmoid kinetic model. The potential degraders (Acetobacterium, Desulfovibrio, Desulfobulbus, and unidentified Peptococcaceae) and fermenters (Lentimicrobium and Petrimonas) were significantly enriched in the acclimated consortia. The AS- and RS-acclimated TMP-degrading consortia had similar core microbiomes. The anaerobic biodegradation of TMP could be coupled with sulfate respiration, which gives new insights into the antibiotic fate in real environments and provides a new route for the bioremediation of antibiotic-contaminated environments.

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Effects of Al3+ on pollutant removal and extracellular polymeric substances (EPS) under anaerobic, anoxic and oxic conditions
Lanhe Zhang, Jing Zheng, Jingbo Guo, Xiaohui Guan, Suiyi Zhu, Yanping Jia, Jian Zhang, Xiaoyu Zhang, Haifeng Zhang
Front. Environ. Sci. Eng.. 2019, 13 (6): 85-.

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The highest removal efficiencies of COD and TN were achieved under 10 mg/L of Al3+.

The highest TP removal efficiency occurred under 30 mg/L of Al3+.

EPS, PS and PN concentrations increased with the addition of Al3+.

Sludge properties significantly changed with the addition of Al3+.

Aluminum ions produced by aluminum mining, electrolytic industry and aluminum-based coagulants can enter wastewater treatment plants and interact with activated sludge. They can subsequently contribute to the removal of suspended solids and affect activated sludge flocculation, as well as nitrogen and phosphorus removal. In this study, the effects of Al3+ on pollutant removal, sludge flocculation and the composition and structure of extracellular polymeric substances (EPS) were investigated under anaerobic, anoxic and oxic conditions. Results demonstrated that the highest chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies were detected for an Al3+ concentration of 10 mg/L. In addition, the maximal dehydrogenase activity and sludge flocculation were also observed at this level of Al3+. The highest removal efficiency of total phosphorus (TP) was achieved at an Al3+ concentration of 30 mg/L. The flocculability of sludge in the anoxic zone was consistently higher than that in the anaerobic and oxic zones. The addition of Al3+ promoted the secretion of EPS. Tryptophan-like fluorescence peaks were detected in each EPS layer in the absence of Al3+. At the Al3+ concentration of 10 mg/L, fulvic acid and tryptophan fluorescence peaks began to appear, while the majority of protein species and the highest microbial activity were also detected. Low Al3+ concentrations (<10 mg/L) could promote the removal efficiencies of COD and TN, yet excessive Al3+ levels (>10 mg/L) weakened microbial activity. Higher Al3+ concentrations (>30 mg/L) also inhibited the release of phosphorus in the anaerobic zone by reacting with PO43-.

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Inhibition of bromate formation by reduced graphene oxide supported cerium dioxide during ozonation of bromide-containing water
Bei Ye, Zhuo Chen, Xinzheng Li, Jianan Liu, Qianyuan Wu, Cheng Yang, Hongying Hu, Ronghe Wang
Front. Environ. Sci. Eng.. 2019, 13 (6): 86-.

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GO or RGO promotes bromate formation during ozonation of bromide-containing water.

CeO2/RGO significantly inhibits bromate formation compared to RGO during ozonation.

CeO2/RGO shows an enhancement on DEET degradation efficiency during ozonation.

Ozone (O3) is widely used in drinking water disinfection and wastewater treatment. However, when applied to bromide-containing water, ozone induces the formation of bromate, which is carcinogenic. Our previous study found that graphene oxide (GO) can enhance the degradation efficiency of micropollutants during ozonation. However, in this study, GO was found to promote bromate formation during ozonation of bromide-containing waters, with bromate yields from the O3/GO process more than twice those obtained using ozone alone. The promoted bromate formation was attributed to increased hydroxyl radical production, as confirmed by the significant reduction (almost 75%) in bromate yield after adding t-butanol (TBA). Cerium oxide (less than 5 mg/L) supported on reduced GO (xCeO2/RGO) significantly inhibited bromate formation during ozonation compared with reduced GO alone, and the optimal Ce atomic percentage (x) was determined to be 0.36%, achieving an inhibition rate of approximately 73%. Fourier transform infrared (FT-IR) spectra indicated the transformation of GO into RGO after hydrothermal treatment, and transmission electron microscope (TEM) results showed that CeO2 nanoparticles were well dispersed on the RGO surface. The X-ray photoelectron spectroscopy (XPS) spectra results demonstrated that the Ce3+/Ce4+ ratio in xCeO2/RGO was almost 3‒4 times higher than that in pure CeO2, which might be attributed to the charge transfer effect from GO to CeO2. Furthermore, Ce3+ on the xCeO2/RGO surface could quench Br and BrO to further inhibit bromate formation. Meanwhile, 0.36CeO2/RGO could also enhance the degradation efficiency of N,N-diethyl-m-toluamide (DEET) in synthetic and reclaimed water during ozonation.

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Rapid control of black and odorous substances from heavily-polluted sediment by oxidation: Efficiency and effects
Kun Li, Min Yang, Jianfeng Peng, Ruiping Liu, Tista Prasai Joshi, Yaohui Bai, Huijuan Liu
Front. Environ. Sci. Eng.. 2019, 13 (6): 87-.

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Oxidants were proposed to rapidly control black and odorous substances in sediments.

NaClO and KMnO4 had excellent efficiency to remove black and odorous substances.

NaClO dramatically accelerated the release of organics, NH4+-N, P, and heavy-metals.

Moderate oxidation had a limited effect on microbial communities.

NaClO of 0.2 mmol/g was viewed to be the optimum option.

The control of black and odorous substances in sediments is of crucial importance to improve the urban ecological landscape and to restore water environments accordingly. In this study, chemical oxidation by the oxidants NaClO, H2O2, and KMnO4 was proposed to achieve rapid control of black and odorous substances in heavily-polluted sediments. Results indicate that NaClO and KMnO4 are effective at removing Fe(II) and acid volatile sulfides. The removal efficiencies of Fe(II) and AVS were determined to be 45.2%, 94.1%, and 93.7%, 89.5% after 24-h exposure to NaClO and KMnO4 at 0.2 mmol/g, respectively. Additionally, rapid oxidation might accelerate the release of pollutants from sediment. The release of organic matters and phosphorus with the maximum ratios of 22.1% and 51.2% was observed upon NaClO oxidation at 0.4 mmol/g. Moreover, the introduction of oxidants contributed to changes in the microbial community composition in sediment. After oxidation by NaClO and KMnO4 at 0.4 mmol/g, the Shannon index decreased from 6.72 to 5.19 and 4.95, whereas the OTU numbers decreased from 2904 to 1677 and 1553, respectively. Comparatively, H2O2 showed a lower effect on the removal of black and odorous substances, pollutant release, and changes in sediment microorganisms. This study illustrates the effects of oxidant addition on the characteristics of heavily polluted sediments and shows that chemical oxidants may be an option to achieve rapid control of black and odorous substances prior to remediation of water environments.

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Municipal wastewater treatment in China: Development history and future perspectives
Jiuhui Qu, Hongchen Wang, Kaijun Wang, Gang Yu, Bing Ke, Han-Qing Yu, Hongqiang Ren, Xingcan Zheng, Ji Li, Wen-Wei Li, Song Gao, Hui Gong
Front. Environ. Sci. Eng.. 2019, 13 (6): 88-.

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The history of China’s municipal wastewater management is revisited.

The remaining challenges in wastewater sector in China are identified.

New concept municipal wastewater treatment plants are highlighted.

An integrated plant of energy, water and fertilizer recovery is envisaged.

China has the world’s largest and still growing wastewater sector and water market, thus its future development will have profound influence on the world. The high-speed development of China’s wastewater sector over the past 40 years has forged its global leading treatment capacity and innovation ability. However, many problems were left behind, including underdeveloped sewers and sludge disposal facilities, low sustainability of the treatment processes, questionable wastewater treatment plant (WWTP) effluent discharge standards, and lacking global thinking on harmonious development between wastewater management, human society and the nature. Addressing these challenges calls for fundamental changes in target design, policy and technologies. In this mini-review, we revisit the development history of China’s municipal wastewater management and identify the remaining challenges. Also, we highlight the future needs of sustainable development and exploring China’s own wastewater management path, and outlook the future from several aspects including targets of wastewater management, policies and technologies, especially the new concept WWTP. Furthermore, we envisage the establishment of new-generation WWTPs with the vision of turning WWTP from a site of pollutant removal into a plant of energy, water and fertilizer recovery and an integrated part urban ecology in China.

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Advances in Fe(III) bioreduction and its application prospect for groundwater remediation: A review
Yu Jiang, Beidou Xi, Rui Li, Mingxiao Li, Zheng Xu, Yuning Yang, Shaobo Gao
Front. Environ. Sci. Eng.. 2019, 13 (6): 89-.

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Microbial Fe(III) reduction is closely related to the fate of pollutants.

Bioavailability of crystalline Fe(III) oxide is restricted due to thermodynamics.

Amorphous Fe(III) (hydro)oxides are more bioavailable.

Enrichment and incubation of Fe(III) reducing bacteria are significant.

Microbial Fe(III) reduction is a significant driving force for the biogeochemical cycles of C, O, P, S, N, and dominates the natural bio-purification of contaminants in groundwater (e.g., petroleum hydrocarbons, chlorinated ethane, and chromium). In this review, the mechanisms and environmental significance of Fe(III) (hydro)oxides bioreduction are summarized. Compared with crystalline Fe(III) (hydro)oxides, amorphous Fe(III) (hydro)oxides are more bioavailable. Ligand and electron shuttle both play an important role in microbial Fe(III) reduction. The restrictive factors of Fe(III) (hydro)oxides bioreduction should be further investigated to reveal the characteristics and mechanisms of the process. It will improve the bioavailability of crystalline Fe(III) (hydro)oxides and accelerate the anaerobic oxidation efficiency of the reduction state pollutants. Furthermore, the approach to extract, culture, and incubate the functional Fe(III) reducing bacteria from actual complicated environment, and applying it to the bioremediation of organic, ammonia, and heavy metals contaminated groundwater will become a research topic in the future. There are a broad application prospects of Fe(III) (hydro)oxides bioreduction to groundwater bioremediation, which includes the in situ injection and permeable reactive barriers and the innovative Kariz wells system. The study provides an important reference for the treatment of reduced pollutants in contaminated groundwater.

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Identifying human-induced influence on microbial community: A comparative study in the effluent-receiving areas in Hangzhou Bay
Yuhan Zheng, Zhiguo Su, Tianjiao Dai, Feifei Li, Bei Huang, Qinglin Mu, Chuanping Feng, Donghui Wen
Front. Environ. Sci. Eng.. 2019, 13 (6): 90-.

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Microbial compositions showed high differences in two study areas.

COD was the key anthropogenic indicator in the coastal wastewater disposal area.

Distinctive microbes capable of degrading toxic pollutants were screened.

Microbial communities in effluent-receiving areas followed “niche theory”.

Microbial community structure is affected by both natural processes and human activities. In coastal area, anthropegenetic activity can usually lead to the discharge of the effluent from wastewater treatment plant (WWTP) to sea, and thus the water quality chronically turns worse and marine ecosystem becomes unhealthy. Microorganisms play key roles in pollutants degradation and ecological restoration; however, there are few studies about how the WWTP effluent disposal influences coastal microbial communities. In this study, sediment samples were collected from two WWTP effluent-receiving areas (abbreviated as JX and SY) in Hangzhou Bay. First, based on the high-throughput sequencing of 16S rRNA gene, microbial community structure was analyzed. Secondly, several statistical analyses were conducted to reveal the microbial community characteristics in response to the effluent disposal. Using PCoA, the significant difference of in microbial community structure was determined between JX and SY; using RDA, water COD and temperature, and sediment available phosphate and ammonia nitrogen were identified as the key environmental factors for the community difference; using LDA effect size analysis, the most distinctive microbes were found and their correlations with environmental factors were investigated; and according to detrended beta-nearest-taxon-index, the sediment microbial communities were found to follow “niche theory”. An interesting and important finding was that in SY that received more and toxic COD, many distinctive microbes were related to the groups that were capable of degrading toxic organic pollutants. This study provides a clear illustration of eco-environmental deterioration under the long-term human pressure from the view of microbial ecology.

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Recovery of Ni(II) from real electroplating wastewater using fixed-bed resin adsorption and subsequent electrodeposition
Tong Li, Ke Xiao, Bo Yang, Guilong Peng, Fenglei Liu, Liyan Tao, Siyuan Chen, Haoran Wei, Gang Yu, Shubo Deng
Front. Environ. Sci. Eng.. 2019, 13 (6): 91-.

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Resin adsorption and subsequent electrodeposition were used for nickel recovery.

Treated wastewater can meet the Electroplating Pollutant Discharge Standard.

The spent resin is completely regenerated by 3 BV of 4% HCl solution.

95.6% of nickel in concentrated eluent was recovered by electrodeposition.

Effective recovery of high-value heavy metals from electroplating wastewater is of great significance, but recovering nickel ions from real electroplating wastewater as nickel sheet has not been reported. In this study, the pilot-scale fixed-bed resin adsorption was conducted to recover Ni(II) ions from real nickel plating wastewater, and then the concentrated Ni(II) ions in the regenerated solution were reduced to nickel sheet via electrodeposition. A commercial cation-exchange resin was selected and the optimal resin adsorption and regeneration conditions were investigated. The resin exhibited an adsorption capacity of 63 mg/g for Ni(II) ions, and the average amount of treated water was 84.6 bed volumes (BV) in the pilot-scale experiments. After the adsorption by two ion-exchange resin columns in series and one chelating resin column, the concentrations of Ni(II) in the treated wastewater were below 0.1 mg/L. After the regeneration of the spent resin using 3 BV of 4% (w/w) HCl solution, 1.5 BV of concentrated neutral nickel solution (>30 g/L) was obtained and used in the subsequent electrodeposition process. Using the aeration method, alkali and water required in resin activation process were greatly reduced to 2 BV and 3 BV, respectively. Under the optimal electrodeposition conditions, 95.6% of Ni(II) in desorption eluent could be recovered as the elemental nickel on the cathode. The total treatment cost for the resin adsorption and regeneration as well as the electrodeposition was calculated.

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A novel sequence batch membrane carbonation photobioreactor developed for microalgae cultivation
Caiyun Hou, Sen Qiao, Yue Yang, Jiti Zhou
Front. Environ. Sci. Eng.. 2019, 13 (6): 92-.

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A novel SBM-C-PBR was constructed for microalgae cultivation.

Membrane fouling was greatly mitigated by membrane carbonation.

NH4+ and P removal rates were around 80% in SBM-C-PBR.

Biomass was completely retained by membrane.

In this study, a novel sequence batch membrane carbonation photobioreactor was developed for microalgae cultivation. Herein, membrane module was endowed functions as microalgae retention and CO2 carbonation. The results in the batch experiments expressed that the relatively optimal pore size of membranes was 30 nm, photosynthetically active radiation was 36 W/m2 and the CO2 concentration was 10% (v/v). In long-term cultivation, the microalgal concentration separately accumulated up to 1179.0 mg/L and 1296.4 mg/L in two periods. The concentrations of chlorophyll a, chlorophyll b and carotenoids were increased about 23.2, 14.9 and 6.3 mg/L respectively in period I; meanwhile, the accumulation was about 25.0, 14.5, 6.6 mg/L respectively in the period II. Furthermore, the pH was kept about 5.5–7.5 due to intermittent carbonation mode, which was suitable for the growth of microalgae. Transmembrane pressure (TMP) was only increased by 0.19 and 0.16 bar in the end of periods I and II, respectively. The pure flux recovered to 75%–80% of the original value by only hydraulic cleaning. Scanning electron microscope images also illustrated that carbonation through membrane module could mitigate fouling levels greatly.

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Trophic mode and organics metabolic characteristic of fungal community in swine manure composting
Jing Peng, Ke Wang, Xiangbo Yin, Xiaoqing Yin, Mengfei Du, Yingzhi Gao, Philip Antwi, Nanqi Ren, Aijie Wang
Front. Environ. Sci. Eng.. 2019, 13 (6): 93-.

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Fungal trophic modes and substrates utilization ability was observed in composting.

Fungi had the higher diversity and more trophic types in thermophilic phase.

Fungi had the higher metabolic potential in fresh swine manure and mature production.

Redox potential, organics and moisture are main factors impacting fungal community.

Composting reduced pathogenic fungi and enrich dung saprotroph fungi in swine manure.

The succession of fungal community, trophic mode and metabolic characteristics were evaluated in 60 days composting of swine manure by high-throughput sequencing, FUNGuild and Biolog method, respectively. The result showed that the fungal community diversity reached to the highest level (76 OTUs) in the thermophilic phase of composting, then sustained decline to 15 OTUs after incubation. There were 10 fungal function groups in the raw swine manure. Pathotroph-saprotroph fungi reached to 15.91% on Day-10 but disappeared on Day-60. Dung saprotroph-undefined saprotroph fungi grown from 0.19% to 52.39% during the treatment. The fungal community had more functional groups but the lower substrate degradation rates in the thermophilic phase. The fungal communities on Day-0 and Day-60 had the highest degradation rates of amino acids and polymers, respectively. Redundancy analysis showed that ORP (49.6%), VS/Ash (45.3%) and moisture (39.2%) were the main influence factors on the succession of fungal community in the swine manure composting process.

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Effective enrichment of Zn from smelting wastewater via an integrated Fe coagulation and hematite precipitation method
Zhan Qu, Ting Su, Yu Chen, Xue Lin, Yang Yu, Suiyi Zhu, Xinfeng Xie, Mingxin Huo
Front. Environ. Sci. Eng.. 2019, 13 (6): 94-.

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98.5% Zn was enriched from Zn-bearing smelting wastewater.

99.5% Fe was hydrothermally precipitated into hematite nanoparticles.

Highly purified hematite nanoparticles were obtained.

The residual Zn was 2169 mg/L, 290 times of that in smelting wastewater.

Coagulation is commonly applied to treat Zn-bearing wastewater from smelting industries (smelting wastewater), and thus the Zn-bearing sludge was considerably produced, which should be solidified before safety disposal. Herein, we demonstrated a novel approach to recycle Zn effectively from smelting wastewater via an integrated Fe coagulation and hematite precipitation method. First, smelting wastewater was coagulated by adding ferric chloride to generate Fe/Zn-bearing sludge (sludge for short). Secondly, the sludge was dissolved to generate an acid solution containing 2.2 g/L of Zn and 39.2 g/L of Fe. Thirdly, the Fe/Zn-bearing solution was hydrothermally treated, and 89% of Fe was eliminated to highly purified hematite block, whereas the percentage of Zn lost was below 1.1%. Finally, the hematite precipitates were collected, and the supernatant was hydrothermally treated again with the addition of glucose. When the molar ratio of glucose to Fe in the supernatant was 1.5, over 99.5% of Fe was precipitated in hematite nanoparticles with a diameter of 10–100 nm, and the residual Fe was 21.5 mg/L. The loss of Zn was below 0.4%, and the residual Zn in the solution was 2169 mg/L, 290 times of that in the smelting wastewater. The major mechanism for Fe removal was the hydrolysis of ferric nitrate into hematite, which was promoted by nitrate consumption in glucose oxidation. This paper is the first report of an environment-friendly method for enriching Zn without generating any waste.

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