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Frontiers of Environmental Science & Engineering

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    2020, Vol.14  No.6

    Microplastics (MPs) have been recognized as a new class of emerging contaminants in recent years. They not only directly impact aquatic organisms, but also indirectly impact these organisms by interacting with background toxins in the environment. Moreover, under realistic environmental conditions, algae, a natural food for aquatic organisms, may alter the toxicity pattern related to MPs. In this research, we first examined the toxicity of MPs alone, and t [Detail] ...

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ISSN 2095-2201 (Print)
ISSN 2095-221X (Online)
CN 10-1013/X
Postal Subscription Code 80-973
Formerly Known as Frontiers of Environmental Science & Engineering in China
2019 Impact Factor: 4.053

, Volume 14 Issue 6

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Nitrogen removal efficiencies and microbial communities in full-scale IFAS and MBBR municipal wastewater treatment plants at high COD:N ratio
Supaporn Phanwilai, Naluporn Kangwannarakul, Pongsak (Lek) Noophan, Tamao Kasahara, Akihiko Terada, Junko Munakata-Marr, Linda Ann Figueroa
Front. Environ. Sci. Eng.. 2020, 14 (6): 115 .
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• Two IFAS and two MBBR full-scale systems (high COD:N ratio 8:1) were characterized.

• High specific surface area carriers grew and retained slow-growing nitrifiers.

• High TN removal is related to high SRT and low DO concentration in anoxic tanks.

The relative locations of AOB, NOB, and DNB were examined for three different kinds of carriers in two types of hybrid biofilm process configurations: integrated fixed-film activated sludge (IFAS) and moving bed biofilm reactor (MBBR) processes. IFAS water resource recovery facilities (WRRFs) used AnodkalnessTM K1 carriers (KC) at Broomfield, Colorado, USA and polypropylene resin carriers (RC) at Fukuoka, Japan, while MBBR WRRFs used KC carriers at South Adams County, Colorado, USA and sponge carriers (SC) at Saga, Japan. Influent COD to N ratios ranged from 8:1 to 15:1. The COD and BOD removal efficiencies were high (96%–98%); NH4+-N and TN removal efficiencies were more varied at 72%–98% and 64%–77%, respectively. The extent of TN removal was higher at high SRT, high COD:N ratio and low DO concentration in the anoxic tank. In IFAS, RC with high specific surface area (SSA) maintained higher AOB population than KC. Sponge carriers with high SSA maintained higher overall bacteria population than KC in MBBR systems. However, the DNB were not more abundant in high SSA carriers. The diversity of AOB, NOB, and DNB was fairly similar in different carriers. Nitrosomonas sp. dominated over Nitrosospira sp. while denitrifying bacteria included Rhodobacter sp., Sulfuritalea sp., Rubrivivax sp., Paracoccus sp., and Pseudomonas sp. The results from this work suggest that high SRT, high COD:N ratio, low DO concentration in anoxic tanks, and carriers with greater surface area may be recommended for high COD, BOD and TN removal in WRRFs with IFAS and MBBR systems.

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Predicting non-carcinogenic hazard quotients of heavy metals in pepper (Capsicum annum L.) utilizing electromagnetic waves
Marzieh Mokarram, Hamid Reza Pourghasemi, Huichun Zhang
Front. Environ. Sci. Eng.. 2020, 14 (6): 114 .
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• There was significant absorption of heavy metals by the pepper in contaminated soils.

• The target hazard quotient (THQ) indices followed the order of Pb>Zn>>Cd » Ni.

• Relationships exist between contaminated plants and electromagnetic wave.

• PCA and random search can select the main spectra and predict THQ for each element.

Given the tendency of heavy metals to accumulate in soil and plants, the purpose of this study was to determine the contamination levels of Cd, Ni, Pb, and Zn on peppers (leaves and fruit) grown in contaminated soils in industrial centers. For this purpose, we measured the uptake of the four heavy metals by peppers grown in the heavy metal contaminated soils throughout the four growth stages: two-leaf, growth, flowering, and fruiting, and calculated various vegetation indices to evaluate the heavy metal contamination potentials. Electromagnetic waves were also applied for analyzing the responses of the target plants to various heavy metals. Based on the relevant spectral bands identified by principal component analysis (PCA) and random search methods, a regression method was then employed to determine the most optimal spectral bands for estimating the target hazard quotient (THQ). The THQ was found to be the highest in the plants contaminated by Pb (THQ= 62) and Zn (THQ= 5.07). The results of PCA and random search indicated that the spectra at the bands of b570, b650, and b760 for Pb, b400 and b1030 for Ni, b400 and b880 for Cd, and b560, b910, and b1050 for Zn were the most optimal spectra for assessing THQ. Therefore, in future studies, instead of examining the amount of heavy metals in plants by chemical analysis in the laboratory, the responses of the plants to the electromagnetic waves in the identified bands can be readily investigated in the field based on the established correlations.

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Enhanced enzymatic removal of anthracene by the mangrove soil-derived fungus, Aspergillus sydowii BPOI
Paul Olusegun Bankole, Kirk Taylor Semple, Byong-Hun Jeon, Sanjay Prabhu Govindwar
Front. Environ. Sci. Eng.. 2020, 14 (6): 113 .
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A. sydowii strain bpo1 exhibited 99.8% anthracene degradation efficiency.

• Four unique metabolic products were obtained after anthracene degradation.

• Ligninolytic enzymes induction played vital roles in the removal of anthracene.

• Laccase played a crucial role in comparison with other enzymes induced.

The present study investigated the efficiency of Aspergillus sydowii strain bpo1 (GenBank Accession Number: MK373021) in the removal of anthracene (100 mg/L). Optimal degradation efficiency (98.7%) was observed at neutral pH, temperature (30℃), biomass weight (2 g) and salinity (0.2% w/v) within 72 h. The enzyme analyses revealed 131%, 107%, and 89% induction in laccase, lignin peroxidase, and manganese peroxidase respectively during anthracene degradation. Furthermore, the degradation efficiency (99.8%) and enzyme induction were significantly enhanced with the addition of 100 mg/L of citric acid and glucose to the culture. At varying anthracene concentrations (100–500 mg/L), the degradation rate constants (k1) peaked with increasing concentration of anthracene while the half-life (t1/2) decreases with increase in anthracene concentration. Goodness of fit (R2 = 0.976 and 0.982) was observed when the experimental data were subjected to Langmuir and Temkin models respectively which affirmed the monolayer and heterogeneous nature exhibited by A. sydwoii cells during degradation. Four distinct metabolites; anthracene-1,8,9 (2H,8aH,9aH)-trione, 2,4a-dihydronaphthalene-1,5-dione, 1,3,3a,7a-tetrahydro-2-benzofuran-4,7-dione and 2-hydroxybenzoic acid was obtained through Gas Chromatography-Mass spectrometry (GC-MS). A. sydowii exhibited promising potentials in the removal of PAHs.

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Region-gridding recycling of bulk organic waste: Emerging views based on coordinated urban and rural development
Wenbing Tan, Dongyu Cui, Xiaohui Zhang, Beidou Xi
Front. Environ. Sci. Eng.. 2020, 14 (6): 112 .
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Bulk organic waste (BOW) has a large output in China. The improper disposal of BOW will not only bring serious environmental pollution, but also cause waste of biomass resources. The viewpoint proposes a region-gridding recycling management system of BOW that highlights the coordinated development of environmental, agricultural and energy elements in urban and rural areas. The viewpoint aims to drive the upstream and downstream industrial chains of BOW treatments, avoid the repeated construction of resource facilities, guide the upgrading of resource-based technologies, promote the professionalization of farmers, and thus built the high-quality modern agricultural recycling industrial park based on system management.

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Diffusive gradients in thin films using molecularly imprinted polymer binding gels for in situ measurements of antibiotics in urban wastewaters
Ying Cui, Feng Tan, Yan Wang, Suyu Ren, Jingwen Chen
Front. Environ. Sci. Eng.. 2020, 14 (6): 111 .
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• Selective molecularly imprinted polymer (MIP) binding gel was prepared.

• MIP-DGT showed excellent uptake performance for antibiotics.

• In situ measurement of antibiotics in wastewaters via MIP-DGT was developed.

• The MIP-DGT method was robust, reliable, and highly sensitive.

Urban wastewater is one of main sources for the introduction of antibiotics into the environment. Monitoring the concentrations of antibiotics in wastewater is necessary for estimating the amount of antibiotics discharged into the environment through urban wastewater treatment systems. In this study, we report a novel diffusive gradient in thin films (DGT) method based on molecularly imprinted polymers (MIPs) for in situ measurement of two typical antibiotics, fluoroquinolones (FQs) and sulfonamides (SAs) in urban wastewater. MIPs show specific adsorption toward their templates and their structural analogs, resulting in the selective uptake of the two target antibiotics during MIP-DGT deployment. The uptake performance of the MIP-DGTs was evaluated in the laboratory and was relatively independent of solution pH (4.0–9.0), ionic strength (1–750 mmol/L), and dissolved organic matter (DOM, 0–20 mg/L). MIP-DGT samplers were tested in the effluent of an urban wastewater treatment plant for field trials, where three SA (sulfamethoxazole, sulfapyridine, and trimethoprim) and one FQ (ofloxacin) antibiotics were detected, with concentrations ranging from 25.50 to 117.58 ng/L, which are consistent with the results measured by grab sampling. The total removal efficiency of the antibiotics was 80.1% by the treatment plant. This study demonstrates that MIP-DGT is an effective tool for in situ monitoring of trace antibiotics in complex urban wastewaters.

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Acute toxicity assessment of drinking water source with luminescent bacteria: Impact of environmental conditions and a case study in Luoma Lake, East China
Xuewen Yi, Zhanqi Gao, Lanhua Liu, Qian Zhu, Guanjiu Hu, Xiaohong Zhou
Front. Environ. Sci. Eng.. 2020, 14 (6): 109 .
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• Acute toxicity assessment was conducted in Luoma lake watershed, East China.

• Impacts of environmental factors on the toxicity testing was fully evaluated.

• Dissolve oxygen had a weak positive correlation with luminescence inhibition rate.

Protecting the quality of lake watersheds by preventing and reducing their contamination is an effective approach to ensure the sustainability of the drinking water supply. In this study, acute toxicity assessment was conducted on the basis of acute bioluminescence inhibition assay using the marine bacterium Vibrio fischeri as the test organism and Luoma Lake drinking water source in East China as the research target. The suitable ranges of environmental factors, including pH value, organic matter, turbidity, hardness, and dissolved oxygen of water samples were evaluated for the toxicity testing of bioluminescent bacteria. The physicochemical characteristics of water samples at the selected 43 sites of Luoma Lake watershed were measured. Results showed that the variations in pH value (7.31–8.41), hardness (5–20 °d) and dissolved oxygen (4.44–11.03 mg/L) of Luoma Lake and its main inflow and outflow rivers had negligible impacts on the acute toxicity testing of V. fischeri. The luminescence inhibition rates ranged from -11.21% to 10.80% at the 43 sites. Pearson’s correlation analysis in the experiment revealed that temperature, pH value, hardness, and turbidity had no correlation with luminescence inhibition rate, whereas dissolved oxygen showed a weak statistically positive correlation with a Pearson correlation coefficient of 0.455 (p<0.05).

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Influences and mechanisms of nanofullerene on the horizontal transfer of plasmid-encoded antibiotic resistance genes between E. coli strains
Qingkun Ji, Caihong Zhang, Dan Li
Front. Environ. Sci. Eng.. 2020, 14 (6): 108 .
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• Sub-inhibitory levels of nC60 promote conjugative transfer of ARGs.

• nC60 can induce ROS generation, oxidative stress and SOS response.

• nC60 can increase cell membrane permeability and alter gene expression.

• Results provide evidence of nC60 promoting antibiotic resistance dissemination.

The spread and development of antibiotic resistance globally have led to severe public health problems. It has been shown that some non-antibiotic substances can also promote the diffusion and spread of antibiotic resistance genes (ARGs). Nanofullerene (nC60) is a type of nanomaterial widely used around the world, and some studies have discovered both the biological toxicity and environmental toxicity of nC60. In this study, cellular and molecular biology techniques were employed to investigate the influences of nC60 at sub-minimum inhibitory concentrations (sub-MICs) on the conjugation of ARGs between the E. coli strains. Compared with the control group, nC60 significantly increased the conjugation rates of ARGs by 1.32‒10.82 folds within the concentration range of 7.03‒1800 mg/L. This study further explored the mechanism of this phenomenon, finding that sub-MICs of nC60 could induce the production of reactive oxygen species (ROS), trigger SOS-response and oxidative stress, affect the expression of outer membrane proteins (OMPs) genes, increase membrane permeability, and thus promote the occurrence of conjugation. This research enriches our understanding of the environmental toxicity of nC60, raises our risk awareness toward nC60, and may promote the more rational employment of nC60 materials.

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Cross-stacked super-aligned carbon nanotube/activated carbon composite electrodes for efficient water purification via capacitive deionization enhanced ultrafiltration
Min Li, Shuai Liang, Yang Wu, Meiyue Yang, Xia Huang
Front. Environ. Sci. Eng.. 2020, 14 (6): 107 .
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• A high-performance electrode was prepared with super-aligned carbon nanotubes.

• SACNT/AC electrode achieved a ~100% increase in desalination capacity and rate.

• SACNT/AC electrode achieved a ~26% increase in charge efficiency.

• CUF process with SACNT/AC achieved an up to 2.43-fold fouling reduction.

• SACNT/AC imparts overall improved water purification efficiency.

The practical application of the capacitive deionization (CDI) enhanced ultrafiltration (CUF) technology is hampered due to low performance of electrodes. The current study demonstrated a novel super-aligned carbon nanotube (SACNT)/activated carbon (AC) composite electrode, which was prepared through coating AC on a cross-stacked SACNT film. The desalination capability and water purification performance of the prepared electrode were systematically investigated at different applied voltages (0.8–1.2 V) with a CDI system and a CUF system, respectively. In the CDI tests, as compared with the control AC electrode, the SACNT/AC electrode achieved an approximately 100% increase in both maximum salt adsorption capacity and average salt adsorption rate under all the applied voltage conditions, demonstrating a superior desalination capability. Meanwhile, a conspicuous increase by an average of ~26% in charge efficiency was also achieved at all the voltages. In the CUF tests, as compared with the control run at 0 V, the treatment runs at 0.8, 1.0, and 1.2 V achieved a 2.40-fold, 2.08-fold, and 2.43-fold reduction in membrane fouling (calculated according to the final transmembrane pressure (TMP) data at the end of every purification stage), respectively. The average TMP increasing rates at 0.8, 1.0, and 1.2 V were also roughly two times smaller than that at 0 V, indicating a dramatical reduction of membrane fouling. The SACNT/AC electrode also maintained its superior desalination capability in the CUF process, resulting in an overall improved water purification efficiency.

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Light-induced variation in environmentally persistent free radicals and the generation of reactive radical species in humic substances
Yafang Shi, Yunchao Dai, Ziwen Liu, Xiaofeng Nie, Song Zhao, Chi Zhang, Hanzhong Jia
Front. Environ. Sci. Eng.. 2020, 14 (6): 106 .
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• Light irradiation increased the concentration of free radicals on HS.

• The increased spin densities on HS readily returned back to the original value.

• The “unstable” free radicals induced the formation of reactive radical species.

• Reactive radicals’ concentration correlated strongly with EPFRs’ concentration.

Environmentally persistent free radicals (EPFRs) in humic substances play an essential role in soil geochemical processes. Light is known to induce EPFRs formation for dissolved organic matter in aquatic environments; however, the impacts of light irradiation on the variation of EPFRs in soil humic substances remain unclear. In this study, humic acid, fulvic acid, and humin were extracted from peat soil and then in situ irradiated using simulated sunlight. Electron paramagnetic resonance spectroscopy results showed that with the increasing irradiation time, the spin densities and g-factors of humic substances rapidly increased during the initial 20 min and then gradually reached a plateau. After irradiation for 2h, the maximum spin density levels were up to 1.63 × 1017, 2.06 × 1017, and 1.77 × 1017 spins/g for the humic acid, fulvic acid, and humin, respectively. And the superoxide radicals increased to 1.05 × 1014–1.46 × 1014 spins/g while the alkyl radicals increased to 0.47 × 1014–1.76 × 1014 spins/g. The light-induced EPFRs were relatively unstable and readily returned back to their original state under dark and oxic conditions. Significant positive correlations were observed between the concentrations of EPFRs and reactive radical species (R2 = 0.65–0.98, p<0.05), which suggested that the newly produced EPFRs contributed to the formation of reactive radical species. Our findings indicate that under the irradiation humic substances are likely to be more toxic and reactive in soil due to the formation of EPFRs.

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Catalytic oxidation of o-chlorophenol over Co2XAl (X= Co, Mg, Ca, Ni) hydrotalcite-derived mixed oxide catalysts
Na Li, Xin Xing, Yonggang Sun, Jie Cheng, Gang Wang, Zhongshen Zhang, Zhengping Hao
Front. Environ. Sci. Eng.. 2020, 14 (6): 105 .
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• Superior catalytic activity observed for o-chlorophenol oxidation on Co2MgAlO.

• The reducibility, oxygen species and basicity influenced catalytic activity.

• The organic by-products were generated in o-chlorophenol catalytic oxidation.

A cobalt-based hydrotalcite-like compound was prepared using a constant-pH coprecipitation method. Cobalt-transition metal oxides (Co2XAlO, X= Co, Mg, Ca and Ni) were investigated for the deep catalytic oxidation of o-chlorophenol as a typical heteroatom contaminant containing chlorine atoms. The partial substitution of Co by Mg, Ca or Ni in the mixed oxide can promote the catalytic oxidation of o-chlorophenol. The Co2MgAlO catalyst presented the best catalytic activity, and could maintain 90% o-chlorophenol conversion at 167.1°C, compared only 27% conversion for the Co3AlO catalyst. The results demonstrated that the high activity could be attributed to its increased low-temperature reducibility, rich active oxygen species and excellent oxygen mobility. In the existence of acid and base sites, catalysts with strong basicity also showed preferred activity. The organic by-products generated during the o-chlorophenol catalytic oxidation over Co2MgAlO catalyst included carbon tetrachloride, trichloroethylene, 2,4-dichlorophenol, and 2,6-dichloro-p-benzoquinon, et al. This work provides a facile method for the preparation of Co-based composite oxide catalysts, which represent promising candidates for typical chlorinated and oxygenated volatile organic compounds.

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Evaluating heavy metal contamination of riverine sediment cores in different land-use areas
Wenzhong Tang, Liu Sun, Limin Shu, Chuang Wang
Front. Environ. Sci. Eng.. 2020, 14 (6): 104 .
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• Metal pollution was studied in riverine sediments from different land-use areas.

• Cd was the most serious heavy metal contaminant in riverine sediment cores.

• Riverine sediment cores from industrial area were most polluted by heavy metals.

• B1 fraction determined metal pollution, risk and toxicity in riverine sediments.

Anthropogenic activities are regarded as the main sources of heavy metal pollution, yet few studies have investigated the effects of land-use setting on heavy metal accumulation in riverine sediments. Based on both total contents and geochemical fractions, heavy metal pollution, risk and toxicity were determined in riverine sediment cores from different land-use areas (mountain area- MA, farm area- FA, city area- CA, and industrial area- IA) of the Yang River Basin in North China. The results showed that FA had higher contents of riverine sedimentary Cu; CA had higher contents of Cd; IA had higher contents of both Cd and Zn. Most riverine sediments from FA and IA were contaminated with the investigated metals, although these concentrations were evaluated to have low potential ecological risk and no toxicity to benthic organisms. However, a high proportion of Cd in the B1 fraction of riverine sediments in IA indicating high risk should receive more attention. The B1 fraction largely determined the contamination, risk and toxicity levels associated with heavy metals in the riverine sediments of the Yang River Basin.

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Photosynthesis and related metabolic mechanism of promoted rice (Oryza sativa L.) growth by TiO2 nanoparticles
Yingdan Zhang, Na Liu, Wei Wang, Jianteng Sun, Lizhong Zhu
Front. Environ. Sci. Eng.. 2020, 14 (6): 103 .
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• The rice growth was promoted by nano-TiO2 of 0.1–100 mg/L.

• Nano-TiO2 enhanced the energy storage in photosynthesis.

• Nano-TiO2 reduced energy consumption in carbohydrate metabolism and TCA cycle.

Titanium dioxide nanoparticle (nano-TiO2), as an excellent UV absorbent and photo-catalyst, has been widely applied in modern industry, thus inevitably discharged into environment. We proposed that nano-TiO2 in soil can promote crop yield through photosynthetic and metabolic disturbance, therefore, we investigated the effects of nano-TiO2 exposure on related physiologic-biochemical properties of rice (Oryza sativa L.). Results showed that rice biomass was increased >30% at every applied dosage (0.1–100 mg/L) of nano-TiO2. The actual photosynthetic rate (Y(II)) significantly increased by 10.0% and 17.2% in the treatments of 10 and 100 mg/L respectively, indicating an increased energy production from photosynthesis. Besides, non-photochemical quenching (Y(NPQ)) significantly decreased by 19.8%–26.0% of the control in all treatments respectively, representing a decline in heat dissipation. Detailed metabolism fingerprinting further revealed that a fortified transformation of monosaccharides (D-fructose, D-galactose, and D-talose) to disaccharides (D-cellobiose, and D-lactose) was accompanied with a weakened citric acid cycle, confirming the decrease of energy consumption in metabolism. All these results elucidated that nano-TiO2 promoted rice growth through the upregulation of energy storage in photosynthesis and the downregulation of energy consumption in metabolism. This study provides a mechanistic understanding of the stress-response hormesis of rice after exposure to nano-TiO2, and provides worthy information on the potential application and risk of nanomaterials in agricultural production.

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Hydroxyl radical intensified Cu2O NPs/H2O2 process in ceramic membrane reactor for degradation on DMAc wastewater from polymeric membrane manufacturer
Wenyue Li, Min Chen, Zhaoxiang Zhong, Ming Zhou, Weihong Xing
Front. Environ. Sci. Eng.. 2020, 14 (6): 102 .
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• Cu2O NPs/H2O2 Fenton process was intensified by membrane dispersion.

• DMAc removal was enhanced to 98% for initial DMAc of 14000 mg/L.

• Analyzed time-resolved degradation pathway of DMAc under ·OH attack.

High-concentration industrial wastewater containing N,N-dimethylacetamide (DMAc) from polymeric membrane manufacturer was degraded in Cu2O NPs/H2O2 Fenton process. In the membrane-assisted Fenton process DMAc removal rate was up to 98% with 120 min which was increased by 23% over the batch reactor. It was found that ·OH quench time was extended by 20 min and the maximum ·OH productivity was notably 88.7% higher at 40 min. The degradation reaction rate constant was enhanced by 2.2 times with membrane dispersion (k = 0.0349 min1). DMAc initial concentration (C0) and H2O2 flux (Jp) had major influence on mass transfer and kinetics, meanwhile, membrane pore size (rp) and length (Lm) also affected the reaction rate. The intensified radical yield, fast mass transfer and nanoparticles high activity all contributed to improve pollutant degradation efficiency. Time-resolved DMAc degradation pathway was analyzed as hydroxylation, demethylation and oxidation leading to the final products of CO2, H2O and NO3 (rather than NH3 from biodegradation). Continuous process was operated in the dual-membrane configuration with in situ reaction and separation. After five cycling tests, DMAc removal was all above 95% for the initial [DMAc]0 = 14,000 mg/L in wastewater and stability of the catalyst and the membrane maintained well.

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Effects of hydraulic retention time on net present value and performance in a membrane bioreactor treating antibiotic production wastewater
Dawei Yu, Jianxing Wang, Libin Zheng, Qianwen Sui, Hui Zhong, Meixue Cheng, Yuansong Wei
Front. Environ. Sci. Eng.. 2020, 14 (6): 101 .
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• The membrane bioreactor cost decreased by 38.2% by decreasing HRT from 72 h to 36 h.

• Capital and operation costs contributed 62.1% and 37.9% to decreased costs.

• The membrane bioreactor is 32.6% cheaper than the oxidation ditch for treatment.

• The effluent COD also improved from 709.93±62.75 mg/L to 280±17.32 mg/L.

• Further treatment also benefited from lower pretreatment investment.

A cost sensitivity analysis was performed for an industrial membrane bioreactor to quantify the effects of hydraulic retention times and related operational parameters on cost. Different hydraulic retention times (72–24 h) were subjected to a flat-sheet membrane bioreactor updated from an existing 72 h oxidation ditch treating antibiotic production wastewater. Field experimental data from the membrane bioreactor, both full-scale (500 m3/d) and pilot (1.0 m3/d), were used to calculate the net present value (NPV), incorporating both capital expenditure (CAPEX) and operating expenditure. The results showed that the tank cost was estimated above membrane cost in the membrane bioreactor. The decreased hydraulic retention time from 72 to 36 h reduced the NPV by 38.2%, where capital expenditure contributed 24.2% more than operational expenditure. Tank construction cost was decisive in determining the net present value contributed 62.1% to the capital expenditure. The membrane bioreactor has the advantage of a longer lifespan flat-sheet membrane, while flux decline was tolerable. The antibiotics decreased to 1.87±0.33 mg/L in the MBR effluent. The upgrade to the membrane bioreactor also benefited further treatments by 10.1%–44.7% lower direct investment.

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Nutrient status and pollution levels in five areas around a manganese mine in southern China
Kehui Liu, Xiaolu Liang, Chunming Li, Fangming Yu, Yi Li
Front. Environ. Sci. Eng.. 2020, 14 (6): 100 .
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• The soil TP level was high or extremely high in all areas.

• TN, OM and available Cu were insufficient in EA, TA and RA.

• All areas reached the heavily polluted level and had high ecological risk levels.

• Mn and Cd were the dominant pollutants.

Nutrient status and pollution levels are the main factors affecting soil restoration. The nutrient status and pollution levels in five areas, an unexplored mine area (UA), an explored mine area (EA), a tailings area (TA), a reclamation area (RA) and an agricultural area (AA), around the Pingle manganese mine in Guangxi, China, were assessed in this study. The results showed that the average total phosphorus in these five areas ranged from 1.05 to 1.57 mg/kg, corresponding to grades of extremely high and high. The average total nitrogen values were 0.19, 0.69, 0.93, 1.24 and 1.67 mg/kg in EA, TA, RA, UA and AA, corresponding to grades of very low, low, medium-low, medium-high and medium-high, respectively. The average organic matter values were 12.78, 8.92, 22.77, 21.29 and 29.11 mg/kg in EA, TA, RA, UA and AA, which corresponded to grades of medium-low, low, medium-high, medium-high and medium-high, respectively. All these results indicated that the total phosphorus was sufficient in these areas, while the total nitrogen and organic matter were insufficient in EA, TA and RA. The available concentrations of Mn and Zn corresponded to the intermediate grade, while the values for Cu corresponded to the very low grade; these might be another factor restricting ecological reclamation. Contamination and ecological risk assessments based on the single contamination index, Nemerow multi-factor index and potential ecological risk index showed that the five tested areas around the Mn mine were considered heavily polluted and presented high ecological risk. Mn and Cd were the dominant pollutants.

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Performance of activated carbon coated graphite bipolar electrodes on capacitive deionization method for salinity reduction
Hossein D. Atoufi, Hasti Hasheminejad, David J. Lampert
Front. Environ. Sci. Eng.. 2020, 14 (6): 99 .
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• Graphite bipolar electrodes act as an appropriate bed for the CDI process.

• Activated carbon Coating improves the application of the electrodes.

• CDI is an environmentally friendly method to apply for brackish water.

• Initial concentration is the most important parameter in the CDI method.

• CDI process in a batch-mode setup needs more development.

This research investigates a capacitive deionization method for salinity reduction in a batch reactor as a new approach for desalination. Reductions of cost and energy compared with conventional desalination methods are the significant advantages of this approach. In this research, experiments were performed with a pair of graphite bipolar electrodes that were coated with a one-gram activated carbon solution. After completing preliminary tests, the impacts of four parameters on electrical conductivity reduction, including (1) the initial concentration of feed solution, (2) the duration of the tests, (3) the applied voltage, and (4) the pH of the solution, were examined. The results show that the maximum efficiency of electrical conductivity reduction in this laboratory-scale reactor is about 55%. Furthermore, the effects of the initial concentration of feed solution are more significant than the other parameters. Thus, using the capacitive deionization method for water desalination with low and moderate salt concentrations (i.e., brackish water) is proposed as an affordable method. Compared with conventional desalination methods, capacitive deionization is not only more efficient but also potentially more environmentally friendly.

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Degradation of polyacrylamide (PAM) and methane production by mesophilic and thermophilic anaerobic digestion: Effect of temperature and concentration
Mona Akbar, Muhammad Farooq Saleem Khan, Ling Qian, Hui Wang
Front. Environ. Sci. Eng.. 2020, 14 (6): 98 .
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• PAM degradation in thermophilic AD in comparison with mesophilic AD.

• PAM degradation and its impact on thermophilic and mesophilic AD.

• Enhanced methane yield in presence of PAM during thermophilic and mesophilic AD.

• PAM degradation and microbial community analysis in thermophilic and mesophilic AD.

Polyacrylamide (PAM) is generally employed in wastewater treatment processes such as sludge dewatering and therefore exists in the sludge. Furthermore, it degrades slowly and can deteriorate methane yield during anaerobic digestion (AD). The impact or fate of PAM in AD under thermophilic conditions is still unclear. This study mainly focuses on PAM degradation and enhanced methane production from PAM-added sludge during 15 days of thermophilic (55°C) AD compared to mesophilic (35°C) AD. Sludge and PAM dose from 10 to 50 g/kg TSS were used. The results showed that PAM degraded by 76% to 78% with acrylamide (AM) content of 0.2 to 3.3 mg/L in thermophilic AD. However, it degraded only 27% to 30% with AM content of 0.5 to 7.2 mg/L in mesophilic AD. The methane yield was almost 230 to 238.4 mL/g VSS on the 8th day in thermophilic AD but was 115.2 to 128.6 mL/g VSS in mesophilic AD. Mechanism investigation revealed that thermophilic AD with continuous stirring not only enhanced PAM degradation but also boosted the organics release from the sludge with added PAM and gave higher methane yield than mesophilic AD.

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Algae (Raphidocelis subcapitata) mitigate combined toxicity of microplastic and lead on Ceriodaphnia dubia
Xuesong Liu, Jianmin Wang
Front. Environ. Sci. Eng.. 2020, 14 (6): 97 .
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• Micro-plastics (MPs) significantly increase Pb toxicity.

• Algae reduce the combined toxicity of MP and Pb.

• The toxicity increase comes from high soluble Pb and MP-Pb uptake.

• The toxicity reduction might come from energy related pathway.

Microplastics (MPs) have been recognized as a new class of emerging contaminants in recent years. They not only directly impact aquatic organisms, but also indirectly impact these organisms by interacting with background toxins in the environment. Moreover, under realistic environmental conditions, algae, a natural food for aquatic organisms, may alter the toxicity pattern related to MPs. In this research, we first examined the toxicity of MPs alone, and their effect on the toxicity of lead (Pb) on Ceriodaphnia dubia (C. dubia), a model aquatic organism for toxicity survey. Then, we investigated the effect of algae on the combined toxicity of MPs and Pb. We observed that, MPs significantly increased Pb toxicity, which was related to the increase in soluble Pb concentration and the intake of Pb-loaded MPs, both of which increased the accumulation of Pb in C. dubia. The presence of algae mitigated the combined toxicity of MPs and Pb, although algae alone increased Pb accumulation. Therefore, the toxicity mitigation through algae uptake came from mechanisms other than Pb accumulation, which will need further investigation.

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Metabolic uncoupler, 3,3′,4′,5-tetrachlorosalicylanilide addition for sludge reduction and fouling control in a gravity-driven membrane bioreactor
An Ding, Yingxue Zhao, Huu Hao Ngo, Langming Bai, Guibai Li, Heng Liang, Nanqi Ren, Jun Nan
Front. Environ. Sci. Eng.. 2020, 14 (6): 96 .
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• Effects of metabolic uncoupler TCS on the performances of GDMBR were evaluated.

• Sludge EPS reduced and transformed into dissolved SMP when TCS was added.

• Appropriate TCS increased the permeability and reduced cake layer fouling.

• High dosage aggravated fouling due to compact cake layer with low bio-activity.

The gravity-driven membrane bioreactor (MBR)system is promising for decentralized sewage treatment because of its low energy consumption and maintenance requirements. However, the growing sludge not only increases membrane fouling, but also augments operational complexities (sludge discharge). We added the metabolic uncoupler 3,3′,4′,5-tetrachlorosalicylanilide (TCS) to the system to deal with the mentioned issues. Based on the results, TCS addition effectively decreased sludge ATP and sludge yield (reduced by 50%). Extracellular polymeric substances (EPS; proteins and polysaccharides) decreased with the addition of TCS and were transformed into dissolved soluble microbial products (SMPs) in the bulk solution, leading to the break of sludge flocs into small fragments. Permeability was increased by more than two times, reaching 60–70 L/m2/h bar when 10–30 mg/L TCS were added, because of the reduced suspended sludge and the formation of a thin cake layer with low EPS levels. Resistance analyses confirmed that appropriate dosages of TCS primarily decreased the cake layer and hydraulically reversible resistances. Permeability decreased at high dosage (50 mg/L) due to the release of excess sludge fragments and SMP into the supernatant, with a thin but more compact fouling layer with low bioactivity developing on the membrane surface, causing higher cake layer and pore blocking resistances. Our study provides a fundamental understanding of how a metabolic uncoupler affects the sludge and bio-fouling layers at different dosages, with practical relevance for in situ sludge reduction and membrane fouling alleviation in MBR systems.

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Optimized determination of airborne tetracycline resistance genes in laboratory atmosphere
Lu Song, Can Wang, Yizhu Wang
Front. Environ. Sci. Eng.. 2020, 14 (6): 95 .
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• Sampling parameters with high efficiency was determined.

• Operational process to detect airborne ARGs was optimized.

• Providing research basis to control airborne ARGs of a laboratory atmosphere

Antibiotic resistance genes (ARGs) have been detected in various atmospheric environments. Airborne ARGs transmission presents the public health threat. However, it is very difficult to quantify airborne ARGs because of the limited availability of collectable airborne particulate matter and the low biological content of samples. In this study, an optimized protocol for collecting and detecting airborne ARGs was presented. Experimental results showed that recovery efficiency tended to increase initially and then declined over time, and a range of 550–780 copies/mm2 of capture loading was recommended to ensure that the recovery efficiency is greater than 75%. As the cell walls were mechanically disrupted and nucleic acids were released, the buffer wash protects ARGs dissolution. Three ratios of buffer volume to membrane area in buffer wash were compared. The highest concentrations of airborne ARGs were detected with 1.4 µL/mm2 buffer wash. Furthermore, the majority of the cells were disrupted by an ultrasonication pretreatment (5 min), allowing the efficiency ARGs detection of airborne samples. While, extending the ultrasonication can disrupt cell structures and gene sequence was broken down into fragments. Therefore, this study could provide a theoretical basis for the efficient filter collection of airborne ARGs in different environments. An optimized sampling method was proposed that the buffer wash was 1.4 µL/mm2 and the ultrasonication duration was 5 min. The indoor airborne ARGs were examined in accordance with the improved protocol in two laboratories. The result demonstrated that airborne ARGs in an indoor laboratory atmosphere could pose the considerable health risk to inhabitants and we should pay attention to some complicated indoor air environment.

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The coupling of sand with ZVI/oxidants achieved proportional and highly efficient removal of arsenic
Sana Ullah, Xuejun Guo, Xiaoyan Luo, Xiangyuan Zhang, Yameng Li, Ziyu Liang
Front. Environ. Sci. Eng.. 2020, 14 (6): 94 .
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• Simply doping sands with ZVI achieved an even activation of ZVI by oxidants.

• Sand doping facilitated proportional As trapping along the ZVI/oxidants column.

• ZVI/sand/oxidants are highly efficient for arsenic removal.

• ZVI/sand/oxidants reduced significantly the Fe2+ leaching and effluent turbidity.

• More than 54% of arsenic was reduced to As(III) in ZVI/sand/oxidants system.

The coupling of zero-valent iron (ZVI) with common oxidants has recently achieved very rapid and highly efficient removal of Heavy metals from wastewater. However, the uniform activation of ZVI throughout the column and the proportional removal of target contaminants are urgently required for the prevention of premature filter clogging and the extension of the effective column operational time. In this study, we successfully achieved this objective by simply doping granular sand with ZVI at appropriate weight ratios. When pure ZVI packed column was spiked with oxidants, the majority of As trapping occurred between the column inlet and the first sampling point. In a packed column with a 1:20 mixture of ZVI and sand, the average As removal efficiency was 36 (1st), 13.1 (2nd), 18.5 (3rd), 19.2 (4th) and 5.9% (5th outlet). The overall arsenic removal performance of the composite filling system of ZVI/sand was equally as efficient as that of the previous pure ZVI-packed system. Moreover, the leaching of Fe was significantly reduced with an increased sand ratio, resulting in clearer water with less turbidity. The results of X-ray photoelectron spectroscopy (XPS) demonstrated that more than 54% of the arsenic was reduced to As(III). X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the extensive corrosion of the ZVI surface, which resulted in various species of iron oxyhydroxides responsible for the highly efficient sequester of arsenic through reduction, adsorption, and coprecipitation.

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Taxonomic and functional variations in the microbial community during the upgrade process of a full-scale landfill leachate treatment plant – from conventional to partial nitrification-denitrification
Binbin Sheng, Depeng Wang, Xianrong Liu, Guangxing Yang, Wu Zeng, Yiqing Yang, Fangang Meng
Front. Environ. Sci. Eng.. 2020, 14 (6): 93 .
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• Upgrade process was investigated in a full-scale landfill leachate treatment plant.

• The optimization of DO can technically achieve the shift from CND to PND process.

• Nitrosomonas was mainly responsible for ammonium oxidation in PND system.

• An obviously enrichment of Thauera was found in the PND process.

• Enhanced metabolic potentials on organics was found during the process update.

Because of the low access to biodegradable organic substances used for denitrification, the partial nitrification-denitrification process has been considered as a low-cost, sustainable alternative for landfill leachate treatment. In this study, the process upgrade from conventional to partial nitrification-denitrification was comprehensively investigated in a full-scale landfill leachate treatment plant (LLTP). The partial nitrification-denitrification system was successfully achieved through the optimizing dissolved oxygen and the external carbon source, with effluent nitrogen concentrations lower than 150 mg/L. Moreover, the upgrading process facilitated the enrichment of Nitrosomonas (abundance increased from 0.4% to 3.3%), which was also evidenced by increased abundance of amoA/B/C genes carried by Nitrosomonas. Although Nitrospira (accounting for 0.1%–0.6%) was found to stably exist in the reactor tank, considerable nitrite accumulation occurred in the reactor (reaching 98.8 mg/L), indicating high-efficiency of the partial nitrification process. Moreover, the abundance of Thauera, the dominant denitrifying bacteria responsible for nitrite reduction, gradually increased from 0.60% to 5.52% during the upgrade process. This process caused great changes in the microbial community, inducing continuous succession of heterotrophic bacteria accompanied by enhanced metabolic potentials toward organic substances. The results obtained in this study advanced our understanding of the operation of a partial nitrification-denitrification system and provided a technical case for the upgrade of currently existing full-scale LLTPs.

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Precursors and potential sources of ground-level ozone in suburban Shanghai
Kun Zhang, Jialuo Xu, Qing Huang, Lei Zhou, Qingyan Fu, Yusen Duan, Guangli Xiu
Front. Environ. Sci. Eng.. 2020, 14 (6): 92 .
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• Air masses from Zhejiang Province is the major source of O3 in suburban Shanghai.

• O3 formation was in VOC-sensitive regime in rural Shanghai.

• O3 formation was most sensitive to propylene in rural Shanghai.

A high level of ozone (O3) is frequently observed in the suburbs of Shanghai, the reason for this high level remains unclear. To obtain a detailed insight on the high level of O3 during summer in Shanghai, O3 and its precursors were measured at a suburban site in Shanghai from July 1, 2016 to July 31, 2016. Using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and concentration weighted trajectories (CWT), we found that Zhejiang province was the main potential source of O3 in suburban Shanghai. When the sampling site was controlled by south-western winds exceeding 2 m/s, the O3-rich air masses from upwind regions (such as Zhejiang province) could be transported to the suburban Shanghai. The propylene-equivalent concentration (PEC) and ozone formation potential (OFP) were further calculated for each VOC species, and the results suggested that propylene, (m+p)-xylene, and toluene played dominant roles in O3 formation. The Ozone Isopleth Plotting Research (OZIPR) model was used to reveal the impact of O3 precursors on O3 formation, and 4 base-cases were selected to adjust the model simulation. An average disparity of 18.20% was achieved between the simulated and observed O3 concentrations. The O3 isopleth diagram illustrated that O3 formation in July 2016 was in VOC-sensitive regime, although the VOC/NOx ratio was greater than 20. By introducing sensitivity (S), a sensitivity analysis was performed for O3 formation. We found that O3 formation was sensitive to propylene, (m+p)-xylene, o-xylene and toluene. The results provide theoretical support for O3 pollution treatment in Shanghai.

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