Amino acid promoted oxidation of atrazine by Fe3O4/persulfate.

In the present study, we demonstrated that the presence of cysteine could remarkably enhance the degradation of atrazine by Fe3O4/persulfate system. The results of electron paramagnetic resonance (EPR) spectra confirmed the combination of cysteine and Fe3O4 exhibited much higher activity on activation of persulfate to generate more SO4•- and •OH than Fe3O4 alone. At pH of 3.0, SO4•- and •OH contributed to about 58.2 % and 41.8 % of atrazine removal respectively, while •OH gradually dominated the oxidation of atrazine from neutral condition to alkaline condition. The co-existing Cl- and HCO3- could quench SO4•-, resulting in the inhibition of atrazine degradation. The presence of low natural organic matters (NOM) concentration (0-2 mg L-1) could enhance the atrazine removal, and high concentration (>5 mg L-1) of NOM restrained the atrazine degradation. During the Cysteine/Fe3O4/Persulfate process, cysteine served as a complexing reagent and reductant. Through acidolysis and complexation, Fe3O4 could release dissolved and surface bound Fe2+, both of which contributed to the activation of persulfate together. Meanwhile, cysteine was not rapidly consumed due to a regeneration process, which was beneficial for maintaining Fe2+/Fe3+ cycle and constantly accelerating the activation of persulfate for atrazine degradation. The reused Fe3O4 and cysteine in the Cysteine/Fe3O4/Persulfate process exhibited high stability for the atrazine degradation after three cycles. The degradation pathway of atrazine included alkylic-oxidation, dealkylation, dechlorination-hydroxylation processes. The present study indicates the novel Cysteine/Fe3O4/Persulfate process might be a high potential for treatment of organic polluted water.

Reduction potential of ammonia emissions and impact on PM2.5 in a megacity of central China.

Ammonia control has attracted attention due to the possibility for fine particles (PM2.5) mitigation. Based on past decade ammonia emissions assessments and future predictions, this study seasonally evaluated the ammonia emissions reduction potential in 2025 and 2030 in Wuhan, a Central China megacity, according to the short-term and long-term predictable policies. Furthermore, combined with the reduction potential, PM2.5 components observation and thermodynamic model, the effectiveness of implementing ammonia emission control to reduce PM2.5 by 2025 and 2030 was explored seasonally. Results indicated that the total ammonia emissions are expected to decrease by 19.6-33.9% in 2025 and 2030 under positive reduction scenarios, or increase by 8.9-11.7% in the absence of any intervention. Livestock holds the largest potential for reducing ammonia emissions accounting for 46.4-52.5% of the total. Improvement of human excrement management in rural regions also contributes a 35-37% potential. Despite the implementation of exhaust requirements, ammonia emissions from vehicles in 2030 are expected to continue to increase by 55.3% and 23.5% under the regular (S1) and enhanced (S2) reduction strategy scenarios, respectively. Seasonally, the most potential source of ammonia reduction in spring, summer and fall remains livestock. While in winter, non-agricultural sources dominate the reduction potential. Further results indicated that by ammonia control is expected to decrease PM2.5 concentration up to 5% (less than 1 µg m-3) in 2025-2030. Despite the better effectiveness in winter, ammonia control won't be an effective way to reduce PM2.5 in Central China in future, from the management policies and areal ammonia-rich conditions.

Simultaneous reduction in cadmium and arsenic accumulation in rice (Oryza sativa L.) by iron/iron-manganese modified sepiolite.

It is challenging to reduce the cadmium (Cd) and arsenic (As) contents of brown rice simultaneously due to their converse chemical behaviors in the paddy soil. Clay minerals, such as sepiolite (SEP), have significant advantages in remediating Cd-contaminated soil. Moreover, iron or manganese oxide loaded SEP can improve the As adsorption efficiency. Herein, ferric nitrate modified sepiolite (NIMS) and iron­manganese modified sepiolite (FMS) were prepared to study their effects on Cd and As accumulation in rice using pot experiments. The results showed that NIMS and FMS had a larger specific surface area than SEP. The application of SEP only decreased Cd content (by 45%), while NIMS and FMS treatments reduced both Cd (by 57% and 87%) and As (by 30% and 25%) contents in brown rice compared with the control. The X-ray photoelectron spectroscopy (XPS) analysis results indicated that MnO2 and MnOOH⁎ in FMS enhanced the adsorption and co-precipitation of Cd as well as the oxidation of As(III) to As(V). The NIMS, as well as the FMS application, increased soil pH, decreased the exchangeable Cd and non-specifically and specifically adsorbed As fractions in soil, and reduced the level of Cd in the pore water. Moreover, NIMS and FMS addition limited the transfer of As from the soil to the roots by enhancing its sequestration in the iron plaque. On the other hand, FMS treatment significantly promoted the uptake of Mn by rice (P < 0.05). The results suggested that both NIMS and FMS were promising materials for simultaneous reduction of Cd and As accumulation in rice. Notably, FMS had better performance in reducing the Cd content in rice than that of NIMS.

Enhanced desorption of cationic and anionic metals/metalloids from co-contaminated soil by tetrapolyphosphate washing and followed by ferrous sulfide treatment.

In this study, a novel approach was employed for the remediation of cationic and anionic metals/metalloids co-contaminated soil by tetrapolyphosphate enhanced soil washing coupled with ferrous sulfide treatment. Tetrapolyphosphate could simultaneously enhance the desorption of cationic metals (Pb and Zn) and anionic metal/metalloid (Cr and As) from the contaminated soil in the whole tested pH range of 2-10. With addition of 0.15 mol/L tetrapolyphosphate at pH 7.0, the removal ratio of Pb, Zn, As and Cr could achieve 83.1%, 70.4%, 75.7% and 66.4% respectively. The fractionation analysis of heavy metals/metalloids demonstrated the release of exchangeable and Fe/Mn bound forms contributed to most desorption of Pb and Zn. The decreases of non-specifically sorbed form and amorphous and poorly-crystalline hydrous oxides of Fe and Al bound form were responsible for most removal of As. The comparison with other common washing agents (EDTA, oxalate and phosphate) under their respective optimal dosage could confirm that tetrapolyphosphate was superior to simultaneously desorb the cationic and anionic metals/metalloids with higher efficiency. After 12 h, applying 150 mg/L FeS at pH 3.5 could totally remove Pb, Zn, As and Cr from the washing effluent by sulfide precipitation, reduction and adsorption processes. Higher pH would inhibit the removal of As and Cr by FeS. Meanwhile, the residual of tetrapolyphosphate could be totally recovered from the washing effluent by employing anion exchange resin. This study suggests tetrapolyphosphate enhanced soil washing coupled with ferrous sulfide treatment is a promising approach for remediation of cationic and anionic metals/metalloids co-contaminated soil in view of its high efficiency and simple operation.

Insights into the underlying mechanisms of stability working for As(III) removal by Fe-Mn binary oxide as a highly efficient adsorbent.

Fe-Mn binary oxide has received increasing interest in treating As(III)-containing polluted groundwater due to its low cost and environmental friendliness. Although the stability of Fe-Mn binary oxide is as important as its adsorption ability, little is known about whether and why Fe-Mn binary oxide is stable during As(III) removal. In this study, five successive cycles were conducted to evaluate the stability of Fe-Mn binary oxide for As(III) removal. As(III) oxidation/adsorption kinetics and the speciation distribution of the released Fe and Mn elements within single Fe oxide, Mn oxide, and Fe-Mn binary oxide were investigated by using characterization techniques of TEM-EDS mapping, selected area electron diffraction (SAED), and XPS combined with a binary component reactor, where Fe and Mn oxides were separated by a semipermeable membrane. The results revealed that Fe-Mn binary oxide could maintain excellent stability, although As(III) oxidation/adsorption behavior was coupled with the release of Fe and Mn ions from its surface. The great stability of Fe-Mn binary oxide for As(III) removal was attributed to the rapid return of aqueous Fe(II) and Mn(II) to the solid surface, which subsequently formed new mineral phases mediated by Fe and Mn oxides, thus considerably decreasing the loss of released Mn(II) and Fe(II).

[Spatio-temporal Distribution Characteristic and Risk Assessment of Heavy Metals in Soils Around Centralized Drinking Water Sources in Wuhan].

In the present study, the spatio-temporal distribution characteristics of heavy metals (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn) in soil around 19 centralized drinking water sources in Wuhan were investigated. Single-factor and comprehensive pollution indexes were used to determine soil pollution levels. The potential ecological hazard index was employed to evaluate soil potential ecological risks. The correlation and cluster analysis were conducted to identify pollution sources. The results showed that higher concentrations of heavy metals were present in soil from centralized drinking water source located in core area than suburb area of Wuhan. The concentrations of heavy metals in soil from centralized drinking water sources near the Yangtze River were higher than that in the sites near the tributaries of the Yangtze River. The average single potential ecological risk index of Hg, As, Pb, Cr, Cu, Ni, and Zn were lower than 40, which suggests a slight potential ecological risk. The average single potential ecological risk index of Cd was 80-160, which indicates a high potential ecological risk. The average comprehensive potential ecological risk index of heavy metals in soil around centralized drinking water sources in Wuhan was 142.12, which corresponded to a slight potential ecological risk. The correlation analysis showed that the sources of Cu, Pb, and Cr were similar and came from transport. The sources of Ni, As, Cr, and Cu were similar and could be attributed to metallurgical industries. The sources of Zn, Hg, and Cr were similar and could be related to antiseptic and catalytic industries. The long-term monitoring of Wuhan Dijiao and Baishazhou waterworks indicated that the concentrations of heavy metals around centralized drinking water sources in Wuhan were markedly decreased after 2017 and that ecological risk may be further reduced in the future.

[Screening of Amendments for Simultaneous Cd and As Immobilization in Soil].

Simultaneously reducing the availability of Cd and As is difficult owing to converse chemical behaviors of Cd and As in soil. In this study, amendments that can simultaneously immobilize Cd and As in soil were determined by an pure soil culture experiment in which flooding and wetting were performed for 30 d each. The effects of sepiolite (Sep), modified sepiolite (IMS and Sep-FM), steel slag (SS), and iron modified biochar (Fe-Bio) on soil pH, Eh, Cd, and As concentrations in pore water, and Cd and As fractions in soil were investigated. It showed that Sep (1%, 2.5%), IMS (1%, 2.5%), Sep-FM (1%, 2.5%), and SS (1%, 5%) treatments increased soil pH value and decreased Eh value and Cd concentrations in soil solution. In addition, As concentrations in soil solution treated with high doses of IMS (2.5%) and SS (5%) were lower than that of CK treatment during the whole incubation period. However, Fe-bio treatment decreased soil pH and increased Eh value and only decreased Cd and As concentrations in soil solution under wet conditions. Compared with the control, the application of the above amendments promoted the transformation of Cd fraction from exchangeable to reducible, oxidizable, and residual. High application rates of IMS (2.5%), Sep-FM (2.5%), and SS (5%) also reduced available As fraction (non-specifically sorbed and specifically-sorbed As fraction), and increased amorphous and poorly-crystalline hydrated Fe and Al oxide-bound As. On the contrary, Fe-bio treatment increased the fractions of non-specifically sorbed, specifically sorbed and residual As in soil. In short, IMS, Sep-FM, and SS are potential materials for remediation of Cd and As contaminated soil. They can effectively immobilize soil Cd and As and promote their transformation to the fractions that plants are difficult to uptake.

Methyl jasmonate mitigates high selenium damage of rice via altering antioxidant capacity, selenium transportation and gene expression.

Beneficial effects of methyl jasmonate (MeJA) on plants under different abiotic conditions have long been demonstrated. This study aimed to figure out how exogenous MeJA mitigated high-Se toxicity in rice from plant physiology and gene express perspective to provide the theory and technique for safe production of Se-rich rice. The results showed that low concentrations of MeJA at 0.1-1.0 µM inhibited high-Se induced nonreversible toxicity by enhancing antioxidant-system and reducing H2O2 and MDA content in rice seedlings. In comparison with control, addition of low concentrations of MeJA at 0.1-1.0 µM reduced the Se content in roots by 13.6-48.8% and in shoots by 52.6-59.9%. Besides, lower concentrations of MeJA decreased the Se(IV) transformation to SeCys and SeMet. The qRT-PCR analysis showed that application of low concentration of MeJA down-regulated the gene expression of OsNIP2;1, and OsPT2 in roots and OsNIP2;1, OsPT2, OsSBP1, and OsCS in shoots, which inhibited Se absorption. However, high concentrations of MeJA at 2.5-5.0 µM decreased antioxidant capacity and increased H2O2 and MDA content in rice seedlings. The results suggested that MeJA at 0.1-1.0 µM can be used to mitigate high-Se toxicity in rice production. This research augments the knowledge for future utilization of MeJA in down-regulating Se levels in crops.

Silicone stressed response of crayfish (Procambarus clarkii) in antioxidant enzyme activity and related gene expression.

Organosilicon has been widely used in various fields of industry and agriculture due to its excellent properties, such as high and low temperature resistance, flame retardant, insulation, radiation resistance and physiological inertia. However, organosilicon toxicity in aquatic animals is seldom known. In this research, two typical silicone or silane coupling agents (KH-560 (3-Glycidoxypropyltrimethoxysilane) and KH-570 (3-Methacryloxypropyltrimethoxysilane)) were used in a hydroponic experiment to evaluate the effects on survival rate, antioxidant response and gene expression in red swamp crayfish (Procambarus clarkii). Crayfishes were grown in black aquaculture boxes containing different concentrations (0, 10, 100 and 1000 mg L-1) of KH-560 and KH-570 for 72 h, and then crayfish samples were harvested and separated into tissues of carapace, gill and muscle for analysis. The results showed that silicone significantly increased malondialdehyde (MDA) content in muscle by 17%-38% except for the treatment of 100 mg L-1 KH-570, and reduced the survival rate of crayfish. Additionally, silicone KH-570 increased the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) by 15%-31%, 17%-35%, and 9%-46%, as well as the contents of ascorbate (AsA) and glutathione (GSH) by 19%-31%, and 23%-29% respectively, in muscle tissue, and similar results occurred in KH-560. In the carapace, however, SOD activity was significantly decreased at high concentrations level of both silicone treatments. Moreover, silicon (Si) content was higher in the abdominal muscle of crayfish after silicone treatment. Assay of gene expression showed an obvious increasing expression of antioxidant related genes (Sod1, Sod2, Cat1, Cat2, and Pod1, Pod2) under silicone stress. The above results suggested that silicone caused an obvious stress response in crayfish in both biochemical and molecular levels.

Synergistic effect of silicon and selenium on the alleviation of cadmium toxicity in rice plants.

Silicon (Si) and selenium (Se), two beneficial elements that alleviate cadmium (Cd) toxicity, are important for agricultural production and human health. However, the effects and related mechanisms of Si-Se interaction on Cd toxicity alleviation are still poorly understood. Herein, a hydroponic experiment was employed to evaluate the effects of Si and Se alone and together, on the growth, Cd content, and biochemical parameters of Cd-treated rice plants. The results revealed that both Si and Se can effectively alleviate Cd toxicity, and a strong synergistic effect of Si and Se was observed. Simultaneous use of Si and Se significantly promoted rice plant growth, decreased malondialdehyde (MDA) content in both the roots and shoots, and reduced Cd translocation factor leading to a significant 73.2 % decrease in shoot Cd content. Additionally, Si-Se interaction increased glutathione (GSH) content, phytochelatin (PC) content and Cd distribution in root cell walls and organelles. Furthermore, the relative expression of OsHMA2 was down-regulated, while those of OsNramp1 and OsMHA3 were up-regulated. The above findings suggest that synergistic effect of Si and Se on Cd toxicity amelioration occurs mainly via regulating gene expression, sequestering Cd in the root cell walls and organelles, and reducing Cd transfer to the shoots.

Remediation of hexachlorobenzene-contaminated soils with alkyl glycoside-enhanced desorption and zero-valent iron-EDTA-air treatment.

In this work, the use of a coupled process, alkyl glycoside (APG) enhanced soil desorption followed by the zero-valent iron-ethylenediaminetetraacetic acid (EDTA)-air (ZEA) Fenton-like system, was investigated for the remediation of a simulated hexachlorobenzene (HCB)-contaminated diatomite soil and a real HCB-contaminated soil. Three surfactants with different concentrations were studied to obtain the suitable soil desorption agent. Compared with APG0810 and Triton x-100, APG0814 showed a better solubilization effect due to its lower critical micelle concentration. With addition of 3000 mg L-1 APG0814, 35% of HCB was removed from contaminated diatomite soil, and a small amount of residual APG in diatomite soil was found to be beneficial for the soil dispersion. After treatment with the ZEA system, the removal efficiency of HCB in the diatomite soil desorption solution reached 76% in 2 h; we observed that a small amount of APG retained in the desorption solution accelerated the HCB removal. A real HCB-contaminated soil was used to verify the remediation effects. This study demonstrates that our approach is a feasible alternative for remediating soil contaminated with hydrophobic organic compounds.

Nitric oxide alleviates selenium toxicity in rice by regulating antioxidation, selenium uptake, speciation and gene expression.

In plants, excess selenium (Se) causes toxicity, while the beneficial effects of nitric oxide (NO) have verified in plants under various abiotic conditions. In order to ensure safely Se-enriched rice production, the objective of the research was to clarify how exogenous NO alleviated high Se toxicity in rice. Under high Se (25 µM) stress, the effects of exogenous NO (by applying sodium nitroprusside, an exogenous NO donor) on growth parameters, Se content, Se speciation, photosynthesis, antioxidant system, expressions of Se transport and metabolism-related genes (phosphate transporter, OsPT2; S-adenosylmethionine synthase 1, OsSAMS1; cysteine synthase, OsCS; Se-binding protein gene, OsSBP1) in rice seedlings were investigated by a hydroponic experiment. The results showed that exogenous NO alleviated high Se-induced irreversible damage to root morphology, growth, photosynthesis, antioxidant capacity and decreased the contents of MDA, H2O2 and proline significantly in rice seedlings. Compared with high Se treatment, application of exogenous NO reduced root Se content (10%), and the Se(VI) decreased by 100% in root and shoot. Besides, exogenous NO decreased the accumulation of inorganic Se speciation in rice roots and shoots. Also, the qRT-PCR analysis showed that down-regulated gene expressions of OsPT2, OsSAMS1 and OsCS affected significantly via exogenous NO. So, the exogenous NO could effectively decrease the toxicity of high Se treatment in rice.

[Stabilization of Arsenic-Contaminated Soils Using Fe-Mn Oxide Under Different Water Conditions].

Fe-Mn oxide (FM) was used to evaluate its stabilization effects on three typical arsenic (As)-contaminated soils in southern China under different water conditions (dry soil, moist soil, and flooded soil). With an increase in moisture content, the toxicity characteristic leaching procedure (TCLP) results for As decreased by 34.78%, 47.62%, and 13.64%, respectively,in Shaoguan,Hechi, and Changde, and then increased by 310.34%, 185.22%, and 23.38%, respectively. The results showed that adding a certain amount of water (30%) had a positive effect on decreasing the As concentration in the TCLP, but excessive amounts (80%) led to As re-release into the soil. The application of FM under flooding conditions has obvious advantages. In the three soils of Shaoguan,Hechi, and Changde, FM significantly reduced the As concentration in the TCLP by more than 99.00%, and reduced the soil available As content by 55.40%, 40.05%, and 16.92%, respectively. FM increased the specificandnon-specific adsorption of As to stabilize the bound fractions of hydrated iron-aluminum oxide, thus significantly reducing the biological effectiveness of soil As and soil environmental risk.FM reduced the available P in the soil in Shaoguan,Hechi, and Changde by 0.60%-6.67%, 15.74%-50.00%, and 32.48-40.39%, respectively. Our study revealed that FM can absorb a small amount of available P, which may limit P uptakeby agricultural products in P-deficient areas, while effectively inhibiting the non-point source pollution of soil to surrounding water bodiesin P-rich areas. The variation in pH after FM application in the three soils was only 0.04-0.07, which had little effect on the soil environment. FM has good prospects for stabilization of flooded As-contaminated soil. The results of this study provide an important scientific basis for soil As stabilization in China.

Comparative efficacy of organic and inorganic silicon fertilizers on antioxidant response, Cd/Pb accumulation and health risk assessment in wheat (Triticum aestivum L.).

In wheat production areas of China, soil lead (Pb) pollution is generally accompanied by cadmium (Cd) pollution and it is of considerable significance in repairing the Cd and Pb co-contaminated soils for safe agronomic production. Organosilicon fertilizer (OSiF) is a new type of silicon (Si) fertilizer that can effectively alleviate heavy metal toxicity in plants, but the mechanisms on its heavy metal detoxification are poorly understood. A soil pot experiment was conducted to evaluate and compare the effects of two OSiFs (OSiFA and OSiFB) and an inorganic silicon fertilizer (InOSiF) on wheat heavy metal uptake and biochemical parameters in a Cd and Pb co-contaminated soil. The results demonstrated that OSiFA, OSiFB and InOSiF could alleviate the Cd and Pb toxicity of wheat, as indicated by increasing wheat grain yield by 65%, 45% and 22%, respectively. The Si fertilizers enhanced leaf gas exchange attributes and chlorophyll content, whereas diminished the oxidative damage, as indicated by a lower level of hydrogen peroxide (H2O2) and malondialdehyde (MDA) content, and lower activity of superoxide dismutase (SOD) and catalase (CAT) activity, as compared with control. Adding OSiFA, OSiFB and InOSiF increased Si uptake in roots and shoots, thus reducing Cd and Pb accumulation in the wheat shoot, bran and flour, especially, flour Cd contents by 17%, 10% and 31% respectively, flour Pb contents by 74%, 53% and 48% respectively. Also, Si fertilizers application decreased the health risk index (HRI) of both Cd and Pb. The grey correlation degrees of OSiFA, OSiFB and InOSiF are 0.72, 0.77 and 0.61, respectively, indicating that the effects of OSiFs on detoxifying Cd and Pb could be better than that of InOSiF in wheat. Thus, the use of OSiFs might be a feasible approach to reduce Cd and Pb entry into the human body through crops.

Ascorbic acid induced activation of persulfate for pentachlorophenol degradation.

In the present study, ascorbic acid (AA) induced persulfate activation was investigated for the further exploration of organic pollutants oxidation by persulfate. We interestingly found that AA showed a significant catalytic activity to persulfate. Under neutral pH and room temperature condition, about 71.3% of pentachlorophenol (PCP, 10 mg L-1) was decomposed in 180 min with 40 mmol L-1 persulfate and 1.0 mmol L-1 AA, while only 15.4% and 3.2% of PCP was removed by alone persulfate and AA respectively. The result of EPR spectra identified sulfate radical (SO4•-) and hydroxyl radical (OH) were generated during the reaction between persulfate and AA. Quenching experiments confirmed that both SO4- and OH contributed to the decomposition of PCP. With the addition of AA augmented from 0 to 1 mmol L-1, the PCP degradation ratio continuously increased. However, excess AA could consume the generated reactive oxygen species (ROSs) that led to the inhibition of PCP degradation. Meanwhile, the PCP degradation by persulfate-AA was strongly pH dependent. The PCP degradation rate was declined as the initial pH increased from 3.5 to 10.5. At pH above 12.5, the base activation began to predominate over AA activation of persulfate. Furthermore, it was observed that the AA inducing persulfate activation was related to the extent of AA ionization, while C6H8O6 promoted the highest persulfate activation for the PCP degradation, and C6H6O62- induced the lowest persulfate activation. This study indicates the high potential of AA induced persulfate activation for treatment of organochlorine contaminated water.

EDDS enhanced PCB degradation and heavy metals stabilization in co-contaminated soils by ZVI under aerobic condition.

In the present study, biodegradable ligand EDDS was employed to assist ZVI on simultaneous remediation of PCB and heavy metals co-contaminated soils under aerobic condition. With addition of 4 mmol L-1 EDDS and 5 g L-1 ZVI, the total removal ratio of PCB reached 75.3%, and the stabilization ratio of Pb and Cu attained 97.1% and 91.9% respectively. EDDS played two key roles during the process. Firstly, the addition of EDDS could enhance hydroxyl radical generation by ZVI and oxygen for the oxidation of PCB including distribution in the soil phase and dissolved form in the aqueous phase. Secondly, free EDDS could accelerate the release of Cu and Pb from the soil phase to the aqueous phase. As the oxidation of EDDS and the increase of pH value during the process, the dissolved Cu and Pb could be efficiently stabilized by iron oxyhydroxide through coprecipitation. Compared with ZVI/Air, ZVI/EDDS/Air treatment could significantly enhance the stabilization of Pb and Cu. The reason was the dissolution of Cu and Pb by EDDS extraction could reduce the mass transfer limitations between heavy metals and iron oxyhydroxide. Therefore, our study suggests a promising alternative for remediation of organic compounds and heavy metals co-contaminated soil.

Identification of fouling mechanisms in MBRs at constant flowrate: model applications and SEM-EDX characterizations.

A fundamental understanding of fouling mechanisms is critical to improving filtration operations. The performance of four parallel membrane bioreactors (MBRs) with different sludge retention times (SRTs) was monitored during long-term constant flowrate filtration. The characteristics of the membrane and transmembrane pressure (TMP) profiles obtained were studied to demonstrate fouling mechanisms. Both classical blocking models and their combined models were evaluated. The intermediate model provided very good agreement with all the TMP data. However, the combined cake-intermediate and intermediate-standard models were more effective in the description of the experimental data. Contributions analysis indicated that the cake, intermediate and standard blocking models were the dominant fouling mechanisms. Scanning electron microscopy and energy dispersive X-ray (SEM-EDX) imaging showed that cake blocking by organic matter and standard blocking by inorganic matter made the main contributions to membrane fouling. The combined cake-intermediate and intermediate-standard models may be applicable to systems where these two models are consistent with the experimentally observed fouling mechanisms in an MBR.

Remediation of arsenic contaminated soil by coupling oxalate washing with subsequent ZVI/Air treatment.

The application of a novel coupled process with oxalate washing and subsequent zero-valent iron (ZVI)/Air treatment for remediation of arsenic contaminated soil was investigated in the present study. Oxalate is biodegradable and widely present in the environment. With addition of 0.1 mol L(-1) oxalate under circumneutral condition, 83.7% and 52.6% of arsenic could be removed from a spiked kaolin and an actual contaminated soil respectively. Much more oxalate adsorption on the actual soil was attributed to the higher soil organic matter and clay content. Interestingly, oxalate retained in the washing effluent could act as an organic ligand to promote the oxidation efficiency of ZVI/Air at near neutral pH. Compared with the absence of oxalate, much more As(III) was oxidized. Arsenic was effectively adsorbed on iron (hydr)oxides as the consumption of oxalate and the increase of pH value. For the actual soil washing effluent, about 94.9% of total arsenic was removed after 120 min's treatment without pH adjustment. It has been demonstrated that As(V) was the dominant arsenic speciation adsorbed on iron (hydr)oxides. This study provides a promising alternative for remediation of arsenic contaminated soil in view of its low cost and environmental benign.

Efficient remediation of pentachlorophenol contaminated soil with tetrapolyphosphate washing and subsequent ZVI/Air treatment.

In this study, we demonstrate that pentachlorophenol contaminated soil can be efficiently remediated with tetrapolyphosphate washing and subsequent zerovalent iron (ZVI)/Air treatment. 2 mmol L(-1) of tetrapolyphosphate could wash away 52.8% of pentachlorophenol (PCP) at pH 7.0 and 84.2% of pentachlorophenol at pH 11.0 from contaminated soil owing to the promotion effect of tetrapolyphosphate on the soil matrix dispersion and the subsequent solubilization of pentachlorophenol. More importantly, tetrapolyphosphate ions remained in the washing effluent could greatly enhance the molecular oxygen activation by ZVI to oxidize the desorbed PCP without any pH adjustment, and also avoid the competitive consumption of reactive oxygen species, as caused by the common organic surfactants in the washing effluent. Therefore, 85.1% of pentachlorophenol could be aerobically removed from the washing effluent by merely using 5 g L(-1) of ZVI. We also interestingly found that the dissolved iron ions released from the soil could enhance the oxidation of pentachlorophenol in the washing effluent, but the dissolved organic matter had the opposite effect. This study suggests the coupling tetrapolyphosphate washing and subsequent ZVI/Air treatment is an optional approach to remediate pentachlorophenol contaminated soil in view of its low cost and environmental benign.

Design of a highly efficient and wide pH electro-Fenton oxidation system with molecular oxygen activated by ferrous-tetrapolyphosphate complex.

In this study, a novel electro-Fenton (EF) system was developed with iron wire, activated carbon fiber, and sodium tetrapolyphosphate (Na6TPP) as the anode, cathode, and electrolyte, respectively. This Na6TPP-EF system could efficiently degrade atrazine in a wide pH range of 4.0-10.2. The utilization of Na6TPP instead of Na2SO4 as the electrolyte enhanced the atrazine degradation rate by 130 times at an initial pH of 8.0. This dramatic enhancement was attributed to the formation of ferrous-tetrapolyphosphate (Fe(II)-TPP) complex from the electrochemical corrosion (ECC) and chemical corrosion (CC) of iron electrode in the presence of Na6TPP. The Fe(II)-TPP complex could provide an additional molecular oxygen activation pathway to produce more H2O2 and (•)OH via a series single-electron transfer processes, producing the Fe(III)-TPP complex. The cycle of Fe(II)/Fe(III) was easily realized through the electrochemical reduction (ECR) process on the cathode. More interestingly, we found that the presence of Na6TPP could prevent the iron electrode from excessive corrosion via phosphorization in the later stage of the Na6TPP-EF process, avoiding the generation of iron sludge. Gas chromatograph-mass spectrometry, liquid chromatography-mass spectrometry, and ion chromatography were used to investigate the degradation intermediates to propose a possible atrazine oxidation pathway in the Na6TPP-EF system. These interesting findings provide some new insight on the development of a low-cost and highly efficient EF system for wastewater treatment in a wide pH range.