Method for establishing soil contaminant discharge inventory: An arsenic-contaminated site case study.

The existing method to survey site pollution is generally based on soil-groundwater sampling and instrumental analysis, which enables us to access the detailed soil pollution status while lacking quantitative association with industrial activities. It is urgent to understand contaminant discharge modes and establish a discharge inventory for achieving process-targeted pollution control. This study took a 40-year phosphate fertilizer-sulfuric acid site as an example and constructed a contaminant tracing method based on on-site investigations and detailed industrial data. These investigations and data were combined to determine the characteristic pollutant of this site, arsenic. And the calculation process of four-pathway pollution modes (atmospheric deposition, wastewater, solid waste leaching, and storage dripping) is derived from the existing acceptance criteria and risk assessment guidelines. They are set to calculate the arsenic's factory-to-soil discharge flux. The absent process contaminant release information and parameters, such as discharge coefficient, were obtained from soil-groundwater pollution control standards and discharge handbooks. It was found that the high concentration of arsenic (around 1930 mg g-1) was preponderantly caused by sulfur-iron slag and tailing leaching (96.19%), while the other pathways accounted for only 0.13% (atmospheric deposition), 3.59% (wastewater) and 0.09% (storage tank). Results were verified by the measured arsenic concentration, and the difference was +16.29%, which was acceptable. Finally, a contaminant discharge inventory was established with high-resolution spatial distribution and time-scale (historical discharge) evolution. The innovation of this study lies in the preliminary construction of a method for formulating soil discharge inventory. This study would contribute to the refined management of site pollution and reduction of source contaminants discharge. In addition, it will help infer the pollution condition of sites that are difficult to sample so as to help the government achieve precise source control.

Dual-layer Janus charged nanofiltration membranes constructed by sequential electrospray polymerization for efficient water softening.

The separation of hardness ions such as calcium and magnesium from hard water can improve water quality, which is important but technically challenging. Nanofiltration (NF) has attracted much attention because of its efficiency, environmental friendliness and low cost. However, common NF membranes with a singly (either positively or negatively) charged layer have insufficient water softening capacity. In this work, two types of dual-layer Janus charged polyamide NF membranes composed of oppositely charged inner and outer layers were developed for the first time by sequential electrospray polymerization strategy for efficient water softening. The effect of the microstructure of the dually charged barrier layer on the separation performance of divalent salt ions was explored. Detailed mechanistic studies revealed that the microstructure of the outer layer of the barrier layer played a crucial role in the ion separation of the Janus membrane due to its control of the reverse transport of ions. Janus charged polyamide NF membrane with a loose outer layer exhibited better water softening performance (93.6% of hardness removed) compared to the singly charged NF membranes due to the simultaneous dual electrostatic effect and no ion reverse transport confinement. This Janus charged NF membrane also possessed good antifouling performance, mainly due to its negatively charged outer layers. The mechanistic insights gained in this study reveal the huge potential of microstructural design toward high-performance Janus charged NF membranes, and provide important guidance on the future development of high-efficiency water softening NF membranes.

CFD-assisted modeling of the hydrodynamic cavitation reactors for wastewater treatment - A review.

Hydrodynamic cavitation has been a promising method and technology in wastewater treatment, while the principles based on the design of cavitational reactors to optimize cavitation yield and performance remains lacking. Computational fluid dynamics (CFD), a supplementation of experimental optimization, has become an essential tool for this issue, owing to the merits of low investment and operating costs. Nevertheless, researchers with a non-engineering background or few CFD fundamentals used straightforward numerical strategies to treat cavitating flows, and this might result in many misinterpretations and consequently poor computations. This review paper presents the rationale behind hydrodynamic cavitation and application of cavitation modeling specific to the reactors in wastewater treatment. In particular, the mathematical models of multiphase flow simulation, including turbulence closures and cavitation models, are comprehensively described, whilst the advantages and shortcomings of each model are also identified and discussed. Examples and methods of the coupling of CFD technology, with experimental observations to investigate into the hydrodynamic behavior of cavitating devices that feature linear and swirling flows, are also critically summarized. Modeling issues, which remain unaddressed, i.e., the implementation strategies of numerical models, and the definition of cavitation numbers are identified and discussed. Finally, the advantages of CFD modeling are discussed and the future of CFD applications in this research area is also outlined. It is expected that the present paper would provide decision-making support for CFD beginners to efficiently perform CFD modeling and promote the advancement of cavitation simulation of reactors in the field of wastewater treatment.

Study and actual application of the electrochemical reactor in flow-through mode based on channel confinement.

The method of enhancing mass transfer and improving reaction efficiency by confinement has attracted much attention in the electrochemical research field. In this research, to make low diffusion-limited electrochemical reactors fieldable, a new electrochemical reactor in flow-through mode was established with the mass-produced Ti/RuO2-IrO2 felt fibers as the electrodes. The effects of voltage, current, and electrode thickness were explored in this study. When the flow mode was switched from flow-by to flow-through, the single-pass degradation effect of rhodamine B rose from 4.4% to 74.8% under the same operating conditions. Meanwhile, a mass transfer model was established based on the results of removal efficiency and electrode channel parameters. The model was in good agreement with the new electrode parameters verification (R2 > 0.970). With this model, it could derive specific results on the effect of pore size change on the treatment effect. The impact of enhancing mass transfer by confining the pore sizes is most clearly gained at a certain range (less than 100 µm). Furthermore, a pilot-scale electrochemical reactor in flow-through mode was built, and excellent performance was shown in the treatment of actual waste leachate. The removal efficiencies of total nitrogen, ammonia, and nitrate were 80.9%, 88.6%, and 64.5% in 30 min, respectively. It will be a promising technology with good prospect.

In Plasma Catalytic Oxidation of Toluene Using Monolith CuO Foam as a Catalyst in a Wedged High Voltage Electrode Dielectric Barrier Discharge Reactor: Influence of Reaction Parameters and Byproduct Control.

Volatile organic compounds (VOCs) emission from anthropogenic sources has becoming increasingly serious in recent decades owing to the substantial contribution to haze formation and adverse health impact. To tackle this issue, various physical and chemical techniques are applied to eliminate VOC emissions so as to reduce atmospheric pollution. Among these methods, non-thermal plasma (NTP) is receiving increasing attention for the higher removal efficiency, non-selectivity, and moderate operation, whereas the unwanted producing of NO2 and O3 remains important drawback. In this study, a dielectric barrier discharge (DBD) reactor with wedged high voltage electrode coupled CuO foam in an in plasma catalytic (IPC) system was developed to remove toluene as the target VOC. The monolith CuO foam exhibits advantages of easy installation and controllable of IPC length. The influencing factors of IPC reaction were studied. Results showed stronger and more stable plasma discharge in the presence of CuO foam in DBD reactor. Enhanced performance was observed in IPC reaction for both of toluene conversion rate and CO2 selectivity compared to the sole NTP process at the same input energy. The longer the contributed IPC length, the higher the toluene removal efficiency. The toluene degradation mechanism under IPC condition was speculated. The producing of NO2 and O3 under IPC process were effectively removed using Na2SO3 bubble absorption.

The ignored emission of volatile organic compounds from iron ore sinter process.

Iron ore sintering is a major source of gaseous and particulate pollutants emission in iron smelt plant. The aim of present study is to characterize the volatile organic compounds (VOCs) emission profiles from iron ore sintering process. Both sinter pot test and sinter simulation experiment were conducted and compared. Out results showed that sinter process produced large quantity of VOCs together with NOx and SO2. VOCs and NO were produced simultaneously in sinter pot test from 3 to 24 min after ignition, flowed by SO2 production from 15 min to the end of sintering. Total VOCs (TVOC) concentration in sinter flue gas was affected by the coal and coke ratio in sinter raw material. The maximum TVOC concentration was 34.5 ppm when using 100% coal as fuel. Sinter simulation experiments found that the number of VOCs species and their concentrations were found by sinter temperature. The largest VOCs species varieties were obtained at 500 °C. Benzene, toluene, xylene and ethylbenzene were major VOCs in sinter flue gas based on the results from both simulation test and sinter pot. It thus demonstrated that in addition to NOx, SO2 and metal oxide particles, sinter flue gas also contained significant amount of VOCs whose environmental impact cannot be ignored. Based on our work, it is timely needed to establish a new VOC emission standard for sinter flue gas and develop advanced techniques to simultaneously eliminate multi-pollutants in iron ore sinter process.

Emission of sulfur dioxide from polyurethane foam and respiratory health effects.

Recently, health damage to children exposed to synthetic polyurethane (PU) running tracks has aroused social panic in China. Some possible toxic volatiles may be responsible for these damages. However, the exact cause remains unclear. We have detected a low concentration of sulfur dioxide (SO2; 1.80-3.30 mg/m3) on the surface of the PU running track. Surprisingly, we found that SO2 was generated from the PU running track, and even such a low concentration of SO2 could induce severe lung inflammation with hemorrhage, inflammatory cell infiltration, and inflammatory factor secretion in mice after 2-week exposure. Prolonged exposure (5 weeks) to the SO2 caused chronic pulmonary inflammation and pulmonary fibrosis in the mice. Peripheral hemogram results showed that platelet concentration increased significantly in the SO2 group compared to that in the control group, and the proportion of blood neutrophils and monocytes among total leukocytes was more imbalanced in the SO2 group (16.6%) than in the control group (8.0%). Further histopathology results of sternal marrow demonstrated that hematopoietic hyperplasia was severely suppressed with increased reticular stroma and adipocytes under SO2 exposure. These data indicate that a low concentration of SO2 generated spontaneously from PU running track outdoors as a secondary product is still harmful to health, as it impairs the respiratory system, hematopoiesis, and immunologic function. This indicates that the low-concentration SO2 could be a major cause of diseases induced by air pollution, such as chronic obstructive pulmonary disease.

Electrochemical study of enhanced nitrate removal in wastewater treatment using biofilm electrode.

Bioelectrochemical enhanced nitrate removal in wastewater with high total nitrogen and low organic carbon was electrochemically investigated focusing on the relationship between biochemical and electrochemical nitrogen cycles. Under optimized external voltage of -0.6 V, apparent nitrate removal rate of bioelectrochemical denitrification was 76% higher than normal biofilm denitrification. And with the introduction of biofilm on the electrode, new reduction peak of N2O, much larger current density, and 0.4 V positively shift of on-set potential of nitrate reduction reaction were observed, suggesting a synergy of electrochemical reaction and biological reaction through enhanced electrochemical reduction of intermediate products from biological process. Oxygen reduction reaction could not be avoided during nitrogen electrochemical reduction reaction since their similar reduction potential. But it led to decrease of oxygen concentration and therefore contribute to biological denitrification. Bacteria community tests also supported a dominant bacteria which could denitrify and use external electron.

Electrochemical nitrate reduction by using a novel Co3O4/Ti cathode.

Co3O4 film coated on Ti substrate is prepared using sol-gel method and applied as cathode material for electrochemical denitrification in this research. Preparation conditions including precursor coating times and calcination temperature are optimized based on NO3--N removal, NO2--N generation, NH4+-N generation and total nitrogen (TN) removal efficiencies. The influences of electrolysis parameters such as current density and NO3--N initial concentration are also investigated. In comparison with other common researched cathodes (Ti, Cu and Fe2O3/Ti), Co3O4/Ti exhibits better NO3--N removal and NH4+-N generation efficiencies. In order to remove NO3--N completely from water, Cl- is added to help further oxidize NH4+-N to N2. TN removal after 3 h treatment increases from 65% to 80%, 90% and 96% with the increase of Cl- from 0 mg L-1 to 500, 1000 and 1500 mg L-1, respectively. The mechanisms of NO3--N reduction on cathode and NH4+-N oxidation on anode in the absence and presence of Cl- are investigated in a double-cell reactor. Actual textile wastewater containing both NO3- and Cl- is also treated and the Co3O4/Ti cathode exhibits excellent stability and reliability. It is interesting to find out that FeCl2-H2O2 Fenton pretreatment is needed to remove extra COD and provide more Cl- to help oxidize NH4+-N to N2 at the same time.

Converting Ni-loaded biochars into supercapacitors: Implication on the reuse of exhausted carbonaceous sorbents.

Biochar derived from waste biomass has proven as a promising sorbent for removal of heavy metals from wastewater. However, proper disposal of such a heavy metal-containing biochar is challengeable. The major objective of this study is to create a reuse way by converting the heavy metal-loaded biochar into supercapacitor. Two biochars were produced from dairy manure and sewage sludge, respectively, and subjected to sorption of Ni from solution, and then the Ni-loaded biochar underwent microwave treatments for fabrication of supercapacitor. The specific capacitance of biochar supercapacitor increased with Ni loading, especially the Ni-loaded biochar further treated with microwave in which the capacitance increased by over 2 times, compared to the original biochar supercapacitors. The increase of capacitance in the Ni-loaded biochar supercapacitor following microwave treatment was mainly attributed to the conversion of Ni into NiO and NiOOH, which was evidenced by X-ray diffraction and X-ray photoelectron spectroscopy. The biochar supercapacitors, especially microwave-treated Ni-loaded biochar supercapacitors exhibited the high stability of specific capacitance, with less than 2% loss after 1000 charge-discharge cycles. This study demonstrated that Ni-loaded biochar can be further utilized for generation of supercapacitor, providing a potential way for the reuse of exhausted carbonaceous sorbents.

Novel recyclable adsorbent for the removal of copper(II) and lead(II) from aqueous solution.

Adsorbents synthesized with biopolymer have been widely used in the removal of toxic metal ions. Novel high-efficiency, recyclable, and low-cost adsorbents have received more and more attention. Chitosan and cellulose are the most abundant biopolymers in nature. Composite modified adsorbent (CSTEC) was synthesized as novel fibrous materials for the adsorption of Cu2+ and Pb2+ ions from water in this study. The functional fiber was characterized to investigate the surface appearance, functional groups, crystallinity, and thermal stability. The kinetics study revealed that adsorption processes of Cu2+ and Pb2+ ions on the CSTEC followed the second-order kinetics model. CSTEC showed better performance (Cu2+, 95.24; Pb2+, 144.93mgg-1) than most of other adsorbents. The co-existing ions (K+, Na+, Mg2+) had no significant influence on the removal of target ions by the CSTEC. The excellent reusability indicated that CSTEC had the promising application in the treatment of toxic metal pollution.

Comparative and competitive adsorption of Pb(II) and Cu(II) using tetraethylenepentamine modified chitosan/CoFe2O4 particles.

In this paper, tetraethylenepentamine (TEPA) modified chitosan/CoFe2O4 particles were prepared for comparative and competitive adsorption of Cu(II) and Pb(II) in single and bi-component aqueous solutions. The characteristics results of SEM, FTIR and XRD indicated that the adsorbent was successfully fabricated. The magnetic property results manifested that the particles with saturation magnetization value of 63.83emug-1 would have a fast magnetic response. The effects of experimental parameters including contact time, pH value, initial metal ions concentration and coexisting ions on single and bi-component adsorption were investigated. The results revealed that the adsorption kinetic was followed pseudo-second-order kinetic model, indicating that chemical adsorption was the rate-limiting step. Sorption isotherms were also determined in single and bi-component solutions with different mass ratio of Cu(II) to Pb(II) (Cu(II)/Pb(II)) and fitted using Langmuir and Freundlich isotherm models. A better fit for Cu(II) and Pb(II) adsorption were obtained with Langmuir model, with a maximum sorption capacity of 168.067 and 228.311mgg-1 for Cu(II) and Pb(II) in single component solution, 139.860 and 160.256mgg-1 in bi-component solution (Cu(II)/Pb(II)=1:1), respectively. The present results suggest that TEPA modified chitosan/CoFe2O4 particles are feasible and satisfactory adsorbent for efficient removal of Cu(II) and Pb(II) ions.

Fast removal of copper ions from aqueous solution using an eco-friendly fibrous adsorbent.

Functional PET fiber (PET-AA-CS) was prepared by oxygen-plasma pretreatment and grafting of acrylic acid (AA) and low-molecular-weight chitosan (LMCS) on the polyethylene glycol terephthalate (PET) substrate. This adsorbent was targeted for quick removal of metal ion in river pollutions with an easy recycling of the fiber after emergency processing. The fabricated PET-AA-CS was characterized by the scanning electron microscope (SEM), contact angle, fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) to look into its morphology, surface functional groups, and adsorption mechanism of copper ions from the aqueous solution. The overall adsorption process of copper ions on the PET-AA-CS was pH-dependent with an optimal pH value of 5.0, at which a maximum capacity of 68.97 mg g(-1) was obtained. The result of fitting also shows that adsorption process follows the Langmuir isotherm and pseudo-second-order model. Moreover, the material shows good stability during 5 cycles of adsorption and desorption, and also shows no significant effect of co-existing ions including Ca(2+), Mg(2+), K(+), Cl(-), and et al. In general, PET-AA-CS developed in this study shows significant benefit of eco-friend and cost-efficiency for fast removal of copper ions in potential river metal pollutions comparing with traditional adsorbents.

Optimization and application of TiO2/Ti-Pt photo fuel cell (PFC) to effectively generate electricity and degrade organic pollutants simultaneously.

A TiO2/Ti-Pt photo fuel cell (PFC) was established to generate electricity and degrade organic pollutants simultaneously. The electricity generation was optimized through investigation the influences of photoanode calcination temperature and dissolve oxygen on the resistances existing in PFC. TiO2 light quantum yield was also improved in PFC which resulted in a higher PC degradation efficiency. Two kinds of real textile wastewaters were also employed in this PFC system, 62.4% and 50.0% Coulombic efficiency were obtained for 8 h treatment. These refractory wastewaters with high salinity may become good fuels in PFC because a) TiO2 has no selectivity and can degrade nearly any organic substance, b) no more electrolyte is needed due to the high salinity, c) the energy in wastes can be recovered to generate electricity. The electricity generated by the PFC was further applied on a TiO2/Ti rotating disk photoelectrocatalytic reactor. A bias voltage between 0.6 and 0.75 V could be applied and the PC degradation efficiency was significantly improved. This result was similar with that obtained by a 0.7 V DC power.

Treatment of mature landfill leachate by internal micro-electrolysis integrated with coagulation: a comparative study on a novel sequencing batch reactor based on zero valent iron.

A comparative study of treating mature landfill leachate with various treatment processes was conducted to investigate whether the method of combined processes of internal micro-electrolysis (IME) without aeration and IME with full aeration in one reactor was an efficient treatment for mature landfill leachate. A specifically designed novel sequencing batch internal micro-electrolysis reactor (SIME) with the latest automation technology was employed in the experiment. Experimental data showed that combined processes obtained a high COD removal efficiency of 73.7 ± 1.3%, which was 15.2% and 24.8% higher than that of the IME with and without aeration, respectively. The SIME reactor also exhibited a COD removal efficiency of 86.1 ± 3.8% to mature landfill leachate in the continuous operation, which is much higher (p<0.05) than that of conventional treatments of electrolysis (22.8-47.0%), coagulation-sedimentation (18.5-22.2%), and the Fenton process (19.9-40.2%), respectively. The innovative concept behind this excellent performance is a combination effect of reductive and oxidative processes of the IME, and the integration electro-coagulation. Optimal operating parameters, including the initial pH, Fe/C mass ratio, air flow rate, and addition of H(2)O(2), were optimized. All results show that the SIME reactor is a promising and efficient technology in treating mature landfill leachate.

Electrosorption-enhanced solid-phase microextraction using activated carbon fiber for determination of aniline in water.

Electrosorption-enhanced solid-phase microextraction (EE-SPME) based on activated carbon fiber (ACF) was developed for determination of aniline in aqueous solution. A porous ACF, served as working electrode in electrosorption procedure, was prepared and attached to a commercial manual SPME device. Parameters affecting the adsorption efficiency were investigated. Under optimized condition, which was 400 mV electrosorption potential, 0.01 M Na(2)SO(4) electrolyte, pH 7, and electrosorption at 40 degrees C for 10 min, the method exhibited wide linear range (0.1-100 microg L(-1), R(2)=0.9980), good repeatability of adsorption (RSD 6.15%, n=6), and low detection limit (0.02 microg L(-1)). The feasibility of the method was evaluated by analyzing lake water spiked with aniline. Comparison was made with direct immersion (DI) ACF-SPME without electrosorption enhancement. The proposed procedure was demonstrated to be a simple, fast, sensitive sample preparation method for determination of aniline in water samples.

Electrochemical effect on denitrification in different microenvironments around anodes and cathodes.

A bio-anode reactor and a bio-cathode reactor were developed to investigate the microenvironments around anodes and cathodes and their effects on denitrification. With an applied current of 40 mA, the oxidation-reduction potentials (ORPs) in the bio-cathode and bio-anode reactors were 100-200 mV lower and 50 mV higher, respectively, than that in the control reactor (a normal bio-reactor). The cathode reaction enhanced denitrification and the anode reaction inhibited denitrification. At 40 mA, the denitrification rate in the bio-cathode reactor was 55.1% higher than that in the control reactor. At 75 mA, the denitrification rate in the bio-anode reactor was just 33.5% of that in control reactor. Electric current of less than 20 mA had no effect on the most probable number (MPN) of denitrifiers, but at 75 mA, the MPN of denitrifiers decreased by 90% in the bio-anode reactor. In the bio-cathode reactor, the MPN of denitrifiers increased more than 100% for the lower ORP environment produced by a cathode reaction at 75 mA.