Zhimin Qiang

Electrochemical generation of hydrogen peroxide from dissolved oxygen in acidic solutions

Hydrogen peroxide (H2O2) was electro-generated in a parallel-plate electrolyzer by reduction of dissolved oxygen (DO) in acidic solutions containing dilute supporting electrolyte. Operational parameters such as cathodic potential, oxygen purity and mass flow rate, cathode surface area. pH, temperature, and inert supporting electrolyte concentration were systematically investigated as to improve the Faradic current efficiency of H2O2 generation. Results indicate that significant self-decomposition of H2O2 only occurs at high pH (> 9) and elevated temperatures (> 23 degrees C). Results also indicate that the optimal conditions for H2O2 generation are cathodic potential of -0.5 V vs. saturated calomel electrode (SCE), oxygen mass flow rate of 8.2 x 10(-2) mol/min, and pH 2. Under the optimal conditions, the average current density and average current efficiency are 6.4A/m2 and 81%, respectively. However, when air is applied at the optimal flow rate of oxygen, the average current density markedly decreases to 2.1 A/m2, while the average current efficiency slightly increases to 90%. The limiting current density is 6.4 A/m2, which is independent of cathode geometry and surface area. H2O2 generation is favored at low temperatures. In the concentration range studied (0.01-0.25 M), the inert supporting electrolyte (NaClO4) affects the total potential drop of the electrolyzer, but does not affect the net generation rate of H2O2.

Electrochemical regeneration of Fe2+ in Fenton oxidation processes.

This study is to establish optimal conditions for the minimization of iron sludge produced in Fenton oxidation processes by electro-regenerating Fe(2+) with constant potential (CPM) or constant current mode (CCM). Results indicate that the optimal cathodic potential for Fe(2+) regeneration is -0.1 V vs. the saturated calomel electrode (SCE) in terms of current efficiency. Keeping the initial Fe(3+) concentration ([Fe(3+)](0)) constant, the average current density produced at -0.1 V vs. SCE (CPM) is approximately equal to the optimal current density applied in the CCM. The suitable pH range is below the pH value determined by Fe(3+) hydrolysis. As expected, increasing cathode surface area and solution temperature notably increases Fe(2+) regeneration rate. At the optimal potential, the average current density increases linearly with [Fe(3+)](0), exhibiting a slope of 8.48 x 10(-3)(A/m(2))(mg/L)(-1). The average current efficiency varies with [Fe(3+)](0), e.g., 75% and 96-98% at 100 and > or = 500 mg/L [Fe(3+)](0), respectively. Once reaching 75% of Fe(2+) regeneration capacity, further regeneration becomes difficult due to Fe(3+) mass transfer limitation. Fe(2+) can also be effectively regenerated by dissolving iron sludge at low pH (usually </=1). The unit energy consumption is 2.0-3.0 k Wh per kg Fe(2+) regenerated.

Simultaneous determination of sulfonamides, tetracyclines and tiamulin in swine wastewater by solid-phase extraction and liquid chromatography-mass spectrometry.

Little is known about the contamination level of antibiotics in swine wastewater in China. The highly complex matrix of swine wastewater, which generally has a chemical oxygen demand (COD) concentration as high as 15,000 mg/L, makes it difficult to detect antibiotics at trace levels. In this work, a highly selective and sensitive analytical method was developed for simultaneous determination of three classes of commonly used veterinary antibiotics including five sulfonamides, three tetracyclines and one macrolide in swine wastewater using solid-phase extraction (SPE) and liquid chromatography-mass spectrometry (LC-MS). The method detection limits (MDL) in the swine wastewater were determined to be between 5 and 91 ng/L, depending on specific antibiotics. Except sulfamethizole, all the other eight antibiotics were detected in the swine wastewaters collected from three concentrated swine feeding plants located in the Beijing (China) area, showing a concentration range of 0.62-32.67 microg/L. These results reveal the representative concentration levels of selected antibiotics in the swine wastewaters of Beijing area.

Residual veterinary antibiotics in swine manure from concentrated animal feeding operations in Shandong Province, China

The scientific interest in the occurrence and fate of antibiotics in animal husbandry has increased during the past decades because of the emergence and development of antimicrobial resistance in pathogenic bacteria. This study developed a method for simultaneous detection of five sulfonamides, three tetracyclines and one macrolide in swine manure with stable recoveries (73.0-110.6%) and high sensitivity (limit of quantification <90 μg kg(-1)). Thereafter, a total of 126 swine manure samples, collected from 21 concentrated animal feeding operations (CAFOs) in Shandong Province of China during summer and winter, were analyzed. The potential influences of different sampling seasons, swine types and food sources on residual antibiotic concentrations were examined in detail. The maximum concentration of residual antibiotic could reach up to 764.4 mg kg(-1) (chlortetracycline), and the detection frequencies were 84.9-96.8% for tetracyclines, 0.8-51.6% for sulfonamides and 4.8% for macrolide. These data reveal that antibiotics were extensively used in CAFOs in this district and the manure may act as a non-specific source of antibiotic residue in farmlands and aquatic environments.

Removal of veterinary antibiotics from sequencing batch reactor (SBR) pretreated swine wastewater by Fenton's reagent

The large-scale application of veterinary antibiotics in livestock industry makes swine wastewater an important source of antibiotics pollution. This work investigated the degradation of six selected antibiotics, including five sulfonamides and one macrolide, by Fentons reagent in swine wastewater pretreated with sequencing batch reactor (SBR). The dosing mode and practical dosage of Fentons reagent were optimized to achieve an effective removal of antibiotics while save the treatment cost. The effects of initial pH, chemical oxygen demand (COD) and suspended solids (SS) of the SBR effluent on antibiotics degradation were examined. The results indicate that the optimal conditions for Fentons reagent with respect to practical application were as follows: batch dosing mode, 1.5:1 molar ratio of [H(2)O(2)]/[Fe(2+)], initial pH 5.0. Under the optimal conditions, Fentons reagent could effectively degrade all the selected antibiotics and was resistant to the variations in the background COD (0-419 mg/L) and SS (0-250 mg/L) of the SBR effluent. Besides, Fentons reagent helped to not only remove total organic carbon (TOC), heavy metals (As, Cu and Pb) and total phosphorus (TP), but also inactivate bacteria and reduce wastewater toxicity. This work demonstrates that the integrated process combining SBR with Fentons reagent could provide comprehensive treatment to swine wastewater.

Determination of endocrine-disrupting chemicals in the liquid and solid phases of activated sludge by solid phase extraction and gas chromatography-mass spectrometry

The highly complex matrix of activated sludge in sewage treatment plants (STPs) makes it difficult to detect endocrine-disrupting chemicals (EDCs) which are usually present at low concentration levels. To date, no literature has reported the concentrations of steroid estrogens in activated sludge in China and very limited data are available worldwide. In this work, a highly selective and sensitive analytical method was developed for simultaneous determination of two classes of EDCs, including estrone (E1), 17beta-estradiol (E2), estriol (E3), 17 alpha-ethynylestradiol (EE2), 4-nonylphenol (NP) and bisphenol A (BPA), in the liquid and solid phases of activated sludge. The procedures for sample preparation, extracts derivatization, and gas chromatography-mass spectrometry (GC-MS) quantification were all optimized to effectively determine target EDCs while minimizing matrix interference. The developed method showed good calibration linearity, recovery, precision, and a low limit of quantification (LOQ) for all selected EDCs in both liquid and solid phases of activated sludge. It was successfully applied to determine the concentrations of EDCs in activated sludge samples from two STPs located in Beijing and Shanghai of China, respectively.

Effect of artificial aeration on the performance of vertical-flow constructed wetland treating heavily polluted river water

Three lab-scale vertical-flow constructed wetlands (VFCWs), including the non-aerated (NA), intermittently aerated (IA) and continuously aerated (CA) ones, were operated at different hydraulic loading rates (HLRs) to evaluate the effect of artificial aeration on the treatment efficiency of heavily polluted river water. Results indicated that artificial aeration increased the dissolved oxygen (DO) concentrations in IA and CA, which significantly favored the removal of organic matter and NH(4+)-N. The DO grads caused by intermittent aeration formed aerobic and anoxic regions in IA and thus promoted the removal of total nitrogen (TN). Although the removal efficiencies of COD(Cr), NH(4+)-N and TN in the three VFCWs all decreased with an increase in HLR, artificial aeration enhanced the reactor resistance to the fluctuation of pollutant loadings. The maximal removal efficiencies of COD(Cr), NH(4+)-N and total phosphorus (TP) (i.e., 81%, 87% and 37%, respectively) were observed in CA at 19 cm/day HLR, while the maximal TN removal (i.e., 57%) was achieved in IA. Although the improvement of artificial aeration on TP removal was limited, this study has demonstrated the feasibility of applying artificial aeration to VFCWs treating polluted river water, particularly at a high HLR.

Fluorescence spectroscopic characterization of DOM fractions isolated from a filtered river water after ozonation and catalytic ozonation

Fluorescence spectra were applied to investigate the structural changes of four dominant dissolved natural organic matter (DOM) fractions of a filtered river water before and after ozonation and catalytic ozonation. The ozonation and catalytic ozonation with synthetic goethite (FeOOH) and cerium dioxide (CeO(2)) were carried out under normal conditions, i.e. pH 7, reaction time of 10 min, and ozone/DOC ratio of about 1. The fluorescence spectra were recorded at both excitation-emission matrix (EEM) and synchronous scanning modes. EEM results reveal that ozonation of these DOM fractions causes a significant decrease of the aromaticity of humic-like structures and an increase of electron withdrawing groups, e.g., carboxylic groups. The catalysts can further improve the destruction of the humic-like structures in catalytic ozonation. Synchronous spectra reveal that ozonation of hydrophobic acid and hydrophilic acid (HIA) yields a significant amount of by-products with low aromaticity and low molecular weight. Catalytic ozonation enhances substantially the formation of these by-products from HIA and improves the destruction of highly polycyclic aromatic structures for all examined DOM fractions.

A comparison of various rural wastewater treatment processes for the removal of endocrine-disrupting chemicals (EDCs)

The removal of six endocrine-disrupting chemicals (EDCs), including estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethinyl estradiol (EE2), bisphenol A (BPA) and 4-nonylphenol (NP), was investigated in 20 rural wastewater treatment facilities (WWTFs) located in a county of Zhejiang Province, China. These WWTFs adopted one of the four treatment processes: activated sludge (AS), constructed wetland (CW), stabilization pond (SP), and micro-power biofilm reactor (MP). Results indicate that all the six EDCs were detected in wastewater samples with NP showing a maximum detection frequency (97%) and a maximum influent concentration (5002 ng L(-1)). After biological treatment, the concentrations of E2, E3 and NP decreased remarkably, while E1, EE2 and BPA exhibited varying removal efficiencies that depended on the specific treatment process and sampling season. In general, the centralized AS process outperformed those decentralized processes (i.e., CW, SP and MP) and a higher removal of E1, EE2, NP and BPA in the AS process was observed in summer (>70%) than in winter. Among the three decentralized processes, the removal of EDCs in the SP process was limited, especially for E1, EE2 and BPA (18-46%) in winter. Due to an incomplete removal, the total concentration of target EDCs increased obviously in the mixing and downstream sections of a local river receiving the effluent from a typical WWTF (practicing AS). This study reveals that the design and operation of rural WWTFs should be optimized if an effective removal of EDCs is to be achieved.

Effects of calcium ions on surface characteristics and adsorptive properties of hydrous manganese dioxide

The effects of calcium ions (Ca(2+)) on the surface characteristics and adsorptive properties of hydrous manganese dioxide (deltaMnO(2)), taking arsenic and humic acid as model pollutants, were systematically investigated. The FTIR spectra and SEM/EDX analyses indicate coordination between Ca(2+) and the surface hydroxyls ([triple bond]Mn-OH) of deltaMnO(2), which leads to an increase of the surface zeta potential. Ca(2+) can facilitate deltaMnO(2) aggregation, as indicated by the particle size distribution (PSD) and on-line flocculating index (FI). The variation of deltaMnO(2) surface characteristics that is induced by Ca(2+) enhances the adsorption of humic acid (HA) and arsenic onto deltaMnO(2). The adsorption of HA is enhanced more significantly by Ca(2+) than that of arsenic, which is positively related to the coordination strength between Ca(2+) and individual pollutants. The SEM/EDX analysis shows the formation of Ca-HA complexes, which have a higher affinity for deltaMnO(2) than HA. The bridging effect of Ca(2+) plays a major role in enhancing HA adsorption onto deltaMnO(2). Due to different interactions between Ca(2+) and pollutants, the adsorption mechanism is pollutant-dependent in the presence of Ca(2+).