Dechlorination by combined electrochemical reduction and oxidation.

Chlorophenols are typical priority pollutants listed by USEPA (U.S. Environmental Protection Agency). The removal of chlorophenol could be carried out by a combination of electrochemical reduction and oxidation method. Results showed that it was feasible to degrade contaminants containing chlorine atoms by electrochemical reduction to form phenol, which was further degraded on the anode by electrochemical oxidation. Chlorophenol removal rate was more than 90% by the combined electrochemical reduction and oxidation at current of 6 mA and pH 6. The hydrogen atom is a powerful reducing agent that reductively dechlorinates chlorophenols. The instantaneous current efficiency was calculated and the results indicated that cathodic reduction was the main contributor to the degradation of chlorophenol.

Decomposition of simulated odors in municipal wastewater treatment plants by a wire-plate pulse corona reactor.

Decomposition of simulated odors in municipal wastewater treatment plants was investigated experimentally by a wire-plate pulse corona reactor. A new type of high pulse voltage source with a thyratron switch and a Blumlein pulse forming network (BPFN) was adopted in our experiments, and the testing malodorants were ammonia, ethanethiol and tri-methyl amine, respectively. The maximum output power of the pulse voltage source and the maximum peak voltage were 1 kW and 100 kV. The experiments were conducted at the gas-flow rate of 4.0-23.0 m3 h(-1). Important parameters, including peak voltage, pulse frequency, capacitance (inductance) of the BPFN, gas-flow rate, initial concentration, which influenced on the removal efficiency, were investigated. The results show that the odors can be treated effectively. Almost 100% removal efficiency was obtained for 32 mg m(-3) ammonia at the gas-flow rate of 4.0 m(3) h(-1). The maximum removal efficiencies of 85 mg m(-3) ethanethiol and 750 mg m(-3) tri-methyl amine at 10.0 m(3) h(-1) were 98% and 91%, respectively. The energy yield of 110 mg m(-3) ammonia was 2.99 g kWh(-1) when specific energy density was 106 Jl(-1). In the cases of ammonia, ethanethiol and tri-methyl amine removal, ozone and nitrogen oxides were observed in the exit gas. The carbon and sulfur elements of ethanethiol and tri-methyl amine were mainly converted to carbon dioxide, carbon monoxide and sulfur dioxide. Moreover, the ammonium nitrates and sulfur were discovered in the reactor.

[Properties of Pesudomonas sp. DN-1 in reduction of nitric oxide chelate absorption solution].

Metal chelate absorption is deemed as a promising method of NO removal in FGD system, but the difficulty in the regeneration of the absorption solution hinders its further development. An original method with microbial reduction is proposed in this paper. With the adding of Psudomonas sp. DN-1, which was newly isolated from wastewater treatment plant, FeII (EDTA) NO will be reduced to the environmentally benign gaseous product of N2, and thus FeII (EDTA) was regenerated simultaneously. The effects of the types and amount of carbon source, FeII (EDTA) NO concentration, pH, temperature and the biomass inoculation on bio-reduction efficiency were investigated. The results showed that the microorganism exhibited good performance on bio-reduction of FeII (EDTA) NO with the carbon sources of glucose. 250 mg x L(-1) glucose was enough for microorganism to reduce 6.50 mmol x L(-1) FeII (EDTA) NO completely. The rate of FeII (EDTA) NO reduction did not increase with adding a larger amount of carbon source. The bio-reduction could be achieved efficiently among the temperature range of 40 - 45 degrees C and a pH range of 6.9 - 7.2. The bio-reduction rate increased with the increasing of biomass inoculation. When FeII (EDTA) NO concentration is less than 11.8 mmol x L(-1), the reduction rate increased as the concentration increases, while the concentration is over 11.8 mmol x L(-1), the reduction rate keeps constant.

[Scale-up study on pulse corona discharge for the removal of toluene].

The scale-up experiments of the decomposition of toluene by pulse corona discharge in wire-plate reactor were investigated. The maximum output power of pulse voltage source was 1 kW, and the maximal peak voltage was 100 kV. The experiments were conducted with a gas-flow rate of 4-16 m3 x h(-1). Different parameters which influenced on removal efficiency were investigated, such as peak voltage, pulse frequency, inlet concentration of toluene, gas-flow rate. The results showed that the removal efficiency was improved obviously when the peak field intensity was changed in the range of 9-12 kV x cm(-1); the removal efficiency 88% was obtained when gas-flow rate, peak voltage, inlet concentration of toluene, pulse frequency were 4 m3 x h(-1), 69 kV, 1180 mg x m(-3), 300 pps respectively. The energy yield of toluene was about 16 g x (kW x h)(-1); the main products of decomposition were CO2 and H2O, few of CO. Combining the removal efficiency of toluene with energy density and inlet concentration of toluene, a reaction kinetic mathematic model was developed. By this model, the decomposition rate constant of toluene was 0.00356 L x J(-1). According to the results, the optimization design for the reactor and the matching of pulse voltage source were reckoned.

Regeneration of nitric oxide chelate absorption solution by two heterotrophic bacterial strains.

Ferrous chelate absorption is deemed a promising method for NO removal from flue gas, but the key problem is the difficulty to regenerate the absorption solution, i.e. the complexes of Fe(II)(EDTA)NO and Fe(III)(EDTA) in the solution. Two bacterial strains isolated recently from the sludge of the denitrification step of a municipal wastewater treatment plant could be applied effectively to regenerate the absorbent were Pseudomonas sp. and klebsiella trevisan sp. Pseudomonas sp. exhibited high reduction ability on Fe(II)(EDTA)NO and the klebsiella trevisan sp. was more suitable for Fe(III)(EDTA) re-duction.

Degradation of chlorophenol by in-situ electrochemically generated oxidant.

A novel in-situ electrochemical oxidation method was applied to the degradation of wastewater containing chlorophenol. Under oxygen sparging, the strong oxidant, hydrogen dioxide, could be in-situ generated through the reduction of oxygen on the surface of the cathode. The removal rate of chlorophenol could be increased 149% when oxygen was induced in the electrochemical cell. The promotion factor was estimated to be about 82.63% according to the pseudo-first-order reaction rate constant (min(-1)). Important operating parameters such as current density, sparged oxygen rate investigated. Higher sparged oxygen rate could improve the degradation of chlorophenol. To make full use of oxygen, however, sparged oxygen rate of 0.05 m(3)/h was adopted in this work. Oxidation-reduction potential could remarkably affect the generation of hydrogen peroxide. It was found that the removal rate of chlorophenol was not in direct proportion to the applied current density. The optimum current density was 3.5 mA/cm(2) when initial chlorophenol concentration was 100 mg/L and sparged oxygen rate was 0.05 m(3)/h.

Biodegradability of terephthalic acid in terylene artificial silk printing and dyeing wastewater.

As the characteristic pollutant, terephthalic acid (TA) was in charge of 40%-78% of the total COD of terylene artificial silk printing and dyeing wastewater (TPW-water). The studies on biodegradability of TA were conducted in a serial of activated sludge reactors with TPW-water. TA appeared to be readily biodegradable with removal efficiency over 96.5% under aerobic conditions, hardly biodegradable with removal efficiency below 10% under anoxic conditions and slowly biodegradable with a turnover between 31.4% and 56.0% under anaerobic conditions. TA also accounted for the majority of BOD in TPW-water. The process combined by anoxic, anaerobic and aerobic activated sludge reactor was suitable for TA degradation and TPW-water treatment, Further, the aerobic process was essentially much more effective than the anaerobic or anoxic one to degrade TA in TPW-water.