Chuanping Feng

Development of a high performance electrochemical wastewater treatment system.

In order to construct a high performance electrochemical system for practical use in industrial and municipal wastewater treatment, laboratory scale electrochemical experiments were performed to select anode materials by applying pulse voltage. Based on the results obtained from laboratory experiments, a pilot plant of electrochemical treatment system (0.3 m3 h(-1)) was successfully developed, in which electrocoagulation and electrooxidation processes were used. The performance of the treatment system was evaluated by treating domestic wastewater, pond water containing algae and wastewater from hog raising. As a result, production of hydroxyl radicals detected with p-nitrosodimethylaniline (RNO) at Ti/RuO(2)-TiO(2) anode was larger than with a platinum anode, and hydroxyl radicals were not detected at Ti anode. Moreover, a significant difference in electrocatalytic properties for ammonia oxidation between platinum and Ti/RuO(2)-TiO(2) electrodes was not observed from the cyclic voltammogram. The removal of T-N, T-P, NH(4)-N and COD from domestic wastewater and pond water containing algae was approximately 90%, while the removal of chlorophyll-a (chl-a) of algae was approximately 100%. Although the electrochemical treatment system was effective on biologically treated wastewater from hog raising, the treatment of raw wastewater was not remarkable. Therefore, the electrochemical treatment system requires pretreatment when used with wastewater containing high concentrations of suspended solids.

Electrochemical degradation of phenol using electrodes of Ti/RuO2-Pt and Ti/IrO2-Pt.

Electrochemical degradation of phenol was evaluated at two typical anodes, Ti/RuO(2)-Pt and Ti/IrO(2)-Pt, for being a treatment method in toxic aromatic compounds. The influences of current density, dosage of NaCl, initial phenol concentration on electrochemical phenol degradation were investigated. It was found that Ti/RuO(2)-Pt anode had a higher oxygen evolution potential than Ti/IrO(2)-Pt anode, which will increase the current efficiency for electrochemical degradation, and the instantaneous current efficiency (ICE) was relatively higher at the initial time during phenol electrolysis. HOCl formed during electrolysis would play an important role on the oxidation of phenol. For the Ti/RuO(2)-Pt anode, phenol concentration decreased from around 8mg/L to zero after 30min of electrolysis with 0.3g/L NaCl as supporting electrolyte at the current density of 10mA/cm(2). Although phenol could be completely electrochemical degraded at both Ti/RuO(2)-Pt and Ti/IrO(2)-Pt anodes, phenol degradation was slower at the Ti/IrO(2)-Pt anode than at the Ti/RuO(2)-Pt anode due to the fact that passivation was to be found at the Ti/IrO(2)-Pt anode.

Denitrification of nitrate contaminated groundwater with a fiber-based biofilm reactor

A fiber-based biofilm reactor was developed using a laboratory-scale apparatus for treatment of nitrate-contaminated groundwater. Denitrification bacteria were inoculated by anaerobic sludge from a wastewater treatment plant. Nitrate removal efficiency, nitrite accumulation, COD and pH in the treated water were investigated under various conditions set by several parameters including hydraulic retention times (HRTs) (24, 20, 16, 12, 8, 4 and 2h), influent nitrate loading (around 50, 100 and 150 NO(3)(-)-N mg L(-1)), pH (5, 6, 7, 8, and 9) and ratios of carbon to nitrogen (C/N=3.00, 2.00, 1.50 1.25 and 1.00). The experimental results demonstrated that the optimum reaction parameters were pH 7-7.5,C/N=1.25 and HRT=8h, under which over 99% of NO(3)(-)-N was removed, almost no NO(2)(-)-N accumulated and COD was nearly zero in treated water when the concentration of NO(3)(-)-N was around 100.00 mg L(-1) in influent.

Simultaneous reduction of nitrate and oxidation of by-products using electrochemical method

Electrochemical denitrification was studied with an objective to enhance the selectivity of nitrate to nitrogen gas and to remove the by-products in an undivided electrochemical cell, in which Cu-Zn cathode and Ti/IrO(2)-Pt anode were assembled. In the presence of 0.50 g/L NaCl as supporting electrolyte, the NO(3)(-)-N decreased from 100.0 to 9.7 mg/L after 300 min electrolysis; no ammonia and nitrite were detected in the treated solution. The surface of the cathode was appeared to be rougher than unused after electrolysis at initial pH 6.5 and 12.0. After electrolysis of 5h at the initial pH 3.0, passivation of the Cu-Zn cathode was observed. The reduction rate slightly increased with increasing current density in the range of 10-60 mA/cm(2) and temperatures had little effect on nitrate reduction. Nitrate could be completely removed by the simultaneous reduction and oxidation developed in this study, which is suitable for deep treatment of nitrate polluted water.

Nitrate removal from groundwater by cooperating heterotrophic with autotrophic denitrification in a biofilm–electrode reactor

An intensified biofilm-electrode reactor (IBER) combining heterotrophic and autotrophic denitrification was developed for treatment of nitrate contaminated groundwater. The reactor was evaluated with synthetic groundwater (NO(3)(-)-N50 mg L(-1)) under different hydraulic retention times (HRTs), carbon to nitrogen ratios (C/N) and electric currents (I). The experimental results demonstrate that high nitrate and nitrite removal efficiency (100%) were achieved at C/N = 1, HRT = 8h, and I = 10 mA. C/N ratios were reduced from 1 to 0.5 and the applied electric current was changed from 10 to 100 mA, showing that the optimum running condition was C/N = 0.75 and I = 40 mA, under which over 97% of NO(3)(-)-N was removed and organic carbon (methanol) was completely consumed in treated water. Simultaneously, the denitrification mechanism in this system was analyzed through pH variation in effluent. The CO(2) produced from the anode acted as a good pH buffer, automatically controlling pH in the reaction zone. The intensified biofilm-electrode reactor developed in the study was effective for the treatment of groundwater polluted by nitrate.

Fluoride removal from water by granular ceramic adsorption

A new medium, granular ceramic, has been developed for fluoride removal from water. Granular ceramic is a solid-phase medium that produces a stable Al-Fe surface complex for fluoride adsorption. BET, SEM, and EDS were used to characterize the physical attributes (particle size, pore size and distribution, surface roughness) of the granular ceramic. Fluoride adsorption characteristics were studied in a batch system with respect to changes in initial concentration of fluoride, pH of solution, and coexisting ions. Fluoride adsorption was found to be pH dependent and the maximum removal of fluoride was obtained at pH 5.0-8.0. equilibrium adsorption data were obtained at 293, 303, and 323 K, and interpreted in terms of the Langmuir and Freundlich isotherm equations. The experimental data revealed that the Freundlich isotherm equation gives a more satisfactory fit for fluoride removal. The adsorption process was observed to follow a pseudo-second-order kinetic model and intraparticle diffusion was indicated to play a major role in fluoride uptake. Fluoride adsorption was reduced in the presence of phosphate and sulfate ions and increased slightly in the presence of chloride and nitrate ions.

Preparation and characterization of porous granular ceramic containing dispersed aluminum and iron oxides as adsorbents for fluoride removal from aqueous solution

Porous granular ceramic adsorbents containing dispersed aluminum and iron oxides were synthesized by impregnating with salt solutions followed by precipitation at 600°C. In the present work detailed studies were carried out to investigate the effect of contact time, adsorbent dose, initial solution pH and co-existing anions. Characterization studies on the adsorbent by SEM, XRD, EDS, and BET analysis were carried out to clarify the adsorption mechanism. The adsorbents were sphere in shape, 2-3mm in particle size, highly porous and showed specific surface area of 50.69 sq m/g. The fluoride adsorption capacity of prepared adsorbent was 1.79 mg/g, and the maximum fluoride removal was obtained at pH 6. Both the Langmuir and Freundlich isotherm models were found to represent the measured adsorption data well. The experimental data were well explained with pseudo-second-order kinetic model. Results from this study demonstrated potential utility of Al/Fe dispersed in porous granular ceramics that could be developed into a viable technology for fluoride removal from aqueous solution.

Treatment of nitrate contaminated water using an electrochemical method

Treatment of nitrate contaminated water which is unsuitable for biological removal using an electrochemical method with Fe as a cathode and Ti/IrO(2)-Pt as an anode in an undivided cell was studied. In the absence and presence of 0.50 g/L NaCl, the nitrate-N decreased from 100.0 to 7.2 and 12.9 mg/L in 180 min, respectively, and no ammonia and nitrite by-products were detected in the presence of NaCl. The nitrate reduction rate increased with increasing current density, with the nitrate reduction rate constant k(1) increasing from 0.008 min(-1) (10 mA/cm(2)) to 0.016 min(-1) (60 mA/cm(2)) but decreasing slightly with increasing NaCl concentration. High temperature favoured nitrate reduction and the reaction followed first order kinetics. The combination of the Fe cathode and Ti/IrO(2)-Pt anode was suitable for nitrate reduction between initial pH values 3.0 and 11.0. e.g. k(1)=0.010 min(-1) (initial pH 3.0) and k(1)=0.013 min(-1) (initial pH 11.0). Moreover, the surface of all used cathodes appeared rougher than unused electrodes, which may have increased the nitrate reduction rate (4-6%).

Behavior of autotrophic denitrification and heterotrophic denitrification in an intensified biofilm-electrode reactor for nitrate-contaminated drinking water treatment

An intensified biofilm-electrode reactor (IBER) was developed to treat nitrate-contaminated drinking water. Different running conditions were conducted to investigate the behavior of autotrophic denitrification (AD) and heterotrophic denitrification (HD) in the IBER. In AD process, the nitrate nitrogen coulomb-reduction rate was used to evaluate the performance of the reactor. The maximum NO(3)(-)-N removal efficiency was 6.8% at the current of 60 mA, while nitrate nitrogen coulomb-reduction rate was 0.024 mg C(-1). The optimum conditions for HD process were C/N=0.8 and HRT=8h, under which complete NO(3)(-)-N removal and no NO(2)(-)-N accumulation were observed. With the cooperative effect of AD and HD in the heterotrophic and autotrophic denitrification (HAD) process, large treatment capacity, high denitrification efficiency, and low nitrite and ammonia accumulation were achieved. The results proved that HAD process was superior to single AD and HD for nitrate removal in the IBER.

Immobilization of heavy metals in sewage sludge by using subcritical water technology

Heavy metals (HMs) immobilization in sewage sludge was investigated by using subcritical water technology (SCWT) in this study. The characteristics of sludge and toxicity of HMs were analyzed after SCWT process. The results showed that besides large reduction in sludge volume, SCWT had some positive effect on HMs dissolution into liquid phase, while the majority of HMs was still accumulated in solid phase. The direct toxicity and bioavailability of HMs in sludge was greatly decreased with no toxicity fractions of HMs highly increased. Pb was always at low risk level and the risk of other HMs was greatly reduced from low risk to no risk after SCWT treatment. Moreover, the leaching toxicity of HMs declined after SCWT and the best result was obtained at 280°C with the metal concentrations in leachate decreased by 97.46%, 93.91%, 86.14%, 73.67%, 71.93% and 10.71% for Cu, Cd, Zn, Cr, Ni and Pb, respectively.