Increased attention has been given to the fate of pollutants such as polycyclic aromatic hydrocarbons (PAHs) introduced to the wastewater treatment plants.Dissolved and adsorbed PAHs were detected in the centralized wastewater treatment plant of a chemical industry zone in Zhejiang Province,China.The most abundant PAHs were the low molecular weight PAHs (e.g.,Acy,Ace,Flu and Phe),accounting for more than 80% of the total 16 PAHs in each treatment stage.Phase partitioning suggested that the removal of PAHs in every treatment stage was influenced greater by the sorption of particles or microorganisms.The removal efficiencies of individual PAHs ranged between 4% and 87% in the primary sedimentation stage,between 1% and 42% in anaerobic hydrolysis stage,between <1% and 70% in aerobic bio-process stage,between 1.5% and 80% in high-density clarifier stage,and between 44% and 97% in the whole treatment process.Mass balance calculations in primary stage showed significant losses for low molecular weight PAHs and relatively good agreements for high molecular weight PAHs as well as in anaerobic hydrolysis,high-density clarifier stage and sludge stream for most PAHs.Great gains of 60%-150% were obtained for high molecular weight PAHs in aerobic bio-process stage due to biosorption and bioaccumulation.Our investigations found that PAHs entering the wastewater treatment plant (WWTP) could be derived from the dyeing chemical processes as the byproducts,and the contribution supported by the largest dyeing chemical group was up to 48%.
Oxidation of S(Ⅳ)to S(Ⅵ)in the effluent of a flue gas desulfurization(FGD)system.is very critical for industrial applications of seawater FGD.This paper reports a pulsed corona discharge oxidation process combined with a TjO_2 photocatalyst to convert S(Ⅳ)to S(Ⅵ)in artificial seawater.Experimental results show that the oxidation of S(Ⅳ)in artificial seawater is enhanced in the pulsed discharge plasma process through the application of Ti02coating electrodes.The oxidation rate of S(IV)using Ti metal as a ground electrode is about2.0x10^(-4)mol·L^(-1)·min^(-1),the oxidation rate using TiO_2/Ti electrode prepared by annealing at500℃in air is 4.5x10^(-4)mol·L^(-1)·min^(-1),an increase with a factor 2.25.The annealing temperature for preparing TiO_2/Ti electrode has a strong effect on the oxidation of S(Ⅳ)in artificial seawater.The results of in-situ emission spectroscopic analysis show that chemically active species(i.e.hydroxyl radicals and oxygen radicals)are produced in the pulsed discharge plasma process.Compared with the traditional air oxidation process and the sole plasma-induced oxidation process,the combined application of TiO_2 photocatalysts and a pulsed high-voltage electrical discharge process is useful in enhancing the energy and conversion efficiency of S(Ⅳ)for the seawater FGD
Titanium dioxide (TiO2 ) thin films were grown onto Indium tin oxide (ITO) glass under atmospheric pressure by chemical vapor deposition (AP-MOCVD) using titanium tetraisopropoxide astitanium precursor. The as-prepared TiO2 /ITO films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and photoelectrochemical measurements. Their photocatalytic (PC) and photoelectrocatalytic (PEC) activities were evaluated based on the results of methyl orange dye (MO) degradation experiments in aqueous solution. The difference between the front side (EE, electrolyte/electrode interface) and the back side (SE, substrate/electrode interface) illumination was evaluated in both photocurrent and MO degradation experiments. The effect of the film thickness on degradation rate by PEC under the two illumination directions was also studied. Stability of TiO2 /ITO film electrode was investigated in repetitive degradation experiments. Overall, the TiO2 /ITO film with thickness ranging from 321 to1440 nm deposited by MOCVD method is an effective photoelectrode for MO degradation under SE illumination in PEC reaction system.
