Xu Zhai

Enhanced ozonation of dichloroacetic acid in aqueous solution using nanometer ZnO powders

Nanometer zinc oxide (ZnO) powders were used as a catalyst to enhance the ozonation for the degradation of dichloroacetic acid (DCAA) in aqueous solution. The batch experiments were carried out to investigate the effects of key factors such as catalyst dosage, ozone dosage, solution pH and tert-butyl alcohol (t-BuOH) on the degradation efficiency of DCAA. Density functional theory (DFT) was adopted to explore the mechanism of generating hydroxyl radical (*OH) on the ZnO surface. The results showed that adsorption and ozonation processes were not effective for DCAA removal, and the addition of ZnO catalyst improved the degradation efficiency of DCAA during ozonation, which caused an increase of 22.8% for DCAA decomposition compared to the case of ozonation alone after 25 min. Under the same experimental conditions, the DCAA decomposition was enhanced by increasing catalyst dosage from 100 to 500 mg/L and ozone dosage from 0.83 to 3.2 mg/L. The catalytic ozonation process is more pronounced than the ozonation process alone at pH 3.93, 6.88, and 10. With increasing the concentration of t-BuOH from 10 to 200 mg/L, the degradation of DCAA was significantly inhibited in the process of catalytic ozonation, indicating that ZnO catalytic ozonation followed *OH reaction mechanism. Based on the experimental results and DFT analysis, it is deduced that the generation of *OH on the ZnO surface is ascribed to the adsorption of molecule ozone followed by the interaction of adsorbed ozone with active sites of the catalyst surface. It is also concluded that ZnO may be an effective catalyst for DCAA removal, which could promote the formation of *OH derived from the catalytic decomposition of ozone.

One-Step Pyrolysis Process for Recover Zinc and Mercury from Spent Zinc-Manganese Batteries

In this paper, One-step pyrolysis process for the recovery of mercury and zinc from spent zinc–manganese batteries is proposed. Laboratory tests were performed to remove mercury and zinc from spent batteries and recover them. Correctitude test were used to analyze the effect of three factors: temperature, weight and time on the removing and recovery efficiency of zinc. In this research, temperature is dominant factor, weight and time are subordinate. After removing mercury, higher temperature could assure the removing efficiency of mercury above 99.9% at the same time of removing zinc. Under 0.02 MPa, efficiency of removing and recycling of zinc were investigated. The removing efficiency is 94.2% at 950 °C and 96.2% at 1000 °C. When the heated time is 1.5 h, the removing efficiency is 95.6%, which reach the aim 95.0%. With the increase of sample weight, the necessary heated time could be kept within 2.5 h without the loss of removing efficiency. The recycling efficiency of zinc could approach 75%. The content of zinc is above 99.0% in condensed zinc product. After being treated, the residue mass is about 40% of sample.

THMs and HAAs Fotmation by Tryptophan during Chlorination Disinfection

Wastewater reuse is an effective solution to water resource shortage problems, which commomly exists in urban areas. And disinfection is necessary to ensure the quality of the reclaimed water. Trihalomethanes (THMs) and haloacetic acids(HAAs) are two main disinfection byproducts(DBPs) in the water treatment process. Nitrogenous organic compounds are important disinfection byproducts precursors in the water. Tryptophan(Trp) is one kind of elementary amino acids, which are typical nitrogenous organic compounds. In this paper, the characteristics of THMs and HAAs formation from tryptophan under different chlorination disinfection conditions has been researched. The influencing factors were investigated, such as reaction time, initial concentration of tryptophan, chlorine dosage, pH and temperature. The results show that the yields of chloroform(TCM), dichloracetic acid(DCAA) and trichloracetic acid(TCAA) are all increased with the reaction time increasing, and the formation rates are all accelerated at the initial period; With the increase of initial tryptophan concentration, the yield of TCM, DCAA and TCAA are all increased at first and then reduced; With the increase of chlorine dosage, the yields of DCAA and TCAA both increased with ; The pH influences the formation of TCM and HAAs greatly. The yield of HAAs are low in the acidic condition and high in the conditions of neutral and alkaline conditions. The yield of HAAs is bigger at 20¿ than other temperature.

Selective Catalytic Reduction of NO with NH3 over Wire-Mesh Honeycomb Supported V2O5 -MoO3/TiO2/Al2O3 Catalyst

A novel V2O5-MoO3/TiO2/Al2O3 metal wire-mesh-honeycomb catalyst prepared by electrophoretic deposition (EPD) was investigated for the selective catalytic reduction (SCR) of NO with NH3. The effects of reaction temperature, space velocity and NH3/NO ratio on the SCR activity were evaluated. The experimental results show that V2O5-MoO3/TiO2/Al2O3 catalyst can achieve satisfied NO removal effect at 350°C; the increase of the space velocity will make NO conversion ratio reduce, except 400°C. NH3/NO ratio has a little influence on NO removal efficiency, which raises slowly with the increasing NH3/NO ratio. At the same time, body structure and surface character of catalyst prepared were characterized by XRD, SEM and XPS. Combining characterization with the results of activity test, the relation between catalyst structure and catalysis performance was analyzed. The results of characterization show that the active component is uniformly distributed on the catalyst carrier as a single layer and high SCR activity is attributed to the strong interaction between TiO2 and V2O5.

Comparison of Chlorogenerated Disinfection Byproduct Formation from Sequential Use Ozone and Monochloramine with Alternative Disinfection

Humic acid were used as model compound. Four oxidation scenarios (ozone/monochloramine, monochloramine, chlorine/monochloramine, chlorine) were conducted to evaluate the disinfection byproducts formation. The disinfection byproducts formation potential (DBPFP) were detected to compare the types of disinfection byproducts formed from different scenarios. Results showed that ozone/monchloramine and monochloramine significantly decreased the formation of trihalomethanes (THMs) and haloacetic acids (HAAs). But after disinfecting with ozone/monchloramine or monochloramine, some nitrogenous disinfection byproducts such as dichloroacetonitriles(HANs) and chloropicrin(CP) could be produced and reach to a much high concentration. From the examination of residual chlorine, we could found that most of monochloramine and chlorine decay were happened during the first 24 hours, and solution pH should be better controlled during monochloramination to prevent monochloramine autodecomposition.

The Effect of Different Natural Organic Matter Fractions on the Ozonation of Micropollutants

The aquatic NOM can be divided into different fractions in a wide range of molecular weight, which usually show different reactivity toward oxidants such as ozone. Fractioning natural organic matters (NOM) sourced from Songhua River with series of ultra membranes, the effect of each fraction on the degradation of BPA and NB by ozonation was investigated. The introduction of NOM fractions exept for NOM5K-10K and NOM3K-5K slightly decreased the removal efficiency of BPA which was highly reactive with ozone. On the contrary, for the refractory organic pollutant NB, NOM fractions especially the fractions with high molecular weight (NOM>10K、NOM5K-10K、NOM3K-5K、NOM1K-3K) promoted its degradation due to the enhancement of chain reaction which accompanied by the formation of hydroxyl radical, and the extent of promotion was dependent on the types and amounts of functional groups contained in NOM fractions. Even though this work is based on one type of NOM, the conclutions of this research are of general applicability.

Removal of Dimethylamine by Ozone Combined with Hydrogen Peroxide (O3/H2O2)

Ozonation of dimethylamine (DMA), the most direct and common precursor of high carcinogenic disinfection by-product N-nitrosodimethylamine (NDMA), in aqueous solutions and in the presence of H2O2 was studied at ozone doses of 1.8mg/L. The removal ratio of DMA increases from 46.7% to 77.1% with the dosage of H2O2 increasing from 0 to 1mM, and the removal rate can be improved by increasing pH. According to the results of H2O2 addition time experiments, hydroxyl radicals might play important roles in the destruction of DMA during combined oxidation process. With the treatment of O3/H2O2 for 24h (containing 0.5mM DMA), the yield of NDMA formation was below our detection limit (0.1¿g/L) and the yield of NDMA formation after chloramination (24h) of DMA containing water could be reduced by 90%.

Colonization of Biological Activated Carbon in Drinking Water Purification

The colonization of columnar activated carbon was developed. Some analysis of several physical–chemical, biochemical and microbiological methods (indicators) used to characterize the BAC biofilms composition and activity was provided. The filtration column filled with columnar activated carbon was operated incessantly for 72 days in the condition of natural colonization in a dynamic flow and poor nutritional status. The mature biofilm was observed after 53 days. By contrast, it was found that the columnar activated carbon showed a faster colonization speed and higher removal efficiency of NH3-N, NO2-N, UV254, CODMn, DOC and AOC, which were 37.2%, 35.8%, 25.2%, 30.2%, 22.7% and 171, respectively.

Degradation of Dichloroacetic Acid in Acidic Solution by Nanosized ZnO Catalyzed Ozonation

Nanosized ZnO catalysts prepared by the precipitation method were used for the degradation of dichloroacetic acid (DCAA) in acidic solution by ozone. Catalyst samples were characterized by measuring the specific area (BET) and X-ray diffraction (XRD). The results showed that the presence of ZnO catalyst obviously improved the degradation efficiency of DCAA in the process of ozonation, 67.9% higher compared with ozonation alone, and operating parameters such as catalyst loading, gas ozone concentration and pH exerted a positive influence on the DCAA catalytic degradation under the same experimental conditions. 25 mg/L of tert-butyl alcohol (t-BuOH) in the aqueous bulk leaded to significant reduction of 67.6% for the degradation efficiency of DCAA in the ZnO catalytic ozonation, indicating that ZnO catalytic ozonation followed a hydroxyl radical (•OH) reaction mechanism. According to the experimental results, it was suggested that nanosized ZnO catalyst exhibited efficient catalytic properties for the acceleration of ozone decomposition and the generation of •OH, resulting in the enhancement of degradation efficiency of DCAA.

Start-Up of Biological Fiber Activated Carbon in Advanced Treatment of Drinking Water

In this paper, start-up of fiber activated carbon for natural start-up in a dynamic flow was discussed, and several physical-chemical, biochemical and microbiological methods (indicators), such as NH3-N, NO2-N, UV254, CODMn, DOC and AOC, were used to characterize the BAC biofilms composition and activity. The results showed that the mature biofilm was observed after 53 days of incessant operation in the condition of poor nutritional status. By contrast, it was found that the fiber activated carbon showed a faster start-up speed and higher removal efficiency of indicators. The average removals were obtained as follows: NH3-N 40.8 %, NO2-N 53.2 %, UV254 18.2 %, CODMn 27.6 %, DOC 15.1 % and AOC 161, respectively.