Beihai Zhou

Enhanced photocatalytic degradation of humic acids using Al and Fe co-doped TiO2 nanotubes under UV/ozonation for drinking water purification.

O3/UV/TiO2 was used to effectively decompose humic acids (HAs) in drinking water. To obtain a large specific surface area and low band gap energy, Al and Fe co-doped TiO2 nanotubes were successfully synthesized using the hydrothermal method. The effect of the optimal co-doped TiO2 nanotubes catalyst on the HAs removal efficiency through O3/UV/co-doped TiO2 process was investigated. The highest HAs removal efficiency (79.4%) that exhibited a pseudo-first-order rate constant of 0.172 min(-1) was achieved, in the presence of 550 °C calcined 1.0% co-doped TiO2 nanotubes with an Al:Fe ratio of 0.25:0.75. The effects of calcination temperature and doping concentration on anatase phase weight fractions, average crystallite sizes, Brunauer-Emmett-Teller surface area, catalyst band gap energy, and catalyst photocatalytic activity were also discussed. The inorganic anions also affected the catalyst photocatalytic ability. In a neutral solution, SO4(2-) slightly promoted HAs removal. However, HCO3(-) was found to significantly inhibit the catalyst activity, whereas Cl(-) had negligible effect on photocatalytic ability.

Biodegradation of geosmin in drinking water by novel bacteria isolated from biologically active carbon

Three strains of Gram-negative bacteria capable of removing geosmin from drinking water were isolated from biologically active carbon and identified to be Chryseobacterium sp., Sinorhizobium sp. and Stenotrophomonas sp. based on physio-biochemistry analysis and 16S rRNA gene sequence analysis. Removal efficiencies of 2 mg/L geosmin in mineral salts medium were 84.0%, 80.2% and 74.4% for Chryseobacterium sp., Sinorhizobium sp. and Stenotrophomonas sp., respectively, while removal efficiencies of 560 ng/L geosmin in filter influent were 84.8%, 82.3% and 82.5%, respectively. The biodegradation of geosmin was determined to be a pseudo first-order reaction, with rate constants at 2 mg/L and 560 ng/L being 0.097 and 0.086 day(-1), 0.089 and 0.084 day(-1), 0.074 and 0.098 day(-1) for the above mentioned degraders, respectively. The biomass of culture in the presence of geosmin was much higher than that in the absence of geosmin.

Effect of metal-ion doping on the characteristics and photocatalytic activity of TiO2 nanotubes for the removal of toluene from water.

Toluene is an extensively used reagent that could cause water pollution and endanger human health. In this work, an O3/UV/ion-doped TiO2 nanotubes process was investigated to obtain the optimum TiO2 nanotubes for effective toluene decomposition. Photocatalytic activity is found to be influenced by the doped-ion type by affecting the ionic radius, valence state, and configuration of the dopant. The calcination temperature and doping concentration, which change the weight fractions of the anatase phase (fA), the Brunauer-Emmett-Teller surface area (SBET), and the energy band gap (Eg) of the catalyst, also affect the photocatalytic activity. When TiO2 is doped with ions, SBET decreases and Eg becomes narrower. The photocatalytic activities of TiO2 for toluene removal increase after doping with Ag(+), Al(3+), Cu(2+), Fe(3+), Mn(2+), Ni(2+), V(5+), and Zn(2+). Moreover, the 1.0% Fe(3+)-doped TiO2 nanotubes calcined at 550 °C have the highest catalytic activity, with a toluene removal efficiency of 70.7%.

Effect of metal ion-doping on characteristics and photocatalytic activity of TiO 2 nanotubes for removal of humic acid from water

The effect of ion-doping on TiO2 nanotubes were investigated to obtain the optimal TiO2 nanotubes for the effective decomposition of humic acids (HA) through O3/UV/ion-doped TiO2 process. The experimental results show that changing the calcination temperature, which changed the weight fractions of the anatase phase, the average crystallite sizes, the Brunauer-Emmett-Teller surface area, and the energy band gap of the catalyst, affected the photocatalytic activity of the catalyst. The ionic radius, valence state, and configuration of the dopant also affected the photocatalytic activity. The photocatalytic activities of the catalysts on HA removal increased when Ag+, Al3+, Cu2+, Fe3+, V5+, and Zn2+ were doped into the TiO2 nanotubes, whereas such activities decreased as a result of Mn2+- and Ni2+-doping. In the presence of 1.0 at.% Fe3+- doped TiO2 nanotubes calcined at 550°C, the removal efficiency of HA was 80% with a pseudo-first-order rate constant of 0.158 min–1. Fe3+ in TiO2 could increase the generation of •OH, which could remove HA. However, Fe3+ in water cannot function as a shallow trapping site for electrons or holes.

Biodegradation of 2-methylisoborneol by bacteria enriched from biological activated carbon

One of the most common taste and odour compounds (TOCs) in drinking water is 2-methylisoborneol (2-MIB) which cannot be readily removed by conventional water treatments. Four bacterial strains for degrading 2-MIB were isolated from the surface of a biological activated carbon filter, and were characterized as Micrococcus spp., Flavobacterium spp., Brevibacterium spp. and Pseudomonas spp. based on 16S rRNA analysis. The removal efficiencies of 2-MIB with initial concentrations of 515 ng·L−1 were 98.4%, 96.3%, 95.0%, and 92.8% for Micrococcus spp., Flavobacterium spp., Brevibacterium spp. and Pseudomonas spp., respectively. These removal efficiencies were slightly higher than those with initial concentration at 4.2 mg·L−1 (86.1%, 84.4%, 86.7% and 86.0%, respectively). The kinetic model showed that biodegradation of 2-MIB at an initial dose of 4.2 mg·L−1 was a pseudo-first-order reaction, with rate constants of 0.287, 0.277, 0.281, and 0.294 d−1, respectively. These degraders decomposed 2-MIB to form 2-methylenebornane and 2-methyl-2-bornane as the products.

Removal of toluene from water by photocatalytic oxidation with activated carbon supported Fe3+-doped TiO2 nanotubes

In this work, activated carbon (AC)-supported TiO2 containing 1.0% (mass percent) of 1.0 at.% (atomic percent) Fe(3+)-doped TiO2 nanotubes (Fe-TNTs) were successfully synthesized. The catalyst was used to effectively decompose toluene in water under O3/UV conditions, and some properties including the morphology, X-ray photoelectron spectroscopy, X-ray diffraction patterns, specific surface area and UV-visible diffuse reflectance spectroscopy were analyzed. A removal efficiency of 90.7% was achieved in the presence of fresh AC-supported Fe-TNTs calcined at 550 °C, with a pseudo-first-order rate constant of 0.038/min. The removal efficiency of toluene was reduced when the catalysts were repeatedly used, since the amount of adsorption sites of the supporting substrates decreased. However, even after AC-supported catalyst was used four times, the removal efficiency of toluene was still sufficient in water treatment. The enhanced photocatalytic activity of AC-supported Fe-TNTs was related to the synergistic effect of AC adsorption and Fe-TNTs photocatalytic ozonation. The water from a petrochemical company in China was used to obtain the removal efficiency of the pollutants, and the toluene and total organic carbon removal efficiencies were 69.9% and 58.3%, respectively.

Isolation and characterization of bacterium capable of removing 2-methylisoborneol from drinking water

For the drinking water treatment, a methodology for isolation of the bacterium capable of removing 2-methylisoborneol (2-MIB) from water was proposed. The procedure of the method was as follows: the sample was gained from the activated carbon whose surface was covered with a mature microbiological membrane, and then continually treated with the mineral salt liquid culture in which 2-MIB was the only carbon source. Finally, four strains were isolated by plate streaks, which were characterized as Flavobacterium spp. and Pseudomonas spp. based on the physiology biochemistry experiment and the data of 16S rRNA analysis.

Removal of MIB and geosmin in drinking water by biological activated carbon process

2-methylisoborneol (MIB) and geosmin cannot readily be removed by conventional water treatments. Biological activated carbon (BAC) process is an attractive option for MIB and geosmin removal. For BAC filter inoculated with a consortium of MIB and geosmin biodegraders, the removal efficiency of MIB (geosmin) in a period of 4d was 100% (100%), and the figure was 75% (90%) for ceramic filter. For BAC filter, removal of MIB and geosmin increased rapidly with the extension of empty bed contact time (EBCT) at first, and resulted in no obvious change when EBCT was longer than 12min. MIB (geosmin) removal efficiency of BAC filter was 99% (99%) at the stage of 12min when filter height was 550mm, among which 32–35% (18–20%) was removed by ceramic filter. The MIB and geosmin concentrations apparently decreased in the up layers of the biofilter (0–100 mm). For MIB and geosmin with an initial concentration of 500ng/L, filter height of 400mm was enough for removing MIB and geosmin to below its odor threshold concentration.

Comparison of the effects between tidal flow and subsurface flow wetlands on sewage treatment

The effects of multi-stage tidal flow(TF) and subsurface flow(SSF) wetlands on the treatment of sewage were compared. The results showed the removals of NH4+-N (ammonia), TN(total nitrogen), SRP(soluble reactive phosphorus), TP(total phosphorus), CODCr(chemical oxygen demand) using the TF wetland increased by 22%, 5%, 1%, 1% and 5% respectively than using the SSF wetland, which suggested the TF wetland was capable of largely enhancing nitrification but slightly on denitrification. The maximum rate of phosphorus and CODCr removal took place in the 1st unit of both TF and SSF wetlands. The removal rate of NH4+-N in all units of the TF wetland was higher than the SSF wetland, while the first three units of the TF wetland were the dominated sink of TN accounting for 100% TN removal of the system; The 4th unit contributed negatively to TN removal because the nitrification was strengthened by higher substrate(NH4+-N) concentration, and the denitrification inhibited by lack of labile carbon.

Study on the characteristics of fillings in soil trench system

Soil trench system is an important way to phosphorus and nitrogen removal by the combination of physical, chemical and biological degradation processes. The specific surface, osmosis, saturation water holdup, cost, adsorption and desorption capacity of four fillings (red soil, sand, coal fly-ash and carbonized rice hull) in soil trench system were analyzed. Taking the removal effect, useful time, construction cost and clogging problem into consideration, the mode of the quantity of four fillings in soil trench system should follow “red soil>coal flyash> carbonized rice hull>sand”.