Gaseous NO was photocatalytically reduced at room temperature by photo-assisted selective catalytic reduction (photo-SCR) with ammonia over TiO2 in this study. NO reduction efficiency and N2 selectivity were determined from gases composition at the outlet stream of photoreactor. Effect of operating conditions, e.g. light intensity and inlet concentrations of ammonia and oxygen, on the NO reduction efficiency and N2 selectivity were discussed to determine the feasible operating condition for photocatalytic reduction of NO. Experimental results showed that selective catalytic reduction of NO with ammonia over TiO2 in the presence of oxygen was a spontaneous reaction in dark. The photoirradiation on the TiO2 surface caused remarkable photocatalytic reduction of NO to form N2, NO2, and N2O under 254 nm UV illuminations, while almost 90% of N2 selectivity was achieved in this study. The ammonia and oxygen molecules played the roles of reductant and oxidant for NO reduction and active sites regeneration, respectively. The reduction of NO was found to be increased with the increase of inlet ammonia and oxygen concentrations until specific concentrations because of the limited active sites on the surface of TiO2. The kinetic model proposed in this study can be used to reasonably describe the reaction mechanism of photo-SCR.
A series of CeO2 supported V2O5 catalysts with various loadings were prepared with different calcination temperatures by the incipient impregnation. The catalysts were evaluated for low temperature selective catalytic reduction (SCR) of NO with ammonia (NH3). The effects of O2 and SO2 on catalytic activity were also studied. The catalysts were characterized by specific surface areas (SBET) and X–ray diffraction (XRD) methods. The experimental results showed that NO conversion changed significantly with the different V2O5 loading and calcination temperature. With the V2O5 loading increasing from 0 to 10 wt%, NO conversion increased significantly, but decreased at higher loading. The optimum calcination temperature was 400°C. The best catalyst yielded above 80% NO conversion in the reaction temperature range of 160°C–300°C. The formation of CeVO4 on the surface of catalysts caused the decrease of redox ability.
Metabolites of algae such as geosmin, 2-methylisoborneol etc. are reported to induce pungent odors into drinking water and attract additional scientific attention. Recently, in China, taste and odor outbreaks in drinking water supply have become increasingly common. In source water affected by eutrophication, dimethyl trisulfide, speculated to be produced by decayed algae, was found to be the source of taste and odor issues and can be removed effectively by usual oxidation agents. In this experimental study, batch scale tests were carried out focusing on the removal of dimethyl trisulfide. Reaction kinetics of dimethyl trisulfide oxidized by potassium permanganate in water had been studied; influence factors such as pH, organic substrate, other existed taste, and odor contaminant in equivalent concentration were also discussed. Results showed that dimethyl trisulfide can be removed by potassium permanganate efficiently; the ratio can reach more than 70% with oxidant dosage of 4 mg·L-1 and contact time prolonged to 120 min. The dimethyl trisulfide decomposition followed a second-order kinetics pattern with a rate constant k = 0.00213 L·(min·mg)-1. Typically, the degradation rate of dimethyl trisulfide was increased with the increasing KMnO4 dosage, but dramatically dropped with the increasing levels of humic acid (1.8–4.5 mg·L-1) and other odor-causing compounds (e.g. β-cyclocitral, 0–1886.0 μg·L-1). Solution pH (5.2–9.0) and initial dimethyl trisulfide concentration did not significantly affected the degradation. This study demonstrates that KMnO4 oxidation is an effective option to remove dimethyl trisulfide from water.
Carbonyl compounds in indoor air are of great concern for their adverse health effects. Between February and May, 2009, concentrations of 13 carbonyl compounds were measured in an academic building in Beijing, China. Total concentration of the detected carbonyls ranged from 20.7 to 189.1 μg·m-3, and among them acetone and formaldehyde were the most abundant, with mean concentrations of 26.4 and 22.6 μg·m-3, respectively. Average indoor concentrations of other carbonyls were below 10 μg·m-3. Principal component analysis identified a combined effect of common indoor carbonyl sources and ventilation on indoor carbonyl levels. Diurnal variations of the carbonyl compounds were investigated in one office room, and carbonyl concentrations tended to be lower in the daytime than at night, due to enhanced ventilation. Average concentrations of carbonyl compounds in the office room were generally higher in early May than in late February, indicating the influence of temperature. Carbonyl source emission rates from both the room and human occupants were estimated during two lectures, based on one-compartment mass balance model. The influence of human occupants on indoor carbonyl concentrations varies with environmental conditions, and may become significant in the case of a large human occupancy.
Soil low-molecular-weight (LMW) organic acids play important roles in the soil-forming process and the cycling of nutrients in Karst regions. In this study, we quantified the contents of LMW organic acids (including lactate, acetate, formate, malate, and oxalate) in soil solution over the Karst region of Guizhou Province, China using ion chromatography. The concentration of total LMW organic acids in topsoil solution ranged from 0.358 to 1.823 μmol·g-1, with an average of 0.912 μmol·g-1. The mean concentrations of lactate, acetate, formate, malate, and oxalate were 0.212±0.089, 0.302±0.228, 0.301±0.214, 0.014±0.018 and 0.086±0.118 μmol·g-1, respectively. There were also significant difference in the contents of these acids among four phases of rocky desertification, and their concentrations decreased with the aggravation of rocky desertification. The concentrations of the LMW organic acids were significantly positive correlated each other. Significant positive correlations were also observed among individual LMW organic acids in soil solution, and between them and soil available P, available K, exchangeable Ca, respectively. Furthermore, the concentrations of LMW organic acids were significantly positively correlated with inorganic anions (chlorides, nitrates, and sulfates) in Karst topsoil solution. Therefore, the concentrations of soil LMW organic acids might be one of driving force in the Karst rock desertification process in Guizhou Province.
A flaw of demand coverage method in solving optimal monitoring stations problem under multiple demand patterns was identified in this paper. In the demand coverage method, the demand coverage of each set of monitoring stations is calculated by accumulating their demand coverage under each demand pattern, and the impact of temporal distribution between different time periods or demand patterns is ignored. This could lead to miscalculation of the optimal locations of the monitoring stations. To overcome this flaw, this paper presents a Demand Coverage Index (DCI) based method. The optimization considers extended period unsteady hydraulics due to the change of nodal demands with time. The method is cast in a genetic algorithm framework for integration with Environmental Protection Agency Net (EPANET) and is demonstrated through example applications. Results show that the set of optimal locations of monitoring stations obtained using the DCI method can represent the water quality of water distribution systems under multiple demand patterns better than the one obtained using previous methods.
It is unclear whether certain plant species and plant diversity could reduce the impacts of multiple heavy metal pollution on soil microbial structure and soil enzyme activities. Random amplified polymorphic DNA (RAPD) was used to analyze the genetic diversity and microbial similarity in planted and unplanted soil under combined cadmium (Cd) and lead (Pb) pollution. A metal hyperaccumulator, Brassica juncea, and a common plant, Festuca arundinacea Schreb, were used in this research. The results showed that microorganism quantity in planted soil significantly increased, compared with that in unplanted soil with Cd and Pb pollution. The order of microbial community sensitivity in response to Cd and Pb stress was as follows: actinomycetes>bacteria>fungi. Respiration, phosphatase, urease and dehydrogenase activity were significantly inhibited due to Cd and Pb stress. Compared with unplanted soil, planted soils have frequently been reported to have higher rates of microbial activity due to the presence of additional surfaces for microbial colonization and organic compounds released by the plant roots. Two coexisting plants could increase microbe population and the activity of phosphatases, dehydrogenases and, in particular, ureases. Soil enzyme activity was higher in B. juncea phytoremediated soil than in F. arundinacea planted soil in this study. Heavy metal pollution decreased the richness of the soil microbial community, but plant diversity increased DNA sequence diversity and maintained DNA sequence diversity at high levels. The genetic polymorphism under heavy metal stress was higher in B. juncea phytoremediated soil than in F. arundinacea planted soil.
In this paper, the effect of pH on biological degradation of Microcystis aeruginosa by alga-lysing bacteria in laboratory-scale sequencing batch biofilm reactors (SBBRs) was investigated. After 10 d filming with waste activated sludge, the biological film could be formed, and the bioreactors in which laid polyolefin resin filler were used to treat algal culture. By comparing the removal efficiency of chlorophyll a at different aerobic time, the optimum time was determined as 5 h. Under pH 6.5, 7.5, and 8.5 conditions, the removal rates of Microcystis aeruginosa were respectively 75.9%, 83.6%, and 78.3% (in term of chlorophyll a), and that of Chemical Oxygen Demand (CODMn) were 30.6%, 35.8%, and 33.5%. While the removal efficiencies of ammonia nitrogen (NH4+-N) were all 100%. It was observed that the sequence of the removal efficiencies of algae, NH4+-N and organic matter were pH 7.5>pH 8.5>pH 6.5. The results showed that the dominant alga-lysing bacteria in the SBBRs was strain HM-01, which was identified as Bacillus sp. by Polymerase Chain Reaction (PCR) amplification of the 16S rRNA gene, Basic Local Alignment Search Tool (BLAST) analysis, and comparison with sequences in the GenBank nucleotide database. The algicidal activated substance which HM-01 strain excreted could withstand high temperature and pressure, also had better hydrophily and stronger polarity.
A bacterium capable of degrading dichlorvos was isolated from the rape phyllosphere and designated YD4. The strain was identified as Flavobacterium sp., based on its phenotypic features and 16S rRNA gene sequence. Strain YD4 was able to utilize dichlorvos as the sole source of phosphorus. In situ enhanced bioremediation of dichlorvos by YD4 was hereafter studied. Chlorpyrifos and phoxim could also be degraded by this strain as the sole phosphorus source. A higher degradation rate of dichlorvos was observed after spraying YD4 onto the surface of rape leaves when compared to the sterilized-YD4 and water-treated samples. The results indicated that pesticide-degrading epiphytic bacterium could become a new way for in situ phyllosphere bioremediation where the hostile niche is unsuitable for other pesticide-degrading bacteria isolated from soil and water.
In this paper, an artificial neural network model was built to predict the Chemical Oxygen Demand (CODMn) measured by permanganate index in Songhua River. To enhance the prediction accuracy, principal factors were determined through the analysis of the weight relation between influencing factors and forecasting object using cluster analysis method, which optimized the topological structure of the prediction model input items of the artificial neural network. It was shown that application of the principal factors in water quality prediction model can improve its forecasting skill significantly through the comparison between results of prediction by artificial neural network and the measurements of the CODMn. This methodology is also applicable to various water quality prediction targets of other water bodies and it is valuable for theoretical study and practical application.
This work aims to identify the main factors influencing the energy-related carbon dioxide (CO2) emissions from the iron and steel industry in China during the period of 1995–2007. The logarithmic mean divisia index (LMDI) technique was applied with period-wise analysis and time-series analysis. Changes in energy-related CO2 emissions were decomposed into four factors: emission factor effect, energy structure effect, energy consumption effect, and the steel production effect. The results show that steel production is the major factor responsible for the rise in CO2 emissions during the sampling period; on the other hand the energy consumption is the largest contributor to the decrease in CO2 emissions. To a lesser extent, the emission factor and energy structure effects have both negative and positive contributions to CO2 emissions, respectively. Policy implications are provided regarding the reduction of CO2 emissions from the iron and steel industry in China, such as controlling the overgrowth of steel production, improving energy-saving technologies, and introducing low-carbon energy sources into the iron and steel industry.
China now faces double challenges of water resources shortage and severe water pollution. To resolve Chinese water pollution problems and reduce its impacts on human health, economic growth and social development, the situation of wastewater treatment was investigated. Excess sludge and greenhouse gases (GHGs) emitted during wastewater treatment were also surveyed. It is concluded that Chinese water pollution problems should be systematically resolved with inclusion of wastewater and the solid waste and GHGs generated during wastewater treatment. Strategies proposed for the wastewater treatment in China herein were also adequate for other countries, especially for the developing countries with similar economic conditions to China.
Dissolved organic matter (DOM) transformation in sequence batch reactor (SBR) fed with carbon sources of different biodegradability was investigated. During the biologic degradation process, the low molecular weight (MW) fraction (<1 kDa) gradually decreased, while the refractory compounds with higher aromaticity were aggregated. Size exclusion chromatography (SEC) and fluorescence of excitation emission matrices (EEM) demonstrated that more biopolymers (polysaccharides or proteins) and humic-like substances were presented in the extracellular polymeric substance (EPS) extracted from the SBR fed with sodium acetate or glucose, while the EPS from SBR fed with slowly biodegradable dissolved organic carbon (DOC) substrate-starch had relatively less biopolymers. Comparing the EfOM in sewage effluent of three SBRs, the effluent from SBR fed with starch is more aromatic. Organic carbon with MW>1 kDa as well as the hydrophobic fraction in DOM gradually increased with the carbon sources changing from sodium acetate to glucose and starch. The DOC fractionation and the EEM all demonstrated that EfOM from the effluent of the SBR fed with starch contained more fulvic acid-like substances comparing with the SBR fed with sodium acetate and glucose.
Lagoon-based municipal wastewater treatment plants (WWTPs) are facing difficulties meeting the needs of rapid population growth as well as the more stringent requirements of discharge permits. Three municipal WWTPs were modified using a high surface area media with upgraded fine-bubble aeration systems. Performance data collected showed very promising results in terms of five-day biochemical oxygen demand (BOD5), ammonia (NH3) and total suspended solids (TSS) removal. Two-year average ammonia effluents were 4.1 mg·L-1 for Columbia WWTP, 4 mg·L-1 for Larchmont WWTP and 2.1 mg·L-1 for Laurelville WWTP, respectively. Two- year average BOD5 effluents were 6.8, 4.9 and 2.7 mg·L-1, and TSS effluents were 15.0, 9.6 and 7.5 mg·L-1. The systems also showed low fecal coliform (FC) levels in their effluents.
