Polycyclic Aromatic Hydrocarbons In Surface Sediments Of The Huaihe River And Application Of Red Mud In Dyes Wastewater Treatment

Part I:The Huaihe River, one of the seven largest rivers in China, flows through Henan, Anhui, Shandong and Jiangsu provinces and into the Hongze Lake in Jiangsu Province. Because of excessive economic growth, industrialization and urbanization, the river has become one of the most polluted rivers in China. In order to evaluate the pollution statues of the Huaihe River, we attempt to combine chemical analysis and toxicity bioassay to investigate the distribution, source, ecological risk and ecotoxicity of polycyclic aromatic hydrocarbons (PAHs) in sediments of the whole Huaihe River. In order to evaluate the potential for serious environmental consequences as a result of anthropogenic contamination, we have selected the Jialu River, an important branch of the Huaihe River, and studied the distribution, sources, tooxicological impacts of PAHs in the surface sediments and the relationships between PAHs and environmental factors. The main results are decribed as follows:(1) The distribution, source, ecological risk and ecotoxicity of PAHs of sediments from 7 sampling sites, named as Xinyang (XY), Huainan (HN), Bengbu (BB), Xuyi (XuY), Fuyang (FY), Mengcheng (MC) and Zhengzhou (ZZ), in the Huaihe River basin, China, have been investigated. The total concentrations of 16 USEPA priority PAHs ranged from 62.9 to 2232.4 ng/g dry weight (d.w.) with a mean concentration of 1056.8 ng/g d.w. Through the assessment of ecological risk, we found that the levels of PAHs in the Huaihe River should not exert adverse biological effects. The total benzo[a]pyrene toxicity equivalent (TEQ) values calculated for samples varied from 0.01 to 194.1 ng/g d.w., with an average of 65.9 ng/g. The toxicity data were accordant with the chemical analysis results in this study. HN, BB and ZZ showed the greatest pollution extent both in the chemical analysis and the study of ecotoxicological effects.(2) The distribution of PAHs has been investigated in surface sediment samples collected in connection with field surveys of 19 sites along the Jialu River. The total concentration of the 16 USEPA priority PAHs ranged from 466.0 to 2605.6 ng/g d.w. with a mean concentration of 1363.2 ng/g. Sediment samples with the highest PAH concentrations were from the upper reaches of the river, where Zhengzhou City is located; the PAH levels in the middle and lower reaches were relatively low. According to the observed molecular indices, PAHs originated largely from the high-temperature pyrolytic process. According to the numerical effect-based sediment quality guidelines (SQGs) of the United States, the levels of PAHs in the Jialu River should not exert adverse biological effects. The total benzo[a]pyrene TEQ values calculated for samples varied from 50.4 to 312.8 ng/g d.w. with an average of 167.4 ng/g. The relationships between PAHs and environmental factors, including chemical properties of sediments, water quality, aquatic organisms, hydrological conditions, and anthropogenic activities, are also discussed. PAHs exerted a potential negative impact on the benthos. Settlement percentage, population density and industrial GDP per capita had a significant influence on the distribution of PAHs.PartⅡ:In recent years, synthetic dyes are extensively used in many industries and large volumes of dye wastewater are discharged. Removal of theses dyes from wastewater has attracted increased attention. Red mud (RM) is a waste material with coagulation and adsorption capacities, which is formed during the production of alumina when the bauxite ore is subjected to caustic leaching. In order to achiving the resource utilization of industrial waste, we have studied the removal of Disperse Blue 56 (DB56), a typical anthraquinone dye, by RM coagulant or adsorbent. The research results are shown as follows: (1) Removal of DB56 by single RM coagulation, single ozonation and combined RM coagulation/ozonation (RM/O3) was carried out in laboratory-scale experiments. RM/O3 treatment exhibited more effective in toxicity removal, color removal and chemical oxygen demand (COD) reduction than the other two methods. The effect of several operational parameters, including initial dye concentration, pH value, RM coagulant dose and O3 dose, on color removal and COD reduction was also investigated. Among these factors, pH value had the most important effect.(2) The ability of RM to adsorb DB56 from water was studied and the condition of adsorption process was optimized. The results showed that the microwave activated RM had good adsorption capacity. The adsorption process was in accord with Langmuir isotherm model. The saturated adsorption amount of DB56 by activated RM was approximately 45 mg/g. The factors that affected the adsorption process included dosage of RM, temperature, and pH value. The optimal condition was 40℃, pH 3.0,15 g/L RM and 30 min reaction time, under which the removal percentages of color, COD and total organic carbon (TOC) reached 99%,64% and 50%, respectively.