| Huaihe river basin is in priority for water pollution control in China. As the biggest tributary in upper reach of the Huaihe River, increasingly serious water pollution of Hong River has become the factor obstructing sustainable development of the watershed. Based on the watershed's conditions as well as its hydrological and water quality observations, this research conducted a multi-factor evaluation of the river's water quality, and analyzed the spatial and temporal characteristics of the pollutants. In addition, the pollutant load from point sources and non-point sources were estimated using four methods:export coefficient, model simulation, run-off division and rainfall-deduction. The estimates were used to identify major pollution sources and their contributions, and determine the order of priority for point and non-point source pollution control, and the suitable technologies. According to these analyses, Hong River watershed control measures were put forward, which include the pilot test of treating dyeing and pharmaceutical wastewater' using advanced oxidation and the application of decentralized sewage treatment technologies. Hence, this study is of both theoretical and practical importance to Hong River watershed pollution control, the improvement of the watershed's ecological environment, and the harmony between the region's environment and economic development. The main findings of the dissertation include:(1) Based on the analysis of the observations of the concentrations of conventional contaminants, organic contaminants and heavy metals at the outlet of Hong River watershed, the research evaluated the water quality conditions of the river and identified the primary pollutants to be COD, NH3-N, and TN. As for organic contaminants, potential environmental risk of OCPs and PAHs was evaluated based on sediment quality guidelines. Results show that HCHs and PAHs levels are at relatively safe levels, while the DDT residues could pose adverse biological effect occasionally. Potential Ecological Risk Index of eight heavy metals (Cd,Fe, Zn,Pb,Cu,Cr,Ni and Mn) in surface sediments was calculated to be32, indicating a lower probability of adverse ecological effects. Based on the spatial and temporal characteristics of the main pollutants, it can be concluded that the deterioration of water quality is due to PSP and NSP.(2) Four methods (export coefficient, model simulation, run-off division and rainfall-deduction) were used to estimate the pollutant load from point and non-point sources. Priority control units and technologies were identified in Hong River watershed. For PSP, Lianjiang River, Hongshu River and Kuiwang River are the three tributaries with the largest amount of pollutant load, accounting for52.5%of COD load and51.6%of NH3-N load. In particular, the COD and NH3-N load of Lianjiang River accounts for28.3%and34%of the total, respectively. The two major pollution sources of the Lianjiang River are dyeing and pharmaceutical industries. The emphasis should be put on the application of advanced oxidation technology. For NSP, pollution load can be cut to33.7%for COD and45.5%for NH3-N from generation to inlet, while can be cut to30.9%for COD and41.5%for NH3-N from inlet to outlet. Mainstream of Hong River and Ru River are the bigger NSP emission units. The emphasis should be put on the application of decentralized sewage including rural domestic and livestock sewage treatment technologies.(3) Oxone has proved to be a suitable oxidant for the decomposition of dyes wastewater, but the reliance on catalyst and ultraviolet radiation makes the oxone process costly and liable to cause secondary environmental pollution. In view of the pollutant load from dyeing industries in the Hong River watershed, this study evaluated the performance of oxone for MO decolorization in the absence of catalyst and under natural sunlight conditions. The impacts of a variety of operation conditions (such as dosage of reagent, initial concentration, and initial pH) and coexisting substances (humic acid, NO3-,metal ions such as Cu2+, Fe3+, and Mn2+) on oxone's decolorization performance have been studied. Study results indicate that the oxone/sunlight system is effective for MO decolorization. A factorial design has suggested that when the initial concentration was100mg L-1, the practical operation conditions for MO decolorization was pH6.04, dosage3m mol L-1, and reaction time30minutes. Under these conditions the decolorization efficiency was96.4%. In addition, study results indicate that the oxone/sunlight system's efficiency in MO decolorization is not affected by possible coexisting substances in industrial wastewaters such as metal ions, HA, and NO3-. Study results obtained when H2O2, CH3OH, and (CH3)3COH were added indicate that the decolorization of MO takes place via oxidation by SO4-. Finally, in combination with sonolysis, ultrasonic can remarkably accelerate the decolorization of the dye and shorten the reaction times in the oxone/sunlight system.(4) In consideration of the pollutant load by pharmaceutical wastewater in Hong River, this study deduced degradation pathway and mechanism by gamma irradiation in diclofenac solutions. The impacts of a variety of factors on degradation efficiency by gamma irradiation have been studied. Study results suggest that gamma ray irradiation has been shown to be an effective way to degrade diclofenac. The degradation efficiency of diclofenac increased significantly with the increase of radiation dose, while decreased with the increase in its initial concentration. Diclofenac degradation efficiency is higher under acidic conditions than in neutral and alkaline media. Study results with three additives (H2O2, CH3OH, and thiourea) indicated that the degradation of diclofenac takes place via two pathways, oxidation by·OH radicals and reduction by eaq-and H·. The extensive coexisting substances in natural waters, such as HA and NO3-, do not affect the degradation efficiency significantly. Based on the identified intermediate products, it is suggested that the transformation pathways are mainly initiated by hydrogen atoms H·, hydrated electrons eaq-, and hydroxyl radicals·OH.(5) Decentralized sewage including rural domestic sewage and livestock sewage has become one of the major pollution sources in Hong River watershed. The application of decentralized sewage treatment technology is a feasible approach to resolve the water pollution issues in the area, where centralized wastewater collection and treatment is limited. Considering the large fluctuations of sewage flow and pollutant load in Hong River watershed, four treatment technologies including integrated tower biological filter (ITBF), constructed wetland (CW), ecological permeable dam (EPD), and capillary infiltration ditch (CID) are chosen and applied in the watershed, which meet the demand of easy maintenance and management and low operation cost.15ITBF projects,1CW project,1EPD project and1CID project have been finished. The concentrations of COD, NH3-N, and TN in the effluent can consistently comply with the1level-B of the municipal wastewater treatment discharge standard (GB18918-2002).
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