Study On Phosphorus Contamination And Rehabilitation Of Urban River Surge

Excessive phosphorus in water body would cause eutrophication, which produces "Shuihua" in freshwater lake or river and gives birth to "Red Tide" in gulf or offing sea. There were 4 different scale "Red Tides" in Pearl River estuary from 1990s. The ecological equilibrium and economy development were greatly affected. The phosphorus contamination of urban river surges of Guangzhou plays an important role in the "Red Tides" of the Pearl River estuary. So, there is great practical significance studying the phosphorus contamination of urban river surges of Guangzhou and related treatment technologies.In this paper, the phosphorus contamination of the urban river surges of Guangzhou was studied by sampling and analyzing. By simulation in laboratory and in suit experiment, the isotherm characters for sediment and overlying water were investigated. The phosphate removing rates and repression of phosphate liberation from sediment were studied using different technologies.The results shows that the TP were 1.38 mg/L— 2.53 mg/L for the six studied urban river surges: Fangcun A, Xinhepu, Shahe, Liede, Tangxia and Chebei. The water quality of the six surges all belong to Under-V according to Standard for Surface Water Environmental Quality. The TP of the six surges' sediments were 2550—4210 mg/Kg. And the TP of the six surges' suspended solid (SS) were 1.64—3.21 times of that of sediments. The TP was effectively removed by the ecological rehabilitation methods using biological materials, and amendment materials for sediment, and blastingoxygen. The water quality of the urban river surge belongs to V, and the ecological rehabilitation for urban river surges was attained.The results of isotherm characters for sediment and overlying water shows that more phosphate would release from sediment at such environmental conditions as higher temperature, or higher pH values, or anaerobic, or with microorganism activities. And additional phosphate would suppress phosphate liberation from sediment. The amounts of the phosphate liberation correlated with the fractions of the phosphorus in the sediment.The phosphate adsorption capacity of the palygorskite, montmorillonite, kaoline clay and zeolite was approximately 4.15, 2.12, 0.67 and 0.44 mg P/g absorbents respectively at the PO43" equilibrium concentration of 100 mg/L and pH 7.0-7.2.The experimental data of phosphate adsorption on these mineral clays could be well fitted by the Langmuir and Freundlich isotherms. The phosphate adsorption capacity of the unmodified, acid treated and acid & thermal treated palygorskite was approximately 4, 7 and 9 mg P/g absorbents respectively at the PO43" equilibrium concentration of 100 mg/L and pH 7.0-7.2.The modified palygorskites had higher adsorption capacities and faster kinetics than the natural sample. It was believed that the surface structural changes of the material play the most important role in the adsorption capacities of the phosphate.And the results of suppressing phosphate liberation from urban river sediment using capping method shows that when the amounts of the capping materials used was 6.0 Kg/ m2, the suppression efficiency of glass bead was 40.0%, and those of river sand, zeolite, fly ash and OPC were 46.7%, 60.0%, 75.6% and 88.9% respectively at 25 °C.Fly ash and OPC were suitable for capping use, and the capping materials had negligible effect on sediment and soil.