Ex-Situ Treatment Of Eutrophic River Water By Constructed Wetlands Of Red-Soil-Granulated Substrate

With rapid and extensive economic development in the recent decades, eutrophication problem of surface water has been growing severer in our country. Constructed wetland, applied widely as a kind of pollutant removal, scene building and ecological technique for water treatment, showed great effectiveness for eutrophic water purification.This thesis aimed at treatment of inflow river branch of Lake Erhai, a classical preliminary eutrophic lake in Yunnan province and suffered "algal bloom" twice in1996and2003, by process of constructed wetland. Sponsored by Lake Erhai project of the Major Science and Technology Program for Water Pollution Control and Treatment, inflow river water of Heini River, with water quality of IV-Vclass level classified by Surface Water Quality Standard, was ex-situ purified to III-IV class level through constructed wetlands. Phosphorus removal substrate made from red soil in Lake Erhai basin was developed, and proper local plants were selected. Then six constructed wetlands were filled with gravels, gravels mixed with red-soil-substrates, and planted with three kinds of plants. Treatment results and the related mechanisms conveved that:1. Red soil showed excellent phosphorus removal property, and it was proved mainly due to existence of iron and aluminum components. Red soil calcined under500℃for lhour showed the best phosphorus property, and the largest adsorption content was25.6mg·g-1, compared with19.8mg·g-1of raw red soil. The dynamics of phosphorus adsorption fitted with the Elovich Model, and isothermal adsorption results matched the Freundlich Model the best.2. The optimal process for red soil granulations should be:granulate the red soil with2%pore-inducer of starch, then calcine the granules at308℃for1h, and500℃for another1h.32h was enough for equilibrium of P adsorption for optimized red soil granulations, with initial P concentration of lmg·L-1and5mg·L-1, and the dynamics matched the First Order Equation and Double-constant Model. The largest P adsorption amount reached13.3mg·g-1, and the isothermal adsorption process matched both with the Linear Equation and the Freundlich Equation. Both pH and organic concentration showed stimulative and prohibitive effects for P adsorption for red soil granulations, which was determined by ranges of pH and organic concentration respectively.3. Constructed wetlands of red-soil-granulated substrate could purify the inflow river water with water quality of IV-V class level to Ⅲ～IVclass level, and wetlands planted with Red Canna and Vetiver Grass showed stable and satisfactory treatment result for N, P and CODMn. Meanwhile, the pollutant of N and p absorbed by plants was insignificant.4. Compared with wetlands of gravel, the TP concentrations inside the red-soil-granules substrated wetlands were higher, while the DP concentration were lower, and the plants grew worse than the plants in gravel wetlands. Phosphorus component and amount analyses revealed that P mainly existed as iron (Fe-P) and calcium (Ca-P) bounded form, while the soluble form which could be absorbed easily was relatively extremely low, and this might explain the unsatisfactory upgrowth of the plants.