Studies On The Treatment Of Slightly Polluted River Water Using Constructed Wetland With Economic Plants At The Estuary Of Lushijiang River In The North Of The Lake Erhai

Currently, with the accomplishment of the major projects in the Eleventh Five-Year Plan, the focus of pollution control in the Lake Erhai watershed shifts from centralized pollution treatment constructions to the comprehensive treatments of low pollutants concentration but high load inflow rivers and low pollution water. The estuary of inflow rivers are the final barrier protecting pollution from entering rivers. At estuaries, water flows more slowly, woth small depth. Because the estuaries have broad area, they are very suited for plants growing and broad constructed wetland building.In this thesis, Erhai ecological service functions have been analysed and studyed, then, reccording to these results, the generation techniques of north farmland pollution which is the main pollution source has been clearly analysed. In terms of this, on the basis of theoretical investigations, We have set up a constructed wetland of 30 mu area(about 2 hectare) with aquatic economic plants at the estuary of the Luoshijiang River in the north of the Lake Erhai, and have studied the purification of slightly polluted river water by the wetland, including TN、TP、KMn O4 and other indexes removal rate. Finally,focusing existing problems on phosphate removal, this research has discussed phosphate removal and recovery by activated aluminaErhai ecological service functions research and evaluation shows that Erhai has very high value in aspects of ecological service, it’s very significant to protect Erhai water for Dali economic、social、and ecological development. But, recently, Erhai water has been threatened, it’s total ecological service functions declined year by year, and it’s main pollution source is north farmland pollution-N pollution.The generation techniques analysis of north farmland pollution indicates that, under rice- broad bean farming mode, which is environmental friendly, the farm outflow little N into water, the net volum flow is-1.65 kg/mu*a, it’s main N inflowway is biological nitrogen fixation(43.3%), second way is organic fertilizer(35.0%), the N outflow way is crops absorption(98.6%); under rice – garlic farming mode, which is environmental polluting, the net N outflow volum is 22.06 kg/mu*a, it’s main N inflow way is fertilizer(84.7%, chemical fertilizer accouting for 62.1%),water environment accounting for 48.9% of the total N outflow volum. Rice – garlic farming mode is badly in need of reasonable fertilizer using and promoting its ratio. Other protecting methods are also in need.Study on the treatment of slightly polluted river water using constructed wetland with economic plants at the estuary of lushijiang river in the north of the lake Erhai shows that the wetland had good removal performance for total nitrogen, total phosphorus, ammonia nitrogen, and nitrate nitrogen, with the average removal efficiencies of 66.4%, 60.3%, 60.4%, and 73.2%, respectively, during nearly three months of runtime. However, it had low removal efficiency with an average value of 5.0% for permanganate index, which was presumed to be due to low concentration of organics in the influent and production of organics from wetland itself. It was found that different aquatic economic plants in the wetland showed different water purification abilities. Purification performance of total nitrogen was in the order: water dropwort>isodon amethystoides>canna indica>water bamboo>swamp cabbage>mint, and total phosphorus was in the order: water dropwort>mint> canna indica> isodon amethystoides>swamp cabbage>water bamboo.Activated alumina was studied for removing phosphate from water, and recovery of adsorbed phosphate on activated aluminum oxide was also tested. Phosphate solution was prepared using distilled water, tap water and Luoshijiang River water, respectively. All of the phosphate adsorption tests of activated alumina were proved to be fitted well with Langmuir isotherm and the respective maximum adsorption amount were 20.88, 32.15 and 29.85 mg?g-1, respectively. The presence of electrolyte in water could be a positive factor for phosphate removal. As the p H value of phosphate solution got lower the Zeta potential of activated alumina increased, which could enhanced the phosphate removal efficiency of activated alumina. The recovery tests indicated that Na OH(0.1mol?L-1) solution could almost completely extract the phosphate adsorbed by activated alumina.