Research On Biodegradation Of Microcystins

In recent years, with the increase in the demand of water quality, the algae toxins pollution arouses people's interest, so it is very important to safeguard people's health through studying the characteristic of algae toxins and exploring its control method. The application of biodegradation process is effective to remove microcystins from water.In this thesis, the degradation of microcystins in the sediments of Dianchi Lake and Taihu Lake was studied and the influence of nutritive elements to the degradation of microcystins in the oxic conditions was investigated. The experimental results indicated that, there were some kinds of microorganisms which can decompose microcystins in the sediments of Dianchi Lake and Taihu Lake, the bacterium in the sediments of Dianchi Lake has stronger ability to degrade microcystins than Taihu Lake. In the sediments of Dianchi Lake, microcystins was degraded to the detection limits within 6 days, but under the same conditions, this value was 20 days for Taihu Lake.Under 20℃ and aerobic conditions, the degradation rate of MC was 17% of the initial concentration in the sediments of Taihu Lake at day 11, and the additions of glucose, potassium dihydrogen phosphate and ammonium nitrate in the sediments changed the degradation rates of microcystins from 17% to 75 % ,73 % ,0 % respectively at day 11. It is concluded that the addition of glucose in the sediments of Taihu Lake can promote the degradation of microcystins, and eliminate the lag phase in the degradation process, and the additon of potassium dihydrogen phosphate can also promote the degradation of microcystins effectively and shorten the lag phase, but the addition of ammonium nitrate hinder the degradation of microcystins. Under the same conditions, the same initial concentrations of microcystins were degraded to the detection limits within 6 days in the sediments of Dianchi Lake, and after the addition of glucose, potassium dihydrogen phosphate and ammonium nitrate, microcystins were degraded to the detection limits within 5, 6, and 20 days respectively. So the addition of glucose and potassium dihydrogen phosphate to the sediments of Dianchi Lake can play an stimulative role in the degradation of microcysins and can shorten the lag phase, however, the addition of ammonium nitrate would hinder the degradation of microcystins. It can be concluded that nutritive elements have strong influence upon the degradation of microcysins in theaquatic environment of Dianchi Lake and Taihu Lake.In addition, the degradation of microcystins in the sediments of Dianchi Lake and Taihu Lake were studied at the different pH in this thesis. It is indicated that the biodegradation of MC is more fast in acidic and neutral conditions than basic conditions in the sediments of Dianchi Lake, however, the biodegradation of MC is more fast in basic and neutral conditions than acidic conditions in the sediments of Taihu Lake.A gram-negative and aerobic bacterium, designated DC1, capable of decomposing microcystins, was isolated from the sediments of Dianchi Lake. The degradation of MC by strain DC1 commenced at day 2, and microcystins were completely degraded within 3 days. The degradation rate of MC was 2.7mg L"1 day"1. The degradability of DC1 and the influence of inoculation quantity on MC degradation have also been studied in this thesis.