Point source pollution control and problem in Lake Dianchi basin

Lake Dianchi is a famous plateau freshwater lake in China,and has been included in national The Three Rivers and Three Lakes treatment project since the 9th Five-Year Plan.In this study,the point source pollution of 2007 and change tendency in last 20 years in Lake Dianchi basin were studied on analysis of point source pollution problem.The results indicated that COD,total nitrogen,and total phosphorus discharged of point source from whole basin in 2007 were 55913t,11222t and 1008t,respectively.COD,total nitrogen,and total phosphorus from domestic sewage contributed 89%,96% and 98% to each total pollution load,respectively.From 1988 to 2007,the point source pollution load yielded in Lake Dianchi basin sustained an increasing trend.However,the final pollution load discharged into lake decreased,especially COD and total phosphorus,for drastic enhancement of ability of sewage treatment.Point source pollution in Lake Dianchi basin can be attributed to four problems:first,city expansion and population growth will put great pressure on water environment of Lake Dianchi basin;second,the combined drainage system of old city region,misconnection of rain sewers and sewage sewers of new city region,and pumping of river water to treat of sewage treatment plants result in pollution of combined waste water overflowing which existed for a long time;third,the sewage treatment ability does not match yield of sewage in some areas,especially during rainy season,the inability of sewage treatment was an outstanding problem;fourth,terminal treatment of point source pollution no longer meet need of protection of Lake Dianchi,and pollution control in whole process should be addressed.