Research Of Lightly Contaminated Water Application In Baihe River Of Erhai Lake By Gravel Contact Oxidization Process

This paper took Baihe River, the inflow river of Erhai Lake, as the research object, and conducteda small scaled simulation research on lightly contaminated water using Gravel Contact OxidationProcess in order to provide technical support for the restoration of a typical reach of Haihe River andultimately cut down the pollution load that enters the Erhai Lake.10sample points were set up in towns and farmlands along the Baihe river. After a year ofsurveillance, water quality of Baihe River was found to be tightly correlated to local climate, tourismand agriculture in Dali. With the effects of surface runoff at the beginning of rain season, all pollutantindicators increase dramatically in every June. After flowing through the towns and farmlands, thewater quality of Baihe river becomes poor at the stream outlet and its nitrogen and phosphorusconcentration is far beyond the standard limit.This experiment used locally accessible marble as the filler and the experimental water wasdirectly obtained from Baihe river. Under the condition of the partition aeration and step feeding, thegravel contact oxidation system took28days to successfully hang the biofilms, and the removal rateof CODMnand ammonia nitrogen reached50%and70%respectively. From a microscopic study, itwas found that the biofilms were rich in biofacies and the main components include sphaerophorus,bacillus, zoogloea, filamentous bacteria, protozoa(vorticella) and a small amount of tinymetazoan(rotifera). After obtaining mature biofilms, the authors began to discuss the effects ofhydraulic retention time (HRT) and the volumetric ratio of aeration zone and anoxic zone (O/A),inflow water distribution ratio and reflux ratio parameters on nitrogen removal efficiency in low C/Nwater. The results showed that the optimum performance was achieved when hydraulic retention timewas4hours, O/A was1:2, inflow water distribution ratio was2:3and reflex ratio was30%. Under arelatively good working condition, the step-feed method greatly outperformed the single point waterinflow method. Average CODMnremoval rate was improved by step-feed method from50.6%to66.3%and average TN removal rate was improved by step-feed method from31.4%to60.9%. Alongthe reactor, nitrification bacteria were mainly found in the aeration zone with the amount of5.58×106,and denitrification bacteria were mainly found in the anoxic zone with the amount of6.49x105.Dissolved oxygen and nitrogen concentration were also tested in the reactor. It was found thatdissolved oxygen decreased gradually along the flow and became0.2mg/L at the outlet. Ammonianitrogen was oxidized to nitrate nitrogen in aeration zone and was reduced to nitrogen gas in anoxiczone, which justifies the distribution characteristics of nitrification and denitrification bacteria. By investigating the water quality in Baihe River watershed, the authors choose Longkan Quay asthe operation site for gravel contact oxidation simulation. In the meantime, by combining landscapedesign this facility can be used to boost local tourism industry.