Hydrochemical Characteristics And Experimental Study Of Nitrate Removal In New Lakeshore District Of Hefei City

The groundwater is not only a precious natural resources, but also a basic element of environment. It is relative to the three problems about "population, resource and enrivonment" directly or indirectly. The pollution of groundwater is more seriously as the increasing population, expanding city size and developing industry and agriculture. The nitrate is a universal environmental factor in most areas of the world and contamination degree is increasing continuously. In our country, the status is serious and present a deteriorative tendency.Chaohu is one of the " three rivers and three lakes" ,which our country do key harmassment on it. In recent years, the stuation of lake eutrophication is more seriously, one of the important reason is non-point source nitrogen and phosphorus. New Lakeshore District locates between Chaohu and old town of Hefei, it is a typical district that its groundwater is impacted greatly by human activities. The district is an important site which interact groundwater system of basin with surface water of lakeshore. So, combined the National Natural Science Foundation of China (No.40672154) and the Program for New Century Excellent Talents in University (No. NCET-06-0541), the title of "hydrochemical characteristics and experimental study of nitrate removal in New Lakeshore District of Hefei city" is determined. It is of theoretical and practical significance.This paper analyzes the water environment quality by the measures of factor analysis and fuzzy comprehensive evaluation method on the basis of the results of international and national research and data gathering, which is about the geomorphy, geology, hydrogeologic condition and the chemical data of groundwater in the New Lakeshore District, Hefei. Nitrate experimental research to the New Lakeshore District have been done according to the pollution status. Conclusions are drawn as follows:(1) The hydrochemistry type of the groundwater in the target area is HCO₃-Na and HCO₃-Ca, which the type of Ca-Na-Mg-HCO₃-Cland Ca-Na-Mg-HCO₃ have large proportion.(2) The nitrate pollution in the most part of New Lakeshore District is out of extent and the range is large which is up to 47.3%. Ammonia and nitrogen is out of extent in some areas and the range is small.(3) The correlation coefficient matrices are obtained based on pollution zoning by factor analysis method. The impact types which chemical contents in the groundwater relative to nitrate spatial difference are obtained by choosing major factors of different zones according to factor analysis gravel diagrams and factor load scatter diagrams after rotation.the results shows that: NH₄⁺, NO₂^-. Ca²⁺, Mg²⁺ are positive correlation to the NO₃^--N pollution, while SO₄^2-, HCO₃^-, pH are negative correlation to the NO₃^-N pollution.(4)Fuzzy comprehensive evaluation shows that: the level of water quality is three grade in the target area and the water quality is good.(5)Try to use field sampling and carry out the recovery experiment by culturing denitrification microflora. The result shows that: nitrate content is gradually decreased with the prolonging of time, the maximum degradation efficiency is up to 57.67%; ammonia content present a tendency of decreasing at first and then increasing; nitrite content present a tendency of increasing at first and then decreasing, it's dominating causes to the accumulation of nitrite. Nitrate content is negative correlation to the pH, and is positive correlation to the DO. In order to strengthen the efficiency of denitrification, pH value can be adjusted to 7 and DO content may be between 0 and 3 mg/1. In shallow soil, the efficiency of denitrification is increasing as the increased depth.