The Study On Nitrate Removal Methods Of Groundwater

Nitrate pollution of groundwater constitutes an important and cosmopolitan environmental problem. Concern for possible health consequences has led to the recommendation of an upper limit of 10 mg Nl-1 in water for human consumption as the World Health Organization's standard.To control the groundwater nitrate pollution, people should prevent nitrate from going to the groundwater and remediation the contaminated groundwater. Scientists have already studied the approaches of nitrate removal. The approaches for nitrate removal had a lot of categories: physical methods, chemical methods and biological denitrifiication. Among the techniques available for the removal of nitrate from water, microbial removal (denitrification) stands out for being the most economical and environmentally sound, as well as for being feasible on a large scale. The biological denitrification had some shortcoming, such as, complex technics, high level of operation, the low denitrification rate, bulky reactor and expensive construction. To improve the biological denitrification, solid organic carbon, cellulose-rich waste was used as the sole carbon and energy substrate as well as the only physical support for bacteria in laboratory denitrification reactors in the study described here.Removal of nitrate from groundwater was studied in laboratory columns packed with solid organic carbon sources (cotton, paper, straw, sawdust). It was found that cotton and paper were suitable carbon sources for water denitrification and at the same time, can serve as the sole support for bacterial growth. Straw and sawdust were not suitable carbon sources for water denitrification. pH of the effluent from different reactors had not obviously changes. pH of the effluent was lower 0.4-0.6 unit than pH of the influent in the papre reactor, and pH of the effluent was lower 0.2-0.3 unit than pH of the influent in the straw reactor. Ammonia was never detected in the effluent. Washout bacteria was relatively high in order of 105 /ml, requiring further disinfection of the treated water.Startup of the reactor using cotton and paper as carbon source was fast. Cotton andpaper dependent denitrification was markedly affected by changes in temperature. The dentrification rate of cotton was 1.5664mgNl-1h-1 and the dentrification rate of paper was 2.1941mgN l-1h-1 at the 14C. The dentrification rate of cotton was 3.3095mgN l-1h-1 and the dentrification rate of paper was 3.3401mgNl-1h-1 at the 25C. The denitrification rate increased with the increase of the temperature. The paper reactor had higher denitrification rate than the cotton reactor. In the low temperature the former had a N removal rate of 60%. The reactor had strong ability to resist hydraulic impact, even at shorter HRT it also could keep very high N removal rate. N removal rate was achieved 99.6%(nitrite was not detected), at temperature of 25 + 1 C, 45.2mgN/l in the influent, and HRT=8.6h. PH had little on denitrification of these reactors: the rates of nitrogen removal were not changed at pH6~9. It is possible for the practical using in the groundwater denitrification because of high denitrification rate, ease of operation, and low cost of the reactor.