The Research On Nitrate Removal From Groundwater By Reverse Osmosis

Groundwater is the only readily available source of drinking water at Xujia Village, Ningjiabu Town, Zhangqiu City, Shandong Province. However, the groundwater of this village has being badly contaminated by nitrate, and the drinking water safety of the villagers is under threat. To ensure the drinking water safety, a combined softening and reverse osmosis (RO) process used for removing nitrate from groundwater has been investaged based on the groundwater characteristics and local villagers'ability for operating the process. And a pilot setup for removing nitrate from groundwater was designed and installed, which treatment capacity is 100 cubic meter per day. The bench and pilot trial results showed that the nitrate reoval efficiency was over 95% as RO process was used to treat groundwater, and the nitrate rejection was almost not effect by the concentrations of NO3-, Cl" and SO42- ions in simulated groundwater; The higher water recovery is, the lower salt rejection.The higher water tempereture is, the higher water production and recovery. Langelier saturation index (LSI) can be used to predict the tendency of calcium carbonate scaling and adjusting the pH value of groundwater is helpful for preventing calcium carbonate scaling. The groundwater with high concentration hardness could be softened by NaCO3 and NaOH, the total hardness would be decreased from about 700mg CaCO3/L to about 90mg CaCO3/L as the Na2CO3 dose was 0.16mmol/L and the pH value was controlled at 11.0. The pilot setup has been running over one month, both nitrate removal efficiency and pure water production were stable, and the concentrations of nitrate and hardness in pure water were lower the maximum contaminant level.In addition, the denitrification process of the concentrate was preliminary investaged in this research. The results showed that the denitrification process of concentrate was affected by C/N ratio, pH and TDS. The higher TDS was, the slower denitrification rate. The appropriate C/N ratio and pH were 2.0 and 7.5, respectively.