The Study On The Immobilized-Cell Membrane Bioreactor For Removing Nitrate From Groundwater

The nitrate concentration is generally high in the groundwater of Zhangqiu City, Shandong province. It poses a threat to drinking water safety of local residents. So it is especially important to reduce the nitrate concentration to the safe level.The immobilized-cell process and membrane filtration process was combined together in this research, and a new membrane bioreactor was developed for removing nitrate from groundwater. First, the making conditions of immobilized-cell membrane were explored. Second, two new membrane bioreactors were designed and constructed, and the effect of carbon source types, C/N, initial nitrate concentration, temperature and pH on denitrification process were investagted in these two bioreactors. Then, the effect of carbon source dosing manner and residual carbon source reusing on denitrification were studied. Finally, the denitrification performance of the two different operation modes was compared, and the stability of immobilized-cell membrane was evaluated.The results showed:(1)The suitable making conditions of immobilized cell membrane were 2%(w/v)of bacterial inoculum,4mm of membrane thickness,4 times of frozen-thawed cycle; (2) Ethanol is a suitable denitrification carbon source. The degradation rate of nitrate is proportional to C/N, initial nitrate concentration, temperature(10℃-30℃), and the suitable C/N ratio, temperature, pH value are 8,30℃and 7-8, respectively; (3) Relative to the single dose of external ethanol, the two-dose supplementation produced better treatment results as evidenced by the lower concentrations of NO2--N and ethanol (as measured by CODMn) of the effluent, and for saving carbon source the residual carbon source could be reused; (4)The two different modes of the new membrane bioreactor showed different advantages during denitrification processes, and the operational system remained stable for about 10 months.