In-situ Biological Denitrification Using Pretreated Maize Stalks As Carbon Source For Nitrate-contaminated Groundwater Remediation

With the rapid development of industry and agriculture, nitrate pollution in the groundwater becomes more and more seriously, resulting from the discharge of untreated domestic and industrial wastewater, excessive use of nitrogen fertilizers.Therefore, to developing an economic and efficient groundwater remediation technology of nitrate pollution is imminent. Biological denitrification is the most effective and economic method to remove nitrate from groundwater. Combining biological denitrification and permeable reactive barrier(PRB) technology is an effective technique for in-situ remediation technology with economic, efficient and maintainability. The choice of filling medium is important because it is the key of the success of PRB technology.In the present study, batch experiments and PRB remediation simulation experiments were both designed with maize stalks that had been pretreated by sodium hydroxide(MSSH) as the electron donor for nitrate removal from groundwater to investigate the denitrification performance. First, many carbon source raw materials were researched by the releasing experiments and batch experiments with comparing the released properties and the denitrification performance to select the best solid carbon source. Next, PRB remediation simulation experiments with the MSSH as the carbon source were conducted to verify the denitrification performance. Finally, the bio-slow sand filtration technology was conducted to removal bacteria for the effluent of simulation experiments.The results showed that:(1)The COD release amount and persistence characteristic of MSSH were better than the other 6 kinds of carbon sources. The nitrogen compounds release amount of MSSH was less than the other 6 kinds of carbon source. In the bath experiments under different nitrogen loading, MSSH was the best solid carbon source with the higher nitrate removal efficiency(> 93%) and the less accumulation of nitrite and ammonia.(2) In PRB remediation simulation experiments, the denitrification performance of MSSH as carbon sources was better than maize stalks. In static remediation experiments nitrate was effectively reduced with a nitrate reduction efficiency of morethan 92%, regardless of whether the system was inoculated with external microorganisms. This was because indigenous microorganisms in groundwater proliferated readily, resulting in stable biofilm formation. In dynamic remediation experiments, external microorganisms were necessary for high nitrate removal efficiency, and the performance of denitrification was positively associated with HRTs.(3) In the bio-slow sand filtration experiments, the removal efficiency of bacteria and E. Colicounts increased as HRTs were prolonged when the inflow were the effluent of simulation experiments and domestic sewage.This study provides technical reference for the practical application of PRB in in-situ remediation technology, which can contribute to the further development of the in-situ simulation technology of the nitrate-contaminated groundwater.