Study On Performance Of Solide Phosphorus Source For Biological Denitrification In In-situ Groundwater Remediation

Owing to the intensive use of fertilizers, animal feedlots, atmospheric depositionand dairy and poultry farming, nitrate contamination of the groundwater has became aworldwide problem. A number of treatments have been developed to removeexcessive nitrate from contaminated water, among which biological denitrifcation is acost-effective and environmental technique for removing nitrate from the groundwater.Many studies have focused on the influence of organic carbon amount and type, pH,temperature, nitrate concentration, dissolved oxygen (DO) and trace elements et.al ondenitrification. Recent study found that limited phosphate may lead to incompletedenitrification and nitrite accumulation. The levels of phosphate present in the aquiferwere found to be too low for the biological denitrification process. Therefore, theaddition of phosphate might be needed when biological denitrifcation was used toremediate the nitrate-contaminated groundwater. One of the Options for P inputs iswater-soluble phosphate sources like triple superphos-phate (TSP) and diammoniumphosphate. However, the liquid phosphate sources are easily increasing the possibilityof exporting P to recipient water courses, which lead to a second pollution.This study was designed to find an alternative phosphate sources fordenitrification in nitrate-contaminated groundwater remediation. PR minerals aresignificant global resources of phosphorus. The objective of present study was toevaluate the feasibility of PR as phosphorous source while the nitrate-contaminatedgroundwater under low-phosphate conditions. The performance of PR to enhancedenitrification under different C/N ratios、T and other conditions were studied.Simulated groundwater was used in this experiment（50mg mgNO3--N/L）. Thephosphorous content of phosphate rock is13.6%. The amount of phosphorous leachedfrom the RP was7.47mg/L. The control experiment demonstrated that PR was analternative phosphate source for biological nitrate removal process.The addition of PR not only increased nitrate remove efficiency but also greatlycontrolled the nitrite accumulation, under different C/N ratios. In present study,40gPR was found to provide adequate phosphate for denitrification. The final denitrification efficiency reached99.6%and the nitrite accumulation s was0.089mg/L for40g PR. The final average P concentration was0.89mg/L, lower than theEPA maximum contamination level (1mg/L).The experimental installation has formed the neutral, reducing condition and lowDO concentration environmental(pH：7.2~8.1，ORP：-130mV~-260mV，DO：1.2±0.3mg/L), which meet the conditions to accomplish the denitrification. when thetemperature raising from15±1°C to25±2°C, The concentration of nitrate and nitriteunder different PR sets in the effluent were reducing, eventually under2.0mgNO-3-N/Land0.1mgNO-2-N/L, respectively. Demonstrating that the improvement of thetemperature enhancing the complete denitrification and reducing the nitriteaccumulation. However, the temperature of the real groundwater usually under15°C,so, adding PR was a better idea to control the nitrite accumulation.Over the course of a30-day experiments，a good biological denitrification effectwere achieved with40g and70g RP served as solid phosphate source. Demonstratingthat PR seem to be a perfect slow-release solid phosphate source for denitrification.So the utilization of PR deposits into the groundwater treatment probably a promisingand cost-effective method for treating the low-phosphate nitrate contaminated water.