Septic Tank Effluent Denitrification with Sulfur/limestone Processes

Septic tanks are the second largest source of groundwater nitrate contamination in Nebraska. In this study, the feasibility of coupling a conventional lateral field with a sulfur/limestone layer to treat nitrate in septic tank effluent was investigated using column reactors to simulate the septic tank soil adsorption system. The effects of different hydraulic loading rates, nitrogen loading rates, the depth of sulfur/limestone layers, and the ratio of sulfur/limestone to gravel on reactors’ performance were investigated. The profiles of ammonium, nitrite, nitrate, sulfate, calcium, and other parameters along the depth of the reactors were measured. Significant nitrification was observed in the sand layer. Significant denitrification, sulfate production, and hardness production were observed in the sulfur/limestone layer. The results showed the sulfur/limestone method was very effective in denitrification, while the high concentration of sulfate and hardness and the existence of sulfide in effluent might be limiting factors in its application.