In situ septic tank effluent denitrification using a sulfur-limestone process

Septic tanks are the second largest source of groundwater nitrate contamination. In this study, the feasibility of coupling a conventional lateral field with a sulfur-limestone (S/L) 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, depth of S/L layers, and ratio of S/L-to-gravel on reactor performance were investigated. The profiles of ammonium, nitrite, nitrate, sulfate, calcium, and other parameters along the depth of reactors were measured. Significant nitrification was observed in the sand layer, while significant denitrification was observed in the S/L layer. Sulfate and hardness were produced in accordance with stoichiometric relationships. The results demonstrate that the S/L method is very effective in denitrification, while production of sulfate and hardness and existence of sulfide in effluent may be limiting factors in its application.