Development of a response surface for prediction of nitrate removal in sulfur-limestone autotrophic denitrification fixed-bed reactors

Sulfur-limestone autotrophic denitrification (SLAD) processes are very efficient for treatment of ground or surface water contaminated with nitrate. However, detailed information is not available on the interaction among some major variables on the design and performance of the SLAD process. In this study, the response surface method was used by designing a rotatable central composite test scheme with 12 SLAD column tests. A polynomial linear regression model was set up to quantitatively describe the relationship of the effluent and influent nitrate-nitrogen concentration and hydraulic retention time (HRT) in the SLAD column reactors. This model may be used for estimating the effluent nitrate-nitrogen concentration when the influent nitrate-nitrogen concentration ranges between 20 and 110mg/L and the HRT ranges between 2 and 9h. Based on our model and the requirement for nitrite control, we recommend that the HRT of the SLAD column reactor be kept ≥ 6 h and the nitrate loading rate less than 200 g NO₃^--N/ day m³ media to achieve high nitrate removal efficiency (>99%) and prevent nitrite accumulation from being >1mg/L NO₂^--N.