Initial Alkalinity Requirement and Effect of Alkalinity Sources in Sulfur-Based Autotrophic Denitrification Barrier System

The present study describes the effects of initial alkalinity and various solid alkalinity sources such as calcite, dolomite, and oyster shell on nitrate removal in a sulfur-oxidizing autotrophic denitrification process. The results showed that denitrification rate increased as the initial alkalinity present in the system increased. Denitrification rates determined by a half-order kinetic model were 0.269, 0.976, 2.631, and 3.110 mg NO3–N1/2/L1/2·day corresponding to the initial alkalinity of 300, 600, 1,200, and 1,800 mg CaCO3/L, respectively. This amount of consumed alkalinity closely matched the theoretical alkalinity requirement. However, when 300 mg CaCO3/L of alkalinity was initially present the sulfur-based denitrification was greatly inhibited. The data indicate that approximately two times initial alkalinity of theoretically required alkalinity is needed for a desirable sulfur-based denitrification reaction. The initial alkalinity dissolution rates were 88, 38, and 14 mg CaCO3/L·day from 5 g of oyster shell, calcite, and dolomite, respectively. Accordingly, only 1.6 and 5% of initial nitrate remained in 7 days for oyster shell and calcite, respectively, but about 15% was still detected when dolomite was used.