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 $3.110\mathrm{mg}\mathrm{N}{\mathrm{O}}_3–{\mathrm{N}}^{1∕2}∕{\mathrm{L}}^{1∕2}\bullet \text{day}$ corresponding to the initial alkalinity of 300, 600, 1,200, and $\mathrm{1,800}\mathrm{mg}\mathrm{Ca}\mathrm{C}{\mathrm{O}}_3∕\mathrm{L}$ , respectively. This amount of consumed alkalinity closely matched the theoretical alkalinity requirement. However, when $300\mathrm{mg}\mathrm{Ca}\mathrm{C}{\mathrm{O}}_3∕\mathrm{L}$ 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 $14\mathrm{mg}\mathrm{Ca}\mathrm{C}{\mathrm{O}}_3∕\mathrm{L}\bullet \text{day}$ from $5\mathrm{g}$ of oyster shell, calcite, and dolomite, respectively. Accordingly, only 1.6 and 5% of initial nitrate remained in $7\text{days}$ for oyster shell and calcite, respectively, but about 15% was still detected when dolomite was used.