Effect of Sulfate Load on Sulfur Removal in Model Constructed Wetlands

Four model constructed wetlands (CWs) were designed to investigate the effects of sulfate load on sulfate and sulfide removal. The results showed that as the sulfate load increased from 1.42 to 7.01 g S m–3 d–1, the sulfate removal rate increased from 1.42 to 3.16 g S m–3 d–1, and the sulfide discharge rate increased from 0.08 to 1.46 g S m–3 d–1. The total sulfur removal rate ranged between 1.29 and 1.74 g S m–3 d–1. The sulfide in the effluent only accounted for 5.55%–46.9% of the removed sulfate. This indicated that CWs can effectively reduce sulfide discharge while removing sulfate. The conversion of dissolved sulfide into deposited sulfur by CW matrix was a main way for sulfide removal. Elemental sulfur, acid volatile sulfide (AVS), and pyrite-sulfur were the main forms of sulfur deposition in this study. The accumulations of these three sulfur compounds were 16.6–36.2, 22.3–36.0, and 49.7–63.6 mg S kg–1 gravel, respectively. Sulfur balance analysis showed that 42.9%–71.1% of the removed sulfate was deposited in the matrix, and only 0.84%–2.34% was absorbed by the plant.