Enhanced biological S⁰ accumulation by using signal molecules during simultaneous desulfurization and denitrification

A high rate of elemental sulfur (S⁰) accumulation from sulfide-containing wastewater has great significance in terms of resource recovery and pollution control. This experimental study used <i>Thiobacillus denitrificans</i> and denitrifying bacteria incorporated with signal molecules (C6 and OHHL) for simultaneous sulfide (S^2–) and nitrate (NO₃^–) removal in synthetic wastewater. Also, the effects on S⁰ accumulation due to changes in organic matter composition and bacteria proportion through signal molecules were analyzed. The 99.0% of S^2– removal and 99.3% of NO₃^– was achieved with 66% of S⁰ accumulation under the active S^2– removal group. The S⁰ accumulation, S^2– and NO₃^– removal mainly occurred in 0–48 h. The S⁰ accumulation in the active S^2– removal group was 2.0-6.3 times higher than the inactive S^2– removal groups. In addition, S⁰/SO₄^2- ratio exhibited that S⁰ conversion almost linearly increased with reaction time under the active S^2– removal group. The proportion of <i>Thiobacillus denitrificans</i> and H⁺ consumption showed a positive correlation with S⁰ accumulation. However, a very high or low ratio of H⁺/S⁰ is not suitable for S⁰ accumulation. The signal molecules greatly increased the concentration of protein-I and protein-II, which resulted in the high proportion of <i>Thiobacillus denitrificans</i>. Therefore, high S⁰ accumulation was achieved as <i>Thiobacillus denitrificans</i> regulated the H⁺ consumption and electron transfer rate and provided suppressed oxygen environment. This technology is cost-effective and commercially applicable for recovering S⁰ from wastewater.