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

A high rate of elemental sulfur (S-0) accumulation from sulfide-containing wastewater has great significance in terms of resource recovery and pollution control. This experimental study used Thiobacillus denitrificans and denitrifying bacteria incorporated with signal molecules (C6 and OHHL) for simultaneous sulfide (S2-) and nitrate (NO3-) removal in synthetic wastewater. Also, the effects on S-0 accumulation due to changes in organic matter composition and bacteria proportion through signal molecules were analyzed. The 99.0% of S2- removal and 99.3% of NO3- was achieved with 66% of S-0 accumulation under the active S2- removal group. The S-0 accumulation, S2- and NO3- removal mainly occurred in 0-48 h. The S-0 accumulation in the active S2- removal group was 2.0-6.3 times higher than the inactive S2- removal groups. In addition, S-0/SO42- ratio exhibited that S-0 conversion almost linearly increased with reaction time under the active S2- removal group. The proportion of Thiobacillus denitrificans and H+ consumption showed a positive correlation with S-0 accumulation. However, a very high or low ratio of H+/S-0 is not suitable for S-0 accumulation. The signal molecules greatly increased the concentration of protein-I and protein-II, which resulted in the high proportion of Thiobacillus denitrificans. Therefore, high S-0 accumulation was achieved as Thiobacillus denitrificans regulated the H+ consumption and electron transfer rate and provided suppressed oxygen environment. This technology is cost-effective and commercially applicable for recovering S-0 from wastewater.