Elementary sulfur in effluent from denitrifying sulfide removal process as adsorbent for zinc(II)

The denitrifying sulfide removal (DSR) process can simultaneously convert sulfide, nitrate and organic compounds into elementary sulfur (S0), di-nitrogen gas and carbon dioxide, respectively. However, the S0 formed in the DSR process are micro-sized colloids with negatively charged surface, making isolation of S0 colloids from other biological cells and metabolites difficult. This study proposed the use of S0 in DSR effluent as a novel adsorbent for zinc removal from wastewaters. Batch and continuous tests were conducted for efficient zinc removal with S0-containing DSR effluent. At pH < 7.5, removal rates of zinc(II) were increased with increasing pH. The formed S0 colloids carried negative charge onto which zinc(II) ions could be adsorbed via electrostatic interactions. The zinc(II) adsorbed S0 colloids further enhanced coagulation–sedimentation efficiency of suspended solids in DSR effluents. The DSR effluent presents a promising coagulant for zinc(II) containing wastewaters.