Ammonia, thiocyanate, and cyanate removal in an aerobic up-flow submerged attached growth reactor treating gold mine wastewater

The objective of the study was to investigate the nitrification process, as well as the bio-chemical removal of cyanate and thiocyanate, while treating gold mining wastewater using an aerobic up-flow SAGR. A total of six SAGRs, each packed with locally sourced pea gravel (estimated specific surface area of 297 m−2 m−3), were operated at various HRTs and tested on both low- and high-strength gold mining wastewaters. The two sets of three SAGRs were operated at HRTs of 0.45 days, 1.20 days, and 2.40 days. Nitrification was successfully achieved in all six SAGRs regardless of the wastewater strength or HRT examined. The steady-state, 20 °C surface area loading rate was determined to be 1.2 g-TAN m−2 d−1 in order to comply with an effluent discharge limit at 10 mg-TAN L−1 (i.e., with the wastewater sources examined). At all ammonia loading rates, thiocyanate was successfully removed, and residual concentrations were below 2 mg–SCN–N L−1. Cyanate appeared to be hydrolyzed and subsequently nitrified. Acute toxicity tests conducted on both daphnia and trout revealed the effluent to be safe for direct discharge. •Over 98% ammonia removal was achieved.•The recommended 20 °C SALR was 1.2 g-TAN m−2 d−1.•Thiocyanate was removed to less than 2 mg–SCN–N L−1.•Cyanate appeared to be hydrolyzed and subsequently nitrified.•Free ammonia could have a negative impact on performance at high pH.