Impact of heavy metals on denitrification of simulated mining wastewaters

The spreading of nitrogenous compounds into the environment is a common challenge during mining industries. Typical explosives used in mining are N-based compounds which lead to nitrogen contamination of groundwater and water bodies. In gold extraction, cyanide used as lixiviant is also another source of nitrogen pollution. The present work aims to investigate the effect of heavy metals on denitrification using batch bioassays. Cu, Ni, Co and Fe influence on denitrification process was studied at pH 7.0. Below 50 mg/L, nickel did not inhibit denitrification, whereas denitrification was repressed at soluble Ni concentrations of 50 and 100 mg/L. Co exerted no inhibition on nitrate removal even at 86 mg/L. Copper slowed denitrification down resulting in 48% of nitrate removal inhibition at soluble Cu concentration of 0.7 mg/L. On the contrary, Fe supplementation resulted in iron oxidation and soluble Fe concentrations ranging from 0.4-1.6 mg/L that stimulated denitrification. The present work indicates that denitrification can somewhat tolerate heavy metals and can be suitable for acid mine drainage remediation.