Investigation of copper inhibition of nitrifying moving bed biofilm (MBBR) reactors during long term operations

Copper, a prevalent heavy metal in industrial mining wastewaters, has been shown to inhibit nitrification in wastewater treatment systems. Biofilm treatment systems have an inherent potential to reduce inhibition. This study investigated the effects of copper concentration on nitrifying biofilms in moving bed biofilm reactor (MBBR) systems across long term operation using influent ammonia concentrations representative of gold mining wastewater. Conventional isotherm models did not adequately model the attachment of copper to the biofilm. Long term nitritation was shown to be uninhibited at influent copper concentrations between 0.13 and 0.61 mg Cu/L. Nitratation was inhibited with influent copper concentrations of 0.28-0.61 mg Cu/L. There was no statistical difference in biofilm characteristics, including biofilm thickness, mass and density, across all copper concentrations tested, however, changes in biofilm morphology were observed. The demonstrated resistance of the nitrifying biofilm to copper inhibition makes the MBBR system a promising technology for treating ammonia in mining wastewaters.