Inhibitory Effects of Copper on Nitrifying Bacteria in Suspended and Attached Growth Reactors

Municipal wastewaters with industrial discharges typically contain heavy metals which may inhibit the biological processes in wastewater treatment plants. In this study, copper inhibition on strict nitrifiers in a suspended growth (SG) reactor and a combined attached and suspended growth (A&SG) reactor was compared. Both reactors were subjected to a continuous copper input of 5 mg/L. When the accumulated total copper concentration in the reactor were approximately 25 mg/L (due to sorption to the biomass), a sharp decrease in nitrification (increase in inhibition) were observed in the SG reactor while nitrification remained the same for the A&SG reactor indicating that attached growth systems were more robust against copper toxicity than suspended growth systems. Using MINTEQA2, the concentrations of various chemical species were estimated and, of the different species present, adsorbed copper in the biomass and aqueous Cu(NH3)(4)(+2) were found to positively correlate with percent inhibition of nitrification. Based on the changes in the concentrations of the two species, Cu(NH3)(4)(+2) was probably the main chemical species responsible for inhibition of nitrification. This study has implications for wastewater treatment plants treating wastewaters with high ammonia and copper present.