Effects of toxicants on nitrifying biomass in flocs vs. carriers.

Effects of chemical toxicants on nitrifying bacteria in flocs and porous carriers were compared. Mean inhibitory concentrations (IC50s) of toxicants were invariably higher in carrier suspensions than floc suspensions. The greatest differences were seen with cyanide, nickel and copper, whereas small differences were observed for the organic toxicants Methomyl and thiourea. Decreasing the size of the carriers lessened their protective effect. The results suggest that carriers would be advantageous for nitrification systems subjected to short-term inputs of heavy metals or cyanide but not helpful for systems subjected to transient inputs of organic chemicals.