Elements of the Inhibition of Nitrifying Bacteria
Laboratory experiments were conducted on ammonia bio-oxidation to nitrates by mixed cultures of nitrifiers in order to quantify the influence of mineral and organic pollutants on biokinetics parameters. First, the inhibitory effects of various heavy metal ions were studied using laboratory scale activated sludge and submerged filter units. Depending on the unit process and the metal involved, inhibitory effects are observed at concentrations above 1 mg/l. Results obtained provide further support for an hypothesis suggested as an explanation of the toxicity of compounds such as heavy metals: this is based on a Freunclich's adsorption law of heavy metals on nitrifying sludge. No change of inhibitory effects are obtained using fixed films in submerged filters. The effects of organic compounds were examined using the same laboratory procedure. Inhibitory effects of organic compounds in submerged filters depend on their absorptive property. Each of the organic compounds involved may affect nitrifying bacteria.