ABSTRACT
All heavy metals are potentially harmful to microorganisms at some level of exposure and absorption. Increased industrialization and domestic activities have accelerated the biogeochemical cycling of many elements, including heavy metals, causing increased deposition of elevated amounts of the metals into natural ecosystems, both aquatic and terrestrial. This chapter presents a study to ascertain the relative susceptibility of nitrifying bacteria under resting versus active metabolic conditions. The inhibitory species selected for study are relatively common metal contaminants found within raw wastewater streams, at levels in the sub– and low–part per million range. The chapter investigates the effect of the three metals lead, nickel and chromium upon the rate of respiration of resting and active nitrifying bacteria. Changes in respiration rate were used as the quantitative benchmark for inhibitory response, following one hour exposure periods. For each inhibition study, mixed liquor aliquots were directly taken from either the continuous-flow culturing reactor or from the isolated batch vessel.
