Potassium cyanide inhibition of mixed bacterial populations
Zintgraff, Gary Douglas
Ward, C. H.
Master of Science
Many substances are known to inhibit cellular respiration. Relatively non-specific inhibitors are generally effective in proportion to the degree of penetration into the cell. However, the mechanism of action of cyanide is specific; cyanide irreversibly binds the iron group of cytochrome oxidase preventing transfer of electrons to oxygen. Hence, microbial sewage treatment processes may be severely disrupted by influx of cyanide bearing wastes. Cyanide toxicity was studied using a biological oxygen demand (BOD) system which was not oxygen limited. Lag times prior to exponential oxygen uptake were directly related to cyanide concentration. Each increase of 2.5 x 10-5 moles/1 KCN extended the lag period 10 to 15 hours. No oxygen up-take was exhibited in 300 hours at 5.0 x 10-4 moles/1 KCN with seed concentrations of 0.5 mg/1 (wet weight). However, at 2.0 mg/1 seed, cultures containing 5.0 x 10-4 KCN reached plateau oxygen demand in 145 hours, indicating the importance of KCN-seed ratio on degree of inhibition. Batch cultures were used to study acclimation of sewage treatment microorganisms to KCN. Three experimental systems were used: aerobic, anaerobic with nitrate as an exogenous hydrogen acceptor, and anaerobic without exogenous hydrogen acceptors. The completely anaerobic system showed the greatest degree of acclimation (relative to control) to KCN based on glucose and soluble carbon removal and cell mass increase. However, the cyanide acclimated aerobic system showed the greatest overall rates of carbon removal suggesting greatest utility for treatment of cyanide bearing wastes.