published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

Experiments were conducted to examine the cause of lag-phase growth during phenol degradation by mixed microbial cultures that had been acclimated to one of four substrates. Four aerated Imhoff cones were inoculated with wastewater sludge and fed one of four substrates: acetate, egg albumin, vegetable oil, or phenol. Inocula from these cones were injected into batch reactors containing phenol. Time-dependent growth was measured by two methods: most probable number (MPN) and epifluorescence microscopy (EM). The MPN technique was used to distinguish two cell concentrations: total cells and a phenol-degrading community within the total; EM was also used to count total cells. The results indicated that a lag in phenol utilization for all cultures, except the phenol-acclimated cultures, was a result of growth of a phenol-degrading subpopulation, and not due to enzyme induction of the existing population. Similar experiments were conducted using 2,4-dichlorophenol (2,4-DCP), which resulted in no growth and no degradation of 2,4-DCP.

Candida tropicalis yeast is a microorganism that possesses high tolerance for phenol and strong phenol degrading activity. This yeast is capable of utilizing phenol as the sole source of carbon and energy without formation of any secondary waste product. Catechol-1,2- dioxygenase was isolated from cytosolic fraction of this yeast by the procedure consisting of chromatography on DEAE-Sepharose and gel permeation chromatography on Sephadex G- 100. The catechol-1,2-dioxygenase was purified to homogeneity. The enzyme activity was followed by HPLC (catechol consumption and/or cis,cis-muconic acid formation). The activity profiles at different temperatures showed temperature optimum of 30řC. Kinetic characterizations were studying in different values of pH. The values of Km and Vmax of 0,52 mM and 17,2 nM/min for consumption of catechol, respectively, and 0,34 mM and 12,6 nM/min for formation of cis,cis-muconic acid, respectively, were found at optimum pH of the reaction, pH 7,6.

Biotransformation and biodegradation rate constants were determined for naphthalene, lindane, and phenol in water samples from three different sources. Rate constants produced from monitoring disappearance of the parent chemical (biotransformation) were compared to those obtained from mineralization of the chemical (ultimate biodegradation) by ¹⁴CO₂ evolution as well as acidification of the residual ¹⁴C-labeled compound (primary biodegradation). Rate constants were statistically different for the three chemicals. The water source affected the rate constants. When biomass measurements of the waters were considered and second-order rate constants were derived, there was no statistical evidence that this parameter gave a reliable rate constant statistic that could be useful in predicting the fate of any of naphthalene, lindane, and phenol in these waters.