Graduation date: 1995

Chlorinated phenols are toxic compounds and often released into natural environments from improper disposal or non-point sources. One important factor in assessing the environmental fate and transport is the rates of microbial degradation in soils and natural waters. In this study, eight chlorophenols (4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 3,4-dichlorophenol (3,4-DCP), 3,5-dichlorophenol (3,5- DCP), 2,3,5-trichlorophenol (2,3,5-TCP), 2,4,5-trichlorophenol (2,4,5-TCP), 3,4,5- trichlorophenol (3,4,5-TCP), and 2,4,6-trichlorophenol (2,4,6-TCP)) were chosen as the model compounds because they represent the major degradation products for the anaerobic metabolic products of pentachlorophenol (PCP). Aerobic degradation rates of all eight compounds were determined under controlled laboratory conditions. A mixed bacterial culture was seeded from a municipal wastewater treatment plant and were grown with acetate as a primary substrate and the eight chlorophenols as secondary substrates. Rates of degradation were measured in a batch reactor with an initial concentration of acetate of 1000 mg/l and of the individual chlorophenol of 0.1 mg/l. Rate of acetate and chlorophenols were modelled using a Monod model. The maximum rate of acetate utilization was zero-order in relation to acetate concentration and first-order with respect to organism concentration. The rate of chlorophenol degradation were zero-order in relation to the chlorophenol concentration. The relative rates of degradation were in general as follows: monochlorophenol > dichlorophenols > trichlorophenols. / Graduation date: 1992

The addition of exogenously supplied hydrogen stimulates PCP reductive dechlorination and increases bacterial growth. While research focuses mainly on pure cultures, few exist capable of aryl reductive dechlorination, and few markers exist to identify reductively dechlorinating bacteria within mixed cultures. Furthermore, most active bioremediation projects stimulate mixed cultures of native biota. This work describes a method to estimate reductively dechlorinating bacterial growth within a mixed soil culture under controlled environmental conditions. The experiments discussed in this paper were performed in a fed-batch reactor. The reactor was operated in a way to maintain environmental conditions such as pH, E[subscript H], headspace concentration, and temperature constant while substrate is allowed to degrade without the corruption of additional changes. Substrate utilization and cell growth were examined under an array of environmental conditions. This dissertation examined the correlation between hydrogen concentration and the growth rate of reductively dechlorinating bacteria. Under low hydrogen partial pressures, between 9.4 x 10������ and 2.9 x 10������ atm, the growth rate of reductively dechlorinating bacteria increased as predicted by dual Monod kinetics with respect to hydrogen and chlorophenol concentration; however, studies showed that the relationship was more complex. At higher concentrations of hydrogen, the observed growth rate of reductively dechlorinating bacteria declined. A dual Monod kinetics model with hydrogen substrate inhibition approximates experimental data. Reductive dechlorination of 2,3,4,5-tetrachlorophenol and 3,4,5-trichlorophenol were also studied. Pentachlorophenol reductive dechlorination primarily produces 3,4,5-trichlorophenol via 2,3,4,5-tetrachlorophenol. The reductive dechlorination of 2,3,4,5-tetrachlorophenol parallels that of pentachlorophenol, and the estimated growth rates based on pentachlorophenol and 2,3,4,5-tetrachlorophenol are very similar. Reductive dechlorination of 3,4,5-trichlorophenol was catalyzed by the PCP reductively dechlorinating bacterial culture after a lag period. 3,4,5-Trichlorophenol was not maintained for extended periods, and multiple additions of 3,4,5-trichlorophenol did not result in measurable growth. / Graduation date: 2001

Aerobic biodegradation kinetics of 4-Chlorophenol (4-CP) and 2,4-Dichlorophenol (2,4-DCP) by acclimated mixed cultures were examined separately and in mixture using batch and sequencing batch reactors (SBRs). Biodegradation abilities of acclimated mixed cultures were also compared with those of isolated pure species. Complete degradation of chlorophenols and high COD removal efficiencies were observed throughout the SBRs operation. During the degradation of 4-CP, 5-chloro-2-hydroxymuconic semialdehyde, (the -meta cleavage product of 4-CP), accumulated but was subsequently removed completely. Chlorophenol degradation rates increased with increasing chlorophenols concentration in the feed of the SBRs. Gradually decreasing feed peptone concentration did not adversely affect chlorophenol degradation profiles in SBRs. Only competent biomass was thought to be responsible for chlorophenol degradation due to required unique metabolic pathways. It was assumed that the fraction of competent biomass (specialist biomass) is equal to COD basis fraction of chlorophenols in the feed of the reactors as competent biomass grows on chlorophenols only. Models developed using this assumption agreed well with experimental data. The performance of a two stage rotating biological contactor (RBC) was also evaluated for the treatment of synthetic wastewater containing peptone, 4-CP and 2,4-DCP at 5 rpm. High chlorophenols (&gt / 98%) and COD (&gt / 94%) removals were achieved throughout the reactor operation up to 1000 mg/L 4-CP and 500 mg/L 2,4-DCP in the feed. Results showed that RBC is more resistant than suspended growth reactors to high chlorophenols load. The change of dominant species during the operation of SBRs and RBC was also followed using API 20NE identification kits.