Anaerobic biodegradation of selected organic compounds with and without inhibition of sulfate reducing bacteria

The primary objective of this study was to investigate the use of hydrogen as a structural substitute or as a reducing equivalent in the anaerobic biodegradation of methanol, methyl tert-butyl ether (MTBE), toluene, phenol, and 2,4- dichlorophenol. In addition, biodegradation rates of these compounds at various initial concentrations with and without inhibition of sulfate reducing bacteria were determined along with anaerobic biodegradation rate constants for each of the compounds studied.

Rates of methanol biodegradation were only slightly altered in molybdate amended microcosms indicating that methanol is a noncompetitive substrate in Blacksburg soil. MTBE biodegradation was slow and followed first order kinetics with respect to initial concentration. Molybdate had no affect on MTBE biodegradation alone, but increased the biodegradation rate in MTBE microcosms which were amended with ethanol. Toluene, phenol, and 2,4-dichlorophenol biodegradation proceeded at two different rate versus initial concentration relationships for lower and upper concentration ranges. Phenol biodegradation followed first order kinetics. The 2,4-dichlorophenol biodegradation rate order varied from 0.78 to 1.75. Monod kinetics were followed by methanol, toluene, and phenol, but not by MTBE, ethanol amended MTBE, or 2,4-dichlorophenol.

Addition of molybdate to inhibit sulfate reduction increased the degradation rates more for compounds which may require hydrogen in a structural position (2,4-dichlorophenol, MTBE) than those which require hydrogen for proton reduction (methanol). Biodegradation or recalcitrant compounds may be stimulated by the addition of organics (such as ethanol) which produce hydrogen upon biodegradation.