Donald F. Goerlitz

The geochemical evolution of low-molecular-weight organic acids derived from the degradation of petroleum contaminants in groundwater

Abstract The geochemical evolution of low-molecular-weight organic acids in groundwater downgradient from a crude-oil spill near Bemidji, Minnesota, was studied over a five year period (1986–1990). The organic acids are metabolic intermediates of the degradation of components of the crude oil and are structurally related to hydrocarbon precursors. The concentrations of organic acids, particularly aliphatic acids, increase as the microbial alteration of hydrocarbons progresses. The organic-acid pool changes in composition and concentration over time and in space as the degradation processes shift from Fe(III) reduction to methanogenesis. Over time, the aquifer system evolves into one in which the groundwater contains more oxidized products of hydrocarbon degradation and the reduced forms of iron, manganese, and nitrogen. Laboratory microcosm experiments with aquifer material support the hypothesis that organic acids observed in the groundwater originate from the microbial degradation of aromatic hydrocarbons under anoxic conditions. The geochemistry of two other shallow aquifers in coastal plain sediments, one contaminated with creosote waste and the other with gasoline, were compared to the Bemidji site. The geochemical evolution of the low-molecular-weight organic acid pool in these systems is controlled, in part, by the presence of electron acceptors available for microbially mediated electron-transfer reactions. The depletion of electron acceptors in aquifers leads to the accumulation of aliphatic organic acids in anoxic groundwater.

Modeling steady-state methanogenic degradation of phenols in groundwater

Abstract Field and microcosm observations of methanogenic phenolic compound degradation indicate that Monod kinetics governs the substrate disappearance but overestimates the observed biomass. In this paper we present modeling results from an ongoing multidisciplinary study of methanogenic biodegradation of phenolic compounds in a sand and gravel aquifer contaminated by chemicals and wastes used in wood treatment. Field disappearance rates of four phenols match those determined in batch microcosm studies previously performed by E.M. Godsy and coworkers. The degradation process appears to be at steady-state because even after a sustained influx over several decades, the contaminants still are disappearing in transport downgradient. The existence of a steady-state degradation profile of each substrate together with a low biomass density in the aquifer indicate that the bacteria population is exhibiting no net growth. This may be due to the oligotrophic nature of the biomass population in which utilization and growth are approximately independent of concentration for most of the concentration range. Thus a constant growth rate should exist over much of the contaminated area which may in turn be balanced by an unusually high decay or maintenance rate due to hostile conditions or predation.

Methanogenesis of phenolic compounds by a bacterial consortium from a contaminated aquifer in St. Louis Park, Minnesota

Anaerobic degradation of phenolic compounds to CH 4 and CO 2 in sewage sludge digestion is well documented. LTtt le is known of the phenomenon in other environments, but i t is thought to be a common occurrence (MAH et al. 1977). EHRLICH et al. (1982) found that methanogenesis is occurring in contaminated ground water at St. Louis Park, Minnesota. The ground water had been contaminated during the operation of a coal tar d i s t i l l a t i o n and wood treatment f a c i l i t y . Phenols, a major f ract ion of coal tar , were observed to degrade in both the ground water and laboratory digestors with a concomitant production of CH 4. The purpose of th is paper is to present the detai ls of the laboratory studies.

Methanogenic degradation kinetics of phenolic compounds in aquifer-derived microcosms

In this segment of a larger multidisciplinary study of the movement and fate of creosote derived compounds in a sand-and-gravel aquifer, we present evidence that the methanogenic degradation of the major biodegradable phenolic compounds and concomitant microbial growth in batch microcosms derived from contaminated aquifer material can be described using Monod kinetics. Substrate depletion and bacterial growth curves were fitted to the Monod equations using nonlinear regression analysis. The method of Marquardt was used for the determination of parameter values that best fit the experimental data by minimizing the residual sum of squares. The Monod kinetic constants (μmax, Ks, Y, and kd) that describe phenol, 2-, 3-, and 4-methylphenol degradation and concomitant microbial growth were determined under conditions that were substantially different from those previously reported for microcosms cultured from sewage sludge. The Ks values obtained in this study are approximately two orders of magnitude lower than values obtained for the anaerobic degradation of phenol in digesting sewage sludge, indicating that the aquifer microorganisms have developed enzyme systems that are adapted to low nutrient conditions. The values for kd are much less than μmax, and can be neglected in the microcosms. The extremely low Y values, approximately 3 orders of magnitude lower than for the sewage sludge derived cultures, and the very low numbers of microorganisms in the aquifer derived microcosms suggest that these organisms use some unique strategies to survive in the subsurface environment.

A column technique for determining sorption of organic solutes on the lithological structure of aquifers

In recent years the problem of ground-water contamination by organic substances of anthropogenic origin and the fate of these solutes has received increased attention. Such contaminants in an aquifer system may be transported in solution, sorbed by sediments, volatilized, altered chemically or metabolized by organisms. The quantitative aspects of these physical, chemical, and biological factors must be determined to understand adequately the fate of the contaminants in the system. The sorption of these organic contaminants on the lithological framework is addressed in this paper as well as the development of a technique to prepare solutions of sparingly soluble compounds. High performance liquid chromatography equipment was used to conduct these studies.

Transport and Degradation of Water-Soluble Creosote-Derived Compounds

Creosote is the most extensively used insecticide and industrial wood preservative today. It is estimated that there are more than 600 wood-preserving plants in the United States, and their collective use of creosote exceeds 4.5xl06 kg/yr (von Rumker et al., 1975). Creosote is a complex mixture of more than 200 major individual organic compounds with differing molecular weights, polarities, and functionalities, along with dispersed solids and products of polymerization (Novotny et al., 1981). The major classes of compounds previously identified in creosote show that it consists of ∼85% (w/w) polynuclear aromatic compounds (PAH), ∼12% phenolic compounds, and ∼3% heterocyclic nitrogen, sulfur, and oxygen containing compounds (NSO).