Role of Bacteria in Decomposition of Injected Liquid Waste at Wilmington, North Carolina: ABSTRACT

Abstract

In 1968, Hercules Chemical, Inc., Wilmington, North Carolina, began injecting organic waste through wells into a saline-disposal zone at depths of 850-1,000 ft. The waste, which is a by-product of dimethyl terephthalate used in the production of synthetic fiber, is composed of water, with a pH of about 4.0, containing approximately 15,000 ppm acetic acid, 5,000 ppm formic acid, and 500 ppm methanol. The movement and composition of the transformed waste have been monitored by a network of 14 observation wells drilled to various depths. The waste-water analysis and monitoring were performed by the U.S. Geological Survey. In June 1972, waste was detected in observation well 14. The microbial population was periodically sampled as the dissolved organic carbon fraction increased. The dissolved organic content increased to 112 mg/1, and then rapidly decreased to 20 mg/l. This sudden decrease in dissolved organic carbon was accompanied by the appearance of gas composed of approximately 60% methane. Each time a decrease in dissolved organic carbon occurred, gas was found and an increase in the total microbial population was measured. Methane gas production is the result of microbial activity. The injected waste contains adequate carbon and energy substrates for the strictly anaerobic, methane-producing bacteria which have been isolated from well 14. In addition to the methane-producing bacteria, other bacteria have been isolated and identified. Microorganisms such as Agrobacterium, Pseudomonas (especially species fluorescens), Proteus, Bacillus, Arthrobacter, Aerobacter, Corynebacterium, and Staphylococcus have been observed. The total microbial population was found to be 25 × 108 organisms per milliliter in well 14 and 30 × 108 organisms per milliliter in the unpolluted aquifer. The source of these bacteria is the natural aquifer, inasmuch as the injected waste is sterile. The wast alone does not support a microbial population for it contains no nitrogen. Such nitrogen substrate is apparently supplied by the natural water in the aquifer. End_of_Article - Last_Page 1594------------