S. Abdul

A laboratory study of the biodegradation of an alcohol ethoxylate surfactant by native soil microbes

Laboratory experiments were conducted to study the biodegradation of a nonionic alcohol ethoxylate surfactant by native microbes from a contaminated site. Three sets of experiments consisting of 13 microcosms were carried out to evaluate the rate of biodegradation and the effect of nutrients and supplementary oxygen on the degradation process. The results from these active microcosms were compared with those for controlled microcosms in which a biocide was added to inhibit biological activities. In the presence of ground water and sterilized soil, surfactant solutions with initial concentrations of 1000, 650, 250, and 180 mgl−1 were reduced to less than 5 mgl−1 in 36 days, 20 days, 17 days, and 17 days, respectively. The biodegradation rate in microcosms with added nutrients was more than twice the rate in the reactor without nutrients. The results from experiments in which various nitrogen and phosphorus nutrients were added showed that a ratio of 10 carbon:2 nitrogen:1 phosphorus was the optimum for the biodegradation of surfactant under the microcosm conditions. The addition of 5 mgl−1 of oxygen in the form of hydrogen peroxide increased the degradation rate of surfactant by 30%. The study showed that microbes indigenous to the soil and ground water at a contaminated site rapidly degrade the low levels of the surfactant that may remain at the site after soil washing, and that the degradation rate can be increased by the addition of nutrients and oxygen.

Contamination of soil and groundwater by automatic transmission fluid: site description and problem assessment.

Soil and groundwater beneath a region of a manufacturing plant are contaminated with automatic transmission fluid (ATF). The extent of contamination was assessed by maximizing the use of real-time data from soil-core sampling and monitoring wells. The number, location, and depth of cores and of monitoring wells were determined during the investigation based on: (1) inspection and analysis of soil-core samples immediately after each core was taken; (2) physical and chemical measurements of core samples at the end of each day; (3) measurements in monitoring wells at several stages during the investigation. This approach differs significantly from the conventional approach of randomly placing wells through the hydrogeologic system. Soil cores were taken and monitoring wells installed at 53 locations. The perched aquifer extends to about 13 ft. and is comprised mainly of sandy materials, which have spatial heterogeneity in size distribution and hydraulic properties. About 208 000 ± 33 000 gal. of ATF has spread over an area of about 64 000 ft.2. The region of ATF contamination is comprised of three distinct and contiguous layers. The center layer is about 2.6ft. deep at its thickest point and extends to about 250ft. at its widest point. The soil in this zone is about 85% saturated with 133 000 ± 21 000 gal. of ATF, which has depressed the water table into the aquifer. The top layer is about 14in. thick and econtains about 50640 gal. of ATF held by capillary forces. The amount of ATF in this zone decreases with height above the center layer from about 85% saturation to residual saturation (20%). The amount of ATF in the deepest layer is near the residual saturation. This layer is 1.0 ± 0.5 ft. thick and has 24 500 ± 12 250 gal. ATF. This investigative approach did not spread the ATF to clean regions of the aquifer as could occur with conventional approaches, and it provided the data needed to assess the problem and to design a cleanup plan. A new approach is being used to recover the free ATF at the site.