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Bioremediation of Soil and Ground Water Impacted with Organic Contaminants

WOODS, WILLIAM B., EMCON Associates, San Jose, CA

Two case studies demonstrate the controlled use of microorganisms to degrade organic contaminants under aerobic and anaerobic conditions. The aerobic study illustrates the degradation of hydrocarbons in a soil matrix. Data are presented that show a two-phase degradation of total petroleum hydrocarbons (TPH) from about 1300 ppm TPH to cleanup levels of 100 ppm or less in two months. Total aerobic microorganism and substate-specific degrader counts were tracked throughout the study. Typical total aerobic counts of 106 colony forming units (CFU)/g and hydrocarbon degrader counts of 104 CFU/g were observed. Hydrocarbon degraders were enumerated on minimal salts media incubated in the presence of hydrocarbon vapors. The anaerobic study documents the successful use of a supplemental carbon ource and fertilizers to stimulate indigenous microbe to degrade ketones. A nutrient mix of a polysaccharide, a nitrate electron acceptor and an inorganic orthophosphate was used to augment 100,000 yd3 of soil contaminated with ketones at about 1000 ppm. Within six months, the level of ketones was reduced to 50 ppm. The key elements of a biotreatment project are discussed (i.e., site characterization, treatability studies, biotreatment design, site construction, system maintenance, final disposal and site closure). The oxygen use (or respiration) rate by microorganisms in the soil is used to measure biological activity and, thus, to determine the mix and concentration of nutrients required to optimize microbial growth. Laboratory microcosms containing about 2 kg of soil are amended with utrients at the level determined using soil respiration rate comparisons. The microocosms are maintained consistent with anticipated field conditions and the soil's contaminant concentration monitored versus time. A field degradation rate is then predicted. The ideal biotreatment system design is presented as the system that is cost-effective, maximizes the microbial transformation rate of the contaminant, and controls the biotreatment such that the surrounding environment is not at risk. Lastly, the benefits of bioremediation vs. other remediation alternatives such as landfill disposal, incineration, and stabilization/fixation are discussed in terms of cost and liability. Cost savings of a factor of two or more can be realized using biotreatment. Degradation to environmentally benign en products of carbon dioxide and water greatly reduces the liability of the generator compared to land disposal and fixation, which do not result in the ultimate destruction of contaminants. Thermal treatments are expensive and require the use of air emission control devices and continuous air monitoring.


AAPG Search and Discovery Article #91009©1991 AAPG-SEPM-SEG-SPWLA Pacific Section Annual Meeting, Bakersfield, California, March 6-8, 1991 (2009)