Impact of bioaugmentation on crude oil degradation in salt-marsh-sediment microcosms

Abstract

Bioremediation is the method of choice for eliminating oil from marshes and is dependent on microorganisms capable of mineralizing oil. Because populations of oil degrading microorganisms are low in marshes there is a potential for increasing bioremediation by inoculation ('bioaugmentation'). In addition, N and P supplementation may help speed up the process. Ten commercial products, comprising eight bioaugmentation (microbial formulations) and two bioremediation (nonmicrobial formulations) products were used to study the role of bioaugmentation, fertilization and temperature on degradation of oil in simulated salt marsh microcosms. Total petroleum hydrocarbons (TPH) were determined by infrared spectrophotometry and oil and grease content by ravimetry. Microbial respiratory activity was determined by gas chromatography and populations were enumerated by plate counts and most probable number estimation. Significant fertilizer by temperature and fertilizer-temperatureproduct interactions were evident. Unfertilized soil treated with products and incubated for 90 d at 10 and 30'C contained 50-79% and 36-67% of the added TPH respectively. Addition of N and P fertilizer to soil incubated at IO'C without products decreased the amount of TPH remaining from 79% to 60% by 90 d. Addition of products resulted in reduction of TPH remaining from 29-57 %. Higher response to addition of fertilizers was obtained by incubating at 30'C but none of the products enhanced oil bioremediation. Fertilizer reduced the TPH content to 17% by 90 d. Numbers of hydrocarbon-degrading microorganisms and total heterotrophic bacteria increased with addition of oil. Addition of some products enhanced the populations in soil by 21 d but the populations did not differ at 90 d. These results indicate that the commercial products may prove useful in enhancing the rate and extent of oil degradation in soil. In addition, the contaminated soils may need fertilizer amendments for maximum oil degradation. During the warm season, addition of fertilizer alone could enhance the biodegradation rates whereas addition of bioaugmentation or bioremediation products along with fertilizer may enhance the degradation rate during the cool season.