TREAT IT OR LEAVE IT? A BENCH-SCALE VIEW COMPARING MONITORED NATURAL ATTENUATION WITH TWO FORMS OF BIOSTIMULATION

Leaking aboveground and underground storage tanks, spillage during transport of petroleum products, and activities associated with industrial processes are common causes of petroleum contamination; contamination that is hazardous to soil and water ecosystems, and is expensive to remediate. Bioremediation, the use of microorganisms to degrade contaminants, can be an effective, economical, and environmentally friendly treatment. Monitored natural attenuation (MNA) permits the native microflora to degrade contaminants without intervention. Biostimulation, the addition of nutrients to stimulate growth of native microbes, primarily employs highly soluble fertilizers that, owing to their solubility, are easily leached resulting in potential eutrophication of aquatic systems. In contrast, biosolids (sewage sludge) release nutrients slowly and in smaller quantities, thus providing an alternative nutrient source for biostimulation. Bench-scale studies conducted over an 8-week period compared biostimulation using two nutrient sources, fertilizer and biosolids, at two differing concentrations, with MNA. In both amended and MNA soils degradation was most rapid in week one, slowing thereafter. Degradation, as % hydrocarbon loss, was greatest in high-concentration fertilizer amended soils (~97%), closely followed by biosolids amended soils (~96%), which was independent of nutrient concentration. Low concentration fertilizer resulted in ~95% degradation. Untreated soils (MNA) yielded ~94% degradation. Results indicate that biosolids can be a preferred nutrient source for biostimulation by adding slow-release nutrients and additional carbon. MNA results suggest that under appropriate circumstances, MNA is a viable remediation strategy.