The biodegradability of leachate from the land treatment of hydrocarbon-contaminated soil was investigated in the laboratory using respirometry and toxicity testing in combination with total petroleum hydrocarbon (TPH) measurements. Soil in land treatment units (LTU) had been contaminated with a diesel-like hydrocarbon mixture formerly used as a diluent for crude oil at an oil field in California. Leachate was collected from two different LTUs for treatability testing in a respirometer under aerobic conditions. Only about 12% reduction in TPH concentration was observed after aeration for 161 days, indicating limited biodegradability of the hydrocarbon constituents in the leachate. Similarly, Microtox® toxicity did not change after 130 days. Leachate biodegradability was further tested by comparison to diluent-contaminated groundwater from the same site. Leachate diluted to the same TPH concentration as the contaminated groundwater was three times less toxic, but was much less biodegradable. The recalcitrance of the leachate hydrocarbons may be attributable to their high molecular weight, since the majority of the TPH was long-chained hydrocarbons of C20 or greater for leachate. In contrast, the diluent contaminated groundwater has a majority of its TPH concentration in short-chained hydrocarbons of C20 or less, which were more easily biodegraded. These short chain hydrocarbons are typically more toxic than the longer chain hydrocarbons, which would explain the observed decrease in toxicity of the diluent-contaminated groundwater during biodegradation.
Available at: http://works.bepress.com/ynelson/15/