On-site treatment of contaminated soils: An approach to bioremediation of weathered petroleum compounds

A bench-scale investigation was conducted prior to on-site bioremediation o f 52,000 cubic yards of contaminated soil containing weathered, structurall y complex petroleum compounds from an inactive oil refinery. Addition of bu lking agents was required to improve soil physical properties. A supplement al study was also conducted to evaluate the effectiveness of bio-enhancemen t products. Loss of n-alkanes was rapid in soil mixtures containing a high nitrogen sludge compost, but very slow in mixtures containing wood products as bulking agents. By completion of;the study at day 110 the isoprenoids p ristane and phytane had nearly disappeared from mixtures containing sludge compost Clearly, pristane and phytane are inadequate biomarkers when condit ions favor an advanced stage of biodegradation. Nearly half the complex bra nched and cyclic alkanes in the unresolved complex mixture also degraded. A fter 70 days, depletion of dibenzo-thiophenes and phenanthrenes was 75 and 90%, respectively. The most;stable PAHs within each group were the highly m ethylated homologues. Because of their complex structures, both steranes an d hopanes were :stable in all soil mixtures. Data were normalized to hopane s as a conserved internal standard or,biomarker Use of hopane-normalized da ta successfully eliminated much of the data variability and permitted a mor e accurate assessment of,biodegradation. A relatively slow decline in fetal hydrocarbons occurred later in the study. This slowing tendency of microbi al utilization is caused,not only by substrate depletion, but also because remaining hydrocarbons are structurally more complex and persistent Because of this, it is important to avoid using kinetic data from early stages of bioremediation to predict later hydrocarbon losses, such as the time requir ed to attain a cleanup standard. In the supplemental study an oleophilic fe rtilizer product accelerated hydrocarbon degradation when compared with a c onventional fertilizer This product will be tested in combination with orga nic bulking agents under field conditions to determine its cost effectivene ss.