Cocomposting of Weathered Hydrocarbon-Contaminated Soil

Abstract

Weathered, hydrocarbon-contaminated soil containing 17,000 ppm mineral oil and grease (MOG) of which 40 percent (wt/wt) was aliphatic, 32 percent (wt/wt) polar and 28 percent (wt/wt) aromatic was cocomposted with maple leaves and alfalfa in a laboratory-scale reactor. The cocompost pH was acidic initially (6.4) but rapidly increased, reaching 8.5 by day 19. During this period the cocompost temperature had risen from ambient to 53°C (day 2) and subsequently, gradually returned to room temperature. The rates of carbon dioxide generation and oxygen consumption were both low during the first 15 hours after which they rapidly rose to 135 mmol CO2/(hr-kg initial dry cocompost) and 180 mmol O2/(hr-kg initial dry cocompost). By day 12 the rates had descended to less than 10 mmol/(hr-kg initial dry cocompost). The RQ (rate of CO2 generation/rate of O2 consumption) was initially about 0.9, but it had decreased to 0.7 by day 2. The maximum rate of MOG degradation (about 600 mg/kg initial dry cocompost-day) occurred at the beginning of the experiment. Soxhlet extraction indicated that 50 percent of the MOG of soil origin was degraded in the first 105 days comparing favorably with landfarming studies with the same soil where only 30 percent of the MOG of soil origin had been degraded after 180 days. MOG fractionation demonstrated that 60 percent of the aliphatics, 54 percent of the aromatics and 83 percent of the polars were degraded during the first 180 days of cocomposting. After 287 days, at least 73 percent percent of MOG of soil origin had been degraded.