Bioremediation of diesel-contaminated soil using spent mushroom compost

Composting has been shown to be an effective bioremediation technique for the treatment of hydrocarbon-contaminated soil (Fermor et al.). In this research, spent mushroom compost (SMC), a sustainable, inexpensive, and abundant byproduct of the mushroom industry, was analyzed for its ability to support the remediation of soil contaminated by a diesel fuel spill. Chitin, a nitrogen-rich polymer derived from crab shell material, was also investigated as a nutrient amendment to counteract the nitrogen loss commonly observed in petroleum-contaminated soils (Brook et al.). The approach was tested on contaminated soil and SMC obtained from the California Mushroom Farm, Inc. The results of this study will be used to guide the implementation of aerobic composting for remediation of diesel-contaminated soil at the site. Sacrificial batch microcosm tests were used to evaluate the effect of substrate/nutrient addition and elevated temperatures on the rate of diesel total petroleum hydrocarbon (TPH) remediation in a series of two experimental phases. In Phase I, the conditions evaluated were soil + SMC, soil + SMC with crab-shell chitin, and soil only (control). In Phase II, TPH removal was monitored at three temperatures typically encountered during composting: 22°C, 30°C, and 50°C. In Phase I, all substrate-amended microcosms were successful at diesel removal. Microcosms amended with SMC and chitin showed an advantage at various points throughout treatment but did not enhance overall TPH remediation when compared to microcosms amended with SMC only. In Phase II, microcosms showed different TPH removal trends at early times depending on temperature, but overall, it was determined that none of the various temperature conditions provided an advantage for remediation. After 160 days, TPH concentrations in microcosms were reduced from 1600 to 210 ppm at 22°C, 180 ppm at 30°C, and 270 at 50°C for removals of 87%, 89%, and 83%, respectively. To characterize the microbial community during the course of treatment, Denaturing Gradient Gel Electrophoresis (DGGE) was performed using bacterial 16S primers. DGGE bands were excised and sequenced for comparison with the GenBank database using the Basic Local Alignment Search Tool (BLAST). These analyses will provide details about bacterial communities present in the biodegradation system. Sorption experiments are also being conducted to investigate the percentage of diesel that irreversibly sorbs to the organic material at various concentrations, and thus the percentage of observed removal that may be attributed to this abiotic factor.