Long-term performance of a land treatment facility for the bioremediation of non-volatile oily wastes

The current study reports on operational and performance aspects of a land treatment facility for managing oily wastes generated from heavy vehicle maintenance over a 5-year period. Samples of soil and groundwater from the land treatment plots were analyzed for a range of contaminants and microorganisms over this period. The soil analyses indicated that the process has been operating efficiently even at high wastewater loadings with maximum degradation rates of 250 mg/kg per day (year 1) and average rates of 10–35 mg/kg per day (years 2–5). Hydrocarbon degraders comprised more than 80% of the total (measured) soil heterotrophic population and were present at 10⁶–10⁸ (per gram soil) once the process was optimized. The facility was capable of treating 140 kl of oily wastewater per day (average petroleum hydrocarbon content of 2% w/v) over the entire period. During this time there was no evidence of accumulation of any major metals or polycyclic aromatic hydrocarbon (PAH) compounds in the soil. Groundwater sampling and analysis indicated that the land treatment facility was not leading to contamination of any groundwater taken from bores in the vicinity of the facility. The land treatment process continues to be effective for treatment of non-volatile waste oils at this remote and high evaporation (arid) site.