Bioremediation with compost of a diesel contaminated soil: Monitoring by dehydrogenase activity and basal respiration
The effect of compost on hydrocarbon degradation was determined during a 120-d incubation period. An evaluation of soil basal respiration and dehydrogenase activity as a monitoring instrument for the bioremediation process of soil contaminated with commercial diesel-oil was carried out. Six soil samples were used: S (control, uncontaminated soil), CS (contaminated soil), CSS (contaminated and sterilized soil), CS1 (contaminated soil plus 1% compost), CS2 (contaminated soil plus 2% compost) and CS3 (contaminated soil plus 4% compost). The relationships between soil biological parameters and the levels of total petroleum hydrocarbons (TPH) residues were investigated. Results show a large loss of hydrocarbons since the first incubation period due to their volatilization. Sterilized soil control (SCS) showed, on the 7th day, a decrease in hydrocarbons of about 40% in weight. Successively, the decrease of TPH was 56% in the contaminated soil (CS). The amendment with compost significantly enhanced TPH degradation only when applied at the highest rate of 4%. At the end of incubation, CS3 achieved a 66% loss rate after volatilization. During the first 14 days of incubation, dehydrogenase activity of CS was significantly higher than S as a result of an efficient use of organic C of TPH. Amendment, particularly the 4% addition rate, increased the dehydrogenase activity of soil with respect to CS and S. The CS showed a rather higher basal respiration than S for the whole incubation period (24 days), so confirming the ability of microorganisms to use the organic C of TPH as a substrate. The incorporation of compost stimulated the basal respiration that increased with incremental addition of amendment. The presence of hydrocarbons exerted its negative influence on mineralization rate (k) of organic carbon, but it was weakened by the presence of compost. The trend of dehydrogenase activity and basal respiration were positively related with that of residual hydrocarbon in soil. Both biological activities can be considered as good qualitative indicators of biodegradation activity of TPH in soil.