Autochthonous microbial responses and hydrocarbons degradation in polluted soil during biostimulating treatments under different soil moisture. Assay in pilot plant

This study investigated autochthonous microbial responses and hydrocarbon degradation in a sandy soil artificially contaminated with Diesel fuel at 20,000 ppm using NPK fertilizer and Ivey surfactant as biostimulating agents. Experiments were carried out at pilot scale at different moisture contents. Dehydrogenase activity and CO2 production, measured as indicator of microbial activity showed cubic linear correlation. NPK-treatment stimulated biodegradation capacity most effectively when moisture was low; an increase in the soil moisture content produced a decrease in the biodegradation capacity of the treated soil. The biodegradation rate for TPH of 0.0454 day−1 at 15% moisture, decreased to 0.0201 day−1 at 25% moisture and to 0.0128 day−1 at 30% moisture. NPK was the most efficient treatment at 15 and 25% moisture for n-alkanes, aromatics and branched hydrocarbons allowing for contaminant removal of between 78 and 100%. Branched and aromatic hydrocarbon degradation was best at 30% of moisture with NPK + Ivey treatment producing removal of 64 and 74% of the contaminant mass, over a period of 28 days. Canonical redundancy analysis showed that the addition of biostimulating agents explained 80.8% of the total variability of the biological and chemical parameters.