Petroleum hydrocarbons pollution are considered as a threat to human health. There are physical and chemical methods to remediation of petroleum hydrocarbons from soil that in addition to high costs and environmental impact, require special equipment and high energy. The objective of this study was to determine the effect of humic acid on corn growth and phytoremediation of TPHs. We used a humic acid extracted from sewage sludge and a commercial humic acid (Humax). Three concentrations for each humic acid (0.5, 1 and 2 g/kg), and three TPH contaminations (1, 2 and 5 percent contamination) were used. This experiment was conducted in a completely factorial design with three replications. Corn plants were harvested 16 weeks after cultivation. Corn yield (roots and sheets) and plant chlorophyll content decreased significantly with increasing TPH concentration. Dispersible clay content of soil and water repellency increased and bulk density and soil structural stability decreased with increasing the TPH concentration. Corn yield increased significantly with increasing 1 gr/kg humic acid. Water repellency and dispersible clay content significantly decreased with increasing humic acid in the TPH contaminated treatments. The soil TPH concentration decreased by 31.19 to 55.66% during the 16 weeks of the growth. The removal of oil pollution was increased with the addition of humic acid, between 7.62% to 33.72% for sewage sludge humic acid and humax, respectively. The efficiency of treatments for the removal of TPH were as follows: sewage sludge humic acid 1 g/kg sewage sludge humic acid 0.5 g/kg sewage sludge humic acid 2 g/kg humax 0.5 g/kg humax 1 g/kg humax 2 g/kg. Key word: Humic acid, TPH concentration, Bioremediation, Water repellency, Dispersible clay content, Soil hydraulic properties
