Semi-Field Assessment of Date-Palm Waste Biostimulation for TPH and PAH Removal from Oil-Contaminated Soil in Iraq

Contamination of soils by petroleum hydrocarbons is a long-standing environmental and public-health issue in oil-producing areas. This study compared natural attenuation and biostimulation using date palm waste for the remediation of crude-oil-contaminated soil collected near the North Oil Company facilities in Kirkuk, Iraq (0–10 cm). The experiment was conducted as an outdoor semi-field, pot study under a rain shelter over 160 days, using 2 kg of soil per pot; palm waste (<5 mm) was added at 500 g per pot in the biostimulation treatment. This study provides preliminary semi-field evidence from Iraq using locally available date palm waste under semi-arid outdoor conditions. Gas chromatography with flame ionization detection (GC–FID) was used to measure total petroleum hydrocarbons (TPH; C8–C40), while gas chromatography–mass spectrometry (GC–MS) was used to measure 18 priority polycyclic aromatic hydrocarbons (PAHs), grouped into 2–3- and 4–6-ring categories; the microbial number was measured as colony-forming units (CFU). Biostimulation reduced TPH from 38,751 mg kg−1 at day 0 to 9205 mg kg−1 by day 40 (76.2% reduction), which was later sustained to 4717 mg kg−1 by day 160 (87.8% reduction). Natural attenuation showed relatively slower and smaller reductions over the same period.