Many organic contaminants found in the soil are associated with industrial emissions and/or spills; these include petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAHs), in particular. PAHs accumulate in soil due to their low aqueous solubility, volatility, hydrophobicity and recalcitrant chemical structures. The environmental persistence and risks associated with human and environmental health emphasize the importance of the treatment of PAH-contaminated soil. Various physical and chemical technologies known to have been employed in remediating PAH-contaminated soils are expensive and have further environmental challenges compared to microbial degradation which is less costly and environmentally sustainable. However, the stimulation of microbial activity with recurrent addition of mineral nutrients is known to damage the soil quality, while soil amendment with the residues of renewable energy production becomes a suitable option due to their nutrient contents, environmental sustainability and economic feasibility. This thesis evaluates the environmental fate and impact of PAHs in the soil and the biodegradation of PAHs in contaminated soils. It further investigates the effects of soil amendment with organic residues, particularly anaerobic digestate (AD) (a semi-solid biogas residue), wood-ash (WA) (a timber combustion residue) and their mixtures on indigenous microbial activity, and how the effects influence the indigenous biodegradation of PAHs. The findings provide insights into the implications of microbial degradation of PAHs in soils lacking in nutrients, the effects of soil amendment with AD and/or WA on biodegradation of PAHs, and the correct amounts of AD and WA that could be used as a combined soil amendment to stimulate indigenous biodegradation of PAHs.