Abstract
This study explores the potential of using cow dung as a bio-stimulant to enhance the biodegradation of xylene, a common contaminant in soils, particularly those impacted by pesticide use. The experimental setup involved adding varying amounts of cow dung (5 g, 10 g and 15 g) to xylene-contaminated soil samples and analyzing the changes in xylene concentration using Gas Chromatography-Mass Spectrometry after the duration of 28 days. At the end of the experiment, the results showed that the physicochemical properties of the soil only as well as the soil samples treated with 5 g, 10 g and 15 g of cow dung revealed that an increase in cow dung concentration causes an increase in the physicochemical properties of soil. The parameters assessed namely the pH, total nitrogen content, total phosphorus content, total organic carbon content and percentage moisture content of the samples increased through the ranges of 6.89 - 9.44, 0.50 mg/NO3 - 1.10 mg/NO3, 7.72 mgPO3/kg - 210.5PO3/kg, 12.45 g/kg - 41.85 g/kg and 0.5% - 1.5% respectively, with an increase in cow dung concentration. However, the Colony Forming Units per gram (CFU/g) of hydrocarbon utilizing bacteria albeit present, decreased with an increase in cow dung, from 658 CFU/g in the soil-only sample to 184 CFU/g in the soil sample treated with 15 g of cow dung. For the xylene concentrations after treatment, the soil only sample and the samples treated with 5 g, 10 g and 15 g of cow dung contained 0.90 ± 0.00 ppm, 0.27 ± 0.02 ppm, 0.32 ± 0.01 ppm and 0.35 ± 0.03 ppm of xylene respectively. The results indicated that increasing the amount of cow dung corresponded with higher xylene concentrations, suggesting an unintended consequence as well as complexities in microbial or biological interactions where cow dung may introduce or augment xylene levels rather than facilitate its degradation. The study concludes that cow dung, albeit having significant microbial content, may not be a viable candidate for the biodegradation of xylene in construction soil and highlights the need for further research into alternative bio-stimulants or conditions that could more effectively promote the biodegradation of such contaminants.

Key words: Xylene, biodegradation, cow dung, construction soil, hydrocarbon-utilizing bacteria, physicochemical.