Comparative Study Of Nitrate Evaluation And Bacteriological Characterisation Of Shallow Groundwater In Adjoining Towns Around Oyo Area, Sw Nigeria

The study aimed at assessing the quality of groundwater from forty-five shallow hand-dug wells (HDs) in adjoining towns of Awe, Akinmorin, Ilora and Oyo within the southwestern Nigeria. The amounts of nitrate and bacterial counts and species identification were carried out in water samples in these communities where groundwater is the major reliable water source using spectrophotometric, multiple tube and plate counts techniques. From the results, nitrate concentration was between 1.48 and 191.8 mg/L in sampled wells and its occurrence in water exceeded the recommended level of 50 mg/L in about 38% of sampled wells across all the towns. Oyo town has the highest nitrate level in water with a range of 5.11 - 191.8 mg/L and average of 71.24 mg/L, compared to 29.87 mg/L in Awe, 41.33 mg/L in Akinmorin, 45.09 mg/L in Ilora. The minimum total bacteria count (TBC) was 26 cfu/100 mL while the total coliform count (TCC) ranged from 14 to 46 cfu/100ml. The presence of coliform bacteria depicts fecal contamination of groundwater in the study area. From the morphological studies, four bacteria species were identified; namely, Bacillus cereus (which is the most abundant), Bacillus species, Pseudomonas aeroginosa and the Klebsiella species. The deepest hand-dug well was 20.8 m in the area and the correlation between the depths of the HDs and nitrate concentrations is negative-indicating that nitrate concentration moderately decreases with increasing well depth. Likewise for bacteria counts, the relationship was indirect in most towns, which depicts that bacterial occurrence will likely fade out as well depth increases in most cases. Also, the cross-plots of nitrate against bacterial counts in groundwater were positive that confirms that high nitrate level in water will favour bacterial activities. From these deductions, deeper wells are recommended and remedial decontamination of functioning wells should be in place in these communities to guarantee safety of human lives.