ABSTRACT
Increase in the indiscriminate disposal of untreated palm oil mill effluents (POME) on agricultural soils can lead to change in the features of soils and their ability to sustain optimal plant productivity. The aim of the study was to evaluate the microbiological and physico-chemical properties of soils polluted with POME.
Soils obtained within University of Benin was air dried and 2kg of the soil was put into sterile polythene bags and were separately polluted with 250, 500, 1000 and 1500 ml of POME with unpolluted soil serving as control. The bags, containing contaminated soil were thereafter left outside under normal environmental condition for 9 weeks. Microbiological and physico-chemical analyses were carried out before pollution, and thereafter weekly. Microbiological analysis was carried out to isolate and enumerate bacterial and fungal species. This was done using standard microbiological techniques. Isolates were identified using cultural and biochemical characteristics. Soil physico-chemical parameters analyzed were soil particle size and texture, pH, electrical conductivity, organic matter, organic carbon, total nitrogen, available phosphorus, exchangeable cations, exchangeable acidity (EA), effective cation exchange capacity (ECEC) and percentage base saturation.
Results obtained showed that the physico-chemical parameters of soil polluted with POME were affected by both concentration of pollutant and duration of exposure. Polluted soils were observed to be more acidic compared to unpolluted soil, indicating the acidic nature of POME. pH values ranged from 5.10 ±0.07 – 5.98 ±0.15, and 5.54 ±0.01 – 6.24 ±0.03 for polluted and unpolluted soils respectively. There was an overall decrease in organic carbon, organic matter, nitrogen, magnesium, potassium and sodium content with increase in concentration of POME and duration of exposure. The values of exchangeable cations and ECEC increased and decreased respectively with increase in POME concentration. However, there was a fluctuation in the values of % base saturation obtained. The sand and clay content of polluted soils were lower and higher with increase in POME concentration respectively. Bacterial colony counts ranged from 10.00 ±1.15cfu/ml to 92.00 ±3.51 cfu/g and 14.33 ±3.84cfu/g to 53.67 ±4.70 cfu/g for polluted and unpolluted soils respectively, and were lowest during the 7th week. During the first three weeks, an increase in the counts of bacteria was observed for 500, 1000 and 1500ml of POME, whereas, fungal counts only increased for 250 ml and 500 ml concentrations of POME. Fungal counts ranged from 3.67 ±1.76–89.00 sfu/g ±2.08 sfu/g and 6.67 ±1.76–63.67 ±4.10 sfu/g for polluted and unpolluted soils respectively. The bacterial isolates recovered were Bacillus cereus, B. subtilis, Enterococcus sp, Klebsiella sp, Micrococcus sp, Pseudomonas spand Staphylococcus aureus.,while the fungal isolates wereAspergillus flavus, Aspergillus niger, Fusarium oxysporium, Mucor mucedo and Penicillium chrysogenum. The most prevalent bacterial and fungal isolates were Staphylococcus aureus and Mucor mucedo respectively, while the least prevalent were Klebsiella sp and Aspergillus flavus for bacteria and fungi respectively. The study showed that the disposal of untreated POME alters the physico-chemical characteristics of receiving soils. However, the increase in the microbial flora of these soils suggests that POME if treated could be used to improve plant productivity on soils, as some of the bacteria and fungi isolated are important in the maintenance of soil fertility.
