MANAGEMENT OF SHEA NUT WASTE WITH INDIGENOUS SOIL BACTERIA

Abstract

Shea nut cake contains high levels of tannins which make it toxic and recalcitrant to biodegradation. Soils receiving shea nut cake are polluted. Microbial removal of tannins from shea nut cake will permit easy degradation of the waste by soil microbes and its conversion to economically useful products. Three hundred and twenty four (324) soil samples were collected at three depths (0-20 cm, 21-40 cm and 41-60 cm) from shea nut cake polluted and unpolluted locations in Jisonayili, Gurugu and Kasalgu in the Northern Region of Ghana, from September, 2010 to July, 2011. A completely randomized multi-factorial design and single factor experiments were used to study the physico-chemical and microbiological properties of the soils and identify potential microbes for the degradation of tannins in shea nut cake. Dependent variables measured were pH, moisture, nitrogen, carbon, tannin contents, bacteria and fungi populations. ANOVA was used to analyze the results. Tannin degrading bacteria were isolated with mineral salt medium supplemented with 2% shea nut cake. GUR/09 and GUR/38 gave good growth in 5% shea nut cake with yeast extracts at room temperature and were identified biochemically as Pseudomonas aeroginosa and Pseudomonas putida respectively. The ability of GUR/09, which performed better than GUR/38, to degrade tannins in fresh and boiled shea nut cake was investigated by inoculating with GUR/09 and monitoring tannin concentration. Moisture, pH, carbon, nitrogen contents and microbial counts were significantly higher in shea nut cake polluted than unpolluted soils and highest (bacteria, 7.566 and fungi, 3.657 log10 cfu) in the 0-20 cm depth. Moisture and bacterial counts were higher in rainy season than dry season with peak in September. Fungal counts were highest in November. Shea nut cake added organic matter and nutrients to the experimented soil which probably increased the microbial populations. Pseudomonas aeroginosa (GUR/09) degraded 92 % tannin in fresh shea nut cake in 20 days and 95% in 20 days when shea nut cake was boiled. Pseudomonas aeroginosa GUR/09 can be used to manage the waste. Polluted soils are reliable sources of bacteria to manage wastes. Government should encourage the use of bacteria to manage agricultural wastes.