PRELIMINARY ASSESSMENT OF BIO-FERTILIZER POTENTIAL OF LIQUID DIGESTATE FROM NCEE PILOT ANAEROBIC BIOGAS PLANT AT THE UNIVERSITY OF BENIN

Abstract

The study was carried out to determine the suitability of liquid digestate from a pilot biogas plant of the National Centre for Energy and Environment (NCEE) University of Benin, for land application.  Digestate from the anaerobic digestion of cattle rumen was characterized, specifically for heavy metal content, presence of microbacteria, nutrient profile and rhizobacterial potentials. All replicate samples of the digestate contained the metals Mn, Cu, Zn, Pb, Cd, Cr, Fe, and Ni which ranged from 12.60-16.00, 30.00-38.00, 50.00-65.00, 0.20-0.60, 0.00, 0.60-0.86, 177.00-194.00, and 1.20 -1.80 mg/kg, respectively. However, their concentrations were lower than the   specified standard limits. Total phosphorus and total nitrogen concentrations were very high and ranges from 1032 to 1409 mg/kg, and 960.06-3237.62 respectively. The presence of heavy metals in the biogas digestate may have been influenced by the grasses that were regularly consumed along with various essential elements to promote optimal nutrient supply and optimum growth rates. The bacterial isolates in the processed digestates were identified to be Bacillus subtilis, Enterobacter aerogenes, Klebsiella spp., Salmonella enterica, Escherichia coli and Clostridium difficle. The isolates in the processed digestates were further assessed for their rhizobacterial potentials and intriguingly. The study found that they could have beneficial effects on plants in that they could fix atmospheric nitrogen, solubilize and produce ammonia and Bacillus subtilis was also discovered to produce the plant growth hormone.