Effect of Urea and NPK Fertilizer on the Anaerobic Digestion of Corn Stover (Corn Cob and Corn Sheath) for Biogas Production in a Batch Mode Bioreactor

The effect of Urea and NPK Fertilizer on the anaerobic digestion of corn stover (Corn cob and Corn Sheath) for biogas production was evaluated. Four (4) bioreactors of 3L capacity were custom designed with plastic material for the anaerobic digestion of the corn stover. The corn cob (CC) and corn sheath (CS) were treated with urea (U) as follows: 3gU /65gCC; 6gU /65g CC; 9gU /65g CC; 3gU /65gCS; 6gU /65g CS and 9gU /65g CS in dry weight bases. Similar ratios of NPK fertilizer were used (3g/65g, 6g/65g and 9g/65g) to treat the corn cob and corn sheath. The bioreactors were separately charged with the different ratios, and were set-up in replicates. The methanogen source (inoculum) was freshly strained cow rumen liquor (20% final volume of bioreactor content).The anaerobic digestion, which was in batch mode, was operated for 31 days hydraulic retention time (HRT) at ambient temperature condition (26-35OC) and pH 5.33 - 8.0. Measurement of the daily biogas yield was by downward water displacement method. Comparative analysis (t- test p?0.05) with the control indicated a significant difference in biogas yield in the test parameters: CC:U 65g/3g, CC:NPK 65g/9g, CS:U 65g/3g, CS:U 65g/6g and CS:NPK 65g/6g, with cumulative biogas yield of 2.18, 2.17, 3.29, 2.71 and 5.51 dm3, respectively. Computer aided regression analysis of the data from the test parameters that showed significant difference indicates that biogas yield is predictable as function of time. This implies the obvious possibilities of developing models for predicting biogas yield from different substrates as function hydraulic retention time (HRT). Supplementation of stover with urea and NPK fertilizer or other substrates rich in potassium and phosphorus holds a prospect in enhancing biogas production, and can be adopted in biogas technology for large scale production. However, further studies on the economics of the process are required.