Production of Biogas from Mono- and Co-Digestion of Agricultural Waste (Cow Dung, Chicken Dropping, and Rice Husk)

Abstract

This study focused on waste to energy technology that utilized mono- and co-digestion of cow dung (CD), chicken dropping (ChD), and rice husk (RH). The fabricated digesters were assessed for the influence of temperature and pH on biogas production from the materials used. The total aerobic bacteria and fungi counts for the mono- and co-digestion of cow dung with chicken droppings had highest number on day zero (1.5x10⁷cfu/ml, 1.6x10⁵cfu/ml and 1.4x10⁸cfu/ml, 1.2x10⁵, respectively), while the lowest counts were recorded on the 35^th day (1.3x10¹cfu/ml, 1.0x10¹cfu/ml and 1.1x10¹cfu/ml, 1.0x10¹cfu/ml, respectively). The highest count of the acetogenic organisms was 1.8x10⁵cfu/ml on the 18^th day whereas no count was observed on the 35^th day. Methanogenic bacteria had a count ranging from 1.0x 10¹ cfu/ml to 3.4x10⁴cfu/ml on the 18^th day. pH was within the range of 5.3 – 8.5 in the digesters. Cow dung  (100% CD) showed the highest cumulative gas production of 41.65m³ compared with chicken droppings (100% ChD) and rice husk (100% RH) which showed values of 8.91 m³ and 0 m³, respectively, within temperature. Furthermore, the co-digestion of 75% CD + 25% ChD, 50% CD + 50% ChD, 25% CD + 75% ChD, 50% CD + 50% RH, and 50% ChD + 50% RH produced biogas values of 20.1m³, 15.13m³, 7.51m³, 5.1m³, and 2.09m³, respectively, at the same temperature range of 36.2^OC - 41.7^OC.

The assay for nitrogen (N), phosphate (P), potassium (K) and sulphate (S) to find the major plant nutrient from the digestate showed that 100% CD was richer in N (1.8mg/l), P (0.5mg/l), and S (0.5mg/l) than the other biomass types, whereas 50% CD 50% ChD had the highest content of P. The present study suggests that the digestion of cow dung, chicken droppings, and rice husk can be an effective means of waste management, pollution control, and generation of renewable energy (biogas) and fertilizers, thereby further strengthening the role of agriculture in the area of food security.