Consequence of C:N and C:P adjustments of rice straw on biomethanation in an anaerobic digester

Abstract

Experiments were conducted at the Faculty of Agriculture, University of Ruhuna, to assess the influence of C:N and C:P ratios on anaerobic digestion of rice straw batch biomethanation. The original rice straw C:N ratio of 80:1 was amended with urea (46% nitrogen) to maintain the C:N ratio between 10:1 to 40:1 After mixing with urea the highest total biogas production of 54.12 1 and maximum methane percentage of 55% were recorded at 30:1 C:N ratio with 8 days of lag phase. The lowest gas production (23.59 1) and minimum methane percentage (18.2%) were given at 10:1 C:N ratio. Concentrated super phosphate was added to adjust the C:P ratio on biogas production between 100:1 to 250:1 while a constant ratio of 30:1. The original C:P ratio of rice straw was 331:1. Adjusting C:P ratio to 200:1 produced the maximum gas yield of 54.99 1 with five days of lag phase. Maximum percentage of methane was also produced at 200:1, while 100:1 C:P ratio gave the lower methane production.