Enhanced biogas production from rice straw by selective micronutrients under solid state anaerobic digestion

Biomethanation of rice straw (RS) was studied in a batch mode at high total solid content (TSC) of 25% in outdoor pilot scale digesters. Performance was monitored for over six months by supplementing Nickel and Cobalt 15 and 10 mg kg−1 RS to each of mesophilic and thermophilic digesters for 35 and 21 days retention time (RT), respectively. The average biogas production from mesophilic and thermophilic digesters were found varying 310 and 396 L kg−1 TS, respectively. The corresponding figures for the control digesters were 225 and 270 L kg−1 TS. Around 37 and 46% higher biogas production was recorded by supplementing the micronutrients in mesophilic and thermophilic digesters, respectively. Methane content in biogas was 57-59%. Matured compost had nitrogen, phosphorus and potassium contents of 1.0-1.2, 1.3-2.2, and 1.2-2.1%, respectively. The results demonstrated that the present process is faster, requires less than 85% water and produces green energy in addition to manure in less time compared to conventional process.