Impact of coconut husk biochar on methane production rate in batch type anaerobic digester fed with cattle dung and cooked kitchen waste

Abstract

The current investigation is a comparative study of anaerobic co-digestion (AcoD) of cattle dung (CD) and cooked kitchen waste (CKW) without and with biochar addition under ambient and mesophilic (35 ± 2 °C) temperatures. The novelty of the investigation is that it focuses on the effect of substrate mixing ratio (SMR), biochar addition, and temperature on AcoD. Initially, four sets of biochemical methane potential (BMP) tests were performed simultaneously, considering the same SMR of 100:0,0:100, 70:30, 60:40, 50:50, 40:60, and 30:70 on mass basis without and with biochar (15 g/L) addition. Considerably, a higher rate of methane (CH₄) yield was achieved for the biochar-added and mesophilic digesters. The maximum specific methane yield (SMY) was detected for the SMR 40:60 for all sets of BMP tests, wherein the SMY for the biochar-added digesters under ambient and mesophilic temperatures were 213.29 and 249.98 mLCH₄/gVS, respectively. Consequently, considering the SMR 40:60, another set of BMP test was performed under ambient temperature by adding varying quantities of biochar: 5, 10, 15, 20 and 25 g/L, to identify the most feasible needed amount of biochar to be added for maximum CH₄ generation. The digester containing 15 g/L biochar exhibited 14.23 %, 9.89 %, 3.00 %, and 7.91 % higher cumulative CH₄ yield than the digesters containing 5, 10, 20 and 25 g/L biochar, respectively, confirming that 15 g/L biochar addition in the slurry of SMR 40:60, can be recognised as the most effective SMR for AcoD of CD and CKW. This study reveals that biochar addition improves the AcoD process.