Effect of biochar and wood ash amendment on biochemical methane production of wastewater sludge from a temperature phase anaerobic digestion process

Biochemical methane production (BMP) assays of acidified municipal sludge were conducted with local char (biochar and wood ash) in granular (0.85-4.75 mm) and powdered ( < 0.075 mm) form. The effects of char addition on BMP were investigated under high acid stress conditions at substrate to inoculum ratios of 2.2, 3.2 and 4.4 g volatile solids (VS)/g-VS and char dosages of 0.2-3.7 g/g VSsubstrate. Powdered biochar at dosage of 0.8-3.7 g/g-VSsubstrate achieved the highest improvement in rate of methane production with 192-461% increase from controls, in the first 16 days. This increase was followed by an early stationary methane production phase and a reduction of total methane yield by up to 25%. Results indicated that the early plateau could be caused by adsorption of volatile fatty acids by the biochar.