The produced biogas was stored in gasbag, treated in 1 Lstripper bottle containing 500 ml of 2 N sulfuric acid to remove
ammonia, and then recycled to the flask. The flask was connected
with a condenser to retain the moisture content. Ferrite powder
(100 g) (commercially known as hand warmer) was employed to
remove oxygen, which contaminated the recycled biogas. The
digestion was initiated by adding 100 g of CM (75% water content),
25 g of the seed sludge and 180 ml of water to obtain the suitable
fluidity of the mixture. NaOH was added to this mixture to elevate
the initial pH to 8.5–9. The experiment was conducted for 4 days.