Comparison of the increase in methane yield using alkali pretreatment for French weed and water lettuce prior to co-digestion

Co-digestion with cow dung was undertaken of French weed (a recalcitrant weed) and water lettuce (a spongy weed). Untreated and pretreated weeds were co-digested separately with cow dung to compare the increase in the methane (CH4) yield. The ratio of weed-to-cow dung-to-water of 10:10:80 was initially prepared. The pretreatment of weeds was performed using 1% sodium hydroxide for 24 hr at 30 degrees C. Both weeds had the potential to produce biogas. The pretreatment increased the CH4 yield for both weeds but differently. The increase in the CH4 yield from co-digestion of the pretreated French weed was clearly greater than for the pretreated water lettuce. Pretreatment increased the CH4 yield obtained from co-digestion of French weed from 174 to 209 L/ kg chemical oxygen demand (COD) degraded. However, the yields of the untreated and pretreated water lettuce were comparable at 209 and 210 L/kg COD degraded, respectively. Thus, a recalcitrant weed such as French weed was worth pretreating prior to codigestion but not a spongy weed such as water lettuce.