Mixture of Pistia stratiotes and cowdung (1:1) gave a biogas yield of 0.62 m3/(m3 day) (CH4 =76.8%, HRT=15 days) (Zennaki et al., 1998). Recently Sharma (2002) observed an increase of 40–80% in biogas production on addition of 1% onion storage waste (OSW) to cattle dung in a 400-1 floating drum biogas reactor.