In the Mekong Delta of Vietnam many household biogas digesters become temporarily limited on pig manure (PM) which constitutes the main substrate. Abundantly available waste biomasses such as rice straw and water hyacinth have not been thoroughly investigated as a supplementary feedstock for small household digesters to secure a more steady production of biogas. In the present study anaerobic co-digestion of PM with water hyacinth (WH) were evaluated in 21 L batch digesters loaded with mixtures of PM/WH in a 1:1 ratio as based on VS at a total loading of 1 g VS/L. Additional experiments were conducted investigating the effect of different types of environmentally friendly pretreatments of WH on biogas production. Our study demonstrates that anaerobic co-
digestion of WH with PM could enhance biogas production by 26.5 to 44.2 %, respectively as compared to control reactors digesting pure pig manure during 60 days of digestion. The use of simple pretreatment methods such as soaking the WH biomass in suspensions mud river sediment or digester effluent also enhanced biogas production from WH as compared to pretreatment in tap or river water.