The synergistic effect of co-digesting water hyacinth (WH) with cow-dung (CD) for optimum biogas production was
evaluated. Different mix ratios of WH to CD were digested in a laboratory scale anaerobic digester over a retention
time of 40 days. The volume of biogas produced was determined using water displacement method. The ultimate
biogas yield and synergy factors for all the mixes were calculated. The third order polynomial curve for the different
mixes had a R2 value of 0.9834 which is quite significant. The curve also showed that the highest ultimate biogas yield
of 141.72 L was produced by 2 WH: 8 CD and impressively makes it the best CD-aided WH digestion mix. The highest
synergy factor of 1.31 was observed for 2 WH: 8 CD which collaborates the fact that the best mix of CD-aided WH
digestion in terms of biogas yield is 2 WH: 8 CD.