Cumulative biogas production was maximum for water hyacinth grown in 20% pulp and paper mill ef-fluent, followed by water hyacinth grown in 20% dis-tillery effluent, water hyacinth grown in 40% pulp and paper mill effluent and water hyacinth grown in 40% distillery effluent and minimum for water hyacinth grown in unpolluted water (Table 2). Initially the biogas production was slow, increased up to 12 days of incu-bation and then reduced gradually. Rate of biogas production was highest during the 9–12 days period in all the treatments (Table 3).
Cumulative biogas production by channel grass was similar to that of water hyacinth (Table 4). However, the rate of biogas production was maximum during 6–9 days of incubation for all the treatments. After-ward, biogas production rate decreased gradually (Table 5).
Relatively greater biogas production from channel grass (29900 cc/kg dry weight) was recorded in comparison of that from water hyacinth (23650 cc/kg dry weight). The biogas production from water hyacinth was enhanced maximum (53.57%) when it was grown in 20% pulp and paper mill effluent and minimum (21.10%) in 40% distillery effluent, whilst the corresponding en-hancements in biogas production by channel grass were 30.85% and 6.13%, respectively after 21 days of slurry incubation (Table 6).