Production of biogas from water hyacinth (Eichhornia crassipes) (Mart) (Solms) in a two-stage bioreactor

A two-stage rumen-derived anaerobic digestion process was tested for the conversion of water hyacinth shoots and a mixture of the shoots with cowdung (7:3) into biogas. Under conditions similar to those of the rumen and loading rates (LR) in the range of 11.6–19.3g volatile solids (VS) l–1d–1 in the rumen reactor, the degradation efficiencies were 38% for the shoots and 43% for the mixture. The major fermentation products were volatile fatty acids (VFA) with a maximum yield of 7.92mmolg–1 VS digested, and biogas with a yield of 0.2lg–1 VS digested. The effect of varying LR, solid retention time (SRT) and dilution rates on the extent of degradation of the water hyacinth–cowdung mixture was examined. Overall conversion of the substrate was highest at the loading rate of 15.4gVS.l–1d–1. Varying the retention times between 60 and 120h had no effect on the degradation efficiency, but a decrease was observed at retention times below 60h. The overall performance of the reactor was depressed by changing the dilution rate from 0.5 to 0.34h–1. By applying a LR of 15.4VS. l–1d–1, a SRT of 90h and a dilution rate of 0.5h–1 in the rumen reactor, and connecting it to a methanogenic reactor of the upflow anaerobic sludge blanket type, 100% conversion efficiency of the VFA into biogas with a methane content of 80% was achieved. The average methane gas yield was 0.44lg–1 VS digested.