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 11.6-19.3 g volatile solids (VS) l(-1) d(-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 7.92 mmol g(-1) VS digested, and biogas with a yield of 0.2 l g(-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 15.4 g VS. l(-1) d(-1). Varying the retention times between 60 and 120 h had no effect on the degradation efficiency, but a decrease was observed at retention times below 60 h. The overall performance of the reactor was depressed by changing the dilution rate from 0.5 to 0.34 h(-1). By applying a LR of 15.4 VS. l(-1) d(-1), a SRT of 90 h and a dilution rate of 0.5 h(-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 0.44 l g(-1) VS digested.