Kinetics of anaerobic digestion of water hyacinth using primary sludge as inoculum

Water hyacinth (Eichhornia crassipes) is one of the fastest growing aquatic weed known to man. They are free-floating perennial aquatic plants with broad, thick, glossy, ovate leaves with long, spongy and bulbous stalks. The feathery, freely hanging roots are purple-black. In India, water hyacinth is largely found in the Kerala Backwaters. But, this natural beauty can be quite deceiving. It chokes waterways, blocks sunlight from reaching native aquatic plants, starves the water of oxygen, killing fish (or turtles) and is a habitat for disease causing vectors. Attempts to curb its fast spread have proved to be futile. However this deleterious weed is a potential source of biomass to produce biogas, which is an eco-friendly biofuel. In this study, primary sludge, obtained from sewage treatment plant was used as inoculum at mesophilic conditions. A series of laboratory experiments using 0.25l bio-digesters were performed in batch operation mode and modified Gompertz equation was fitted. The kinetic parameters, biogas yield potential (P), the maximum biogas production rate (R_m) and the duration of lag phase (λ) were estimated in each case. The results show that Primary Sludge Inoculum (PSI) improved biogas yield significantly and nearly two times when compared to water hyacinth substrate without PSI.