Abstract

A comparative study of the effect of different pre-treatment methods on the biogas yield from Water Hyacinth (WH) was carried out. The WH  charged into metallic prototype digesters of 121 L capacity were pre-treated as: dried and chopped alone (WH-A), dried and treated with KOH (WH-T), dried and combined with cow dung (WH-C), while the fresh water Hyacinth (WH-F) served as control. They were all subjected to anaerobic digestion to produce biogas for a 32 day retention period within a mesophilic temperature range of 25 to 36^°C. The results of the study showed highest cumulative biogas yield from the WH-C with yield of 356.3 L/Total mass of slurry (TMS) while the WH-T had the shortest onset of gas flammability of 6 days. The mean biogas yield of the fresh Water Hyacinth (WH-F) was 8.48 ± 3.77 L/TMS. When the water Hyacinth was dried and chopped alone (WH-A), dried and treated with KOH (50% w/v) (WH-T) and dried and combined with cow dung (WH-C), the mean biogas yield increased to 9.75 ± 3.40 L/TMS, 9.51 ± 5.01 L/TMS and 11.88 ± L/TMS respectively. Flammable biogas was produced by the WH-F from the 10^th day of the digestion period whereas the WH-A, WH-T and WH-C commenced flammable gas production from the 9^th, 6^th and 11^th day respectively. Gas analysis from WH-F shows Methane (65.0%), CO₂ (34.94%). WH- A contained Methane (60.0%), CO₂ (39.94%). WH-T contained Methane (71.0%), CO₂ (28.94%), while WH-C had Methane (64.0%) CO₂ (35.94%). The other gases were found in the same levels and in trace amounts in all the systems. The overall results showed that treating water Hyacinth with chemical did not have a significant improvement on the biogas yield. It also indicated that water Hyacinth is a very good biogas producer and the yield can be improved by drying and combining it with Cow dung.

Key words: Water hyacinth, biogas production, pre-treatment, biogas yield, flammable biogas production, biodigester.