Effects of temperature and pretreatment conditions on mixed-acid fermentation of water hyacinths using a mixed culture of thermophilic microorganisms

The MixAlco (TM) process biologically converts biomass to carboxylate salts that may be chemically converted to a wide variety of chemicals and fuels. This study investigated the use of water hyacinths as a feedstock, comparing digestibility after each of four different pretreatments at two fermentation temperatures (40 and 55 degrees C). Water hyacinths were treated with excess lime (0.3 g Ca(OH)(2)/g dry biomass). Short-term treatment occurred for 1 and 2 h at 100 degrees C. Long-term treatment occurred for 4 and 6 weeks at 50 degrees C. Treated water hyacinths were fermented with marine microorganisms for 28 days and acid concentration (g/L), conversion (g volatile solids (VS) digested/g VS fed), and selectivity (g acid/g VS digested) were measured. All pretreatments out performed fresh feedstock fermentations. The 40 degrees C fermentations exhibited greater acid yields and selectivity than the 55 degrees C. The 1-h hot-lime pretreatment exhibited the best overall outcomes at approximately 250%, 200%, and 125% increases relative to the fresh water hyacinths in total acid, conversion, and selectivity, respectively. The results show that with a gentle 1-h hot-lime pretreatment, water hyacinths can be fermented to produce liquid fuels, thus creating an economic value to water hyacinths that are cleared from choked waterways. (C) 2010 Elsevier Ltd. All rights reserved.