Water Hyacinth as a Potential Source of Biofuel for Sustainable Development

Abstract

Water hyacinth (Eichhornia crassipes), a noxious weed and fast growing perennial aquatic plant found in lakes and ponds all over Guwahati is affecting the ecosystem in a deleterious manner. It tampers with aquatic life by deoxygenating the water and depleting nutrients for young fish in sheltered bays. It also blocks supply intakes for the hydroelectric plant, interrupting electrical power. Contrastingly, owing to high cellulose and hemicellulose content in its biomass and having a wide distribution in Assam, it was selected for our study. Therefore, using water hyacinth for bioethanol production can tackle the pollution problem owing to fossil fuel emissions and control its growing extent in water bodies. In the present research, water hyacinth was used for bioethanol production involving simultaneous hydrolysis and fermentation at shake flask and reactor level using different saccharifying enzymes and potential fermentative microbes. Candida shehatae, utilizing pentoses was used along with Saccharomyces cerevisiae in simultaneous saccharification and fermentation (SSF) experiments. The substrate was subjected to three pretreatments viz. wet oxidation, phosphoric acid–acetone treatment and ammonia fibre expansion (AFEX). Recombinant E. coli BL21 (DE3) and BL21 (plysS) cells harbouring expressing Glycoside hydrolase family 5 (GH5) and family 43 (GH43) genes from Clostridium thermocellum were employed for cellulase and hemicellulase production respectively. Trichoderma reesei cellulase and Bacillus subtilis AS3 producing thermostable cellulases were also engaged in saccharification process. The wet oxidation-treated water hyacinth conferred an ethanol titre of 0.90 g/L with B. subtilis cellulase and 1.26 g/L with T. reesei cellulase amid a fermentative microbial combination of S. cerevisiae and C. shehatae. A higher ethanol titre (1.69 g/L) was achieved with an enzymatic consortium of GH5 cellulase and GH43 hemicellulase along with S. cerevisiae and C. shehatae. Contrastingly, AFEX pretreatment yielded a maximum ethanol titre of 1.98 g/L with same enzymatic consortium and bioethanol producers. Consequently, on scaling up the SSF experiments with 5% (w/v) AFEX-pretreated substrate in shake flask and bioreactor along with S. cerevisiae and C. shehatae, an ethanol titre of 9.78 and 17.97 g/L were obtained respectively.