Extraction of volatile fatty acids (VFAs) from water hyacinth using inexpensive contraptions, and the use of the VFAs as feed supplement in conventional biogas digesters with concomitant final disposal of water hyacinth as vermicompost

A procedure has been developed for extracting volatile fatty acids (VFAs) from water hyacinth (WH) using simple and inexpensive equipment of the type commonly available in the rural households of the third world countries. The VFAs thus extracted were used as feed supplement in cow dung-fed floating-dome biogas digesters. As tens of thousands of such digesters are in operation across the third world, the aim of these studies has been to provide for such digesters feed derived from phytomass, especially for use whenever animal dung is in short supply or is unavailable. The VFA extraction was based on aerobic/facultative degradation of water hyacinth and significant quantities were extracted from each WH charge daily for upto 6 days. When cow-dung slurry was fortified with the VFAs and fed to a conventional biogas digester, it yielded about 22% higher quantity of biogas per unit feed than was obtained from equivalent mass (dry weight basis) of the unfortified cow-dung slurry. The technique developed by us enables phytomass to be utilized as feed supplement in biogas digesters without causing the problems of solids accumulation, frothing and clogging known to be associated with phytomass feed. After VFAs have been extracted from it, the 'spent' water hyacinth Was vermicomposted and used as soil conditioner-cum-fertilizer. (c) 2005 Elsevier B.V. All rights reserved.