Date of Award

12-2011

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Biological Engineering

Advisor

G. Peter van Walsum

Second Committee Member

M. Clayton Wheeler

Third Committee Member

Adriaan R.P van Heiningen

Abstract

Biomass is a renewable resource which can be used for energy production as a substitute for fossil fuels. Conversion of terrestrial lignocellulosic biomass in to ethanol is the widely known conventional process to produce liquid biofuel. However the conversion of marine macro algae to biofuel draws attention at present. Use of marine biomass sources have some advantages over terrestrial lignocellulosic biomass such as less competition for land and fresh water resources, no interference with food crops, little or no lignin content, and high growth rates. The conversion of biomass to carboxylic acids via mixed culture acidogenic digestion offers many advantages over conventional sterile fermentation process such as: no need for sterilization, no need of genetically modified organisms, low capital cost, and ability to produce longer chain carboxylic acids. The produced carboxylic acids can be chemically up graded in to value added chemicals or mixed alcohol biofuel. In this study a seaweed-derived biomass source was biologically converted into a mixture of carboxylic acids using a mixed culture of microorganisms. Algefiber® was the biomass used; it is a waste biomass from seaweed processing (FMC Biopolymer, Rockland, ME). It is an alkaline treated industrial waste which has higher ash content than conventional terrestrial lignocellulosic biomass sources. Despite its high ash content, acidogenic fermentation of Algefiber® carried out under conditions of inhibited methanogenesis produced carboxylic acids ranging from one to seven carbons (Formic acid to Heptanoic acid). Fermentations were carried out at two temperatures, 35°C and 55°C. Acetic acid was the prominent acid produced at both temperatures, though mesophilic temperature (35°C) gave higher carboxylic acid yield and a higher percentage of longer chain acids. A combination of Algefiber® and chicken manure gave the highest acid concentration of 18 g/L at 15 % solid concentration. Carboxylate salts of the fermentation-derived acids were thermally decomposed in to mixture ketones which had acetone, 3-pentanone, 2-hexanone, 3-heptanone, 2-heptanone, and 4-octanone as major products. These ketones can be hydrogenated to form the longer chain mixed alcohols which contain higher energy density than ethanol due to presence of longer chain alcohols such as propanol, butanol etc.

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