Seasonal aspects relating to the use of macroalgae as a biofuel

Abstract

To assess their suitability as a biofuel feedstock, principally for methane production from anaerobic digestion, this thesis investigates seasonal changes in biochemical composition of nine UK macroalgae; Ascophyllum nodosum, Fucus serratus, F. vesiculosis, Laminaria digitata, L. hyperborea, Mastocarpus stellatus, Palmaria palmata, Porphyra umbilicalis and Ulva lactuca. These represent three major phyla; Chlorophyta, Ochrophyta and Rhodophyta. This is the first analysis of seasonal biochemical changes in lypholized mass, fatty acid methyl esters (FAME), protein, soluble saccharides and anaerobic digestibility for the majority of the species listed. Biomass was sampled monthly over two years. Methods for analysing large sample sets were developed which reduced chemical usage and waste production. Statistical analysis was by ANOVA and the post-hoc Tukey method. There were differences (P<0.01) between species and overall mean lypholized weight ranged from 28.5 to 14.4 % and recovered FAME 3.32 to 0.70 %, protein 22.0 to 13.4 % and soluble saccharides 44.2 to 1.2 %. Within species, there were significant effects of year, season and month of collection. For anaerobic digestion, methane gas production varied between -1 species from 1.00 to 0.02 L g (P<0.01) and the percentage methane from 40.8 to 24.9 % (P<0.01). Macroalgae collected in winter and spring produced higher percentage methane (P < 0.05). Regression with subsets and principal component analysis of lypholized mass, fatty acid methyl esters (FAME), protein, soluble saccharides did not provide robust predictive models and other additional factors must influence methane gas production. Buffering was not required and stable anaerobic digestion was achieved in saline conditions of 35 ‰ with a pH of 7.0 to 7.6. Fucus serratus and F. vesiculosis suppressed the activity of the methanogenic biota compared to the control and the biochemical mechanisms employed by these species to achieve this merit further investigation. Laminaria digitata, L. hyperborea, Palmaria palmata and Porphyra umbilicalis show potential to be used as biofuel and large-scale biomass trials are recommended.