Towards an integrated microalgal biorefinery

This research explores the valorisation of a proprietary microalgal strain (ALG01, provided by AlgaeCytes Ltd.) as a renewable, biobased feedstock into chemicals, materials and (bio)energy within the context of a zero-waste biorefinery. Four main areas of research are reported, namely: i. the preliminary characterisation of ALG01; ii. the isolation, purification, and characterisation of water-based microalgal proteins; iii. the tandem production of defibrillated celluloses and protein isolation from hydrolysates via acid-free hydrothermal microwave processing and their subsequent characterisation and, iv. The production and characterisation of bio-oils and bio-chars via microwave pyrolysis processing.
Water-soluble proteins were isolated successfully using ultrafiltration with up to 5% yield (weight of extracted protein-containing fraction/ initial weight of biomass) and 70% purity (percentage of protein of the overall protein-containing fraction) for the spent biomass protein retentates obtained at 180oC microwave processing.
A range of defibrillated cellulose were successfully produced using acid-free hydrothermal processing with materials processed at 200oC and 220oC forming hydrogels. Confocal Laser Microscopy using Carbotrace 480, a fluorescent optotracer, shed more light on the spatial distribution of cellulose in the samples with cellulose congregating in lumps of small grains. Clear links have been established between the capability of forming hydrogels and the amount of cellulose present in the samples, with higher amounts of cellulose present resulting in better hydrogel formation capability. Two publications have resulted from the work on defibrillated celluloses.
The residual biomass left after protein extraction was subsequently valorised through microwave pyrolysis, yielding bio-chars, which achieved energy densification of up to 37% for spray dried biomass derived chars, and a 65% higher HHV (higher heating value) for spent biomass derived chars. The bio-oils mostly consisted of saturated fatty acids such as myristic, palmitic and stearic acid.
Overall, this research has resulted in significant new knowledge in the development of microalgal zero-waste biorefineries.