Algal Biomass as a Binding Agent for the Densification of Miscanthus

Purpose Lignocellulosic biomass has been regarded as an important future energy source due to its excessive availability; however, the wide application of this material for many applications is restricted by the high costs associated with densification, transportation, thermo-chemical pretreatment and conversion. In order to increase the density of lignocellulosic biomass, it is typically compressed into pellets or briquettes. This frequently requires the addition of additives, which may negatively impact the economics of the process. Environmentally-friendly binding agents that can be obtained inexpensively are therefore desirable. This study examines the change in physicochemical properties of densified Miscanthus straw where algae were used as a binding agent. Methods The algae (Rhizoclonium spp.) was obtained as a waste product from a local algal-based wastewater treatment system, dried and then added as a fine powder to milled Miscanthus. The material was then compressed into discs using a mounting press, which were then assessed for calorific value, compressive strength and sugar content. Results We found that the algae-Miscanthus discs with blends of up to 30 % algae had similar calorific values compared to Miscanthus alone (17.4 MJ kg(-1)), with significantly reduced calorific values at higher blends. Furthermore, Miscanthus discs mixed with algae had significantly greater compressive strength at blends at or above 20 % algae content compared to pellets made from 100 % Miscanthus (39 N). The strength of the discs was directly proportional to the percentage of algae in the mixture, with a maximum strength of 189 N for blends with 90 % algae. The glucose content of blends below 30 % was not statistically different than 100 % Miscanthus. Conclusion These data provide support for the use of algae as a binding agent for biomass destined for bioenergy and bioproduct processes, and highlight an additional end use for algal biomass.