Hydrodynamic cavitation mediated Spirulina valorisation with insights into phycocyanin extraction and biogas production

Commercial phycocyanin extraction is energy-intensive and lacks scalability. Alternatively, this study reports the systematic investigation of hydrodynamic cavitation for intensified phycocyanin extraction from Spirulina. Additionally, biomethane potential of the residual biomass, obtained after phycocyanin extraction was also investigated. The biomethane generation rate decreased with an increasing number of passes while the biomethane potential remained unaffected. To reliably compare phycocyanin extraction across systems, dimensionless normalised yields were defined. A normalised phycocyanin yield of 4.3 (52 mg phycocyanin g^-1) at an inlet pressure of 150 kPa and 90 passes was identified (optimum cavitation). Lowest specific energy input (0.06kWh kg^-1) was calculated for processing 100 g L^-1 Spirulina, which is one to two orders of magnitude lower than current state-of-the-art. Furthermore, a net energy gain of 600-2497kWh kg^-1 obtained from biomethane generation showcased a viable Spirulina biorefinery, intensified via hydrodynamic cavitation. This work provides a route for phycocyanin extraction with significantly reduced energy input and potential for wider bioproduct extraction and biorefining from a range of biomasses via hydrodynamic cavitation.