Self-sustainable azolla-biorefinery platform for valorization of biobased products with circular-cascading design

Abstract

As the circular bioeconomy is gaining momentum around the globe, biorefinery will play a key role in the framework of sustainability as integral component. A self-sustainable biorefinery model using azolla cultivation was designed at the focal point of a circular loop. This model is aimed to enable a cascading valorization of bio-based products through a series of sequentially integrated biological/thermal unit operations. Azolla pinnata with an inherent ability to sequester CO2 along with simultaneous nitrogen fixation capability will serves as a potential and renewable carbon resource (feedstock) for the integrated unit operations viz., acidogenesis, photosynthesis, hydrolysis, and pyrolysis. The cascading loop is initiated by acidogenesis of spent wash (distillery wastewater-DSW) in a semi pilot scale bioreactor for the production of biohydrogen and volatile fatty acids (VFA). Treated spent wash after acidogenesis (TSW) was used as feed for Azolla pinnata cultivation, which eventually depicted good COD and nitrates removal efficiency. Harvested A. pinnata biomass (AB) showed presence of good amount of carbohydrates (237 mg/g) and proteins (160 mg/g) along with 11% of lipids (composed of 22% omega fatty acids) thus making it a good nutritional feed for livestock. AB after lipid extraction was subjected to mild acid-hydrolysis and the hydrolysate was used as substrate for acidogenesis to facilitate circular/closed loop operation. The techno-economics of biorefinery process evaluated using SuperPro Designer software depicted the feasibility of the integrated strategy. This study extends the scope of biobased platform with self-sustainability as core objective.