Microwave-assisted pretreatment of harmful algal blooms for microbial oil-centered biorefinery approach

Utilization of harmful algal blooms (HABs) for the cultivation of oleaginous microorganisms can provide dual benefits of mitigating the toxicity from the aquatic reservoirs and generation of copious media for biodiesel production. In the present investigation, microwave-assisted dilute alkali-freeze pretreatment was optimized to develop a low-cost growth medium from HAB dried biomass. The electron micrographs along with the elemental analysis confirmed the efficient breakage of HABs after the microwave-assisted hydrolysis treatment as compared with the acid hydrolysis. Moreover, the sugar analysis revealed similar to 46% higher carbohydrate content in microwave-assisted hydrolysate as compared with acid hydrolysate. The microwave-assisted hydrolysate and conventional dilute acid hydrolysate were then used to cultivate microalga (Chlorella minutissima) and yeast (Trichosporon cutaneum) for biomass and lipid accumulation and compared to artificial media. Microalga showed similar to 1.3- and 2-fold higher dry cell weight (DCW) and lipid content, respectively, while the yeast growth increased by similar to 27% with lipid content of 30%. The fatty acid profiles and biodiesel properties were also amenable to the international biodiesel standards. Hence, the present study provides a proof-of-concept of utilizing HAB hydrolysate for culturing oleaginous microorganisms for potential biodiesel production.

Automated summary

The present study optimized the microwave-assisted dilute alkali-freeze pretreatment to develop a low-cost growth medium from harmful algal blooms (HABs) dried biomass. The efficient breakage of HABs and higher carbohydrate content were confirmed in the microwave-assisted hydrolysate. Microalga and yeast cultivated in the hydrolysate showed increased biomass and lipid content, with fatty acid profiles and biodiesel properties meeting international standards. This study provides a proof-of-concept for utilizing HAB hydrolysate to culture oleaginous microorganisms for biodiesel production.