Dilute nitric acid pretreatment of Ulva biomass for production of fermentable sugars and its validation using Design of Experiments (DoE)

Macroalgae have been commercially explored for their high-value metabolic intermediates. However, high carbohydrate content and absence of lignin have attracted scientific community to determine its sustainability as a land-independent biomass for microbial fermentation. The current work focuses on process development for pretreatment of Ulva biomass using Design of Experiments (DoE) to obtain sugar-rich stream. Three independent parameters were studied viz. biomass loading rate, catalyst concentration, and reaction time for DoE model prediction to understand their individual and interactive impact on saccharification. Maximum sugar extraction was observed at 8% biomass loading with 2% nitric acid concentration in 60 min at 121 °C. Total carbohydrate yield of 95.96% was obtained and the hydrolysate was used for lactic acid fermentation. The obtained stream was used as the sole carbon source for microbial production of lactic acid.

The predicted response values obtained were in line with the experimental values and the overall conclusion of DoE was found to be fit and statistically significant (P < 0.05). This work presents an efficient and scalable pretreatment process for maximum extraction of total carbohydrates from Ulva. The process provides a foreseen perspective to explore vast waterbodies for biomass as substrate for fermentation of important microbial intermediates.