Integration approach of microalgae cultivation with biomethanation derived wastewater as nutrient source for sustainable bioethanol production.

Anaerobic digestate wastewater (ADW), a nutrient-rich byproduct of anaerobic digestion, offers a sustainable medium for microalgae cultivation, reducing eutrophication risks from direct disposal. This study developed a dilution-based cultivation strategy using ADW as a nutrient source to generate microalgal biomass for bioethanol production. Among the tested dilutions, 2 % ADW exhibited highest biomass productivity of 73.50 ± 0.07 mg L-1 d-1 at lab scale while, scale-up cultivation (200 L) with 2 % ADW achieved84.58 ± 1.77 mg L-1 d-1. Nutrient removal efficiencies of 97.16 ± 0.47 % ammonia, 80.20 ± 0.57 % nitrate, 73.80 ± 0.95 % phosphate, and 75.28 ± 3.15 % COD were observed. The harvested biomass contained 47.57 ± 1.04 % carbohydrate, 20.15 ± 1.05 % lipid, and 22.69 ± 0.23 % protein. Acid pretreatment released 141.24 ± 2.33 mg g-1 reducing sugars, producing 65.80 ± 0.25 mg g-1 bioethanol after 24 h. Overall, the study demonstrates an integrated, eco-friendly approach for nutrient recovery and bioethanol generation from ADW. The work highlights the dual benefit of wastewater valorization and renewable biofuel production.