Generation of biofuel from anaerobic digestion of Scenedesmus obliquus grown in energetic-laden industrial wastewater: Understanding microalgae strains, co-digestants, and digestate toxicity

Microalgae as a substrate for anaerobic digestion (AD) offer promising outcomes over other conventional feedstocks. In this work, the generation of biofuel in the form of biogas via AD using wastewater-grown microalgae was investigated. In particular, batch screening of different microalga strains and co-substrates, culminated into the evaluation of biomethane potential (BMP) from AD of Scenedesmus obliquus grown in energetic-laden wastewater through benchtop-scale semi-continuous reactor. Effectiveness of AD was evaluated for biogas yield, volatile solids (VS) removal, and kinetics for various microalga strains as potential substrate candidates. High carbon content co-digestants were also investigated including return activated sludge and waste office pulped paper. At semi-continuous scale, the specific BMPs associated with of 15, 20, and 30 days hydraulic residence times (HRT) were determined as 67.0, 86.6, and 86.3 ml CH₄/g VS (added) with average methane content of 70%. In addition, toxicological assessments showed that AD effluent was benign towards renew growth of biomass, thus showing the potential for nutrients recover.