Microalgae derived biomass and bioenergy production enhancement through biogas purification and wastewater treatment

Microalgae were grown in 12-L airlift photobioreactors (PBR) containing biodigested swine manure (BSM), cattle manure (BCM) and domestic sewage (BDS), with 5% v/v, 25% v/v and 30% v/v respectively and compared with synthetic medium CHU. BSM with biogas/air mixture (10% CO2) injection on the 8th day led to of 13,257 ± 430 × 104 cell mL−1, and 2.0 ± 0.16 g L−1 dry biomass with a 26% lipid content, which was approximately 70% higher than with air. After microalgae purification, biogas at the PBR outlet averaged 91% v/v CH4. In terms of bioenergy: i) the biogas lower heating value (LHV) increased from 22,554 to 33,294 kJ m−3 (47.6%) with BSM, and similarly with BCM and BDS; ii) lipid content was increased, and iii) biohydrogen production is expected to increase from the PBR. For wastewater bioremediation, the microalgae Tetradesmus obliquus were able to remove 99.3% of ammonia and 99.2% of phosphorus concentration from BSM. There was a 96% BOD (628 mg L−1 to 23.3 mg L−1) and 91% COD reduction (1262 mg L−1 to 132 mg L−1). There was a 70% increase in biomass production and up to 4-fold lipid content increase with the procedure in comparison to air injection.