Immobilized oleaginous microalgae as effective two-phase purify unit for biogas and anaerobic digester effluent coupling with lipid production

Oleaginous microalga Scenedesmus sp. was immobilized in alginate-gel beads and applied as two-phase purify unit for biogas and anaerobic digester effluent from palm oil mill. Optimal microalgal cell concentration and bead volume ratio were 10(6) cells mL(-1) and 25% v/v, respectively. The use of 20% effluent and light intensity at 128 mu mol.proton.m(-2) s(-1) most promoted CO2 removal by immobilized microalgae and achieved the maximum CO2 removal rate of 4.63 kg-CO2 day(-1) m(-3). This process upgraded methane content in biogas (> 95%) and completely remove nitrogen and phosphorus in the effluent. After process operation, 2.98 g L-1 microalgal biomass with 35.92% lipid content were recovered by simple sieving method. Microalgal lipids are composed of C16-C18 (> 98%) with prospect high cetane number and short ignition delay time. This study has shown the promising biorefinery concept which is effective not only in CO2 fixation, biogas upgrading and pollutant removal but also cost-effective production of microalgae-based biofuel.