One of the major problems in microalgae biodiesel production is the separation of microalgae biomass from water. Base on several life cycle assessments, the separation process involved high energy input and causing negative energy balance in producing microalgae biodiesel. In the present study, microalgae were immobilized/entrapped in gel beads and allowed to grow. Since the gel beads are denser than water, they can be easily collected through filtration, hence, simplifying the overall separation process. Various parameters were investigated to optimize the growth of immobilized microalgae and the optimum conditions were identified as follow: alginate to microalgae volume ratio of 0.3, Ca2+ concentration of 2 %, organic nutrients concentration of 50 mL (equivalent to 13.09 mg/L nitrate), initial culture pH of 4 and photoperiod of 24 h. 0.50 mg biomass/bead was attained on day-10 through this optimum culture conditions. Apart from that, a strategy to co-immobilize nutrients into microalgae beads was studied to minimize free cells culture (cells that released to water due to beads rupture) and to reduce water consumption. Through this strategy, it was found that microalgae biomass yield increased to 0.67 mg/bead in a shorter culturing time (5 days culture) with insignificant amount of free cells culture detected.
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