Optimization of dissolved air flotation technique in harvesting microalgae from treated wastewater without flocculants addition

Abstract

Harvesting is a crucial step in biofuel production from microalgae. The expense of harvesting operation is estimated to be 20%–30% of the total biofuels production cost. Dissolved air flotation (DAF) is a well known technology for separating solid particles from liquid streams such as wastewater. This technology has been introduced for microalgae harvesting in the past few years. However, the high operating cost has been a hurdle to commercialization of this technology for microalgae dewatering. High power consumption for air compression and high cost of chemical coagulants are two main cost items. In this study, the DAF process was optimized without the use of chemical coagulants. It was found that saturator could be running at the low pressure of 3 atm to reduce the power consumption to 0.0025 kW h/m3 that was a reasonable value compared to similar DAF units that used chemical coagulants. Statistical analysis revealed that concentration of algal solution was the most significant factor to gain maximum removal efficiency. In this study, high concentration of algal solution along with low flow rates of air-saturated water contributed to the unprecedented removal efficiency of 91% without flocculation.