Operation parameters optimization of a hybrid dead-end/cross-flow forward osmosis system for microalgae dewatering by response surface methodology

Abstract

The high energy consumption of the microalgae dewatering process results in microalgae being less economically feasible as a new bioenergy material. As an energy-saving method, forward osmosis (FO) filtration can be applied in microalgae dewatering to reduce membrane fouling and energy consumption. In this study, a novel hybrid dead-end/cross-flow FO system was proposed to obtain highly efficient microalgae dewatering. The effects of agitation speed, draw solution concentration, and pH on microalgae and membrane flux reduction volume concentration factors were investigated using Box-Behnken design (BBD) of response surface methodology (three factors and three levels). The results demonstrated that the higher the draw solution concentration and agitation speed, the higher the volume concentration factors. When the draw solution concentration and agitation speed reached their maximums (5M and 500r, respectively), the maximum volume concentration factor was obtained (3.73). pH exhibited the greatest influence on flux reduction. The flux reduction decreased more with an increase in pH (pH>7). When the pH was neutral or acidic, the influence of pH on flux was insignificant. This study provided a more efficient method for dewatering and reduced energy consumption by applying a BBD to optimize the operation parameters of a novel hybrid dead-end/cross-flow FO system for microalgae dewatering.