(35c) Ultrasound-Assisted Dewatering System for Microalgae Dewatering and Harvesting

Algal biomass is a promising sustainable source of biofuels and bio-based products due to its rapid growth, carbon sequestration abilities, and high-value biochemical content. However, the high-water content of algal suspensions poses a significant challenge for cost-effective dewatering, which remains an energy-intensive and often inefficient step. Conventional dewatering processes typically rely on thermal, mechanical, or chemical methods, including high energy requirements, risk of thermal degradation, and added costs. This study investigates the potential of ultrasound-assisted misting as an innovative, energy efficient dewatering technique to enhance water removal from algal suspensions. The aim is to demonstrate the feasibility of ultrasonic dewatering to achieve high-concentration algal suspensions without extensive chemical or thermal inputs.

The dewatering apparatus consists of a single 2.4 MHz piezoelectric transducer mounted at the base of a separation chamber. Upon activation, the transducer generates ultrasonic waves that create an upward-directed mist stream from an algae suspension. This mist is entrained in a nitrogen gas stream introduced at the chamber inlet and directed toward a mist collector, where it condenses and is removed from the system. Initial algae concentrations of 0.5 g/L are progressively enriched over eight ultrasonic misting stages, with each successive test starting from the concentration achieved in the preceding stage. With a single transducer prototype, results indicate that we can concentrate algae from an initial concentration of 0.5 g/L to 16 g/L over the eight-stage operation, achieving an enrichment ratio of 1.2-1.6 per stage using single transducer.

A predictive model was developed to estimate the number of stages required for achieving targeted concentration of algae in the suspension, and the model was validated against experimental data. Our findings suggest that the required number of misting stages can be precisely predicted by incorporating misting efficiency and target moisture content, providing a valuable tool for scaling up the dewatering process.

This study advances ultrasonic-assisted misting as a feasible method for algal dewatering, with the potential to significantly reduce energy costs in biofuel production and other algal bioproducts. The validated model for staging, combined with insights into time and airflow impacts, offers a promising framework for industrial applications where efficient, scalable, and energy-effective dewatering is critical.