(404f) Comparison between Multi-Stage and Single Stage Microalgaedewatering Processes

The depletion of fossil fuel resources, increase in crude oil prices and the proved evident that the earth’s climate is going through global warming as a result of the continuous emissions of greenhouse gases (GHGs) to the atmosphere has resulted in the search for an alternative third-generation fuel. Bio-fuels such as biogas, biodiesel, and bioethanol produced from biological processes are considered promising alternatives to fossil fuels. Bio-fuels have different advantages over fossil fuels such as low toxicity, high biodegradability, low net CO₂ production, are renewable and sustainable, and contains less or no sulfur. Biofuels can be produced from anaerobic digesters, biological materials (sugar, corn, vegetable oils .. etc), and bio-wastes. However, due to the high pre-treatment and operational cost of these processes and the competition with the human food chain, the search for new bio-sources has been a major research endeavor globally. Microalgae which has a rapid growth rate, high lipid and carbohydrate contents and limited competition with food crops is considered as an attractive feedstock for biofuel production. In addition, microalgae have a great potential for carbon capture wastewater treatment and bio-sequestration. Although a significant amount of research work has been reported on improving the production of microalgae using different bio-reactors and pond systems, research work that focuses on establishing simple, effective and low-cost downstream dewatering operations is limited. The high cost associated with dewatering large-volumes of microalgae cultures has been the primary hindrance to the development of industrial-scale microalgae biofuels. Thus, The present work focus on improving the separation and dewatering of microalgae after cultivation period in a cost-effective and simple way. The study investigates the conditioning and dewatering of microalgae using single and multiple conditioning stages, determine the optimum conditioner doses, and determine the effect of operational conditions on dewatering performance. Multi-stage conditioning process using ferric chloride and polymer resulted in better settling and algae dewatering when compared to the single stage conditioning using polymer or ferric chloride. The amount of conditioner used in multi-stage conditioning processes was less than the doses required for single stage process. The optimum conditioner doses obtained for a small volume of algae solution was slightly different from optimum doses obtained for higher volumes due to differences in mixing requirements. Ferric chloride was found to be better conditioner for the studied microalgae. The presented method could be useful in monitoring and optimize the polymer concentration and minimize the excessive use of polymers.