Concentration and Dewatering of Micro-algae Cultures with High Throughput Ceramic Membranes

Significant capital and operational cost reductions are required for algal energy to become widespread. The cost of harvesting algae from 0.1–0.5 wt.% in cultures to 20-30 wt. % concentrates is a critical driver for initial capital, energy and resource costs of algal fuel and products. Energy-efficient and scalable harvesting technologies must be developed for the algal industry to thrive. Cross-flow filtration and vacuum filtering using unique ThinSieveTM membranes recently developed at Molecule Works Inc. are proposed to harvest algae in two process steps. The cross-flow filtration concentrates an algal culture into thick slurry of 2- 5 wt.% solid. Then, the concentrate is dewatered on a vacuum filter into wet cakes of 20-30 wt. % solids. The membranes are the critical component that determines cost and efficiency of the membrane processes. Molecule Works’s ThinSieveTM membranes comprise a 50 micro-meter -thin porous metal sheet with ceramic coatings. The uniform and small-size pores on the membrane surface exclude algal cells and allow 100% algal harvesting. Since no strange chemicals or materials are used in the membrane process, almost all (>99%) the water and soluble in original cultures can be recycled. Thinness of the ThinSieveTM membrane provides exceptionally high flux compared to the other membrane materials of similar pore sizes and enables fabrication of membrane modules with high packing density (>1000 m2/m3). The ceramic/metallic material is biocidal and resistant to bio-fouling and bonding by biological cells, which are rich in algal cultures. The ThinSieveTM membrane can be cleaned and reused for long-term operation. The high flux, high membrane packing density, and reusability of the ThinSieveTM membrane makes it possible to reduce energy consumption and capital cost by 30% relative to DOE’s base case. In Phase I, the ThinSieveTM membrane structures will be optimized to achieve the proposed performance targets for the concentration and de-watering of a few different algal species. Effective membrane cleaning methods will be developed to obtain stable filtering performances through periodic cleaning/regeneration. A cross-flow module prototype of 1-m2 membrane area will be assembled to demonstrate the feasibility of building high throughput membrane modules. The process design and economic analysis will be conducted to show the pathways of achieving >30% cost reduction goal.