Zobi® based processes for ultra-low energy algal harvesting and dewatering

Technical Report · Mon Apr 15 00:00:00 EDT 2019

OSTI ID:1509781

Hazlebeck, David; Rickman, William

The cost of harvesting and dewatering is a major driver for capital and energy costs of algal fuel and other algal products. Algae grown in open ponds and photobioreactors are dilute, 0.01 to 0.2%. A concentrated algae slurry, 20-30%, is needed for processing algae to produce oil and protein meal. Multiple harvesting and dewatering steps are typically required to concentrate the algae from the ponds to the level needed for processing. The current DOE baseline harvesting and dewatering approach of dissolved air floatation (DAF) with centrifuges has both high energy use, ~1.4 kWh/m3, and high capital costs, ~$152,000/million gallons per day (MGD). In commercial algae operations, all attempts to utilize DAF for algae harvesting have failed, and centrifuges typically only achieve 25% to 30% of the rated throughput used in the DOE baseline models. Furthermore, DAF requires expensive chemical addition, centrifuges damage algae cells, and neither achieves 100% capture efficiency, so the portion of the algae and other microbiota are returned to the ponds reduces the cultivation stability and lowers the productivity. The goal of this project is to develop a low cost, low energy, universal, set of integrated unit operations to concentrate algae from pond or photobioreactor concentration to 20-30% solids. The Zobi harvester®, developed and commercialized by Global Algae Innovations (Global Algae) and TSD Management Associates (TSD) provides a great start toward meeting this goal. A commercial installation of a Zobi system is pictured in Fig. 1. The Zobi® is a membrane- based harvest system attains an outlet algae concentration of 15-18%. The Zobi® system is a major breakthrough in harvesting that overcomes all of the technical issues DAF and centrifuge approach with a similar capital cost and 3% of the energy use. The technical advantages of the Zobi® are: (i) achieves 100% capture efficiency, (ii) is universally applicable to any microalgae, (iii) does not require any flocculants or additives, and (iv) is scalable to 100’s of millions of gallons per day (MGD). This project builds on the success of the Zobi harvester to extend the capabilities so that the overall project goal is achieved. The specific goals are to maintain the four technical advantages listed above while achieving: (i) 20-30% outlet concentration (ii) 30% reduction in capital cost relative to the baseline (iii) 90% reduction in energy demand relative to baseline In the Phase I effort, the objectives were to develop and obtain harvesting data on five different approaches and use the data to demonstrate the potential for an integrated harvest and dewatering system to achieve the specific project goals listed above while maintaining the advantages of the Zobi harvester®. The five approaches tested were: Modified Zobi® operational parameters Zobi® harvesting with filter press dewatering Zobi® harvesting with a crossflow filter Zobi® harvesting with a novel unit operation Replacing the Zobi harvesting with combination of settling and a Zobi harvester® in any of the other four approaches All of the Phase 1 objectives were achieved. The key performance parameters were used in a techno-economic model to calculate the capital cost and energy use. The Phase I results are summarized in Table 1. All five of the approaches tested met the Phase I targets for outlet concentration, energy-use, capture efficiency, and scalability. Three of the approaches met all of the performance targets and showed promise in meeting the capital cost target. Of these three, a Zobi harvester® integrated with a crossflow filter was selected as the best approach for Phase II research and development develop a new integrated harvest system to concentrate an algae slurry from cultivation pond concentration to over 25% solids with 100% removal of the algae and microbiota, an energy use of less than 0.14 kwh/m3 and a capital cost of less than $106,000 per million gallons per day of capacity.

• Research Organization: Global Algae Innovations
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: SC0018804
• OSTI ID: 1509781
• Type / Phase: SBIR (Phase I)
• Report Number(s): DOE-GAI-1804
• Country of Publication: United States
• Language: English