Algae show promise for removing nutrients like phosphorus and nitrogen from wastewater due to their natural absorption abilities. However, the widespread use of algae-based wastewater treatment is limited by challenges related to system footprint, mass transfer and maintaining optimal conditions for algae growth.
By re-orienting an algal biofilm vertically onto a conveyor belt, Gross-Wen Technologies’ (GWT; Slater, Iowa; www.algae.com) Revolving Algal Biofilm (RAB) system (photo) overcomes these hurdles with its unique design that maximizes algae surface area and optimizes the gas-liquid interface. “One of the largest engineering obstacles with algae systems is how to effectively deliver CO2 to the algae and get oxygen out of the system. One way to do that is to create more surface area, making gas exchange more rapid and no longer a limiting factor to productivity,” says Martin Gross, CEO and co-founder of GWT.
RAB Systems (Source: GWT)
Algae growth rates can also pose issues in water-treatment systems, especially in obtaining the right configuration of light, water and CO2. “Most algae systems involve microscopic cells floating in a liquid, and you need to get light into the depths of the liquid, and it’s quite difficult. In our system, we bring the algae out of the liquid and have more surface area to receive the light, so we more effectively deliver light and CO2 to the algae by creating this extended surface area vertically,” adds Gross.
The vertical setup also uses equipment footprint more efficiently than conventional horizontally oriented algae systems. And, the ability to easily scrape the nutrient-enriched algae off the films creates a salable product in the form of a solid biomass that can be used as a fertilizer.
To date, the largest application of the RAB system is located at a facility treating food waste in Pasco, Wash. The 4-million-gal/d system treats water coming out of anaerobic digesters for eventual discharge. GWT also recently announced a new patent, in collaboration with the Metropolitan Water Reclamation District of Greater Chicago, for the application of RAB technology for enhanced removal of total dissolved solids (TDS) from wastewater.