RICE HULL BIOFILTER DESIGN: LAB AND COMMERCIAL SCALE RESULTS

Rice hulls have been explored for use as a biofriendly and economical biofilter media.  Lab scale studies suggest they are not significantly different from EN (plastic) media in their ability to host bacteria in biofilters at levels of total ammonia nitrogen (TAN) from 3-6ppm.  Two factors are critical in differentiating this media and engineering has been done to adapt to the media.  First, their density is different from that of the EN plastic media, so reactors must be designed to accommodate their density.  Second, they do biodegrade slowly over time and small pieces can break off and must be removed to reduce BOD.  Hence, both solids reduction techniques and correct flow design in biofilters are necessary.

Rice hulls are available in many developing countries, so use of rice hulls as media in biofilters could be advantageous and economically viable in these areas.  A separate project focused on the economics of this  technology and possible low cost applications for more sustainable aquaculture.

Removal rates ranged from 70-84% in laboratory studies up to 6 ppm.  A commercial scale vortex reactor was designed and built using rice hulls as biomedia.  This reactor worked up to 60ppm TAN, but design improvements were required to keep the biomedia moving with an airlift driven vortex.  

A technique was used to remove about 10% of biodegraded biomedia every 2 weeks and an economic analysis suggests this media may be useful in developing countries where capital costs must be minimized but labor costs may remain low, allowing an economic use of this biobased system.This may especially benefit developing countries to use this more affordable technique for biofiltration in their aquaculture industries.