EVALUATION OF RICE HULLS AS A BIOCARRIER FOR A THREE PHASE BIOREACTOR
Rice hulls have a shape and structure comparable to the floating synthetic plastic beads used in PolyGeyser® tank filters. Their oblong shape facilitates biofilm protection, given that rice hulls have a larger surface area on which bacteria can grow. In addition, because they are largely composed of silica, they undergo very little decay. Rice hulls constitute a versatile media that could be used with a 3-phase reactor (air, water, and rice hulls). They sink, but have a low bulk density. Thus, it allows for aeration with less air volume (cfm), which eventually translates into less horsepower and energy costs. This project measures the nitrification capacity of rice hulls in and a RAS in comparison to similarly shaped "enhanced nitrification or EN" floating media.
However, potential disadvantages of using rice hulls include the paucity of prior data. The limits of their durability must be investigated. They eventually become part of sludge when they decay, and therefore travel down to the filters claifier chamber where they are evacuated as biodegradable sludge.
In a preliminary study, the ammonia daily removal rate was 80%. The EN reactor, however, had a daily ammonia removal rate of 76%, which implies that they might be more removal-efficient than EN beads. Nevertheless, for nitrogen removal, results were not valid. Acclimation did not begin until the last day of monitoring for the rice hull reactor. Therefore, results are quite weak. The removal rate was calculated to be 36%. The EN, however have a daily removal rate of 82%. The preliminary experiment did not extend over a long enough period of time for results to be conclusive. Nevertheless, the increase in removal once acclimation was achieved allows us to expect a considerably higher nitrogen removal rate with rice hulls. Future research should also consider the trophic level of the water. Preliminary results suggest that rice hulls are most appropriate for mesotrophic environments (usually associated with fingerling biofilters) where TAN/nitrite concentrations ranges from 0.3 mg-N/m3 to 0.5 g-N/m3. For statistical analysis, a hypothesis to be verified is formulated, that is, rice hulls can be cost effective compared to EN media for 3 phase reactors. Secondly, the statistical analysis will help determine the organic removal rate for BOD5 reduction in, as well as the nitrogen reduction capacity VTR (g of nitrogen per m3 rice hull per day). The findings would quantify the removal of ammonia and nitrite and explore the feasibility of substitution, especially to the benefit of developing nations that may opt for a more affordable integration of modern biofiltration in their aquaculture industries.