Doctor of Philosophy (PhD)
The engineering of floating media biofilters has been optimized over the years. The backwashing process has made them more energy and water efficient. Likewise, moving bed bioreactors (MBBR) are gaining interest and popularity because they are relatively affordable to build. Yet, developing countries’ aquaculture production remains largely excluded from the advances made in recirculating aquaculture systems (RAS). This discrepancy is partially driven by the high costs of media such plastic beads and Kaldnes (KMT) media, commonly used in MBBR.
This dissertation evaluates the usability and profitability of rice hulls (RH), an abundant by-product in many developing nations, as a sinking biocarrier in a 3-phase filter system for low loading applications. The hulls have a shape, structure, and specific surface area of 1850 m2/m3,comparable to synthetic plastic “EN” beads used in PolyGeyser® tank filters. Yet, their production cost is negligible.
A lab experiment compared the TAN removal capacities of RH and EN media in a 3-phase reactor configuration, in ultra-oligotrophic, oligotrophic, and lower mesotrophic conditions. The RH displayed a volumetric TAN conversion rate (VTR) of 1025 g-N/m3, and the EN displayed a VTR of 1219 g-N/m3, proving RH to be a viable biocarrier. RH partially degraded after 18 days in the reactor, and were evacuated as sludge. Because of their small size and sinking properties, the RH also lack the clarifying abilities of other media such as EN of Kaldnes (KMT) media.
A commercial-scale recirculating aquaculture system (RAS) with a RH bioreactor (RHBR) was designed for tilapia fingerling production, based on a conservative RH VTR of 700gN/m3. A cost analysis showed that ownership costs for a facility using this RAS were $0.11/lb. for fingerlings in the U.S. or Europe, and $0.06/lb. for a fingerling facility in a developing country with abundant availability of fish and rice. Operation, maintenance, and storage associated with media replacement are the major drivers of costs. A comparative analysis showed that while an RHBR is not significantly profitable in most western countries, it shows promising potential in rice-producing developing countries, allowing them to opt for a more affordable integration of modern biofiltration in their aquaculture industries.
Greensword, Marlon A., "Rice Hull Bioreactor for Recirculating Aquaculture" (2017). LSU Doctoral Dissertations. 4101.
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