DESIGN OF EBB–AND–FLOW BIOREACTOR (EFBR) FOR IMMOBILIZED “HAIRY ROOT” CULTURES: PART I. PRELIMINARY DESIGN MODELS AND CULTURE PARAMETERS

Abstract

The ebb–and–flow bioreactor (EFBR) is characterized by the repetitive ebbing and flowing or periodic rising and falling of its liquid medium. An experimental 2.5–L bench–top EFBR prototype was fabricated for growing immobilized Hyoscyamus muticus “hairy root” cultures for the production of secondary metabolites. Ideal mathematical models were formulated for the EFBR’s gas–phase duration (.tG) and liquid–phase duration (.tL), the former based on the assumption that the limitation in sugar (nutrient) would precede the limitation in oxygen, and the latter based on the premise that the limitation in oxygen would precede the limitation in sugar. Plug flow was assumed for filling and draining. The following EFBR culture parameters, required by the mathematical models, were quantified experimentally or analytically: maximum root sugar consumption rate (SCRmax) = 0.00147 g sucrose/min–L, maximum root oxygen consumption rate (OCRmax) = 1.26 mg/min–L, average fresh weight to dry weight ratio (FW/DW) = 20 g/g, average root–entrained medium to fresh weight ratio (REM/FW) = 0.5 mL/g, and oxygen mass transfer coefficient in medium (kla) = 0.128/min. Using the EFBR mathematical models and these culture parameters, the calculated maximum gas–phase duration [(.tG)max] was 5.7 h, and the calculated maximum liquid–phase duration [(.tL)max] to avoid nutrient limitation was 6.0 min.