Microfiltration cell‐recycle pilot system for continuous thermoanaerobic production of exo‐β‐amylase

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Abstract
A microfiltration cell‐recycle pilot‐scale system was developed comprised of a conventional continuous‐flow fermentor connected to an in situ steam‐sterilizable cross‐flow ceramic filter with a backflushing device. A microcomputer was used to control filtration pressure, tangential flow velocity, and backflushing. Performance of the system was tested with the anaerobic production of thermostable extracellular β‐amylase at 60°C by Clostridium thermosulfurogenes on maltose or malto‐dextrin media. Filtration rates during continuous cultivation were between 20 and 60 L/m2/h. The maltodextrin and cell debris occurring at high retentate flow rates or filtration pressures impaired the performance of the filter. Backflushing initially improved the permeate flux to 42% in a maltose medium and to 10% in a maltodextrin medium, but the effect diminished with time. The productivity of β‐amylase (as much as 48 U/mL/h) and concentration of biomass (as much as 14 g/L) were increased 11‐ and 12‐fold, respectively, if compared to values obtained in a chemostat. The concentration of β‐amylase rose to 220 U/mL in the reactor, which was 5.5‐fold more than under comparable conditions in a chemostat.