The NHB SUHF™ and SUHB™designs use time proven technology for the pressurized bag retention vessel as well as in the agitation, mixing, aeration, and automation and control strategy. We have done extensive prototype testing to verify the oxygen mass transfer capabilities and mixing times as well as power input for the fermentor Rushton turbine impellers and the cell culture low shear pitched blade impellers:
1. Pressurizable BAG RETENTION VESSEL (brv)
The SUHF™ and SUHB™ Bag Retention Vessels (BRV) are uniquely designed to accommodate the operating pressure rating as well as provide support to the entire bag. This includes the use of support faceplates at all bag port openings. The BRV is fully equipped with HTS (heat transfer surface) for metabolic heat removal and includes a 1" fibreglass insulation with cover. The BRV is sized similar to the L/D for a vertical tank however going horizontal for an equivalent sized vertical fermentor, the SUHF™ and SUHB™ have approximately 65% more HTS available and about 75% higher free board surface area. Both have beneficial advantages in optimizing the processes.
The agitator impellers for both fermentation and bioreactors are based on identical geometry as can be found in conventional vertical systems. This approach provides a very close comparison for optimized performance when migrating from existing vertical systems to the new horizontal form factor. The Rushton turbine impeller has the traditional 20:5:4 ratio of diameter:blade width:blade height. In addition the impeller diameter is in accordance with most published "rules of thumb" again for consistancy thus mixing performance can be accurately predicted using well characterized formulae.
The low shear pitched blade cell culture impeller also uses the standard impeller diameter to tank diameter ratio of 0.5 ratio. The three large pitched blades closely replicates the numerous cell cultures used in operating systems around the globe. Rotation speed and tip speed are in the usual range currently deployed in production systems.
The importance of aeration and gas dispersion to achieve good oxygen mass transfer (OTR) cannot be understated. This is at the heart of the ability of microbial systems and to a lesser extent cell culture systems to provide the necessary respiration for active cell growth and metabolism. The SUHF™ sparge ring can deliver up to 1 VVM air and 1 VVM oxygen directly to the underside of the turbine impeller where it is then dispersed into the broth. A single or multiple orifices are drilled into the sparge ring and in the case of modular expansion, multiple sparge rings are connected in serial manner by in-bag tubing.
The SUHB™ sparge ring is equipped with multiple 20 micron micro spargers for a maximum flow of 0.1 VVM air and 0.1 VVM oxygen. These micro spargers provide small bubble size under the pitched blade impeller where they are mixed into the broth to achieve homogenous dispersion and maximize availability of oxygen for mass transfer into the cells.
It is important to consider that any increase in pressure inside the bag will improve OTR. Thus the 5 psig capability of the pressurized bag is an asset to optimizing microbial and to a lesser extent mammalian cell growth. A good rule of thumb is that every increase of 5 psig in operating pressure will increase the OTR by about 33%. Thus a bag operating at 5 psig will automatically outperform a non pressurized bag due to the increased driving force from pressure.