Traditional vs. CellFerm Pro STBR Design and Capability
Traditional bench-scale STBRs are generally operated analogous to production-scale vessels, meaning independently (Figure 1). Control actions for each reactor are determined via a programmable logic controller (PLC) executing simple PID algorithms.
Ancillary equipment integration, or the development of a supervisory control and data acquisition system (SCADA) for multiple SBTRs, frequently requires custom third party hardware and software. Without a SCADA program, data from parallel cultures can only be compared after manual compilation.
In contrast, the CellFerm Pro STBR system, from Dasgip (Jlich, Germany), was designed specifically for parallel operation (Figure 2). The CellFerm Pro system uses a Windows XP-based SCADA program. This program allows simultaneous set-up, calibration, operation, and shut down of up to eight STBRs. Due to the presence of a personal computer, advanced control schemes are possible.
For example, the program can calculate oxygen uptake rate (OUR) using predicted influent gas composition and culture volume and dissolved oxygen (DO). Feed profiles or OUR-based feeding can be performed. Process events, such as pH or DO values or trends, can trigger control actions, such as feeds with variable time delay.
The SCADA program also simplifies data analysis. Data from all reactors are plotted in real time. It is also possible to export spreadsheets containing all online information, including process variables, set points, control parameters, calibration data, and process events.
Finally, batches are executed via guided work flows, and most procedures have step-by-step instructions, which can significantly reduce the learning curve for inexperienced operators or those unfamiliar with process controls terminology.
The hardware capabilities of a CellFerm Pro and traditional STBR system are similar. Pressurized reference gel pH, polarographic DO, and platinum RTD temperature probes are used. Thermal mass flow controllers are used for air, O2, CO2, and N2 addition. Per vessel agitation and temperature control is possible. Liquid addition is achieved via peristaltic pumps.
However, the CellFerm Pro system is distinguished by allowing up to four, precisely controlled, continuously variable peristaltic pumps per vessel, as opposed to traditional STBRs, which generally use fixed speed, on/off, peristaltic pumps. Precise pump estimates are used to estimate culture volume for OUR calculations and to prevent vessel overflow.
Finally, the CellFerm Pro is distinguished from traditional STBR systems in terms of size and cost. A traditional 3-L bioreactor system, using jacked vessels equipped with stainless steel headplates and mechanically coupled impellers, can cost three to four times as much, and require two to three times the bench space, per vessel, compared to a CellFerm Pro system equipped with 1-L magnetically coupled paddle agitated spinners, when installation costs and ancillary equipment are considered.