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African Journal of Biotechnology Vol. 2 (8), pp. 233-236, August 2003 Available online at ISSN 1684–5315 © 2003 Academic Journals

Full Length Research Paper

Constructional features of a 15-litre home-made bioreactor for fed-batch fermentations

Biotechnology Centre, LadokeAkintola University of Technology, PMB 4000, Ogbomoso, Nigeria. 2 Advanced Physics Laboratory, Sheda Science and Technology Complex, Abuja, Nigeria.
Accepted 15 July 2003

A 15-litre bench-top multipurpose bioreactor was designed and constructed. The vessel is a glass type with a stainless flat headplate incorporating 9 access ports allowing for a variety of interchangeable probes and actuators. Thestirring speed ranges between 0 and 250 rpm, the aeration rate (0-2 l/m), the pH control loop uses HI 1131 probe, two 100 ml bottles of HCl and NaOH solutions and operates a close feedback system. The temperature control module is a close loop using a PT 100 RTD thermocouple and an auxiliary vessel containing a cooling solution. The aeration and feed flow rates are open loops. The systemincorporates attributes of a good bioreactor design as discussed by Naraendranathan (1998). Sterility is achieved by autoclaving different units of the system. This machine has been tested on an array of local standard fermentation processes. Key words: Fermentation, bioreactor, control, sensors, actuators. INTRODUCTION Bioreactors offer a possibility to provide an optimally controlled environment formicrobial fermentation processes, a condition required for optimal yield (Williams, 2002). With this, one can specifically alter the metabolic fluxes and divert the cell’s resources to more desirable pathways while inhibiting unwanted ones. For instance, by imposing a given temperature profile on the culture, one can selectively denature certain enzymes, thus prioritizing some metabolic routes overothers within the cell (Gueguim-Kana et al., 2002). Process control through bioreactor in submerged cultures is based on the measurement of physical, chemical and biochemical properties of the broth, such as pH, dissolved oxygen, temperature, agitation rate and others, using dedicated probes followed by the manipulation of the physicochemical properties of the culture with suitable actuators (Limand Lee, 1991). Some of the actuated parameters are: the agitation speed, the aeration rate, the heating intensity or cooling rate, and the nutrients feeding rate, acid or base valve. Precise environmental control is of considerable interest in fermentations since oscillations may lower the system efficiency (Yegneswaran et al., 1991), increase the plasmid instability (Namdev et al., 1993) andproduce undesirable end products (Diaz et al., 1996). Attributes of a good bioreactor design as discussed by Naraendranathan (1998) include: an economical, robust and simple mechanical design, an easy operation under aseptic conditions, a flexibility with respect to various process requirements, an absence of dead zones, giving good control to bulk flow, and a good heat and mass transfer. In this workwe have implemented the features above in a home-made bioreactor constructed from locally available materials.
MATERIALS AND METHODS Bioreactor vessel The bioreactor vessel is a Pyrex glass of size (ID 25 x HT 30 cm) with a stainless steel top plate of 20.5 cm diameter and 5 mm thickness. Various ports and standard nozzles (ID 10 mm) are provided on the stainless plate for actuators and probes.These include pH, thermocouple, and dissolved oxygen probes ports, defoaming, acid and base ports, inoculum port, pipe for sparging process air, agitator shaft and spare ports (Figure 1). A Teflon “O” ring secures the stainless top plate to the glass vessel; addition

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Afr. J. Biotechnol.

yielded the dynamic stability required,...
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