Improved process control with a pHauxostat for application in biotechnology

The pHauxostat is a unique control technique which was proposed nearly half a century ago but has found limited use up to date. This study highlights the results whereby the pHauxostat was analysed, categorized and a theory developed. pHauxostats can be categorised into Category A or B pHauxostats and further sub-divided into A1 or A2 and B1 or B2. The pHauxostat is successfully modelled by using alkalinity as a parameter whereby an alkalinity yield coefficient is defined. This alkalinity yield coefficient can be determined by applying half reactions, and together with traditional biological growth models the process can be described theoretically. This enables the applications of the technique in a predictable and controlled way with the possibility of wider use. The technique can be described as a self-regulating control technique in biotechnology whereby the pH is used as the controlled output variable and the feed (rate and/or concentration) the manipulated input variable.