Toluene removal in an automated cyclical bioreactor

A control scheme was developed for the automation of toluene removal in a c yclical bioreactor. Toluene was added to the self-cycling fermenter by diff usion across a silicone membrane. Transient dissolved oxygen, carbon dioxid e evolution, and oxidation-reduction potential (ORP) were screened as poten tial control variables. Through experimentation, ORP was deemed most effect ive. Control algorithms based on realtime estimates of the first and second derivatives of the ORP signal were tested. Although both approaches result ed in stable operation of the reactor, average toluene removal efficiencies of 95% were realized when control was based on the second derivative. This was significantly higher than the 77% efficiencies obtained when the contr ol scheme centered on the first derivative of the transient ORP signal. The system developed was self-regulating, ensuring that a high toluene removal rate, on the order of 1.1 g h(-1), was maintained from cycle to cycle.