Simultaneous computer control of pH in multiple environmental laboratory bioreactors

This paper describes the design, construction and operation of a computeriz ed pH control system for environmental laboratory reactors. Since pH is oft en a key environmental parameter in environmental process reactors, it is i mportant to have a dependable control system. The design criteria for this system were that it must accurately control pH in 16 different readers with the additional flexibility of allowing each reactor to be controlled and g raphed independently at any selected pH. Sampling intervals, mixing interva ls, pump-on time, feed volume injection and tightness of pH control (e.g., +/- 0.02 to 0.2) measurement were also possible for each reactor individual ly. The pH, pump-on time intervals and feed injection volumes were logged i nto a spreadsheet so that output graphs could be generated automatically fo r all 16 reactors for up to three years of operation. The supplies, model n umbers and costs of main components will be described as well as the detail ed instructions on how it was built. Examples are given of operating condit ions and output.