In this article a simple feedback controller approach for the regulation of Cr(VI) from electrochemical mixed-flow reactors in series is presented. The control approach is based on simple step response models obtained experimentally during the operation of three electrochemical continuous reactors in series. Based on simple first-order model and first-order model plus input delay to account for dead times induced by the measurement of the Cr(VI) two controllers are derived. The proposed controllers are composed of two parts: an uncertainty observer to compensate uncertainties and neglected terms in the input-output models and an inverse dynamics feedback controller. Numerical simulations show good closed-loop performance and robustness properties.