An automatically controlled alternate oxic-anoxic process for small municipal wastewater treatment plants

A patented automatic control device was applied to management of an alternate oxic-anoxic process in a small wastewater treatment plant (700 PE). The control system enabled the optimal time-length of the aerobic and anoxic phases to be determined by analyzing the dissolved oxygen and the oxidation-reduction potential data. Moreover, also a time set point was introduced to establish the maximum length for the two phases. Results showed high performances in biological nitrogen removal (0.7-5.2 mg of NO3-N L-1 in the effluent) and a reliable control of the treatment process also during wet weather events. In comparison with extended aeration plants of similar size, lower energetic consumption was observed, generally <200 Wh PE-1 day-1. The automatic control device was a reliable system that gave a good performance in a small wastewater treatment plant with low investment and managing costs.