Flexibility Analysis of Activated Sludge Systems

Wastewater treatment system flexibility represents system capacity of ensuring required effluent standards for different operational conditions. Flexibility analysis can be considered an useful tool to foresee system performance corresponding to influent load increase or admissible effluent standards reduction. It is based on the evaluation of suitable indexes related to system performance, which can be calculated by means of process simulation models. In the paper is presented a system flexibility analysis referred to activated-sludge systems aimed at ammonia and biodegradable organic substrates removal from wastewater. A coupled design model of biological and settling phases is proposed, considering both suspended and dissolved substrates to attain, in explicit terms, the volume of the oxidation basin and the surface of the sedimentation tank, having assigned influent and effluent wastewater characteristics. The procedure for evaluating system flexibility, based on the same coupled model, is presented too.