How should we implement quaternary treatments in Wastewater Treatment Plants? A techno-economic analysis

Micropollutants are a class of compunds found at trace level in the environment . They are released by several sources, but the wastewater treatment plant represent one of the biggest. In fact, they are not designed to remove micropollutants. Currently, the revision of the Urban Wastewater Treatment Directive (UWWTD) addresses the problem of micropollutants (MPs) released by wastewater treatment plants (WWTP): a specific set of pharmaceuticals and cosmetics are required to be removed with a minimun efficiency of 80%. Among the best available technologies suggested and largely studied there are adsorption and ozonation. These technologies are widely known for drinking water, but they are scarcely applied in WWTP. Moreover, these technologies can be implemented with different configurations, but there are no indications on the design and type of implementation in the revision of the UWWTD. Furthermore, in the future the directive could be modified to include more MPs in the set of the targeted MPs, such as PFAS. With this study we propose an approach to evaluate the costs associated with quaternary treatments, depnding on several factors. A model was developed in WEST (DHI A/S) to predict the removal of ozonation and activated carbon, and evaluate the best configuration for the selected wastewater, evaluating costs when specific target removal are set. Not only the 80% removal will be used as target, but also the removal that allows to guarantee a negligible risk in the effluent. CAPEX and OPEX costs will be analyzed and the result will be compared between the different configurations considered, in order to identify the best solution. In particular, adsorption will be considered both as Powdered Activated Carbon (PAC) with recirculation and as Granular Activated Carbon (GAC) in columns. Pore diffusion and surface diffusion are included in the model and competition with the organic matter is considered, using the simplified Ideal Adsorbed Solution Theory (IAST) model. Different combinations of filtration, GAC/PAC, ozonation and clariflocculation are compared in this study. This study provides an useful approach and tool to allow water utilities identifying best quaternary solutions for their own WWTP, based on influent characteristics, WWTP layout, target removal, and costs.