Innovative approaches for urban wastewater treatment: filtration, adsorption and algae photobioreactor

This work explores innovative approaches to wastewater treatment, focusing on solutions designed to address the environmental and infrastructural challenges posed by climate change, with reference to urban contexts. Two experimental systems were studied: microalgae photobioreactors, located at the San Cesario Sul Panaro wastewater treatment plant, specifically an RWP and a TGR, with the aim of evaluating the removal efficiency of nitrogen, phosphorus and microorganisms; and the TREAT CSO pilot plant, located near the overflow chamber of the Bologna treatment plant, which combines filtration and fixed-bed adsorption columns for the treatment of combined sewer overflows (CSO) to assess the removal of a wide range of pollutants, including heavy metals, solids, BOD, COD and nutrients. In the following work, the characteristics of wastewater and CSO were first described, with a brief insight into the most common types of photobioreactors for algae cultivation and also into the techniques currently applied to reduce the impacts generated by CSO. In addition, all the methods used to evaluate pollutants removal, and the operation of the two different systems were described. Photobioreactors showed high removal efficiency of macronutrients (nitrogen and phosphorus), with the closed photobioreactor (TGR) showing higher productivity than the open pond (RWP); however, microbiological removal remained low, suggesting the need for a further disinfection phase. In the TREAT CSO system, on the other hand, there was good removal of a wide range of pollutants, including heavy metals, solids, BOD, COD and nutrients. Overall, the results suggest that although both technologies are promising, further experimentation and integration between the systems may be needed to achieve optimal pollutant removal and scalability within a circular economy context.