Scenario analysis as decision support for the potential restoration of the heavily modified water bodies in Lombardy. Case study : Lambro, Seveso and Olona rivers

Pollution of surface waters and the level of degradation of the water quality is a major concern since polluted water bodies can pose a threat for human health and aquatic organisms, and reduce the well being of people since the gains attained from a water body as a resource also will be affected negatively. Therefore it is a vital issue to find the best promise for the restoration of these highly polluted water bodies. The aim of this study is to contribute decision making process by evaluating different scenario analysis for the restoration activities of a heavily modified water body in Lombardy region –a case study; Lambro, Seveso, Olona system. A two dimensional stream water quality model, QUAL2K, was used in order to make the scenario analysis. In the context of the study two scenario analysis have been done which are called ‘PTUA’ and ‘MBR’. The first scenario includes the upgrade of current WWTPs to better the removal of nutrients and some inorganic solids and, the latter includes installment of MBRs as an advanced wastewater treatment method. The results indicate that the MBR installment gives better results on the abatement of the pollutants, namely BOD, COD, ammonium, nitrate nitrogen and total phosphorus; on the other hand, the upgrade of WWTPs also satisfies the threshold values in most of the river length but at a lower extend. The following economic analysis regarding the costs of two different restoration activities revealed that the MBR installments cost more than the upgrade costs of the WWTPs. The final decision should be made taking into account that the concerned river system is a HMWB, and therefore ‘good ecological potential’ instead of ‘good ecological status’ should be achieved according to WFD in order to avoid disproportionate costs of the restoration activities.