Toxicity and pollutant impact analysis into urban river due to CSO overflows

Navile Channel (Bologna, Italy) is artificial, derives from the Reno river, and receives water also from the urban catchment and from the WWTP main outlet. Discharges usually range from few cubic meters per second, especially during dry periods in summer times, up to several cubic meters per second during wet weather. The WWTP outflow increases the Navile Channel’s flow by up to 1800 liters per second, during dry weather period. During storms the urban catchment contributes mainly through CSOs, whose harmful effect was object of previous studies (Artina et al., 2004a). To collect flow and water quality data in both dry and wet weather conditions, on the Navile Channel two measuring and sampling stations were set, upstream and downstream the WWTP main outlet. The study shows that CSOs activate even with slight events, spilling a huge amount of pollutants into the Navile Channel, with concentrations of orders of magnitude higher than in dry weather flow, showing also an acute toxicity behavior.