Quality of municipal wastewater compared to surface waters of the river and artificial canal network in different areas of the Eastern Po Valley (Italy)

The aim of this study was to analyse the macro (Ca, Mg, K, Na, P, S and Si) and micro (Al, B, Ba, Co, Cr, Cu, Fe, Li, Mn, Mo, Ni, Sr, V and Zn) elements in the wastewater effluents of five treatment plants situated in towns located in the eastern Po Valley (Italy). Two of the plants (Imola and Castenaso) discharge wastewater into rivers (Santerno and Idice rivers, respectively in the Reno basin) while the other three (Codigoro, Copparo and Tresigallo) empty into a complex network of artificial canals (Burana–Po di Volano basin). The wastewater pollution hazard on surface water bodies was studied and the wastewater suitability for irrigation was assessed by comparing the physicochemical and microbiological characteristics with the water quality of artificial canals used for irrigation purposes. From November 2006 till July 2007, samples of surface water and wastewater were collected monthly in 21 georeferenced sites. The metal constituents were determined by Inductive Coupled Plasma Optical Emission Spectrometry. The data were analysed using cluster analysis (CA). The results of CA showed that wastewater characteristics depend on the plants’ potentiality, their efficiency and type of waste. The CA carried out on fresh water showed that the water characteristics of the sampling point of the Reno basins were different with respect to the Burana–Po di Volano basin. CA was also used to differentiate studied sites between the two basins and within the same basin to distinguish the different pollution sources. The geolithological and environmental matrices together with anthropogenic activities lead to a greater variety in the composition of surface water as compared to wastewater, due to the controlled conditions imposed during treatment processes. The results show a good suitability of wastewater for irrigation uses, especially in comparison to the water drawn from the drainage network of the Burana–Po di Volano basin. The levels of Escherichia coli found in the wastewater preclude its use for irrigation purposes. In fact, Italian law (Legislative Decree 152/2006) establishes values of E. coli that are too low for the reclamation and reuse of wastewater in agricultural areas. The levels detected both in wastewater and fresh water exceeded this legal value, even if the E. coli levels found in wastewater are actually lower than those detected in surface water bodies and artificial canals (420–946 CFU/100 mL of E. coli in treatment plants vs. 2246 CFU/100 mL in artificial canals and 15,729 CFU/100 mL in river water). Significantly, the analysis of samples upstream and downstream of the plants showed that wastewater has no impact on the level of metal constituents in the surface water bodies.