Treated municipal wastewater as a sustainable water source for irrigation in Mediterranean countries: A case study in Apulia (Southern Italy).

In order to mitigate water stress in the Mediterranean area, treated municipal wastewater is among the most readily available alternative water resources. Apulia (Southern Italy) is one of the Mediterranean regions most heavily affected by water shortage, although its economy is strongly based on irrigated agriculture. Nevertheless in Apulia only 1% of treated wastewater potentially available for reuse in agriculture is presently used, mainly because of regulatory constraints and public acceptance. Within the EU funded project Water4Crops different types of treatment schemes are applied at the pilot scale to treat municipal wastewater and polish secondary effluents for reuse in irrigation. In the present study, results from test field experiments carried out at Castellana Grotte (Apulia) are presented. Three different crops (processing tomato, fennel and lettuce) were grown in succession on sandy loam soil and drip irrigated with three water sources: the effluent of the local full scale municipal wastewater treatment plant (WWTP), the effluent of a pilot scale non-conventional treatment technology, and a conventional source (well water). The full scale WWTP is composed of a conventional activated sludge process followed by sand filtration, coagulation-flocculation and chlorination (conventional tertiary treatment). The pilot plant is an integrated process scheme called IFAS/MBR (Integrated Fixed-film Activated Sludge/Membrane BioReactor) followed by UV disinfection. In order to evaluate the effects of higher ammonia and nitrate concentrations on crop yields and quality, the IFAS/MBR pilot plant was operated for partial nitrogen removal (mainly nitrification). Reclaimed water quality was monitored in terms of chemical and microbiological parameters and compared with conventional well water. Microbiological indicators were also measured at harvesting time in soil and on the edible parts of crops. Chemical analyses of soil and crops were also performed in order to assess possible variations across the different water sources adopted. Results showed that the pilot plant had better removal performance in terms of suspended solids and faecal indicators with respect to the full scale WWTP. The effluent of the full scale WWTP complied with the Italian standards for reuse in agriculture, except for chlorine and E. Coli, while the effluent of the pilot plant exceeded the limit values only in terms of ammonia and nitrate. As for the agronomic results, crop yields where significantly higher in plots irrigated with treated wastewater. In particular the higher content of nitrates in the pilot plants effluent strongly enhanced the lettuce yield. Microbiological indicators E.Coli and Salmonella were never detected in soil and edible parts at harvesting time.