The nitrogen role in vegetables irrigated with treated municipal wastewater

The reuse of treated municipal wastewater for irrigation is an established alternative toconventional water, in many countries of the world, particularly where or when water resourcesare extremely limited. Wastewater reuse could represent a double benefit when used inagriculture, helping overcome any lack of water resources and additionally, enriching the soilwith nutrients - especially nitrogen and phosphorus.In the experimental site of Castellana Grotte (Apulia region, Southern Italy) during the 2012/13and 2013/14 growing seasons, vegetable crops (fennel and lettuce) in succession were dripirrigatedwith three different water sources. Two reclaimed water streams, obtained by applyingdifferent treatment schemes to the same municipal wastewater (an effluent from the full-scaletreatment plant and an effluent from the Integrated Fixed-film Activated Sludge – MembraneBioReactor pilot plant) and a conventional source, to verify the crops response and nutrientcontribution through wastewater supply.Both lettuce and fennel yields were enhanced by the high content of nutrients in the effluent ofone of the treatment plants, which had been operated for partial nitrogen removal. For Fennel2013/14, wastewater-reuse led to a 54% reduction of nitrogen supply in relation to the other plotsnormally fertilized. In this way, an estimated saving of about 98.00 € ha-1 was achieved.Crops irrigated with treated wastewater operated for partial nitrogen removal (IMBR) showedearly ripening (8 days for lettuce and 35 days for fennel 2013/14) and better quality than othersnot similarly-treated. However, the wastewater presented a nitrate content in excess of legal limits(35 mg L-1, D.M. 185/2003). Therefore, the contribution of nutrients increased production (47 vs32 t ha-1in IMBR and WELL 2012/13 fennel theses, 53 vs 31 t ha-1in IMBR and WELL 2013lettuce theses and 40 vs 31 t ha-1in IMBR and WELL 2013/14 fennel theses respectively) andimproved product quality, while simultaneously saving money for chemical fertilizers notsupplied, producing less environmental impact.