Treated wastewater irrigation: how to manage water salinity without reducing its nutrients content?

Abstract

Context and purpose of the study ‐ Nutrients in municipal treated wastewater (N, P, K, mainly) are a particular advantage in this source over conventional irrigation water sources, so supplemental fertilizers would sometimes not be necessary. However, additional environmental and health requirements are taken into account for this source of irrigation water. Most treated wastewaters are not very saline. Salinity levels usually ranging between 500 and 2000 mg/L (ECw = 0.7 to 3.0 dS/m). However, there may be instances where the salinity concentration exceeds the 2000 mg/L. Anyway, appropriate water management practices should be followed to prevent soil salinization, regardless of the salt content of the treated wastewater and plant sensibility. The ability of soil to self–cleanse in each rain event decreases the salinity supplied with treated wastewater, but this will depend on the balance between supply‐water and rain‐water. The aims of this study were to assess the effect of fertigation with municipal treated wastewater, on the soil‐plant‐fruit‐ wine system and the need, in some cases, to control salinity thresholds (Na + and Cl‐ ions) of irrigation water by membrane technology.

Material and methods ‐ Two experimental vineyards of Viognier B and Carignan N. were monitored for growing seasons 2017 and 2018. Two different water sources were compared: drinking water (DW) and municipal treated wastewater (TWW) at two irrigation levels by drip irrigation system. Vegetative growth was monitored once a week. Berry fresh weight and juice composition (primary metabolites) were determined at harvest. Soil sampling was carried out at postharvest for analytical determinations. Given that, in the event of low rainfall, excess sodium and chloride resulting from irrigation with TWW are not leached from the soil. This paper looks at the process membrane technology, most adapted by which salt levels in irrigation water can be reduced.

Results ‐ TWW played a substantial role in the shoot growth and the variation of irrigation level caused significant difference compared to the irrigation with DW. Moreover, yeast assimilable nitrogen was higher in grapes from vines irrigated with TWW. Wine sensorial quality was mainly influenced by irrigation levels. Results showed a higher Na 2O content in soils that have received TWW. Success in using TWW for crop production will largely depend on adopting appropriate strategies aimed at optimizing crop yields and quality, maintaining soil productivity and safeguarding the environment. Electrodialysis, from homogeneous membranes technologies does not filter the water, but extracts a quantity controllable in line of dissolved salts (Na+ and Cl‐ in particular selectable) under the effect of an electric field, in order to adapt to the soil or crop concerned. In the context of vineyard sustainability and an eco‐responsible approach, electrodialysis can be seen as an agricultural water treatment technology reliable and fit for purpose.