Ecotoxicological risk assessment as a decision tool for the valorisation of winery wastewater treatment byproducts to agricultural purposes

Abstract

A simple and economical process consisting in the precipitation with slaked lime (Ca(OH)2) was applied to winery wastewater. The process not only removed organic matter and other contaminants but also simultaneously captured atmospheric CO2. In order to help the wine industry to advance to the objective of circular economy, treatment byproducts (supernatant and sludge) have been reused for agricultural purposes due to their physicochemical properties compatible with these applications. In addition to an exhaustive study of the physicochemical characteristics, the ecotoxicological impact of these by-products were also evaluated through the bioindicators: Thmanocephalus platyurus (mortality bioassay after 24h), Vibrio fisheri (luminescence inhibition after 30 min) and Pseudokirchneriella subcapitata (growth inhibition after 72h).Raw winery wastewater showed high toxicity to all bioindicators, being classified as class 4 (Toxic Unit (TU); classification proposed by Personne, 1999). According values of TU of 20% for T. platyurus (24h), 9.17% for V. fisheri (30 min ) and 100% for P. subcapitata (72h) were found. After treatment (treated WW), the toxicity significantly dropped to class 2, with values of TU of 1.34% for T. platyurus (24h), 2.92% for V. fisheri (30 min) and 3.97% for P. subcapitata (72h).After the immediate one-step lime precipitation process (treated WW), the supernatant was diluted 1:4 (v/v) with groundwater (GW) to generate the so-called effluent nutrient solution (WWNS) which did not present any type of toxicity to the bioindicators used.Accordingly, an assay was carried out to the production of red pak choi, using three different conditions: irrigation with groundwater (control); pH soil correction with organomineral fertilizer and groundwater irrigation; and irrigation with wastewater nutrient solution (WWNS). After the assay none of the soils showed any type of indirect ecotoxicity.The pigment of the red pak choi cultivar produced in this study was evaluated through the analysis of chlorophyll a, chlorophyll b and carotenoids, showing the benefits to the healthy development of the plant.