Abstract
This study was aimed at making progress on the valorisation of table olive wastewater that currently represent a big environmental problem for factories. Concentrates from vacuum evaporation of the wastewater generated during processing of black ripe olives treated with KOH were tested as fertilisers of tomato plants in open field assays for three consecutive crops. Fertilisation was performed by drip irrigation every 15 days; the first treatment being 15 days after transplanting, and a total of five fertilisation treatments were carried out. A phytotoxic effect was not observed on plants or fruit in any case but higher yield (fruit/plant and g/plant) was obtained in comparison to irrigation with only tap water. Moreover, the combined use of the olive concentrate with inorganic nitrogen supply (NH4NO3), in order to comply with the nutrient needs of plants, was also tested. The results demonstrated that the olive concentrates could be a good substitute for inorganic potassium (as KNO3) during the cultivation of tomato plants without any negative effect on the tomato quality (pH, °Brix, sugars, organic acids) or content of bioactive substances (phenolic compounds and carotenoids).
Highlights
Several salt-free streams from table olive processing did not show a phytotoxic effect on Mediterranean plants cultivated under greenhouse conditions such as tomatoes, cucumbers, peppers and strawberries (De los Santos et al, 2019, 2020)
These concentrates were obtained from the spent KOH and washing solutions of black ripe olive processing, so the pH of the mixtures before vacuum evaporation was very high (>11 units) but was dropped down to 5.2–5.8 units with HNO3 before application to the tomato plants
The results obtained in the present study disclosed that the irrigation of tomato plants in open field assays with black olive wastewater concentrates did not give rise to toxic symptoms in both fruit and plant
Summary
That are gaining momentum in research devoted to olive waste management (Valenti et al, 2020). In this context, the use of solid and liquid olive waste for agricultural purposes has been evaluated in recent years, for waste from the olive oil extraction process (Vagelas et al, 2009; Vella et al, 2016; Elkacmi and Bennajah, 2019; Quasem, 2020). The substitution of NaOH with KOH during the debittering stage of Spanish-style green olives has been recently investigated with the aim of applying the spent alkaline solutions for tomato plant growth (García-Serrano et al, 2019, 2020b)
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