Novel technique for degradation of silver thiosulfate present in wastewater of the post- harvest treatment of ethylene-sensitive flowers

Abstract

Silver thiosulfate (STS) used in the post-harvest treatment of ethylene sensitive flowers is a potent producer of environmental damage because the silver cation (Ag+) remains in the soil and groundwater for long periods and can migrate to drinking water systems and cause health problems in humans. This study presents a novel treatment of wastewater contaminated with STS that includes three steps: i) oxidation of STS by bacteria isolated from sulfur springs of the Ecuadorian highlands which were added to artificial wastewater or wastewater containing STS from floriculture. The results indicate that approximately 60% of thiosulfate is oxidized to sulfate and 10% is absorbed by the bacteria at acidic pH, ii) biosorption of silver cation with fungi pellets of Cladosporium cladosporioides fungi. The adsorption tests show that the maximum adsorption capacity was 16 mg/g pellet using pellets prepared with fungi of 11 days of growth at pH 6, iii) regeneration of fungi pellets using 4N nitric acid solutions. With this acidic regenerant, it was recovered 69% of silver accumulated within the fungi pellets and the adsorption capacity of the regenerated fungi decreased to 15.4 mg Ag+/g in the second adsorption cycle.