Mixing degree effect in the photodegradation of olive mill wastewater

Abstract

Currently, in olive oil producing countries, wastewater from olive mills is collected in large evaporation ponds without any treatment. This overall situation presents an environmental problem due to their high organic load and the presence of toxic and inhibiting growth compounds. Photo-Fenton reaction can be used to degrade the pollutant compounds that present in OMWs. The degree of mixing inside the photoreactor is a key parameter to increase the photodegradation of organic matter. For this reason, experiments were performed in a semi-industrial batch stirred photo-reactor (10 L capacity). The agitation rates were varied in each experiment as follows 60, 150, 300, 400, and 500 rpm. The experimental results showed that the photoreaction has developed in two steps, an instantaneous reaction that takes place in the first five moments and a second reaction that is slower and lasts up to three hours. During the instantaneous reaction, the conversion based on total organic carbon (TOC) increases with the augment of agitation rate, however, during the second step the maximum conversion (XTOC = 0.9) is recorded at 300 rpm in the first 100 min. The common operating conditions were initial pH = 3, hydrogen peroxide equal to that determined by the stoichiometry of the reaction, oxidant/catalyst ratio = 0.03, temperature = 20 °C and four artificial ultraviolet lamps to provide sufficient ultraviolet irradiation. The final treated water could be used in irrigation.