Abstract
Wastewater from the olive oil industry is an environmental problem which is growing in the Mediterranean region. Presence of phenolic compounds and high organic matter load are characteristics of this effluent that make it difficult to treat. In this study, the applicability of sulfate radical based advanced oxidation processes (SRbAOPs), using peroxymonosulfate (PMS) as oxidant, was evaluated in the treatment of synthetic olive mill wastewater (OMW). Different procedures for PMS activation were studied such as activation by Fe(II), radiation (visible and UV-A) and ultrasounds. The operation conditions were optimized by testing pH values, Fe(II) and PMS loads. At optimal conditions ([PMS] = 1600 mg/L, [Fe2+] = 700 mg/L and pH = 5) 60 ± 2% COD removal was achieved. This process shows to be selective since complete degradation of 3,4,5-trimetoxybenzoic acid was obtained after 3 min of reaction. The addition of light, PMS/LED/Fe(II) and PMS/UV-A/Fe(II), did not increase the efficiency of organic matter removal, with 56 ± 2% and 58 ± 1% of COD removal, respectively, comparatively to PMS/Fe(II) (60 ± 2%). PMS activated by ultrasounds led to 52 ± 3% and 23 ± 2% removal of phenolic compounds and COD, respectively, after 60 min. Toxicity tests using Lepidium sativum showed that treatment with PMS/UV-A led to a treated sample with mild inhibition of plant growth.
Highlights
Over the last 20 years, olive oil production and consumption has been constantly growing with the olive oil industry being one of the largest in the world [1,2]
In this study different techniques for peroxymonosulfate (PMS) activation were evaluated, first by one electron transfer using Fe(II) as transition metal catalyst and secondly by homolytic cleavage of the peroxide bond of HSO5− by photolysis and sonolysis [16,18]. These techniques for PMS activation were assessed for the treatment of a synthetic olive mill wastewater, composed by a mixture of different phenolic compounds
The results showed that the optimal conditions for PMS activation by Fe(II) are 1600 mg/L of PMS, 700 mg/L of Fe(II) at pH 5
Summary
Over the last 20 years, olive oil production and consumption has been constantly growing with the olive oil industry being one of the largest in the world [1,2]. It should be noted that the Mediterranean region alone produces 97 % of worldwide olive oil, while other European Union (EU) countries produce 80–84% [3] This region is responsible for environmental problems due to the large production of liquid and solid wastes resultant from that industry, namely olive mill wastewater (OMW) and olive pomace (OP). OMW are complex effluents due to their high variability associated with different olive cultivation and processing practices, but overall OMW present acid pH (~5) and high chemical oxygen demand (30–318 g/L). These streams are toxic mainly due to the high content of phenolic compounds (0.5–24 g/L). The conventional treatment processes usually based in biological systems are generally not very efficient for such type of wastewater
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