Effects of High Voltage Electrical Discharge Plasma on Olive Mill Wastewater Treatment

Zoran Herceg,Mia Ivanov,Klara Kraljić,Tomislava Vukušić Pavičić ,Tibela Landeka Dragičević,Dijana Grgas

doi:10.3390/su13031552

Abstract

High voltage electrical discharge plasma technology (HVED) is considered as a promising technology for wastewater remediation due to its fast removal rate and environmental compatibility. Olive mill wastewater (OMWW) treatment presents crucial environmental issues because of its high organic load and intense toxicity and phytotoxicity. The effect of cold plasma at frequencies of 60 Hz and 120 Hz, with injected gas (air, oxygen and nitrogen) and with and without the addition of FeCl3x6H2O, during 30 min, on degradation and removal of organic compounds, as well as polyphenols from OMWW, were investigated. The efficiency of cold plasma was monitored by pH, temperature, electroconductivity, redox potential, oxygen saturation and reduction of chemical oxygen demand (COD) and polyphenols. The best removal efficiency of 50.98% of organic compounds was achieved at 120 Hz with nitrogen and the addition of FeCl3x6H2O, and a 60.32% reduction of polyphenols at a frequency of 60 Hz with the air and FeCl3x6H2O added was obtained. Also, the plasma treatment resulted in a decrease in coloring intensity, with the most significant color change at 120 Hz with the addition of FeCl3x6H2O with nitrogen and air.

Highlights

Olive mill wastewater (OMWW) represents the main liquid waste of the olive oil production process [1,2,3,4]
The qualitative and quantitative high-performance liquid chromatography (HPLC) analysis of raw OMWW has shown that hydroxytyrosol and tyrosol are the most abundant phenolic compounds, but OMWW contains 40 other phenolic compounds [1,5]
The aim of this study is to explore the effect of High voltage electrical discharge plasma technology (HVED) on OMWW treatment using selected process parameters: frequency, treatment time, injected gas and the presence of Fenton reagents

Summary

Introduction

Olive mill wastewater (OMWW) represents the main liquid waste of the olive oil production process [1,2,3,4]. OMWW, a brown to blackish liquid, is acomplex mixture of water, sugar, nitrogenous substances, organic acids, polyphenols, polyalcohols, pectins, mucilages, tanins, lipids and inorganic substances [2,3,4]. Due to complex composition and high organic load (4–18 g/100 g), low pH, high chemical oxygen demand (COD up to 170 gO2 L−1 ) and extremely high phenolic content (0.5–24 gL−1 ), OMWW is highly ranked among the most polluting byproducts of the agro-industrial sector. OMWW is still a challenge for efficient treatment, despite progress in research and development of treatment methods [7] The qualitative and quantitative HPLC analysis of raw OMWW has shown that hydroxytyrosol and tyrosol are the most abundant phenolic compounds, but OMWW contains 40 other phenolic compounds [1,5].

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Conclusion