Electro-Oxidation as an Effective Technology in Removal of Persistent Organic Pollutants of Wastewater from Processing Pistachios

Humans discharge a great amount of harmful synthetic compounds and chemicals into the environment through their daily activities. Some of these compounds and chemicals are able to enter the water cycle, thereby polluting it and threatening consumer health [1]. Treatment of wastewater containing chemical compounds is one of the solutions for reducing risks caused by them and environmental pollution [2]. Agriculture and the associated industries are among the major sources of wastewater production [3]. Iran is the largest producer of pistachios in the world, with a large share of its non-oil exports being allocated to pistachios. Accordingly, the US and Turkey are the second- and third-largest producers of pistachios in the world, respectively [4]. Pistachio processing industries have been developed similarly in the world countries [5, 6]. Wastewater from processing agricultural products is one of the environmental pollutants. Approximately, 6m³ of wastewater is produced for the processing of each ton of pistachios [5, 7]. Wastewater from processing pistachios contains persistent organic pollutants (POPs), such as phenolic compounds, with the removal of which from the wastewater being very difficult. Pistachios' outer green skin, making up about 40% of the fruit weight, contains phenolic compounds. Accordingly, it is worth noting that wastewater from processing pistachios contains a great amount of phenolic compounds, which is significantly higher than that in other industrial effluents [8]. Based on the classification made by the US Environmental Protection Agency (EPA), phenolic compounds, because of their low biodegradability, high toxicity, long-term ecological hazards, and bio-cumulative properties, are considered as persistent organic pollutants and inhibitors of microorganisms in biological wastewater treatment systems [5].