Hydrodynamic cavitation based advanced oxidation processes: Studies on specific effects of inorganic acids on the degradation effectiveness of organic pollutants

https://doi.org/10.1016/j.molliq.2020.113002Get rights and content
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Highlights

  • Type of inorganic acid plays a dominant role in by-products formation.

  • Simple change in acidification reagent provide effective minimization of by-products.

  • Effective formation of sulfate radicals from sulfate ions by cavitation

  • Highly effective degradation of contaminants by cavitation aided by sulfate anions

  • Highest degradation efficiency obtained in presence of SO42− comparing to Cl and NO3

Abstract

The use of cavitation in advanced oxidation processes (AOPs) to treat acidic effluents and process water has become a promising trend in the area of environmental protection. The pH value of effluents – often acidified using an inorganic acid, is one of the key parameters of optimization process. However, in the majority of cases the effect of kind of inorganic acid on the effectiveness of degradation is not studied.

The present study describes the results of investigations on the use of hydrodynamic cavitation (HC) for the treatment of a model effluent containing 20 organic compounds, representing various groups of industrial pollutants. The effluent was acidified using three different mineral acids. It was demonstrated that the kind of acid used strongly affects the effectiveness of radical processes of oxidation of organic contaminants as well as formation of harmful secondary pollutants. One of important examples is a risk of formation of p-nitrotolune. Sulfuric acid was the only chemical used for acidification which caused effective treatment with lack of formation of monitored type of secondary pollutants. The best treatment effectiveness – during a 6-hour cavitation process - in most cases much above 80% along with 90% TOC removal was obtained in the case of sulfuric acid. Nitric acid provided lower effectiveness (above 60% for most of the compounds). The worst performance are reported for hydrochloric acid – below 50% of degradation for most of the compounds.

Keywords

Hydrodynamic cavitation
Sulfate radicals
Advanced oxidation processes (AOPs)
Volatile organic compounds (VOCs)
Hydroxyl radicals

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