Hydrodynamic cavitation based advanced reduction process (ARP) for degradation of 2-nitrophenol in aqueous environment.

Hydrodynamic cavitation (HC) along with acoustic cavitation are emerging techniques in wastewater treatment for degradation of toxic, refractory and non-biodegradable pollutants. The energy released during cavitation phenomenon has a number of applications in advanced oxidation processes (AOPs). In contrast this paper presents an effective activation of dithionite (DTN) under HC as advanced reduction process (ARP). The developed process of HC/DTN was tested for the first attempt to perform the reductive degradation of 2-nitrophenol (2-NP) in water. The complete degradation of 2-NP was achieved within 15 min at optimal conditions of Cv 0.27 with rred 8.33, pH 11, 20 ± 2.5 °C ensuring a synergistic index (ξ) of 9.47. These results demonstrated HC as an effective tool for DTN activation. The degradation of 2-NP was primarily contributed by sulfur dioxide anion radicals (SO2•-) and hydrated electrons (eaq-), while oxidizing radicals (i.e., HO• and SO4•-) played minor role. The degradation pathway of 2-NP in HC/DTN was proposed relying on the identified intermediates using gas chromatography coupled to mass spectrometry (GC-MS). The main intermediates of 2-NP degradation were aniline and hydroquinone confirming the combined ARP/AOP action of HC/DTN. The total treatment cost of 1 m3 of contaminated water by the developed HC/DTN process was estimated as 1.08 euros according to the economic feasibility analysis. Along with rapid degradation, simple instrumentation and ultra-low costs, HC/DTN offers a promising solution for industrial water treatment.