Cavitation based wastewater treatment of recalcitrant organic pollutants (Dicofol, BDE-209, HBCD, PFOS, PFOA)

Water pollution has been an environmental concern for many years, which have attracted numerous researches for an effective wastewater treatment method to address the issue. Cavitation based wastewater treatments is one of the emerging advanced oxidation processes (AOPs), which has recently drawn attention due to its effectiveness in pollutant removal. But, the effectiveness of cavitational treatment in the elimination of persistent organic pollutants (POPs) is still at an early stage, while considering the wide range of recalcitrant pollutants to be eliminated. Dicofol, Decabromodiphenyl ether (BDE-209), Hexabromocyclododecane (HBCD), perfluorooctanesulfonic acid (PFOS) and Perfluorooctanoic acid (PFOA) are listed or recommended persistent organic pollutants (POPs) under Stockholm convention. For the past several years, numerous reports indicated the detection of above-mentioned POPs in the environmental matrix and hence their elimination via efficient methods is of priority, because of their carcinogenic, endocrine disruptive, hepatotoxic and bioaccumulative nature. POPs are mostly recalcitrant towards conventional treatment methods. Thus, the mineralization of pollutants, treatment duration, energy efficiency etc. are some of the vital concerns to be addressed. The research investigated the sonochemical based method for the removal of Dicofol, BDE-209, HBCD, PFOS and PFOA (PFOX), whereas hydrodynamic cavitation (HC) was implemented for the removal of Dicofol. The effect of various parameters had been studied distinctively by considering sonication power, HC inlet pressure, treatment duration, pH, reaction solution temperature and initial pollutant concentration. The degradation products were monitored by gas chromatography mass spectrometry (GC-MS), liquid chromatography mass spectroscopy (LC-MS), high-performance liquid chromatography (HPLC) and liquid chromatography mass spectroscopy (LC-MS) analysis. GC-MS analysis in selected ion monitoring mode (SIM) and liquid chromatography tandem mass spectrometry (LC–MS/MS) in multiple reaction-monitoring mode (MRM), were performed for accurate monitoring of the concentration of parent compounds. The sonochemical degradation of Dicofol, HBCD, BDE-209, PFOX (PFOS and PFOA) in aqueous media has been investigated using a 20-kHz probe type sonicator with power inputs from 150 to 450 W, whereas the Hydrodynamic cavitation (HC) treatment of Dicofol has been investigated by a liquid whistle reactor (LWR) with an inlet pressure in the range of 3-13 bar. Under optimum conditions of solution pH, reaction temperature, ultrasonic power density and HC inlet pressure, the extent of degradation of Dicofol was found to be 86 % and 100 % within 60 min of ultrasound and HC treatment respectively. Sono-Fenton treatment of BDE-209 demonstrated a complete degradation within 80 min of treatment, whereas sonochemical treatment of PFOX indicated complete disappearance of the parent compounds within 80 min treatment as well. HC treatment of Dicofol illustrated highest mineralization efficiency with 85 % TOC removal within 1 h of treatment. Best mineralization efficiency of sonochemical treatment was achieved for HBCD with 72 % TOC removal within just 40 min of treatment. Overall, cavitation-based wastewater treatments have emerged as potential techniques for the elimination POPs and progressive research is expected to bring out superior treatment efficiency