Treatment of overhaul wastewater containing N-methyldiethanolamine (MDEA) through modified Fe–C microelectrolysis-configured ozonation: Investigation on process optimization and degradation mechanisms

Highlights: • Overhaul wastewater was treated with ozonation-microelectrolysis-ozonation process. • Microelectrolysis could destroy the structure of MDEA, but ozone had no effect. • The effects of operating parameters on MDEA removal were investigated. • The degradation mechanism of MDEA in microelectrolysis was discussed. -- Abstract: In this study, the microelectrolysis system was applied to generate strong reductants, such as free hydrogen [H] and ${\text{O}}^{\bullet }$, and thus removing N-Methyldiethanolamine (MDEA) in overhaul wastewater. Effects of initial influent pH, mass ratio of filings to wastewater, air aeration rate, and reaction temperature on the removal of MDEA were investigated intensively. Experimental results indicate that optimum removal rate of MDEA can be obtained at pH = 2, inlet air rate = 1 L min⁻¹, mass ratio of filings to wastewater = 1:1 and temperature = 25 °C. About 96.0% Total Organic Carbon (TOC) in overhaul wastewater can be mineralized by ozonation–microelectrolysis–ozonation (OMIO) treatment process. By analyzing the effluent at various stages, it was established that microelectrolysis played a leading role in the destruction of MDEA. The degradation mechanism of MDEA has been clarified through detecting the degradation products with Gas Chromatography–Mass Spectrometer (GC–MS). Subsequently, ozone reacts with intermediate products generated by MDEA degration through OH· pathway under alkaline condition. In short, these results suggest that OMIO system should be proposed as a promising treatment process for the MDEA wastewater.