Efficient degradation of ethanolamine by UV/chlorine process via organic chloramine photolysis: Kinetics, products, and implications for ethanolamine wastewater treatment

Abstract

The degradation of ethanolamine (ETA), a recalcitrant pollutant containing a primary amine moiety, can be significantly enhanced in a water treatment with chlorination followed by UV (UV/chlorine) via photolysis of the N-Cl bond of monochlom- (N-Cl ETA) and dichlom-ethanolamine (N-Cl-2 ETA) which are formed from the reaction of chlorine with ETA. This study investigated the reaction kinetics, products, and mechanisms of ETA degradation in UV254/chlorine and the effects of process variables on ETA's treatment efficiency. Fluence-based, photolysis rate constant (k(UV)) was 1.0 x 10(-3) cm(2)/mJ for N-Cl ETA and 1.3 x 10(-3) cm(2)/mJ for N-Cl-2 ETA. UV/chlorine was found effective at treating ETA under wide-ranging conditions for the free available chlorine (FAC) dose over ETA concentration (i.e., [FAC[(0)/[ETA](0) >= 1), pre-chlorination duration (i.e., >a few minutes), and solution pH (i.e., 2-11), due to the rapid formation of N-Cl ETA from the reaction of HOC1 with the amine of ETA (k of 1.2 x 10(8) M-1 s(-1)). Increasing the FAC dose was capable of enhancing the degradation rate of ETA so that it attained a k uv of 1.5 x 10(3) cm(2)/mJ at [FAC](0)/[ETA](0) of 3, mainly due to the formation of N-Cl-2 ETA (>= 75%) and to a lesser extent from the involved OW reaction. The energy consumption of UV/chlorine to achieve a 90% ETA abatement ranged from 0.22 kWh/m(3) ([ETA](0) = 0.025 mM) to 3.59 kWh/m(3)([ETA](0) = 10 mM). Ammonia, formaldehyde, and glycolaldehyde were the major degradation products of the UV/chlorine treatment of ETA, which could have formed through the photolysis of N-Cl bonds forming aminyl radicals and their transformation via a 1,2-hydrogen shift and beta-scission. Overall, this study provides useful kinetic and mechanistic information for designing an effective UV/chlorine process for treating ETA wastewater.