Kinetics and mechanism for degradation of dichlorvos by permanganate in drinking water treatment

Abstract

Permanganate Kinetics MechanismDrinking water treatment a b s t r a c tThe degradation kinetics and mechanism of dichlorvos by permanganate during drinking water treatment were investigated. The reaction of dichlorvos with permanganate was of second-order overall with negligible pH dependence and an activation energy of 29.5 kJ$mol À1. At pH 7.0 and 25 C, the rate constant was 25.2 AE 0.4 M À1 s À1. Dichlorvos was first degraded to trimethyl phosphate (TMP) and dimethyl phosphate (DMP) simultaneously which approximately accounted for <5% and !95% with respect to phosphorus mass, respectively. Further oxidation of DMP generated a final byproduct, monomethyl phosphate (MMP). MMP was for the first time identified as a major byproduct in chemical oxidation of dichlorvos. The kinetic model based on degradation mechanism and determined reaction rate constants allowed us to predict the evolution of dichlorvos and its byproduct concentrations during permanganate pre-oxidation process at water treatment plants. These results suggest that even though the dichlorvos concentration in surface water complies with the surface water quality standards of China (50 mg L À1 ), its concentration after conventional water treatment will most probably exceed the drinking water quality standards (1 mg L À1). Moreover, luminescent bacteria test shows that the acute toxicity of dichlorvos solution evidently increased after permanganate oxidation.ª 2009 Elsevier Ltd. All rights reserved. w a t e r r e s e a r c h 4 3 ( 2 0 0 9 ) 3 4 3 5 -3 4 4 2 Introduction

Permanganate oxidation of diclofenac: The pH-dependent reaction kinetics and a ring-opening mechanism

“…3, the ln k values exhibit a good linearity (R 2 = 0.99) with the reciprocal of temperature (1/T). The activation energy of the Mn(VII)/DCF reaction was then calculated to be 26.2 ± 0.4 kJ mol À1 , which is comparable to that of Mn(VII)/dichlorvos (29.5 kJ mol À1 ) and Mn(VII)/microcystins (28.8 kJ mol À1 ) reactions (Rodríguez et al, 2007;Liu et al, 2009). Fig.…”

“…However, our result was not consistent with this hypothesis. It is well documented that the pHdependence of the second-order rate constants between Mn(VII) and a large number of organic compounds generally increased with increasing pH, like phenol and lincomycin (Hu et al, 2010;Jiang et al, 2012), or had no obvious pH-dependence, like ciprofloxacin, carbamazepine, and dichlorvos (Hu et al, 2008(Hu et al, , 2010Liu et al, 2009). An opposite case is trimethopaim (Hu et al, 2010), where the second-order rate constants of the Mn(VII)/trimethopaim reaction decreased with increasing pH like those of the Mn(VII)/DCF reaction.…”

Kinetics and mechanism for omethoate degradation by catalytic ozonation with Fe(III)-loaded activated carbon in water

“…In fact, TMP has been reported as a major byproduct generated from oxidation of other OPPs. For example, it was detected in the oxidation of dichlorvos by permanganate (Liu et al, 2009). TMP was also identified to be a byproduct from the degradation of dichlorvos and dimethoate in a TiO 2 -mediated photocatalytic process, which could be further oxidized to O,O-dimethyl phosphonic ester (Evgenidou et al, 2006).…”

Degradation mechanism of alachlor during direct ozonation and O3/H2O2 advanced oxidation process

“…Therefore, the transformation of alachlor during direct ozonation and AOP O 3 /H 2 O 2 would yield many degradation byproducts. Concerns were raised regarding the byproducts formed since sometimes pesticide degradates were equally or even more toxic than their parent compound (e.g., dichlorvos) (Liu et al, 2009). However, until now the identification of alachlor degradation byproducts during direct ozonation and AOP O 3 /H 2 O 2 is limited, and related degradation pathways are not clear.…”