Kinetics of Metolachlor Degradation by Zerovalent Iron

Metolachlor may pose a threat to surface and ground water qualities due to its high solubility in water, Zerovalent iron (ZVI) releases $e^-$ which can degrade the organochlorinated compounds. The objective of this research was to evaluate the kinetics of metolachlor degradation as affected by ZVI sources [Peerless unannealed (PU) and Peerless annealed (PA)] and ZVI levels (1 and 5%) under batch conditions at different metolachlor concentrations (200 and 1000 mg/l) and temperatures (15, 25, and $35^{\circ}C$). The effectiveness of ZVI on metolachlor degradation was assessed by characterizing the dechlorinated metolachlor byproduct molecules. Metolachlor degradation by ZVI followed the first-ordered kinetics with a higher rate constant at higher level of ZVI treatment. At 5% (w/v) of PU and PA treatment, the half-lives of metolachlor degradation were 9.93 and 6.51 h and all of the initial metolachlor were degraded in 72 and 48 h, respectively. Rate constants (k) of metolachlor degradation were higher at the lower initial metolachlor concentration. The metolachlor degradation by ZVI was temperature dependent showing that the rate constant (k) at 15, 25, and $35^{\circ}C$ were 0.0805, 0.1017, and 0.3116 /h, respectively. The ZVI-mediated metolachlor degradation yielded two byproduct molecules identified as dechlorinated metolachlor $(C_{13}H_{18}NO)$ and dechlorinated-dealkylated metolachlor $(C_{12}H_{17}NO)$. The PA ZVI was more effective than PU ZVI in metolachlor degradation.

Zerovalent Iron에 의한 Metolachlor의 분해 Kinetics

본 연구에서는 ZVI 종류[Peerless unannealed(PU), Peerless annealed(PA)]별 처리농도(1, 5%, w/v), 초기 metolachlor 농도(200, 1000 mg/l) 및 온도(15, 25, $35^{\circ}C$)가 metolachlor의 분해에 미치는 kinetics를 평가하였다. ZVI에 의한 metolachlor의 분해는 first order kinetics모델로 설명할 수 있었다. ZVI의 처리 농도가 증가할수록 metolachlor 의 분해속도가 빨랐다. 5%(w/v)의 PU와 PA ZVI를 처리시 metolachlor의 분해 반감기는 각각 9.9와 6.5 h 이었고 metolachlor는 72 및 48 h 에 모두 분해되었다. metolachlor의 분해상수(k)는 초기 metolachlor 농도가 낮을 때 컸다. ZVI에 의한 metolachlor의 분해는 온도가 높을수록 증가되었고 15, 25, $35^{\circ}C$에서 metolachlor의 분해상수(k)는 각각 0.0805, 0.1017, 0.3116 /h 이었다. ZVI에 의한 metolachlor 분해 시 2종류의 분해산물이 동정되었는데 이는 탈염소화된 metolachlor$(C_{13}H_{18}NO)$, 탈염소화-탈알킬화된 metolachlor$(C_{12}H_{17}NO)$이었다. PA ZVI가 PU ZVI 보다 metolachlor를 분해하는데 효율적임을 알 수 있었다. ZVI는 탈염소화기작에 의해 metolachlor를 분해함을 알 수 있었다.