Ultrasonic decomposition of dichlorvos and alachlor: Kinetics and identification of products and intermediates
Abstract
The sonochemical decomposition of dichlorvos and alachlor in a batch reactor was investigated. Dichlorvos was irradiated with 500 kHz ultrasound. Increasing total acoustic power input from 86 to 161 Watts resulted in an increase in the rate constant. The change in rate constant due to sparge gas (argon, oxygen, and argon/oxygen (60/40% v/v) mixture) at a power of 161 Watts was also investigated, with the argon/oxygen mixture giving the highest rate constant. A pathway for dichlorvos decomposition was proposed. Alachlor was irradiated with ultrasound at an input power of 128 Watts with oxygen or ozone as a sparge gas. The fastest decomposition achieved was with the combination of ozone and sonication at either 358 or 618 kHz. The addition of humic acids to the system slightly inhibited the decomposition of alachlor. The product chloride was identified and quantified, and several organic intermediates were identified. The efficiency of sonication to treat alachlor present in a high strength industrial wastewater (obtained from Monsanto Corporation) was also investigated. This waste had initial Total Organic Carbon (TOC) of 4500 ppm and initial Chemical Oxygen Demand (COD) of 12500 ppm. The combination of sonication at 358 kHz with ozone was able to achieve a decrease in alachlor concentration of 80% and a slight decrease in the TOC and COD. Buffering the solution at pH 10 increased the degradation of alachlor in its manufacturing waste as compared to the unbuffered solution.
Degree
Ph.D.
Advisors
Hua, Purdue University.
Subject Area
Civil engineering|Environmental engineering|Environmental science
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