title: Study on the kinetics and transformation products of salicylic acid in water via ozonation.
abstract: As salicylic acid is one of widely used pharmaceuticals, its residue has been found in various environmental water systems e.g. wastewater, surface water, treated water and drinking water. It has been reported that salicylic acid can be efficiently removed by advanced oxidation processes, but there are few studies on its transformation products and ozonation mechanisms during ozonation process. The objective of this study is to characterize the transformation products, investigate the degradation mechanisms at different pH, and propose the ozonation pathways of salicylic acid. The results showed that the rate of degradation was about 10 times higher at acidic condition than that at alkaline condition in the first 1 min when 1 mg L(-1) of ozone solution was added into 1 mg L(-1) of salicylic acid solution. It was proposed that ozone direct oxidation mechanism dominates at acidic condition, while indirect OH radical mechanism dominates at alkaline condition. A two stages pseudo-first order reaction was proposed at different pH conditions. Various hydroxylation products, carbonyl compounds and carboxylic acids, such as 2,5-dihydroxylbenzoic acid, 2,3-dihydroxylbenzoic acid, catechol, formaldehyde, glyoxal, acetaldehyde, maleic acid, acetic acid and oxalic acid etc. were identified as ozonation transformation products. In addition, acrylic acid was identified, for the first time, as ozonation transformation products through high resolution liquid chromatography-time of flight mass spectrometer. The information demonstrated in this study will help us to better understand the possible effects of ozonation products on the water quality. The degradation pathways of salicylic acid by ozonation in water sample were proposed. As both O3 and OH radical were important in the reactions, the degradation pathways of salicylic acid by ozonation in water sample were proposed at acidic and basic conditions. To our knowledge, there was no integrated study reported on the ozonation of salicylic acid in water, in terms of transformation products, kinetic, mechanism, as well as degradation pathways.
authors.affiliation: Department of Civil & Environmental Engineering, The National University of Singapore, Block E1A, #07-03, No.1 Engineering Drive 2, Singapore 117576, Republic of Singapore; PUB Water Quality Laboratory, Water Quality Office, PUB, 82 Toh Guan Road East, #04-03, Singapore 608576, Republic of Singapore.
authors.forename: Ruikang
authors.initials: R
authors.lastname: Hu
authors.affiliation: PUB Water Quality Laboratory, Water Quality Office, PUB, 82 Toh Guan Road East, #04-03, Singapore 608576, Republic of Singapore.
authors.forename: Lifeng
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Department of Civil & Environmental Engineering, The National University of Singapore, Block E1A, #07-03, No.1 Engineering Drive 2, Singapore 117576, Republic of Singapore. Electronic address: ceehujy@nus.edu.sg.
authors.forename: Jiangyong
authors.initials: J
authors.lastname: Hu
mesh_terms: D052918:Environmental Restoration and Remediation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry*; D020156:Salicylic Acid / Q000737:chemistry*; D014865:Waste Disposal, Fluid; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D014874:Water Pollutants, Chemical; D010126:Ozone; D020156:Salicylic Acid
keywords: Kinetics; Mechanism; Ozonation; Pathways; Salicylic acid; Transformation products