Determination of EDTA in Dairy Wastewater and Adjacent Surface Water

Abstract

An HPLC-UV analytical method was developed to determine ethylenediaminetetraacetic acid (EDTA) in dairy wastewater and surface water. The optimizing separation was achieved by reversed-phase ion-pair liquid chromatography on a C18 column using methanol as mobile phase solvent, tetrabutylammonium bromide as the ion-pair reagent in pH 3.3 formate buffer solution at a flow rate of 0.9 mL min -1 with a UV detector at 265 nm. No interference of Ca, Mg or NO3 - was detected. Method performance was evaluated in terms of linearity, repeatability and reproducibility. The method detection limit was 5 µg L -1 . The contents of EDTA in dairy effluents were 72 ~ 261 µg L -1 at a large dairy site. A change of EDTA concentration was observed downstream of the dairy effluent discharge, but this was well under the predicted no effect concentration for aquatic ecosystem. Keywords—Dairy wastewater, EDTA, HPLC, surface water. I. INTRODUCTION LEANING of equipment for production plants is a key process in the dairy industry to ensure safe products with high quality. It has been demonstrated (1) that using synergic effects of single components in chemical mixtures, for instance adding an effective complexing agent, is more likely to achieve an improved cleansing result with lower concentration compared to aqueous solutions merely containing the basic component of sodium hydroxide. The main function of complexing agents in a cleaning solution is to prevent precipitation of calcium, magnesium and heavy metal salts, which can cause deposits to appear on both the cleaning equipment and the plant to be cleaned (2). At present, ethylenediaminetetraacetic acid (EDTA) is the cheapest and most suitable complexing compound for many technical purposes, and is used in large quantities (3). In the New Zealand dairy industry, EDTA has been used as a cleaning additive to improve the cleansing efficiency during the clean-in-place (CIP) procedure. Nearly all applications eventually result in the release of EDTA to the aquatic environment (2), (3). In the late 1980s, the environmental impacts of EDTA were scrutinized in Europe, as EDTA occurred at a higher concentration in surface waters than any other identified anthropogenic organic compounds that may