TOTAL DISSOLVED AMINO-ACID-ANALYSIS IN NATURAL AND DRINKING WATERS

Recent studies have pointed out the importance of nitrogen compounds, such as amino acids, on chlorine consumption of drinking water: chlorine demands of amino acids would range from 2 to 16 mol Cl2/mol of amino acids. Better knowledge of amino acid concentrations in water could lead to improve water treatment and so, water quality on distribution networks. The general objective of this study is to quantify total amino acids in surface waters and drinking waters. For that purpose, OPA precolumn derivatization followed by HPLC analysis with fluorimetric detection was used. Natural water samples were first hydrolysed under acidic conditions. Amino acid analysis were carried out on raw surface waters from three french rivers (Oise, Seine, and Marne), and on the water treatment plant of Mery sur Oise (Paris, France). Analysis were performed at different steps of the treatment plant: storage, flocculation-sedimentation, sand filtration, interozonation, GAC filtration, postozonation and chlorination. The global amino acid concentration measured ranged in most cases from 50 to 250 mug l-1, expressed as carbon content (i.e. 20 to 90 mug l-1 N). Major compounds were glycine, serine, alanine, aspartic acid, glutamic acid, threonine and valine at concentrations ranging from 0.2 to 0.9 mumol l-1. Seasonal variations were observed, with an increase of total amino acid concentrations in raw waters at spring and summer periods. Based on our previous studies, we can estimate chlorine consumption of treated water due to these compounds between 0.4 to 1 mg l-1 Cl2.