DEVELOPMENT AND AUTOCALIBRATION OF AN INPUT-OUTPUT MODEL OF CHLORINE TRANSPORT IN DRINKING-WATER DISTRIBUTION-SYSTEMS

Chlorine concentrations within drinking mater distribution systems (DW DS) must be maintained between an Environmental Protection Agency (EPA ) enforced minimum and maximum values driven by formation of harmful d isinfectant byproducts. These control objectives are difficult to meet because chlorine mass in water decreases over time and mixing at pipe junctions causes a change in concentration, The DWDS input-output (I- O) model developed here takes these factors into account, as it expres ses the chlorine concentration at a given pipe junction and time as a weighted average of exponentially decayed values of the concentrations at all adjacent upstream junctions: the exponential decay models chlo rine reactions and the weighted average reflects the effect of mixing at the pipe junction, The upstream junction concentrations are known i f they are a chlorine treatment point, or can be calculated in the sam e manner as the original unknown junction concentration. This is the b asis for a recursive procedure with which the I-O model backtracks thr ough the DWDS until all paths from consumption to treatment are found. Before implementing any control schemes based on the I-O model, measu red data from real systems are used to calibrate the model off-line. S ince the I-O model finds all paths from treatment to a given measureme nt, the reaction rate associated with chlorine decay at the pipe wall can be adjusted to improve predicted chlorine concentrations, Results from actual DWDS show that model accuracy is increased when calibrated in this way.