Foreword

Drinking water from underground sources is still largely prevalent in Italy compared to surface sources (the former covers 87.5%, the latter 12.5%, according to an ISTAT study in 1987). The quality of the underground water coming from wells of various depths is of course affected by the geochemical make-up of the ground, but also - and very much so -by human activities on the imbriferous basin feeding the water table that the wells are drawn from. One quality problem with underground water has by now been proven to be strongly affected by human activity (agriculture, industry and town life) - pollution by N03- nitric ions. The MAC for this was set in the EEC Directive 778/80 (adopted in Italy as D.P.R. 236/88) at 50 mg/l. The serious nature of the nitrate problem in Italy is due not only to the MAC being overstepped in limited individual areas (where the concentration may be as high as 150 mg/l), but especially to the extent of the territory involved, where the stratum used for drinking water is progressively rising (Marche, Emilia Romagna, Lombardy and Veneto). It is no coincidence that this is one of the most densely populated areas of Italy, and uses about one third of all drinking water in the country. The territory where Consorzio A.M.I, draws its underground water is no exception as far as the nitrate issue is concerned, although it has limited peaks that rarely exceed concentrations of 70 mg/l. However, the excellent overall quality of the water drawn has led A.M.I, ever since 1990 to look for nitrate treatment technology solutions which would alter the natural features of the water as little as possible, while providing good performance in terms of nitrate ion abatement, high percentages of recovery and low power consumption.

2 THE DECISION TO USE POLARITY REVERSAL ELECTRODIALYSIS TECHNOLOGY (EDR)

A.M.I, first used electrodialysis technology (henceforth abbreviated as EDR) in 1990. At the time, the decision to adopt this kind of technology (which has rarely been applied to water supply systems anywhere in the world, even less so in Europe1) was inspired by its intrinsic features and by its many applications in the food industry. Generally speaking (Figure 1), EDR belongs to a range of technologies which use membranes to separate

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