Already in 1990-91 - as was mentioned in paragraph 2 - A.M.I, had experimented using a rented EDR plant. The groundwork of data and experienced collected at the time was a

Figure 4

starting point for A.M.I, in developing the tender specifications for the supply of the current pilot plant (see block diagram of the system). We would like to underline here the creative role of A.M.I, in establishing "minimum system parameters" which the manufacturer had to comply with, and especially the direct involvement of the manufacturer in the following stage of performance of the experimental tests. The programme of experimental tests was divided into two stages:

• The first stage was to check the achievement of the "minimum parameters" set down by A.M.I. in the plant supply specifications.

• During the second stage, after the steps decided on during the first stage were achieved, variations were set to the machine cycle in order to make improvements, both general and finalised to specific ends (reducing the consumption of additives, greater recovery, letting out less concentrated brine).

The following "minimum parameters" which it was necessary to comply with were set during the first experimentation stage:

a) Ion N03~ removal percentage: 70% (as an average)

b) specific power consumption: 0.79 kWh/m3 water production c) percentage of brine discharge: < 15%

Simultaneous compliance with the three established parameters also had to be guaranteed for minimum continuous period of time, whatever variations there might be in the quality of the incoming water. Figure 5 is a graph showing the incoming and outgoing trend (from the treatment) of ion N03~ concentration, and the relevant abatement percentages. Fig. 6 shows the trend of the technical and management data gathered during experimentation (kWh/m3 ratio and relevant recovery percentage). The data show that the conditions set at the beginning were not only complied with; they were even improved upon (especially in the case of parameter b). Parameter c) is a special matter. Although this value can be set easily on the system, operating on an incoming by-pass valve, its achievement when associated with simultaneous achievement of the other two parameters is not so automatic, especially in the case of long term tests.

We can summarise as follows the plant conditions that were set and kept throughout the first phase (April to November 1997):

• polarity reversal cycles every 55 minutes

• acid washing with HC12% solution every 23 production hours

• antiscaling product proportioning: about 2 ppm on the concentrated flow

• sulphamic acid proportioning on the electrolyte circuit, depending on conductivity set up value of 15000 (xS/cm.

As one can see, die tests during the first experimentation phase displayed two outstanding features:

a) high percentages of water recovery: >90%

b) high frequency of acid washing of the membrane packet (once a day, during the washing phase, since the plant had one line only, no treated water was produced).

The high percentage of water recovery, calculated as the ratio between water produced with a low nitrate concentration and the untreated water being fed in, obviously lead to the production of a concentrated discharge with high percentage of ion N03~.

Therefore, during the second experimentation phase, substantial modifications were made to the plant conditions in order to cut consumption down:

• polarity reversal cycles every 20 minutes

• acid washing using 2% HC1 solution once a week

• sulphamic acid proportioning with conductivity set on the electrolyte at 10500 fiS/cm.

Conductivity Plant Harmfull


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