Initial situation in July 2015::
In a membrane plant for drinking water in southern Germany tripolyphosphate is used as antiscalant.
When taken water samlpes from the plant it has been found that the pH in the concentrate discharge line is significantly different from the pH of the concentrate coming out of to the system.Therefore it is likely that CO2 gases out from the concentrate on its way through the sewer line, which leads to a raised pH. This fact favors as well the precipitation of lime.
After checking the water analyzes it can be assumed that in the concentrate discharge line mainly lime is formed with a little tripolyphosphate placed in. In a concentrate stream of 14.4 m³ / h in the sewer pipe mathematically 514.8 g/h calcium or 1.285 kg of lime/h is precipitated. This high deposition leads to a slow clogging of the pipe.
Replacement of tripolyphosphate previously used by the powerful hardness stabilizer FreeFlow 18.
FreeFlow 18 is low in phosphorus, stabilizes in laboratory tests without any problems up to an LSI of +3.24 and is able to solve and to discharge existing deposits.
Situation in September 2015:
The change from tripolyphosphate to FreeFlow 18 was done on 13th of July 2015.
The doese rate of FreeFlow 18 to the feed stream is 3 mg / l.
After 6 weeks, an initial check of the concentrate discharge line was held in the sewer manhole: the massive deposits had been almost completely dissolved.
Thus, a cost-intensive cleaning of the concentrate discharge line could be avoided by switching the antiscalant to FreeFlow 18.