Stabilisation of aggressive drinking water in Sofia’s water supply system

It is well known that soft surface water used for drinking purposes has an aggressive (corrosion) effect on iron and cement-containing facilities in water supply systems, leading to premature depreciation and secondary pollution of drinking water with corrosion products.
In Bulgaria, near 55% of drinking water is provided by surface water sources, including 100% the water in Sofia’s Water Supply System and near 90% of water distribution network is made by materials with no corrosion resistance properties – steel, iron, asbestos cement and concrete. Despite this good known data, no technically and economically substantiated solution has been found so far to address the aggressiveness (corrosion) of drinking water in the country.
World experience shows that an appropriate solution to the problem should be sought through the stabilization treatment of aggressive water. Based on a series of long-term experimental studies, the effectiveness of the known and successfully applied in the world practice methods of stabilization treatment was evaluated for water in Sofia. It has been found that the only highly efficient method for reducing corrosion in steel and cast iron by up to 78% in a one-year period and by over 92% over a long period of time is the remineralization of water with lime and carbon dioxide.
The economic efficiency of applying the remineralization treatment of water in Sofia was assessed and it was found that in the short term (from 2020 to 2026) and the mid-term period (from 2027 to 2047) a saving of 124 million BGN to BGN 267 million can be achieved.