Concrete Washwater

Siltbuster have developed a range of systems specifically to deal with high pH concrete washwater as a result of work carried out on construction sites.

Why treat concrete washwater?
High pH (alkaline) water can look clean after the solids have been removed, yet this “silent polluter” is corrosive and can cause damage to vegetation and ecosystems, killing fish and other aquatic life. Water that comes into contact with freshly exposed or poured concrete becomes roughly pH 13 making it as strong and corrosive as oven cleaner. A common misconception is that dilution can be used as a method of treating the high pH but this is not practical because the pH scale is logarithmic, so vast quantities of water are needed for a small change.

 

Sources of alkaline water on construction sites

  • Washing down of machinery used with fresh concrete – chutes, drums, pumps
  • Cutting or coring of concrete structures
  • Hydrodemolition (high pressure water cutting)
  • Surface water runoff from concreted areas
  • Crushed demolition materials

 

The benefits of Carbon Dioxide for pH adjustment
Traditionally a high pH would be treated with mineral acid (sulphuric or hydrochloric) or citric acid reagents. These chemicals need careful handling (specialist training and PPE) and are difficult to dose correctly, with overdosing to form acidic water a strong possibility.

With carbon dioxide it is virtually impossible to acidify the water through overdosing. It is safer and easier to use and is the most cost effective solution. Furthermore Carbon Dioxide does not elevate BOD, chlorides and sulphates etc in the water which would otherwise be secondary pollutants.

 

pH scale

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