Concrete: Concrete washwater – big implications
Concrete – “James Tucker of Siltbuster outlines the importance of treating concrete washwater on construction sites”.
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Without careful planning, significant water pollution incidents can far too easily arise on construction sites. Cementitious water is one of the most common and challenging waters with which construction sites have to contend. Under environmental legislation, concrete washwater cannot be released to surface or groundwater without a bespoke discharge permit from the Environment Agency. Therefore, measures to control, store and treat concrete washwater before discharge will need to be implemented. Given that it can be caused by an array of day-to-day building activities – whether it’s through washing down mixing trucks, chutes, skips and equipment, hydrodemolition, grouting or tunnelling – construction firms must prioritise its management and develop control over these processes.
The Problem
Concrete washwater is highly alkaline even though it may appear visibly clear. Its pH is 12–13, which is the same as domestic oven cleaner, making it highly damaging. The release of untreated highly alkaline water into the aquatic environment can have devastating effects on the health and biodiversity of the receiving waterbody. One measure that firms can adopt to better manage concrete washwater is to establish a designated washout area well away from drainage gullies, surface water drains and water bodies. This serves to contain slurry, solids and any liquids generated during the washing down of equipment that has come into contact with fresh concrete. At this point, the liquid phase should be treated to ensure its safe disposal.
Not Dilution
When it comes to dealing with such water, dilution isn’t practical or cost-effective due to the pH scale being logarithmic. It would take 10,000 litres of water to reduce the pH of 1 litre of concrete washwater from 13 to an acceptable 9, as typically stipulated in Environment Agency discharge consents. Using mineral acids as neutralising agents isn’t the answer either. Sulfuric and hydrochloric acids, for example, are dangerous to handle, must be securely stored, can easily end up creating polluting acidic water, and create ‘secondary pollutants’ – sulfate and chloride. Citric acid has its own issues, increasing the biochemical oxygen demand of water above the limits that are acceptable to the Environment Agency.
Article by James Tucker, Business Development Manager (Construction)
