How does ‘blue gold’ become a priority?
900 million cubic metres of water are consumed each year by the construction sector in France, according to the study “Water Consumption in the Construction Sector in France” published in 2019 by the Seine-Normandie Water Agency.
3,600 cubic metres of water are used every day in France for cleaning concrete skips, representing 792 million litres over 220 working days — an estimate established by ECL-Econet based on its field experience.
Given these figures, it is essential to consider solutions that reduce water consumption on construction sites while preventing environmental pollution linked to wastewater discharge. The main polluting fluids generated on civil engineering sites include concrete washout slurry, suspended solids (TSS), as well as fuels and lubricants from construction machinery.
Suspended solids (TSS) are fine, insoluble particles present in water, originating from various mineral sources (sand, silt, clay) or organic matter. These particles may carry pollutants. Turbid water can also endanger aquatic life by causing oxygen depletion or reducing light penetration.
Also known as “cement laitance”, washout slurry is a liquid mixture of water, cement and fines that forms a white film on the surface of curing concrete. During the cleaning of tools (shovels, trowels, buckets), drum mixers, concrete skips or batching plants, wash water must be collected and treated. If discharged untreated into the environment or into sewers, it causes pollution. Treatment solutions may include filtration, sedimentation, separation or biological treatment to remove contaminants and allow water to be safely reused or discharged.
pH neutralisation of construction wastewater
Construction wastewater can have a very high pH due to the presence of concrete and mortar residues. If released into rivers or lakes without proper treatment, these alkaline waters can disrupt the natural balance of ecosystems. pH measures the acidity or alkalinity of a solution on a scale from 0 to 14, where 7 is neutral, values below 7 are acidic and values above 7 are alkaline. Among the available treatment options for high-pH wastewater, CO₂ neutralisation via confined injection stands out as an efficient and environmentally friendly solution.
The ECONET system relies on this principle by using a chemical reaction between CO₂ and water to lower the pH of wastewater. This reaction makes certain contaminants more soluble and therefore easier to treat. The key difference between confined CO₂ injection (used by ECONET) and micro-bubble CO₂ injection is that the latter introduces CO₂ directly into the water as microbubbles. This method is less effective because part of the CO₂ escapes into the atmosphere and the distribution in the water is less uniform. Maintaining an appropriate pH balance in the environment is crucial. Construction wastewater must be properly treated before discharge to avoid adverse effects on ecosystems and water quality.