EnviroHub System Enables HS2 Site to Safely Reuse Their Concrete Washout Water
As part of an industry trend, it is becoming increasingly common that contractors are specifying that grey water cannot be used in the manufacturing process of concrete for certain applications. Grey water is the name given to the water that is produced following the washing out of concrete trucks into wedge pits.
In this instance our client, Aggregate Industries had specified that from a quality perspective they couldn't have the reuse of grey water in their products.
This is important because Aggregate Industries would normally recycle grey water as it helps their production costs, and they don't have to dispose it off-site (which is a challenge from an environmental compliance perspective). More than anything else however, this means they have to use fresh water constantly for their concrete production which is expensive.
Atlantic Pumps worked with Aggregate Industries to specify what their client considers clean water to be, and how we were going to turn the dirty grey water into clean water using the EnviroHub system so it could be safely re-used.
What was put in place was a series of treatment tanks. The process begins with the user pumping grey water from their wedge pits into an EnviroHub TT10 Treatment Tank which is then dosed with a coagulant and a flocculant using an EnviroHub TU02 Dosing Unit. The coagulant is to remove the charges in the particles and the flocculant is to clump the solids together and make them settle faster.
This then goes through two stages of mixing (fast and slow) and then from there it goes into an EnviroHub HL50 Lamella Tank, where the solids drop out following flocculation. The sludge leaves the bottom of the tank at around 70% solids (toothpaste consistency). The sludge is pumped away into a holding bay where any residual water runs off and returns to the wedge pits. These solids are relatively dry and can then be disposed of from the site.
The clean water from the Lamella Tank flows into a pH Correction Unit (an EnviroHub CT03) which uses CO2 to treat the high pH alkaline laden water, by pumping CO2 through a ceramic sparger - a small disk that lets out very small air bubbles of CO2.
The CO2 bubbles attach themselves to the lime particles in the water which is causing the alkalinity. They calcify and drop out bringing the pH of the water back to neutral. That water is now cleaned and pH neutral and available to be used within the product, or if required, it can be safely discharged off-site.
The client can also use the EnviroHub Monitoring Unit to monitor the quality of the water they are using in the process. This data can be viewed on an online portal. Reports can be generated to demonstrate to their client that the product they are putting back into the concrete is compliant with their requirements.
From a cost perspective, Aggregate Industries can reuse the site water rather than having to use expensive mains water.
From an environmental perspective, water is being saved by being recycled and they are not discharging harmful water off-site.
Any surplus water discharged from the site will now be perfectly safe for the surrounding environment.