EnviroHub Enables Recycling of Concrete Washout Water on HS2 Site

Overview

Working closely with the contractor and concrete supplier for HS2, Atlantic Pumps overcame the twin issues of clean water for on-demand concrete mixing and concrete washout water treatment, by installing an EnviroHub site water recycling system.

Challenge

Quality control is vital for on-site mixing of high specification concrete for structural infrastructure, making clean water a must for civil engineering companies constructing new transport links such as motorways and railways. This can be a challenge for new development sites, where an abundance of concrete washout /wastewater is produced before the water utilities are available.

A case in point is HS2 construction, where the contractor had to work to Aggregate Industries’ stringent standards on water quality, while moving into new ground. They had site wastewater from the groundworks and concrete washout that could have traditionally been reused as greywater for new concrete batches, and a lack of onsite clean water supply.

Solution

Atlantic Pumps installed an EnviroHub system that recycled the concrete washout and grey water onsite, bringing it to Aggregate Industries’ high spec, for use in fresh concrete production.

EnviroHub is a modular system of water treatment tanks that is configurable to the water parameters that require monitoring and correction. Each unit is designed for ease of transport and deployment, and joined together with quick-connect pipework and power sockets. Wireless, two-way control for data and commands (manually or pre-programmed) is enabled via the Control Module.

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.

Results

The series of treatment tanks was quick to install and allows periodic relocation as the work site moves. It solves the issue of what to do with cement and concrete washout water, allowing this and other greywater to be recycled on site instead of trucked away. The reduction of heavy construction traffic alone makes a positive contribution to site safety, plus reducing neighbourhood disturbance and emissions. Further savings are made by the reduced reliance on buying in fresh water or abstraction licences.

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 live on an online portal, with text and email warnings of approaching quality deviances. Reports can be generated to demonstrate to external stakeholders that the water used for the concrete is compliant with standards.

Benefits

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 process water discharged from the site will now be free of silt and within the licensed pH neutrality levels, protecting the surrounding environment and the contractor from pollution claims.

Any surplus water discharged from the site will now be perfectly safe for the surrounding environment.

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