The 22nd of March is World Water Day. Water is the most consumed resource on earth but according to WWF only 1% of our 326 million trillion gallons of reserves are fresh water suitable for human use. It is a key resource in recycling processes, helping to clean waste of any contaminants so that it can be processed into clean, high quality products ready to be circulated back into the economy. It is essential for the recycling industry to find circular solutions for the process water they use in order to conserve this dwindling resource.
Why is washing important
To create a clean, high quality recycled product the waste materials need to be washed of any contaminants before being processed to create new products. For example, our washed sand and gravel products can be used in concrete production so without washing out organic materials present on the recycled aggregates may interfere with the concrete mix and have a detrimental effect on strength.
How does it work
At our recycling plant, we have invested heavily in a closed loop wastewater management system. The system simultaneously cleans and recirculates the water back into the plant creating a clay by-product in the process which is traditionally used as a recycled liner in water attenuation applications and as a cohesive fill material. However, we are currently working with Heriot-Watt University on a Knowledge Transfer Partnership to find higher value uses for the material. This type of water management system only requires a 10% top up of water making it highly efficient, conserving vital natural resources. The key components for our filtration system are the clarification tank and filter press.
Once construction, demolition and excavation waste has been fed into the plant, it is washed and screened. At this point the gravel is graded into three different sizes: 4-10mm, 10-20mm and 20-40mm then deposited into the relevant stockpiles. The resulting waste, anything below 4mm, makes its way to the hydrocyclones where 0-2mm soft sand and 0-4mm sharp sand are separated and deposited into their individual stockpiles.
The remaining waste water makes its way to our ‘aquacycle’ clarifying tank where a polyelectrolyte flocculant solution is added. The solution makes the heavier particles sink to the bottom whilst the clean water on the top continuously overflows the weir and is sent to the water storage tank. From the water storage tank, the clean water gets recirculated back into the plant to ensure the materials are free of contaminants.
The residual slurry is predominantly clay based and is sent to our filter press where it is pumped at high pressure between fine filter cloths that remove any leftover water to create clay cakes. This modern water management system removes the need for tailings dams and settling ponds creating a process that is far less water intensive, and lower risk to the environment and health and safety. An added benefit of the system we use is that the by-product, which makes up approximately 20% of output, can be extracted ready to be reused in a variety of different applications.
Recycled aggregates and other recycled products can be created without the need to exhaust scarce natural resources. With the help of modern technology, the recycling industry has moved away from traditional water intensive methods and embraced innovative solutions ensuring that nothing goes to waste. The recycled products created at our Livingston based recycling facility demonstrate this showing how waste can be given a new life without costing the earth.