Recently, our Sustainability Director Charles Kane initiated a digestate dewatering trial at our Gorst Energy anaerobic digestion (AD) plant, aiming to reduce the liquid content of our soil enhancer (digestate), and to produce water that is clean enough to release back into the environment.

What is digestate dewatering?

Digestate dewatering is the process in which liquid is removed from the by-product of AD. This produces dry fibre compost, like Rainbarrow Farm’s Bloomin Amazing.

It can be done through application of mechanical presses, centrifugal force, or evaporation. We have been using a new, multistage process to extract water that is clean enough to reintroduce to local watercourses.

Solid separation from belt press

Although our screw press method extracts the largest possible proportion of solid material from raw digestate, we still need to remove more. So, we run it through a machine that squeezes all the remaining solid material out and leaves the digestate liquid without any solids (which looks like dirty water).

Next, we put it through a staged-filtration system to remove any remaining fine particles. By this point, there are absolutely no solids left.

Filtration process for the liquid fraction from the belt press

The final stage involves a membrane system with tiny holes forcing the liquid under pressure and removing things at an elemental level. We are then left with clean water!

RO Output is ~85% water and ~15 concentrated nutrients

Why should AD plants do it?

• Clean water production: One of the most significant advantages of dewatering is the production of clean water. This water can be reused within the plant, reducing the overall water footprint of AD.
• Volume reduction: Dewatering significantly reduces the volume of digestate, meaning storage and transport is less expensive and more environmentally friendly. This is particularly important for facilities located far from agricultural areas where the digestate might be used as fertilizer.
• Ensures compliance: Digestate dewatering helps AD plants to comply with ever-increasing legislation and regulations around nutrients and water.
• Nutrient concentration: The fraction left after dewatering is rich in nutrients, making it a valuable fertilizer. Concentrating these nutrients also makes it easier to spread, ensuring that plants and crops are fed what they need, when they need it.

What does it mean for the future of AD?

Successful digestate dewatering is a game changer for AD. By reducing waste volume, concentrating valuable nutrients, and producing clean water, it tackles environmental challenges whilst reducing costs.

As the climate crisis continues, the way we respond to changes as a community sets the tone for the future. Digestate dewatering stands out as a key technology in the circular economy, transforming waste into valuable resources and contributing to a more sustainable future.

Get in touch to find out more.