EnviTec Biogas : Soil-improving by-product holds key to future

The economic and environmental benefits of Anaerobic Digestion (AD) as a means of producing renewable energy are already well documented.

But one aspect of the industry often overlooked are the opportunities to put the leftover material, produced by the AD process, to good use.

It's a subject worth a much closer look, because the fertiliser produced by the generation of biogas can play a major role in the future of sustainable farming.

At EnviTec Biogas UK, we are seeing that the value of digestate is becoming increasingly acknowledged and for good reason.

Digestate is rich in nitrogen, potassium and phosphorus - making it an ideal fertiliser which can replace the need to outsource synthetic products.

It has been shown to provide huge benefits to farmers and landowners keen to improve soil conditions and, ultimately, increase their yield.

Digestate can be processed further for maximum efficiency and the solid fibre can be separated from the liquid.

The separated solids have a uniformity much like compost and can be stacked in yards or fields for use as a soil conditioner or used as animal bedding - a method popular in Germany.

In the USA dried digestate is increasingly replacing sand as dairy bedding thereby avoiding the problems sand causes in wearing mechanical handling and blocking drains.

After separation, the solid fibre remains high in potassium and phosphorus and can be processed into pellet form and sold to garden centres.

The remaining liquid fraction can be easily pumped into a slurry lagoon after the process and used as a nitrogen-rich fertiliser.

It's a subject on the radar of The National Non-Food Crops Centre (NNFCC). Established in 2003, NNFCC is an international consultancy providing expertise in the conversion of biomass to bioenergy, biofuels and bio-based products.

Lucy Hopwood, lead consultant for Bioenergy and Anaerobic Digestion at NNFCC, has looked closely at the process.

She said: "It's difficult to assess the real monetary value of digestate as there has been a lack of knowledge and confidence in it in the UK.

"But the organic fertiliser from AD has much higher nutrient content than artificial fertiliser at the same price, so that creates financial savings for the farmer.

"Displacing the need for carbon intensive synthetic products also creates a huge benefit to the environment and is a major contributor to increased carbon savings."

Before joining the EnviTec Biogas UK team as an in-house biologist, Gareth Thomas spent several years working in a research-based role looking at the viability of digestate.

Gareth, a marine biology graduate of Bangor University, agrees the product has a significant role in the future of sustainable farming in the UK.

He said: "Digestate will have a hugely positive impact and we need to raise awareness of what can be done with it to get the best from the material and help farmers and landowners of AD plants reap further benefits."