DML plan to install a two state digestate enhancement process. Firstly the digestate will be separated into its solid and liquid fractions. The solid will be used as a soil conditioner. The liquid fraction will be dried in order to remove 50% of the water leaving a concentrated liquor. This process will half the volumes of digestate DML need to store during the NVZ closed spreading period, allowing them to spread this valuable product when the weather conditions are correct and crop demand is at is highest. As a result DML expect nutrient utilisation to rise from 50% to 80% reducing their annual fertiliser bill. Spreading of the solid fraction will create additional employment and improve the soil condition. This is expected to increase crop yields by 5% after one year.
Being located in an NVZ, DML have a limited spreading window in which to apply their digestate to their crops. The over winter closed period is 4 months. DML to develop a solution to prevent them from under utilising this valuable organic fertiliser in the future. To meet this target, DML have focused on a digestate enhancement project. This is a two stage process which first involves separating the digestate into its solid and liquid fractions. The fibrous solid fraction makes an excellent soil conditioner and can be worked into the ground to improve soil health and soil organic matter. The liquid fraction is then pumped to the second phase of the project process where it is dried using excess heat from the AD Plant in order to evaporate water. During this process ammonia is also volatilised but this nitrogen gas is captured and stored.
This project will enable DML to meet the following objectives:
Spread Digestate in a timely manner allowing full utilisation of the contained organic matter and nutrient
Half the volume of digestate needing to be spread, therefore increasing productivity and reducing spreading costs
Use enhanced digestate to reduce artificial fertiliser use