Digestate dryer: Anaerobic Digestion (AD) in a biogas plant is a well proven process in which organic matter breaks down naturally in the absence of oxygen to produce two valuable products – biogas and digestate. Biogas is an extremely useful source of renewable energy, whilst digestate is a highly valuable biofertiliser. Digestate is an organic fertiliser product that is mostly spread to land. The nutrient content of digestate varies dependent on the feedstock mix and the process configuration, but typically material contains reasonable levels of essential nutrients N, P and K.
The issue of securing suitable markets for digestate is more of a problem for larger plants and those based in urban situations where access to a suitable land bank for spreading is more restricted or costly. In many cases storage requirements and costs of transport and distribution can be reduced by mechanical or thermal treatment.
Thermal drying relies on using surplus heat emanating from a combined heat and power (CHP) engine or occasionally a dedicated biogas boiler.