In several European countries effective use of the heat generated during processing of biogas to power is obliged by law and/or supported by public funds. In this context, EBA would like to draw attention to possible unnecessary wasting of heat in the digestate (fermentation residue from the anaerobic digestion process) drying process, which could be considered as economically justifiable heat consumption eligible for funds.
Drying of digestate is a relatively old technology and was first introduced (and tested) in 1980‘s. The technology was supposed to transport concentrated mineral content of digestate from areas with intensive agricultural production to areas with shortages of organic and mineral supply in agricultural land. However, this concept was shortly rejected because of the dramatic reduction of nitrogen content during drying , which resulted in the degradation of fertilising effect of the digestate.
Nowadays, we observe an effort to reintroduce the digestate treatment technology in several countries in Europe. This phenomenon is related to an artificial promotion or obligation to use heat produced at biogas plants. The technical, economic and environmental scarcities of digestate drying are presented here .