CIGR XVII th World Congress – Québec City, Canada – June 13-17, 2010 1 XVII th World Congress of the International Commission of Agricultural and Biosystems Engineering (CIGR) Hosted by the Canadian Society for Bioengineering (CSBE/SCGAB) Québec City, Canada June 13-17, 2010 DRYING CHARACTERISTICS AND NITROGEN LOSS OF BIOGAS DIGESTATE DURING DRYING PROCESS CLAUDIA MAURER 1 , JOACHIM MÜLLER 2 1 University of Hohenheim, Institute of Agricultural Engineering – Tropical and Subtropical Group (440e) Garbenstr. 9, D-70599 Stuttgart, claudia.maurer@uni-hohenheim.de 2 University of Hohenheim, Institute of Agricultural Engineering – Tropical and Subtropical Group (440e) Garbenstr.9, D-70599 Stuttgart, joachim.mueller@uni-hohenheim.de CSBE100724 – Presented at Section IV: Rural Electricity and Alternative Energy Sources Conference ABSTRACT Digestate occurring during the fermentation of biomass in biogas plants contains high content of major plant nutrients like phosphorus, potassium and nitrogen. Due to the high water content of biogas digestate (90 – 97%) it is not economically justified to transport the digestate over longer distances. Reducing water content of biogas digestate by drying is an option to reduce volume and therefore alleviate transportation costs. However, during drying the digestate emits volatile compounds due to decomposition which are not yet sufficiently known in quality and quantity. Therefore, the objective of this study was to investigate the drying behavior and the change of digestate composition. Drying was performed in a hybrid solar/waste-heat dryer, which uses solar energy besides waste heat of a combined heat and power unit (CHP) and the exhaust air of a micro turbine. In this experiments 60 t of liquid digestate were applied. Climatic data were measured inside and outside the drying hall. Dry matter (DM) and organic dry matter (ODM) were measured on a daily basis. Furthermore, energy consumption of waste and solar heat were recorded and related to the quantity of dried feedstock. Chemical analysis of total nitrogen, ammonium, phosphate, potassium oxide, magnesium oxide and calcium oxide was undertaken before and after the drying process and losses of nitrogen were calculated. Specific energy consumption depended on the climatic conditions and most of the energy consumption was covered by the waste heat of the CHP. During the drying process a significant loss of nitrogen was observed. Keywords: Digestate, drying of digestate, nitrogen loss, hybrid solar/waste-heat dryer INTRODUCTION Germany has worldwide the highest number of installed biogas plants (Weiland 2009). In the year 2008 4,000 biogas plants were operating (FNR 2009) and about 500,000 ha of agricultural land was used to cultivate renewable feedstock (Schüssler 2009). This is equivalent to a theoretical biogas potential of 417 PJ/a, whereof 85 % arises from biogas production in the agricultural sector (FNR 2009). It is expected that no stagnation will take place in the near future. Therefore, the number of biogas plants should continue to increase as well as the amount of digestate that is a by-product of the fermentation process. Wet fermentation processes take the biggest part of the fermentation in the