The BIOTECH Plants
As the ARTIs, the BIOTECH market level plants are based on a floating-drum design including a recirculation loop to optimise moisture content (HEEB 2009). The feedstock (often market wastes) is put in the inlet tank from where it is flushed into the main digester tank for anaerobic digestion (3 m diameter and 3 m depth, HEEB 2009). To increase the retention time for solids, there is a baffle in the middle of the tank and orthogonal to the flow direction. The baffle holds back unsuspended solid compounds of the waste, whereas liquids can easily flow over (much like septic tanks or biogas digesters, see also factsheet (see also small scale digesters or biogas settlers). This leads to an increased retention time for unsuspended solids and therefore to an improved decomposition of this compounds. The digested liquor (digestate) flows into the effluent tank from where a pump, run with electricity of the produced biogas, transports it up into an overhead storage tank. From the tank, the digestate is then used to flush the feedstock from the inlet tank into the digester tank avoiding the need of fresh water for flushing (HEEB 2009).