Pilot-scale, two-stage, thermophilic batch anaerobic digestion of sugar beets
Whole sugar beets without the tops and without size reduction were anaerobically digested in a batch, two-stage, thermophilic, pilot-scale digestion system. The two-stage system consisted of a solids digester (SD; 150 L working volume) into which the sugar beets were loaded and an anaerobic filter (AF; 600 L working volume). The methane yield from the system was 305 L at STP/kg volatile solids (VS) loaded and was obtained within 17 days. This is equivalent to 52 L of methane at STP/kg sugar beet as received from the stockpiles. 60% of the methane was formed in the AF and the rest in the SD. The methane yield from this pilot system was 80% of that obtained in laboratory scale trials. 90% of the total methane produced in the AF was collected within 10 days. A 10 day residence time would yield a total of 256 L at STP/kg VS or 84% of total yield from pilot scale system. The digester required addition of nitrogen and phosphorus nutrients. The biogas may not require hydrogen sulfide clean up before utilization.