Comparison of pasteurization and integrated thermophilic sanitation at a full-scale biogas plant - Heat demand and biogas production

Sanitation is required for biogas plants handling slaughterhouse and food waste according to EU legislation. The standard method is pasteurization at 70 °C for 60 min, but integrated thermophilic sanitation (ITS), requiring 52 °C for 10 h in the digester, has been approved by the Swedish Board of Agriculture. This work compares pasteurization and ITS regarding heat demand and biogas production, using a full-scale plant in Uppsala, Sweden, as a case study. The plant currently uses pasteurization and thermophilic (52 °C) digestion. The impact of pasteurization on biogas production and process performance was examined at laboratory-scale. The heat demand for pasteurization was surveyed at the full-scale plant, while for ITS a process design was developed and the heat demand was theoretically calculated. The results showed that pasteurization had no significant effect on process performance or biogas production. The heat demand of pasteurization was measured to be 1.92 ± 0.29 MJ (kg VS)−1 (64.7 kWh t−1), while ITS was calculated to require 1.04 MJ (kg VS)−1 (35.1 kWh t−1). This represented 9% and 5% of biogas energy production, respectively. Changing sanitation method to ITS would hence reduce the heat demand at the plant by 46%, corresponding to annual savings of 4380 GJ (1.22 GWh).