45–60°C (45–60°C pasteurisation)
Also known as: pathogen kill temperature · digestate hygienisation
The temperature range used for pasteurisation or hygienisation of digestate — holding material at 45–60°C for sufficient time eliminates most pathogens including Salmonella and E. coli.
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What is 45–60°C?
The 45–60°C band defines the mesophilic-to-thermophilic transition zone where digestate is held to inactivate pathogenic microorganisms before land application. Indian SATAT-scheme CBG plants that sell Fermented Organic Manure under FCO 1985 (amended 2021) routinely target the upper end of this range — typically 55°C held for at least 24 hours — to satisfy hygienisation requirements similar to EU Animal By-Products Regulation 1069/2009 thresholds (70°C for one hour for Category 3 material).
The microbiology behind the kill window is well established. Salmonella spp. and Escherichia coli O157:H7 show population reductions of more than 5 log units when exposed to 55°C for 30–60 minutes; Listeria monocytogenes requires 60°C for similar inactivation. Helminth eggs (Ascaris) and Mycobacterium paratuberculosis are more thermotolerant and may need 60°C plus longer residence to fully inactivate. Thermophilic digestion at 50–55°C inside the digester itself provides in-situ pasteurisation, eliminating the need for a separate hygienisation tank.
Trade-offs are important. Holding at 60°C consumes 30–50 kWh of thermal energy per cubic metre of digestate, which can equal 5–8% of the plant's gross biogas output if heat recovery from engine jacket water is poor. Above 60°C, ammonia volatilisation accelerates sharply, stripping plant-available nitrogen and reducing fertilizer value by 15–25%. Below 45°C, kill rates drop below the threshold needed for FCO compliance, and the digestate fails Salmonella tests at the State Agriculture Department lab.
- Indian thermophilic digesters (52–57°C) provide built-in pasteurisation, while mesophilic digesters (35–40°C) need a separate hygienisation step.
- Hold time is as important as temperature — 55°C for 4 hours is roughly equivalent to 60°C for 1 hour in pathogen kill.
- FCO testing requires absence of Salmonella in 25 g of finished FOM and total coliforms below 1,000 MPN/g.
- Heat recovery from CHP engines typically supplies 60–70% of the energy needed for hygienisation, making the operation cost-neutral at scale.
Common questions about 45–60°C
Plain-English answers to what people most often ask.
Is hygienisation at 45–60°C mandatory for digestate use in India?
How long does digestate need to be held at 45–60°C?
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