Mass and energy balances in high dry solids digestion following thermal hydrolysis pre-treatment

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Courtesy of Cambi AS

Contents of Presentation
  • Reconciling biogas production with mass balances
    • Classic VSR methods
    • Interferences in classic methods in high DS% digestion
    • COD and biogas approach
    • KPI for advanced digestion
  • Optimising energy balance for THP in CHP projects
    • Maximising sources of heat
    • Minimising uses of heat
    • The optimum energy balance

Energy in Sludge COD or VS

  • COD - Chemical Oxidation Demand is a fundamental way of measuring the energy value in sludge
  • There is a direct correlation between COD and kWh
  • In average formula biomass 1kg COD = 3.5 kWh
  • Average sludge organic matter = 1.7 kg COD/Kg VS
  • 1 kWh = 101 litres methane at 25C
  • Therefore 1 Kg VS = about 6 kWh biogas = about 920 litres
    per kg VS (at 65% CH4)
  • Mass balances that achieve more than 1m3 biogas/kg VSR for sewage sludge are dubious as it is the substrate not the process that defines the specific gas yield.

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