Digester Process Analyzers — Biogas Plants

Online and laboratory analyzers used to monitor digester health, biological stability, and loading conditions in anaerobic digestion systems.

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Technician rule: If gas quality drops suddenly, check pH, VFA, and ammonia before touching gas analyzers. Most biogas issues start in the digester, not the gas line.

Why Digester Process Monitoring Is Critical

  • Prevents digester souring and biological collapse
  • Maintains stable methane production
  • Detects overload and toxic conditions early
  • Improves long-term digester life

Key Parameters Measured

  • pH: biological operating window indicator
  • VFA: volatile fatty acid accumulation
  • Alkalinity: buffering capacity
  • Ammonia (NH₃/NH₄⁺): toxicity risk
  • Temperature: mesophilic / thermophilic control

Common Analyzer Types

  • Online pH analyzers (submersible / flow-through)
  • VFA analyzers (online or lab-based)
  • Alkalinity titration systems
  • Ammonia analyzers or ISE sensors

Typical Installation Locations

  • Digester slurry recirculation lines
  • Digestate outlets
  • Laboratory sampling points
  • Equalization and feed tanks

Common Plant Problems

  • Sudden pH drop due to organic overload
  • VFA accumulation causing methane reduction
  • Ammonia inhibition from protein-rich feed
  • Poor probe life due to fouling and scaling

Maintenance & Best Practices

  • Regular probe cleaning and inspection
  • Calibration using fresh buffer solutions
  • Cross-check online readings with lab tests
  • Trend monitoring rather than spot values

Discussion

Share digester failures, VFA excursions, ammonia inhibition cases, and recovery strategies from real biogas plants.