Fate of phosphate during anaerobic digestion of sludge from an EBPR plant

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Courtesy of Cambi Group AS

Phosphate at Whitlingham STW
  • Phosphorus Consent Requirement
    • To comply with a total phosphate limit of 1.54 mg/l on an 80%ile basis: this is equivalent to an annual average of 1.0 mg/l (UWWTR for PE’s > 100,000) assuming the usual lognormal distribution or 80% removal
    • To achieve this standard in a sustainable way, and without using metal salts
    • Enforcement Date: 31/7/04
    • 80% N removal by 2008
  • Enhanced Biological Phosphorus Removal (EBPR) plant

Enhanced Biological Phosphorus Removal

  • Cycling of activated sludge through anaerobic, anoxic and aerobic phases
  • Phosphorus is taken up from the sewage by poly-p bacteria in the activated sludge in the aerobic phase and released in the anaerobic phase
  • The mixed liquor in the anaerobic phase must be fully depleted of dissolved oxygen and oxidised nitrogen - this is accomplished by passing the activated sludge through an anoxic zone prior to the anaerobic zone
  • The presence of soluble, readily biodegradable COD (SRBCOD), preferentially as short chain volatile fatty acids (SCVFA), promotes the release of phosphorus from the activated sludge in the anaerobic zone
  • Anaerobic/aerobic cycling must be continuous

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