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Controlling sludge settleability in the oxidation ditch process.

K J Hartley1

  • 1Ken Hartley Pty Ltd., Forest Lake, Qld 4078, Australia. k.hartley@uq.net.au

Water Research
|November 13, 2007
PubMed
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Controlling sludge settleability in activated sludge processes is achievable by optimizing the anoxic fraction. Maintaining equal effluent ammonia and nitrate nitrogen concentrations improves sludge settleability and reduces total nitrogen.

Area of Science:

  • Environmental Engineering
  • Wastewater Treatment
  • Microbial Ecology

Background:

  • Sludge settleability is crucial for efficient activated sludge process operation.
  • Oxidation ditches are widely used for nitrification-denitrification.
  • Specific sludge volume index (SSVI) is a key indicator of sludge settleability.

Purpose of the Study:

  • To develop an operating technique for controlling sludge settleability in oxidation ditches.
  • To investigate the relationship between anoxic fraction and SSVI.
  • To establish an empirical model for predicting SSVI variations.

Main Methods:

  • Utilized effluent ammonia:nitrate ratio as a surrogate for anoxic fraction.
  • Developed a three solids retention time moving average nitrogen ratio model.

Related Experiment Videos

  • Analyzed operating data from full-scale oxidation ditch plants.
  • Correlated SSVI with readily biodegradable chemical oxygen demand (RBCOD).

    • Main Results:

    • A simple empirical model accurately replicated long-term SSVI variations.
    • SSVI was found to be lowest at an optimum anoxic fraction.
    • Increased RBCOD correlated with lower SSVI.
    • Best sludge settleability occurred at an ammonia:nitrate ratio of approximately 1.

    Conclusions:

    • Optimal anoxic fraction for nitrification-denitrification activated sludge processes minimizes SSVI.
    • An operating rule of maintaining equal effluent ammonia and nitrate nitrogen concentrations is effective.
    • This operational strategy leads to improved sludge settleability and reduced total nitrogen discharge.