LESSON B3: ANAEROBIC SEWAGE TREATMENT > Anaerobic Treatment technology > High rate systems
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High rate systems

One of the major successes in the development of anaerobic wastewater treatment was the introduction of high-rate reactors in which biomass retention and liquid retention are uncoupled. The anaerobic high–rate systems enables the application of a relatively high loading rate, while maintaining long SRT at relatively short HRT due to sludge immobilisation. The main advantages and drawbacks of the anaerobic High rate systems applied for sewage treatment are shown in Table 2. In these systems, wastewater flows through the anaerobic sludge where purification takes place through complex bio - physical - chemical interrelated processes. Organic matter is converted into biogas and sludge.



Advantages

Drawbacks

  • A substantial saving in operational costs as no energy is required for aeration; on the contrary energy is produced in the form of methane gas, which can be utilized for heating or electricity production.

  • The process can handle high hydraulic and organic loading rates. Thus, the applied technologies are compact.

  • The technologies are simple in construction and operation; so they are low cost.

  • The systems can be applied everywhere and at any scale as little if any energy is required, enabling a decentralized application.

  • The excess sludge production is low, well stabilized and easily dewatered so does not require extensive costly post treatment.

  • The valuable nutrients (N and P) are conserved which give high potential for crop irrigation.

  • Need for post treatment, depending on the requirements for effluent standards.



  • No experience with full-scale application at low/moderate temperatures.



  • Considerable amount of produced biogas, i.e. CH4 and H2S remains in the effluent especially for low strength wastewater (sewage).



  • Produced CH4 during anaerobic sewage treatment is often not utilised for energy production.

Table 2: Advantages and drawbacks of anaerobic sewage treatment in anaerobic High rate systems



Different high–rate systems were developed over the last three decades including the anaerobic filter, the upflow anaerobic sludge blanket (UASB), the fluidised and expanded bed reactors and the baffled reactors.

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