Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms

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Courtesy of LEVAPOR GmbH, Biofilm Technologies

1. The problem

Existing municipal effluent treatment plants designed earlier for the BOD removal are usually not suitable for nitrification at low temperatures, because of :

  • Small plant dimensions and low sludge age, respectively
  • Biokinetical reasons.

Consequences are that in the cases of nitrification expensive plant extensions are required.

2. Our problem solution results in

Plants being upgraded into fluidised bed reactors using microorganisms immobilised on adsorbing LEVAPOR-carrier.

Nitrifying bacteria immobilised on adsorbant carriers become more robust and efficient, produce lower quantities of excess sludge and are able to maintain their activity even after a storage over 12 months.

3. EXAMPLES:

A. Upgrading of a small municipal WWTP with aerated basin of 45 m³, for nitrification in winter, by filling it with 12 vol.% of LEVAPOR carrier

Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms

As a possible alternative to plant extension, it was considered to establish the nitrification by a susequent WWTP- upgrading via immobilisation of nitrifying sludge on 12 vol.% of adsorbing LEVAPOR-carrier.

Process data

Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms

Results:

After addition into the basin the carrier cubes became colonised and fluidised directly and despite the low temperatures (November) the nitrification was established at 17°C within two to three weeks and kept efficient achieving 70 to 80% nitrification over several months, despite even the lower temperatures in December (12 °C).

Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms
Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms

Nitrification performance of the plant at different temperatures

Summary

  • Immobilising the activated sludge, nitrification was established within 2 to 3 weeks.
  • The nitrification remained stable and efficient, even at lower temperatures, of 8 to 13°C with increased volumetric N-loading rates.
  • The existing aeration system was proven as sufficient for almost a complete fluidisation of the colonised carrier cubes.
  • Removal of excess biomass from the surface of the carrier cubes occurred automatically by fluidisation without any additional measure.

B. Nitrification and removal of hazardous pollutants from municipal effluents ( pilot plant trials)

Comparison of immobilised -LEVAPOR-carrier - vs. suspended sludge

Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms
In two parallel operated fluidised bed reactors, each of 3,1 m³, nitrification and hazardous pollutant removal of immobilised and suspended biomass have been compared. In addition to higher degree of nitrification and denitrification ( due to inner pores of carrier cubes ), immobilised biomass achieved also a remarkably higher removal of polycondensed aromatic compounds.

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