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
  • of biokinetical reasons.

Consequences are in the cases of required nitrifications expensive plant extensions.

2. Our problem solution means the

Plant upgrading into fluidised bed reactors using microorganisms immobilised on adsorbing LEVAPOR-carrier.

Immobilising nitrifying bacteria on adsorbing carriers they

  • become more robust and efficient,
  • do produce lower quantities of excess sludge and
  • are able to maintain their activity even after a storage over 12 months.

3. Examples

Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms

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

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 to low temperatures (November) the nitrification has been established at 17°C within two to three weeks and kept efficient, achieving 70 to 80% nitrification over several months, despite to lower temperatures in December (12 °C).

Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms
TKN-inlet- and NH4N-/NO3N-outlet concentrations during nitrification at 10 to 17°C by immobilised microorganisms.
Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms

Nitrification performance of the plant at  different temperatures

Summary

  • immobilising of the activated sludge, nitrification has been established within 2 to 3 weeks
  • the nitrification remained stable and efficient even at lower temperatures, of 8 to 13°C and increased volumetric N-loading rates
  • the existing aeration system was proven as sufficient for a practically full fluidisation of the colonised carrier cubes.
  • removal of excess biomass from the surface of carrier cubes occurred automatically by fluidisation without any additive measure.

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

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

Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms
Pilot plants 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. Additionally 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.
Nitrification of municipal effluents in fluidised bed reactors using immobilised microorganisms
Enhanced elimination of hazardous pollutants by biomass immobilised on adsorbing, porous carrier.

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