Biological Treatment System, type FBR

The wastewater (after primary treatment) is pumped into the aeration basin, which is filled with an activated sludge/water mixture. Activated sludge are flocks of bacteria, also called biomass. In the presence of oxygen, the pollution in the wastewater will be decomposed by these bacteria.

The oxygen is supplied to the wastewater by a fine bubble diffuser system or by surface aeration. The aeration system is designed to supply optimal conditions in order to decompose the main pollutants present in the wastewater. In general the pollutants are organic compounds, comprising of carbon, hydrogen and nitrogen.

Eventually almost all the pollutants will be converted into carbon dioxide, nitrogen gas, water and excess sludge. The water flow is continuously pumped out of the aeration basin, to be processed by a special flotation unit to separate the activated sludge from the clean effluent. This flotation system is capable of handling a high solids loading and has the advantage of thickening the activated sludge up to approximately 5% dry solid content.

Microscopically small air bubbles adhere to the activated sludge, which has been reinforced by the dosing of polyelectrolyte. The sludge floats to the surface of the flotation unit where it is mechanically dewatered and skimmed off by a scraper mechanism.

Advantages of biological wastewater treatment systems, type FBR system:

  • Continuous discharge of purified water, 24 hours/day;
  • A high degree of reliability, since the sludge separation by flotation is hardly sensitive to variations in the activated sludge quality;
  • Very low suspended solids content in the effluent, compared to conventional clarifiers;
  • Small dimensioning of the aeration basin compared to conventional treatment systems with the same capacity;
  • The activated sludge flotation system is less than half the size of a onventional clarifier;
  • Very high dry solid content (3 - 5%) of the excess sludge, without the use of further dewatering equipment, resulting in only a fourth of the sludge volume retrieved by conventional systems;
  • A relatively high BOD5/COD reduction up to 99.9%.