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Rotating biological contactor

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Rotating biological contactor

Schematic diagram of a typical rotating biological contactor (RBC). The treated effluent clarifier/settler is not included in the diagram.

A rotating biological contactor or RBC is a biological degradation of the wastewater pollutants takes place.

Operation

A schematic cross-section of the contact face of the bed media in a rotating biological contactor (RBC)[6]

The rotating packs of disks (known as the media) are contained in a tank or trough and rotate at between 2 and 5 revolutions per minute. Commonly used plastics for the media are polythene, PVC and expanded polystyrene. The shaft is aligned with the flow of wastewater so that the discs rotate at right angles to the flow with several packs usually combined to make up a treatment train. About 40% of the disc area is immersed in the wastewater.

Biological growth is attached to the surface of the disc and forms a slime layer. The discs contact the wastewater with the atmospheric air for oxidation as it rotates. The rotation helps to slough off excess solids. The disc system can be staged in series to obtain nearly any detention time or degree of removal required. Since the systems are staged, the culture of the later stages can be acclimated to the slowly degraded materials.

The discs consist of plastic sheets ranging from 2 to 4 m in diameter and are up to 10 mm thick. Several modules may be arranged in parallel and/or in series to meet the flow and treatment requirements. The discs are submerged in waste water to about 40% of their diameter. Approximately 95% of the surface area is thus alternately submerged in waste water and then exposed to the atmosphere above the liquid. Carbonaceous substrate is removed in the initial stage of RBC. Carbon conversion may be completed in the first stage of a series of modules, with nitrification being completed after the 5th stage. Most design of RBC systems will include a minimum of 4 or 5 modules in series to obtain nitrification of waste water.

Aeration is provided by the rotating action, which exposes the media to the air after contacting them with the wastewater, facilitating the degradation of the pollutants being removed. The degree of wastewater treatment is related to the amount of media surface area and the quality and volume of the inflowing wastewater.

History

The first RBC was installed in West Germany in 1960, later it was introduced in the United States and Canada. In the United States, rotating biological contactors are used for industries producing wastewaters high in Biochemical Oxygen Demand (BOD)(e.g., petroleum industry and dairy industry).

Secondary clarification

Secondary clarifiers following RBCs are identical in design to conventional humus tanks, as used downstream of trickling filters. Sludge is generally removed daily, or pumped automatically to the primary settlement tank for co-settlement. Regular sludge removal reduces the risk of anaerobic conditions from developing within the sludge, with subsequent sludge flotation due to the release of gases.

See also

References

  1. ^ C.P. Leslie Grady, Glenn T. Daigger and Henry C. Lim (1998). Biological wastewater Treatment (2nd Edition ed.). CRC Press. ISBN 0-8247-8919-9. 
  2. ^ C.C. Lee and Shun Dar Lin (2000). Handbook of Environmental Engineering Calculations (1st Edition ed.). McGraw Hill. ISBN 0-07-038183-6. 
  3. ^ Tchobanoglous, G., Burton, F.L., and Stensel, H.D. (2003). Wastewater Engineering (Treatment Disposal Reuse) / Metcalf & Eddy, Inc. (4th Edition ed.). McGraw-Hill Book Company. ISBN 0-07-041878-0. 
  4. ^ Frank R. Spellman (2000). Spellman's Standard Handbook for Wastewater Operators. CRC Press. ISBN 1-56676-835-7. 
  5. ^ Mechanical Evolution of the Rotating Biological Contactor Into the 21st Century by D. Mba, School of Engineering, Cranfield University
  6. ^ Beychok, Milton R. (1967).  

External links

  • Design Criteria for Rotating Biological Contactors
  • Implementing Rotating Biological Contactor Solutions
  • Applying the Rotating Biological Contactor Process
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