Rotating biological contactor
It consists of a series of closely spaced, parallel discs mounted on a rotating shaft which is supported just above the surface of the wastewater.
As the micro-organisms grow, they build up on the media until they are sloughed off due to shear forces provided by the rotating discs in the sewage.
Approximately 95% of the surface area is thus alternately submerged in waste water and then exposed to the atmosphere above the liquid.
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.
RBC's regularly achieve the following effluent parameters for treated waste water: BOD5: 20 mg/L, Suspended Solids: 30 mg/L and Ammonia N: 20 mg/L.
Better discharge effluent parameters can be achieved by adding a tertiary polishing filter after the RBC to lower BOD5, SS and Ammonia Nitrogen.
An additional UV or Chlorination step can achieve effluent parameters that make the water suitable for irrigation or toilet flushing.
Secondary clarifiers following RBCs are identical in design to conventional humus tanks, as used downstream of trickling filters.
This issue was successfully addressed by Eric Findlay C Eng when he was employed by Severn Trent Water Ltd in the UK following a period of failure of a number of plants.
