Blackburn Wastewater Treatment Plant Upgrade Study

Section 4.0 - Blackbum Treatment Options
Nitrifying RBCs
The above aerated lagoon system will be unable to produce a nitrified effluent.
Therefore, if ammonia removal is required, a mechanical process such as a
rotating biological contactor (RBC) must be added to treat the lagoon effluent
to reduce the levels of ammonia. The process would be smaller than one
needed to treat raw wastewater, as the organic loads in the lagoon emuent are
significantly reduced.
An RBC consists of a series of discs on which a fixed film of biological
material is grown and maintained. The discs are mounted on a driveshaft,
which rotates the discs through the wastewater. Oxygen is transferred to the
biomass from the atmosphere during the time that the disc is out of the
wastewater.
An RBC can be hydraulically loaded at 0.03 - 0.08 m3/m2/d for combined BOD
removal and nitrification. For separate nitrification, the hydraulic loading can
be increased slightly to 0.04 - 0.10 m3/m2/d. To treat the anticipated ADWF of
1,750 m3/d, approximately 16,700 m2 of media is required.
At wastewater temperatures below 12S°C, the size of the RBC must be
adjusted to achieve the same levels of performance. If the wastewater
temperature is as low as 4OC (lagoon effluent could conceivably be lower in
this climate), the area of the media must be increased by a factor of at least 2.5.
Therefore a total area required to achieve nitrification at 4OC is in the order of
42,000 m2. As the wastewater spends upwards of 20 days in a relatively
shallow lagoon, the temperature of the effluent entering the RBC during the
coldest periods is likely to approach 0°C. The surface area correction curves
for media, below 4OC are quite steep, and it appears impractical to size an R3C
in this temperature range.
Nitrifying RBC
Hydraulic loading rate, m3/m2/d
Temperature correction factor
Surface area, m2
Without temperature correction
With temperature correction
Number
Disc diameter, m