Discuss process design consideration for Rotating Biological Contactors (RBC).
Answers
Rotating biological contactors (RBC), also called rotating biological filters, are fixed-bed reactors consisting of stacks of rotating disks mounted on a horizontal shaft. They are partially submerged and rotated as wastewater flows through. They are used in conventional wastewater treatment plants as secondary treatment after primary sedimentation of domestic grey- or blackwater, or any other biodegradable effluent. The microbial community is alternately exposed to the atmosphere and the wastewater, allowing both aeration and assimilation of dissolved organic pollutants and nutrients for their degradation.
Advantages
High contact time and high effluent quality (both BOD and nutrients)
High process stability, resistant to shock hydraulic or organic loading
Short contact periods are required because of the large active surface
Low space requirement
Well drainable excess sludge collected in clarifier
Process is relatively silent compared to dosing pumps for aeration
No risk of channelling
Low sludge production
Disadvantages
Continuous electricity supply required (but uses less energy than trickling filters or activated sludge processes for comparable degradation rates)
Contact media not available at local market
High investment as well as operation and maintenance costs
Must be protected against sunlight, wind and rain (especially against freezing in cold climates)
Odour problems may occur
Requires permanent skilled technical labour for operation and maintenance