The RBC Process

The Rotating Biological Contactor ( RBC ) process is an efficient fixed film wastewater treatment technology. It is well-suited for secondary and/or advanced treatment in municipal or industrial applications. The process consists of corrugated plastic media arranged around a horizontal shaft, placed in a tank. The media is slowly rotated. 40% of the media surface area is submerged in wastewater. Organisms in the wastewater attach and multiply on the rotating media until they form a thin layer of biomass. This fixed film growth presents a large, active population for the biological degradation of organic pollutants.

Whilst rotating, the media transports biomass and wastewater into the air and Oxygen is absorbed. The wastewater contains dissolved oxygen and organic materials which are then diffused into the biomass and metabolized. Continuous growth of the biomass is allowed via the corrugated media which allows wastewater and air throughout the surface area. Depending on temperature, organic loading and other variables the biomass thickness varies, as the media rotates, excess biomass shears off at a steady rate, allowing for a stable process with minimal operator input. The sheared off biomass flows through the RBC system for removal in a final clarifier.

Benefits of the process:

·       Consistently high spec treated water quality

·       Stable process with minimal operator interface; microbes accommodate organic and hydraulic fluctuations

·       Low Solids Generation – RBC generate fewer, more concentrated solids than activated sludge. This results in smaller clarifiers and reduces the size of solids handling systems. The mass of solids produced by RBC is 10% to 20% less than for activated sludge, due to the longer solids retention time.

·       Modular construction allows lower upgrade and retrofit costs

·       Low noise, no odour

·       Low environmental impact, Small footprint: reduced excavation costs

·       Minimal head loss through system

·       Low power consumption and overall running costs (low whole life costs)

·       Low maintenance: simple gearbox and bearing lubrication

·       No Sludge Return – In order to maintain a large mass of microorganisms in the system, activated sludge plants need to return activated sludge that settles in the secondary clarifiers back to the aeration tank. This requires pumping and operational control. This requires energy, pump maintenance, and close process monitoring. Since the required mass of microorganisms in the RBC system is attached to the media surface, no sludge return pumping is required.

·       Reduced life cycle costs – as compared to suspended growth systems

Advantages over Activated Sludge

Activated Sludge and RBC processes use similar biological cultures, and produce high levels of treatment. The biggest difference being that RBC has over 95% of the biological solids attached to the media. This in turn allows for better process stability, because the biomass is attached to the media, the RBC system does not require recycling and since the microorganisms in a fixed film system are attached to a media, they cannot wash out with increased flows. Also fixed film systems generally have a greater mass of microorganisms, making them better able to handle organic load increases. Daily peak flows of 2.5:1 can be handled by the RBC process with no adjustment. The most attractive feature of the RBC process when compared to the activated sludge process is power consumption. RBC power consumption is approximately 25% of the activated sludge requirement. The power savings provided by RBC pays the plant back in 20 years.

·       The RBC process requires a lot less maintenance as there are fewer moving parts and less mechanical equipment

·       Nitrification: The RBC process can achieve high degrees of nitrification with only a single settling tank and without sludge recycling. Activated sludge plants require far more elaborate treatment stages to achieve nitrification.

·       RBC requires fewer operators with less experience and qualifications, leading to significant operation savings, estimated at a half of the activated sludge process but can also be fully automated allowing for only a monthly inspection thus removing the need for operators.

·       Flexibility: low flow is detrimental to activated sludge plants.

·       Upgrading: Activated Sludge’s, expansions and upgrades are difficult and costly. RBC plants, on the other hand, when loaded less than designed, typically achieve excellent effluents without additional control. Due to its modular construction, low hydraulic head loss and shallow excavations, the process is comparatively easy to upgrade and expand.

·       Sludge Characteristics: Sludge produced by the RBC process settle well, allowing shallower final clarifiers designed for higher overflow rates. Activated sludge is prone to settling problems, and requires a compaction zone for sludge recycling, leading to larger clarifiers.

Can RBC Replace Activated Sludge in larger plants?

Just like activated sludge, RBCs are a modular process and are scalable to any plant size.

However, in most cases, large wastewater treatment plants serve communities that began building their wastewater treatment plants before the invention of RBCs and therefore are committed to the activated sludge process. Thus, it is relatively uncommon for RBCs to be found at large plants. Not because they are not appropriate, but because the plants are already using the activated sludge process and it is natural to expand using the same process. However, there are cases where RBCs have been added to activated sludge plants to increase the level of treatment where a smaller footprint and reduced energy costs are desired.

Applications

The RBC process can handle:

·       Organic carbon removal (BOD),

·       Nitrification,

·       De-nitrification,

·       Phosphorous removal

·       or various combinations.

Typical applications:

·       Flows ranging from 2.5 m3/h to over 113 ML/D

·       Municipal wastewater treatment

·       Food and beverage wastewater treatment  e.g. meat packing, bakery, dairy, brewery, winery

·       Landfill leachate 

·       Refinery and petrochemical wastewater treatment

·       Pulp and paper wastewater treatment

·       Septage treatment

·       Many general industrial wastewaters

·       Aquaculture

·       Removal of colorants eg tanneries, fabric and textile industries

·       Removal of mining chemicals