COMPARISON OF CASS™ vs. OTHER

SBR TECHNOLOGIES

Essential Features of CASS™

1. Self-Regulating Technique for filamentous sludge bulking control through the selector and return flow of sludge biomass to that part of the reactor. This is a unique feature.
2. The selector typically allows the CASS™ reactor basin approximately 20-30% smaller than competitive systems. This derives from the use of stored carbon sources for denitrification and phosphorous removal and not having to oxidize the associated BOD.
3. CASS™ operates with interrupted flow during the decant sequence and therefore prevents any possibility of short-circuiting and effluent deterioration.
4. The CASS™ design incorporates nitrogen and phosphorous removal which is integral to the containment of filamentous sludge bulking.
5. The CASS™ VARI-SKIM™ decanter is mechanically designed to operate with a constant rate of discharge without stop-start operation. This strategy prevents straggler floc scour from the sludge blanket.
6. The floor plan of a CASS™ two basin plant is typically square. Length to width ratio of the CASS™ basins is not limited to any set proportions.
7. The CASS™ decanter support is much more robust and is designed to take up all operating stresses within the frame support.
8. The CASS™ decanter positively excludes floating materials.

Intermittent Cycle Systems:

• Intermittent Cycle Systems are designed with two compartments within the basin without the return of sludge. The first compartment is sized at between 10 and 33% of the total tank volume. In operation this section loses its biomass solids during non-aeration in-flow sequences (i.e. fill-settle), totally preventing the selectivity concept of operation. This occurs for 50% of the time in a typical four hour domestic wastewater time cycle. The inlet zone is also too large to be consistently functional. There are numerous plants which have bulking sludge because of the lack of filamentous control mechanisms.
• Operate with continuous inflow to each basin.
• Require specific length to width dimensioning to be effective. Also, the process design requires a very low F/M to enable operation with continuous flow to each basin.
• Continuous inflow results in short-circuiting of influent to the effluent decant end and hence effluent quality deterioration.
• Require additional mixing equipment to achieve phosphorous removal.
• Decanter does not (to our knowledge) have a positive floating solids excluding mechanism.
• Decanter support is embedded into the end of the concrete wall. The holding bolts have been known to give way.
• Decanter operates with a stop-start motion to approximate a continuous constant rate of discharge. This pulsing of flow causes release of straggler floc from the sludge blanket.
• Cannot be sized using credits for organic load reduction through the selector.
• Does not offer a self-regulating feature for filamentous sludge bulking control.
• The standard facility does not allow inherent nutrient removal.

Disadvantages of SBRs Utilizing Jet Aeration:

• Decanter - discharge orifices are always submerged, prone to partial clogging and partial closure on completion of discharge phase.
• Decanter requires automatic decant control valve to stop outflow from the basin.
• Discharge capacity per foot of decanter separation is less than CASS™ VARI-SKIM™.
• Flexible joint for decanter operation is subject to failure.
• Operator cannot view the quality of discharge waters flowing out of the basin because of the submerged outlet.
• Discharge rate is not constant using a floating or fixed point decanter assembly.
• Constant discharge rate requires an extra control valve/mechanism.
• Decanter consists of numerous ports which generate point source approach velocities.
• Decanter is less efficient due to porthole orifice configuration and depth of overall assembly. This enforces a limit on withdrawal rate due to interaction with the sludge layer.
• Cannot use decanter as basin emergency overflow.
• Decanter is prone to loss of MLSS during aeration sequence through poor sealing.
• Due to fill-ratio operation, cannot guarantee continuous filamentous sludge bulking control.
• Jet aeration system is prone to clogging and abrasion wear.
• Jet aeration requires fine screening of raw sewage which will increase the amount of screenings to be disposed.
• Fine screening produces contaminated screenings (fecal matter) which requires further equipment for dewatering/washing.
• Efficiency of jet aeration systems is limited. Efficiency curve is parabolic, i.e. very limited gas to liquid rate for efficient operation.
• Denitrification strategy of anoxic mixing promotes filamentous sludge bulking.
• Jet aeration efficiency drops below 3 lb. O2/HP/hr.
• Jet aeration requires blowers and pumps for operation.
• Operates with larger installed power and larger basin sizes by comparison with CASS™.
• Requires influent distribution pipe manifold the length of the basin for operation.
• Fill-ratio operation does not maximize use of basin and time. Fill-ratio operation reduces effective time available for aeration.
• Reactor and operations strategy gives limited scale-up capability, e.g. 20 MGD.