Liquid Process Alternatives Evaluation: DP034-1

Discussion Paper Summary

The Core Area Wastewater Management Project consists of four key elements:

  • Source Control
  • Distributed wastewater treatment
  • Water reuse and resource recovery
  • Wet weather flow management

Distributed treatment will include a secondary treatment plant at Macaulay/McLoughlin Point, where much of the liquid treatment will occur. In order to better plan for the type and size of plant needed at the Macaulay/McLoughlin Point site, CRD consultants studied the options available for liquid treatment, including technologies, process alternatives and the footprint needed for each. Both primary and secondary treatment technologies were studied, to find the best combination of the two for the limited size of the Macaulay/McLoughlin Point site.

Primary Treatment Technologies

The three technologies studied included conventional primary clarifiers, Lamella clarifiers and Actiflo®.

Conventional Primary Clarifiers
CPCs use a settling process in a calm basin to remove solids through gravity. About 40-60% of solids can be removed in this way. CPCs require no chemicals but require a significantly larger footprint.

Lamella Clarifiers
Lamella clarifiers use plate settlers, which are used to decrease the footprint of primary settling tanks. Parallel, inclined plates in rectangular sedimentation plates allow the wastewater to flow in a current; settled solids slide down the inclined plates to a basin below.

Actiflo®
Actiflo is a proprietary high flow clarification system that uses sand and lamella tube settling to produce clarified effluent. More solids can be removed than in traditional methods of clarification and the process occurs rapidly, however, chemicals and sand must be used.

Conclusions

Overall, Lamella clarifiers were found to be the best solution for the site. A Lamella clarifier layout can accommodate technology advances and will not limit the process selection in the detailed analysis phase.

Secondary Treatment Technologies

The three treatment technologies considered for this phase were conventional activated sludge, biological aerated sludge and membrane bioreactor.

Conventional Activated Sludge
CAS is a well proven suspended growth process. Wastewater is directed to a bioreactor where it mixes with activated sludge. After transfer to a secondary clarifier, a portion of the solids are returned to the primary clarifier to facilitate continued digestion.

Biological Aerated Filters
BAF is an attached growth process that uses a submerged, aerated reactor on a surface bed of clay or synthetic granules. BAF eliminates the need for a secondary clarifier, as effluents are produced with low total suspended solids (TSS). This process also has a footprint of up to 50% less than a CAS system.

Membrane Bioreactor
The MBR is a suspended growth activated sludge process in which the final liquid/solid separation is done using micro- or ultra-filtration. MBR differs from CAS in that treated effluent is separated using membranes instead of secondary clarifiers, the absence of which results in a decreased footprint.

Conclusions

Both BAF and MBR systems could be used successfully at Macaulay/McLoughlin Point, but MBR systems can handle a higher strength of wastewater effluent. As Macaulay/McLoughlin will be receiving sludge from distributed plants in its incoming wastewater, MBR was selected as the best technology in this evaluation.

Findings

Lamella primary clarifiers were chosen along with Membrane Bioreactors to provide information that will be used to develop a preliminary plant layout for the Macaulay/McLouglin Point wastewater treatment plant. This choice will not rule out other viable choices from being selected as more detailed analysis is performed.