Alternative Processes Considered
The alternative technologies (processes) were identified based on their potential to meet the Pulp and Paper Effluent Regulations, minimize environmental risks, and be cost effective.
The recommended process was then selected based on the following criteria:
- Optimization - What process will reliably result in quality treatment, given the characteristics needing to be treated?
- Efficiency - Can the process treat the volume of effluent?
- Economic Viability - Can the process allow for the continued viable operation of the mill?
- Flexibility - Can the process operate across operating conditions? (e.g. seasons)
- Footprint - Can the process fit on the mill property, without impacting adjacent natural features and property owners?
Several treatment process alternatives and combinations were considered. These included:
- Sequencing Batch Reactors;
- Rotating Biological Contactors;
- Biological Aerated Filters;
- Moving Bed Bio-Reactors;
- Anaerobic Treatment;
- Tertiary Treatment; and
- Closed Loop (Zero Effluent).
The evaluation concluded that an activated sludge treatment (AST) process is recommended.
The other treatment technologies had a variety of drawbacks including capability to treat the specific type and volume of effluent from the NPNS facility. System reliability was also considered. Tertiary treatment, for example, was not chosen due to the significant footprint requirements, high operating costs and potential for that system to not operate properly through different seasons of the year.
Closed Loop System
At the onset of the design phase a closed loop (zero effluent) treatment alternative was immediately ruled out as it is not an option for Northern Pulp. A closed loop system does not exist anywhere in the world for an elemental chlorine free (ECF) bleached kraft pulp mill.
The concept is not technically or economically achievable.