Piloting UV disinfection at Ladysmith’s wastewater treatment plant

The Town of Ladysmith is located on the east coast of Vancouver Island with an estimated population of 9,031. The town's wastewater treatment plant currently discharges disinfected effluent from its secondary treatment process into Ladysmith Harbour. Shellfish-harvesting in Ladysmith Harbour is a significant resource for the local Stz'uminus First Nation and for the shellfish growers industry. These stakeholders are concerned about norovirus, which may be found in sewage discharge. Norovirus is a concern for shellfish health and can cause highly contagious gastroenteritis in humans if contaminated shellfish are consumed.

The plant currently uses approximately 16,700 litres/year of sodium hypochlorite for chlorination and 16,900 litres/year of calcium thiosulfate (a dechlorinating agent). Avoiding the use of sodium hypochlorite would mitigate risks associated with handling the chemical, including spills and discharging excess chlorine into the environment. It would also eliminate the requirement for regular transport of sodium hypochlorite and calcium thiosulphate from the mainland.

The town intends to pilot UV disinfection at the plant to meet the commitment set out in its Liquid Waste Management Plan. This plan was prepared in accordance with and approved by the Province of British Columbia's Ministry of Environment, which provides strategies for wastewater management over 20 to 30 years. The plan includes a recommendation to conduct a pilot study on the feasibility and cost-effectiveness of UV disinfection of the plant’s effluent, and to include inactivation of viruses as a component of the study. Vancouver Island University is also supporting the project through provision of sampling and laboratory services. It will be able to use this work in a broader study of the presence of norovirus in wastewater discharge into marine waters.

The pilot is intended to meet two objectives. First, it will accurately determine the effectiveness of UV disinfection on the post-MBBR/DAF secondary effluent that is discharged from the plant. This is because effluent quality characteristics such as total suspended solids and UV light absorbance may impact disinfection. Second, it will compare the effectiveness of UV disinfection against the current practice of chlorine disinfection on viruses, in addition to its ability to meet the currently regulated fecal coliform standard.

Innovative aspect(s): The effectiveness of UV disinfection on both bacteria and viruses in secondary waste water effluent is not well established, nor are there currently any regulatory requirements for viruses. There is great potential to develop an innovative practice to treat wastewater effluent to eliminate microorganisms, particularly norovirus, which is prevalent in effluent.

Replicability: Other coastal municipalities may use the lessons learned from this pilot in their own wastewater treatment systems. British Columbia’s Ministry of Environment, Environment Canada, Health Canada, Vancouver Island University and other coastal communities similar to Ladysmith with interests in protecting shellfish harvest areas have expressed a strong interest in this research.

Environmental benefits:

• If UV disinfection is found to be a viable alternative to chlorination and UV can replace the use of sodium hypochlorite, then the parameter of total residual chlorine will no longer need to be monitored as an indicator (because chlorine will not be used)
• The target will remain at 200 fecal coliforms/100 mL or less in the effluent post-UV disinfection, which meets the province’s regulatory discharge levels for fecal coliforms
• Reduced male specific coliphage concentration to 1 PFU/100 mL from 1,440 PFU/100 mL

Economic benefits:

• Decrease in facility operating and maintenance costs
• Increased employment, especially in the local shellfish industry
• Extended lifespan for the wastewater treatment facility due to reduced exposure to corrosive chemicals
• Stimulus for local economy

Social benefits:

• Improved public health with inactivation of norovirus reducing risks of public outbreaks of gastroenteritis from contaminated shellfish consumption
• Increased public education and awareness
• Improved access to recreation and physical activities as this project may allow recreational shellfish harvesting in areas previously closed due to sewage contamination