How Wastewater Treatment Works
How does wastewater treatment work?
Wastewater treatment can encompass a number of steps, which filter, clarify and clean wastewater from start to finish. Currently, the CRD region employs a variety of wastewater treatments, some of which filter and some of which provide secondary treatment.
Preliminary Treatment
Preliminary treatment screens out coarse solids (rocks, rags, plastics, etc.) and grit (sand and gravel) which are normally sent to landfill. Wastewater is screened down to 6mm sized particles at the CRD's Clover Point and Macaulay Point Facilities, where preliminary treatment is currently in effect. The screened wastewater then continues unimpeded to outfalls, where it is discharged through two deep ocean outfalls into the marine waters of Juan de Fuca Strait.
Primary Treatment
Primary treatment screens wastewater, and performs some rudimentary treatment to remove crude solids and skim off grease, oil and fat. Wastewater sits in settling tanks, which are designed to hold the wastewater for several hours. During that time, most of the heavy solids fall to the bottom of the tank, where they become a thick slurry known as primary sludge. The material that floats is also skimmed from the surface of the tanks. Both the primary sludge and skimmed material are typically pumped or trucked to a solids treatment processing plant.
Secondary Treatment
Secondary (or biological) treatment removes dissolved oxygen-demanding organic substances by using bacteria to convert degradable organic matter into bacterial cells. The wastewater is then clarified by separating treated liquid from grown bacterial cells using gravity. Bacteria and sludge is then either processed onsite or sent to a separate solids treatment facility.
Tertiary Treatment
Tertiary treatment further treats effluent to remove nitrogen, phosphorus, fine suspended particles and microbes, and to kill or disable disease-causing organisms and viruses. It is possible to treat effluent in this phase, resulting in a non-potable reclaimed water source, which can be reused in a variety of ways.
What is the CRD doing?
The CRD is exploring treatment technologies as a way of recovering wastewater components for reuse and for energy purposes. Some of the most advanced wastewater technologies emerging today occur in tertiary treatment. For more on the environmental benefits of treatment processes, read about our environmental strategy.