How Treatmant Works
What Is Wastewater?
Wastewater, liquid waste, and sewage are terms for "used" water and the wastes that it carries. Basically, they are terms for what is flushed down the toilet or washed down the drain. Wastewater can also include rain water, groundwater or snow melt (inflow and infiltration) that make their way into sanitary wastewater pipes. It includes fats and grease, organics, minerals and chemicals in solution/ suspension in the water.
Wastewater treatment is essential to protect our water resources, the environment, and human health. Treated wastewater can also produce useable resources such as water, biosolids, heat, and electricity.
Wastewater drains into a network of pipes maintained by sewer serviced municipalities and the Regional District of Nanaimo. Sewer systems are built to follow the natural slope of land, generally flowing towards the sea front. This design allows gravity to do most of the work transporting the wastewater to one of four wastewater treatment plants. For residential areas that are lower than adjacent lands or treatment plants, the wastewater must pass through a pumping station to pump the liquid into the plants. Treatment of our wastewater is an essential process that prevents contamination and destruction of our waterways, and our natural water resources.
1. Preliminary Treatment
Wastewater is pumped and gravity fed into the treatment plant through the headworks, which is composed of screens and grit tanks. The screens remove rags, sticks, plastic and larger objects. Grit tanks settle out heavy particles like sand and stones. The screenings and grit are transported to the Regional Landfill for disposal.
Following preliminary treatment, the wastewater flows into a primary settling tank where it is held for several hours allowing solid particles to settle to the bottom of the tank. Fats, oil and grease are skimmed from the tanks, dried and sent to the landfill. The settled particles, known as primary sludge, is collected and pumped to a digester or holding tanks for further treatment into into reusable biosolids. Water is removed from the biosolids, surplus water from the dewatering process is returned to the headworks.
Primary treatment allows for the physical separation of solids and grease from the wastewater, and removes approximately 50% of Biological Oxygen Demand (BOD) and 60-70% of Total Suspended Solids (TSS) to produce an effluent with BOD and TSS not exceeding 130 mg/L.
Chemically-enhanced Primary Treatment provides the addition of a chemical or chemicals at the primary sedimentation stage. During this step, a coagulant (e.g. alum) and flocculants (e.g. anionic polymer) are added to the effluent to enhance the settling of solids, further reducing TSS and BOD levels.
Presently, Greater Nanaimo and Nanoose Wastewater Treatment Plants provide Chemically Enhanced Primary Treatment. The final effluent after treatment is discharged to the Strait of Georgia.
Following primary treatment, effluent is pumped to the secondary treatment stage where it is aerated and biologically treated. It may take one of several forms; for example, either a trickling filter (French Creek) or a sequencing batch reactor (Duke Point). The growth of micro-organisms results from the consumption of organic matter in the wastewater as their food supply. The micro-organisms create a solid organic material called secondary sludge. Secondary sludge is thickened, pumped to digesters and converted into reusable biosolids. Water is removed from the biosolids, surplus water from the dewatering process is returned to the headworks.
Secondary treatment is a biological treatment process that removes up to 90 percent of BOD and TSS and produces an effluent quality with BOD and TSS not exceeding 45 mg/L.
The French Creek and Duke Point Treatment Plants discharge secondary treated effluent into the Strait Georgia.
4. Tertiary Treatment
Also known as advanced treatment, tertiary can use chemical, physical or biological treatment processes to remove wastewater constituents that cannot be removed by secondary treatment. Tertiary treatment can produce phosphorus levels less than 1.0 mg/L, BOD and TSS levels less than 5 mg/L, and low nitrogen levels.
Tertiary treatment is typically used when there is discharge to lakes or rivers and the phosphorus levels need to be significantly reduced, or if there is a desire to reclaim effluent. Currently, no treatment plants in the RDN that use tertiary treatment.
- Disinfection: Secondary effluent can be disinfected using several different methods, most commonly using, ozone or ultra-violet (UV) technology before being released into the receiving environment. Duke Point further treats its final effluent with UV disinfection.
- Odour Control: For more information on RDN Odour Control program, visit the Odour Control page.
- Resource Recovery: It is possible to extract valuable resources from treated wastewater.
- BOD (Biochemical Oxygen Demand) is a measure of the quantity of oxygen consumed by microorganisms to break down organic matter in water. A high BOD means that there will be less oxygen; and oxygen is essential for the survival of aquatic life. Thus, high BOD levels result in the contamination of the receiving (marine) environment.
- TSS (Total Suspended Solids) are solid pollutants that would be captured on fine filter paper. They are visible in water and decrease water clarity. High concentrations of TSS can cause many problems for aquatic life.
Click HERE for a further explanation of wastewater terms.
What is liquid waste?
Liquid waste, wastewater, and sewage are terms for "used" water and the wastes that it carries. Basically, they are terms for what is flushed down the toilet or washed down the drain. Wastewater can also include rain water, groundwater or snow melt (inflow and infiltration) that make their way into sanitary wastewater pipes.
How is household water consumption connected to wastewater?
The majority of wastewater in the RDN comes from residential water use. By conserving water at home, we can reduce the cost to treat wastewater.
How is wastewater treated in the Regional District of Nanaimo?
The majority of wastewater in the RDN is treated by public wastewater (sewer) systems or privately-owned onsite systems (such as septic systems). A small number of properties are authorized by Island Health (VIHA) to use pump and haul services. Typically, pump and haul services are used by properties with failing onsite systems or by those who cannot connect to public wastewater systems and are unable to obtain Ministry of Health approval for a conventional septic disposal system.
How do I know if I'm on sewer?
If you benefit from sewer services, your property tax and/or utility bill will include a charge for this service. Most people living within Nanaimo, Lantzville, Parksville, Qualicum Beach and French Creek receive sewer services. However, some properties within municipal boundaries have a private onsite (septic) system and some people in the Electoral Areas have sewer.
What levels of wastewater treatment are provided in the RDN?
The RDN owns and operates four wastewater treatment facilities:Greater Nanaimo Pollution Control Centre (GNPCC) French Creek Pollution Control Centre (FCPCC)
All facilities provide preliminary and at least primary treatment (GNPCC and NBPCC provide chemically-enhanced primary treatment). FCPCC provides secondary treatment and DPPCC provide secondary treatment with UV disinfection. More information on the different treatment levels is provided here.
What laws regulate municipal wastewater treatment?
Municipal wastewater treatment is governed by the provincial Municipal Wastewater Regulation and federal Wastewater Systems Effluent Regulations. These regulations include mandatory minimum effluent quality standards that can be achieved through secondary wastewater treatment or better. They also include requirements for monitoring, record-keeping, reporting and toxicity testing.