How Treatment Works

Wastewater treatment is essential to protect our water resources, the environment and human health. Wastewater refers to ‘used’ water or anything that is flushed down the toilet or washed down the drain.  

Collection System 

To begin treatment, wastewater from households and businesses must travel to a treatment facility. . First, the collection system moves wastewater through an interceptor to the pump station. In Nanaimo, Lantzville, Parksville and Qualicum Beach, as well as on Snuneymuxw First Nation Lands, the collection system is operated by those communities. In Electoral Areas A, E and G, the Regional District of Nanaimo operates six small collection systems.  Sewers are built to follow the natural slope of land, allowing gravity to do most of the work to transport wastewater. Low elevation areas use a pump station to pump the wastewater to a treatment plant through a forcemain.   

Types of Treatment  

The RDN owns and operates four wastewater treatment facilities, providing different types of treatment: 

• Greater Nanaimo Pollution Control Centre (GNPCC) provides secondary treatment 

• French Creek Pollution Control Centre (FCPCC) provides secondary treatment 

• Nanoose Bay Pollution Control Centre (NBPCC) provides chemically enhanced primary treatment 

• Duke Point Pollution Control Centre (DPPCC) provides secondary treatment with UV disinfection 

Preliminary Treatment  

Wastewater entering the treatment plant first passes through screens and grit tanks. The screens remove rags, wipes, 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. 

Primary Treatment  

After preliminary treatment, wastewater flows into a primary settling tank where it is held for several hours. Time and gravity allow solid particles to settle to the bottom of the tank. The settled solids, known as primary sludge, are collected and pumped to a digester for further treatment into reusable biosolids. 

Fats, oil and grease that float to the top of tanks, are skimmed off, dried, and sent to the landfill. Chemically enhanced Primary Treatment adds clumping compounds (a coagulant and flocculant) to enhance the settling of solids.  

Primary treatment removes about half of the Biological Oxygen Demand (BOD) and 60-70% of Total Suspended Solids (TSS), to produce effluent with a BOD and TSS not exceeding 130 mg/L. 

Secondary Treatment  

Following primary treatment, effluent is pumped to the secondary treatment stage where it is aerated and biologically treated. 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 more than 90 percent of BOD and TSS and produces an effluent quality with BOD and TSS not exceeding 45 mg/L. 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 often 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 facilities in the RDN use tertiary treatment. 

Frequently Asked Questions