Collected wastewater flows to one of Metro Vancouver's five sewage treatment plants to be treated before being released into the Fraser River, Burrard Inlet or the Strait of Georgia.

Wastewater contains a number of different types of waste products, some of which are called suspended solids. Suspended solids are a key component of wastewater because, as they break down naturally, the decaying process uses up oxygen in the water. One important measure of this process is the biochemical oxygen demand placed on the water by the breakdown of the total suspended solids.

Reduced levels of oxygen available in water can create problems for marine and aquatic life. It is because of this need for oxygen that the treatment process is designed to remove the total suspended solids (TSS) and reduce the biological oxygen demand (BOD) of the treated effluent. 

Primary treatment
Primary treatment is a mainly mechanical process that removes between 30 and 40 per cent of BOD and 50 per cent of the TSS. Iona Island and Lions Gate Wastewater Treament Plants both provide primary treatment to the wastewater before the effluent - the remaining water - is released into the surrounding marine environment. 

Secondary treatment
Secondary treatment is a biological process that removes up to 90 per cent of BOD and the TSS. Lulu Island, Annacis Island and Northwest Langley Wastewater Treatment Plants provide secondary treatment to the wastewater before the effluent - the remaining water - is released into the Fraser River. 

Ongoing expansion and improvements
Metro Vancouver is constantly working on improvements to the wastewater treatment plants. These changes have increased system capacity to accommodate population growth in the Lower Mainland as well as to improve the efficiency of the treatment process.

 current sewerage construction projects