Sunday, June 12, 2011

An Introduction to Wastewater Treatment

Wastewater treatment technologies and their developments are significant in the lives of all people. This is true whether they are conscious of the intricate system under the earth or not. Vancouver, with its population of 2 million, produces around 1 billion liters of wastewater every single day. In cities throughout the world, wastewater must be transported and treated with care in order to contribute to creating a high standard of living for its people.

When wastewater from a city reaches a wastewater treatment plant, it goes through a pretreatment process. Here a 6mm mesh is run through the water to catch plastics or stones or any inorganic matter, which could disrupt the wastewater treatment system. After pre-treatment there are three levels of cleaning technologies available for the water; primary, secondary and tertiary.

Afterwards, the wastewater is transferred into a sedimentation tank. This step of primary treatment is primarily a physical process, where the water is allowed to settle into its different components. The oils and greases rise to float on the water, and the biological waste drops to the bottom to form sludge. This treatment stage can remove approximately 60% of TSS (Total Suspended Solids) from the wastewater. The layers are separated and the solid waste is brought to landfills treated and dried in lagoons to later be used as biosolids. In Vanoucer 2 of its 5 major treatment plants, Iona and Lions Gate plants, still only treat the water with primary treatment.

Secondary treatment can be found in the Northwest Langely, Lulu Island and Annacis island plants. The secondary treatment processes can remove up to 90 percent of the organic matter in wastewater by using biological treatment processes. Generally, anaerobic bacteria is added to the wastewater to break down sugars, fats, and short chain carbon molecules. There are many different types of secondary wastewater treatment technologies available.

The third level or stage of treatment is tertiary treatment. Few cities in the world have achieved the successful implementation of this technology. The controversy in tertiary treatment is its very high costs as well as the end product. The water is clean enough to be returned into the taps of the city. Generally populations are uncomfortable with the use of this type of water. Tertiary treatment generally includes various types of disinfection and microfiltration. It is often called ‘water polishing’ or ‘effluent polishing’.

Recently the Canadian Council of Ministers of Environment announced that all wastewater treatment facilities in the country must be at least secondary treatment plants. In the next 20 years Metro Vancouver plans to upgrade Iona and Lions Gate to fulfill these regulations, as well as fulfill the city’s own sustainability goals.

Click here for a nice explanation of wastewater treatment with visuals:

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