In preliminary treatment, large solid material is screened out before sewage receives further treatment or is released into the environment. Preliminary treatment alone does virtually nothing to reduce suspended solids, biological oxygen demand (BOD), bacteria, or toxins. Sewage which has been given preliminary treatment still represents a serious environmental and human health hazard and therefore cannot be considered "treated" at all.
In this region, Victoria is the only community that routinely uses only preliminary treatment. The "Core" area of Victoria consists of the City of Victoria, Oak Bay, Esquimalt and Saanich and has a population of about 300,000. The two preliminary treatment plants that serve the Core area discharge a total of 335,000 cubic metres (88 million gallons) of sewage every day.
Primary treatment is a physical process in which the sewage flow is slowed down in settling tanks or lagoons. The thicker part of the wastewater -- the sludge -- is then removed from the bottom and disposed of in a variety of ways. Floatable solids, oil and grease are usually skimmed off the surface before the remaining effluent is discharged into a waterbody.
Conventional primary treatment removes 25-40% of the BOD and 40-60% of the total suspended solids. With the aid of chemicals, these two components can be reduced by 50% and 90% respectively. Primary treatment reduces fecal coliform levels by 45-55%. It removes about half of the metals but little if any of the other toxics.
The Greater Vancouver Regional District releases 2.3 million cubic metres (605 million gallons) of primary treated effluent into the Fraser River and Georgia Strait every day. Other British Columbia facilities using only primary treatment include Campbell River and Ladysmith.
In the US, the federal Clean Water Act generally requires all jurisdictions to use at least secondary treatment. There have been substantial delays in implementing this requirement. In Washington, King County Metro's West Point and Alki facilities are still using primary treatment, as is the treatment plant for the city of Concrete. The West Point facility is in the process of upgrading to secondary treatment, while sewage now going to the Alki facility will be rerouted to secondary treatment facilities. Metro expects these upgrades to be complete by January 1996. Concrete's primary treatment facility will be improved in the near future, but secondary treatment will not be considered until 1997 at the earliest.
アメリカでは、連邦のClean Water Actは一般的に少なくとも第二の処理を使用するためにすべての管轄権を要求する。 この要求を実施するのに十分な猶予がある。ワシントンでは、King County Metro's West PointやThe West Point 工場が 第二処理へアップグレードする過程に入るが、一方でAlki工場へ現在入る工場は別ルートで第二処理工場へ送られる。 主要都市圏はそれらのアップグレードが1996年の1月に完璧になるだろうと予期している。 コンクリートの初期処理工場は近い将来改良されるが、しかし第二処理は早くても1997年までは検討されないだろう。
BC government policy is to require all communities to have a minimum of secondary sewage treatment. However, no specific time frame has been established to fully implement this policy. According to the Ministry of Environment, the implementation schedule will depend on the assimilative capacity of the receiving environment, the ability to pay for treatment works, population growth, and public input. The Ministry is currently working on developing new Municipal Sewage Discharge Criteria to replace the existing criteria, set in 1975. It is highly unlikely that any new permit application would be approved for primary treatment, but it is not clear when (or whether) existing systems will be forced to upgrade to secondary treatment.