Canvey Island Sewage Works

Canvey Island

In early 2012 we had a visit to the Anglian Water treatment works by Thorney Bay. As someone mentioned on our Facebook Page “I think this is a real treasure on the island, so glad your covering it!”. In 2012 we visited the site accompanied by an Anglian Water employee who showed us how the site works. The site that lays at the southern end of Thames Road, was officially opened in 1967.

Historical Background

Canvey Island, situated on the North side of the Thames Estuary above Southend, is at a level of 8 ft. below normal tides. In about the year 1620 it was drained and dyked by Dutch engineers who were given land in recompense of their services. Some of the original Dutch houses have been preserved and many roads bear Dutch names. The flat terrain dictates the subdivision of foul drainage into small zones, each having its own pumping station to lift the flow to the next zone until it reaches the main pumping station at Long Road: sewage, therefore, tends to be septic on arrival. There is also some infiltration of saline ground water. The Long Road pump station was constructed thirty years ago to pump the sewage through an 18 in. rising main to a 24 in. outfall main laid through the sea wall and extending 500 ft. into the river. New pumps have been installed in the pumping station and a new 24 in. rising main laid in parallel to the existing 18 in. main. Both these rising mains now discharge to the treatment works which are situated at such an elevation that the effluent will discharge to the River at all states of the tide through the existing outfall pipe. – This was included in the brochure from it’s official opening.

How it works

Today, the site is still used on a daily basis. (For those of you that like ‘technical bits’ then you’ll love this as it explains what the site does.) You can see some of the site in our short video below, of some clips of the site. Canvey Island Sewage Treatment Works is an “Activated Sludge” treatment site taking in and treating all the waste water flows from Canvey Island. It is fed from the Terminal Pumping Station in Long Road which is in turn fed by many smaller pumping stations all over the island. The flow enters the site and first passes through large screens to remove mainly rags but also any other large objects which would cause problems to the process should they get through, any flows during storm conditions which the works is not capable of treating overflow a weir and after screening is discharged to sea. Next the flow passes through a grit collector which removes all the smaller heavy objects which would cause blockages and wear to pumps, pipework etc. These 2 parts of the treatment process are known as Preliminary Treatment.

The flow then passes through tanks know as Primary Settlement Tanks (PST’s) and is called Raw Sewage where the flow is slowed right down and enables the heavier solids in the flow to sink to the bottom of the tank where it is removed and tankered off site to a treatment centre off Canvey in the local area usually Rayleigh, Basildon or Tilbury. This mass of settled solids is known as sludge and this part of the process is known as Primary Treatment. The flow from the PST’s now enters a large tank called an Aeration Tank filled with what is called Settled Sewage. This liquid is now free from rag, grit and settleable solids and is just cloudy waste water. The tank is full of bacteria and other micro organisms that feed on the organic matter in the cloudy water and are constantly fed with oxygen to promote an ideal environment for them to exist and multiply. The contents of this tank are known as Activated Sludge and the process is called Secondary Treatment. After the flow has passed through this tank which may take anything from 6 to 24 hours it passes through 2 more settlement tanks known as Final Settlement Tanks where the once cloudy sample full of suspended fine solids now settle to the bottom of the tank and are removed as was the sludge in the PST’s. The now clear treated liquid passes over a weir and is discharged to sea and has to comply with srtict consent parameters layed down by the Environment Agency. This process takes place constantly day in day out throughout the year.

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