A small sewage treatment plant was installed by W E Farrer on the slope below Canwick Hall in the early years of the 20th century.

Sewage pipes entered the plant from the left into brick lined digestion tanks covered in a concrete slab.

From here the treated sewage, now mainly in liquid state, passed through a filter bed (to the right of the photo) and emerged in an acceptably pure condition.

Note: the plant lies on private land and is not accessible to the public.

Raw sewage enters from the left.

A = inlet pipe junction and gate valves in brick chamber;

B = digestion tanks, with inlet and outlet pipes;

C = outlet channel from digestion tanks to filter bed; 

D = filter bed, with aeration pipes (cover details not shown);

E = outlet chambers with ground level outfall and higher level overflow;

F = soakaway chamber for overflow;

Drawing by Ken Redmore

Raw sewage entering the plant passed over a stone trap which collected small, dense, "foreign" items.

It then flowed into this open Y-shaped ceramic channel where the sewage could be directed into one or other of the two digestion tanks.

Metal stopper plates dropped into slots to close access to the tanks when needed.

A tank was taken out of use in this way when maintenance work had to be carried out or sludge removed.

One of the two inspection covers over the digestion chambers.

The name of W E Farrer of Birmingham and Cardiff, who manufactured and installed small sewage treatment plants across the country, is clearly shown on the cast-iron cover.

Regular access was needed for the removal of sludge from the bottom of the tanks.

This was usually done by hand with a long-handled scoop, care being taken to minimise loss of essential bacteria on the liquid surface and also to reduce exposure to the air.

Inside one of the brick-lined digestion chambers.

Raw sewage entered through the horizontal element of this T-shaped steel pipe at the level of the liquid in the tank.

The vertical part of the pipe allowed foul air to escape above the liquid surface level in the tank whilst the incoming sewage was forced to enter below surface level.

The level of liquid in the tank was kept constant by a similar exit T-pipe at the same level on other end of the tank.

Bacterial action, which required about 24 hours to complete the digestion process, took place in a "froth" on the liquid surface.

Treated effluent from the digestion tanks passed into an open horizontal channel and then through a short centrally placed pipe (shown here) which was directed towards the filter bed.

The liquid dropping from this pipe ran into a horizontal channel positioned over the centre of the filter bed cover.

A horizontal metal channel was balanced over the centre of the filter bed cover on two bearings or tipper devices (shown here).

The horizontal channel was divided longitudinally in two.

When the liquid effluent from the tank had filled one half of the channel its weight caused the channel to tip to one side and drop the liquid on that side of the cover.

The action of tipping brought the other half of the channel into position to be filled, and so, in due course, sewage was tipped over the other side of the filter bed cover.

The cover, made of corrugated iron, had regular perforations to distribute the liquid sewage across the filter bed.

Only very small fragments of the cover have survived.

This simplified textbook illustration of a Farrer plant shows the design and function of the cover over the filter bed.

This drawing suggests that the corrugated iron fragments which survive at Canwick are from a later replacement cover.

The plant illustrated here, unlike the one at Canwick, has a single digestion tank (or septic cesspool).

In the right foreground is the filter bed, approximately 5m long x 2.5m wide and 1.2m deep. 

It was filled with coke breeze or foundry slag which provided a large inert surface for aerobic bacteria to work on the effluent as it trickled down.

Essential air for the process was supplied through 8 vertical clay pipes, 3 of which can be seen in this photograph.

Fragments of the cover support can be seen lying across the surface of the bed.

Some members from the SLHA Industrial Archaeology team are examining one of the inspection chambers.

The base of the filter bed was covered with perforated tiles, of which this is a fragment.

Small lugs on each tile (seen here at the top left) kept them an inch or so above the concrete floor to allow the treated effluent to flow away underneath the raft of tiles.

The tiles at Canwick are stamped "Newham Patent Tile".

At the edge of the filter bed were two valve chambers into which filtered effluent entered.

The exit pipes, in the valve chambers at the level of the base of the filter bed, were covered by hinged and weighted cast-iron discs.

Each valve could be opened and closed by means of a shaft attached to the end of the plate.

A close-up photograph of the cast-iron valve which covered the exit pipe.

The valve plate was pivoted at a fixed point to the left and linked by free moving pivot to the upright control shaft to the right.

The valve plate bears the name:
"William H Farrer"

It has not been possible to trace the original pipes that would have dispersed the effluent.

These would probably have been loosely jointed clay pipes in a herringbone arrangement to ensure wide dispersal of the liquid.

The land below the sewage plant, once owned by the Canwick estate, was cultivated and probably gained benefit from the residual organic material in the effluent.

As shown in this photograph, the land is now part of a golf course, formed in 1972.

There is a manhole with inspection cover about 100 metres from the plant, evidence of a significant change in effluent dispersal at this time.

Shortly after World War Two Canwick Hall was converted into flats and by 1957 a total of 20 properties were connected to the sewage plant.

In order to cope with times of excessive flow of sewage a further outflow pipe was fitted near the top of one of the inspection chambers.

The outflow pipe - in effect an overflow - was linked to a brick-lined soakaway chamber, a short distance away.

Any effluent would quickly drain away through the loosely pointed brick walls and the unlined base composed of natural porous limestone.

C R Lucas and Son, a Lincoln firm, did most of the small building work on the Canwick Hall estate when it was owned by Jesus College, Cambridge, following the death of the last of the Sibthorp family.

It was this firm that constructed the additional outflow and soakway, and their name appears on the inspection cover.

Undated postcard.

Possibly the word "breakwater" on the card is being used as a euphemism for the outfall? 

A tunnel is shown here on the 25 inch OS map published 1889.

The sign in the foreground reads "Keep off outfall"! 

Located near the Quebec Road car park. 

DB 29 June 2019