Keeling’s Sewer Gas Exhausters and Destructors

An item in Charman’s Reminiscences Of Epsom  intrigued your webmaster.  Under the entry for Church Road Epsom appears:-

At the corner of Providence Place an apparatus in the form of a lamp post was erected, the invention of Mr. G.R. Keeling, a member of the local board, for destroying fever gases. This has only been moved a few years ago.

Believed to be George Ratcliffe Keeling Senior, c.1862/3
Photograph by Cuthbert John Hopkins, courtesy of Bourne Hall Museum

(The inventor was George Ratcliffe Keeling senior – see The Keelings of Epsom – and “the local board” was Epsom’s Local Board of Health, of which Mr Ratcliffe was Chairman in 1882.)

From the time of Hippocrates till the late Victorian age people thought diseases like cholera were caused and spread by foul smelling air (sometimes called night air).   This theory was known as miasma (from the ancient Greek for pollution) and the elimination of bad odours from waste became an important issue for cities and towns.

Bad smells are frequently caused by biogas formed from rotting organic matter (including the waste from the human body).  The biogas forming in sewers can build up to dangerous levels so needs to be vented to reduce the risk of explosions.  This is usually done by connecting the top of the sewer pipe to a tall, vertical open-ended vent pipe, frequently called a stink pipe. Because most gases rise these vent pipes are usually located at high points in the main sewer system.

A London Board of Health hunting after cases like cholera.

Around the 1880s inventors came up with solutions to the bad smells coming from stink pipes. One solution was to ‘burn off’ the biogas using heat but the problem with biogas is that the levels of the flammable methane it contains change during the day and from season to season. This means that you cannot rely on the biogas to be the main source of heat.

So the inventors developed sewer gas destructor lamps which used town gas to draw up the biogas from the sewer, pass it over hot plates that greatly reduced the smells and then discharge it into the air.  This was packaged into what looked like a large street gas lamp.

But by the early 1900s scientific advances into the causes of illness discredited the miasma theory and investigations into the effectiveness of sewer gas destructor lamps showed that generally they were little better than a standard stink pipe.  For a while sewer gas destructor lamps continued to be used where stink pipes were needed near tall buildings that were affected by sewer gas smells.

After a bit of research, we found an item in the British Medical Journal for 17 March 1888 which for some readers will be a bit boring and technical but is included for those who are interested in the details:

KEELING’S SEWER GAS EXHAUSTER AND DESTRUCTOR.

We are informed by the proprietor that during several months past Richmond, Ealing, Epsom, Leicester, East Dereham, and other towns have applied Keeling’s Sewer Gas Exhausters and Destructors to extract and cremate the gases arising from organic decomposition. It is urged that the discharge of sewer emanations through ground level gratings is a crude and indefensible system. Nothing, it is said, conduces to the prosperity of a town or locality so much as a high repute for pure air.

It is stated that Keeling’s apparatus has been tested by certain experts chemically as to its destructive power, and mechanically as to its economy. It consists mainly of an iron column with a powerful furnace, which produces an intense heat by the combustion of a small quantity of coal gas, and causes a strong current of air to pass constantly through it in all states of weather. The peculiarity of the furnace consists in a series of ribbed metal cones, which divides the sewer air into minute streams, and subjects it to contact with hot surfaces through a sufficient length to destroy the excess of organic matter which impregnates it.

The Ealing Local Board requested Dr. Russell, of the Chemical Laboratory, St. Bartholomew’s Hospital, to test the action of the apparatus on the Ealing sewers, and to analyse the sewer air before it enters the column, and also after it passes through it. Dr. Russell’s report was laid before the board on March 1st, and it contains the following description and results of his tests:

“In my first experiment, I introduced into the current of air 0.3 cubic centimetre of ether; this ether was completely oxidised; no smell of ether could be recognised at the top of the stove, only a slight smell of some of the products of the oxidation of the ether. The next experiment was with sulphuretted hydrogen, a gas which in extremely small quantities can be recognised by its smell, and a gas which often occurs in sewers. I generated this gas in a flask, and conveyed it by means of a tube to one of the openings at the base of the stove, so that the air passing through the stove was largely charged with this gas. Although smell is so very delicate a test for this gas, and although this gas was passed into the base of the stove for half an hour in a tolerably rapid current, not the slightest indication of any un-decomposed gas was recognisable at the top of the stove or elsewhere. The smell of the product of oxidation, sulphurous acid, was very perceptible.  The above experiments were very satisfactory.”

On February 11th the following experiments were made at Ealing Dean.

“To test fully the change brought about by passing the air from the sewer through the destructor, two kinds of experiments were made, and in each case the air delivered from the top of the destructor was compared with the air extracted at the same time from the sewer itself. Permanganate of potash is known to oxidise most organic impurities in air, and is the best indicator we have of the amount of such impurities in any sample of air. Two experiments with the air from the top of the ventilator showed, as a mean result, that it required seven volumes of oxygen to oxidise the organic matter in a million volumes of air. or as it is usually expressed, this air contained seven volumes of organic matter in a million volumes. A sample of air collected in a field near contained six volumes of organic matter in the million.” A bottle was lowered into the sewer, and by means of an aspirator filled with the air to be tested, it was found to contain twenty-one volumes of organic matter, that is three times as much; thus the heat in the destructor is sufficient to cause ” efficient oxidation of the organic matter in the sewer air, any sulphuretted hydrogen present would, as shown by the first experiments, be converted into sulphurous acid, which would act on the permanganate in the same way as the organic matter does.

The second class of experiments was to determine whether the micro-organisms or germs known to be abundant in sewer air are destroyed by the heating process carried on in this destructor. To determine this, I drew air from the top of the ventilator by means of an aspirator, for thirteen minutes, through sterilised glass wool; this wool was afterwards carefully introduced into a flask containing a cultivating medium. An exactly similar experiment was made with air from the sewer, after four days, the flasks, which had been kept at a temperature most favourable for stimulating growth, were examined; in the air which had the wool through which the sewer air had been drawn there were at least 7,000 distinct colonies or growths; two experiments with air from the top of the ventilator were made, one gave only six colonies and the other fourteen, a striking illustration of how efficiently organisms are destroyed by the method of heating used in this form of destructor. As a definite proof of the high temperature which the cones inside the destructor attain, I placed a piece of sheet lead in the inverted cone immediately above the burner; this lead became melted. The melting point of lead is known to be 617°F.”

The following data are stated to be approximately correct. A No. 6 Bray’s gas burner, regulated to consume 6 cubic feet of coal gas per hour, will give sufficient heat to exhaust and destroy 3,000 cubic feet of sewer gas per hour, or 72,000 cubic feet in 24 hours. A dozen destructors will be sufficient for a town of 20,000 inhabitants, costing for gas, on an average, £6 per annum, per destructor-less than £100 per annum for the twelve destructors. One destructor will keep a thousand yards of 12-inch  sewers clean, say in three directions. The column may also be used as a lamp column.

If sewer ventilation by a furnace is considered a desirable method of meeting the difficulty it would seem that Keeling’s destructor is an efficient means of creating a definite extraction of foul sewer air in stagnant conditions of weather, and regard less of external temperature.

Peter Reed 2022