How the system worked
The two halves of the Main Drainage Scheme, north and south of the river, are broadly similar, and the principle upon which each is based was very simple. In short, get the sewage to the east of London, store it until high tide, then release it.
On each side, three intercepting sewers at different levels divert sewage away from the river and lead it, by gravity where possible, or by pumping where necessary, towards the outfalls at Beckton on the north and Crossness on the south. At each outfall, covered reservoirs enabled the sewage to be stored until high tide, and then discharged into the river on the ebb tide. The major pumping stations to fill the reservoirs were located at Abbey Mills near West Ham, and at Crossness itself on the south bank.
The northern system runs from Chiswick in the west via the Victoria Embankment, to Old Ford in the east. Sewers from the high ground in the north of London also join this system, combining in the Northern Outfall Sewer. The sewage is lifted at Abbey Mills, and thence by gravity to the Beckton reservoir. Abbey Mills is a splendid example of Victorian industrial architecture in the Byzantine style, and originally contained eight Cornish beam engines, now alas replaced by electric pumps.
The southern system contains three levels of intercepting sewers. The Low Level Sewer from Putney to Deptford picked up the Bermondsey branch and was joined by the High Level Sewer from Balham and the higher Effra Branch from Crystal Palace and Norwood; these combined at Deptford, and were there lifted some twenty feet to discharge directly into the Thames at Deptford Creek. By 1860, work was proceeding on the Southern Outfall Sewer, and this, when complete, took the the effluent from Deptford via Plumstead, and thence to Crossness. Here the sewage was pumped up into a reservoir 6.5 acres in extent by 17 feet deep, holding 27 million gallons, and was released at high tide to flow out on the ebb, towards the sea.
There was no attempt to treat the raw sewage: Bazalgette's concern was to get rid of it. Since the success of the enterprise rested on the use of the tides - two in each 24 hours - it follows that the reservoir had to be emptied in six hours, in order to utilise all of the ebb tide. In fact, to give some margin of safety, emptying had to take place in less time than this. And as soon as the ebb tide began to turn, the outlet culverts from the reservoir were closed by penstocks, and pumping continued, raising the incoming sewage from the deep-level culverts into the reservoir. Just before high tide in the river, the sluices connecting the reservoir and the river would be opened.
There were, of course, other regulations made concerning the supply of clean water to London at this time, but without Joseph Bazalgette's magnificent scheme, these would not have begun to deal with the essential problem - the appalling contamination of the River Thames. The success of these measures can be gauged by the fact that there was just one final outbreak of cholera in London in 1866 - just one year after HRH started the pumps at the opening ceremony.