The shortcomings of Bazalgette's scheme
Although Bazalgette's achievement was huge, his system simply shifted the problem downriver. As the sewage was discharged into the Thames untreated, problems were building up. Large mudbanks of sewage began to form downriver from the outfalls. Even worse, the sewage took a long time to clear the Thames, as incoming tides brought it back part of the way.
|The Princess Alice disaster. © NMM|
The dreadful state of the river near the outfalls was highlighted by the Princess Alice tragedy of September 1878. The pleasure steamer sank after a collision with a collier in Galleons Reach, not far from Beckton.
|The Princess Alice disaster: bringing the dead ashore at North Woolwich Pier. © NMM|
Around 650 people died that evening in the biggest ever disaster on the Thames. Few of the victims died in the actual collision - most drowned in the toxic combination of raw sewage and industrial pollutants.
A Royal Commission gathered in 1882 to debate the next step. It recommended chemical treatment of the sewage. From 1887, the liquid effluent was separated from the solid sludge. Only the former was discharged into the river. The sludge was removed by special boats for disposal at sea.
|The sludge vessel Henry Ward (1923). © NMM|
The sludge boats
Surprisingly, the best description of the work of London’s sludge boats comes from a sermon by the distinguished Methodist preacher William Sangster (1900-60). Always eager to use unconventional associations in his sermons, he used sludge disposal as a metaphor for divine forgiveness.
London has four sludge vessels. They are tankers really, with a cargo-carrying capacity of 1,500 tons. On every weekday tide, two of the sludge vessels set out laden with this unwanted and perilous matter and travel down the Thames to Black Deep, a depression on the bed of the ocean, fifteen miles off Foulness.
When the vessel reaches Black Deep, the valves are opened and the complete cargo runs out in about twenty minutes. Down it goes, down into the salt aseptic sea. A dark stain spreads over the wake of the ship, but so wide is the ocean, and so deep the delivery, and so briny the sea that, within one hour, samples of water taken either from the surface of the sea, or the bed of the estuary prove to be completely innocuous. The sludge has gone, devitalized of all evil power, and never
Full circle - changes in the 1990s
Since the 1990s, the treatment of London's sewage has changed again. To comply with European Union legislation forbidding the dumping of sewage at sea, this method has been discontinued.
|Bridge carrying the Northern Outfall Sewer over the River Lea. © NMM|
Almost half of London's sewage sludge is now sold in pellet form as a fertilizer for agriculture.
Intriguingly, London's sewage has now come full circle, as much of it now fulfils the same functions as the night soil of centuries past.