Bazalgette and London's sewage
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 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.
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 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.
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.
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.