London's microbiota - a torch for Carting Lane
10 Dec 2019
Night and day a light burns brightly in Carting Lane, a quiet street between the Strand and Savoy Place. Its purpose is to protect Londoners from bacterial metabolites. The light belongs to Webb’s Patent Sewage Gas Destructor lamp, the last of its kind in London, patented in 1895 by a Birmingham builder, Joseph Edward Webb, to improve “the extraction from sewers of the gases or vapours collected or generated therein, and the destruction of such gases prior to their passing into the atmosphere”.
The problem of London’s sewage was notorious in the 19th century when all the city’s effluent found its way into the Thames, where it made its way sluggishly down to the sea, ebbing and flowing with every tide. As a result, the river became an open sewer: the source of foul smells and pathogens. This shameful situation was eventually dealt with, not by microbiologists but by engineers, most notably Joseph Bazalgette, Chief Engineer to the Metropolitan Board of Works, who transformed London by building a number of east-west sewers to intercept the waste before it reached the Thames, and carry it eastwards for discharge downstream. Plans for dealing with the scandal of London’s sewage had been grinding very slowly through the system for many years but famously received their final impetus from what is known as the Great Stink of 1858 when, in a very hot summer, the smell outside the Houses of Parliament was so severe it caused a wholesale retreat of Lords and MPs from rooms bordering the Thames and serious discussion of the possibility of temporarily abandoning the Palace of Westminster altogether. It seems that, apart from the will of the electorate, nothing galvanizes politicians into action more than the smell of over-ripe sewage on a hot summer’s day because by the following year Bazalgette had begun to build. His system of 83 miles of new sewers was essentially complete by 1865 and still plays a major role in dealing with London’s sewage to this day.
Removal of the sewage from public water courses into a closed system was obviously a major step forward, but some problems still remained, most notably the absence of any biological treatment of the sewage downstream, which came later at Beckton, now the largest sewage treatment works in Europe. Another was from the bacterial decomposition of sewage which occurred while it was still in transit in the system. Since this is a largely anaerobic process, the sewage gas it produces contains a cocktail of reduced compounds such as methane, a potential explosion risk, and unpleasantly malodourous (and toxic) compounds such as hydrogen sulfide arising from sulphate reduction. Fortunately, their low oxidation state means that they can be oxidized by burning in air thus removing the explosion and nuisance risk, and this is the basis of Webb’s invention.
The presence of methane in sewage gas has led to the common misconception that it also fuels the Webb lamp and has led some to refer to Carting Lane with a name that rhymes and is somehow felt more appropriate. In fact the lamp is powered by natural gas (originally coal gas), the sewage gases are drawn up a tube from the sewer below by the heat in the lamp and are incinerated at the high temperatures created in the specially designed lamp head.
Though the last in London, many Webb lamps were erected around Great Britain and abroad and several are now officially listed and preserved as historic monuments. Recognizing this, the Carting Lane lamp was in fact rebuilt a few years ago after a lorry backed into it. The largest number of lamps appears to have been in the city of Sheffield where there are more than 20 still in existence. In a less august forum than SfAM, this might lead to unseemly speculation as to whether this is due to some special feature of the gut microflora or the diet of the residents of Sheffield. I am reliably informed that the local surfeit of sewage gas is in fact a result of the topography of Sheffield where the number of hills means there is a greater chance of pockets of gas accumulating in the system. To suggest anything else is a calumny on the noble burghers of Sheffield.
SfAM President 2011-2014