Air Freshener

March 28, 2011

Today is the 192nd anniversary of the birth, in 1819, of Sir Joseph Bazalgette.  Sir Joseph was a civil engineer, not a physician; but, through his work, he probably contributed at least as much to human health as any doctor then living.  He was the Chief Engineer of the Metropolitan Board of Works in London, and designed a new sewer system for London, a design accepted by the Board in 1859.

For centuries, one of London’s primary sources of water for drinking and washing had been the River Thames and its tributaries.  Unfortunately, many of these streams were highly polluted with sewage and industrial waste, from local businesses like tanneries, slaughterhouses, and breweries.  The problem of contaminated water had become acute by the 19th century, due to the growth of industry and increases in population.  Ironically, another factor contributing to the problem was the introduction of the water closet (a water-flushed toilet), which greatly increased the volume of sewage produced, overflowing the cesspits that were a principal disposal mechanism, and sending raw sewage into the rivers via the storm drains.

Epidemics of cholera became common in the first half of the century.  Although a London physician, Dr. John Snow, had concluded that the disease was caused by contaminated water, the idea was not widely accepted in the 1850s; consensus opinion was that cholera was caused by a miasma, or contaminated air, recognizable by its foul smell.   (I’ve noted in another context that travelers in the 17th century, approaching a city at night, could smell its proximity long before they could see lights.)

In the summer of 1858, the weather was unusually hot and dry, and the flow of the Thames and its tributaries was below normal.  Exposing more of the beds of these streams, which were in many cases essentially open sewers, resulted in a pervasive smell of sewage throughout London, an event still known as the Great Stink.  There was grave concern for health, especially since most people still thought cholera was spread by bad air.  Curtains soaked in chloride of lime were hung at the windows of Westminster Palace to protect Members of Parliament, and plans were underway to evacuate Parliament and the Law Courts to upstream locations away from London.  (The Today in Science site has a short satirical piece from a then-current issue of Punch, the humour magazine.)

Cooler weather and heavy rains finally brought the Stink to an end, and Bazalgette’s sewer system design was undertaken to prevent such “bad air” from returning.   The system was constructed, at very considerable expense, during the period 1859-1865, and is still in use today, in part because Sir Joseph was a very conservative engineer, and provided capacity considerably in excess of the requirements at the time.  The system created a network of sewer “tributaries”, with small local sewers leading into about 450 miles of main sewers, which in turn emptied into six large “intercepting” sewers, three on each side of the Thames, which carried the sewage to the Thames Estuary, downstream from London.  (Today, of course, it goes through treatment plants first.)

When asked to think of actions that improved human health, many people cite the discovery of antibiotics, or perhaps the discoveries of how diseases are transmitted (by mosquitoes, for example).  These were certainly important, but major improvements came from civil engineering projects, like the London sewers, that finally provided people, especially in cities, with reliably clean water.


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