One of the NRNs major survey projects has been the monthly testing of the water quality of various selected sites around Eynsham and now also at South Leigh. We undertook this because unpolluted waterways are a vital necessity if we are to achieve nature recovery in and around our watercourses.
At the forefront of this project is the vexed issue of the pollution of the Thames and its tributaries, one of which being the Limb Brook, which runs beween South Leigh and Eynsham.
Sewage from Eynsham and surrounding villages is processed at the Cassington Sewage Treatment Works (STW), which is operated by Thames Water. Cassington STW is one of the many sewage treatment works that repeatedly release raw sewage directly into the Thames and its tributaries.
A small group of Concerned Parties were offered a guided tour of the Works, which took place in mid-December 2021 and it seemed an ideal opportunity to understand more about how the sewage from 17000 souls is processed.
This Article began as Kevan Martin's report about that visit. Somehow it morphed into Long Mead's Long Read for New Year 2022. Please feel free to dip in and out - or just look at the pictures.
Walking in to Cassington's Sewage Treatment Works (STW) and seeing the reactors and settling tanks was a déjà vu experience for me – probably for two reasons: Firstly, Long Mead has its own package sewage treatment plant that operates on exactly the same principles (although we release its effluent into a drainage field, not into the Thames), and secondly, during my misspent youth I did research for my Master’s degree in Civil Engineering in a Water Resources lab. The title of my thesis was, ‘ The kinetics of enhanced phosphorus removal in the activated sludge system.’
What is ‘activated sludge?’ you ask, 'And what's it got to do with sewage in the Thames?’ Well, if you read on you will find many answers, but since you are sitting comfybold and two-square...let me begin by perambulating around the delicate and historical problem of how we dispose of human waste.
Its just fertilizer!
First, why treat sewage at all? Why not just use it as fertilizer and put it directly on arable fields as humanure? This is of course what farmers traditionally did, and many still do. Indeed, the million or so tonnes of sludge from treated sewage we generate each year is used in agriculture, because of the nutrients it still contains. In towns, however, disposing of raw sewage by making it into fertilizer for agriculture is not an easy option, but ‘night soil’ (i.e. urine and faeces) collected in a ‘honey bucket’ is still practised in towns and cities worldwide for use as fertilizer.
In China the collection in honey buckets was delicately called ‘emptying nocturnal fragrance’. In Japan, the night soil of rich households fetched higher prices as fertilizer, presumably because rich people’s diet was more varied and more nutrients were present in their night soil. In Mexico, the Aztecs built wicker containers called chinampas – effectively compost heaps - to receive sediment, night soil and decaying vegetation, upon which they planted the crops of a market garden; some of these still exist. In the Amazon, the terra preta de indio or ‘black earth of the indians’ probably reflects a similar ancient practice. In Tudor England a ‘gong farmer’ collected the contents of privies and cesspits at night. Later a privy midden involving an outhouse and associated midden was used to dispose of waste. These in turn were superseded by pail closets, which required emptying, and water closets, in which the waste was flushed into a sewer system.
Sewers, Part I.
Sewers have a long history. Ancient Athens piped its sewage to a reservoir and then channelled it to the Cessiphus river for use as fertilizer. Ancient Romans built the cloaca maxima to take their waste water to the Tiber river; it still functions. In London, inadequate and leaking sewers and cesspits led to contamination of the drinking water and repeated outbreaks of cholera and typhoid.
That the Thames was badly contaminated was already long-appreciated – in 1372 Edward III forbade throwing waste into the Thames, and in 1388 an Act of Parliament, ‘forbade the throwing of waste into ditches, rivers, and watercourses.’ Although the increase in flush toilets might have improved household hygiene, it had the inadvertent consequence of contaminating the aquifers and water courses from which drinking water was drawn beecause the pipes leaked. Diseases were almost inevitable, as the Thames itself was used as an open sewer, receiving untreated human waste, discharge from industries, and slaughterhouse effluent.
Dr. John Snow (1813-1858) pioneered an epidemiological approach to discover the source of a cholera outbreak. His statistical mapping of the addresses of the fatal cases led him to identify a water pump in Broad Street, Soho as the source of the major cholera outbreak of 1854. The solution was to remove the pump's handle (a replica pump is still there as his monument). Although he could not identify the cholera bacteria in the pump water, he produced some of the earliest scientific evidence that cholera was water-borne, and not due to ‘miasma’ as the Victorians generally supposed.
The Pause that Refreshes: Drinking Thames Water.
Dr. Snow’s research had shown convincingly that waterborne contaminants from sewage could enter drinking water (Snow himself always drank boiled water). Provision of safe drinking water, in cities at least, where sewage contamination was concentrated, meant finding some method of purification. John Doulton had a pottery at Lambeth and as early as 1827 had developed a ceramic water filter. His son Henry, was commissioned by Queen Victoria in 1835 to produce a water filter for use in the royal household and finessed his father’s prototype. The pores in the ceramic ‘candles’ he developed are small enough to filter out all bacteria, viruses, and probably prions as well.
Doulton’s ceramic filters are now incorporated as a modification of the Berkefeld filter, a German invention that used diatomaceous earth as the filter. The British Berkefeld gravity filter accompanied British missionaries across the world to provide them with safe drinking water. (We are not told what water their converts drank). Although not missionaries, we also use a British Berkefeld on Horseshoe Island to filter our drinking water, which we draw directly from the Thames. The addition of silver and charcoal to Doulton’s ceramic filter provide a further disinfection step and the charcoal removes most pesticides, herbicides and organic solvents. Arguably, our filtered Thames water is purer (and better tasting) than Oxford’s water, 80% of which drawn from the Thames and is therefore highly chlorinated to reduce the concentration of waterborne pathogens (that’s ‘reduce’ not ‘eliminate’).
Sewers, Part II
Despite repeated outbreaks of cholera in London, it took the hot summer of 1858 to produce a sufficiently ‘Great Stink’ immediately outside the Houses of Parliament before the politicians were moved to do something radical about Thames pollution and they urgently voted in a Bill to build a new sewer system. The chief engineer of London’s Metropolitan Board of Works, Sir Joseph Bazalgette (1819-1891), was put in charge and given a £3million budget (raised by a tax levy) to build a sewer network that would capture London’s sewage and surface water from rain and release it further downstream to be swept out to the estuary on the ebbing tide.
To hide the northern one of the two major 'intercepting' sewers he located on either side of the Thames, Bazalgette built the new embankments of Albert, Victoria, and Chelsea. The final outfall into the Thames was on both sides of the river: at Crossness on the South bank and Beckton on the North bank.