“Be it known that I, Karl Imhoff, a subject of the German Emperor, residing at Bredeney, near Essen, in Germany, have invented a certain new and useful improvement in treating sewage”. A great deal has changed, both globally and in the world of sewage treatment since Karl Imhoff patented his invention in 1910. The benefits of storing sewage in a tank to reduce its putridity and quantity had been noted in the years preceding Imhoff’s invention, although the concepts for the need of sewage treatment date back to a report by Sir E. Chadwick on the Health of the Working Classes published in 1842. However, it was a severe cholera epidemic which incentivized Parliament to pass the Nuisance Removal Act in 1855 which began the scientific study of the chemistry and biology of sewage sludge. The first forms of sludge treatment were straightforward collection and diversion to the nearest water-course rather than allowing it to accumulate near dwellings. It wasn’t until 1857 that it was a legal requirement to remove suspended matter or “deodorize” sewage prior to its “admission to the streams”. United Kingdom in the mid-19th century was undergoing unprecedented technological development, and the waste materials from the industries which fuelled this development also found their way into the water system. According to textbooks written at the time, sewage sludge would contain wastes from tanneries, wool mills, dye works and paper works, as well as coal ashes, slag, solid refuse from earthenware manufacturers and metal works, soil, stones, clay from quarries and mines, road grit and filth from the streets, and last but not least a variety of animal carcasses. When sewage sludge was passed into comparatively small rivers from high population density areas, it caused severe pollution. So much so, that the varied industries of the Victorian era blamed the sewage for spoiling their water supply. Not surprisingly, the original drivers for sewage treatment were to reduce river pollution. An Act of 1861 was passed which required that sewage be purified and freed from faecal and other putrescible matters prior to stream and river discharge.
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