Changes

By the 16th and 17th centuries, it was determined that potassium nitrate needed for gunpowder could come from human waste. European cities soon used their public latrines as a way to collect materials that would then be used to create potassium nitrate used for gunpowder. This industry helped to create a way to recycle and remove waste from public areas, helping cities to become more health and grow by the late Medieval and early modern periods<ref>For more on the use of human waste for gunpowder, see: Cressy, D. (2013). Saltpeter: the mother of gunpowder (1st ed). Oxford: Oxford University Press.</ref>.

Overall, however, the system that was already in ancient societies in the Near East, Asia, and Rome largely did not develop further to be very different until the modern Industrial Age in by the late 18th and 19th centuriescentury. The One of the main innovation innovations that developed sanitation was the introduction of mechanical pumps. Large sewer systems could not now be created with better tunneling technologies that could ignore gravity and pumping stations could be used to move water irrespective of the terrain slopeacross a city. Cities As cities during this time became unhealthy as populations expanded and people migrated to citiesas the Industrial Revolution developed, this became an important technical development. By the late 19th century, chemical treatment was used to treat waste water, mostly in the form of using chlorine to treat water. Sand filtration was also used introduced to clean water, with the introduction of sand filtration to London in 1829<ref>For more on sanitation's development in the 19th century, see: Juuti, P., Katko, T. S., & Vuorinen, H. S. (Eds.). (2007). Environmental history of water: global views on community water supply and sanitation. London: IWA Pub.</ref>.

The world's first modern sewer system was in London (Figure 2). It was developed to have 450 miles of sewers that used large tunnels that applied a combination of gravity and pumping stations to move waste water. This enabled London to handle its very rapidly growing population, reversing the many problems, such as typhoid, the city had with disease outbreak in the earlier part of the 19th century. Paris in the late 19th century also witnessed large-scale expansion. Similar to London, the mixture of waste water with drinking water made typhoid and other epidemics widespread. The city responded by building 600 kilometres kilometers of aqueducts that brought potable spring water into the city, while underground sewers were built that drained waste, with dirty water used to help flush sewage away from the city. Other cities in North American and Europe built similar systems during the 19th century. By the 1880s, flush toilets, known as water closets, began to be marketed and installed just as large sewer systems became increasingly established in urban centers in Europe and North America. By the early 20th century, chemical treatment of sewage became more established<ref>For more on how cities transformed as sanitation improved, see: McGranahan, G. (Ed.). (2001). The citizens at risk: from urban sanitation to sustainable cities. London ; Sterling, VA: Earthscan.</ref>.

In the 20th century, sewage treatment plants began to be established with the innovation of using activated sludge or natural bacteria and protozoa as part of the waste water treatment process. In this case, tanks or pools of waste water would be treated with bacteria to help breakdown waste. Chemical treatment was also utilized<ref>For more on modern sanitation systems, see: Jenkins, D., Wanner, J., IWA Conference Activated Sludge - 100 Years and Counting, & International Water Association (Eds.). (2014). Activated sludge - 100 years and counting: [papers delivered at the Conference “Activated Sludge ... 100 Years and Counting!” held in Essen, Germany, June 12th to 14th, 2014]. London: IWA Publ.</ref>.