Farmers, recognizing the value of excreta, were eager to get these fertilizers to increase production and urban sanitation benefited. This practice was also called gong farmer in England but carried many health risks for those involved with transporting the excreta and fecal sludge. Besides direct use, excreta was also processed to produce pure chemicals. Using nitraries and nitre beds, one extract the nitrogen within as potassium nitrate (KNO3), a key ingredient in gunpowder. KNO3 was also responsible for the discovery of nitric acid in the 17th century. Traditional forms of sanitation and excreta reuse have continued in various parts of the world for centuries and were still common practice at the advent of the Industrial Revolution. Even as the world became increasingly more urbanised, the nutrients in excreta collected from urban sanitation systems without mixing with water were still used in many societies as a resource to maintain soil fertility, despite rising population densities. Decline in recovery of nutrients from human excreta in dry systems Recovery of nutrients from excreta in non-sewered sanitation systems was addressing the sanitation problems in settlements in Europe and elsewhere and was contributing to securing agricultural productivity. However, the practice did not become the dominant approach to urban sanitation in the 20th century and was gradually replaced with sewer-based sanitation systems without nutrient recovery (apart from agricultural reuse of sewage sludge in some cases) – at least for cities that can afford it. There were four main driving factors that led to the demise in the recovery and use of excreta and greywater from European cities in the 19th century: Growth of urban settlements and increasing distance from agricultural fields. Increasing water consumption and use of flush toilet: Water flushing greatly increased the volume of sewage, at the same time diluting the nutrients, making it virtually impossible for them to be recovered and reused as they previously were. Production of cheap synthetic fertilizers, making any efforts to recover and reuse the nutrients and organic material from the large volumes of sewage obsolete. Political intervention as a consequence of the perceived need for a change with regards to how to deal with odorous substances: Up until the end of the nineteenth century the dominant theory on the spread of illness was the miasma theory. This theory stated that everything that smelled had to be gotten rid of because inhaling bad smells was thought to lead to