Sewage farms comprise agricultural land irrigated and fertilised with sewage.

A precursor to modern sewage treatment

Sewage treatment

Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...

 systems, household sewage

Sewage

Sewage is water-carried waste, in solution or suspension, that is intended to be removed from a community. Also known as wastewater, it is more than 99% water and is characterized by volume or rate of flow, physical condition, chemical constituents and the bacteriological organisms that it contains...

 was collected from towns and cities and transported to nearby farm lands. During the middle ages this was accomplished with hand-carried buckets, but as local populations grew, during the Industrial Revolution

Industrial Revolution

The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...

 sanitary sewer

Sanitary sewer

A sanitary sewer is a separate underground carriage system specifically for transporting sewage from houses and commercial buildings to treatment or disposal. Sanitary sewers serving industrial areas also carry industrial wastewater...

 systems were built. These used a network of pipes and pumps to transport sewage beyond the city boundaries to large rented grasslands, into which the sewage trickled down. Berlin once rented 20 sewage farms occupying about 10,000 hectares.

Some of these farms remained in use until the end of the 20th century, at which point it became apparent that as it was usually contaminated with industrial waste, sewage was unsuitable for use as a fertiliser. Therefore, sewage plants began to replace sewage farms. Modern sewage farms are usually combined with such plant, so that they irrigate the land with reclaimed water

Reclaimed water

Reclaimed water or recycled water, is former wastewater that is treated to remove solids and certain impurities, and used in sustainable landscaping irrigation or to recharge groundwater aquifers...

. Some types of untreated sewage can be used on a sewage farm, or filtered through a constructed wetland

Constructed wetland

A constructed wetland or wetpark is an artificial wetland, marsh or swamp created as a new or restored habitat for native and migratory wildlife, for anthropogenic discharge such as wastewater, stormwater runoff, or sewage treatment, for land reclamation after mining, refineries, or other...

.

A small-scale example of a sewage farm exists at Chester Zoo

Chester Zoo

Chester Zoo is a zoological garden at Upton-by-Chester, in Cheshire, England. It was opened in 1931 by George Mottershead and his family, who used as a basis some animals reported to have come from an earlier zoo in Shavington. It is one of the UK's largest zoos at...

, where elephant droppings and urine is filtering through a reedbed.