Editing Autonomous building (section)

===Sewage===
{{see also|Anaerobic digestion}}

====Resource====
[[Image:Nature Loo Waterless Composting Toilet Pedestal.jpg|thumb|right|A composting toilet]]
[[Composting toilet]]s use bacteria to decompose human [[feces]] into useful, odourless, sanitary compost. The process is sanitary because soil bacteria eat the human pathogens as well as most of the mass of the waste. Nevertheless, most health authorities forbid direct use of "[[humanure]]" for growing food.<ref>{{cite book |title= The Humanure Handbook: A Guide to Composting Human Manure|last= Jenkins|first=J.C. |year= 2005|publisher= Joseph Jenkins, Inc.; 3rd edition|location=Grove City, PA |isbn= 978-0-9644258-3-5|pages=255 |url=http://www.humanurehandbook.com |access-date=24 February 2019}}</ref> The risk is microbial and viral contamination, as well as [[heavy metal toxicity]]. In a dry composting toilet, the waste is evaporated or digested to gas (mostly carbon dioxide) and vented, so a toilet produces only a few pounds of compost every six months. To control the odor, modern toilets use a small fan to keep the toilet under negative pressure, and exhaust the gasses to a vent pipe.<ref>See [[composting toilet]] for references.</ref>

Some home sewage treatment systems use biological treatment, usually beds of plants and aquaria, that absorb nutrients and bacteria and convert greywater and sewage to clear water. This odor- and color-free [[reclaimed water]] can be used to flush toilets and water outside plants. When tested, it approaches standards for potable water. In climates that freeze, the plants and aquaria need to be kept in a small greenhouse space. Good systems need about as much care as a large [[aquarium]].

Electric [[incinerating toilet]]s turn excrement into a small amount of ash. They are cool to the touch, have no water and no pipes, and require an air vent in a wall. They are used in remote areas where use of septic tanks is limited, usually to reduce nutrient loads in lakes.

[[NASA]]'s [[bioreactor]] is an extremely advanced biological sewage system. It can turn sewage into air and water through microbial action. NASA plans to use it in the crewed [[Mars]] mission. Another method is NASA's [[urine]]-to-water [[distill]]ation system. A big disadvantage of complex biological sewage treatment systems is that if the house is empty, the sewage system biota may starve to death.

====Waste====
Sewage handling is essential for public health. Many diseases are transmitted by poorly functioning sewage systems.

The standard system is a tiled leach field combined with a [[septic tank]]. The basic idea is to provide a small system with primary [[sewage treatment]]. Sludge settles to the bottom of the septic tank, is partially reduced by [[anaerobic digestion]], and fluid is dispersed in the leach field. The leach field is usually under a yard growing grass. Septic tanks can operate entirely by gravity, and if well managed, are reasonably safe.

Septic tanks have to be pumped periodically by a [[Cesspool emptier|vacuum truck]] to eliminate non reducing solids. Failure to pump a septic tank can cause overflow that damages the leach field, and contaminates ground water. Septic tanks may also require some lifestyle changes, such as not using garbage disposals, minimizing fluids flushed into the tank, and minimizing non-digestible solids flushed into the tank. For example, septic safe toilet paper is recommended. However, septic tanks remain popular because they permit standard plumbing fixtures, and require few or no lifestyle sacrifices.

Composting or [[packaging toilet]]s make it economical and sanitary to throw away sewage as part of the normal garbage collection service. They also reduce water use by half, and eliminate the difficulty and expense of septic tanks. However, they require the local landfill to use sanitary practices.

Incinerator systems are quite practical. The ashes are biologically safe, and less than 1/10 the volume of the original waste, but like all incinerator waste, are usually classified as hazardous waste.

Traditional methods of sewage handling include [[pit toilet]]s, [[latrine]]s, and [[outhouse]]s. These can be safe, inexpensive and practical. They are still used in many regions.