Indoor Reuse
Graywater Systems
Indoor Reuse
Greywater can also be reused indoors (example: toilet flushing), though requires filtration and disinfectant and currently is not allowed under many code jurisdictions. Once graywater has been highly filtered and treated it technically ceases to be Graywater and is more accurately referred to as “reclaimed water”.
Net energy benefit?
In residential contexts its usually most practical to utilize greywater outside, but exceptions include very large houses that have high water use and minimal outdoor irrigation, or larger buildings like apartments. Re-using graywater indoors requires creating a system that treats the water for indoor use.
Don’t store Graywater
The high amounts of nutrients and suspended solids and bacteria in graywater rapidly multiply under storage to turn into noxious septic blackwater, which is why graywater is never stored for long periods of time. Disinfection can prolong the potential retention time before graywater turns septic.
Filtration and Disinfection
Graywater passes through an approved filter and then can be disinfected by an acceptable method using one or more disinfectants such as chlorine, iodine or ozone. Sometimes the graywater is required to be dyed blue or green with a food grade vegetable dye before such water is supplied to the fixtures to make it easy to see visually that the water is non-potable. Distribution piping and reservoirs must be identified as containing non-potable water by pipe color or with metal tags. Potable water is to be used as a source of makeup water for the graywater system, with the potable water supply protected against backflow. In California, Treated graywater intended for indoor use shall meet the California Department of Public Health criteria, under Title 22 in the California Code of Regulations. Many countries follow California’s Title 22 for graywater
regulations. The World Health Organization has also developed standards for graywater that are similar to the USEPA guidelines.
Physical/ Chemical Greywater Treatment Systems
Storing greywater longer than 24 hrs requires treatment to reduce the bacteria and other microorganisms that can multiply in stagnant water. Physical and chemical treatment systems utilize disinfection and filtration while biological treatment uses aeration and membrane type bioreactors.
Many treatment and storage systems also incorporate activated carbon and/or clay filters and disinfection (e.g., chlorination, purification with ultraviolet radiation).
Biological Treatment Systems
Biological treatment technologies include membrane filters to remove contaminants, bacteria, and viruses along with aerobic biological treatment involving aeration to increase dissolved oxygen and activate bacteria to consume the oxygen and digest organic contaminants.
Some systems include media for bacteria to attach to and grow on and also includes membrane bioreactors (MBR), which relies on bubble aeration to mix effluent and limit clogging of the membrane pores. Membranes typically consist of hollow fibers and flat sheets that have a pore size of 0.1 to 0.4 microns, thus filtering out particulates, spores like giardia , cryptosporidia, bacteria, and even viruses.
