The bathroom of the future may resemble a greenhouse more than a lavatory. As cities around the world struggle with wastewater management problems, there is growing interest in a new-old form of wastewater management called living machines. ("Living Machine" is actually a trademarked term owned by Living Machines, Inc., but much like Kleenex and Xerox, the term may already be passing into wider use.)

Living machines are a type of constructed wetland that duplicate the natural water purification systems of wild wetlands. They use aquatic plants, fish, clams, algae, and other organisms to treat sewage and wastewater.

Conventional sewage treatment requires high levels of chemical inputs, including environmentally harmful chemicals such as chlorine. It often produces large amounts of sludge, which may be toxic due to inadequately sequestered heavy metals and other elements, and which must be disposed of. Improper disposal of toxic sludge has been documented on numerous occasions in the United States, including spreading it on agricultural fields, dumping it in oceans and waterways or on public lands, and even abandoning it in urban alleyways.

Living machines do not require chemical inputs, and produce much less sludge due to their conversion of water, organic matter, and nutrients into biomass. Living machines also provide improved sequestration of most heavy metals and better filtering of microscopic colloidal materials and suspended particles than conventional water treatment methods. Living machines are capable of treating water to tertiary treatment standards, and often even to potability, though this depends on the exact makeup and toxicity of the influent.

Unlike conventional treatment plants, living machines can also provide outside financial benefits through aquaculture in tanks where the later stages of treatment are performed. The Chinese have used "night soil" as fertilizer for their rice paddies for millennia, although their system is not intensive enough to prevent possible disease or parasite contamination and is better used as an example than a model

Living machines must be designed carefully for the general makeup and quantity of influent in order to be most effective. Inadequately designed systems may be labor and management intensive, and may not meet treatment standards.

Living machines have not been tried on a truly municipal scale and their effectiveness on that scale is uncertain. With current designs, they are best suited for corporate use or use by small communities. Although residential living machines exist, the current technology requires more space (about the area of a two car garage for an average three bedroom home) and more money (about 2.5 times the cost of a conventional sewage system) than many homeowners are willing to invest. As the designs improve, however, residential living machines are expected to become increasingly common.

One of the best known living machines is the solar aquatic system built by Jim Davis for the rural Indiana headquarters of Paws, Inc., the corporation that oversees the Garfield comic strip. The Paws, Inc. system treats 8,500 gallons per week.

New England Biolabs in Ipswich, MA is home to another, which treats 27,500 gallons per day, according to a case study (PDF) about the system.

The Noorder Dierenpark (Emmen Zoo) in the Netherlands cleans 260,000 gallons of wastewater every day in its living machine, and produces potable water on the other end.

Information about many other living machine projects can be found at Worrell Water Technologies.