Living Machines - Design Theory

Design Theory

The scale of Living Machine systems ranges from the individual building to community-scale public works. Some of the earliest Living Machines were used to treat domestic wastewater in small, ecologically-conscious villages, such as Findhorn Community in Scotland,. Some treated the mixed municipal wastewater for semi-urban areas, such as South Burlington, Vermont (this plant closed recently). The latest-generation Tidal Flow Wetland Living Machines are being used in major urban office buildings, military bases, housing developments, resorts and institutional campuses.

Each system is designed to handle a certain volume of water per day, but the system is also tailored for the qualities of the specific influent. For example, if the influent contains high levels of heavy metals, ecological wastewater treament systems must be designed to include the proper biota to accumulate the metals. During the “spring cleaning” season, there may be high levels of bleach in the water. This sudden concentration of a toxin is an example of a steep gradient.

• Steep gradients are drastic changes in conditions throughout the system that challenge the ecosystem to become resilient and stable. A well-designed treatment system requires little management, so managers may intentionally create abrupt environmental or biochemical changes to promote ecosystem self-regulation. This mimics nature’s power and trains the ecosystem to adapt to influent variations.

• Designers seek to increase the surface area of contact that biota have with the sewage to promote high reaction rates. When organisms have ready access to the sewage, they can treat it more thoroughly.

• Ecological wastewater treatment systems are cellular, as opposed to monolithic, in design. If influent volume or makeup changes, new cells can be added or omitted without halting or disturbing the ecosystem.

• Photosynthetic plants and algae are important for oxygenating water, providing a medium for biofilms, sequestering heavy metals and many other services.

Species diversity is a design goal that promotes complexity and resiliency in an ecosystem. Functional redundancy (the presence of multiple species that provide the same function) is an important example of the need for biodiversity. Snails and fish filter sludge and act as diagnostics; when a toxic load enters, snails will rise above the water level on the wall of the tank.

• The micro-ecosystem of a Living Machine system can be integrated with the macro-ecosystem just as ecosystems fade into one another naturally. This connection is commonly made with an outdoor constructed or natural wetland into which the effluent flows. Some living machines are partially or completely open to the outdoors, and this promotes interaction with the surrounding environment.

The above points are an incomplete synthesis of a paper by Todd and Josephson.