Living machine

The Living Machine installation in the lobby of the Port of Portland headquarters, which was completed and ready for occupation May 2010. The decentralized wastewater reuse system contributed to the headquarter’s certification as a LEED Platinum building by the U.S. Green Building Council.

Living Machine is a trademark and brand name for a patented form of ecological sewage treatment designed to mimic the cleansing functions of wetlands.^[1] Similar to Solar Aquatics Systems,^[2] the latest generation of the technology is based on fixed-film ecology and the ecological processes of a natural tidal wetland, one of nature’s most productive ecosystems.^[3][4] The diversity of the ecosystem produced with this approach allows operational advantages over earlier generations of Living Machines and over conventional waste water treatment technologies.^[5]

The Living Machine system was commercialized and is marketed by Living Machine Systems, L3C, a social benefit corporation based in Charlottesville, Va. The trademark Living Machine is owned by Dharma Group, LC, the parent company of Worrell Water Technologies.^[6]

The Living Machine is an intensive bioremediation system that can also produce beneficial byproducts, such as reuse-quality water, ornamental plants and plant products—for building material, energy biomass, animal feed. Aquatic and wetland plants, bacteria, algae, protozoa, plankton, snails and other organisms are used in the system to provide specific cleansing or trophic functions. The tidal process operates outdoors in tropical and temperate climates. In colder climates, the system of tanks, pipes and filters may be housed in a greenhouse to prevent freezing and raise the rate of biological activity.

The initial development of the technology in the United States is generally credited to Dr. John Todd, an ecological designer, and evolved out of the bioshelter concept developed at the now-defunct New Alchemy Institute. The Living Machine system falls within the emerging discipline of ecological engineering, and many systems using earlier generations of the technology are built without being dubbed a Living Machine.

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,.^[7] Some treated the mixed municipal wastewater for semi-urban areas, such as South Burlington, Vermont (this plant closed recently).^[8] The latest-generation Tidal Flow Wetland Living Machines are being used in major urban office buildings, military bases, housing developments, resorts and institutional campuses.^[9]

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.^[10] 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.^[11] 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.^[12]

The above points are an incomplete synthesis of a paper by Todd and Josephson at the Wayback Machine (archived July 11, 2007).

Comparison with conventional treatment

Björn Guterstam critiques conventional wastewater treatment for five different inadequacies that living machine systems address. This evaluation explains the basis of his five points of contention:^[13]

• First, conventional treatment focuses narrowly on treating water and produces an often toxic sludge as a by-product of this cleaning process. Living machine systems can greatly reduce this sludge by conversion into biomass.
• Conventional treatment uses environmentally harmful chemicals (namely chlorine) to disinfect effluent following precipitation of solids (sludge) from the wastewater stream. Ecological treatment uses biological processes instead of chemical inputs.
• Traditional processes do not adequately sequester heavy metals, and the sludge can also contain manmade organic compounds that are extremely difficult to break down. Some critics assert that the disposal of this sludge is not responsibly overseen in the United States, so the excess sludge is sometimes spread on public forest or even agricultural land, dumped in landfills or the ocean, and sometimes incinerated.^[14] This not only pollutes the environment with unnaturally high concentrations of toxins but also wastes a valuable resource. Living Machines can sequester heavy metals by plant uptake and the plants can be incinerated and the metals isolated in ash for safe storage. These life-giving machines convert sludge into organic tissues such as fish, flowers and medicinal plants that have human uses.

A contained microsystem can be very successful in recycling nutrients, organic matter, and water. Depending on the toxicity and makeup of the influent, living machines can treat water to tertiary treatment standards and even reach potable standards for most or all metrics. This excellent organic recycling is possible if the biosolids are not heavily contaminated with persistent pollutants (such as aluminum, which retards biotic growth). Mixed domestic/industrial municipal influent is more polluted, so a living machine may not always be able to treat every contaminant to levels that would not stress the ecosystem that receives the effluent. In this case, more treatment is necessary, which can be achieved by drainage into constructed wetlands which provide a different type of ecosystem that provides a fresh lineup of ecological players and services that can further process pollutants.

• Previous generations of Living Machine systems have employed clams to filter colloidal materials and fine suspended solids. Conventional treatment runs into engineering troubles when it attempts to handle these microscopic particles.^[15][16]
• Conventional treatment is capital and energy intensive, whereas natural treatment is design intensive (and also management intensive if it is not well designed). The embodied fossil fuel energy in the heavy industrial infrastructure used in traditional activated sludge treatment is much greater than in the construction of a living machine system with a large greenhouse, manufacture of plastic tanks, mechanical aerators, pumps and valves among other equipment.

Guterstam contends that traditional facilities require larger capital investment and demand more labor and energy costs than their ecological counterparts. It is difficult to make a generalization about economic comparisons because thus far living machine systems have only been built for single commercial buildings. The next step in the development of these systems would be a larger scale ecosystem that has more diversity and higher populations to treat a larger volume of sewage. Until there is an equivalence of scale, economic comparison between the two systems is somewhat awkward and speculative. However, it is safe to say that Living Machine systems are ecologically superior.

Conventional wastewater treatment is heavily embedded in our industrial toolkit. A worldwide revolution in wastewater treatment would require an entire industry and profession to make a major disciplinary shift from a focus on industrial engineering to ecological engineering, applied biology and ecology. Living Machine systems have yet to be made on a comparable scale to conventional treatment plants, and this “biology of scale” could bring benefits or drawbacks in efficiency.

Built components

In tropical and temperate climates, Living Machine systems can be outdoors, as the temperature will sustain sufficient biological activity throughout the winter. In cold climates, a greenhouse is used to keep water temperatures warm so that plants do not winterize. Supplemental heating may also be necessary.

Living Machine systems use screens, biofilters, plumbing, large plastic tanks, reed beds, rocks, fans, pumps and other mechanical devices. Every system is tailored to the volume and makeup of the sewage. Some are stand-alone greenhouses, while others are built into larger buildings.

John Todd and Michael Shaw have a patent on a device called an "ecological fluidized bed" which is essentially a pumice-filled tank with a concentric inner tank that contains wetland plants. Pumps rapidly recirculate water to maximize the filtration rate of this device.^[17]

Living Machine System Process

• “Fixed film ecology” has superseded systems based on hydroponics or a fluid medium. In fixed film systems the wetland cells are filled with a solid aggregate medium extensive surface area for beneficial biofilm (treatment bacteria) growth. Fixed film ecology allows for denser and more diverse micro-ecosystems to form than does a liquid medium. These ecosystems go well beyond bacteria to include a variety of organisms up to and including macro-vegetation.
• Tidal cycles (filling and draining the wetland in accelerated tidal action—12 or more cycles per day) are used to passively bring oxygen into the wetland cells. This action mimics the same type of biological action of natural tidal estuaries. Tidal Flow Wetlands replace the need to blow air into a liquid medium and use gravity to bring atmospheric oxygen into the cell when it is drained.

Hydroponics and Aquaculture

Some ecological wastewater treatment systems, including first-generation Living Machine systems, employed hydroponics and even aquaculture. However, these processes are not part of today's Tidal Flow Wetland Living Machine systems.

• The first step of the process is an anaerobic settling tank. This closed anaerobic tank serves as a pre-treatment to allow solids to fall out of suspension and precipitate to the bottom of the reactor to reduce the turbidity of the water. A variety of anaerobic bacteria are present in this tank; they generate acids and ferment methane. This step may be unnecessary if the influent has low levels of solids.
• Next, the sewage flows through a biofilter of bark and humic materials. This gives the influent its first filtration and reduces the odors prevalent in anaerobic conditions.
• The mixture then moves into a series of aerobic tanks. The first tank is a dark, closed-top aerobic reactor that serves as a transitional step. The next tank is an open-top, aerobic reactor that contains photosynthetic algae that fix oxygen back into the formerly anoxic, turbid water. This provides oxygen and organic food (dead algae) for biological metabolism and respiration. Microbial communities proliferate, and eventually must consume all of the photosynthetic algae so that the algae do not choke out macrophytes in later steps.
• Many types of bacteria immobilize pollutant minerals, but certain species of bacteria are crucial to nutrient conversion. Specifically, Nitrosomonas and Nitrobacter work in steps to nitrify ammonia, making it into nitrates, which are available for plant and microbial uptake. These bacteria need calcium carbonate to catalyze this reaction, so managers must maintain sufficient calcium levels in the water. Denitrifying bacteria such as Pseudomonas fluorescens convert nitrates into gaseous nitrogen, which is volatilized in these open aerobic tanks.^[18] Denitrification is the most desirable sink for nitrogen in living machines.^[19] Protozoa have been shown to be capable of coliform and pathogen suppression.^[20] Microbial breakdown is the primary biological treatment of both the conventional activated sludge process as well as these aquatic ecosystem sludge reactors.
• Higher plants are grown hydroponically in the aerobic tanks and provide multiple services. The most common plant used is water hyacinth (Eicchornia crassipies), which has filamentous aquatic roots with a high specific area. These feather-like roots provide a stable habitat for microbes, and over time a bacterial biofilm builds up around the roots.^[21][22] Water hyacinth, bulrush and other macrophytes sequester heavy metals. The bodies of these plants can be harvested and burned, and the heavy metals can be chemically isolated to take them out of the environment. Brassica juncea growing in waste streams has been found to contain up to 10% of its dry weight in lead.^[23]

• Plankton carries out multiple functions in the system with varying efficacy. Zooplankton feed on extremely small (<25 µm) particles. In juvenile stages they feed on particles smaller than 1 µm.^[24] Conventional waste treatment cannot process these fine suspended solids.^[25] Although zooplankton do consume these fine particles, which are difficult for conventional treatment systems to process, the placement of plankton in the system is more valuable as a trophic link. Plankton can eat microbes, which are abundant in the system, and the plankton is an ideal food for filter feeding fish and mollusks. This food chain transfers biomass to higher trophic levels and increases the diversity and complexity of the ecosystem. John Todd thinks that “Since zooplankton can exchange the volume of a natural body of water several times per day it is difficult to overstate their importance in ecological engineering.”^[26]
• According to Björn Guterstam, another one of the most well-published and experienced ecological engineers, this theoretical role has not been as successful in practice. He concedes that phytoplankton populations have been limited by toxic and somewhat deoxidized water at the bottom of tanks, as well as light limitations. Phytoplankton are primary producers, which provide food for larger zooplankton species, so the zooplankton population drops with its photosynthetic counterpart.^[27] Because these principles have been implemented only on a small scale, these systems have a lowered buffering capacity due to issues of scale and separation from the macroecosystem, even though genetic and functional diversity is encouraged.
• Aquaculture can take place in more dilute tanks downstream after the eutrophication-causing contaminants have been ameliorated. Snails slide along the tank walls and graze on slime and sludge buildup, cleaning the tank. This self-regulation improves light penetration, which stimulates photosynthetic forms of algae, bacteria and plankton. Filter feeders sift through large volumes of water each day and consume the bacteria and plankton that are small enough to pass through. Mollusks such as mussels and snails, as well as some fish, are filter feeders. Detritus-feeding fish consume larger particles of suspended biosolids. Herbivorous fish are excluded from tanks where macrophytes carry out useful functions (such as biofilm hosting), but when plants are eventually harvested from the system, this plant tissue can be fed to a tank of herbivorous fish for aquaculture production.^[28]
• A single Anodonta freshwater clam can filter as much as 40 litres/day of water, absorbing colloidal materials and other suspended solids at a removal rate of 99.5%. Many freshwater clams are in danger of extinction, in part because some have gills that perform poorly in polluted environments.^[29] Since some of these clams can sequester colloids from streams or lakes, this provides an ecosystem service by slowing the erosion of soil colloids. Humans can strike up a symbiotic relationship with the clam genera Unlo and Anodonta by providing a clean habitat (when the water reaches the clam tank it is cleaner than some of their wild habitats). In exchange for a good home, the clams could aid humans by filtering colloids and suspended solids out of our wastewater. It is yet to be determined if the clams break up these colloids at all or if it is feasible to recycle clam compost back into field (which increases cation exchange capacity—-an agricultural benefit). Ecological engineering supports symbiotic relations between different species to serve the needs of humans as well as promoting the health of the ecosystem.

Future horizons

In a 2000 report to the USEPA on a South Burlington, Vermont, living machine, Ocean Arks International outlined five key areas which could shape the future of this field.^[30] The foremost “possible breakthrough areas” is the ongoing classification of species by the biochemical, biological and ecological roles they play and how those roles effect other species under the context of wastewater treatment. The breakthrough would be to study the function of organisms in hopes of being able to more readily and successfully manage overall ecosystem function. Browne et al. (in press) have looked into the structuring of aquatic systems for water treatment.^[31]

Trophic management is used to influence entire systems by selective predation based on diagnosing an imbalance and analyzing the web of ecosystem classifications, roles and relationships. This management technique exploits the close interconnections of the food web, trophic cascade, to send a ripple down through the living community. This stewardship technique is predicated upon an advanced understanding of the conditions in the ecosystem and modeling the dynamic relationships down the trophic cascade. The trophic cascade in lakes has been researched by Carpenter and Hall.^[32]

Living Machine systems have been composed largely in closed greenhouses which can only react minimally with the surrounding ecosystem, and where populations have been heavily managed to foster equilibrium. If a Living Machine were subject to the ecology of invasions, new species would be free to colonize the system, and natural selection would dictate the success of any species. This would be true ecosystem self-design and self-management partnered with human stewardship.

Photosynthetic changes, specifically the control of light exposure is another powerful management practice capable of slowing or accelerating primary production. This is similar to the idea of trophic management, except that it manipulates the other end of the food web.

Finally, there is economic potential for methane generation, market crops such as flowers, fish, tomatoes, lettuce and other foods tolerant of hydroponic conditions, useful plants or medicinals. Combined with the revenue from wastewater treatment these services could turn living machines into pollution sinks and economic generators.^[33] It is well documented that a small, well-planned system in a good location can be economically viable. If a living machine can subsist in Alaska, it seems reasonable that ecologically engineered sewage treatment can be tailored to work smoothly in warm developing countries.

Public sanitation and equitable access to water in very poor countries are grave problems. Living machines could be a low-capital approach to treating and recycling water, but skilled biologists may be a limited resource as well. A brick-pool living machine was built by Americans in Auroville, Indiana.^[34]

List of Living Machines

This is a dynamic list and may never be able to satisfy particular standards for completeness. You can help by expanding it with reliably sourced entries.

• 2012-San Francisco Public Utilities Commission (SFPUC) Headquarters, San Francisco^[35]
• 2010-Port of Portland Headquarters, Portland, OR, USA http://www.portofportland.com.^[36]
• 2009-Furman University, Greenville, SC, USA.^[37]
• 2009-Old Trail School, Bath, OH, USA^[38]
• 2007-Vive Verde EcoCentre, Lake Worth, FL^[39]
• 2007-Esalen Institute, Big Sur, CA, USA
• 2007-Northern Guilford Middle School, Guilford County Public Schools, Greensboro, N.C.^[40]
• 2002-El Monte Sagrado Resort, Taos, NM, USA
• Missouri Department of Conservation - Anita Gorman Discovery Center, Kansas City, MO, USA http://mdc.mo.gov/areas/kcmetro/discovery/info/
• Oberlin College, OH, USA http://www.oberlin.edu/ajlc/systems_lm_4.html
  

  An earlier generation Living Machine installation, built in 2000, at Oberlin College with a settlement tank in the foreground and filtering tanks in the background
  .
• Berea College, Berea, KY, USA http://www.berea.edu/sens/ecovillage/ecomachine/default.asp
• South Burlington, VT, USA
• Islandwood Education Center - Bainbridge Island, WA: http://www.islandwood.org/default.php
• Arcata Marsh, Arcata, CA, USA
• see Living Designs Group, http://www.livingdesignsgroup.com/eng-project-master-list/
• BedZED, Sutton, London, UK (not operating currently)
• Findhorn, Scotland, UK
• Corkscrew Swamp Sanctuary, Naples, Fl, USA (http://www.corkscrewsanctuary.org/Information/LivingMachine.html)
• Clatsop Community College - MERTS Campus, Astoria, OR, USA https://www.clatsopcc.edu/about-ccc/campuses/merts/living-machine
• Penn State University, State College, PA, USA
• Ohio State University, Columbus, OH, USA - Dairy Wastewater Treatment
• Harbor Park (Budapest, Hungary)
• PAWS, Inc., Muncie, IN, USA
• Conserve School, Land O' Lakes, Wisconsin^[41]
• Darrow School - New Lebanon, NY, USA (http://www.darrowschool.org/page.cfm?p=34)
• EVA Lanxmeer - Coevorden, Netherlands (http://www.eva-lanxmeer.nl/docs/bebouwing.html)
• Sharon I-89 Northbound Rest Area - Sharon, VT, USA
• Julian Woods Community- http://directory.ic.org/619/Julian_Woods_Community

See also

• Bioremediation
• Rain garden
• Anaerobic digestion
• Constructed wetlands
• Biomimicry

References

1. Living Machine Systems, L3C, http://www.livingmachines.com. "Factsheet: Tidal Wetland Living Machine System -- Description and Scientific Basis." http://www.livingmachines.com/images/uploads/resources/tidal_wetland_living_machine_technology_description.pdf. Retrieved 2011-8-18.
2. Maple Reindeers Group. Ontario Science Centre Solar Aquatics System.
3. United States Environmental Protection Agency. "Importance of Wetlands." http://www.epa.gov/bioiweb1/aquatic/importance.html. Retrieved 2011-8-18
4. Water and Waste water Plant Directory. NEB Solar Aquatic System
5. Living Machine Systems, L3C, http://www.livingmachines.com. "Creating a Sustainable Water Infrastructure for the 100000st Century" whitepaper. Kirksey PE, Will. Retrieved 2011-8-18.
6. United States Patent and Trademark Office. "Trademark Applications and Registration Retrieval" page. http://tarr.uspto.gov/servlet/tarr?regser=serial&entry=76264897. Retrieved 2011-8-18.
7. Ecovillage Findhorn: Biological Waste Water Treatment
8. http://www.epa.gov/owmitnet/mtb/living_machine.pdf
9. McNair, Dave. "The Tao of Poo: Can Worrell's Green Sewage System Save Water and Planet?" The Hook. June 11, 2009. Retrieved 2011-9-24.
10. Todd, Nancy J. 2005, A Safe and Sustainable World: The promise of Ecological Design. Island Press, Washington D.C.
11. Todd, John and B. Josephson. “The Design of Living Technologies for Waste Treatment.” Ecological Engineering 6 (1996) 109-136.
12. Todd, John and B. Josephson. “The Design of Living Technologies for Waste Treatment.” Ecological Engineering 6 (1996) 109-136.
13. Guterstam, Bjorn. 1996. Ecological engineering for wastewater and its application in New England and Sweden. Ecological Engineering 6 (96- 108).
14. Wilson, Duff. "Fateful Harvest: The True Story of a Small Town, A Global Industry and a Toxic Secret." Harper, 2002.
15. Guterstam, Bjorn. 1996. Ecological engineering for wastewater and its application in New England and Sweden. Ecological Engineering 6 (96- 108).
16. Todd, John and B. Josephson. “The Design of Living Technologies for Waste Treatment.” Ecological Engineering 6 (1996) 109-136.
17. John Todd et al. "Ecological fluidized bed method for the treatment of polluted water." US Patent #548U6291
18. Brady, Nyle and Weil. The Nature and Properties of Soil 14th ed. Prentice Hall
19. Teal, John. 1997, “Contribution of Marshes and Salt Marshes to Ecological Engineering.” Chapter 16 in C. Etnier and Bjorn Guterstam. Ecological Engineering for Wastewater Treatment, 2nd Ed. CRC Press, Boca Raton.
20. Pike, E.B. and E.G. Carrington, 1979. The fate of enteric bacteria and pathogens during sewage treatment. In: A. James and L Evison (Eds.). Biological Indicators of Water Quality. John Wiley, London, pp. 2001-2032.
21. Austin, David. “Parallel Performance Comparison Between Aquatic Root Zone and Textile Medium Integrated Fixed-Film Activated Sludge (IFFAS) Wastewater Treatment Systems.”
22. Peterson, S.B. and J.M. Teal. 1996, “The role of plants in ecologically engineered wastewater treatment systems.” Ecological Engineering. 6(1-3): 137-148.
23. Nanda Kumar, P.B.A., V. Dushenkov, H. Motto and I. Raskin, 1995. Phytoextraction: the use of plants to remove heavy metals from soils. Environ. Sci. Technol., 29: 1232-1238.
24. Austin, David. “Parallel Performance Comparison Between Aquatic Root Zone and Textile Medium Integrated Fixed-Film Activated Sludge (IFFAS) Wastewater Treatment Systems"
25. Guterstam, Bjorn. 1996. Ecological engineering for wastewater and its application in New England and Sweden. Ecological Engineering 6 (96- 108).
26. Todd, John and B. Josephson. “The Design of Living Technologies for Waste Treatment.” Ecological Engineering 6 (1996) 109-136.
27. Guterstam, Bjorn. 1997, “Ecological Engineering for Wastewater Treatment: Theoretical Foundations and Practical Realities.” Chapter 7 in C. Etnier and Björn Guterstam. Ecological Engineering for Wastewater Treatment, 2nd Ed. CRC Press, Boca Raton.
28. Sifa, Li. 1997 “Aquaculture and its role in ecological wastewater management.” Chapter 3 in C. Etnier and Bjorn Guterstam. Ecological Engineering for Wastewater Treatment, 2nd Ed. CRC Press, Boca Raton.
29. Karnaukhov, V.N., 1979. “The role of filtrator mollusks rich in carotenoid in the self-cleaning of fresh waters.” Symp. Biol. Hung., 19: 151-167.
30. "Ecological Design: Towards A Post-Engineering Perspective." http://www.oceanarks.org/ecodesign/postengineering/
31. Browne, B., R.A.F. Seaton & P. Jeffrey, In press. “Some propositions on the structuring of aquatic ecologies for water treatment.” Journal of Environmental Science and Health.
32. Carpenter, S. R. & J.F. Kitchell, eds. 1993. The Trophic Cascade in Lakes. Cambridge University Press.
33. "Ecological Design: Towards A Post-Engineering Perspective." http://www.oceanarks.org/ecodesign/postengineering/
34. Architecture for Humanity, "Design Like You Give a Damn." p.294
35. Freese, Alicia. "Building's Articificial Wetlands Mimic Nature." http://baynature.org/articles/artificial-wetlands/ Bay Nature. July 22, 2012. Retrieved 2012-8-19.
36. Port of Portland, http://www.portofportland.com. "Apr. 20, 2010: Green Office Building is New Home for Port Staff." http://www.portofportland.com/Media_HQ_PressKit.aspx. Retrieved 2011-8-18.
37. Jan. 26, 2011 letter, Brannen Anderson, Professor and Chair, Department of Earth and Environmental Sciences, Furman University.
38. "OTS promotes environmental stewardship with 'Living Classroom'." Akron.com. May 20, 2010. Retrieved 2011-10-9.
39. Cruger, Roberta. "Florida fountain treats wastewater." Treehugger.com. May 9, 2009. Retrieved 2011-10-9.
40. Innovative Design architects website, Northern Guilford Middle School project. Retrieved 2011-10-9.
41. The Green Machine,Conserve School Website, Retrieved 12-07-13

External links

• Landscape Machine concept, Wageningen University, the Netherlands
• Living Machine, L3C website
• Living Machines article
• Solar Aquatics Systems, the original Living Machine with transparent tanks
• Interview with Nancy Todd, "Living Machines use waste water, sunlight, plants, and fish to produce abundant fresh food", In Context, Fall 1995
• "Putting human waste back in its place: at the bottom of the food chain", In Context, 1993