The Crestone Eagle, April 2004:
The alchemy of plant-treated sewage
A visit with David Austin and his Living Machines
story & photos by Roni S. Chernin
David Austin is an unusual blend of balanced and gentle male energy. With advanced degrees in aquatic ecology and environmental engineering, he is one of an elite group of practicing ecological engineers worldwide. As director of R&D for Living Machines, Inc. (a division of Dharma Living Systems) in Taos, he has developed a process where plants digest sewage, producing clean, usable water.
How the wetland environment is created for microbes to clean the water
In a Living Machine®, plants are carefully matched to the right “soil” (an engineered aggregate) to best support their roots and ecology. Most soils have a slightly negative electrical charge, so the positive ions in water adhere to the soils. In wastewater key nutrients like ammonia have positive ions. Ammonia “sticks” to the soil when the wetland is flooded. When drained, the ammonia remains “stuck” in thin films of water. When exposed to air, oxidation happens very quickly—accelerated by the plants and soil. With oxygen, one type of bacteria quickly converts ammonia to nitrate, which other bacteria use in the next flood cycle to consume other pollutants. The plants, roots and aggregate together support the community of healthy, sewage digesting microorganisms.
Solid materials get digested in place by the microbe community living in the plant’s roots. This process simply asks plants to do what they already do well, and provides the support where needed. The human engineering includes a programmed controller governing the pre-treatment and pumps that circulate water through the system. The system processes about the last 2/3 of the treatment. Flooding and draining by pumps allow these man-made wetlands to be much smaller than conventional treatment wetlands, because they are better aerated. Aeration by pumping and draining is more energy efficient than traditional aeration techniques. Energy consumption is estimated to be 25% of that used by the advanced treatment in an activated sludge system. The trade-off is that this system occupies a bigger area than conventional wastewater treatment.
Other Living Machine® systems have plants with roots growing in aerated water. The first stage happens in a tank partially filled with an artificial media he calls “plastic rigatoni” in a low aeration mix. Above that tank, a biofilter with compost and more “rigatoni” controls odors. Removing many of the pollutants in sewage, this initiates the process for the plants to finish. Aeration uses more energy than the wetlands, but allows Living Machines to be small enough to fit into greenhouses. Coincidentally, plants that thrive in aerated tanks also thrive in greenhouses. The wetlands system grows almost any plant that likes wet roots.
A miniature jungle in hot tubs
The R&D facility hides on the road into Taos in a nondescript unlabeled building. When you walk in, it is warm, moist, and smells like a greenhouse. The R&D facility contains “high rate wetlands in bathtubs”. The tropical plants include healthy specimens of umbrella plants, Calla and canna lillies, elephant ear, purple taro and black willow. A septic tank contains a blend of sewage made to duplicate the typically generated kind composed of horse manure, cheese whey, urea pellets and well water. (That did smell like sewage!) Detergents, papers and other solids typically found in sewage were not included because they normally drop out of this process before the reactions start. To keep the sewage “fresh”, he adds about 5 gallons of horse manure per month.
A programmed controller orchestrates pumps in the septic tanks and tubs. Water from the septic tank alternates flooding and draining through the large planter tubs which contain an aggregate of expanded shale, similar to a road base. It is a geotechnical fill made to construction standard. For David, determining the most effective material was the most difficult part. The pollutants in the water are broken down as it gets pumped through the series of planter tubs.
In this prototype, the end product gets a “non detect” for key pollutants, which means that usable water is being created from wastewater. After a final disinfection process it passes EPA and state standards for application on landscapes. There are five US and several international patents pending on this and other Living Machine® Systems.
Another simpler version of this technology can run by solar panels. First developed for a World Bank project in Africa, it has good potential for remote areas. Requiring more space than the parent system, it is still a significant improvement in wastewater treatment technology.
Living in balance with biology – the Biolarium.
The El Monte Sagrado in Taos showcases a Living Machine under real life conditions and treats the wastewater for the facility. The large greenhouse structure contains swimming pools, the plants, a waterfall, and photovoltaics. El Monte is one of Travel & Leisure’s top 25 hotels in the world, and prides itself on its commitment to sustainable practices. The spa water is not part of the system; Federal regulations require a disinfectant, so Curoxin, a less harsh chlorine dioxide product, is added.
Plants do their waste metamorphosis magic
Wastewater from the lodge circulates through the biolarium plants for cleaning, then is re-used for grounds irrigation. The waterfall aerates and displays the finished clear water from the Living Machine. Large koi eat algae off the rocks.
The outdoor heated soaking pond has fish and plants on a separate treatment system. Storm water collected in the lower storage pond is also used for irrigation, “keeping the local water local”.
A sewer or septic alternative
Living Machines are designed to treat wastewater from neighborhoods and small towns and to fit into local sewage collection systems. Advanced treatment and reuse is cost competitive, around $10,000 per home in a medium size development. Traditional septic costs $3-5,000, but requires larger lots to prevent groundwater contamination. A home sized advanced treatment system in an area with poor soils might cost $20,000 or more. Conventional sewers, treatment and reuse can cost $15,000 per home or more. Living Machine systems are appropriate for developments of about 300 homes, and can realize substantial savings against the infrastructure of typical gravity sewer systems.
Where water is scarce, technologies that can create clean water from wastewater are increasingly attractive. David believes these systems are good science, good engineering and good business.