Most wastewater treatment plants squat on the seedy outskirts of towns. Drab, energy intensive and fetid, they can use harsh chemicals and are often ineffective against certain pathogens.
For decades scientists have been investigating healthier and smarter alternatives to conventional treatment systems. In the 1940s and 50s, despite the belief then that higher plants can’t withstand polluted waters, Dr Käthe Seidel from The Max Planck Society discovered that bulrushes don’t just survive polluted conditions, they restore them. This earned her the mocking moniker ‘Bulrush Kate’, but did not prevent Seidel from developing a system of basins containing plants that transformed polluted water into a cleaner end product. In time, though, it became clear that microorganisms, not plants, are the heavyweight cleaners.
Following in Seidel’s footsteps, the ecologist H.T. Odum created guiding principles for the emergent fields of ecological design and ecological engineering. These principles were based on his conviction that a sustainable future depends on our ability to incorporate nature’s closed-loop, systemic design into our own. Dr John Todd picked up the baton in the early 1970s. After experimenting with ecologically engineered solutions to various other applications, including architecture, aquaculture, and food production, the Canadian biologist developed what he called the ‘Living Machine’. This is a biologically sophisticated, low energy wastewater treatment system that mimics natural purifying mechanisms such as marshes and wetlands. The machine is also beautiful. So beautiful, in fact, that black and grey water could be treated under our noses and we would bend down for a whiff.
A first at Findhorn
The first Living Machine was installed in 1995 at the world-renowned Findhorn Ecovillage in Moray, Scotland, and continues to treat the waste of approximately 300 people. Here’s how it’s done: sewage is first collected in three 30m3 anaerobic tanks that are buried outside of the greenhouse (where the rest of the system is stored). The tanks encourage the growth of anaerobic bacteria, which break down organic and inorganic materials. According to Michael Shaw, a founding member of The Ecovillage Institute at Findhorn who was present when the Living Machine was installed, the bacteria that form in anaerobic environments are among the oldest life forms on Earth, up to 3,000 million years old. Inside the greenhouse are two rows of nine tanks that operate in parallel. After becoming sufficiently soupy in the initial septic tanks, the water flows by gravity to the fourth, closed tank inside the greenhouse, where air bubbles are ushered in to convert the effluent to an aerobic state. The introduction of oxygen kills anaerobic bacteria, giving off a gas that is then filtered out to prevent odours.
The most important task of the next four open aerobic reactors is to maximize the surface area on which a diverse array of microbial communities, or biofilm, can flourish and therefore digest particles in the water. Diversity, as elsewhere in nature, is key to resilience. To achieve this, suspended plant racks support plants with long roots upon which bacteria multiply. Daffodils are among those that Findhorn uses, though any long-rooted plant that can withstand high strength wastewater will work. These plants also consume nutrients and destroy harmful pathogens in the water, which is so rich, according to Sukanya, who maintains the Living Machine, that duckweed trebles its usual growth of 20-30cm each day.
In the next clarifier tank, activated sludge flock, which is a sticky substance comprised of free-swimming bacteria that clump together, separates from the rest of the water and sinks to the bottom of the tank. This sludge is then shuttled back to the first anaerobic tank for another round of treatment. Shaw notes that whereas many wastewater treatment facilities dispose of their sludge daily, Findhorn only disposes of its every four or five years. As a result, the system is less environmentally hazardous, less expensive - and including gas used to keep the greenhouse at 5°C as well as electricity required by aeration pumps - only uses 40,000 kWh annually.
|A schematic diagram of the Findhorn Living Machine system. Click the image to see an enlarged version
Dealing with nitrogen
Whether achieved conventionally or holistically, the final task of any water treatment system remains the same: nitrify ammonia, denitrify the resulting nitrate, and remove phosphorous. The majority of this work occurs in the next three ecological fluidised beds. Filled with highly porous material (such as gravel) that ‘carries’ biofilm, the beds are subjected to alternating anaerobic and aerobic treatments facilitated with special air pumps. According to original Living Technologies Ltd. literature, the ‘aerobic operation provides reductions in Biological Oxygen Demand (BOD) and Total Suspended Solids (TSS)’, while the anaerobic operation enables denitrification.
Finally, this polished water is sent to a pond before the water is pumped underground to nearby sand dunes in Moray. The Scottish Environmental Protection Agency (SEPA) regularly conducts quality checks, and in the fifteen years of its operation, Findhorn’s Living Machine has never been out of compliance. The genius of the system is the genius of nature: virtually nothing goes to waste. Every organism provides food for the next step in the food chain until the cycle is complete. Of course, an even more complete system would pump the finished product back to use for non-potable purposes, but the Living Machine at Findhorn was a first generation installation that has since undergone numerous permutations. Today, the trademark Living Machine technology is offered exclusively by Worrell Water Technologies, LLC, while Dr Todd and others have split off in different directions around the world.
|The Living Machine® system at Old Trail School in Ohio is an advanced wetland system, composed of three different wetland processes which treat 5,000 gallons of wastewater per day. Photo courtesy of Worrell Water Technologies, LLC
The next generation
Worrell’s most recent development borrows its inspiration from tidal wetlands. Wetland ecosystems act as a buffer zone: stormwater runoff from either urban or agricultural land, sewage discharge or other contaminated water flows into the tidal wetland, which then naturally purifies the water before it is released to rivers or bays. According to the Queensland Environmental Protection Agency, a healthy wetland system, which floods and drains twice a day, ensures that water is suitable for drinking and for other uses such as irrigation and industry. When Worrell took over the Living Machine, he wanted to do away with the activated sludge and the secondary clarifier stage of water treatment. By incorporating tidal wetland ecology into the Tidal Wetland Living Machine System® (TWLM), while maintaining the basic steps of the original technology, he was able to do just that.
After the initial septic treatment, water in the TWLM is flushed through a series of wetland cells that are flooded and drained, which transfers oxygen to the wastewater. Compared to the TWLM, Findhorn’s aeration pumps devour energy. Austin and Nivala wrote in Ecological Engineering that tidal wetland systems reduce the energy demand to about 25 per cent of that required by activated sludge systems. Also, nitrification and denitrification occur differently: nitrification takes place when the wetland cells are drained, and denitrification occurs when they are flooded. This cycle may occur up to fourteen times a day depending on how heavily loaded the wastewater is, says Will Kirksey, Worrell Water Technologies’ Vice President, and eradicates methane and nitrate byproducts.
|The Living Machine® system is the architectural centerpiece in the lobby of the Port of Portland’s new headquarters office facility at the Portland International Airport. Photo courtesy of Worrell Water Technologies, LLC
A commercial reality
In a testament to the growing acceptability of the technology, the Port of Portland in the US recently commissioned Worrell to produce a TWLM system to treat 5,000 gallons of their wastewater each day. At the end of the flood and drain cycles, the water is disinfected as an extra precaution before it is returned to the system for cooling towers, and to flush toilets.
The TWLM system also includes internet-operated control technology that can be modified with on-site touch screens, and the even have an iPhone application that can adjust cycle frequency as necessary. When questioned about using advanced technology despite ecology’s proven finesse, Kirksey responds that technology may not replace nature, but it can help nature to restore itself.
The experience at Findhorn demonstrates, however, that while the microorganisms and plants bloom, the human component is more fallible: Sukanya frequently fishes out bottles and other rubbish that are flushed through and block Findhorn’s sewage system. Or the pumps – which cost approximately £1,000 each – wear out and have to be replaced. Still, the TWLM boasts exceptional water treatment, with no theoretical limit to potential capacity, that can be used in municipalities, residential and office developments, schools, hotels, zoos, farms, and other facilities.
Tafline Laylin is a freelance journalist
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