The natural way to clean wastewater

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Courtesy of BioCycle Magazine

John Todd founded Ocean Arks International in the 1980s, where he started to experiment with processes that mimic natural ways to purify wastewater. He built a greenhouse and ran sewage through a series of tanks, with plants suspended in the flowing waters, and constructed marshes made of sand and gravel. No chemicals were added, but plenty of aquatic creatures from snails to small fish were brought in at different stages to clean the waters.

Todd regarded his concept of Eco Machines - using ecological engineering to mimic natural processes to treat wastewater - as a start to “embracing a new relationship to the natural world which can sustain us all.” Over the years he refined his ideas and broadened the scope of his thinking. Now he calls for “ecological and economic integration” where the whole concept of waste literally disappears, and is replaced by supplying materials as inputs to processes that create value for society.

THE BEGINNINGS
One of the first Eco Machines was installed adjacent to the wastewater treatment plant in Providence Rhode Island. There, for five years, Todd demonstrated that natural systems could “successfully remove nutrients, toxic chemicals and heavy metals from city sewage.”

He argued that Eco Machines were capable of achieving tertiary treatment at a lower cost than conventional technologies without the use of toxic chemicals that harmed the environment. Furthermore, Todd maintained that flowers and fish could be grown, not only for aesthetic purposes but to offset the costs of running wastewater treatment facilities.

His ideas attracted attention at the U.S. Environmental Protection Agency (EPA). In the early 1990s, the EPA funded a study of four demonstration projects using Todd's “Advanced Ecologically Engineered Systems (AEES)” in Frederick County, Maryland, South Burlington Vermont, Harwich Massachusetts and San Francisco California. The goals for the AEES systems were similar to established standards for conventional wastewater treatment plants: BOD < 10mg/l; TSS < 10mg/l; Ammonia Nitrogen <5mg/l; Total Nitrogen <10mg/l; and Total Phosphorus <3mg/l.

The EPA evaluation - which focused on the systems in Frederick County and South Burlington - found “the currently designed process capable of meeting all of these goals (with municipal wastewater influents) except those for Total Phosphorus. The AEES systems were able to remove about half of the phosphorus, “which would not always be sufficient to meet the 3 mg/L standard” for typical municipal wastewaters, noted the EPA report. The evaluation also showed that AEES systems “provided significant removal of fecal coliforms.” In the South Burlington demonstration “wastewater influent typically contained 8 2 106 MPN/10mL while the final effluent averaged 1,200 MPN/100mL.”

Although the demonstrations were successful, the projects themselves shut down after funding from EPA ran out in the late 1990s. However, private companies followed along to market AEES systems for municipal and industrial applications. John Todd continued to design natural systems through Ocean Arks and the for-profit firm he set up with his son Jonathan, John Todd Design.

NATURAL SYSTEMS
In the world of natural systems, each situation is truly unique. Designs for wastewater treatment depend not only on the amount and strength of the wastewater, but on climatic conditions at the site and the types of plants and organisms adapted to thrive on the contaminants in the flowing stream.

With that in mind we visited two different AEES applications in New England. At New England BioLabs in the Boston area, the Eco Machine “takes waste from lab enzyme production, treats it and releases it into a wetland environment.” The influent varies by season - in the winter it is mostly from production (plus rest rooms, kitchen, etc.), whereas in the summer, HVAC cooling tower water comprises a large amount of the flow. The system is designed to handle 27,500 gallons/day. It came on line in January 2005, and ramped up to full scale in June of that year.

The Eco Machine is enclosed in a greenhouse kept at a constant 80°F throughout the year. A screen over the glass closes at night to retain heat. Andrew Posner, Operations Manager, performs all the tests required of a small wastewater treatment plant and reports that the system consistently meets its goals: BOD<30, TSS<30, TN<10 as well as state standards for heavy metals.

Wastewater entering the system flows into a 16,600 gallon blending tank. From there it is pumped to a splitter box where water is directed into one of six treatment trains. Each train contains four tanks, 6 feet high and 6 feet in diameter capable of holding 1,100 gallons. Tanks are open at the top with floating racks constructed of PVC, holding an array of plants (usually 8 or 9 different species). Depending on the nutrients available, one plant tends to dominate in each tank.

After traveling through those four tanks, which takes about half a day, the wastewater hits a clarifier - an 11 foot tank that holds about 6,000 gallons. There bacteria and other debris settle out within three hours. Clean water runs by gravity to a sand filter and then into a constructed wetland, planted with tropical plants such as cana lilies and banana trees. Posner describes harvesting bananas, grown with the treated wastewater, in the middle of a Massachusetts winter.

After the wetland, water runs into a UV disinfection unit and is discharged to a leachfield a quarter of a mile away. Stringent regulations were imposed by the state of Massachusetts as a condition for the facilities' permit due to concerns for nearby wetlands. To date, the AEES has met them all.

The second AEES installation we toured was at the Sharon Rest Stop, off Highway 89 in southern Vermont. It replaced a failing septic system when the state expanded its Vietnam Memorial at the site. The AEES was designed to serve 2,000 visitors a day in the summer tourist season. Water from the restrooms flows into two underground tanks which function as an anaerobic reactor and a biosolids holding tank. From there it is pumped to a 10-foot tall anoxic reactor, buried about a third of the way in the greenhouse cement floor. Air is supplied by a diffuser. Beneficial organisms convert nitrate to nitrogen and remove BOD from the wastewater.

Water is then pumped into a covered aerobic reactor where most of the remaining BOD is removed. Next, water flows to three hydroponic reactors, each 7 feet tall buried about a third of the way in the greenhouse floor. These open tanks hold vegetation supported on racks with plant roots extending into the wastewater. After that the water goes to a clarifier where solids settle out by gravity. The now clean water flows through a sand filter and is subject to chlorine disinfection and then dechlorination before being reused for toilet flushing or allowed to overflow into a reduced size leachfield.
“The Eco Machine is much easier to maintain than a septic system,” says Louise Caldera of Vermont's Building and General Facilities Department. “I don't have to worry - is the septic going to fail or do I have to switch over to the other leachfield?” Department staff maintains the greenhouse and cuts back vegetation on a regular schedule.

Visitors like the system as well. The colorful variety of plants growing in the tanks surprises visitors, especially on cold winter days. Caldera and others point to the value of showing how wastewater is treated to help dispel the public's “out of sight, out of mind” mentality.

THE RESTORERS
Early on, John Todd recognized that natural systems were as applicable to polluted waterways as to municipal wastewater. Alongside the Eco Machine, he developed and trademarked the Restorer technology for ponds, streams and canals. Restorers are “floating structures that provide the foundation and substrate to support a diversity of life forms…that constitute an aquatic community ecologically engineered to be complex and balanced.” A fine bubble aeration system circulates water through plant roots enmeshed in fabric. The roots of the plants form a living media. Aeration accelerates the ability of those ecosystems to clean polluted waters.

Todd's team designs Restorers mainly for industrial applications. Tyson Foods approached Todd when its plant in Berlin, Maryland was prohibited from discharging wastewater into a local fishing site near Chesapeake Bay. He designed a system that arranged 12 Restorers side by side to treat one million gallons/day of process wastewater. “Textile baffles hanging below the 12 structures create a meandering flow pattern that maximizes water movement through both plant root mass and treatment media,” explains Todd. The result: contaminants were reduced by 95 percent, energy use decreased by 70 percent, and solids by 20 percent. Tyson Foods saved money and met state standards for discharge into open waters.

Restorer technology also has municipal applications. Fuzhou, China, a city of 6 million people, dumps all of its wastewater into canals that run throughout the city before emptying into a large river. Rather than piping the polluted water to a remote wastewater treatment facility, the city government sought an affordable and low-maintenance treatment system within the canal itself. Todd and his Chinese partners built a Restorer on the Fuzhou Canal that handles 750,000 gallons of sewage per day.

The installation uses 12,000 plants from 20 native species. Bacteria adapted to digest sludge and grease are introduced at two separate points along a 500 meter linear Restorer topped by a wood plank walkway. Plants are normally trimmed to allow for new growth. The system met the city's water quality goals in 2002 when it was constructed and became a “pleasant place to stroll” for neighborhood residents.

Eco Machines and Restorers may need less care than traditional wastewater systems but they still need to be maintained; water quality has to be monitored, vegetation pruned, filters and pumps changed, and fish, flowers or food grown in the system harvested. “Operators have to be trained to keep up natural systems designs,” says Todd. At New England Biolabs, the on-site operator monitors and maintains the system and one of Todd's employees goes out every week or two to assure client satisfaction. In China, on the other hand, “as long as we were involved the Restorer worked well,” he adds. But he's heard that the city didn't change filters regularly and “we have no idea how it's worked since we left.”

WHAT NEXT?
The next step in Todd's vision of sustainability is Ecological Integration. “Why can't we design urban communities which put together all the pieces?” he asks. “In fact we can, as the BedZED community near London shows. There, an EcoMachine is situated atop a power station which keeps the greenhouse warm during winter months. No water is discharged to the city's sewer system; instead water is gathered and used on site and returned to the ground where it fell.” The Beddington Zero Energy Development (BedZED) is a carbon-neutral eco-community that incorporates innovative approaches to energy conservation and environmental sustainability.

Todd and his students at the University of Vermont are currently working on a storm water park for the city of Burlington. The park will feature a constructed wetland to treat storm water flowing off the streets of the city before it is released into Lake Champlain. It will “take a problem” from contaminants flowing into the Lake after heavy rains and “celebrate a new solution,” he notes.

He looks forward to a third order of design that he calls Ecological and Economic Integration. An example is a 700 acre Eco Park he and his colleagues are designing in the Intervale section of Burlington. He envisions that excess heat from a wood fired power plant and waste from a local brewery could serve as inputs to a sophisticated Eco Machine that supports aquatic microfarms and other year round food growing opportunities all the while treating the community's wastewater.

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