June 21, 2007 | General

Biosolids Opportunity In Tacoma, Washington

BioCycle June 2007, Vol. 48, No. 6, p. 37
In addition to gaining public acceptance, the Tagro product line has created an income stream for the city – $400,000 in 2006.
Sally Brown and Dan Thompson

TACOMA, Washington is one of the few municipalities in North America that truly looks at its biosolids as an opportunity rather than a liability. The anaerobically digested biosolids cake is viewed as the starting point from which to make much bigger and better things, all with the consumer in mind.
Tacoma, located 30 miles south of Seattle, has two wastewater plants that provide secondary treatment. The average flow is about 27 MGD, yielding 4,000 tons of dry solids. The Tacoma Sewer Utility has a dual digestion system at its Central Plant – first stage aerobic thermophilic digesters fed pure oxygen, followed by a set of digesters operating in an anaerobic thermophilic/mesophilic range. The resulting Class A solids are dewatered in a two-stage belt filter press.
An article in BioCycle five years ago, “Dual Digestion System Yields Class A Biosolids” (August 2002), provided technical details on the flow into the plant and the digestion process, and even made mention of what Tacoma does with their Class A cake. At the time, the city was producing Tagro (short for Tacoma Grows) Classic, a blended soil material made of cake, sand and sawdust. Since then, Tagro has expanded its repertoire. The cake is now mixed with aged bark, sand and sawdust in different proportions, and aged to make Tagro Mulch and Tagro Potting Soil.
The bags for the potting soil, as well as the sales and marketing materials for the mulch and the classic mix, don’t shy away from the fact that biosolids are the basis for all three products. This is clearly stated in the literature. However, emphasis for all of the products is on the miracles that they can work in the garden. Tagro also maintains a website (http://www., which has sections for the home as well as the commercial user. The home page starts with the question: “How does your garden grow?” The reply: “With Tagro premium soil products, it will grow faster, greener, better.” There is a section on the site called “What’s in Tagro?” Here the emphasis is on plant nutrients (Table 1). Research by two local universities showing Tagro is better for plants than commercial or chemical products is cited. The site also mentions the products are made from Class A biosolids (the USEPA’s highest rating) and includes trace metals content (Table 2).
Much more attention is paid to the benefits associated with use of the products than any potential hazards. The garden at the plant, the wall of ribbons from the County Fairs and garden shows, as well as the long line of customers waiting to fill up, attest to this basic fact. The questions that Team Tagro is asked are generally about when more mulch will be available and how to best use the line of products in their gardens. When questions about subjects like pharmaceuticals in the wastewater solids arise, they are answered, but these questions are few and far between.
Tagro is a household word in Tacoma. A day spent in the Tagro office really drives that point home. Two people answer the phones for delivery orders; the board with the next month’s deliveries fills up as you watch. Outside, it is first come, first serve for the different products. People from all walks of life and all parts of the world live in Tacoma and they all seem to come for their Tagro. Recent immigrants from Asia, older guys in their pickups, ladies in their BMWs and even an occasional man in a suit (a rarity in the Pacific Northwest) are all customers.
What you also notice is a feeling of pride from the staff involved with production and sales. In many ways, Gordie Behnke and Tom Amundson are the heart and soul of the operation. Both are avid gardeners. Behnke is often the spokesperson for Tagro, giving workshops for gardeners, treatment plant operators and local school children. He’ll bring buckets of cake, sand, aged bark and sawdust, and let the audience try their hand at making their own mixes. Sticking your hands right into the cake is part of the whole process.
In addition to gaining public acceptance, Tagro has created a source of income for the City of Tacoma. While local citizens can load up on Tagro Classic for free, the mulch and the potting soil are available for a price (delivery is available as well for a fee). For a city of 200,000, sales were close to $400,000 in 2006 – not an insubstantial sum for a material that most municipalities pay to have taken away. Table 3 shows costs and revenues for the biosolids program over the past four years; Table 4 breaks down production costs and price margins.
The Tagro model illustrates that pride in product and a focus on what the consumer wants can be the basis for a successful biosolids business. Class A cake offers a wide range of end use options. Mixing the cake with other materials is what yields consumer friendly products. Another municipality in the area, Abbottsford, British Columbia, saw what Tacoma was doing and started experimenting with mixtures themselves. With the aid of Sylvis Environmental, the City of Abbotsford also has developed a soil product using biosolids as a base. Just like in Tacoma, demand for Val-E-Gro is high. The citizens of Tacoma are not unique in the world in their acceptance of biosolids. What is unique is Team Tagro’s focus on creating products whose benefits are clearly shown with every tomato plant or rose bush planted.
Sally Brown is a Research Associate Professor at the University of Washington in Seattle. Dan Thompson is Wastewater Division Manager with City of Tacoma Environmental Services.
Kristen McIvor
I had never heard of biosolids before. To be honest, I’d never even thought about the concept. Sure, I was aware on some level that treated sewage would make good fertilizer, but I’d never made the connection between what went down my toilet and where it went. But I did know about growing food, believed in the power of community gardens to bring people together, and felt strongly that urban dwellers could begin to play more of an active role in providing food for themselves. And so it began…
Through a series of random connections, I came to be sitting in the office of Sally Brown, faculty at the University of Washington and a local biosolids guru. After I explained my interests in local food and urban agriculture, Sally looked at me and smiled. “Now, hear me out,” she said, and began to talk about biosolids, Tacoma, and me.
The City of Tacoma happens to make a Class A “Exceptional Quality” biosolids product, the highest rating. Called “Tagro” (short for Tacoma Grow), it’s safe enough to distribute to local residents with no restrictions. In fact, it’s safe enough for vegetable gardening. The idea was this: use Tagro to promote urban agriculture within the City of Tacoma.
My interest was piqued, but I wasn’t sold yet, so we decided to take a tour of the wastewater treatment plant, the home of Tagro. At the plant, I met the guys who have made Tagro the success it is today, and got to see the stuff close up. I don’t know what I was expecting it to look or feel like, but not something as innocent and compost-like as Tagro.
I still wasn’t sure I would be able to promote the idea of growing vegetables in human waste. Some quick Internet research brought up more questions. What about heavy metals? What about all the industry that dumps in the sewer? Could this really be safe for food? I’m an organic food person, spending a high percentage of my mediocre income to make sure my food is safe. One of the reasons I am an advocate of growing my own food is because I don’t automatically trust the food I see in the store. Conscious of the environmental and social cost of Big Agriculture, I wasn’t sure that treated sewage was a move in the right direction. But I was intrigued by the idea of turning wastes into resources, and the idea of using local biosolids for local food production started to seem elegant in a way – recycling at its finest, closing the loop.
So I dug into the research, and asked a lot of questions. I found out that, yes, there are heavy metals in biosolids, but that the levels in Tagro are lower than the background levels in my own front yard. I found out that flame retardants also show up in biosolids, but not in anywhere close to the concentrations they are found in my pajamas, or in my couch cushions. The more questions I asked, the more it became clear that the people who’d been spreading biosolids for years had asked all the same questions. The body of research was not only deep but wide. I ordered six cubic yards of the stuff for my own vegetable garden at home.
Since that day, I’ve talked to many local people about Tagro and urban agriculture, and found an overwhelmingly positive community response. Faculty and students at four different universities, advocates for low-income housing, a local 4-H club, long-time community activists, environmental educators, nutritionists, Master Gardeners and city staff have all responded enthusiastically to the idea of using Tagro locally to support growing food in the city.
Community gardens teach children about ecological cycles and the importance of healthy food, provide immigrants and low-income residents with access to fresh and culturally appropriate vegetables, and act as a catalyst for neighborhood groups to come together. By promoting community gardening with biosolids, we also can facilitate an understanding of the importance of wastewater treatment, increase opportunity to recycle biosolids locally, and demonstrate the ability of biosolids to improve quality and safety of urban soils.
It really is a beautiful solution to many of the chronic problems cities face: what to do with waste, food coming from farther and farther away, neighborhoods where neighbors don’t know one another, impoverished and contaminated urban soils. By turning waste into a resource to bring communities together around fresh food, Tacoma is taking a big step towards creating a sustainable city. It won’t happen overnight. We’ve just begun, and we’ve got a long way to go. But it will happen.
Kristen McIvor is a Ph.D. candidate at the University of Washington.

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