April 15, 2005 | General

Trends In Class A Biosolids Production

BioCycle April 2005, Vol. 46, No. 4, p. 30
Wastewater treatment plants from across the nation report techniques for creating a “consumer friendly product” that brings cost savings and pathogen reduction. Part II
Sally Brown

IN the survey that was conducted for this article, two municipalities used Class A biosolids either to retain existing agricultural markets or open new ones. In one case, the Eastern Municipal Water District in New Jersey pasteurizes biosolids through the use of heat exchangers, notes Ann Briggs from the wastewater agency. When the process is up and running, Class A pathogen reduction is achieved. Following pasteurization, the biosolids are dried on drying beds, then applied to a sod farm. This type of farming operation offers a very desirable potential market for biosolids generators. Sod farms are often located near municipalities, reducing costs associated with transport. In addition, a routine operation at sod farms is removal of a portion of the topsoil layer with each sod harvest. In order to grow lush sod, high rates of nitrogen are required. For these reasons, sod farms would appear to be a large potential market for Class A biosolids that is still recognizable as biosolids cake. (See Part I in March, 2005 BioCycle – “Evaluating Benefits of Class A Biosolids Cake Production.”)
Orange County, California provides another example of a decision to produce Class A primarily for agricultural markets. In Orange County, about 60 percent of the biosolids produced are processed outside of the treatment plant to achieve Class A pathogen reduction. This is done by composting the portion of the biosolids targeted for the home gardener and by lime addition for an agricultural product. Lime addition results in a product that is similar in appearance and odor to the Class B cake. It is somewhat drier and has less of an ammonia smell, but according to Michael Moore, manager of the program, “we still treat it like Class B and direct land apply it so as not to cause a nuisance. We call this product Agricultural Grade Class A and recognize that it is not consumer friendly.” The Agricultural Grade Class A goes to exactly the same end users as the Class B.
In Orange County, the decision to produce a Class A biosolids was based on a number of factors. These include regulatory restrictions associated with Class B biosolids and reduced restrictions for Class A biosolids. In addition, both the county’s Environmental Management System for biosolids and the Long Range Biosolids Management Plan supported a move to Class A to gain greater public acceptance. Moore notes that for both programs, public outreach and education are essential components. “Public acceptance is of prime importance for Class A products as well as for Class B land application. Outreach, education and public involvement are needed for any operation.” The transition to Class A production has not been without problems, he adds. “Because of our new Class A lime stabilization, a nearby land owner is experiencing increased odors and flies. Our processing unit is relatively close to their main office and it releases a lot of ammonia and the water at the processing site appears to attract flies. In addition, because the nitrogen content is lower in the Class A product, farmers are applying at higher rates, which also may cause more odors than the Class B product. We are working to mitigate these issues.”
Moore adds that the compost component of the Class A program is gradually achieving its desired end. A local customer base is being established for the finished product: “Our Class A compost is quite different in that the product is treated like a valuable resource.” Although the final compost is more acceptable to the public, there are problems associated with composting. Facility neighbors have expressed concerns and a high level of community outreach and relationship building will be required to gain public acceptance of the facility.
Orange County has been producing a Class A biosolids off and on since the 1980s. It initially shifted to Class B in order to save money. Annual operating costs for the Class B program three years ago were $4.5 million. Having a mixed Class A and B operation has doubled annual operating costs. Costs are also further expected to increase with installation of a facility to dry and pelletize the biosolids.
It would appear that production of Agricultural Grade Class A is not in and of itself sufficient to achieve the dual goals of cost reduction and increased public acceptance. The lime stabilized cake has many of the same beneficial characteristics as anaerobically digested cake (with lower fertilizer value and higher lime value). However, it also appears to have many of the same negative characteristics including high moisture content and odor. It has been perceived to increase vector attraction and there are complaints from neighbors at the mixing facility. In other words, public acceptance concerns did not magically go away with the introduction of a Class A material. Expenses also have not gone down. This is a case where a traditional land based application approach has been continued, with the substitution of Class A for Class B materials. It’s possible that in the political climate of Southern California, continuation of an agriculture based Class B program was no longer feasible. Increased costs associated with Class A production should be looked at in that light. It also appears that the municipality has decided to opt for pelletization, rather than attempt to find a means to produce a Class A cake that is consumer friendly.
In the Pacific Northwest, the Midwest and the Northeast, there are some examples of municipalities making a conscious decision to produce Class A cake as an initial step towards developing local markets.
In Centralia, Washington, the waste-water treatment plant opted for lime stabilization to achieve Class A. This decision was made cooperatively with input from a Citizen Advisory Committee and the City Council. Both groups were aware of concerns related to Class B biosolids and saw lime stabilization as a cost-effective means to achieve Class A. As part of the decision making process, the Mayor of Centralia was taken on a tour of a plant that produced and sold Class A biosolids and was convinced that this was the appropriate route for his municipality. Although Centralia now produces a Class A cake, it has the consistency of “crunchy peanut butter” with a more palatable odor, like cement being worked rather than peanuts. That consistency, however, does not lead to easy use in a home garden. Jim Fleming, the program manager views this as a step in a process towards achieving a locally based program: “Our previous Class B product cost us $35/wet ton to transport and land apply. The City did not want to look at that cost for the rest of time, when Class A allowed either sale or giveaway to the public. Class A was chosen so that we could use our production locally. We are in the midst of a marketing study to search out local customers to sell the material to. We are also looking at equipment and processing needs to transform the ‘pasty’ form being produced into a more home-user friendly consistency – all with active support of the City Council.” Although the success of this approach remains to be seen, it appears that involving multiple stakeholders early on in the decision making process, and making the decision without great local pressure for immediate change, bode well for the program.
The city of Bremerton, Washington produces a Class A cake through a heat treatment process, which increases the solids content of the finished product to 22 percent. However, it still has an odor associated with it, according to John Poppe, former manager of the program, noting that a well-trained nose can distinguish between the old and the new materials. One of the largest benefits that Bremerton has seen with Class A is the reduction in regulations and monitoring requirements for its use. The City had a silviculture-based Class B program and still applies the Class A cake to forest sites. However, as a result of having a Class A product, additional sites have become available. These include gravel pits and baseball fields.
In New Hampshire, Resource Management, Inc land applies both anaerobically digested (Class B) and RDP lime-treated (Class A) biosolids. The Class A cake has fewer regulatory restrictions associated with land application, but currently both materials go to similar sites. These include agricultural lands for forage crop production and as a component of manufactured topsoils for reclamation projects. Although the RDP process is sufficient to reach Class A, there is still an odor associated with the product. Because of the odor and other properties “there are some limits on its use, as it is still a 26 percent cake that you do not want the average gardener wading around in,” according to Charley Hanson, a project manager for Resource Management. Adding a high carbon wood ash during the RDP process is being tested, and seems to be very effective at absorbing odors. If this works on a full-scale basis, Resource Management plans to start charging for the cake and identifying more visible sites for marketing. On the other hand, “once the anaerobically digested cake gets A status, we will continue to market to the same types of outlets as before as there is no physical improvement to that material,” he explains. “But we will not need to do site specific permitting.” The per dry ton cost of handling the materials is currently $70 for the RDP processed biosolids and $192 for the anaerobically digested cake.
Madison, Wisconsin has an award winning Class B liquid land application program, applying biosolids to local farms. According to Dave Taylor, all liquid is subsurface injected and has been since the advent of the program. Although public support for the program is high, injection restricts the months where land application is feasible. All of the biosolids that are produced must be land applied during a six month window – two months in the spring, and four months in the fall. A decision was made to build a TPAD system, and use a portion to make a blend based on a Class A cake for greater flexibility: “Producing a soil like material that could be used in an agricultural setting basically provides flexibility and expands our application window,” says Taylor. “These were the two primary motivators in our decision making.” Production of the soil material is not expected to replace the liquid program. It is expected that at most, it will use 25 percent of the biosolids produced. Conversion of the digesters to the TPAD process is underway, as is installation of the blending facility. The new processes are expected to be on line by the end of 2005.
Adds Taylor: “The decision to go to Class A for both our liquid and soil like material was initially driven by operational concerns, not marketing concerns. We needed additional digestion capacity and had some other issues to address. TPAD allowed us to address these needs. The production of a Class A product was initially viewed in a ‘value added’ context. As we progressed in our planning efforts, the ability to produce a Class A product took on greater importance. We have not had any significant issues related to land application of a Class B product, however, we felt producing a Class A product in a cost-effective manner would be a good business/marketing decision.”
It is not expected that Class A will immediately reduce costs “With respect to production of a Class A soil like material, our costs during the first few years will probably be greater than the costs associated with our agricultural land application program,” he notes. “There are lots of reasons for this, including the significant amount of research that will be required to support product development and marketing. Once the program is established, I suspect that the costs could very well be less than the cost to operate our agricultural land application program.”
Madison has started “playing” with different mixtures to create a soil material. This began with visits to the Tacoma plant several years ago. The treatment plant will evaluate whether partnering with a local private company to develop blends makes sense. “The rationale is that a private sector company may be able to offer experience in blending and mixing operations that the District doesn’t have,” says Taylor.
Based on this limited survey, several trends are apparent from the programs that have been described. The most important is two fold: Producing a Class A biosolids cake can result in very large cost savings for a municipality, however, the cost savings do not follow as an immediate consequence of removing the pathogens. The programs that have achieved the greatest success, Everett and Tacoma, realized either early on in the process or through trial and error, that achieving Class A pathogen reduction was the first step in a process of developing a consumer friendly product.
For a Class A program to realize financial gains, it is important to reduce or eliminate the transportation costs associated with beneficial use of the biosolids without greatly increasing processing costs. For the vast majority of programs in larger municipalities, this means identifying users other than conventional agricultural outlets for a material that looks and smells similar to anaerobically digested biosolids cake. Programs based in primarily urban areas may have to develop a market for the biosolids within the municipal structure and/or with residents in the municipality. For this to be successful, certain of the characteristics of the biosolids cake have to be altered to be more user friendly and to have a more acceptable appearance. It is possible to achieve Class A pathogen reduction and simultaneously improve the appearance and marketability of the biosolids. Conventional technologies that accomplish this, such as composting or pelletizing, can yield products suitable for local markets and are not generally associated with public acceptance challenges, however, the cost to produce them may far exceed the savings associated with reduced transportation and revenues from product sales.
If a program opts for a stabilization technology that achieves Class A pathogen reduction but does not dramatically alter the appearance, moisture content or odor of the biosolids, then Class A must be viewed as a first step in a process towards developing a product that will be suitable for local markets. Achieving Class A will reduce permitting and regulatory requirements, which will save time and money but alone isn’t sufficient to guarantee the success of a local program. Attempts to market cake as such are likely to fail because it is not consumer friendly. As pointed out in this article, several municipalities have successfully developed products using Class A cake as a basis. The prime example of this approach is the City of Tacoma.
Other municipalities have copied this approach with success. Everett is perhaps furthest along of the cases discussed in this paper. As a result of blending its biosolids with ash, Everett is able to use all material locally at a cost of less than $10/ton compared to the $30/ton cost associated with land application in forestry and agriculture. Bremerton, Centralia, Madison and Resource Management Inc. in New Hampshire are following a similar approach. In each case, the program managers have understood that making a consumer friendly product is integral to success. Cost savings are projected but are expected only in the long term. For all of those municipalities, the decision to produce a Class A biosolids was the first step in a product development process. All expect to find greater end use options and greater flexibility as a result of having a Class A material. In addition to the programs detailed above, Chris Peot from DCWASA (DC Water & Sewer Authority) toured the Tacoma facility to see how this approach could be applied in the Washington D.C. area. It would seem that blending using locally available materials offers a cost effective means to create a user friendly product from Class A cake. Development of programs based on blending may be a new paradigm for biosolids managers attempting to go the next step from successful Class B agricultural programs.
It must also be understood that getting rid of the pathogens does not necessarily eliminate all concerns regarding beneficial use of biosolids. The example of Vancouver, BC makes it clear that concerns over biosolids safety don’t immediately disappear with the pathogens. As with all things, use of biosolids has associated benefits as well as risks. For a program to be successful, it must be recognized that the benefits associated with biosolids far outweigh the risks. When a consumer friendly product is developed, it seems that consumers have no problem realizing this. And the municipalities have no problem recognizing the environmental and cost benefits as well. It would seem that the group with the most to lose from the transition to a Class A product are the farmers who have reaped the benefits of Class B cake for many years.
Sally Brown is a Research Assistant Professor, Soil Remediation, in the College of ForestResources, University of Washington. This article is based on a paper presented at the 2004 Northwest Biosolids Management Associations “Biofest” conference (

Sign up