June 15, 2004 | General

How Novices Became Experts On The Compost Learning Curve

BioCycle June 2004, Vol. 45, No. 6, p. 40
The start-up and operation of the Beltsville composting process provided a thorough education in organic materials handling, windrow size, odor management, compost quality and public acceptance.
James F. Parr

IN THE EARLY 1970s, I was appointed Chief of the USDA-ARS (Agricultural Research Service) Biological Waste Management & Organic Resources Laboratory in Beltsville, Maryland. The Environmental Protection Agency’s Clean Water Act had required that public wastewater treatment plants shift from primary to secondary treatment which resulted in the following: Increased production of sludge (biosolids); Insufficient anaerobic digestion capacity; and Increased ultimate disposal by landfill, ocean dumping and incineration.
Since ultimate disposal methods would likely be short-lived, there was growing interest in the feasibility of sewage sludge application to agricultural or forest lands as a “useful” organic amendment. Thus, USEPA/Cincinnati decided to fund a major research program on sewage sludge composting with the research to be conducted by USDA-ARS scientists and engineers in cooperation with the Maryland Environmental Service. In staffing the biological waste management and organic resources laboratory, we were able to attract some really “top notch” chemists, engineers, microbiologists, plant scientists, soil scientists, agronomists, and even two economists (acquired “on loan” from USDA’s economic research service) to conduct the research program. some of our original staff are still involved professionally on aspects of sewage sludge management and utilization including Dr. Eliot Epstein, private sector; Dr. Patricia Millner, USDA-ARS; Dr. John Walker, USEPA (now retired); and Dr. Rufus Chaney, USDA-ARS. Nevertheless, when we came together as a research team, very few of us knew very much about either sewage sludge or composting and, thus, we proceeded to take our places on the learning curve.
And learn, we did, especially from our mistakes and lack of foresight! The following brief accounts of lessons learned are based on problems we encountered at the USDA-ARS sewage sludge composting facility and solutions rendered to ensure an efficient and effective composting process technology and high-quality product. Even though these lessons were learned 30 years ago, there may be some relevancy for sludge composting initiatives today. The lessons are listed in the approximate order in which we learned them.
Lesson #1
It’s difficult to conduct composting research trials at a compost production facility – but not impossible.
Our research grant – negotiated with USEPA and the Maryland Environmental Service – called for construction of a composting pad to explore the feasibility of processing a certain number of tons of mixed primary/secondary sewage sludge each day from the District of Columbia’s Blue Plains wastewater treatment plant. Our intention was to develop a dual purpose production and research facility. But it’s said that “the streets of hell are paved with good intentions,” and we found that production soon takes over leaving little time/energy to do research trials.
The sludge – 150 to 200 wet tons delivered to the pad daily – had to be dumped appropriately, mixed with wood chips or other bulking material, built into windrows (or later, aerated piles), periodically turned for aeration then after 30 days placed in curing piles (four to six weeks). Finally, after screening to recover/recycle the wood chips, finished compost was placed in storage piles.
Meanwhile, we were trying to determine the effects of such variables as sludge/bulking agent mix ratios, temperatures, moisture content, and windrow turning frequency on the composting process, screening and compost quality. A logical solution might have been to separate production entirely from research, which I was sorely tempted to do. But thank goodness I didn’t, because before too long observation and intuition came to the forefront and both initiatives – production and research – began to feed off one another, somewhat symbiotically.
Lesson #2
Scientists and engineers utilizing sewage sludge from a particular POTW for compost production or research must know its chemical, physical and sometimes microbiological properties prior to composting, and what industries are utilizing the sanitary sewer system.
Chemical, physical and microbiological properties of sewage sludge can significantly affect compost process technology and product quality. We found, as others have, that the chemical properties (i.e., heavy metal, PCB, lime, or pesticide content) and physical properties (i.e., solids and moisture content) can vary markedly over the short-term depending on inflow, how the plant is operated, and maintenance problems. Such variations, especially in chemical properties, can often cause aberrations in compost chemical quality.
These same concerns also apply to cocomposting of sewage sludge with other organic wastes. A few years ago, researchers at Washington State University were cocomposting sewage sludge with clippings from lawns that had been treated with a turf herbicide (i.e., Dow Agrisciences clopyralid). Unfortunately, the thermophilic conditions achieved in the composting system failed to sufficiently degrade or inactivate the herbicide to prevent residual carryover into the compost product. Consequently, compost users experienced severe phytotoxic effects on vegetable and ornamental species.
Lesson #3
Using bioassay tests can help to detect potential phytotoxic effects from heavy metals and residual organics (e.g. pesticides) in sewage sludge composts and cocomposts.
We used bioassay tests routinely throughout our sludge compost production and compost research programs to good advantage. Such tests allowed us to avoid potential phytotoxic problems and gave us confidence that we were producing safe, reliable and “plant-friendly” compost products.
Lesson #4
We found that the windrow method was not adequate for composting raw limed sewage sludge because of the high potential for odor emissions.
It became apparent that the windrow method of composting was yielding incompletely composted sewage sludge. Temperature monitoring indicated that we were not getting far enough into the desired thermophilic (50° to 70°C) range for good composting to occur. Not surprisingly, odor problems intensified. The situation became even worse when it started to rain and a temperature inversion settled over the composting site.
Yet, we still tried to process our sludge allotment from the Blue Plains plant but soon ran out of wood chips – and all hell broke loose. We created one big stink! Our phones rang constantly, we stopped traffic on the Baltimore-Washington Parkway and were soon visited by U.S. Congresswoman Gladys Spellman who demanded an explanation. After getting it, she advised us to shut down immediately and to go back to the drawing board, which we did. This was how the Beltsville aerated pile method of sewage sludge composting was conceived.
Lesson #5
Attempts to mask offensive sewage sludge odors at a composting site by spraying with some “pleasant smelling odoriferous formulation” found abandoned in a warehouse, can dramatically exacerbate the problem.
Yes, in sheer desperation we did try this, but the interaction of the two generated an odor that was far more offensive than sewage sludge by itself.
Lesson #6
The Beltsville aerated pile method became a highly effective means of composting sewage sludge because it provided for control of odors, aeration and temperature.
Yet, “good housekeeping” needs to be done every day at a composting facility to prevent odors.
Lesson #7
Land application of incompletely composted sewage sludge invariably results in a crop of tomatoes.
The incompletely composted sewage sludge remaining from our windrow method was placed in a curing pile where some further composting occurred. Finally, it was given to the Maryland Parks Department who was looking for “organic matter” in developing a new park. This resulted in about 20 acres of tomatoes of all shapes, colors and sizes. Tomato seeds remain viable even after passing through the human digestive tract and when composting temperatures don’t reach the thermophilic range. The thermophilic temperatures obtained with the Beltsville aerated pile method effectively destroyed the tomato seeds. After this, we never again found tomatoes growing at compost land application sites.
Lesson #8
It is absolutely vital to develop and maintain good public relations with people and communities in close proximity to a sewage sludge composting facility to minimize the “NIMBY” syndrome as much as possible.
I saved this until last, really to emphasize that it’s probably the most important lesson of all. Usually scientists, engineers and laboratory directors are reluctant to engage in public relations and feel they can go it alone. But on issues as sensitive as composting/recycling of sewage sludge (i.e., biosolids) or MSW, it’s pretty important to have most of the public on your side. I’ve really been impressed by how supportive the public can be if they know what you’re trying to do, and why it’s important.
Certainly there are those who’ll always view these operations negatively, and some certainly wanted Congresswoman Spellman to shut us down forever, but she said “this is important research, let’s give them another chance.” Some of our “neighbors” suggested that they’d be even more supportive if they could get some compost for their lawns/gardens.
By then we were producing a very high-quality product – so, on alternate Saturday mornings we opened the gate so each family could get a canful or a few gunny sacks of compost. A few years later when we received a major achievement award from then USDA Secretary Bob Bergland, Congresswoman Spellman attended the presentation and asked to have a photo taken with our staff which she then included in her newsletter to district constituents.
While other “lessons” were learned as our research and development program proceeded, these are the ones that will remain so vividly in my memory of the USDA-ARS sewage sludge composting project at Beltsville.
James Parr spent his professional career largely with USDA’s Agricultural Research Service as a Research Scientist and National Program Leader on aspects of soil organic matter management. He served as Chief of the USDA-ARS Biological Waste Management and Organic Resources Laboratory at Beltsville, Maryland during 1975-84 where he directed sewage sludge composting research and development programs.

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