BioCycle September/October 2019
I recently did a podcast for the Water Environment Federation on biosolids. My main point in the podcast was biosolids are a resource and should be treated as such. Only if the agencies that make the material understand this and use it as their operating principle will their programs be successful. Right now the programs that operate this way are the exception rather than the rule. The fact that my husband listened to the podcast in full earned him innumerable brownie points. I got a Linkedin request or two, some people I worked with said nice things — all within the realm of what you would expect.
I did not expect the email from someone in Florida talking about the negative impact biosolids have had there on water quality. I really did not expect the second email from a different person in Florida, talking about the same thing. These guys really cared about their state and the environment and were trying to find a way to make things right. Both were polite enough, and didn’t call biosolids the equivalent of the black plague. However, they were sure that the biosolids were the critical factor in turning lakes bright green instead of blue. The second email provided a link to an article in the Orlando paper as evidence.
While the article does not prove that biosolids are the culprit in turning the lake green, they do suggest that something is rotten in the state of Florida in terms of biosolids management. Look a little farther than the lake and you can see that plenty is rotten in the state of Florida in the overall case of nutrient management. Florida is an example of a highly fragile ecosystem pushed to the brink. Soils are often just sand, meaning they drain quickly and have a limited capacity to bind nutrients. Due to high rainfall and high temperatures, soils that have particles other than sand are highly weathered and acidic, again making them poor sponges to filter or limit movement of nutrients.
Groundwater is near the surface making it easy to contaminate. In fact, excess phosphorus and nitrogen have caused extensive damage to many of the lakes and wetland systems in Florida including Lake Okeechobee and most famously the Everglades. Many of these systems are phosphorus limited, meaning that excess P can really send them reeling. To address that, the Florida Department of Environmental Protection (FL DEP) has set limits on biosolids application in certain areas so that the material is based on the phosphorus needs of the crop rather than the nitrogen needs.
Because biosolids have a low N:P ratio, this effectively limits application rates. Scientists at the University of Florida have done a lot of research to see how much of the phosphorus in biosolids is actually able to cause environmental harm, generally finding that only a small fraction of the total is available. In other words, both regulatory and research work has been done to address the issue of biosolids as a source of excess nutrients in Florida ecosystems.
Based on these two factors, it is highly unlikely that if biosolids applications are done as per regulations, that biosolids are the culprit in turning the lakes green. However, the two emails and the newspaper article show that while that work may seem complete to the researcher or the regulator, it is far from complete for those in the state concerned about environmental quality. If you take a look at the larger issues, these are more like bandaids on a scrape rather than setting the bones that also broke with the fall. Let’s play doctor here and take a look at the issue as a whole.
Dr. Brown’s Diagnostics
Florida is home to about 20.5 million people. An additional 119 million come to visit each year. Figuring that each guest stays about a week, that adds up to another 0.33 million residents. At 30 lbs of biosolids/person/year, that totals about 312,000 dry tons/year of biosolids. Back of the envelope is pretty close to the FL DEP total of 340,000 dry tons. Maybe the food is just so good there that people produce a little extra. That is a significant amount of biosolids. Right now about one-third is applied to farms, another third goes to “distribution and marketing” (likely homeowners and landscapers), and the last third is landfilled. First thought is no wonder there is a problem finding a place to put it, no wonder they need to landfill a third. That thought is not supported by the data on land use. Let’s take a look at the different types of land in Florida that might welcome the application of a nutrient-rich resource.
Farms in Florida account for 9.5 million acres. Biosolids can be applied annually if there is a need for added fertility. At this point, applications are restricted to the P needs of the crops. To get some idea of the ratio of biosolids to farmland, I divided the tons of biosolids by the total farmland acreage and got 0.004 or about 0.4 tons of biosolids/year/acre. That is not enough to meet the fertilizer needs of even the most frugal crop. If you consider that only a third of the biosolids produced currently goes to farmland, the number gets even lower. In fact, a study by Trimmer and Guest (2018) estimated that the nutrients in Miami’s biosolids would need to travel at most 150 miles to meet the nutrient demands of the surrounding farmland. Miami is the single largest city in the state with 5.5 million people or about a quarter of the population.
Florida has 4.8 million single family homes. There are also 1,250 golf courses, with an Internet search finding that each course has about 74 acres of turf. We are talking lots of lawn. Lots of pretty flowers and palm trees — no wonder people like to go there. Plus the fact that you have to mow all year long. A long growing season means lots of growth, which in turn means a bigger demand for fertility than a lawn in Minnesota. If each home used some nice biosolids-based product to keep their garden growing that would mean about 140 lbs of biosolids for each yard. Enough for your grass but not enough to keep the golf courses green. While a third of the biosolids produced goes to places like golf courses and landscaping, this suggests that this market has room to grow.
Forests take up about 17 million acres in the state. Much of that is privately held and a portion is used for commercial tree growth. Loblolly pines are grown to make paper and other products. As much of the soil in the state is poor, growth rates of the trees are likely limited. Studies in New Zealand and the Pacific Northwest have repeatedly shown a growth response and even improvement in soil quality with use of biosolids to fertilize the trees. A normal application rate of biosolids to forest plantations in the Northwest is about 3 dry tons/acre, applied every 3 years or so. That means if all of the biosolids produced in Florida went to forestry, there would be enough to apply to 113,000 acres or 0.7 percent of the available forestland each year. As far as I know, there are no active programs applying biosolids to forests in the state.
I went on line to see what each of the largest cities in Florida had to say about their biosolids programs. It turns out not very much. All I could find about the material from Miami was that the city commissioned a consulting firm to look at new options for expanded treatment. The proposal I found said that 10 percent of biosolids is composted, some is applied to farmland, and the rest is landfilled. Tampa/St. Petersburg on the West Coast of the state is the second largest city (when combining populations). All I could find about their programs was that the wastewater division had spent big on a new facility that would magically turn the biosolids into methane and would power much of the city fleet. Turns out that magic and reality rarely connect and that magic frequently comes in well over budget. Orlando was the only city I found that had actual information on their program, which was easy to find and pretty easy to read.
When I asked one of the scientists I know from the University of Florida about biosolids in the state she said she would check into “the way the material is disposed” for me next week. One typically uses something that has value and disposes of material that is waste. One of my points in the podcast was that biosolids program managers should make products that they are proud of. Products that they would use in their own backyards. That is a message that has not been heard by the producers in Florida or the scientists.
For this column I used Florida as an example. The same column could have been written for the majority of states and biosolids programs in the country. As the brief diagnosis of available land in Florida shows, there is plenty of room for biosolids. There is enough demand for fertility that farmers and residents in the state purchased 43,000 tons of P205 (phosphate) in 2011. The total P in the biosolids is only a small fraction of that — likely about 8,500 tons. Appropriate use of biosolids in Florida would likely help the P problem, not contribute to it.
Appropriate use of biosolids in general could do a lot to help this fragile ecosystem, providing slow release nutrients and adsorption capacity at the same time. To really be environmental stewards, we have to use the resources at hand, use them properly and be proud of our actions. If program managers embrace this and use this concept as the basis for their programs, biosolids would be viewed as an asset rather than a waste. Those guys that emailed me and program managers are playing for the same team. It is time that everyone recognizes that.
Sally Brown is a Research Professor in the College of the Environment at the University of Washington. She authors the Connections Column in BioCycle, and is a member of BioCycle’s Editorial Advisory Board.
Trimmer, J. T. and J. S. Guest. 2018. Recirculation of human-derived nutrients from cities to agriculture across six continents. Nature Sustainability, 1:427-435.