Thursday, May 6, 2010

Why I love biosolids

Bok choy from my home garden grows in a combination of native topsoil and biosolids compost.

In the last few weeks several people have come to me asking about the safety of biosolids-use in their home gardens, and moreover, have asked why I advocate the use of biosolids. In short, biosolids composts are safe, highly-regulated, sustainable, climate-friendly products, that your plants will LOVE. They are high in nutrients, support healthy soil microbial communities, and improve the tilth (physical attributes) of soil. Farmers around the world, including US farmers, have known this for ages.

 Me holding a handful of Groco compost at the Alleycat Acres Beacon Hill site.

The other day I walked into a home improvement center and was inundated by the perfume of synthetic fertilizer. My immediate visceral response was that of revile, which soon followed by nausea and a head ache. I realize that I am particularly sensitive to fertilizer, but these immediate physical responses got me thinking... is it really biosolids that we should are be running scared from? This is when it hit me, if I could just tell the world what biosolids really are, we would all lining up to dig our spades into this black gold.

What are biosolids?
Biosolids are a product from the wastewater treatment process, and are EPA-regulated under the Clean Water Act. In US cities, everything we flush, throw down the kitchen sink, and wash down the bathroom shower ends up at the wastewater treatment plant. Some people call biosolids sewage sludge, but the term biosolids specifically refers to treated sewage sludge.  Here our wastewater gets cleaned via a system of filters, and the solids are left behind. While the clean water is either being used for irrigation as "reclaimed water", or sent into our rivers, lakes, or oceans, the solids go under treatment. There are a wide range of ways in which our solids can be treated (like artists, engineers can be quite creative). One popular method is for the solids to go under anaerobic digestion. In this method, industrious microorganisms literally eat the solids. While the microorganisms are feasting, they emit methane gas, which we can be used to power the wastewater treatment facility. During the anaerobic digestion process, pathogenic organisms such as E. coli, salmonella, and helminths either get eaten by the good microorganisms, are heat-destroyed, or a combination of the two, depending on the type of digester. What is eventually left at the end of this process, is no longer the original solids, but mostly the dead (and some live) bodies of the microorganisms who consumed our waste.

A digester tank, used to treat sewage sludge, to make biosolids

Dr. Craig Cogger, one of my graduate advisers, standing next to a pile of biosolids cake. I took this photo immediately before applying the cake to research plots at WSU Puyallup a couple weeks ago.

At this stage we have what is called biosolids "cake". While the cake may be safe to distribute to the public, it is not very easy to use (too wet). So, cake is generally applied to farm land. Here in the PNW, some of our cake is actually applied to timber plantations, which significantly increases the growth rate of our timber forests. Another thing we do with biosolids cake is compost it. Seattle's cake gets composted by Sawdust Supply company, located in the hip Seattle neighborhood of Georgetown. Sawdust Supply mixes the King County cake with sawdust from local timber mills, and composts the combination for over a year. The end result is a light, fluffy, dark compost, that is stable, free of odors, and well... simply beautiful.

Andy Bary, soil scientist from WSU Puyallup, rototilling biosolids into the new research plots. Just look at how beautiful that fine sandy loam is! The soils in Puyallup make me drool.

Before biosolids can be applied to farm land, or distributed to the public for home garden use, they must be vigorously tested, and meet stringent safety regulations. I take comfort in knowing that biosolids are heavily regulated. They are far more heavily regulated than manures, yard waste composts, and fertilizers.

 A handful of Groco compost, which is made from King Co. biosolids and sawdust.

What about heavy metals?
In the pre-Clean Water Act days heavy metals were a problem in sewage sludge. At least they were in the handful of places where sewage sludge was actually produced. Realize that in the pre-Clean Water Act days we emitted a lot of raw wastewater into our rivers, lakes, and oceans. As water quality standards have strengthened, the amount of biosolids produced has increased. In addition to eliminating the practice of raw wastewater disposal, the Clean Water Act took aim at reducing heavy metal concentrations in our wastewater system.

Today we no longer find heavy metals in unsafe concentrations. This is mostly thanks to strict upstream regulation, meaning that industry is monitored and not allowed to dispose of toxic waste into the sewer system.

Somewhat ironically, biosolids can be used to reclaim soils that have been contaminated with heavy metals. My graduate committee chair, Dr. Sally Brown, has used biosolids to clean up seriously contaminated sites, like mine tailings.

What about pharmaceuticals and other trace organics?
Pharmaceuticals and other organic compounds are not regulated in biosolids. This does not mean, however, that this topic has not been researched! When EPA set the guidelines for biosolids regulation, they decided not to regulate substances like PCB's, dioxin, and estrogenic compounds, because concentrations are so incredibly low, that they are rarely found. When these compounds are detected, they are in such low concentrations that risk assessment studies (conducted independently by EPA and several U.S. Universities) find risks to the public and environment to be negligible. Despite the fact that these substances are not federally regulated, public works agencies such as King County biosolids division, routinely monitors for these substances... just to be sure. What are the chances fertilizer producers check, just to be sure?
The fact that substances like dioxin, PCB's, and estrogenic compounds exist in the environment is bad, the fact that they are in background level concentrations in biosolids is good. The fact that government agencies and universities continue to monitor and study these compounds is also good.
     Food for thought: manure products that we can buy at nurseries generally come from CAFOs (feed lots), where all of the animals are prophylactically pumped with hormones and antibiotics. At least here in King County there are enough healthy folks and hippies who want natural alternatives to pharmaceuticals that it is only a fraction of us who are excreting meds into the waste stream.

Why I am an advocate:
I am a huge advocate of all compost, including biosolids compost. I use it in my own ornamental and edible beds. It is my feeling that if we are to truly move to a zero waste society, it is our responsibility as citizens to use as many recycled products as possible, including our yard waste, food waste, and biosolids. I purchase quite a bit of compost each year and apply it to my garden beds. Since I live in the city of Seattle I purchase Cedar Grove, a yard waste/food waste compost, Groco, a biosolids/sawdust compost, and Tagro (city of Tacoma), another biosolids-based soil amendment. Also, biosolids compost tends to be very high in plant nutrients, and is an extremely consistent product (little to no seasonal variations), making it a dream for us gardeners. Biosolids are perfect for growing plants, the fact that it is safe is critical, the fact that it is sustainable and therefore responsible to use, well that's just gravy.

My first radish of the season. Grown in soil amended with both biosolids compost.

No fertilizer needed here. Spinach, herbs, lettuce, and radishes growing in one of my veggie boxes. 

A few cool sites with great information:


  1. Ms Kurtz, You should always question what you think you know about compost.It is interesting that King County folks came up with the word biosolids for biological active sludge. You might also want to research the term Fecal coliform - it might surprise and dismay you.

  2. Jim, thank you for your interest in my blog. I see that you are adamantly opposed to biosolids-use, so I don't expect to change your mind with my post. Perhaps, however, you will like some of the recipes I have posted? Anyhow, I actually do know quite a bit about fecal coliform. Immediately after graduating from college (Environmental biology, Columbia University), I started work at Soil Control Lab, in Watsonville, CA. There I tested literally thousands of samples for fecal coliform concentration (biosolids, various compost products, drinking water, waste water, surface water, storm water, etc...). If I never have to conduct another fecal coliform test for as long as a live, I won't be dissapointed. What I learned from all this testing, is that we do not have to worry about fecal coliform, or the other potentially dangerous microorganisms. If the fecal coliform are present in unsafe concentrations, the product cannot be distributed or land-applied, but rather needs to be further processed to remove any harmful microorganisms (a very simple process). Fecal coliform are all around us which is why they are such great indicator organisms! We know that if the fecal coliform are gone, so are the bad guys. Pretty cool.
    Thanks again for your interest,

  3. Kate, thank you for posting this information. I am also a grad student, currently researching uses for solid human waste for a project on zero waste. I appreciate your write-up very much!

    Laura T., Seattle

  4. Thanks for the feedback Laura.
    Are you also at UW? My first year of school I was funded by a WA DOE zero waste grant. Is that what you are doing?

  5. Sounds like the EPA doesn't require testing for more than a handful of contaminants. Check out this link. It gives results of tests showing uptake of drugs and other chemicals into plants from biosolids and treated effluent.

  6. I read the above article posted by Mark S., which is somewhat misleading. The bottom of the article clearly states that the researchers actually added more chemical contaminants to the biosolids rather than monitoring existing levels. What they were testing was where the chemical uptake from biosolids was going, not how much.

    1. Yes the study, they admit, has limitations, but what was the result of the test?

      "The researchers report that the antimicrobial chemicals concentrated in the plants leaves and were measured at the highest levels of the five chemicals analyzed. As the biocides move from soil and wastewater to the leaves, human, wildlife and livestock could be exposed to these drugs."

      I'm all for putting biosolids to beneficial use, I'm just uneasy with using it in my veggie garden until further studies are done.

  7. I'm an avid gardener in Renton, and have always had an aversion to Cedar Grove primarily because Seattle allows people to put cardboard food containers in their compost as well as napkins and any other type of wood-based food paper product. A lot of these are bleached with dioxins. Plus who knows what kind of chemicals people use on their yard waste thats put into the compost. Do you know where to go to read up on studies done to determine the levels of these compounds found in Cedar Grove? I'm a 2 time breast cancer survivor, and my gut feeling is that our cancer epidemic is in part caused by all these compounds in our environment, and we're willingly spreading them on our food gardens!

  8. Great article and respectful handling of the skeptics in the Q&A. It should be noted that if we don't put these biosolids to beneficial use, they will be likely be trucked to a landfill. Or we can stop discharging wastewater from our homes. Alternative fertilizer sources either consume massive amounts of energy (nitrogen fixation and phosphate mining) or they are likely from CAFOS, as you note.

    1. First of all how is it the taxpayers duty to find a way to dispose of industrial and medical toxic waste?

      MOST OF THE TOXINS found in the waste water are from industry and medical! Why do people completely overlook industry and medical when talking about this problem? Maybe if we had a government who gave a **** about us and the environment they would force industry and medical NOT the taxpayer to find safe ways to dispose of their toxins. If that were the case then we wouldn't have this issue because the levels of toxins would truly be of no concern and most likely the total number of different toxins wouldn't be in the hundreds.

      I do agree though that the fertilizer industry uses HUGE amounts energy and waste! Most fertilizer use is for production of corn and GMOs. Industrial (again) farming has nuked their farm land which requires more and more fertilizer. Again though it is the industry that is destroying the land and the government promoting it which is causing more energy wasting fertilizers (by the way fertilizer companies are the same companies that sell the seeds and run the industrial farms! They have invested interest in destroying the land and causing these problems because they profit) But government is industry so they make us taxpayers pay for the toxic mess!

  9. Composting kills pathogens (e.g. coliform). According to Prof. Sally Brown (U of Washington), the biggest problem with using biosolids in agricture, is not to humans, but to aquatic organisms.....gonadal intersex in fish. Abe

  10. My wife is a microbiologist and she indicated that class A biosolids pose no risk to humans and the environment if tested to EPA and even stricter state standards and are used properly, even in the home garden. One interesting note, our water quality for metals is not far behind biosolids, so watering your garden from a municipal source may be just as laden with metals and dioxins. These are in such small concentrations in either case they pose no danger, in fact look at the max loading for each metal per yearly application of biosolids, it would take 100s of years depending on the metal to hit the maximum for application to the land. This does not take into account for mineralization of the metals in the soil. Bottom line, even if using class B biosolids correctly, the danger of pathenogenic contamination is virtually nil and given time the biosolids decompose in the soil and are rendered harmless. I have used a local Virginia product and one from Wisconsin called Milorganite on all of my plantings from Cold Hardy Palm trees and Bananas to veggies and fruit trees. My blood level for lead (I have it checked because I am an avid shooter) has actually gone down and mercury is well below the accepted level too. I compared it to when we were still using leaded gasoline in the 1980s and my blood level for mercury and lead in that time period was slightly highier. Biosolids and humanure when used properly are as good and safe as any other manure product, in fact, maybe safer since they are regulated more. My group, the Virginia Palm Society uses the local and Milorganite biosolid products and have yet to have a bad experience or any member becoming sick from their use. Overall everyone I have had using them has nothing but postive things to say and recommend it to others. Kate Kurtz, keep up the good work and don't let the phecophobes rain on your parade! :' )

  11. Perhaps the E.coli is reduced to insignifcant levels, but what of all the chemical contaminants excreted in human waste as well as industrial chemicals flushed down drains? I'm talking about flame retardants, antibiotics, detergents, synthetic fragrances, pesticides, hormones, anti-foaming agents, etc. These things DO NOT "compost down" and become inactive like live microbes might. They persist for years in the enviroment, and are implicated in many diseases such as cancer and auto-immune conditions. You are doing a HUGE disservice to the public by recommending spreading biosolids on their gardens and fields! Do your research people, and get out of the back pocket of these money-making at all costs corporations!

  12. Prove it...where is your data? The tactic that well, just well since they are there, even in very, very small concentrations that they will cause harm is not fact. The reality is very little in the way of harmful waste is ever put down our drains to the sewer as there are monitoring programs in place with very strict testing done at the processing facilities. The fact remains that biosolids are a very safe and benefitial resource to agriculture and horticulture with no documented mass contamination or even one illness when they are used properly. It amazes me how chicken manure is "organic" certified when the antibioitcs and other drugs used to keep our poultry health end up in their manure while biosolids are somehow more dangerous. Don't drink tap water either or well water as it may have these chemicals in them too. Give me a break, the regulations, testing and load limits are there for a reason and there is no reason anyone has given with hard data that shows they are somehow dangerous in the slightest.

  13. John S's comments show how easy it is for the corporations such as Monsanto, ConAgra and Dupont, not to mention all the drug companies to continue polluting our environment with disease causing chemicals and compounds. Where's the "hard data?" That's's difficult to show where the specific pollutants are coming from, so they get away scot-free. No-one's to blame! How convenient. But think about all the people who take hormones and other drugs that get excreted out in their poop. Think about the hand soaps we use with triclosans (antibiotics), the drain cleaners, the lawn care products and driveway oil that gets washed into the storm drains. This stuff doesn't get magically washed out of the poop at the waste water plant. It collects and concentrates. And yes, it HAS been measured and found to occur in biosolids. My recommendation is to go organic. Don't buy chicken manue in bags. Know where your manure comes from! So many people now-a-days keep chickens in the urban environment. Make friends with them. Get the manure...probably for free. Don't buy Cedargrove compost--make your own with your organic yard waste! Cedargrove and other composters use yard waste from everyone...people who use pesticides and herbicides indiscriminantly. It's in their compost! GO ORGANIC. Don't believe the hype about the may help your plants grow, but you will be polluting your environment and yourselves!

  14. Once again there go the platitudes of what if.....well there are REGULATIONS, TESTING and DATA that support the use of biosolids as being safe if processed and used properly. Hormones and pharmecuticals are in such small trace amounts in the 10s of parts per billion they aren't even a consideration. Again, put your money where your keystrokes are, show me the incidents or data where biosolids have caused harm to the environment! Guess what, it doesn't exist because there aren't any, only the shrill alarmist cry from wanna-be enironmental experts. Your water source that you may be using everyday to wash, drink and water your plants has these super diluted contents in them. The EPA and USDA which I will say is much more experience than yourself put the regulations and load limits together based on science, not alarmist feelings. FACT: Biosolids are an excellent fertilizer and soil amendment that has produced many benefits for man and the environment.

  15. Hi Kate, thanks for the really informative post. I was particularly interested in the part were you mention "Here in the PNW, some of our cake is actually applied to timber plantations" as my folks raise pine for saw timber and the soil could *really* benefit from some biosolids. I wondered if you have any more information on this, I am specifically interested in the application of biosolids after cuts (would seem difficult to me but perhaps I am missing a detail?) and who one contacts in their respective county about getting biosolids, and maybe even if there are subsidies? (its wasn't clear to me if these biosolids are usually available for free or a fee).


  16. Our energy and goods are often produced far away from our homes. Someone ends up living near that industry, and it's often the poorest folks. To be fair, everyone needs to share in the fruits of our labor, and the mess. We all poop. Where should it go? Putting the biosolids into landfills seems wasteful. Perhaps more testing needs to be conducted per batch, but the theory of reusing it as compost is quite sound. On a side-note; In my area, "environmentalists" are happy to consume the goods and service produced by coal, gas and nuclear power systems (which they are opposed to). Strangely, they've also been the fiercest critics of wind farms, which would 'spoil the natural beauty and kill birds'. WTF? Anyhow.. Good work, Kate! We need more people like you, gettin' hands dirty :-)

  17. Ya know....I have no degree in anything. I do not work in any industry mentioned nor do I see the boogey man attacking us. But, I thoroughly enjoyed your article. I live in Pensacola and I have been thinking about starting a garden. I eat organic as much as I can. Organics are limited here in the eat all you want buffet panhandle area.
    My concern with our food supply has been twofold. One is the CFOA concept of our meat supplies and two has been the use of pesticides and herbicides to our fruits and vegetables. I must admit though if I had not read your article I would not have thought much about where my compost came from at the garden supply store.
    I was in the water filtration business and one of the things that I started really looking at was fluoride. At the time regulation said 4 ppm in water for flouride and 15 ppb for lead and 10 ppb for arsenic.
    Fluoride is more toxic than lead and almost as toxic as arsenic yet the EPA standards are so crazy. Ppm and ppb makes a world of difference. Now the reason I say all that is when you talk about meeting govt "Standards" not everyone that does not trust them is a crazy right wing conspiracy nut. Some of us can actually do math. Wouldn't the absolute beat compost be made in my backyard by me? Would that not be the greenest most organic method? Would that not be socially responsible? I am not being facetious in asking these questions I am curious why that was never mentioned. Just make your own compost. What if all the neighborhood farmers did not use herbicdes on their clippings etc and everyone had to compost to be part of the ckmmunity farm? I am just saying...heehee. Great article thanks again.

  18. This is a nice article. thank you for posting this information and thanks for sharing.

  19. Hi Kate and fellow readers,

    If we want great biosolids without the whole question of the household and industrial chemicals that go into sewers, a great option is to collect feces separately, without mixing them with water, by using Urine-diverting Dry Toilets (UDDTs). Any chemicals present at least went through someone once before ... and eventually maybe we can convince people to not take so many pills. More info at,, and my blog Also have a look at this 2-part interview:

    You can also see some of our "finished biosolids" in this video:

    Keep up the good work.

  20. I am confused on how this is safe? EPA did a survey 74 random biosolids Grade A samples from around the country and they found

    The four anions were found in every sample.

    27 metals were found in virtually every sample, with one metal (antimony) found in no less than 72 samples.

    Of the six semivolatile organics and polycyclic aromatic hydrocarbons, four were found in at least 72 samples, one was found in 63 samples, and one was found in 39 samples.

    Of the 72 pharmaceuticals, three (i.e., cyprofloxacin, diphenhydramine, and triclocarban) were found in all 84 samples and nine were found in at least 80 of the samples. However, 15 pharmaceuticals were not found in any sample and 29 were found in fewer than three samples.

    Of the 25 steroids and hormones, three steroids (i.e., campesterol, cholestanol, and coprostanol) were found in all 84 samples and six steroids were found in at least 80 of the samples. One hormone (i.e., 17a-ethynyl estradiol) was not found in any sample and five hormones were found in fewer than six samples.

    All of the flame retardants except one (BDE-138) were essentially found in every sample; BDE-138 was found in 54 out of 84 samples.

    That is safe?

  21. The concentrations of these compounds is so low and they are often substances we use on ourselves in much, much greater concentrations, the fact that they are found in ultra low concentrations in biosolids makes it a joke to even worry about. Most of these compounds are organic in their chemical make up and unlike chlorinated dioxins, do break down into their simple elemental components. Given that the tap water we use to water our gardens have in some cases, greater concentrations of these compounds, what is the point in even worrying about them. If you are using anti-bacterial soap everyday and absorbing it into your skin directly in much greater concentrations than are found in biosolids, what possibly would be the harm in finding ultra low concentrations in the biosolids? That defies logic and until there is concrete PROOF, not feelings that biosolids are harmful, never mind they have been used for almost 90 years in horticulture and agriculture with no one getting sick, I and many others will continue to use them and enjoy the awesome benefits of their use.

  22. Hi Kate,

    I appreciated your post. I am one of those people that is on the fence when it comes to biosolids. On the one hand, I am an avid gardener and am constantly in need of more compost. Biosolids could easily fill that need without breaking the bank. On the other hand, I'm scared of applying anything to my soil that might damage it or harm my family's health. What is one to do? I wish I had the knowledge and equipment to could conduct my own studies, that way I could be 100% confident in its safety.

    A few years ago, I unknowingly applied bagged biosolids to my fruit trees. I thought I had found a great source of organic compost, because it smelled earthy and sweet and was very heavy. My trees loved it. Maybe I'll try it on my non-food areas this year, and to let myself get more comfortable with the idea.

  23. Thanks, Kate, for your very informative post. I recently came across a free source of compost made from biosolids and was excited to use it on my garden until I started to read all of the biosolid scare articles. After researching it, reading your article and others, I am coming to the conclusion that it it safe to use for in my back yard garden. I guess it depends on how much of a purist one is. There are toxins all around us, in everything we breathe and eat. It is impossible to live in a toxin free world. I'm sure the compost I make myself has toxins in it too, as well as the native soil in my backyard. I have to do the best I can to live in this world and decide what to grow my food in and what to eat. This seems an economical alternative and it allows me to grow more of my own food, which is always better than buying food from the grocery store!

  24. Thanks for the informative post Kate. I work in the biosolids industry in Ontario and it makes me sad when I see how against biosolids people are. This is a very valuable resource we have, that we just throw away when we put it into a landfill or incinerate. This is a very informative video created by the Water Environment Association of Ontario that I suggest anyone who is skeptical about biosolids should watch:

    Biosolids are treated and regulated anywhere they are applied to agricultural land, especially in Ontario. Manure and chemical fertilizer isn't nearly as regulated. Manure isn't even treated before it goes to the field. There are a lot of research papers out there that indicate that pharmaceuticals and other "contaminates" are either removed through treatment or cannot last in harsh environments such as an agricultural field.
    Our society NEEDS to move towards sustainable development for future generations. Biosolids application is a sustainable way to get rid of our "waste" that benefits the agricultural community as well as the environment. In nature, EVERYTHING is reused, nothing goes to waste. Waste is a human term, and we really need to change that.

  25. Excellent post, thanks for sharing. Have you considered creating videos for some of your posts? I think it would be a great idea.

    Jaclyn from the Rhode Island video production company

  26. Can I just say what a relief to find someone who actually knows what theyre talking about on the internet. You definitely know how to bring an issue to light and make it important. More people need to read this and understand this side of the story. I cant believe youre not more popular because you definitely have the gift.

  27. Living in the American SW, where mining is THE Industry, I am particularly interested in using biosolids to homeopathically reclaim mining tailings...Everybody could get on that outhouse! Great way to go!

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  30. What about non treated biosolids?

  31. Growing Food in Human and Industrial Waste must stop! More scientists join outcry against land-applied sewer sludge (aka biosolids) See - and

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