Heavy Metals the Encore – Because You Asked for More

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My last post began the discussion of heavy metals in biosolids, a topic that can provoke a noisy reaction. So let’s keep rockin’! Heavy metals in compost don’t seem to get the same response as heavy metals in biosolids. For some reason, heavy metals are associated primarily with biosolids.  That is incorrect.  This post continues the analysis.

Simple reasons why heavy metals are present in both compost and biosolids

Though it’s often thought that compost is the purest of substances, it too has metals, and these are also subject to regulatory limits.

A review of research bore out that compost has regulatory limits for heavy metals similar to biosolids. This should not be a surprise because both biosolids and compost from food scraps are composed of many of the same organic materials, such as proteins and fats.

With biosolids, the difference is that the food was eaten first.

Municipalities are required to submit information on biosolids quality, which enabled me to access information. I accessed a land application report from the Water Pollution Control Department in Lafayette, IN – the plant where I started my career, as well as a land application report from Angola, IN where I spent six years as the superintendent. (Thanks to Brenda Stephanoff from IDEM for her assistance.) Data on commercial compost is publicly available. For comparison I found compost information in separate reports from a solid waste facility in Lincoln, NE and a food compost site in State College, PA.

Comparison 1Comparison 2

It’s worth noting that it appears some biosolids have much higher levels of some metals, but this is relative. Not only do the charts show all metals are below EPA standards, all the values for biosolids are certainly within an order of magnitude of the compost values. The North East Biosolids & Residuals Association has compiled a much more comprehensive evaluation on metals in compost and biosolids. Thanks to Ned Beecher.

It’s a fact that compost and biosolids have the same regulatory limits for heavy metals.

For more information on this same subject, San Francisco Public Utilities compared commercial compost against composted biosolids in 2010 to evaluate compliance with heavy metal limits.  The utility determined that pollutant metals results were lower than the pollutant limits listed in Part 503 Rule Table 2-1.

Lorraine Herity’s master’s thesis from Ireland  showed sewage sludge met limits for heavy metals more often than compost.

Comparison 3

Number and Percentage of Samples in Compliance with Irish EPA Guidelines. Lorraine Herity. 2003. A Study of the Quality of Waste Derived Compost In Ireland. Queens University of Belfast.

The conclusion – you will find that the same heavy metals of concern are present in both compost and biosolids. Presence does not equate to risk or hazard.



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The focus of my work at InSinkErator® is about how food waste impacts municipal infrastructure and in particular, wastewater treatment plants. Climate change is also an important factor in the discussion. I count myself fortunate to have met so many accomplished people as a result of the work I do — many of whom are considered “gurus” in their respective fields and whose knowledge I’ve been fortunate enough to experience and on occasion, tap into.

I hope through this blog to maintain a personal connection with the experts I’ve met by writing about a wide variety of topics and inviting input and discussion.  A few of the initial ideas I’d like to explore are:

  • -Energy production
  • -Operational and maintenance challenges in collections systems
  • -PCPPs; food waste and PCPPs
  • -Beneficial reuse of biosolids and public education
  • -Peak phosphorus
  • -Reports and observations from the conferences I attend and occasionally present at, including WEFTEC, NACWA, BioCycle, NEBRA and others
  • -Research I am working on
  • -The “brain drain” in the industry
  • -Interesting projects from around the world and in particular, the work of National Geographic Explorer  T.H. Culhane  

I’m very interested in hearing from readers about topics of interest for discussion. Please comment or email me if there’s something you’d like for this blog to tackle. It’s my hope to bring together a variety of voices and thus, a number of ideas.

Cloaca Maxima, the sewer system built in the sixth or seventh century B.C. by one of the ancient rulers of Rome. (Public Domain. Courtesy Lalupa, Wikipedia).