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.

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.

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.

If you’re like me, your career path included a variety of positions, including those you could not foresee. My first jobs during high school were dishwashing and bussing tables. A few years later, I worked at the university car wash and delivered pizzas.  Then, with a bachelor’s degree, I landed a laboratory laborer’s position at the local wastewater treatment plant.  Wastewater superintendent came next, followed by operations supervisor at a larger facility. During these years, I had the privilege to scrub clarifier weirs, clean out sludge lagoons, troubleshoot pumps and lift stations and take dissolved oxygen readings in sub-zero weather.  At the time I never dreamed that one day I’d be presented with an opportunity others call glamorous — video narration.

Here, as they say in Hollywood, is the backstory: In my role at InSinkErator I hear concerns, especially from collections system managers, that food waste will cause or contribute to overflows. Food waste is often perceived as solid, and while it is the largest fraction of the municipal solid waste stream, it is hardly solid. In fact food waste is at least 70% water; fruits and vegetables are closer to 90%. Since this material has essentially the same specific gravity as human waste, sewers with sufficient velocities to transport sewage solids are adequate for transporting the discharge from disposers since most particles are less than 3 mm in size. There’s a good discussion of this topic within the larger discussion of the use of food waste disposers as a tool for reduction of European MSW at *CIWEM

Admittedly, I never gave a lot of thought to the impacts of disposers on sewers before coming to InSinkErator. But in viewing a few demonstrations where our lab collects the discharge from disposers for grind performance analyses, I realized there was an opportunity to provide collection people with a better look. We eventually produced a technical video and when we decided narration would enhance it, I was called upon.

I don’t know how many times I’ve kidded around playing a radio broadcaster, you know, “Sunday-Sunday-Sunday, at the Memorial Coliseum…”  This session was my chance to sit in a professional sound booth with headphones and a microphone.  It was quite an experience, and convinced me that it’s fun to step out of the “comfort zone” — provided that zone doesn’t involve a sludge tank.   

I’ll let you judge how I did. 

Does the video make the case that food waste is easily transported via collection systems?  

*The Chartered Institution of Water and Environmental Management (CIWEM) is the leading professional body for the people who plan, protect and care for the environment and its resources, providing educational opportunities, independent information to the public and advice to government. Members in 98 countries include scientists, engineers, ecologists and students.