A Counterpoint to Composting (If you’re listening)

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I once heard that had the food waste disposer not been invented in 1927, now would be the perfect time. Why? Well, because of the convergence of two environmental megatrends – landfill diversion of organics and resource recovery at wastewater treatment plants, where municipalities produce clean water, and sometimes fertilizer and energy.

Think about it, food waste is at least 75% water, and with the trend of keeping organics out of landfills, it makes sense to leverage disposers, already present in 60 million households in the U.S. (52% of all homes), to manage this waste as a liquid rather than a solid. Right?

Unfortunately, it is difficult to even have a civil conversation with staunch environmentalists that favor composting because of four universal myths and misconceptions about disposers. Never mind that composting is only available to 2.74 million households across 198 cities across the U.S., or less than 2% of all U.S. citizens! I sometimes get exasperated in trying to have a lucid conversation on this subject because many times I don’t even get beyond the myths of environmentalists. For example:

Myths 1 & 2 – Water and Electricity Use
“Disposers can’t be good for the environment – they use water and electricity.”

Ugh! To have a rational discussion, we must move past the debate on water and electricity use associated with disposers, moot points and already discussed ad nauseum in this blog. The perception is disposers use a lot of water simply because they use water. The truth is it is not exorbitant. In fact, it is negligible and totals only 1% of the total household usage. Electricity usage is almost laughable at a mere 3-4 kwh or $0.50 per year. And all treatment plants produce clean water, which is why some of them have adopted the name water reclamation plant! Here’s a little factoid: for every ton of food waste diverted from a landfill to a treatment plant, we recover about 165 gallons of water, because food waste is around 75% water. Enough said.

Myths 3 & 4 – Impacts to Plumbing and Sewers and Overloading of Treatment Plants
“Sewers and treatment plants were made for sewage, not food waste, and mixing food waste with sewage contaminates a potential resource; food waste is just not good for these systems. Besides, sending food waste to the treatment plant disallows composting?”

We inevitably come to the concern that not all wastewater infrastructure is the same, and that is very true, but the only difference between food waste and sewage solids, is one has been eaten first! Since food waste and human waste is essentially the same density, sewers designed to transport sewage are perfectly designed to transport finely ground food waste.

And yes, many treatment plants actually do make fertilizer instead of landfilling their biosolids. According to research gathered by the Northeast Biosolids and Residuals Association, about 55% of all biosolids are beneficially reused. We could do better, but responsible environmentalists should help debunk the myths associated with their safety to increase beneficial use of biosolids. Land application of biosolids is sustainable and completes the circular economy.

As far as energy production, of the 16,000 wastewater treatment plants in the U.S., over 1,200 have anaerobic digestion. This means that only about 8% of all plants have the ability to create energy, either heat or power, or both. Although this seems like a relatively small number of all treatment plants, these plants account for around 50% of all wastewater flows in the U.S. In other words, most major metropolitan areas have anaerobic digestion employed to help manage sewage solids.

Not too long ago, we dumped all our raw sewage into streams and rivers – Cincinnati did so until the late 1950’s! Even after building wastewater treatment plants, some cities like NYC still dumped their sludge into the ocean up until the 1980’s. But cities are moving forward with sustainability efforts. Just this week it was reported that citizens in a Milwaukee program can pay $12.75 to participate in a pilot composting program. Instead of trying to invest in municipal composting programs, which requires new collection and processing systems at very high costs, city leaders should consider leveraging wastewater treatment plants and the existing base of disposers already present in homes.
I wonder if a U.S. city will ever consider subsidizing the purchase and installation of disposers?

By the way, the City of Milwaukee issued a press release in 2009 encouraging residents to use their disposer, and the Milwaukee Metropolitan Sewerage District also encourages their use. In essence, why not feed a disposer and starve a landfill?


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.


Elemental Composition of Biosolids vs. Soil

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Center for Urban Horticulture, University of Washington. 2002. “Using biosolids for reclamation and remediation of disturbed soils.” Plant Conservation Alliance, Bureau of Land Management, US Department of Interior, U.S. Environmental Protection Agency. Special thanks to Ned Beecher and Chuck Henry


Better than dirt

As I mentioned in my post last month, biosolids are the byproduct of wastewater treatment and are processed to reduce pathogens, which results in a material that’s much different than human waste. Biosolids are comprised of the remaining cell walls of microorganisms left over from the treatment process, as well as the organic biomass remaining after digestion. On an elemental level, the composition is somewhat similar to soil. Except it’s better.


The main difference between biosolids and soil is that biosolids have more Carbon and less Silicon. It also has more Nitrogen and Phosphorus. So not only are biosolids good fertilizer, the organic content of biosolids actually helps to replenish soils by adding more carbon.

Biosolids also help soil retain more water. Replacing carbon and improving the moisture holding-capacity of soils reduces the negative impacts of erosion, a challenge for all farmers.

Contrary to what people think, biosolids are a lot more (and less) than a bag of waste.