My last column on per- and polyfluoroalkyl substrates (PFAS) caused a number of you to question the veracity of my reporting. I can assure you I would never knowingly report inaccurate information in such a highly regarded publication as Label & Narrow Web. My editor would tar and feather me and pitch me into oblivion! It is absolutely true that PFAS substances, “forever chemicals,” have been found in sludge here in Chicago. Subsequently, that same sludge has been used as gardening soil to grow vegetables. 

It is also true that neither state nor federal agencies have the technology to test for acceptable levels of PFAS in our water treatment plants. As I said earlier, there remains a serious gap between what we know and what we don’t know about PFAS contamination. Suffice it to say, just in the last 30 days, 3M has announced it will phase out the use of PFAS chemistry by 2025. 

As one of my readers pointed out, the question now is, “Why wait until 2025? If they (3M) know they are contributing to risks to human health, why are they waiting for two years to eliminate this toxic chemistry?” I am not going to be presumptuous to try to explain the 3M rationale, but I sure could hazard a guess if pressed!

In the meantime, let’s morph into the subject that I promised to write about in my last column: anaerobic digestion. I’m also going to touch briefly on pyrolysis (another process used to convert byproduct into usable feedstocks). All of these processes take byproduct and convert it into usable materials.

Methane gas, for example: instead of being released from landfills into the atmosphere, it can be captured and converted to biogas by anaerobic digestion. Cow manure and chicken waste use anaerobic digestion to make fuel that can replace fossil fuel. Agricultural byproduct can be converted into useful material via anaerobic digestion. And so on. In fact, some of the waste in our industry can also be used as feedstock for anaerobic digestion. However, the economics become questionable when we consider feeding matrix into this process.

Much of our RNG (renewable natural gas) is manufactured using anaerobic digestion. In fact, my reference to BP’s pending acquisition of Archaea Energy is what triggered my interest in explaining
anaerobic digestion.

Just to digress for a moment, that deal is now done. BP North America owns Archaea Energy.  The reason BP wanted Archaea is because of its business model: Archaea operates 50 RNG and landfill gas-to-energy facilities here in the US. These facilities produce 6,000 barrels of “oil equivalent” a day (boe/d) of RNG. This will give BP a huge increase in its biogas capacity. And, of course, biogas is friendly, versus that black stuff they currently suck out of the earth and ocean. 

According to a press release, after completing the Archaea deal, BP announced that Archaea has a “development pipeline of more than 80 projects,” which will grow its RNG volume “tenfold,” up to 70,000 boe/d. The BP vision is obviously to be less dependent on fossil energy.  I know this is a long digression, but guess what: Archaea uses anaerobic digestion to convert waste-gas to biogas. Voila! The importance of this process.

Many of us became familiar with anaerobic digestion as a solution for disposing of cow and chicken waste.  It is used to convert biodegradable waste and sewage sludge (that word again) into useful materials like fertilizer and biogas.

Anaerobic has several meanings:

• Relating to, involving, or requiring an absence of free oxygen.
• Relating to or denoting exercise that does not improve the efficiency of the body’s cardiovascular system in absorbing and transporting oxygen.

Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to manage waste or to produce fuels. Much of the fermentation used industrially to produce food and drink products, as well as home fermentation, uses anaerobic digestion. Anaerobic digestion is widely used as a source of renewable energy. 

The process produces a biogas, consisting of methane, carbon dioxide, and traces of other “contaminant” gases. This biogas can be used directly as fuel, in combined heat and power gas engines or upgraded to natural gas-quality biomethane.  The nutrient-rich digestate also produced can be used as fertilizer.

So, anaerobic digestion works with biodegradable materials and processes them “without oxygen.” There are four distinct stages, all chemical reactions. I’ll leave these unstated as I don’t want to stress your chemistry background, much less mine. Of all the different aspects of anaerobic digestion, the four process stages, batch or conversion, temperature and time, probably the most important aspect is feedstock. The feedstock to be processed – animal waste, methane, etc. – will define the overall systems and specific choice of production specificity. 

In summary, we are using anaerobic digestion today in a vast number of applications, with the objective of reducing the emission of greenhouse gases, which affect climate change. 

These include:

• Replacement of fossil fuels
• Reducing and/or eliminating the energy footprint of waste treatment plants
• Reduce methane emissions from landfills
• Displace industrially-produced chemical fertilizers
• Reducing vehicle movements
• Reducing electrical grid transportation losses
• Reduce dependence on LP gas for cooking
• Part of the zero-waste solution

Just think of two of the above, capturing methane from landfills and replacing inorganic fertilizers.  The improvement to greenhouse gas and contaminated water runoff is huge.

Anaerobic digestion uses a closed container called a reactor that is designed based on the feedstock.  The vessel contains complex microbial combinations that digest (break down) the waste and produce biogas or solid material that is discharged. (A pretty neat illustration on how AD works (US-EPA) is on page 30.)

Pyrolysis is a bit different from anaerobic digestion, although it is also processed in an inert environment, without oxygen. It is the “thermal decomposition of materials at elevated temperatures. It involves a change of chemical composition.” Like anaerobic digestion, pyrolysis is used in the treatment of organic materials but occurs at higher temperatures.  The process is used regularly in the chemical industry to “produce ethylene; forms of carbon from petroleum, coal, and even wood.” It is used to produce natural gas (mostly methane) into hydrogen gas and “carbon char” in a variety of industrial applications.

Pyrolysis is, in many cases, a precursor to additional processing. For example, I have been involved in a development project that uses pyrolysis to break down the chemical composition of polyvinyl chloride (PVC) so it can be used in a fuel application. Pyrolysis eliminates the chloride and makes the feedstock acceptable for fuel. Mind you, this is a development project. The successful conversion and economics on a commercial basis are still to be determined.

My interest in pyrolysis is in the potential to use non-recyclable substrates, such as laminated PVC, that are currently landfilled. Pyrolysis would not only allow us to eliminate landfill but also eliminate the need to segregate highly noxious materials and allow their use in alternative fuel applications.

As we begin 2023, we need to be mindful of available technology that will make us a better industry. Anaerobic digestion and pyrolysis are just two of the many processes that we need to consider to make pressure sensitive a friendlier technology.

Another Letter from the Earth


Calvin Frost is chairman of Channeled Resources Group, headquartered in Chicago, the parent company of Maratech International and GMC Coating. His email address is
[email protected].