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Roger Guzowski

Jan 31, 2013

Roger Guzowski



Compost Kin, Part 2

Second Cousins

Food waste is one of the largest components left in the waste stream, especially in regions that have already enacted other recycling programs. As such, composting and related activities are one of the most popular “next steps” to many campus and municipal recycling programs.

However, before embarking on such a program, you need to understand that composting is not the art of making food waste disappear out of a trash can. Composting is a specific biological process. Unfortunately, there are a lot of similar and related processes (let’s call them “kinfolk of compost”) that too often get lumped together under the compost name. That causes a lot of confusion and leads to a lot of bad decision making. So to help alleviate both, let me try to give an overview of some of closely-related kinfolk in the compost family and how they might affect your decision-making when it comes to diverting food waste and related kitchen organics.

One of the biggest variables relates to other kitchen organics. Should you compost paper napkins or corrugated cardboard from the kitchens? What about compostable foodserviceware? Should you use BPI-certified compostable PLA plasticware (I would not consider anything that is not at least BPI certified)? What about compostable paper plates or paper cups (which are typically either unlined or lined with a thin layer of compostable PLA plastic “wax”)? Are those things really compostable and worth the investment? The answer may depend on your end-market.

Anaerobic Digestion

To oversimplify, anaerobic digestion(AD) is like composting in the absence of oxygen. It uses a different set of micro-critters that break down materials. The primary byproducts are methane (not sure what the micro-critter equivalent of “pull my finger” or “did someone step on a duck” is, but you get the idea) which is captured for energy and a digestate that can then be composted or further processed into fertilizer.

Now AD is an evolving market and there are several variations. As such, I will apologize now if you read this a year or two after I write it and something has changed. But having said that, at this time, there are a few keys to AD that might impact your food waste collection program.

The first is that AD markets are typically looking for a feedstock that is more nitrogen-rich than a traditional compost pile. Those flatulent little micro-critters typically have a carbon-nitrogen zen closer to 20:1. As such, an AD based end market may be less interested in taking large slugs of carbon-rich materials like cardboard in your mix.

AD may also have significant problems with compostable PLA plastic. PLA plastic needs to maintain a certain temperature to begin breaking down. The problem is that AD typically happens as a temperature lower than that and as a result some studies have shown that the PLA plastic does not break down in the digester.

Another key to AD is that those feedstocks are typically being ground up and mixed into a slurry. As such AD markets may be very interested in working with you to invest in on-site pulpers that will do some of that grinding on site (think something along the lines of a traditional garbage disposal that discharges into a collection tank as opposed to food waste going into a dumpster).

The third thing is that your AD market may also be very interested in your fats, oils, and greases. Remember, the primary goal of AD is to make methane and they are looking for feedstocks that will increase methane. Think along the lines of feeding your Uncle Murray a mix of broccoli, cabbage, and chili and then sitting back and watching the hijinks ensue. As such, your AD market may be able to take some of those materials that you are paying separately for a grease rendering company to take.

Pig Farming

Many decades ago, garbage collection meant someone coming around to pick up food waste to feed to pigs (as opposed to coal ash which was the other big waste stream). In fact, there are still waste collection firms today whose history dates back to their days as a pig farmer doing this sort of “garbage” collection.

In some regions, there are still pig farmers who collect food waste for their pigs. This might still be an option for your food waste. However, be aware that because we use pigs for meat, in many areas, regulations have changed so that this food must now be cooked before feeding it to the pigs. Also be aware that if you are collecting food waste as pig feed, you are likely going to have to limit your collection to just food, as opposed to other organic materials.


Worms are the new pigs. There are a number of programs that collect food waste to use it as worm food, a process called vermicomposting. Worm castings (worm poop for those of you who still get a chuckle out of that term) are one of nature’s great fertilizers and soil conditioners. That makes vermicomposting a popular option, especially for those who will be using the castings as a soil conditioner in campus gardens and landscapes. One advantage of using food waste for worm food as opposed to pig food is that because we don’t use worms directly as meat, unless we are reenacting a Judy Blume book, food waste does not need to be cooked before serving it to the worms. For optimum throughput, you may need to shred the food waste because, well worms are small. From that standpoint, vermicomposting might be a good match for programs that are using food pulpers to process their food waste.

Although worms may be able to process some other organic feedstocks, choosing vermicomposting as an option is likely to limit the inclusion of other organics like cardboard and compostable foodserviceware.

Microbial garbage disposal

With an increase in discussion about food waste “diversion” regulations (those that focus on waste generators keeping food waste out of the trash, but that don’t focus on what the alternative is), there has been a corresponding increase in a category of machines that I would collectively refer to as microbial garbage disposals. Decades ago, mechanical garbage disposals revolutionized the waste industry. You no longer needed a pig farmer to come around and collect the garbage. You could grind that garbage in your sink and send it to the sewer. It wasn’t until later in life when I began to understand the history of the garbage industry that I fully appreciated why my grandparents used to refer to the garbage disposal as the “electric pig.” The problem that we realized after we collectively switched to the electric pig is that there is no “away.” Sending the food waste down the sewer didn’t make it go away, it just transferred the costs and issues from those of the pig farmer and landfill to those of the sewage treatment plant.

The new version of the electric pig is the microbial pig. There is a generation of technology that is coming over from urban markets in Asia that essentially uses microbes to transform the solid food waste into a liquid waste that is sent down the sewer. Put your food waste in the machine and presto, your food waste goes away. If this sounds familiar, you may share some of my apprehension. Although I by no means consider myself an expert on wastewater issues, I have already heard grumblings from colleagues in the wastewater industry about BOD and pH issues related to these machines that give me cause for concern. And though I have talked to manufacturers of the machines that there are fixes for those issues, those fixes seem to add additional cost. While these technologies may ultimately prove to be a valuable solution in the highly urbanized areas (urban areas similar to those from whence they came) – areas that have logistical issues with other collection options – I would proceed with caution and skepticism in areas that have other composting and AD options. I think the costs of the units are high, the capacities are low enough that you are not going to be using them for anything but pure food waste, and if you are just flushing the resulting liquid down the drain, you really don’t have any sort of value-added product to show at the end of the process for all those expenses.

For all of you out there that have kinfolk that are “a little different,” the same is true of the composting family. Some of those differences are positive, and some may be less so. As some of you might say about members of your own family, “it’s best to know what you are getting into before you get too involved.” Do you have experiences collecting food waste for one of these “kinfolk of compost” endmarkets? If so, as always, feedback is always encouraged.