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Compost Kin, Part 1

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 kinfolk in the compost family and how they might affect your decision-making when it comes to diverting food waste and related kitchen organics.

In this part 1, I am going to focus on “traditional” aerobic composting, and some variations therein that may impact how you collect your food waste for composting. Let’s call them the immediate family of compost. This immediate family typically involves one of the following variations:

  • Composting on-site in an in-vessel composting unit. This is composting on site in some sort of enclosed container that does the mixing and aerating of the compost for you. There are a wide range of in-vessel units from highly mechanized units with lots of sensors, aerators, and probes; to insulated tubs with a glorified ice auger to do the mixing; to a new generation of what looks like a modified rock tumbler or cement mixer.
  • Composting on-campus by adding food waste to an existing “green-waste” leaf and landscape waste compost pile.
  • Shipping your food waste to an off-campus commercial composting facility.
  • Shipping your food waste to an off-campus on-farm composting facility.

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.

In traditional aerated compost, you are using a whole host of micro-critters to break down a mix of your food waste and other organic materials. The residual material makes an excellent nutrient-rich soil amendment. One important consideration is that these micro-critters are a little zen. They like things with a certain balance, especially when it comes to carbon and nitrogen. Most composting operations strive for a carbon/nitrogen ratio of about 30:1. The problem is that food waste is typically very nitrogen rich. Thus, your composter needs a lot of carbon to offset that nitrogen-rich food. They also typically want a carbon source that will break down in the compost pile in roughly the same time frame as the food waste. That might affect your decision making if you look to expand beyond food waste into other foodservice organics.

For example, adding paper napkins, as long as they don’t have any funky inks & dyes in them, should be an easy addition to any of the aerobic composting options. They are carbon-rich and break down quickly which should keep your end market happy. Napkins are also easy for your diners to understand.

Another common foodservice item for composting is cardboard especially if you are in an area where it is difficult to get your dining services cardboard picked up for recycling (and if you can keep it free of excess packing tape and those stick-on packing slip pouches). Cardboard is much easier to deal with in open piles, regardless of whether those piles are on-campus, on-farm, or are a commercial composting facility. If you are using an on-site in-vessel machine, you are likely to struggle composting cardboard. The first issue is because those in-vessel units typically have limited capacities and may not have sufficient volume to include cardboard. However, even if you size the unit large enough that you have sufficient capacity, most in-vessel units are going to struggle to handle large sheets or boxes of cardboard. In some machines, those sheets or boxes are not likely to fit through the feed opening. If there is a pre-mixer part of the in-vessel unit it is unlikely to be able to handle large sheets of cardboard, and any auger or mixer inside of the unit is also unlikely to be able to handle that material unless it is already broken down. One option would be to pre-shred that cardboard. I have seen some animal bedding in stores that is essentially just shredded cardboard. Something like that would make a great carbon component for your compost pile, but that cardboard shredding adds equipment and labor costs that you might not be able to justify.

Another big variable is compostable foodserviceware. There are two main categories, compostable paper products and compostable plastic. The problem with compostable plasticware is that in too many compost situations it does not break down as quickly as the food waste, especially if the compost pile does not maintain optimal conditions the entire time. If you are composting via an on-campus pile or on-farm pile that might be turned more sporadically, this might especially be an issue. That leaves your end market with a product that they have to screen out of the pile before they can use the rest of the compost. It is also difficult for some composters to identify whether the plastic in their pile is compostable plastic that has not yet broken down or non-compostable plastic that was mistakenly dumped into the compost. The result is that some composters screen out and discard anything that hasn’t broken down within a certain time frame. All of that adds cost and headaches for your end market. Now, I don’t know about you, but most of the time I approach my vendors with an idea that is going to add headaches and cost for them, their response is typically not “Woo hoo. Sign me up. I’ll do that pro bono.” Instead, my experience is that they find ways to transfer those costs and headaches back to me, sometimes with interest. In addition, to me, it also defeats the purpose of investing in compostable plasticware if it is just going to get screened out and thrown away by your composter.

If you are looking for an alternative, compostable paper offers some potential benefits. If it is uncoated, it has the potential to suck up some of the excess au jous from your food waste, making your food waste less sloppy. Paper products also typically break down in a period of time that is similar to the food waste or other wood product feedstocks that your composter is likely using. Lastly, paper is very carbon-rich stuff, so it helps to balance out the nitrogen-rich food waste, and gives your end-market a more balanced product to work with to keep those zen micro-critters happy. From my experience, as long as your composter can handle the added volume of material that comes with taking the paperware, they are often able to do so with fewer headaches (for both you and them) than with other compostable foodserviceware.

Do you have composting experiences that you would like to share with other readers? As always, feedback and comments are always welcome.

Written by

Roger Guzowski
Roger Guzowski

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