Feed a Disposer, Starve a Landfill

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A colleague of mine once said, “Had the disposer never been invented, today would be a great time.” This is because of what I call the three environmental mega-trends – food waste reduction, landfill diversion, and resource recovery. Consider these facts. #1 – The United States Environmental Protection Agency and Department of Agriculture announced a joint goal to reduce food waste 50% by 2030. #2 – Five states have regulatory mandates or goals to divert organics from landfills, and four more are considering similar guidelines. #3 – Wastewater treatment plants are being re-branded as ‘water resource recovery facilities’ because they produce clean water, energy and fertilizer.

The food waste disposer is at the intersection of these mega-trends. It is the perfect solution for accomplishing all three goals. This is never more evident than in Racine, my home, where the disposer was invented by John Hammes in 1927. A local zero waste initiative began within the last year, partly because the City Administrator Jim Palenick recognized the Kestrel Hawk landfill will soon face closure, perhaps in as few as four years. The Zero Waste Committee has already acknowledged disposers as part of the solution, and the wastewater treatment plant will most certainly benefit from increased biogas production for making energy in its anaerobic digesters.

We pay relatively little for garbage and utility fees, and we just want our trash and sewage to disappear. Unless the garbage truck misses a pickup, or we have sewage backing up in our basement, everything is hunky-dory. We simply “flush and forget.” In other words, unless something affects our everyday lives, we take these utilities for granted. However, with the landfill closure looming, residents of Racine will most likely face higher solid waste costs soon, as officials evaluate other options – new sites and further distances.

If residents used their disposers more to reduce food waste in the trash, it is possible to not only prolong the life of the landfill, but also help the wastewater utility produce more of their own energy to reduce operating costs. Perhaps residents could even pay less for trash removal by asking for smaller waste containers. At the invitation of Greening Greater Racine a few weeks ago, I shared this message of using disposers to help Racine’s efforts to a group of about 45 people at the public library, and will also participate in a panel at the Golden Rondelle on March 15th. So far, I continue to hear a similar theme – people are reluctant to use their disposer.

To help people gain confidence in using their disposer and prevent problems in their plumbing, we created an instructional video. My hope is that people will begin to use their disposer for more than just plate scrapings. Take note. Don’t fill the disposer, turn it on and then add water. Operate it just the opposite – water first, disposer second, then gradually add food waste, and then make sure to let the water run a few seconds after grinding. I guarantee this method allows for grinding virtually any kind of food waste, significantly reducing the amount of trash sent to the curb.


Finely Ground Food Waste is Fluid Fuel

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In some regions, urban populations are denser than a decade ago. So, we could say urban density is variable. By contrast, the density of a “substance” is a physical property that does not vary. Density of a substance is a known quantity expressed as mass per unit volume. For example, the density of water at 400C, is 1 mg/ml. Why is this relevant?

It is relevant because food also has a density of 1 mg/ml. So, if food waste is 70-90% water to begin with, and it has the same density as human waste and water, there should be no issue with wastewater professionals concerned about “solids” settling out in sewers and causing blockages and overflows. Properly designed and constructed sewers will transport this material very efficiently to the treatment plant without causing any issues. Make sense?

The danger here is some people cling to their well-intentioned perceptions versus scientific fact. This dogmatic attitude can prevent our water resource recovery facilities with anaerobic digesters from taking advantage of a great opportunity to boost biogas and move towards energy independence.

Utilities of the Future

According to a database of information on U.S. infrastructure, there are 1,236 publicly owned treatment works utilizing anaerobic digestion to process sewage sludge into biosolids. The wastewater industry is rebranding itself into water resource recovery facilities – makers of clean water, energy and fertilizer. Just last year the National Association of Clean Water Agencies specifically recognized 61 of these facilities as “Utilities of the Future.” Of these 61 plants, 26 are actively seeking high strength waste to feed directly into their digesters. These feedstocks to boost biogas include food waste.

Certainly, delivering food waste directly to digesters is more efficient than letting it go through the entire plant. This is because only about half would be separated and processed into biogas through primary clarification. The other half would end up being processed in the energy intensive aeration process. This is one of the reasons why the Sustainable Food Waste Evaluation by WERF (2012) determined codigestion of hauled waste delivered directly to wastewater treatment plants results in the lowest greenhouse gas emissions. However, if codigesting food waste improves biogas production, even if only half ends up in the digester, these municipalities should consider encouraging the use of residential and commercial disposers to add more feedstocks to their digesters and boost biogas production even more. There are two reasons why municipalities should at least have a conversation on this opportunity.

First, food waste sent to a water resource recovery facility means it avoids being landfilled. Second, even though less energy is generated than if it were piped directly to a digester, there is still a net energy gain according to research by Leverenz and Tchobanoglous. More importantly, the high carbon to nitrogen ratio will help the plants remove nutrients from their effluent, reducing the negative impacts of eutrophication on our streams, rivers and lakes.

Unfortunately, in my discussions with wastewater professionals, the perpetuated myth that food waste clogs sewers almost always supersede all rational thought, so I would like to remind my esteemed colleagues and friends that in the end, shouldn’t pure science trump preconceived notions?

Food for thought/


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?