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?
A couple months ago in Reno, Nevada I presented at the Onsite Wastewater Mega-Conference – mega because it was a joint conference for the National Association of Wastewater Technicians and the National Onsite Wastewater Recycling Association.
Much of my work is focused on centralized wastewater treatment, but this event was centered on decentralized treatment (septic systems). Since I recently wrote a whitepaper on how it is okay to have a disposer on a septic system, it was the perfect venue for further discussion on the topic.
After listening to the plenary speakers Robert Siegrist and George Tchobanoglous, as well as Andrew Sawyers of the USEPA, the conference theme was clear – “managing a precious resource, water.”
Emphasis was placed on new terminology and a paradigm shift in how we view decentralized systems. As wastewater professionals, we were encouraged to adopt the lexis of treatment systems instead of septic systems and “water recycle and reuse” versus disposal. We were also encouraged to consider the optimum use of carbon, in which food waste and sewage can be used to make energy and fertilizer.
Most people I spoke with didn’t express concern about disposers on septic systems. However, there were questions at the conclusion of my presentation on the impacts of the additional 20-30% load and FOG, especially where new systems are now requiring effluent screens on the tanks. This might be resolved by simply requiring a two-compartment tank, as is the case in Minnesota.
I came away from the conference with thoughts regarding the fundamental science that is overlooked with disposers. Food waste is 70-90% water, and disposers were designed to quickly and conveniently grind the remaining solids into fine particles that can be sent through plumbing pipes without clogs.* By grinding food waste into very small particles, disposers exponentially increase the surface area available for microorganisms to break down the organics.
By adding water, the slurry starts to undergo hydrolysis, fermentation and acidification. Soon-to-be published research from Cornell shows that this happens very quickly. Even when the slurry is held in a tank. Mix slurry with the biology of a sewer or a septic tank, and it’s easy to see how the food waste rapidly breaks down.
Perhaps this is why treatment plants in areas where 90% of homes have a disposer are not experiencing organic overload and why there is no evidence that disposers are the cause of septic system failures.
*ASSE standards require disposers to grind so that all particles are less than one-half inch. Most particles are actually between one-eighth and one-quarter of an inch.
Bad odors often elicit gnarled faces, loud incomprehensible reactions, and even gagging. This is because we are created in such a way to instinctively react to things we should avoid. Garbage, and specifically food waste, provokes this reaction because the decay of organic material results in emissions such as ammonia, sulfides, mercaptans, and butyric acid, as well as bioaerosols. Both types of emissions are to be avoided, because there are potential health implications from exposure to either of them.
Ew! What’s That Smell?
Decay of organic material requires microorganisms like bacteria to convert complex molecules and break them down into simpler ones like carbon dioxide and water. Unfortunately, during the process of decay, some malodorous chemicals from the garbage bin are telling us that not only should we have gotten rid of that rancid stuff sooner, but also that there are potentially harmful bacteria lurking in there!
Recent research from Open University in the UK investigated the release of bioaerosols from trash and revealed that after four weeks, bacteria types increase, resulting in the release of higher levels of endotoxins. The research did not indicate a significant increase earlier than two weeks. While the authors mention more study is needed, they also recommend conducting risk assessments for waste collectors since there is a known dose response relationship for endotoxins.
A few cities in the U.S.A. recently started biweekly trash pick-up. However, putrescible waste must be collected weekly, so where cities invest in green bin programs to collect organics, they can justify less frequent, biweekly trash pick-up. Nevertheless, it is not a good idea to let your organics stay in the trash for a lengthy time. Most everyone has experienced the smell of rotten garbage in much less time than two weeks. That being said, most trash is picked up much more frequently than every four weeks, but if you want to end the odors, why not avoid bioaerosols or endotoxins altogether and use your garbage disposer!