In-sink-erate this!
Proper care and feeding of a garbage disposal.
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In-sink-erate this!
Hi all!
Welcome to Make it Green Girl’s Quick and Dirty Tips for an Earth Friendly Life. Today we are going to discuss a smelly subject – trash! In my episode about the 3 “Rs,” I talked about how to reduce, reuse, and recycle to ease the burden on our landfills. Another place that our society deals with the waste that’s produced by exploding populations living in close quarters is the waste water treatment plant. All your household waste from your showers, toilets, and sinks go to the waste water treatment plants, so today I’m going to let you know how you can reduce your sewage load on these already over-taxed facilities.
Listener Mary from Milwaukee Wisconsin wrote, “Is it better to toss table leftovers down the garbage disposal, or to put them in the trash?” This is a great way to start off the discussion, because waste water treatment plants have to deal with all the crud that people throw down the disposal. There are some things the plants are built to handle, and others that just mess things up.
Our Sewer System
Let me begin by saying that the waste water treatment plant staff do not have an easy job. They deal with whatever comes from city sewers, and have to make a waste stream safe enough to send back into the environment. A slough of raw sewage pours in from developed areas, containing lists of chemicals that get longer each day. Some businesses can drain to sewers as well, so it’s not just poopy water the plant staff have to deal with – industrial chemicals are their responsibility, too. While the water that comes out of waste water treatment plants is not potable, it’s still gotta go to a river, stream, or golf course somewhere, so it’s subject to stiff rules about the quality of the water leaving the plant, or effluent water. Both increased chemical loads coming in and stricter effluent regulations have placed a huge burden on our municipal systems. Not only that, but many plants are aging or operating a full capacity already. So here’s how you can help lighten the load.
Don’t Flush It – Trash it!
The first step in waste water treatment is mechanical, called primary treatment because it happens first. In this step, a large mechanized rake is used to remove macroscopic objects that come in from the sewers. There’s not a whole lot that can fit down your drains at home, but even the small stuff can cause big problems.
A colleague of mine who works in waste-water treatment plants told me that the most irritatingly common item collected in the trash racks are feminine hygiene products and condoms. This is mostly because they tend to evade these screens. Tampon applicators can sneak through sideways, and condoms deflate a swim right on by. Both of these items tend to float as well, which means they make it past the settling tanks and clog up the system downstream. Neither of these things belong in your toilet, even if the box tells you it’s ok. Just throw them in the trash. They will be going to the same place either way – the landfill, so do your waste water treatment plant a favor. Think before you flush.
Grit and Grime
Next in line in mechanical treatment are a series of settling tanks, which are just big vats that slow down the motion of the water, and causes little bits of dissolved sand and dirt to fall to the bottom of the tank where it’s collected. Lighter particles of fat and oil float to the top where they are skimmed off. Neither sediments nor oily films are allowed in the discharge waters.
In the settling tanks, macroscopic organic particles can float on by because they are less dense than or the same density as water. Coffee grounds are a great example; because they are saturated, they don’t always float to the surface or sink to the bottom, they kinda hover in between. In this same family of small, persistent invaders are tough fruit and vegetable rinds like oranges and bananas and stubborn calcified bones and eggshells. This will become a problem downstream because they can clog up the pumps and grind the whole system to a halt.
Fats and oils that make it to the settling tank have already gone too far. While the plant is capable of dealing with these wastes, the pipes in your home and under your streets are not. Fats, oils, and grease tend to clump together, even after you’ve cleaned it out of YOUR drain, which can cause dangerous backup in the sewers. When it rains, or if the system gets completely clogged, your community and your local environment could be in for a raw sewage swim. Small amounts of oils and grease can be thrown in the trash in a sealed container. If your family produces large amounts of used fat, you can store it in a jug under the sink until it’s full, then take it down to the landfill or recycler. My community’s recycling service will even pick up used cooking oil if it is placed in gallon jugs next to the regular recycling.
Sludge Digestions – Max and Mini
The second phase of waste water treatment is the biological processes, also called secondary treatment. This step is designed to degrade all the dissolved biological compounds in the water like sugars and starches, alcohol, tiny food particles, etc. In most plants, the secondary sewage is treated in aerated tanks called sludge digesters. Little bacteria – which my professor calls Max and Mini – bathe themselves in the nutrient rich water, happily eating whatever we couldn’t somach. The end product is far less organic compounds – Max and Mini ate them all and belched out some carbon dioxide and pure water, plus some various fermentation products. The biological treatment steps are the reason most waste water treatment plants smell bad.
Some plants also have anoxic sludge digesters, which are kept away from the air to starve the sludge of oxygen. This promotes the growth of species who hate oxygen, called anerobes. These beneficial bugs usually produce methane instead of carbon dioxide, which can be a source of energy to the plant if collected an burned in a natural gas turbine engine. This methane product is usually called biogas to distinguish it from natural gas, which comes from petroleum. The East Bay Municipal Utilities District (EBMUD) waste water treatment plant in Oakand, California produces 90% of the energy it takes to run the plant with the methane collected from it’s sludge digesters.
Happy Bugs are Good Bugs
Max and Mini can’t eat everything. As amazing as microorganisms are at breaking down everything we throw at them, Max and Mini don’t have the time to deal with all the waste that comes their way. Those peels, bones, and coffee grounds will get eaten away eventually, but much more slowly than the dissolved sugars because they are so much bigger. Plus, Max and Mini are like humans – given the choice, they go for the easy meal that tastes sweet. They’re going to digest the sugars and starches long before they ever get to your week old coffee grounds.
Coffee grounds DO make great compost material, though, so stay tuned for what to do with all those food scraps that I just told you you can’t insinkerate anymore.
Another thing Max and Mini have a hard time stomaching are household hazardous and medical wastes. They simply cannot digest mercury and heavy metals, so flushing broken thermometers, lightbulbs, and batteries is definitely out. These need to be taken to qualified recyclers, if you have them in your community. We were encouraged to flush medical wastes like expired medications for a long time because it would keep them out of the hands of kids and pets going through your trash, as well as criminals who sought them for drug purposes. However, Max and Mini can’t keep up, so those drugs that are dissolved into our water go straight into phase three of treatment, where they either pass through unscathed and enter local watersheds, or become chemically altered into far more dangerous by-products.
To keep your meds out of the trash AND out of the water, see if your pharmacy has a take back program or if there’s a drop-off point at your local hospital or urgent care. Otherwise, we may become a nation of drug users just by drinking the water.
Chemical Treatment
After mechanical and biological treatment is finally chemical treatment, also called tertiary treatment. Tertiary treatment systems vary widely, and can include anything from simple chemical precipitation of leftover chemicals or full-scale constructed wetlands. In this step, the water is also disinfected with a strong oxidizer like ozone or chlorine, and is sometimes irradiated with ultraviolet light to degrade any remaining organic compounds and kill any Max or Mini who might feel like escaping the sludge digester restort.
Before the water can be discharged to the environment, it must be free of harmful microorganism that live in sewage, like fecal bacteria from household toilets. Ozone and ultra-violet light can both accomplish this last goal, but cannot provide lasting protection from the water. Ozone degrades too quickly to be of use downstream, and ultraviolet light does not have any effect beyond where the light shines. Chlorine is almost always added if the plant contains additional equipment that can turn sewage into potable water again, because it lingers in the water, protecting your water from dangerous microbes al the way to your faucet.
One reason many have called the practice of chlorinating into question is that it produces small amounts of disinfection by-products, or DBPs, especially trihalomethanes, or THMs. These by-products are the result of incomplete degredation of chemicals in the wastewater by poor Max and Mini. They are created in miniscule amounts, but we have very little knowledge about their action in the environment and our bodies. In short, anything you can keep out of the drain that isn’t obviously food (or at least it was until you forgot it three weeks ago in the fridge), it belongs in the trash, not down the drain.
Ok, just so were clear. Don’t flush hygiene products, eggshells or oil. Take your medicines back to the pharmacy. Compost your food scraps. Be kind to your sewage treatment system, and it will be kind to you.