What happens to water when we’re done with it

Out of sight, out of mind. (At my age, alas, I no longer live within the confines of that dictum. I can forget, misplace and overlook things that are smack in front of my face. But I digress.)

 

What many folks can’t see they can indeed overlook. And all too many Americans have never seen what happens to the water that flows down the kitchen sink and out of the house. But with each load of laundry or flush of the toilet, we create wastewater that’s mingled together and heads toward treatment plants.

 

The average American makes 100 gallons of wastewater per day. While it’s natural to think that sewage water is icky, it’s also a fact that sewage is natural — and it’s even interesting from a biological point of view.

 

I’ve toured a couple of sewage treatment plants, and I’ve taken college students through one of them. As a geologist, I have long noted that such facilities are typically built on floodplains. That’s partly so sewage can flow by the force of gravity down to them from surrounding houses and schools, and partly because their large pools for processing water require flat areas. Of course, when a river floods the sewage treatment plant can be inundated, one of the greatest disadvantages to putting them in floodplains.

 

Treatment plants start to process sewage by blowing air bubbles through it. Oxygen in the bubbles helps sewage decay, an important first step in treatment.

 

Sewage next enters tanks where sediment or sludge can accumulate on the bottom and scum on the top. The sludge is processed in tanks called digesters. The area around the digesters is often the smelliest part of the plant. (And I do mean pungent!)

 

Digesters use heat and bacteria to break down the fundamental essence of our poop. One goal is to get rid of microorganisms that would cause disease. The solids that emerge from the digesters are often sent to landfills but are sometimes used as fertilizer.

 

Another product of treatment plants is methane gas that’s created in the digesters. Methane is the main ingredient of what the utility company sells you as “natural gas.” A few treatment plants make use of the methane, burning it for heat or to generate electricity.

 

The liquid portion of wastewater is often filtered through sand. This helps get rid of bacteria and fine solid particles still lingering in the water. In some places carbon filtration is used, a step that helps remove fine organic particles. Finally, chlorine is often added to kill remaining microorganisms.

 

Those of us who exercise in swimming pools and snort chlorine up our noses know that it’s a serious chemical. So all remnants of chlorine in the water must be neutralized before the treated water flows into a river.

 

If you want an indoor toilet where you don’t have a hookup to a municipal wastewater system, you can create your own little disposal system in the form of a septic tank. Inside the tank are bacteria that can live without oxygen. Septic systems are far from perfect, but they do help break down sewage. Water flows from the tank out under the soil, usually via a bed of gravel.

 

For the nontraditional, it’s also possible to have indoor convenience with what’s called a composting toilet. I had such a toilet for several years in a travel trailer, and it worked well for me.

 

I had quite an animated conversation about that toilet at a sewage treatment plant one day. The supervisor of the plant and I both shared an interest in how sewage is broken down by microorganisms. (You meet good people at treatment plants.)

 

Lately my water bill roughly doubled – and yours may have, too. What’s at issue is better handling of storm water run-off from streets and parking lots. Such water contains oil and the like, at least in trace amounts.

 

As you wash a greasy frying pan tonight or start a load of laundry, take just a moment to consider that the water that leaves your home goes back to the Earth. We face different choices about water treatment, but the condition water is in when it reaches local rivers is our ultimately our responsibility.

 

Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. Follow her on the web at rockdoc.wsu.edu and on Twitter @RockDocWSU. This column is a service of the College of Agricultural, Human, and Natural Resource Sciences at Washington State University.