What happens to the water you flush down the toilet? What about the water that goes down the drain when you shower or wash your hands? These are questions that I never gave much thought to before I became interested in greening up bathrooms. But Wikipedia and the USGS have helped educate me. I’m hoping to take a trip to a water treatment center to verify all of this, but in the mean time, here’s a simplified look at what happens to the water we use:
- Water from the sink, shower, toilet, and so on (now contaminated with chemicals and waste) goes down the drain and heads for either a wastewater/sewage treatment plant or a septic tank. I’m going to focus on the sewage treatment plant in this post.
- At the treatment plant, water goes through a primary or mechanical treatment where 60% of suspended solids are removed. Machines remove large objects including human waste, sand, gravel, rocks, oils, greases, rags, fruit, cans, and other objects that could clog or damage the equipment. These solids are usually sent to a landfill.
- The remaining liquid goes through a secondary treatment where aerobic bacteria breaks down soap, detergent, human waste and food waste. The bacteria consume the organic components and combine the less soluble parts into blocks called floc (which are removed).
- Finally, the water goes through a tertiary treatment where it is filtered and disinfected so it can be released back into the environment. Here are some common steps taken during this stage of treatment:
- Nitrogen and phosphorus are removed (if necessary) to prevent algae blooms (where algae acts like cancer - it multiplies, uses all of the oxygen in the water, releases toxins and kill animals).
- Treatment facilities disinfect with chlorine, ozone, or ultraviolet light to reduce the number of microorganisms in the water. Chlorine is commonly used because of its low cost, however, it can be toxic to the environment and aquatic life. Ozone is much safer but expensive. UV light is safer but high in maintenance and not always as effective.
As you can imagine water treatment plants use large amounts of energy to clean water. Unfortunately, most of the water that goes into these treatment plants comes from excessive water use and didn’t need to go down the drain in the first place.
If we can all reduce our water usage in the bathroom by brushing our teeth without the water running, by taking shorter showers, by adding water displacement devices to our toilet tanks, or by purchasing other water saving products, we can significantly cut down the amount of energy we use to clean water at water treatment plants.