Description of Challenge
Normally, our sewage is treated with toxic chemicals and discharged into the sea. These processes pollute our natural environment.
How can we treat our wastewater ecologically?
“The sea is the universal sewer” Jacques Yves Cousteau
“Pollution is just an unused resource”, Bill Mollison
“We won't have a society if we destroy the environment.” Margaret Mead
Solution
There are many different ways of processing sewage ecologically, including reed bed systems and compost toilets. One such method is called the Living Machine. Pioneered by US ecological designer Dr John Todd in the 1970s, the Living Machine works by mimicking a natural wetland system.
It uses advanced science and engineering processes, combined with beneficial bacteria, to treat wastewater to the point where it can be safely reused. In addition, the sewage plant may start to resemble a beautiful greenhouse!
To work properly the system needs a minimum intake of waste waster, depending on the size of the tanks, so the water won’t stay still and keep moving through the tanks. To be valuable, it is recommended for use by at least 100 people or more.
The sewage is first collected in the septic tanks which is a closed tank, fully covered by soil. Its purpose is to filter all the big particles and foreign elements out of the system. Once the tank is filled up to a certain level the sewage moves further to the next tank.
The aerobic tanks are the ones where the magic happens. With a combination of oxygen, plants and microorganisms the water is “revived.” The tanks are embedded 2 meters into the ground to provide enough height to filter the oxygen out of the air. The airpumps are one of the few parts of the living machine which need external resources.
The plants provide the surface for the biofilm, which takes care of the pollution. Pollution means the water has an excess of nutrients, which needs to be broken down to a “clean” level. The plants only do up to 5% of the job, so the main nutrient transformation is done by the micoorganisms. The more tanks you add the cleaner your water gets, but the more sewage intake you need.
After the aerobic tanks, the water goes through a different tank, where special plants cover the whole water surface, so no sunlight can reach the water and undermine the process of forming algae. This process is called enthrophic process, which is important to minimise the sludge.
The final tanks have ecological fluidised beds, which provide a lot of surface where the nutrients can stick to “polish” up the water.
The whole process takes 4 days, with several cycles within these days. It’s important to know, this process is a bacterial process and therefor not filtering viruses. It would take additional steps like UV filters, glass filters, osmosis to guarantee drinking water quality. After the whole process the water has EU swimming quality.
The best solution might be to let the water run back into a pond or lake and let it filter through the earth into a well and gather it back with a borehole. So you create a closed loop, including a pond for the surrounding nature.
Pros and Cons
Pros:
- Decentralize the sewage system
- Environmentally friendly
- Economically worth it after a couple of years
- Water provides hydration for plants in the tanks and afterwards
- No maintenance required
Cons:
- High initial costs
- Requires building permit
- Takes up space the size of about 2 houses
- Needs to be above freezing temperature / works slower with lower temperatures
