Full disclosure, I have been extremely busy working on my master's project recently, meaning other things have been left somewhat to the side. However, I think the subject of my project aligns well with the subject of sustainability and the image of Step3Project in general, so the time has not entirely been off path.
What we are doing is trying to improve the efficiency of highrise buildings by generating energy from falling water after it has been used by the occupants. If you remember all the way back to your highschool science classes, you'll recall that diagram of potential and kinetic energy. Where a stationary ball on top of a hill has substantial potential energy, and as it falls, that potential turns to kinetic energy-in the form of increasing speed at the bottom of the hill. This happens because energy needs to be conserved over a system - but you can ignore the boring hum drum that is the proof.
The same idea applies to elevated water. Pumps are used to bring the water to the end users on the higher floors, and once they use it that water has potential that transforms to kinetic energy (motion) as it falls back down to the sewers. Turbines are designed to turn kinetic energy and pressure into electrical energy using a generator. The internal workings are not important, if you'd like to learn more send me an email, but moving on. This means if a turbine is inserted at the bottom of the wastewater pipe, all of the energy from the falling water can be turned into electricity and offset the energy that it takes to pump the water up the building.
Issues that will need to be overcome are what to do with suspended solids, how to create reservoirs and where the reservoirs should be placed to maximize power output by collecting fluid from above and releasing it through the turbine below.
Analyzing data from a test building located in Ottawa Ontario, it's been determined that about 580 kWh of power per day which is enough to offset the usage of 113 people in the building. I will continue to update as things progress!
While not a massive amount of energy, but the thing to remember is sustainability is a puzzle that combines a lot of different pieces in order to achieve a larger goal. This can become one of those pieces.