Summer Session, Week 4
Tuesday, June 25, 2013
Trip to Pittsburgh Water and Sewer Authority
The water that the PWSA (and all other water treatment plants in the Unites States) treats is used in Pittsburgh for everything from drinking water to flushing our toilets.
The process begins when the plant takes in large amounts of river water from the Allegheny, which is held in huge underground tanks before being pumped up to be treated. The first line of filtration captures large debris like leaves, sticks and even fish that were pumped up with the water by passing it through huge metal screens. Gravity is used to an advantage, as chemicals that cause impurities like bacteria and algae to coagulate and sink to the bottom of treatment tanks. These coagulates can then be removed from the water.
Due to Pittsburgh's limestone bedrock, water that is taken in from the Allegheny River has a slightly basic pH of ~7.2. In order to aid the coagulation process, the water is treated to adjust the pH to 6.9, as the reaction of the coagulant chemical with biological matter is sped up at a lower pH.
The water then sits for days in large open tanks that fill the space of an entire warehouse. These are called sedimentation basins. The plant introduces charcoal, which works in much the same way as a carbon filter such as a home-use Britta filter works. Finally, it is passed through microfilration filters that are only large enough to let a water molecule through. This then removes more unwanted compounds from the water that are too large to pass through the membrane of the filter. At last, it is pumped out for use.
The Water Works PWSA supplies water to Reserve township, Fox Chapel, Aspinwall, the city of Pittsburgh, South Side, Millvale, etc. The facility typically serves 300,000 residents of the city, and up to 500,000 people on a workday, as people drive into the city for work. The Water Works on average puts out 65 million gallons of clean drinking water a day.
The amount of energy it takes to do this, from running the machines to just turning the lights on is ~$5 million.
Clean, treated water is used in many different industries, even fracking. Alternatively, the water can be drawn directly from the water source that supplies drinking water to people.
Pictures from our tour can be viewed here.