Processing water after it has been used into potable water is a complex mix of chemical, mechanical and electrical engineering disciplines. The mechanical problems to be solved include things like how we store water, how we deliver water and creating special equipment for each unique process required when treating water. In the US we pay for water usage per thousand gallons. And it’s generally quite a bargain.
Consider the fact that water weighs 8.3 pounds per gallon. The capacity of water treatment plants is usually defined in millions of gallons a day. Plant sizes may range from 20 to 50 MGD. That’s 160 million pounds of water processed per day for the smaller plant size. Just to move that amount of material is an impressive mechanical problem.
Lifting water into water towers or ‘lift stations’ in order to create pressure to deliver water is pure mechanical work. Just like the definition of horsepower; lift 550 pounds one foot in one second. So there are millions of horsepower expended each day just to move the water and waste materials. At a cost of electricity of around 5 cents per horsepower, which is also an incredible bargain, the process of recycling water is quite energy intensive.
The primary machine required for moving water is the pump. From Archimedes invention of the screw conveyor in 200 BC we have been moving water to enhance irrigation in the agricultural community. The invention of the screw has led to the screw pump, progressive cavity pump and a host of variations. In 1475 early forms of the centrifugal pump were invented to lift mud. Sliding vane pumps came along in the late 1500’s and as with all things mechanical, the number of improvement and variations has become almost infinite in the years since.
In all of these machines, the electric motor has proven to be the most effective means of powering the pump. For this reason there is a great deal of attention paid to the efficiency of the electric motor. But motor efficiency, while the most obvious, is not where the money is. The real mechatronic challenge is understanding the pump as a machine especially in circumstance where it is being operated below the full load point. In most pump applications the output of the pump is regulated by a valve and the motor and pump are operated at full load. This means that the input power between full load and the setpoint is being wasted. Given the number of pumps in operation, this is a huge waste of energy.
Getting around to all the pumps to evaluate and improve their performance is a giant mechatronic challenge.