The Energy-Water Connection

ADVERTISEMENT

Environmental engineers apply the first and second laws of thermodynamics in every project they plan and develop. The first law of thermodynamics states that energy can neither be created nor destroyed. The form of energy, however, can change. For example, the motion energy inside a turbine changes to electricity. The second law of thermodynamics states that energy flows from a region of high concentration to a region of lower concentration, much as water flows downhill. By the second law of thermodynamics, water at the top of a waterfall contains a high concentration of energy. As it pours over the waterfall and fills a basin, the energy concentration changes. The water that settles into the basin at the bottom of the waterfall holds a lower concentration of energy. This principle has been used for centuries to power daily operations.

Flowing water illustrates another component of energy—potential energy versus kinetic energy. Water at the top of the waterfall before flowing over the edge contains potential energy, that is, a form of stored energy. As the water pours downward it loses potential energy and gains kinetic energy, the energy of motion. All of the different types of energy

Operations that generate energy from flowing water—hydroelectric dams, wastewater treatment plants, mills— rely on capturing water’s kinetic energy. Water at the top of the waterfall in this diagram holds high potential energy, but after it reaches the bottom of the waterfall it contains low potential energy. Power plants take advantage of this transition.

in the solar system can be classified as either potential or kinetic, as the following table shows.

Energy can change from one type to another, as mentioned, illustrated by the following example:

1. A racehorse converts the chemical energy in hay to motion energy.
2. A person converts electrical energy to thermal energy by turning on an oven.
3. Plants convert radiant energy from the Sun into chemical energy through photosynthesis.

Water’s use as an energy source throughout history has usually been as motion energy. Wastewater treatment plants can take advantage of the natural flow of water to power operations, but wastewater offers an additional energy source in the form of biomass. Biomass is organic matter in wastewater that comes from plant and animal wastes. In the wastewater treatment industry, biomass represents a source of chemical energy that can be converted to other forms such as thermal energy.