Wastewater Treatment
Treatment Process
Let's start by seeing how to collect wastewater and transfer it to a treatment facility.
1. Collecting wastewater
What's the first step in treating wastewater?
JCW and other wastewater treatment organizations clean used water almost the same way that nature would, only we speed up the process. If the water was left alone in a stream or lake, it would naturally clean itself, but that could take a long time. The first thing we have to do, then, is collect the wastewater and transport it to a wastewater treatment plant.
The transfer system
Wastewater leaves your home through a service line that collects waste from sources like toilets, sinks, and dishwashers. It flows from the service line to a larger "main" sewer line that transports the flow to one of our wastewater treatment plants.
In Johnson County there are over 1,800 miles of sewer lines. They are usually made of plastic, iron, or clay.
Sewer manholes allow us to access the sewer lines to inspect and clean them. Manholes can be very dangerous. Only JCW personnel should open and enter them!
Sanitary sewers are not designed to carry rain waste only water from homes and businesses. Rain water goes into storm sewers and creeks. You can see storm sewer inlets along the curb on many streets.
JCW uses pump or lift stations to help carry the wastewater to one of our plants. Lift stations are needed to pump the sewage to a geographic high point where gravity takes over and sewage flows to a treatment plant.
After the wastewater reaches the plant, the treatment begins! The first thing that happens is called Preliminary Treatment.
2. Preliminary Treatment
Usually the first thing that happens at the treatment plant is the used water goes through a bar screen. The screen catches and removes large things from the water (such as paper cups, leaves, sticks, surf boards).
Next the water goes through a grit removal chamber. The grit chamber removes heavy things like gravel, seeds and coffee grounds (grit). When the water enters the chamber, the “grit” settles to the bottom and is removed. The material removed by the screen and grit chamber is usually disposed of in a landfill. The water flows to the next stage of treatment called primary treatment.
3. Primary Treatment
After grit and large solid materials are removed from the wastewater, many smaller solid particles still remain. To remove these particles, the wastewater is sent through large tanks called clarifiers. In the clarifier the flow moves very slowly, and small solid particles settle to the bottom and are removed.
This process is called sedimentation. The material that is removed is called sludge. The sludge is treated separately. The remaining wastewater contains mostly dissolved wastes and goes to the next stage called secondary treatment.
4. Secondary Treatment
The work of secondary treatment is a biological process accomplished by living organisms. Bacteria and other microscopic organisms grow by using the waste for food. This is a process that occurs in nature all the time. At the treatment plant we just speed up the process.
Wastewater treatment facilities create a utopia for microorganisms: optimal food, optimal oxygen, and plenty of space to grow. As the microorganisms feed on the waste we’ve flushed away, they grow and divide. Very happily! As the organisms feed and grow, the water gets cleaned. Microorganisms that feed on the waste in the water are bacteria and protozoa. We sometimes call them “the bugs.”
The wastewater has lots of food to help the microorganism grow. But they also need lots of oxygen. The wastewater itself doesn’t have very much oxygen, so we have to make sure the environment has plenty of oxygen for them.
JCW has two different methods of making a good environment for the microorganisms to eat and grow and clean the water.
Consider taking a look at our set of instructions on how to view a drop a wastewater under a microscope. Identifying and counting microorganisms takes skill and practice. Could you do it? Try playing our Micromatch game to see.
At some of our treatment plants we use trickling filters, which pour water over tanks filled with rocks. The microorganisms live on the rocks, which are surrounded by air. As the wastewater trickles past them, they eat the waste and grow. This trickling of the water helps provide the oxygen to help the microorganisms grow.
Some of our treatment plants grow microorganisms in large tanks. We blow air into the tanks full of wastewater and microorganisms to add oxygen to them. The air is bubbled in the water and mixes “the bugs” and food and oxygen together.
When we treat wastewater this way, we call it the activated sludge method. With all of this food and air, the microbes grow and multiply very rapidly.
Pretty soon the population of bugs gets too large, and some of them need to be removed to make room for new bugs to grow. We remove the excess bugs by sedimentation in the same kind of tanks used for primary treatment.
In the tank, the bugs sink to the bottom and we remove them. The settled bugs, along with settlement in the primary stage are both referred to as activated sludge. The sludge is treated separately. The remaining wastewater is now much cleaner. In fact, after primary and secondary treatment, about 85% or more of all pollutants in the wastewater have been removed. The remaing wastewater goes on for tertiary (meaning third) treatment.
Consider viewing our 360 degree panarama of one of our plants. You can also zoom in closer on areas. (You'll need a QuickTime Player loaded on your desktop to view it. Use your browser's back button to return to this page.)
5. Tertiary Treatment
Disinfections
Before we release the treated water back to a stream or river, we kill any microorganisms in it that might cause disease. At some of our facilities we use a solution that contains chlorine to kill the organisms. Extra chlorine left in the wastewater is then removed by another chemical. At other facilities we use ultraviolet (UV) light to disable the microorganisms. The special lights kill the microorganisms.
Effluent
Where does wastewater go when we’re done? After the wastewater is cleaned, we put it back into a stream or river where it’s safe for fish to live, animals to drink, and humans to swim and play! Wastewater that is cleaned and sent back to the streams is called effluent.
Can Surfer Dudes and Dudettes help? You bet! Conserving and caring for water helps us help you and benefits the environment, also.