How Wastewater Treatment Works & Why It's Important

overhead shot of large sewage treatment plant

Do you ever wonder what happens to the waste that you flush down your toilet or the dirty dishwater that flows down your drain?

Any water that has been used and requires cleaning before being placed back into a water system is considered wastewater. Before the water can be released back into the water system, it needs wastewater treatment.

Without it, the polluted water enters the water system and contaminates not only the water, leading to dying plants and wildlife, but also could end up back in the water system requiring extensive treatment before going back into your home.

Stage One of Wastewater Treatment

Wastewater comes from many places, including rainwater. The water contains everything from feces and urine to sticks and other debris. It’s estimated that 35 percent of wastewater is made from solid objects.

The first step is the removal of the objects. The water first goes through a coarse screen that traps all the larger debris. The coarse screen has openings about 10 millimeters in length.

Once the larger pieces are removed, it goes through a pumping station and into a fine screen that removes even smaller debris.

All the solids are taken from the treatment plant to the landfill.

The last aspect of stage one is the placement of the water in settling tanks, where any residual scum floats to the top and sludge settles on the bottom. The scum is skimmed from the top and sludge removed from the bottom.

This is treated separately from the wastewater.

Stage Two of Wastewater Treatment

The water is free from sludge and other solids, but it’s nowhere near clean. Other contaminants must be removed.

The wastewater is mixed with oxygen and bacteria designed to eliminate the other polluting materials and the oxygen helps them work faster.

Once the bacteria have broken down the materials, the water once again goes to settling tanks where the sludge settles and is removed.

At this point, the water is 85 to 95 percent clear of contaminants and is almost ready to place back into the water system.

Final Removal of Remaining Contaminants

Wastewater treatment plants use several combinations of methods to remove the remaining contaminants in the water. The most common method is to run the water through a sand filtration system.

There are two main types of sand filtration systems: surface and depth filters. With surface filters, contaminants become trapped within a permeable surface, but with depth filters, contaminants are trapped inside a porous material.

Sand filters filter material through direct collision, surface charge attraction, diffusion, and small force attraction.

Once the water goes through the filter, it’s treated with UV light or chlorine and discharged into the water system.

Treating Sludge and Scum

We talked earlier about the sludge and scum taken from the settlers and processed separately.

The sludge is infused with bacteria and feeds on sludge for up to 20 days. The bacteria eat the organic matter and generate carbon dioxide and methane gas.

This can be used to heat the treatment plant since it’s combustible, and much of the odor of the sludge is eliminated since there is little organic matter left. The sludge goes to a large centrifuge that spins quickly to separate the liquid from the solid.

The liquid goes back through the treatment process and the remaining matter is used to fertilize fields.

Advanced Methods of Treatment

Wastewater also includes water from industrial and agricultural sites.

These have contaminates not found in residential and commercial wastewater. For these types of wastewater, they go through additional purification steps.

In biological nutrient removal, the water goes through three different tanks filled with varying amounts of oxygen. Each is filled with a bacterium that thrives in those conditions.

The water goes through each tank where phosphorous is removed and ammonia breaks down to nitrate and nitrogen gas. The bioreactors house the water for about nine hours before it’s moved to a settling tank, and the sludge removed from the bottom.

This method gets out contaminates the standard processes cannot.

Small Community Wastewater Treatment

As you can guess, a large scale wastewater treatment plant is expensive to maintain. There are regular inspections, upgrades, and maintenance, cost of employees and their certification.

Most small communities cannot afford such an advanced system. Instead, they use wastewater lagoons. The lagoons are large reservoirs of water anywhere from five feet to over nine feet deep.

Shallows lagoons are best for primary treatment. The water enters the reservoir where it sits for about six days and the sludge settles to the bottom.

The problem with shallow lagoons is they are not effective in removing most of the contaminants.

Larger lagoons can hold water for six months and up to a year, allowing for more sludge to be sent to the bottom. Most of these lagoons are only emptied once a year.

If there is no river or lake to send the wastewater, some communities drain it onto land. The bacteria in the soil can naturally break down and remove any contaminants in the water.

Improper Water Treatment

The Environmental Protection Agency is in charge of making sure water treatment plants stay within compliance.

If they empty untreated or improperly treated water into lakes and rivers, then it could have a devastating effect on plants and wildlife.

Many small communities have a difficult time operating and maintaining water treatment systems, but less expensive and alternative methods are developed every day.

Treated Water is Safe Water

Many times, the water used in wastewater treatment makes its way back into the water system.

You want to make sure the water that comes through your tap is clean and refreshing. It all starts when you flush your toilet or send water down your drain.

If you want to learn more about wastewater and how it's treated, then please contact our experts today.