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What happens after you flush?

When it comes to wastewater, most people probably would like to take an “out of sight, out of mind” approach.

The toilet flushes and the waste disappears into a mysterious world underground, eventually getting taken care of by someone, somewhere far away.

In reality, wastewater treatment is a complex procedure that mixes natural processes with modern technology. And it takes many people to dispose of our waste in a way that is both safe for people and the environment.

So, what does happen when you flush the toilet? It depends where you live. There are two types of wastewater treatment processes; septic systems or municipal treatment facilities. Basically the concept is the same, just handled on different scales of size.

Septic Systems

People who live in rural areas or who don’t have access to a public waste treatment plant often deal with sewage through an underground, septic systems installed specifically for their home and located on their property near their homes. A typical septic system has a tank that receives the waste and lines or a pit to dispose of the treated liquid waste after bacteria has broken down solids in the tank.

The tank separates waste into three parts: solids or “sludge,” liquids and a layer of floating “scum” on top. Anaerobic bacteria, which can live in an oxygen-free environment, break the solids down into a liquid. The bacteria then treat the liquid, creating a gas that is released through the home’s sewage vent.

The oxygen-free environment inside the tank deactivates some disease-causing germs. The liquid is then sent to a nearby drain field where pipes take it through gravel or other materials, filtering the water as it is carried down by gravity. The remaining water evaporates through the soil.

Wastewater Treatment Plants

If you live in or near a populated area, you are probably connected to a municipal or regional wastewater treatment or sewage system. Such systems use gravity to move wastewater from your home through pipes installed underground, so treatment plants are typically located at low elevations. In larger communities, or areas with varying terrain, lift stations are used to help push the sewage through the pipes to the plant.

There are a variety of methods used to treat sewage, but here’s a general breakdown of the process. These techniques are used at water treatment plants operated by the Brazos River Authority.

As wastewater enters the treatment plant, it is screened to remove non-sewage items such as rags, sticks or any other solids that might damage or clog the equipment. This material is sent to landfills.

The sewage next goes into tanks where grit is settled out and taken to landfills so it doesn’t harm downstream treatment processes. Next, the wastewater moves into aeration tanks, which move the sewage around to expose it to oxygen and naturally occurring bacteria. The bacteria break organics down into carbon dioxide and water and cause small particles to clump together, forming flocculants, or “floc.”

The wastewater then enters a settling tank. Here, the “floc” settles to the bottom and is pumped out as “biosolids” also known as “sludge.” The biosolids either enter large “digester” tanks or return to the treatment process for more aeration. In the digester, bacteria further break down or digest the organic material. This part of the process takes 20 to 30 days. This digested material, its volume and odor now greatly reduced and harmful microorganisms removed, is either taken to a landfill or sometimes further processed for use as a soil conditioner.

Meanwhile, the water from the top or overflow of the settling tank is sometimes filtered by gravity through sand, reducing color, odor and other undesirable factors such as turbidity, a cloudiness caused by suspended particles.

Finally, the treated wastewater flows into a tank where it is disinfected by chlorine. The chlorine is then neutralized, oxygen is added, and the treated liquid, known as effluent, is released into the environment to once again begin the water or hydrologic cycle.

What shouldn’t flush

Probably one of the most misunderstood points regarding wastewater treatment is that you should never use a toilet as a trashcan. Toilets, septic systems, and sewage treatment plants are designed to handle water, waste, and easily-degradable toilet paper. But household refuse, even more dense paper can cause problems.

Such trash can cause blockages in toilets or pipes in one’s house, potentially resulting in a costly visit by a plumber. Also, some materials cannot be broken down in septic systems, which soon could become overwhelmed and call for another costly visit by a professional. Trash can also interfere with the processes at waste treatment plants. Because of that, many have screening systems to filter sewage before treatment.

Toilets or other drains also should not be used to dispose of household hazardous waste, such as cleaners, auto fluids, and many types of oil. Sewage treatment systems are designed to treat organic matter and can’t handle hazardous waste.

It’s also very important to remember that the toilet is not the proper place to dispose of medications that are no longer needed. In recent years both fish and public water systems have tested positive for human hormone and other medications that wastewater treatment can not remove. You may dispose of medications by taking them to any local pharmacy.

The Authority operates wastewater systems for the cities of Temple/Belton, Hutto, Clute/ Ridgewood, Georgetown, Sugar Land, Liberty Hill, Lee County Fresh Water Supply District No. 1, Round Rock, Cedar Park and Austin.