What Happens to Toilet Paper After You Flush It?

How TP Is Created

Toilet paper is a relatively recent invention compared to the lengthy history of humans expelling waste. (Other strategies for keeping clean in the bathroom have included water sprays, sticks, leaves, and even corn cobs.)

The first documented reference dates to sixth-century China, and toilet paper made from rice was created for Chinese royalty in the 1300s. In the Western world, the first TP was sold in the late 1800s, originally as individual squares and then later in rolls that had to be cut with special dispensers. 

The soft, perforated toilet paper we use today is, like most other paper, made from trees. The wood is debarked, chipped, and pulped, then cooked to separate out its component parts: cellulose (a compound that makes up the cell walls of plants), lignin (a substance that binds wood fibers together), and hemicelluloses (other compounds found in plant cell walls). The majority of the resulting toilet paper is made up of cellulose, which is held together with a little bit of lignin and water to make a paper stock that’s sprayed onto mesh screens and then dried into sheets.

What Happens After You Flush

After you push the flush handle, anything in your toilet is whisked away down the pipes. (It’s important to never flush anything other than waste and toilet paper, which are capable of being broken down in wastewater treatment, as we’ll see.) 

If you have a septic system, the pipe pathway may be relatively short. If you live in a place connected to municipal water, the toilet paper may travel through miles of pipes before reaching a treatment plant. The paper fibers come apart pretty quickly in the water from the toilet, but the cellulose molecules stay intact at this point. In order to break down fully, those cellulose molecules need help from microorganisms — in this case, bacteria that use it as an energy source. 

With septic systems, whatever you flush down the toilet empties into a tank buried in your yard, and bacteria in the tank will start to break it down, a process that could take weeks or months. The partially broken-down molecules of cellulose form a sludge that settles at the bottom of the tank. It is eventually emptied by a truck that takes it to be processed along with municipal waste.

If you’re connected to a municipal wastewater system, your toilet paper journeys to the wastewater treatment plant. TP accounts for about 40% of the solid waste that’s processed by these plants. 

At the plant, wastewater is filtered into heavy solids and liquids, and about 80% of the cellulose from toilet paper is diverted to solid waste treatment. The cellulose that remains in liquid waste is consumed by microbes; by the time the waste water is sent back out into surface water (lakes, rivers, and the like), only a trace amount of cellulose remains.

The cellulose from toilet paper that becomes solid waste is mixed with biological waste in big tanks where bacteria break it down into fatty acids, which are then turned into methane by other microbes. Some treatment plants use the methane gas to generate electricity or to keep the tanks heated. 

After treatment, any solid waste that remains has its liquid removed through a centrifuge, drying bed, or filter press. The resulting product may be used on land as fertilizer, sent to a landfill, or incinerated and turned to ash. So in the end, your toilet paper’s molecules could wind up on land, in the water, or even in the sky.