What is Sewage Sludge?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 10 November 2019
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Sewage sludge is a thick sludge of solid materials which settle out from wastewater during the treatment process, whether the wastewater is being moved through a home septic system or a commercial sewage treatment plant. Once sludge is separated from wastewater, it undergoes processing of its own. Fully processed sludge must be disposed of or utilized in some way, and there is a great deal of debate in some regions of the world about appropriate handling for sewage sludge.

One major component of sludge is, of course, fecal material, complete with accompanying bacteria. Sewage sludge also contains everything else which ends up in a septic or sewer system, including toilet paper, tampons, and a wide variety of other materials such as food, chemical waste, and so forth. This is one of the problems with sewage sludge; pure fecal material can be processed and reused fairly easily, but sludge can be heavily contaminated, which may make it dangerous to handle.

Under normal conditions, sewage sludge will rapidly undergo anaerobic fermentation, with bacteria which thrive in an oxygen-free environment breaking down the sludge. This is sometimes used alone for processing, but sewage sludge can also be chemically treated. The treatment process also involves allowing evaporation to occur so that the sludge becomes more solid, with less liquid, making it lighter and easier to handle. Evaporated sludge may be pelletized for convenience.


One use of sludge is in agriculture. Although the use of fecal material on food crops may be restricted in some areas, sludge can be used to fertilize landscaping, and can in fact make an excellent alternative to chemical fertilizers which might otherwise be used to fertilize landscaping. Sewage sludge is, after all, rich in nutrients, and there is a long history of using human waste in agriculture throughout the world. Sludge can also be containerized, or buried, with burial involving dried sewage sludge to limit the amount of space required.

Concerns about the use of sewage sludge revolve around ingredients other than fecal material which it might contain. For example, sludge often contains traces of prescription medications such as antibiotics, which could breed antibiotic resistance if untreated sludge was introduced to the environment, along with hormones and other drugs which may be harmful. It can also contain heavy metals, toxic chemicals, and a variety of other substances which could be dangerous. Heavy treatment can potentially make sludge more dangerous by adding chemicals, and deplete it of nutrients, making it less suitable as a fertilizer.


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Post 4

Because we had a poor drainage system, our sewage sludge could not escape properly. It gathered in the yard and created a horrible smell. The dogs started to play in it, and I knew we had to do something.

My husband took a shovel and dug a better drainage ditch from the pipe outward and down the hill. That helped a little bit, but what really fixed the issue was when the landlord came over with a backhoe, dug the entire area up, and replaced the old pipes. It turns out that the landlord had been mowing over the area with a tractor a few months before and had broken the pipe.

Post 3

Sewage sludge is used to fertilize our local park. It’s part of the neighborhood’s green initiative. Everything in the park is made from recycled materials.

Flower beds of begonias, dianthus, and cosmos surround the gazebo and playground area. They are always covered in big, healthy blooms, and their leaves are so green.

The walking trail leads to a larger flower garden fed by sewage sludge. Rose bushes, hydrangea, zinnias, and hibiscus thrive here. They have some of the biggest blooms I have ever seen.

When most of the neighborhood’s flowers and grass suffers during the hot, dry summer months, the sludge-fed park greenery goes unaffected. Some people are starting to catch on and fertilize their gardens with it.

Post 2

When our septic system started bubbling up into the yard, we had to call some professionals in to pump the sludge out. They found some things in there that got me in trouble with my parents.

The box of tampons said that they could be flushed, so I did. I didn’t know any better, until I found out that they played a part in clogging up the system. Also, there was a huge amount of toilet paper.

My dad told me to never flush tampons again. He also said to only flush toilet paper with feces on it, and to throw all other paper in the garbage.

Post 1

I found out that sewage sludge makes a great fertilizer by observing the area of grass and flowers that grows over where the septic tank drains. I noticed that it was so much greener than the surrounding area.

The grass there was a deep green. I planted daylilies in the area, and they flourished. I never had to give them any additional fertilizer. All I had to do was keep them watered.

I would probably feel weird about planting vegetables there, because I would be concerned with the health hazards of eating them. However, the area is ideal for my flower garden.

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