What happens when raw sewage is dumped into water

Raw sewage causes microorganisms in the water to go into overdrive.

What happens when raw sewage is dumped into water
March 15, 2018

Is Dilution the Solution?

 Many decades ago, it used to be said that “the solution to pollution is dilution.” Basically, when small amount of raw sewage is dumped into a flowing body of water, a natural process of stream cleaning, or self-purification begins.

But while the science behind the phrase is still true, the reality is there are very few small sewage discharges anymore. Most raw sewage discharges are large and harmful. But it does beg the question: What is the effect of dumping raw sewage into a body of water?

What IS Raw Sewage?

First, what is meant by “raw sewage?” Essentially, raw sewage is wastewater that has not been treated. It has two sources. There’s sewage from kitchen, bathrooms and even laundries. But there is also more solid waste from cooking, dishwashing, toilets, showers and sinks. It all causes the water quality to deteriorate and that affects aquatic ecosystems. Three things can happen when raw sewage enters a body of water: It will be dissolved, it will become suspended in the water column or it will sink to the bottom and stay there.

Raw sewage contains a variety of dissolved and suspended impurities. The organic materials are food and vegetable waste. When that waste hits the water, microorganisms begin to decompose the materials. That uses up some of the dissolved oxygen in the water because those microorganisms use it in their metabolism.

Microorganisms Feast on Sewage, Creating More Problems

The bigger problem is that raw sewage causes eutrophication, which is an increase in the concentration of chemical elements required for life. Think natural systems on steroids. The nitrates, phosphates and other organic matter found in human waste serves as a food for algae and bacteria. That algae and bacteria switch into overdrive, growing to the point where most of the dissolved oxygen that is naturally found in water is used up. That makes it tough for other organisms in the water ecosystem to live because they are basically being strangled.

Fish kills and algae blooms are all part of this problem. In addition, the pathogens in raw sewage can contaminate ecological systems and also sicken humans and animals. Raw sewage typically contains viruses and bacteria as well as health-harming microorganisms. Plus, there are other chemicals in raw sewage that are simply toxic to fish, shellfish, animals and other creatures in the water environment.

So, the contamination of sewage flowing into a body of water causes a detrimental chain reaction. What begins as an overdose of chemical elements, can ultimately ruin the ecosystem in place and is harmful to the environment. 


—Frank Graff 

Frank Graff is a producer/reporter with UNC-TV, focusing on Sci Tech Now North Carolina, a weekly science series that airs Tuesdays on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!


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