Easy Sustainability Answers

What’s the history of sewage treatment? How do biosolids fit in?

Adriene Hill Aug 2, 2010

The circle of life. Milorganite pellets (photo above) are made from recycled waste, aka biosolids, and used to help fertilize crops and improve land

Listen: It’s a fertile market for recycled human waste.

Waste disposal is a fact of life. Even the Bible includes instructions for disposing of our excrement: “And thou shalt have a paddle upon thy weapon; and it shall be, when thou wilt ease thyself abroad, thou shalt dig therewith, and shalt turn back and cover that which cometh from thee.” (Deuteronomy 23:13)

According to a fascinating article that appeared in Scientific American called “How Does Sewage Treatment Work?”, before indoor plumbing, the average person used less than five gallons of water every day. Now that we can flush — U.S. residents use about 100 gallons of water use a day. That’s a whole lot of wastewater that’s got to go somewhere.

For years big cities in the U.S. took that water and dumped it directly (sans treatment) into whatever big body of water was nearby. In San Diego, for example, up until 1943 raw sewage went straight to the Pacific Ocean and San Diego Bay. Not good for swimming, that’s for sure.

Why not recycle some of that waste instead? People started treating, processing, and turning their wastewater into “biosolids”. Biosolids are the byproducts of the wastewater treatment process (they are not “raw” human waste, so don’t freak out). They can come as liquids, soils or pellets and are often used to help fertilize crops and improve land.

Milwaukee has been making a product called Milorganite for decades (see photo above); they sell it at big box stores to homeowners in search of lush lawns. A 36-pound bag will cost you about $15 from Amazon.com.

(For you film buffs out there, apparently Milorganite makes an appearance in the movie “Caddyshack”.)

The EPA has guidelines (PDF) about the amount of pathogens and chemicals that can be contained in biosolids applied to land.

According to a Q&A on their website:

Are biosolids safe?

The National Academy of Sciences has reviewed current practices, public health concerns and regulator standards, and has concluded that “the use of these materials in the production of crops for human consumption when practiced in accordance with existing federal guidelines and regulations, presents negligible risk to the consumer, to crop production and to the environment.

The EPA site also includes other questions and answers about biosolids–including this gem:

Do biosolids smell?

Biosolids may have their own distinctive odor depending on the type of treatment it has been through. Some biosolids may have only a slight musty, ammonia odor. Others have a stronger odor that may be offensive to some people. Much of the odor is caused by compounds containing sulfur and ammonia, both of which are plant nutrients.”

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