Activated Sludge

Activated sludge is produced when sewage is aerated by air bubbled rapidly through it. Certain types of active bacteria coagulate the organic matter which settles out leaving a clear liquid that can be discharged or used for irrigation. Activated sludge is generally heat-treated and dried before being sold. It is the method used to produce Milorganite or Hou-Actinite.

From the Milwaukee Journal Sentinel, an article about how Milorganite (the name comes from Milwaukee Organic Nitrogen) is made: Here's what you should know about Milorganite and a recent study showing it may contain 'forever chemicals', dated June 7, 2021 by Laura Schulte.

Milorganite — the name is derived from Milwaukee organic nitrogen — is composed of heat-dried microbes that digest the organic material in wastewater, manufactured by the Milwaukee Metropolitan Sewerage District, according to milorganite.com. MMSD captures wastewater flowing into it and uses naturally occurring microbes to digest the nutrients commonly found in waste, like nitrogen, phosphorus and potassium.

After the organic material has been consumed, the clean water is then returned to Lake Michigan, and the resulting material is dried and sold as fertilizer.

For more information, visit Wastewater Digest. This article What is Activated Sludge? explains the process and steps involved. 

  Wastewater treatment plant, and finished Milorganite pellets. Photos via Radio Milwaukee.

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