The MWRD treats an average of 1.3 billion gallons of wastewater each day via its seven water reclamation plants. The MWRD is the wastewater treatment and stormwater management agency for the Municipality of Chicago and 128 suburban communities throughout Cook County. They work every day to mitigate flooding and convert wastewater into valuable resources like clean water, phosphorus, biosolids and natural gas.

As biological phosphorus removal becomes a growing staple of wastewater treatment for the MWRD, the infrastructure and technology must also adapt to accommodate this additional process. Biological phosphorus removal requires more capacity than conventional biological treatment, and the challenge is creating this capacity without having to build completely new aeration tanks at facilities like Stickney Water Reclamation Plant (WRP), designed to handle up to 1.44 billion gallons in a day.

In response, resourceful MWRD staff designed an experimental first-of-its-kind system to intensify the biological treatment of wastewater to provide a range of benefits including treating larger flows with less infrastructure. The design aims to improve solids settling by adding a “high-rate settling tank,” retaining more of the active microorganisms responsible for cleaning the water and collecting nutrients in the existing aeration tanks.

Surrounded by sprawling tanks and massive treatment systems, the 350-gallon tank appears a small find tucked away in a nondescript gatehouse at Stickney WRP. But the pilot scale system could unlock remarkable potential in the biological stages of wastewater treatment. In this important stage, after wastewater is filtered through primary treatment, the water enters aeration tanks that receive pumped air much like an enormous aquarium air diffuser. There, a carefully maintained population of microorganisms use oxygen from the air to break down the remaining suspended solids and remove soluble organics, phosphorus, and ammonia through nitrification.

Once tied into the MWRD’s aeration battery at Stickney WRP, MWRD scientists will analyse whether adding the high-rate settling tank can improve and expedite the settling of solids. The experimental system is expected to be able to treat wastewater in as little as three hours, compared with the conventional process that takes a minimum of four and a half.

The MWRD is a circular initiative, because it recovers resources, like phosphorus and other nutrients and it returns them for valuable reuse opportunities, but also does so with the intention of protecting downstream water quality from harmful algal growth caused by excess nutrients in the water.

Photo taken by U.S. Army Corps of Engineers Chicago District on Flickr