Chicago MWRD pilots 'geopool' sludge dewatering at Calumet plant

Chicago MWRD pilots 'geopool' sludge dewatering at Calumet plantThe district has approved pumping and dosing equipment to test a slow-dewatering alternative prompted by infrastructure delays associated with the CTA Red Line expansion project.

The board approved $380,886 for centrifugal pumps and polymer dosing systems to support the trial.

The 160-foot diameter geopools will take approximately 15 days to dry post-digested sludge to a 25% solid density.

The experimental, warm-weather technique serves as a stopgap until permanent centrifuges come online in 2028.

The Metropolitan Water Reclamation District of Greater Chicago (MWRD) has approved the purchase of equipment to pilot a new sludge dewatering technique at its Calumet Water Reclamation Plant. During an April 2, 2026 meeting, the Board of Commissioners approved a $104,886 purchase order to Flow-Technics Inc. for two centrifugal pumps and a $276,000 order to Polydyne Inc. for two polymer dosing systems. The equipment will support the district's recent acquisition of "geopools"—160-foot diameter, above-ground structures designed for slow sludge dewatering. Executive Director Murray explained that the pilot is directly tied to the ongoing Chicago Transit Authority (CTA) Red Line expansion project, which has impacted the timeline for installing permanent dewatering infrastructure. New centrifuges at the Calumet plant are not expected to come online until 2028. "The advantage here is that we know that it could be a couple years before the centrifuges are put in place," Murray said, noting that the geopools will allow the district to pump low-solids, post-digested sludge directly into the pools rather than relying on tanker trucks. The geopool technology relies on settling and evaporation. According to staff, it takes approximately 15 days to fill a pool and achieve a 25% solid density, which is the district's target for sending biosolids to farms for beneficial reuse. Unlike traditional lagoon drying, the geopool process does not require mechanical agitation. While acknowledging that the process is much slower—noting that "what you can do in minutes in the centrifuge, you can do in days in these geopools"—staff highlighted the method's lower energy and chemical requirements. However, the technology is limited to warm-weather operations and consumes significant space in the plant's drying cells. Despite the pilot being prompted by the Red Line expansion, MWRD will not seek cost recovery from the CTA. District officials emphasized that the geopools are an experimental procedure that, if successful, could be deployed at other locations, including directly inside storage lagoons. Once the permanent centrifuges are operational in 2028, the district plans to either move the geopools to another site or use them in combination with the centrifuges during the summer months.