Case Study

Midwest Chemical Converts Illinois Municipal Reclamation District to Liquid Emulsion Sludge Dewatering Polymer


Midwest Chemical & Equipment (MWCE) contributed to system design and chemical understanding in the transition from Mannich polymer to emulsion polyacrylamide flocculant on the sludge dewatering application at a suburb sewer district of Chicago. MWCE incorporated Norchem polymer preparation systems and diluted polymer aging tanks to achieve high efficiency of the flocculant in dewatering centrifuges.

Previous Situation

The water reclamation district (WRD) was using a cationic polymer flocculant manufactured by the Mannich-Reaction.

- Strong odors present
- Usage of over 1,000 gallons per day (GPD) on neat Mannich polymer
- Addition of CO2 gas to adjust pH for better flocculation
- Inconsistent total cake solids ranging from 22-24% on produced biosolids
- Centrate problems with foaming and high TSS


A system for injecting activated emulsion-based polymer was designed, proposed and implemented at the WRD, with the following goals achieved:

- Significant reduction of polymer usage and cost
- Eliminated CO2 addition
- Stabilized dewatering performance (cake/concentrate)
- Usage reduced to less than 70 GPD
- Cake solids increased to 24-25%
- Less foaming/total solids released in the centrate

ROI: Cost savings was a primary driver of the conversion from Mannich polymer to emulsion polymers.

Cost Savings Analysis

Cost benefits after the switch to emulsions: - 29% savings in polymer & CO2 costs (approx. $113,000 annually) - 15% reduction in solids hauling costs (nearly $50,000 annually) - Total annual cost savings of $161,000 - Added benefit of increased space availability (due to less biosolids storage needed) - 3-month payback on initial equipment investment

Chemical Cost Comparison (Annualized)

System Design

MWCE incorporated the existing bulk tank, aging tanks and gear pumps to feed chemicals to the centrifuge. Two Norchem AnCAT systems and piping was added from the bulk tank to the aging tank. The system was designed to feed the emulsion product out of either totes with quick disconnect or the bulk tank storage. Filtered plant water and electric utilities were run to the AnCAT units, which feeds up to 300 GPD of neat polymer per day at up to 20 GPM diluted solution. Norchem's robust design requires little maintenance and their patented mixing kinetics fully activate the polymer for maximum efficiency.


In making the conversion to emulsion polymers, the WRD not only experienced significant cost savings, they have provided a healthier and happier work environment. Employees are very satisfied with the odor reduction, the reduced frequency of polymer deliveries and the consistent performance of the centrifuge.
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