Treating laundry waste water: Cationic polymers for removal of contaminants and decreased fouling in microfiltration

The goal was to select coagulants and a coagulation process for treating laundry wastewater. The long-term goal is for application in Army mobile treatment units with solids removal using microfiltration (MF) and for which a robust operation with small coagulant volumes are desirable. Laundry wastewater usually has very high pH thus strong base cationic polymers are good coagulant candidates. Seven quaternary amine polymers were examined to determine effects of coagulant dose on zeta potential (ZP). Four of the polymers were further evaluated for sedimentation of contaminants, specific resistance to filtration, and cake compressibility during filtration. A low molecular-weight epichlorohydrin/dimethylamine (epi/DMA) polymer was tested further because of greatest increase in ZP with low polymer dose, lowest specific resistance to filtration, and good removal of contaminants. Flocculation for 10 min resulted in greatly improved removal of cake by hydraulic washing compared to 2 and 5 min flocculation. Fouling during multi-cycle membrane operation was greatly reduced with coagulant additions less than half the charge-neutralization (CN) dose. Low polymer dose results in decreased chemical demand and reduced sludge production. Successful treatment using from 50% to 100% of the CN dose provides more robust operation under field conditions.