Coagulation strategies to decrease fouling and increase critical flux and contaminant removal in microfiltration of laundry wastewater

The principal objectives were to identify optimal treatment of laundry wastewater using coagulation and microfiltration (MF) so as to decrease fouling, increase critical flux, and increase contaminant removals. Experiments were designed to simulate operation of the Army’s shower water reuse system (SWRS) which operates using constant-flux MF membranes with 0.22 μm pores. The SWRS is a transportable wastewater treatment system that is used in remote locations. Critical flux was measured using quick step-flux tests and also using multi-cycle tests with the objective of identifying rapid methods for evaluating design and operation of coagulation/MF systems. Low molecular weight quaternary amine polymers were effective coagulants that resulted in low coagulant doses, low chemical volume, and good coagulation/MF using a range of doses. Charge-neutralization (CN) and under-dosing (UD) at 40% of CN improved contaminant removals, decreased fouling, and increased critical flux from 45 L m −2 h −1 (LMH) for raw wastewater to a maximum 450 LMH using CN. The increased critical flux and good results over a wide range of coagulant doses can result in up to a 10-fold increase in water production for each SWRS unit and robust operation even in remote locations and with limited technical backup and perhaps changing water quality conditions. Low coagulant doses result in decreased transportation and storage requirements. In addition to practical application to the SWRS and similar operations, the results demonstrated the utility of quick step-flux tests for design and operation testing.