Membrane Integrity Monitoring with Distributed Laser Turbidimetry

The objective of this study was to determine whether distributed laser light-scattering turbidimetry is a viable approach for monitoring membrane integrity. The study consisted of two phases. Phase 1 measured the sensitivity and minimum detection levels of four monitoring instruments. Phase 2 determined the minimum breach size (and corresponding log removal) required for detecting a change in water quality for each instrument. The water quality used in phase 1 was controlled using quantifiable particle count addition with 0.026-, 1.0- and 5.0-μm fluorescing microspheres. Membrane integrity monitoring was studied in phase 2 by feeding an increasingly breached membrane with either raw water or water pretreated by coagulation/settling and either known concentrations of 5.0-μm microspheres or powdered activated carbon (PAC). The results indicate that distributing existing technology sensors throughout a membrane rack may provide greater benefits than working to increase the sensitivity of a single detector. Also, laser light source turbidimeters are more sensitive than white light source turbidimeters or particle counters when raw or PAC-amended water is considered.