Real-time detection of early-stage calcium sulfate and calcium carbonate scaling using Raman spectroscopy

Early-stage scaling detection is a crucial component for optimizing proactive anti-fouling measures that enhance membrane lifetime and decrease operation costs. In this work, we utilize Raman spectroscopy to detect and chemically quantify multiple scalants during bench-scale reverse osmosis desalination. The experiments were conducted with a commercial brackish water thin-film composite membrane at a feed pressure of 1.2 MPa (175 psi) and a feed flow velocity of 4.2 cm/s. Raman measurements were performed in real-time at a laser excitation wavelength of 785 nm. Experimental results from single-feed solutions of CaSO4 and CaCO3 show consistent detection of the corresponding scalants with less than a 15% permeate flux decrease at detection inclusive of the permeate decline due to compaction. Experiments utilizing a mixed-feed solution containing CaSO4 and CaCO3 were also conducted. Results for the mixed-feed experiments showed detection of CaSO4 scaling only. Subsequent analysis indicated that a modified sampling strategy was required for successful real-time detection of both CaSO4 and CaCO3 scaling.