Fouling analysis and control in a DCMD process for SWRO brine

Fouling remains a significant challenge in the application of membrane distillation process to the desalination industry. This study was focused on the characterizations of fouling layer on the membrane of a membrane distillation process fed with real seawater reverse osmosis concentrate. The deposit morphology and compositions of foulants were determined using different analytical methods, including scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDS), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), atomic force microscopy (AFM) and contact angle measurement. Organic and inorganic foulants were identified in the fouling layer. The organic deposits characterized by FTIR were polysaccharides, proteins, and humic like substances. Inorganic foulants mainly consist of calcium carbonate, calcium sulfate and halite. The fouling and wetting was effectively controlled by the chemical conditioning of the feed using sodium hypochlorite (NaOCl). The combination of NaOCl-added conditioning and membrane cleaning with 3% HCl restored the permeate flux up to 70-85% and stabilized the electrical conductivity of the distillate for extended time.