Membrane fouling and cleaning in long term plant-scale membrane distillation operations

In this work, we first show the findings of autopsy performed on the membranes used in the Scarab AB^® membrane distillation (MD) system at the solar MD pilot plant in Plataforma Solar de Almeria (PSA) in Spain. The fouling and the damage endured by the MD membranes during intermittent long-term (2010-2013) solar-powered operation in the pilot plant were assessed and characterized. Different cleaning strategies were used to remove the fouling layer and restore the membrane properties. Data regarding relevant membrane characteristics for the MD process, such as contact angle, gas permeability, porosity, liquid entry pressure, mechanical strength, etc., and their relationship with the membrane performance under MD operation were discussed and analyzed. Scanning electron microscopy (SEM) was employed to study the morphology of the fouled and cleaned membranes and characterize the membrane damage. The identified best cleaning procedure was then applied in the MD plant system at PSA. Results suggested that cleaning effectively removed a great part of the fouling and reduced the wetting of the membranes. However, this improvement was offset by the effect of inactive periods during which wetting processes were favored.