DEVELOPMENT OF A MEMBRANE FOULING INDEX BASED ON PILOT STUDIES WITH LOW PRESSURE MEMBRANES OPERATED UNDER VARYING CONDITIONS AND WATER QUALITIES

摘要

The primary goal of this WRF funded research was to (i) contrast NOM-related foulingpotential for different types of waters (allochthonous versus autochthonous); (ii) develop apredictive tool(s), either a surrogate parameter(s) or a fouling index, to estimate foulingpotential. Interactions between water quality, pre-treatment chemicals, membrane materials,and membrane configurations were tested at pilot-scale under various operating conditions.Pilot studies were conducted at two locations: at the Tampa WTP, FL (predominantlyallochthonous NOM) utilizing Zenon’s immersed membranes and at the White River WTP(predominantly autochthonous NOM), IN using US Filter’s CMF-L pilot unit, utilizing raw,coagulated and clarified waters as feed. The pilot testing program was designed todistinguish between three types of NOM-based fouling: hydraulically reversible fouling,chemically reversible fouling, and irreversible fouling. Membrane filtration cycle wasevaluated through quantification of membrane flux decline rates. At both locations,increased flux and recovery caused comparable loss of flux, however, the benefit wastemporary; long term fouling rate was comparable to baseline conditions. Of the differentchemical wash regimes evaluated, the most significant reduction in fouling was observedusing chlorine (sodium hypochlorite), followed by caustic (in combination with acid). Thefouling results from these pilot studies with waters of varying quality were correlated toHPSEC, EEM data, compared and contrasted. The resultant data were then represented interms of the unified membrane fouling index (UMFI) concept. The concept of UMFI wasdeveloped as a key analytical tool for this project to quantify the fouling rate encounterednot only in constant pressure, as used with the bench-scale stirred cell tests, but also inconstant flux filtration as employed in the hollow fiber bench- and pilot-scale testing.Various statistical tools were used to probe linkages between fouling (UMFI) and NOMcharacteristics and/or membrane properties and/or operating conditions. It was found thatallochthonous NOM had the lowest fouling potential as compared to autochthonous NOM.