REMOVAL OF NATURAL ORGANIC-MATTER FROM 2 TYPES OF HUMIC GROUND WATERSBY NANOFILTRATION

The efficiency of nano filtration (NF) in producing drinking water fro m two types of humic ground waters was studied on site at a pilot scal e in Denmark. At one site, the natural organic matter (NOM) consisted almost entirely of humic acids with a concentration of 20-22 mg C/l, a broad molecular weight distribution and a large fraction of high mole cular weight NOM. At the other site, the initial NOM concentration was 7-11 mg C/l with 60% of the NOM as fulvic acids and a narrow molecula r weight distribution around 2000 D. A spiral wound NF membrane with a nominal molecular weight cut-off (MWCO) of 200-500 D and a feed space r of 0.75 mm in diamond configuration demonstrated superior NOM remova l for both waters. Membrane productivity decline was observed due to t he accumulation of NOM on the membrane surface or the precipitation of inorganic salts such as calcite (CaCO3), dependent upon NOM and inorg anic water chemistry types. Accumulated NOM was removed with an alkali ne detergent recovering the initial membrane productivity by 90%, wher eas the inorganic precipitation was removed with an acidic detergent f ollowed by the alkaline detergent, recovering the initial productivity completely. A spiral wound NF membrane with a nominal MWCO of 180 D a nd a feed spacer of 1.25 mm in parallel configuration exhibited the sa me product water quality, but a higher and more stable membrane produc tivity than the first membrane. High cross flow and low operating pres sure reduced the membrane productivity decline. Nanofiltration of humi c ground water resulted in efficient removal of NOM and a stable produ ctivity, if differences in NOM and inorganic raw water composition wer e considered in designing the nanofiltration process. (C) 1998 Elsevie r Science Ltd. All rights reserved.