APPLICATION OF NANOFILTRATION FOR RECYCLING OF PAPER REGENERATION WASTE-WATER AND CHARACTERIZATION OF FILTRATION RESISTANCE

The potential of using nanofiltration (NF) membranes in purification o f the effluent from paper regeneration wastewater treatment plant was investigated. The change of filtration resistance for various NF membr anes and the mechanisms responsible for the resistance were identified . The mahyority of the pollutants remaining in the wastewater were mos tly nonbiodegradable and ware less than MWCO 3000 in size, indicating micro- or ultrafiltration may not be applicable. Among the five NF mem branes used in this study, NTR-759HR showed the highest rejection effi ciency; 98.5% and 99.5% for TOC and color, respectively. The TOC conce ntration of the permeate could be maintained at less than 0.7 mg/L reg ardless of the concentration of the feed solution. However, the permea te flux steadily decreased with time up to 50% of the initial value at the recovery rate of 89%, To investigate the possible mechanisms resp onsible for the reduction of permeate flux, the observed total filtrat ion resistance was divided into three categories; (1) the intrinsic me mbrane resistance for pure water (R-m), (2) resistance due to concentr ation polarization (R-cp), and (3) resistance due to membrane fouling (R-f). The increase of filtration resistance for NTR 7410 could be exp lained by membrane fouling while those for NTR-759HR and NTR-7250 are attributed to the osmotic pressure build-up due to concentration polar ization. The different mechanisms for the flux reduction were studied.