NANOFILTRATION OF CAUSTIC AND ACIDIC CLEANING SOLUTIONS WITH HIGH CODPART 1 - RECYCLING OF SODIUM-HYDROXIDE

In the present work the performance of nanofiltration in the recovery of caustic cleaning solutions, coming from the dairy industry, with hi gh COD (23.0 and 12.0 kg/m(3)) was investigated. Surprisingly, the per meate flux was higher for the caustic solution with the significantly higher COD. This was on the average about 1.4 x 10(-5) m(3)/m(2)/s, wh ereas in the second case the filtrate flux was about 0.9 x 10(-5) m(3) /m(2)/s. In the permeate of the more highly polluted solution a COD of 0.5 kg/m(3) was measured. The COD of the second permeate stream was 1 .5 kg/m(3). The noticeable lower contamination could be attributed abo ve all to the higher flux. The degree of pollution (COD) was therefore not the principal determining factor of the permeate quality. While t he flux rose linearly with increasing pressure, measurements showed in both cases that the cross-flow velocity had no influence on the perfo rmance of the nanofiltration. This could be explained by the pulsation effect of the feed (circulation) pump used. The quantity of the recyc led base was dependent mainly upon the recovered volumetric yield (pra ctically no NaOH retention), which was around 90%. (C) 1998 Elsevier S cience Limited. All rights reserved.