Investigation of scaling inhibition and biofouling potential of different molecular weight fractions of a PAA antiscalant

Abstract

This study investigates the scale inhibition performance of a commercial polyacrylic acid-based (PAA) antiscalant used for drinking water production and its molecular weight fractions (≤ 500 Da, ≥ 500 Da). The investigated antiscalant is used to prevent sulfate and carbonate scaling in treatment of drinking water sources by reverse osmosis or nanofiltration (RO/NF). Based on two complementary tests involving determination of induction time in a batch test and rate of flux decline in a lab-scale RO/NF plant, concordant results were obtained, proving that the overall performance of commercial PAA was controlled almost entirely by the higher molecular weight fraction. The low molecular weight fraction, which is potentially more permeable through the NF/RO membrane, showed poor inhibition against both sulfate and carbonate scalants. Furthermore, measurements on the assimilable organic carbon (AOC) by flow cytometry reveals that the low molecular weight PAA fraction has low biological stability, as its potential transport into the permeate of a NF270 nanofiltration membrane was inferred by elevated AOC values in the NF-permeate. These results are crucial information for water utilities, plant engineering, regulatory bodies and public authorities with respect to the possible operation of RO/NF especially in drinking water production.