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Item type:Publication, Access status: with files , Evaluation of inorganic scaling and scaling inhibition by antiscalants in high-pressure membrane filtration for drinking water treatmentReverse osmosis (RO) and nanofiltration (NF) are established processes for removing hardness, sulfates, nitrates, trace organics, and other anthropogenic contaminants. However, membrane scaling remains a major operational challenge and is commonly overcome by adding antiscalants. Key issues with antiscalant use include varying effectiveness of different active ingredients, their dosage considerations and environmental concerns over the disposal of concentrate streams containing these chemicals. This study evaluates the effectiveness of various commercial antiscalants, focusing on appropriate evaluation methods, dosage behaviour and potential side-effects. Key objectives include (i) comparing methods for detecting scaling and inhibition potential and (ii) investigating scale inhibition performance against gypsum and calcite salts. A detailed evaluation of the molecular weight fractions and biological growth potential of PAA-based antiscalant was also examined. Additionally, the performance of a novel phosphorus (P)-free, plant-based CMI antiscalant was experimentally assessed. Evaluation of various methods for assessing scaling and antiscalant performance revealed significant differences based on scalant applicability, setup complexity, material requirements, and level of precision. Both the stirred-beaker test and membrane crossflow filtration were suitable for testing with gypsum and calcite, capturing differences in scaling behaviour and antiscalant performance. The stirred-beaker test, while simple to set up, effectively assessed threshold inhibition using induction time derived from rate of change of turbidity of the solution. The crossflow filtration test offered deeper insight into antiscalant performance under practical filtration conditions by monitoring rate of flux decline and followed by SEM characterization, but was more resource and time -intensive. Among the antiscalants tested, P-based ATMP, DTPMP, PAA+DTPMP showed better gypsum scale inhibition at 1 mg/L TS than at 0.5 mg/L TS, whereas PBTC performed poorly at both doses. In contrast, P-free PAA and CMI exhibited strong gypsum inhibition even at low dosages. In the case of calcite, ATMP and PBTC showed strong threshold inhibition at low dosage, whereas DTPMP performed comparatively poorly. Interestingly, the PAA+DTPMP and PAA antiscalant showed poor threshold inhibition, but good calcite dispersion property. CMI demonstrated strong threshold inhibition for calcite at all tested dosages. In nearly all cases, antiscalants modified the crystal structure and original morphology of the scaling salts. In-depth examination of the commercial PAA antiscalant and its molecular weight fractions (≤500 Da and ≥500 Da), revealed that the low molecular weight PAA fraction showed poor inhibition against both gypsum and calcite, while the high molecular weight PAA fraction demonstrated excellent inhibition potential. Bioavailability testing indicated that the low molecular weight fraction had higher biological growth potential, given by increased total cell count (TCC). Since the fractions ≤ 500 Da may potentially pass through less dense NF/RO membranes, it highlights additional challenges associated with antiscalant application in drinking water treatment. Overall, this study defined suitable test conditions and parameters for evaluating scaling inhibition in NF/RO, thereby supporting informed decision-making for the safe use of antiscalants in drinking water treatment.Publicationtype: Doctoral Thesis135 34 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Investigation of scaling inhibition and biofouling potential of different molecular weight fractions of a PAA antiscalant(Springer, 2024-05-06); ; 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.Publicationtype: Journal Article32 26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Characterization and performance of LbL-coated multibore membranes : zeta potential, MWCO, permeability and sulfate rejection(Multidisciplinary Digital Publishing Institute (MDPI), 2020-12-10); ; ; The characterization of membranes is suitable to investigate changes in the membrane properties caused by Layer-by-Layer (LbL) modification. Besides permeability, rejection, and molecular-weight cut-off (MWCO), which give information about the modification of the separation behaviour of the membrane, the zeta potential is capable of describing the surface charge of the membrane and its variation impacted by the properties of the polyelectrolyte multilayers (PEM). In this study, a new method for zeta potential measurement of hollow fibre membranes with several capillaries was developed and further investigations on the LbL modification of such membranes were performed. The results showed that an LbL coating with 8 DL PDADMAC/PSS led to a significant increase in the membrane charge of more than 20 mV. The coating with a different number of polyelectrolyte (PE) layers showed a zig-zag behaviour, comparable to data from flat sheet studies. However, in contrast to most flat sheet membranes, the charge curve assumes a totally negative trajectory at neutral pH. Further experiments on the MWCO of the LbL-modified membrane showed a reduction in the pore diameter from approx. 20 nm to less than 2 nm, reaching the range of nanofiltration membranes. With information on both the zeta potential and the MWCO, it was found that the rejection mechanism in LbL-modified multibore membranes is a complex interplay between the sieving effect due to reduction in the pore diameter and the repulsion effect of the charged membrane.Publicationtype: Journal ArticleScopus© Citations 10 212 259