Evaluation of inorganic scaling and scaling inhibition by antiscalants in high-pressure membrane filtration for drinking water treatment
Citation Link: https://doi.org/10.15480/882.17621
Publikationstyp
Doctoral Thesis
Date Issued
2026
Sprache
English
Author(s)
Advisor
Referee
Muff, Jens
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2025-11-28
TORE-DOI
Citation
Technische Universität Hamburg (2026)
Reverse 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.
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.
Subjects
Reverse osmosis
scaling
antiscalants
phosphonates
polyacrylic acids
carboxymethyl inulin
effectiveness tests
bioavailability
DDC Class
660: Chemistry; Chemical Engineering
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