Client Citation Analysis
Primary surface measurement reported
Sessile-drop contact angle (CA) measurements using a water droplet were used to evaluate surface hydrophilicity of mixed liquor and membrane samples. The results section reports contact angle changes for the membrane samples.
Dropometer attribution in the paper
CA measurements were conducted employing a “droplet sessile CA method (Droplet Smart Tech Inc., Markham, ON, Canada).”
How the surface-tension / contact-angle data were used in the study
Contact angle changes were used to compare employed membranes versus unused membranes under different SRTs and to support interpretation of SRT-linked changes in membrane surface properties during sludge digestion.
Replication / reliability statement
Both the mixed liquor and membrane samples underwent triplicate analyses, with subsequent computation of average values.
Primary surface / interfacial measurement
Contact angle (CA) measurements were performed using a sessile droplet method with a 3 μL water droplet to determine surface hydrophilicity.
Supporting measurements
Surface characterization included FTIR for residual foulants, SEM/EDX for membrane morphology and elemental composition, and XPS for elemental composition/chemical state/surface characteristics. The study also reports zeta potential (mixed liquor supernatants), SEM-image-derived surface roughness (Ra, Rq) and pore size distribution (ImageJ-based analysis), SEM texture analysis (Gwyddion), and particle size distribution (laser diffraction).
Contact angle (sessile CA)
droplet sessile CA method (Droplet Smart Tech Inc., Markham, ON, Canada)
Zeta potential
zeta potential analyzer
FTIR
Bruker Tensor 37 FTIR (Bruker Co., Ltd.)
Freeze-drying (sample preparation)
Labconco freeze dryer (Kansas City, MO, USA)
SEM / EDX
Hitachi SU70 scanning electron microscope (Tokyo, Japan) equipped with EDX capabilities
Sample coating for SEM
spray carbon coater model 12,560 (Latham, NY, USA)
XPS
Axis Supra XPS system (Kratos Analytical Ltd., Manchester, UK)
Particle size distribution (laser diffraction)
Malvern Mastersizer 2000 system (Malvern Instruments, Worcestershire, UK)
Surface roughness / pore-size image analysis
ImageJ version 1.51p (NIH, Bethesda, MD, USA) with SurfCharJ-1q plugin
SEM texture analysis
Gwyddion (open-source software)
Contact angle measurements were conducted employing a droplet sessile CA method (Droplet Smart Tech Inc., Markham, ON, Canada) using a 3 μL water droplet to determine surface hydrophilicity; mixed liquor and membrane samples underwent triplicate analyses with average values computed.
In the results and discussion, the contact angle outputs support comparisons of employed versus unused membranes across SRT conditions and are used in the interpretation of membrane surface-property changes during sludge digestion.
If you track membrane wettability as fouling builds up, we can show you the same sessile drop contact angle workflow on your membranes.
SRT-linked contact angle decreases on employed membranes
Compared to unused membranes, contact angles of employed membranes decreased by 20% (32-day SRT), 24% (45-day SRT), and 39% (55-day SRT).
Statistically significant effect of SRT on contact angle
The authors report that solids retention time significantly impacted contact angle values (p < 0.01).
Wettability change used in residual-fouling interpretation
The authors state that the contact angle change indicates wettability of the employed membrane declined during sludge digestion, and they discuss wettability deterioration in relation to membrane fouling resistance and performance.
What it shows
Shows permeability of pristine membranes and employed membrane after physical/chemical cleaning and reports membrane resistances under different SRTs.
What it shows
Illustrates pore size distribution comparisons between used and pristine membranes.
What it shows
Presents FTIR spectra for pristine and used membranes and discusses band intensity differences across SRT conditions.
What it shows
Provides SEM images and surface textures of virgin and used membranes under different SRTs after physical and chemical cleaning.
Within the paper’s residual-fouling characterization workflow, contact angle measurements provide a surface-property indicator that is used alongside morphology (SEM) and surface chemistry (FTIR/XPS) to compare membrane condition across operating SRTs.
The study uses these wettability-linked outputs to support its interpretation that membrane surface properties evolve during sludge digestion and to suggest that wettability changes may affect fouling resistance and membrane performance under different SRT conditions.
Defined sessile-drop CA settings
A 3 μL water droplet was used for contact angle measurements, with triplicate analyses and averaging reported for mixed liquor and membrane samples.
SRT comparison is built into the CA reporting
Contact angle changes are reported as percent decreases for employed membranes versus unused membranes at 32-, 45-, and 55-day SRT conditions.
CA is positioned as part of a multi-technique surface characterization set
Contact angle measurements are presented alongside SEM/EDX, FTIR, XPS, and SEM-image-based roughness/pore metrics in the residual fouling characterization workflow.
Statistical support accompanies the CA trend
The authors report a significant SRT effect on contact angle (p < 0.01), supporting comparisons across operating conditions.
The authors measured the water contact angle of unused and used flat sheet PVDF membranes with a sessile drop contact angle method credited to Droplet Smart Tech Inc., using a 3 μL water droplet. Membrane and mixed liquor samples were analyzed in triplicate and the values averaged.
Compared with the unused membrane, the authors report contact angle decreases of 20% at the 32 day SRT, 24% at the 45 day SRT and 39% at the 55 day SRT after primary sludge treatment. They report that the effect of SRT on contact angle was statistically significant (p < 0.01).
The authors use the SRT dependent contact angle change as evidence that the wetting behavior of the membrane surface changed during sludge digestion, and they discuss how changes in membrane wettability can affect fouling resistance and performance. The paper reports the change as a percentage relative to the unused membrane rather than as absolute angles, and no mixed liquor contact angle values are given in the results.
