Primary surface measurement reported
The contact angle of mixed liquor suspended solids (MLSS) was measured as part of the study’s MLSS surface-property characterization across operating phases.
Client Citation Analysis
Effect of organic loading rates on the membrane performance of a thermophilic submerged anaerobic membrane bioreactor for primary sludge treatment from a pulp and paper mill
This study evaluates how changing organic loading rate (OLR) and hydraulic retention time (HRT) affects membrane performance and mixed-liquor suspended solids (MLSS) properties, including MLSS contact angle measured using a Dropometer.
At-a-Glance Summary
Dropometer attribution in the paper
The Methods state that “contact angle of MLSS was measured by using Dropometer M-3 (Droplet Smart Tech Inc. Canada),” using pure water as a probe fluid for the contact angle measurement.
How the contact-angle data were used in the study
Contact angle values are reported by operating phase and discussed in the MLSS “surface properties and dewaterability” results, where the authors interpret changes in contact angle in terms of hydrophobicity trends across different OLR/HRT operating conditions.
Paper Details
Title
Effect of organic loading rates on the membrane performance of a thermophilic submerged anaerobic membrane bioreactor for primary sludge treatment from a pulp and paper mill
Authors
A. Bokhary; M. Leitch; B.Q. Liao
Journal
Journal of Environmental Chemical Engineering
Year
2022
Volume
10
Pages / Article
107523
License
2213-3437/© 2022 Elsevier Ltd. All rights reserved.
What Was Measured
Primary surface / interfacial measurement
The study reports MLSS contact angle measured using pure water as the probe fluid, with values summarized by operating phase.
Supporting measurements
In the same MLSS “surface properties and dewaterability” dataset, the authors report zeta potential, dewaterability (capillary suction time), soluble microbial products (SMP), and MLSS concentration by phase, alongside discussion of operating-condition effects.
Contact angle (MLSS)
Dropometer M-3 (Droplet Smart Tech Inc. Canada)
Zeta potential (MLSS)
ZetaPALS zeta potential analyzer (Brookhaven, Holtsville, NY, USA)
Dewaterability (digestate)
Capillary Suction Time (CST), model 304 series (Triton Electronics Ltd., UK)
Particle size distribution (feed samples and MLSS samples)
Malvern Mastersizer instrument (Malvern Instruments Ltd., UK)
Membrane surface/section imaging
SEM (SU-70, Hitachi, Japan)
Membrane sample coating
sputter coater (Model 12560, Fullam, USA)
Pore size / surface porosity from SEM micrographs
ImageJ processing software version 1.51p
FTIR (membranes)
Bruker Tensor 37 FTIR spectroscopy (Bruker Co., Ltd.) and windows-based spectroscopy software
XPS (MLSS and membranes)
X-ray photoelectron spectrometer (XPS)
pH
Oakton pH 700 benchtop meter
Elemental analysis (C, H, N, S)
elemental analyzer (Vario El Cube, Germany)
Elemental concentrations (permeates)
ICP-OES (inductively coupled plasma - optical emission spectroscopy) elemental analyzer
Biogas composition
gas chromatograph machine (GC-2014, Japan)
Reactor mixing
magnetic stirrer blade (Barnstead Thermolyne, Cimarec Plate Stirrer, USA)
TMP monitoring
omega analog pressure gauge
Peristaltic pump control
Gralab 451 timer
Role of the Dropometer
The paper reports that the contact angle of MLSS was measured using Dropometer M-3 (Droplet Smart Tech Inc. Canada), with pure water used as the probe fluid for the contact angle measurement.
These contact angle values are used to compare MLSS surface-property behavior across the study’s three operating phases (defined by different OLR/HRT conditions) and are interpreted by the authors as hydrophobicity trends.
Bring This Measurement Into Your Lab
If you characterize sludge or biosolids hydrophobicity across operating conditions, we can show you a water contact angle workflow on your samples.
Key Findings
Phase-dependent MLSS contact angle
The reported MLSS contact angle is 64.3 ± 3.2° in Phase I (OLR 2.2 ± 0.16), 24.6 ± 3.04° in Phase II (OLR 3.9 ± 0.19), and 43.5 ± 5.8° in Phase III (OLR 1.5 ± 0.10), as listed in Table 2.
Reported contact angle range and phase trend
The authors state that the contact angle of the mixed liquors ranged between 24° and 64°. In Table 2 it was highest in Phase I, lowest in Phase II, and partly recovered in Phase III when OLR was reduced, as the authors also describe.
Hydrophobicity interpretation in the discussion
In the MLSS surface-properties discussion, the authors describe a “hydrophobicity” recovery when OLR decreased to 1.5 ± 0.10 kg‑TSS/m³·d, corresponding to the Phase III contact angle value reported in Table 2.
SMP trend discussed alongside contact angle
The authors report that soluble microbial products (SMP) followed the same “hydrophobic trend,” with the highest SMP concentration observed at the lower OLR and vice versa.
Figures & Visuals
What it shows
Summarizes zeta potential, dewaterability, contact angle, SMP, and MLSS concentration for Phases I–III.
What it shows
Lists the digestion conditions used to define Phases I–III (including HRT and OLR) that frame the contact-angle comparison
What it shows
Shows membrane flux versus operating time with phase labels, providing the operating timeline context for the phase-based MLSS property reporting.
Why It Matters
Within the study’s stated scope, MLSS properties are evaluated alongside membrane performance to understand how operating conditions (OLR/HRT) relate to sludge characteristics under thermophilic submerged anaerobic membrane bioreactor operation treating primary sludge from a pulp and paper mill.
The Dropometer-derived MLSS contact angle is one of the reported MLSS “surface properties,” and the authors use the phase-by-phase contact angle results to describe changes in hydrophobicity trends across operating conditions, discussing these trends in parallel with SMP behavior.
Expert Perspective
Practical Takeaways
Dropometer method as described
For MLSS wettability characterization in this study, contact angle is measured using Dropometer M-3 (Droplet Smart Tech Inc. Canada) with pure water as the probe fluid.
Phase-based contact angle reporting
MLSS contact angle is presented by operating phase in Table 2, enabling direct comparison across the study’s three OLR/HRT conditions.
Reported magnitude of change across operating conditions
Across Phases I–III, the reported MLSS contact angle values shift from 64.3 ± 3.2° to 24.6 ± 3.04° to 43.5 ± 5.8°.
Interpreted as hydrophobicity trend
The authors discuss the contact-angle changes in terms of a hydrophobicity trend across operating phases and relate SMP behavior to the same trend.
Frequently Asked Questions
What did the Dropometer measure in this study?
The authors measured the contact angle of mixed liquor suspended solids (MLSS) from a thermophilic submerged anaerobic membrane bioreactor using a Dropometer M-3 (Droplet Smart Tech Inc.), with pure water as the probe fluid. The values are reported for each of the three operating phases in Table 2, alongside zeta potential, dewaterability and soluble microbial products (SMP).
What values were reported, and how were they interpreted?
The MLSS contact angle was 64.3 ± 3.2° in Phase I (OLR 2.2 kg TSS/m³·d), 24.6 ± 3.04° in Phase II (OLR 3.9 kg TSS/m³·d) and 43.5 ± 5.8° in Phase III (OLR 1.5 kg TSS/m³·d). The authors describe hydrophobicity recovering when the OLR was lowered, and report that SMP followed the same hydrophobic trend.
What was outside the scope of the contact angle work?
The Dropometer values in this paper are for the MLSS; contact angle values for the membranes themselves are not reported. Membrane performance was assessed separately by monitoring flux and transmembrane pressure (TMP), with SEM and FTIR used to examine the membranes.