RO/NF

UFMBRChemicals

C A S E S T U DY
RO | UF | MBR | ANTISCALANT

Water Treatment Chemicals
Regensdorf, Switzerland

Low Dose, High-Strength Sludge Dewatering Solution by ROPUR RPI®
for Breaking Down Struvite Scaling
BACKGROUND
Wastewater treatment plants ( WWTP) often
experience a disruption in their operations dueto the complex chemical reactions in the watercleaning process, further lowering the plant
efficiency down to a critical level. A common
cause is the rapid formation of rock-solid blue
cement known as Struvite crystals that affects
all metal surfaces during sludge dewatering.
THE CHALLENGEAt the ARA Wüeri in Regensdorf, Switzerland,
after digestion, a centrifuge dewaters theproduced sludge. Following CO2 degassing, thechange in composition and physicochemical
properties rapidly promotes the Struvite scale
formation on all metallic surfaces during thisprocess. Furthermore, Struvite scaling is rapid
and furtive and creates an underestimated risk
for failure and a severe impact on operationalcosts. Numerous testing with chemicals toprevent or impede the scaling inside and after
the centrifuge could not eliminate the problem.

Figure 1: Dewatering centrifuge

ARA Wüeri teamed up with a research group at the FHNW and Toray Membrane
Europe AG (TMEU) to investigate the scaling and find a solution. TMEU introduced
ROPUR RWI®-8000, an innovative water treatment chemical that specificallytargets Struvite scaling. The team would test to determine the scale inhibitor'seffectiveness in maintaining the plant's stable operations and minimize any hidden
maintenance costs associated with equipment replacements.
DEWATERING PROCESS
Dissolved CO2 is aggressively released in the centrifuge area because:1.

The tenside injected (dewetting agent) slightly reduces the CO2 solubility inwater;

2.

The salt's local micro-concentration (when TS particles separate from thefluid) triggers an unstable state in the dissolved CO2 gas;

3.

The centrifuge's mechanical movements (pressure changes) optimize the gas
exchange (with O2 and N2 saturating the fluid and kicking out the CO2) andCO2 release.
DENI

NITRI

Wastewater

Treated water

ExcessSludgeFigure 2: Schematic of wastewater treatment process
03-CH-MB5-Regensdorf-202108

1 of 2Dewatering
ProcessFigure 3: ARA Wüeri centrifuge with deposits (top) andwithout (bottom)

C A S E S T U DY
RO | UF | MBR | ANTISCALANT

Low Dose, High-Strength Sludge Dewatering Solution by ROPUR RPI®
for Breaking Down Struvite Scaling

INNOVATIONThe ROPUR RWI®-8000 was developed using state -of-the art analytical techniques like laser-focused beam reflectancemeasurement, which in real-time can count the number ofparticles but also segment the particles according to their size.
Actual sludge samples from the ARA Wüeri in Regensdorf wereanalyzed by adding a few doses (in ppm) of ROPUR RWI®-8000
to the sludge water exposed to a CO2 degassing. Upon dosing,
the number of particles immediately reduced by 99.4%. The
same method was applied to evaluate the optimal dosing rate for
ROPUR RWI®-8000, which yielded rates ranging between 25 to50 ppm.
The WW TP at ARA Wüeri uses ROPUR RWI®-8000 daily forits sludge dewatering process with great success, effectivelyinhibiting the Struvite scale from plugging or cementing inside
the centrifuge and subsequent mother liquor pipes. Furthermore,
the cleaning frequency was reduced by a factor of four, as shownin Figures 4 and 5 below.

Figure 4: Before ROPUR RWI®-8000 is dosed

ROPUR RWI®-8000: THE IDEAL REFERENCE
Based on the latest generation of ion scavenging molecules
effective at low dosing value, lab studies show that the ROPUR
RWI®-8000 prevents Struvite formation for four hours after
dosing, allowing the dewatering process to occur efficiently.
Compared to similar chemicals on the market, ROPUR RWI®8000 expressed the most excellent efficiency at 25 and 50 ppm
dosing rate, as shown in Figures 6 and 7.
Additionally, ROPUR RWI®-8000 per forms well in wide pH
deviations, minimizing issues regarding the remaining CO2 /Hydrogenocarbonate ion present in the mother liquor. Studies
further revealed that ROPUR RWI®-8000 keeps all potential
Struvite particles as small as 10 µm in size, which is a remarkableachievement. Users report significant savings in costs andsimplification of the wastewater treatment process.

Figure 6: Particle counts in the range between 10 and 100 µm over timein SWW containing 25 mg/L of antiscalants from competitors A, B and
ROPUR RWI®-8000; vertical dashed lines represent the time point when
12M NaOH was dosed for pH adjustment.

Figure 5: After ROPUR RWI®-8000 is dosed

Figure 7: Particle counts in the range between 10 and 100 µm over timein SWW containing 50 mg/L of antiscalants from competitors A, B and
ROPUR RWI®-8000; vertical dashed lines represent the time point when
12M NaOH was dosed for pH adjustment

TORAY MEMBRANE EUROPE AG (TMEU)
Grabenackerstrasse 8b, Muenchenstein 1 CH-4142, Switzerland

www.water.toray
info.tmeu.mb@mail.torayLinkedIn

www.ropur.com+41 61 415 8710

www.csmfilter.com

YouTubeMarks designated with a ™ or ® are trademarks of Toray Industries, Inc.
All information presented herein is believed reliable and in accordance with accepted engineering practices. Toray makes nowarranties as to the completeness of this information. Users are responsible for evaluating individual product suitability forspecific applications. Toray assumes no liability whatsoever for any special, indirect or consequential damages arising from thesale, resale or misuse of its products. © 2021 Toray Industries, Inc. Subject to change without notice.
03-CH-MB5-Regensdorf-202108

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