EXHAUST GAS SCRUBBER INSTALLED 

ONBOARD MT “SUULA”

PUBLIC TEST REPORT

20 JUNE, 2010
Compiled by Wärtsilä Finland Ecotech Scrubber Project Team. 

© Wärtsilä 

 
© Wärtsilä PUBLIC TEST REPORT Page 3 (30) 

ABSTRACT 

Background 

IMO and EU legislation is clearly moving towards lower levels of permitted 

exhaust gas sulphur oxide emissions from ships. These regulations offer the 

choice of compliance by using expensive fuels with less sulphur, or by cleaning 

exhaust gases thus enabling ships to use cheaper traditional marine fuels. This 

report describes testing as a part of the development of a marine exhaust gas 

cleaning system. 

Test targets 

The testing targets of an exhaust gas scrubber installation onboard the MT 

“Suula” include certification of the scrubber, exhaust gas cleaning performance 

measurements, analyses of the scrubber effluent and other liquids, testing of 

effluent cleaning unit operation and analyses of generated sludge, 

measurements of alkali and water consumption, scrubber noise attenuation and 

exhaust gas plume observations. In addition some special tests were carried out 

and system reliability was studied. 

Test execution 

Testing was started in 2008 and completed in 2010. The MT “Suula” travelled 

mainly around the Baltic Sea, but also visited North Sea harbours. Normal ship 

operation was not interrupted or limited during the tests. Test data was recorded 

in many ways, including a tamper-proof recording device. Gas and liquid 

samples were taken. Classification societies surveyed the certification process. 

Test results 

Test results were very positive. “Germanischer Lloyd” and “Det Norske Veritas” 

certified the scrubber system. The measured sulphur reduction was excellent, 

well within the International Maritime Organisation’s (IMO) most stringent limits. 

Furthermore, other measured exhaust and effluent parameters were favourable. 

The effluent was very clean, and the sludge produced by the water cleaning unit 

was found suitable for normal disposal at port reception facilities. The scrubber 

and its auxiliary systems worked with a good level of reliability. Sea conditions 

did not affect or limit the scrubber’s use. 

Conclusion 

The marine exhaust gas fresh water scrubber is ready for introduction onto the 

market. 
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TABLE OF CONTENTS 

1 INTRODUCTION ........................................................................ 6

1.1 SCRUBBER PROJECT BACKGROUND ............................................................6 

1.2 LEGISLATION DEVELOPMENT ...................................................................7 

1.3 SCRUBBER ONBOARD THE MT “SUULA” ......................................................8 

2 RESEARCH OBJECTIVES ............................................................ 9

2.1 TECHNICAL AND ENVIRONMENTAL OBJECTIVES ..............................................9 

2.2 SCRUBBER TEST PROGRAM .....................................................................9 

3 TEST RESULTS AND ANALYSES .................................................. 9

3.1 CERTIFICATION TESTS ........................................................................ 10 

3.2 PARTICLE MEASUREMENTS.................................................................... 13 

3.3 CONTINUOUS EMISSION MONITORING SYSTEM (CEMS) ................................ 14 

3.4 SULPHUR TRIOXIDE TEST ..................................................................... 16 

3.5 REMOVAL OF NITROGEN OXIDES ............................................................. 17 

3.6 DYNAMIC TEST ................................................................................. 17 

3.7 PLUME ........................................................................................... 18 

3.8 NOISE ........................................................................................... 20 

3.9 EFFLUENT COMPOSITION AND QUALITY ..................................................... 21 

3.10 TESTS WITH WATER PRODUCED IN AWP-PROCESS ....................................... 23 

3.11 SLUDGE QUANTITY AND QUALITY ............................................................ 23 

3.12 SYSTEM RELIABILITY .......................................................................... 25 

3.13 CORROSION TESTS ............................................................................ 25 

3.14 HEALTH AND SAFETY ASPECTS ............................................................... 26 

3.15 ENERGY CONSUMPTION ....................................................................... 26 

4 LEGISLATION DEVELOPMENT .................................................. 27

4.1 GENERAL........................................................................................ 27 

4.2 IMO RESOLUTION MEPC.185(59) ........................................................ 27 

4.3 EU DIRECTIVE 2005/33/EC ................................................................ 28 

5 SUMMARY ............................................................................... 29

5.1 TEST TARGET ................................................................................... 29 

5.2 TEST RESULTS.................................................................................. 29 

5.3 RECOMMENDATIONS........................................................................... 29 

5.4 CONCLUSIONS ................................................................................. 29 

 
© Wärtsilä PUBLIC TEST REPORT Page 5 (30) 

Abbreviations 

AWP/AWT Advanced Water Purification system, Advanced wastewater treatment 

system 

CEMS Continuous Emission Monitoring System 

CO2 Carbon dioxide 

EU European Union 

GRP Glass Reinforced Plastic 

IMO International Maritime Organisation 

MARPOL International Convention for the Prevention of Pollution from Ships 

MEPC Marine Environmental Protection Committee (IMO) 

MT Motor Tanker 

NaOH Sodium hydroxide 

NOx Nitrogen Oxides 

PAHphe Polycyclic Aromatic Hydrocarbons, phenanthrene equivalence 

SECA SOx Emission Control Area 

SOx Sulphur Oxide 
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1 INTRODUCTION 

1.1 Scrubber project background 

Within the Finnish maritime cluster, the first idea to initiate a marine SOxscrubber development project was born in 2005 and was based on developing 

environmental legislation for the reduction of emission of sulphur oxides. Four 

companies started to discuss the possibility of developing a marine scrubber. 

These four companies developed a project plan and an application for R&D 

funding together. Wärtsilä was selected as project leader. The scrubber project 

was considered a challenging, cross-scientific R&D project, offering opportunities 

for partners to increase their knowledge and opening possibilities for cooperation 

between research institutes and universities with relevant enterprises. One of 

the reasons for public economical funding was the beneficial ecological effect of 

the project. 

In September 2007 the project steering committee decided to install a test 

scrubber on the tanker MT "Suula", owned by Neste Shipping. The first start of 

this scrubber was on the 10th November 2008 and was simultaneously the 

beginning of the project testing phase. 

Figure 1. Exhaust gas scrubber onboard the MT "Suula". 
© Wärtsilä PUBLIC TEST REPORT Page 7 (30) 

1.2 Legislation development 

The MARPOL Annex VI convention was adopted by the IMO in 1997 and ratified 

in 2004. The most important regulation was and still is regulation 14, limiting 

the emission of sulphur oxides in SOx Emission Control Areas (SECAs) to a level 

corresponding to 1.5 % sulphur in the fuel. 

The IMO revised MARPOL Annex VI regulations for the prevention of air pollution 

from ships among others include the following parts relevant for this R&D 

project: 

 Regulation 3, exceptions and exemptions, covers trials for ship emission 

abatement technology research and emissions from petroleum activity. 

 Regulation 4, equivalents, allows alternative fitting, material, appliance, 

procedure, fuels or compliance methods. Selective catalytic reduction and 

scrubbers are permitted. 

 Regulation 14, sulphur oxides and particles, limits the use of high sulphur 

fuels. The reduction scale is globally from 4.50 to 0.50 % sulphur and 

inside the emission control areas from 1.50 to 0.10 % sulphur. No “MicroAreas” are specified in the rules. 

 Regulation 17 requires port reception facilities for scrubber residues. 

Global sulphur limits in fuel mass are shown in figure 2. Fuel type is not 

regulated which means that both HFO and distillate are permitted. Exhaust gas 

cleaning is an allowed alternative under Regulation 4 to achieve any regulated 

limit. 

Figure 2. IMO sulphur limits for years 2008-2020 (% mass). 
Page 8 (30) PUBLIC TEST REPORT © Wärtsilä 

1.3 Scrubber onboard the MT “Suula” 

The scrubber principle is shown in figure 3. A medium speed 680 kW auxiliary 

engine feeds exhaust gas to the scrubber. The installed scrubber system is of 

type: fresh water, closed loop, main stream, wet sump and packed bed. The 

material is glass reinforced plastic (GRP). In use, uncleaned effluent is not 

pumped into sea from the scrubber. Impurities are collected in effluent 

treatment unit, pumped to the sludge tank and finally moved onshore for final 

disposal. 

The working principle of a fresh water scrubber is based on a process whereby 

acid can be neutralised using an alkaline chemical. In a scrubber, exhaust gas 

sulphur oxides are removed to wash water which contains sodium hydroxide. As 

a result, the chemical sulphur compounds sulphates are formed from the 

exhaust gas sulphur. These neutralised products flow into the sea through the 

water treatment process. Adding the resulting sulphur compounds to seawater is 

not a problem because seawater contains some 1015 (1,000,000,000,000,000) 

tonnes of sulphur in seawater as sulphate overall. 

The scrubber consumes technical fresh water which evaporates into the 

atmosphere with the exhaust gas. This evaporation is minimized with the use of 

the scrubbing water cooler. 

Figure 3. Fresh water scrubber operational principle.
© Wärtsilä PUBLIC TEST REPORT Page 9 (30) 

2 RESEARCH OBJECTIVES 

2.1 Technical and environmental objectives 

The technical target of the project was to develop a suitable abatement 

technology, based on scrubbers, for sulphur oxides in the exhaust gases of 

marine diesel engines and oil-fired boilers. Scrubbers are widely known in landbased applications. However, in the marine environment, specific IMO 

regulations and ship design requirements prevented a straight adaptation of 

land-based designed scrubbers for marine applications. 

The general environmental goals of Wärtsilä Corporation are as follows: 

 Supply power solutions offering high efficiency with low environmental 

load. 

 Continuously improve the environmental performance of its products and 

services. 

 Enable the tightening of the relevant international environmental 

regulations of e.g. IMO and World Bank which are considered a basis for 

R&D. 

These objectives were also guidelines for this project. By using scrubber 

technology, the sulphur content in the atmosphere could be drastically reduced 

or virtually eliminated. 

2.2 Scrubber test program 

The scrubber test program was assorted to following segments: 

 System start-up 

 Certification tests 

 Exhaust gas cleaning efficiency tests 

 Particle tests 

 Noise tests 

 Dynamic tests 

 Sludge tests 

 Tests with cleaned sewage water (AWP test) 

 Corrosion tests 

 Exhaust gas plume measurements 

3 TEST RESULTS AND ANALYSES 

The scrubber’s own automation system was used for measurement data 

collection. In addition, manual parameter recording was used to help with this 

work. Accredited and special measurements were done by subcontractors like 

Pöyry Finland Oy, Turku University of Applied Sciences or Wärtsilä Vibration, 

Environment and Measurement Technology Department. These organizations 

produced their own reporting. 

Several fuel, gas and water samples were taken from the scrubber system 

during the test period. These samples were analyzed later in accredited 

laboratories. 
Page 10 (30) PUBLIC TEST REPORT © Wärtsilä 

Certification required classification society inspections onboard the MT “Suula”. 

Germanischer Lloyd and Det Norske Veritas had their own personnel involved in 

the certification process. 

3.1 Certification tests 

The purpose of the tests was to demonstrate the scrubber performance to the 

certifying bodies for certification of the unit under the IMO Marpol regulations. 

The certification process was started in accordance with IMO Resolution 

MEPC.170(57). These regulations were slightly improved when the IMO in July 

2009 adopted IMO Resolution MEPC.184 (59). 

These regulations define limits for parameters which were measured during the 

tests. The accredited independent body, Pöyry Finland Oy, carried out 

measurements and the tests were performed with both high (3.4 %) and low 

sulphur (1.5 %) heavy fuel oil. 

The Wärtsilä scrubber system is designed to efficiently remove the sulphur from 

the exhaust gases. The certification tests were performed with four different 

scrubber load levels (8 %, 40 %, 70 % and 100 %) and emission measurements 

took place simultaneously before and after the scrubber. SO2 reduction is 

demonstrated by measuring SO2 and CO2 concentrations in the exhaust gas after 

the scrubber. The results are presented in Table 1. Measured sulphur dioxide 

removal efficiency was 100 % for all operating conditions, throughout the load 

range, even when using high sulphur fuel. 

Test 1 2 3 4 5 6 7 8 

Engine test load % 8 40 70 100 8 40 70 100 

Fuel sulphur content % 

m/m 

1.5 1.5 1.5 1.5 3.4 3.4 3.4 3.4 

SO2 after scrubber (*) ppm-v 0 0 0 0 0 0 0 0 

CO2 after scrubber %-v 4.7 6.1 6.5 6.6 4.6 6.0 6.4 6.7 

SO2/CO2 ratio ppm/% 0 0 0 0 0 0 0 0 

(*) A ‘0’ value indicates the result was below measurable limits (~2 ppm). 

Measurement equipment from a 3rd party accredited company has an accuracy of 

±2 ppm. For reference 0.1 % S corresponds to 20...30 ppm. 

As a part of the certification test, effluent quality was demonstrated to 

classification societies. The Wärtsilä scrubber fulfils all the effluent quality 

requirements due to the efficient Wärtsilä water treatment unit. The IMO 

resolution MEPC.184 (59) defines limits for pH, turbidity, PAHphe and nitrate 

content. Also, metals in the effluent were measured. The tests showed that after 

the water treatment unit, PAHphe concentration (figure 4) and turbidity (figure 5) 

are clearly under IMO limits. 

Table 1. Sulphur removal efficiency during certification tests.
© Wärtsilä PUBLIC TEST REPORT Page 11 (30) 

Figure 4. Phenanthrene in the effluent. 

Figure 5. Turbidity in the effluent. 

Sodium Hydroxide (NaOH) is added to the scrubbing water circulation to 

maintain the process pH and consequently the efficiency of SO2 removal. Due to 

efficient NaOH dosing and monitoring, the pH of the effluent was over 6.5 which 

is the IMO limit for the effluent pH (figure 6). Certification tests also proved that 

nitrate concentration in the effluent is under IMO limits. 
Page 12 (30) PUBLIC TEST REPORT © Wärtsilä 

Figure 6. pH in the effluent. 

Figure 7. Nitrate in the effluent. 

One of the main targets of the MT "Suula" project was to get approval for the 

scrubber. For the Suula tests, a separate two-day program was created. As well 

as the performance, the safety of the installation was approved. Wärtsilä SOx

scrubber performed successfully in the tests, and is the first ever marine 

scrubber issued with a certificate. The certification was carried out by major 

classification societies: Det Norske Veritas and Germanischer Lloyd. 

5,8

6

6,2

6,4

6,6

6,8

7

7,2

7,4

7,6

7,8

1,5 3,4

pH

Fuel sulphur content (% m/m)

PH IN THE EFFLUENT

IMO limit: The pH of the effluent should not be lower than 6.5.

Effluent

IMO limit

DISCHARGE WATER NITRATE CONCENTRATION

Suula

Test load 100%.

0

10

20

30

40

50

60

70

3,4

Fuel sulphur content (% m/m)

mg/l

Normalized nitrate concentration

IMO limit
© Wärtsilä PUBLIC TEST REPORT Page 13 (30) 

Under MARPOL regulations, it is mandatory to keep certain exhaust gas cleaning 

system documents onboard. Such documents are, for example, the EGC-SOx

Technical Manual (ETM) which describes the cleaning system technology, system 

performance and maintenance needs. 

Another important document is the EGC Record book which is a log book for 

service and maintenance. The onboard Monitoring Manual (OMM) describes the 

monitoring instruments of the cleaning system and contains a device list, 

maintenance requirements and calibration procedures. All MARPOL-related 

documents were approved during the Suula certification process. 

3.2 Particle measurements 

Particle washing tests were performed with the standard ISO-8178, and Turku 

University of Applied Sciences carried out the measurements. 

Particles were measured before and after the scrubber and tests were performed 

with five different scrubber load levels (10 %, 25 %, 50 %, 75 % and 100 %). 

The fuel sulphur contents were 1.5 % and 2.1 %. 

Tests proved that the scrubber system removes exhaust gas particles from the 

exhaust gas. The highest particle reduction (65 %) was with high sulphur fuel 

and with an engine test load of 75 %. 

Figure 8. Particulate reduction in scrubber. 

PARTICULATE MEASUREMENTS ISO-8178

Reduction (%)

0

10

20

30

40

50

60

70

10 20 30 40 50 60 70 80 90 100

Test load(%)

PM reduction (%)

Reduction, S 1,5%

Reduction, S 2,1%
Page 14 (30) PUBLIC TEST REPORT © Wärtsilä 

3.3 Continuous Emission Monitoring System (CEMS) 

A CEMS was used to monitor sulphur dioxide, nitric oxides, oxygen and carbon 

dioxide content in exhaust gases during the tests. In the following charts, the 

accuracy of the system is shown. CEMS results were compared to measurements 

of an accredited company (Pöyry Finland Oy). Based on the manufacturer’s 

information, all the analyser channels have been tested and approved to be 

within the requirements of the MEPC.103 (49) Chapter 5 Appendix 3. Careful 

installation, maintenance and calibration processes are needed to guarantee 

reliable operation of the CEMS. 

The analyser type used in MT “Suula” had exhaust gas sampling lines and 

sampling probes which were electrically heated. This arrangement consumed 

energy and there were some air leaks, failure currents and moisture problems, 

especially in the sampling lines after the scrubber. Dirty exhaust gases had to be 

filtered before the analyser and these filters had to be replaced frequently. Also, 

the calibration gases for the analyser had to be stored onboard. One extra 

weakness in the CEMS was the limited age of some analyser components. 

The pilot test demonstrated reliable means for monitoring, documentation and 

certification of the scrubbers also without CEMS. 

Figure 9. CEMS accuracy in CO2 measurements 

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

0 20 40 60 80 100

CO2 measurements (%‐vol)

CO2 after scrubber

CO2 after scrubber, CEMS

Power (%)
© Wärtsilä PUBLIC TEST REPORT Page 15 (30) 

Figure 10. CEMS accuracy in NOx measurements 

Figure 11. CEMS accuracy in SO2 measurements 

0

200

400

600

800

1 000

1 200

1 400

0 20 40 60 80 100

NOx measurements (ppm)

NOX after scrubber (ppm)

NOX after scrubber, CEMS (ppm)

Power (%)

0

100

200

300

400

500

600

700

800

900

1 000

0 20 40 60 80 100

SO2 measurements (ppm)

SO2 before scrubber (ppm)

SO2 before scrubber, CEMS

(ppm)

Power (%)
Page 16 (30) PUBLIC TEST REPORT © Wärtsilä 

 Test 

1 

Test 

2 

Test 

3 

Test 

4 

Test 

5 

Test 

6 

Test 

7 

Test 

8 

SO2 after scrubber 

Pöyry Finland ppm 0 0 0 0 0 0 0 0 

CEMS ppm 2.3 2.3 0.8 0.8 0 0 0 0 

Portable instrument ppm 0 0 0 0 0 0 0 0 

CO2 after scrubber 

Pöyry Finland %-v 4.7 6.1 6.5 6.6 4.6 6 6.4 6.7 

CEMS %-v 4.45 5.8 6.15 6.45 4.3 5.65 6.05 6.3 

Portable instrument %-v - 5.8 6.13 6.45 4.4 5.8 6.2 6.5 

3.4 Sulphur trioxide test 

SO3 was measured from the exhaust gas after the scrubber, with Pöyry Finland 

Oy carrying out the measurements. It was determined by applying the method 

EPA8. SO3 is very difficult to measure; a continuous measurement method is not 

available. Therefore, the SO3 content in the exhaust gases was measured only 

with an engine test load of 100 %. The measurement results showed that after 

the scrubber, no sulphite was detected in the exhaust gas. 

Unit Value 

Engine test load % 100 

Fuel sulphur content % m/m 1.44 

Sulphite (SO3

-

) mg/m3n dry 0 

Based on the IMO regulations, SO3 content in the exhaust gas shall not be 

measured. When considering the results of the EPA8, the approach of IMO is 

reasonable; SO3 is an exhaust gas parameter not to be monitored. 

Table 2. Comparison between different exhaust gas measurement devices.

Table 3. SO3 reduction in scrubber.
© Wärtsilä PUBLIC TEST REPORT Page 17 (30) 

3.5 Removal of nitrogen oxides 

The scrubber NOx removal efficiency was tested during the Suula tests. The NOx

reduction was tested with both high and low sulphur fuel and four different 

scrubber load levels. The average NOx reduction was with high sulphur fuel 8.1 

% and with low sulphur fuel 5.3 % (figure 15). 

Figure 12. Scrubber NOx reduction. 

3.6 Dynamic test 

A dynamic test was carried out to measure how well the scrubber works during 

engine power transients. During the test, the engine was exposed to artificially 

fast load variations in both directions. These results are shown in the chart 

below. Sulphur dioxide concentration in exhaust gas was continuously practically 

zero when engine load increased from 200 kW to 440 kW and decreased to zero. 

The scrubber automation system was able to maintain stable parameters and 

100 % SOx reduction throughout all transients. 

SCRUBBER NOx REDUCTION

Scrubber performance was tested with low sulphur fuel and high sulphur fuel 

and on four different scrubber load levels (8, 40, 80 and 100%).

0

2

4

6

8

10

12

40 140 240 340 440 540 640

Engine test load (kW)

NOx reduction (%)

NOx reduction, S 1,5 %

NOx reduction, S 3,4 %
Page 18 (30) PUBLIC TEST REPORT © Wärtsilä 

Figure 13. Wash water pH, exhaust gas CO2 and exhaust gas SO2 historical trend 

recorded in dynamic test. The CO2 concentration is load dependent also in 

steady-state conditions, being an inherent feature of engine aspiration.

3.7 Plume 

Some of the scrubbing water is evaporated in the scrubber and thus the clean 

exhaust gas after the scrubber has a high relative humidity, although the 

absolute water content is lower than in normal exhaust gases without a 

scrubber. High water content in the exhaust gases may appear as white plume 

coming out of the exhaust pipe. To minimize the evaporation (and fresh water 

consumption), the scrubbing water is cooled with sea water in a heat exchanger. 

This arrangement reduces the visibility of white plume. 

A dedicated plume test was done in order to visually evaluate the plume. The 

test was done in summer 2009 in Porvoo harbour. The engine load was relatively 

stable during the test and the sea water cooling pump capacity was varied to see 

the impact on scrubbing water temperature, and consequently on exhaust gas 

temperature and water content (plume). The test was based on visual 

observations. 

Auxiliary engine 

no.3 stopped 

Wash water pH 

CO2 in 

exhaust gas SO2 content in exhaust 

gas (sulphur in fuel) 

Load of auxiliary 

engine no.3 

Auxiliary 

engine no.3 

loaded alone

Two auxiliary engines 

loaded

Shaft generator loaded 

alone 

Auxiliary engine no. 3 

running without load 
© Wärtsilä PUBLIC TEST REPORT Page 19 (30) 

Figure 14. Sea water cooling on (normal operation mode). 

Figure 15. Sea water cooling off (abnormal operation mode). 

Test conditions:

Engine load 320... 350 kW Ambient air temperature 22... 24 °C 

Fuel sulphur content 2.1 % Wind speed 9... 11 m/s 

 Sea water temperature 9 °C 

Based on the observations made during the test, the following was concluded: 

 Sea water cooling of the scrubbing water has a notable effect on exhaust 

gas plume. 

 With normal cooling, the plume is very thin, transparent and very rapidly 

mixed with the ambient air. 

 With the cooling switched off, the plume is a thick white cloud, however it 

does still mix rapidly with ambient air. 

 During all operating conditions the plume lift was very good. A change 

was noticed only in the thickness of the plume. Down wash, condensation 

or acid rain was never detected. 
Page 20 (30) PUBLIC TEST REPORT © Wärtsilä 

3.8 Noise 

The noise properties of the scrubber were estimated by sound pressure 

measurements on the top of the chimney. The layout of the test system made it 

possible to guide the exhaust gases either through the original silencer or 

through the scrubber. The sound pressure in both cases was measured in 

different directions. The average 1/3-octave spectrum of the values at a distance 

of 2 meters are presented in the results graph. 

At low frequencies (12.5 Hz to 100 Hz), the silencing properties of the test 

scrubber are quite equal to the original exhaust noise silencer. This frequency 

range is dominant in linear scale (dotted lines in figure 16). 

At higher frequencies (1 kHz and upwards), the silencing properties of the test 

scrubber and the silencer are also equal. The noise in this frequency range is 

relatively low and thus not significant. 

At mid-frequencies (in this case 150 Hz to 1 kHz), the silencer is more efficient 

than the test scrubber. 

However, the highest dominating noise peak at 125 Hz on the A-weighed scale 

in dB(A) emitted through the original silencer is reduced when conducting the 

gas through the test scrubber instead of the silencer. Therefore, the scrubber 

and silencer emitted the same total noise level in terms of dB(A). 

The size of the test scrubber is smaller than commercial applications. Therefore 

it can be expected that the scrubbers in larger commercial installations will show 

better performance than a silencer at low frequencies (such as the ignition 

frequency). On the other hand, a slight reduction of the noise attenuation at mid 

frequencies may be expected. 

Figure 16. Sound pressure from the scrubber exhaust pipe. 

0,0

20,0

40,0

60,0

80,0

100,0

120,0

12.5 Hz

16 Hz20 Hz25 Hz

31.5 Hz

40 Hz50 Hz63 Hz80 Hz

100 Hz125 Hz160 Hz200 Hz250 Hz315 Hz400 Hz500 Hz630 Hz800 Hz

1 kHz

1.25 kHz

1.6 kHz

2 kHz

2.5 kHz

3.15 kHz

4 kHz5 kHz

6.3 kHz

8 kHz

10 kHz

12.5 kHz

Lp [dBA]

fm 1/3 Octave Band [Hz]

Sound pressure 2 m away from the top of the chimney

Comparison between the scrubber and the silencer

Silencer, Linear weighing, total = 105 dB

Scrubber, Linear weighing, total = 107 dB

Silencer, A-weighing, total = 80 dBA

Scrubber, A-weighing, total = 80 dBA
© Wärtsilä PUBLIC TEST REPORT Page 21 (30) 

3.9 Effluent composition and quality 

The bleed-off treatment unit removes the accumulated impurities from the 

scrubbing water. Clean effluent from the unit is discharged overboard. The water 

treatment unit performance tests were part of a broader testing programme of 

the Wärtsilä scrubber. 

The water quality has been a significant research target and over 70 water 

samples were taken from the scrubbing water, effluent and technical water. The 

tests were performed with fuel sulphur content of 1.5 %, 2.2 % and 3.4 %. Also, 

as a part of the certification tests, the effluent quality was demonstrated to 

classification societies, showing that the Wärtsilä scrubber fulfils all the effluent 

quality requirements. The effluent quality tests confirmed that the main 

component (beside water) in the effluent is harmless sulphate. 

Water %-mass >75 

Sulphate %-mass <25 

Sulphite %-mass <1 

Nitrate %-mass <0.2 

Nitrite %-mass <0.2 

Metals as sum %-mass <0.006 

Hydrocarbons as sum C10-C40 %-mass <0.0001 

The bleed-off treatment unit cleaning efficiency was excellent regardless of the 

fuel sulphur content. The reduction of the hydrocarbons C10-C40 and the PAH 

(Polycyclic aromatic hydrocarbons) was almost 100 % at the bleed-off treatment 

unit when tested with different fuel sulphur contents. 

Continuous measurement of the PAHphe equivalence in a reliable way is 

challenging using existing technology. Firstly the device has to detect the 

minimal amount of the specific PAH compound in flowing water, and secondly 

the device must be capable of measuring the concentration of this compound. 

Traditional sampling and laboratory analyses onshore are a more reliable 

approach to monitor the PAH content in effluent. Research work will continue to 

find best methodology for PAH monitoring in the effluent. 

The bleed-off treatment unit removes metals efficiently from the scrubber water. 

The analysed metals from the effluent are defined in the IMO Resolution 

MEPC.184(59). The turbidity criterion in the IMO Resolution limits the 

permissible amount of metals. 

Table 4. Main components in the effluent.
Page 22 (30) PUBLIC TEST REPORT © Wärtsilä 

Figure 17. Reduction in concentration of chemical components in the bleed-off 

treatment unit with fuel sulphur content 3.4 % m/m. 

Figure 18. Reduction in concentration of chemical components in the bleed-off 

treatment unit with fuel sulphur content 1.5 % m/m. 

100 98 97

66

0

10

20

30

40

50

60

70

80

90

100 Reduction (%)

REDUCTION OF COMPONENTS IN THE BLEED-OFF TREATMENT UNIT

Fuel sulphur content 3.4 % m/m

Hydrocarbons as sum C10-C40

PAH-16

PAH-16: Phenanthrene

Metals as sum

100 99 98

83

0

10

20

30

40

50

60

70

80

90

100

Reduction (%)

REDUCTION OF COMPONENTS IN THE BLEED-OFF TREATMENT UNIT

Fuel sulphur content 1.5 % m/m

Hydrocarbons as sum C10-C40

PAH-16

PAH-16: Phenanthrene

Metals as sum
© Wärtsilä PUBLIC TEST REPORT Page 23 (30) 

3.10 Tests with water produced in AWP-process 

Black and grey water from vessels can be treated by using Advanced 

Wastewater Treatment systems (AWP) that provide biological treatment, solid 

removal and disinfection. The applicability of the effluent from AWP system as a 

water source to a SOx-scrubber was tested in June 2009. The test was 

performed by Turku University of Applied Sciences at the request of Wärtsilä 

Finland Oy. The purpose of the test was to evaluate potential sensory (smell), 

microbiological and chemical factors that may affect the usability of AWP water 

as the water source for Wärtsilä’s SOx- scrubber. 

The AWP effluent from a modern cruise ship was collected and used in the field 

test. During the test run the AWP water was fed into the scrubber system to 

replace the existing scrubbing water. Various microbial studies were made from 

the samples taken from the scrubber system before, during and at the end of 

the test run to reveal the viability of selected bacteria and viruses in the 

scrubber conditions. Also, chemical analyses were made to follow the changes in 

the chemical composition of the scrubber water during the test. The chemical 

and microbiological analyses were performed in the laboratory. 

During the test no changes in the SOx-scrubber water composition were found 

that could make the use of AWP water inapplicable to the scrubber use. These 

field tests did not reveal any potential negative consequences on human health 

or comfort. 

3.11 Sludge quantity and quality 

The impurities in the exhaust gas are trapped in scrubbing water. The bleed-off 

is cleaned in a treatment plant and the cleaned effluent can be discharged into 

the sea. The impurities are left in the sludge, which is collected into the sludge 

tank to be emptied into port waste reception facilities. The amount of generated 

sludge is approximately 0.1 to 0.4 kg/MWh, in other words less than 10 % of 

‘normal’ sludge. 

Sludge generated in the scrubber process is similar to other engine room sludge, 

and can therefore be conducted to the same tank. The scrubber sludge may not 

to be incinerated. Therefore in ships where ‘normal’ engine room sludge is 

incinerated, the scrubber sludge is conducted to separate sludge tank. 

The sludge samples have been taken from the scrubber pilot plant. The samples 

were analysed in accredited laboratories. The fuel sulphur content during the 

sludge Sampling was 1.49 % m/m. The following tables represent the typical 

Composition and properties of scrubber sludge: 

Unit Value Laboratory 

Dry matter % 21.3 Nablabs 

 

Table 5. Analysed results from the sludge
Page 24 (30) PUBLIC TEST REPORT © Wärtsilä 

Unit Value Laboratory 

pH 5.6 Eurofins 

Density kg/l 1.0406 Eurofins 

Ash 550oC % d.m 58.9 Eurofins 

Oil Hydrocarbons as sum mg/kg d.m 252000 Eurofins 

Metals as sum mg/kg d.m 52977 Eurofins 

Calorimetric heat value MJ/kg 17.22 Nablabs 

Effective heat value MJ/kg 16.25 Nablabs 

Unit Value Laboratory 

PAH-16 sum μg/l 33 Eurofins 

Benzene μg/l <d.l Eurofins 

Toluene μg/l <d.l Eurofins 

Ethylbenzene μg/l <d.l Eurofins 

m/p-Xylene μg/l <d.l Eurofins 

o-Xylene μg/l <d.l Eurofins 

MTBE μg/l <d.l Eurofins 

TAME μg/l <d.l Eurofins 

Hydrocarbons as sum mg/l 3,8 Eurofins 

Chloride (Cl) mg/kg 60 Eurofins 

Sulphate (SO4) mg/kg 25600 Eurofins 

Nitrate (NO3) mg/kg 157 Eurofins 

Nitrite (NO2) mg/kg <d.l. Eurofins 

<d.l. = below reliable determination limit of analysis method 

dm = dry matter 

The scrubber sludge contains water (79 %) and dry matter (21 %). The 

composition of the dry sludge is mainly hydrocarbons, ash and metals. The 

water emulsion contains hydrocarbons, metals and sulphate. Sludge quantity 

and quality depend on fuel oil quality. Coagulation and flocculation chemicals are 

added in bleed-off treatment processes, and the composition of such chemicals 

is reflected in the sludge analysis. 

Based on the test results from MT “Suula”, waste reception facilities in Finland 

and Sweden have confirmed that the sludge from the scrubber bleed-off 

treatment unit can be safely handled and disposed of in ports in the same way 

as other sludge from ships’ engine rooms. 

It is also technically possible to reduce the water content of the sludge. In this 

process, sludge from which the water has been removed is packed in sacks. 

Table 6. Analysed results from the sludge’s dry matter

Table 7. Analysed results from the sludge’s aqueous phase
© Wärtsilä PUBLIC TEST REPORT Page 25 (30) 

3.12 System reliability 

The system performed well. 

The scrubber hull was made of GRP which proved to be an excellent solution in 

contact with corrosive liquids inside the scrubber. Exhaust gas heat was well 

under control and no material failures were detected. 

Automation and process control was based on Wärtsilä’s diesel engine control 

components which were known to be robust and reliable. As normal with process 

automation, the control parameters needed some tuning during the test period. 

In addition, control interface and programs could be developed. 

The standard of the main instruments in the system were “process industry 

quality” with good corrosion protection. However, some components suffered 

from low quality. The amount of water and dirt in instrument air is most 

important for the reliability of pneumatic control components. The CEMS system 

should be designed to be operated with wet exhaust gases. 

Furthermore, mechanical components, for instance pumps and pump shaft 

sealings, must be selected carefully. Some components and instruments in the 

scrubber system require regular maintenance. 

Ship inclinations, accelerations, vibrations and load transients caused no 

interruptions to scrubber operation. Rough sea states had no effect on sulphur 

reduction. 

The main challenge for the test scrubber was winter. Suula’s installation was 

temporary and therefore installed outside the funnel. The running profile of the 

system was not continuous. Therefore freezing occurred in the scrubber during 

system lay days. This is not relevant for permanent, commercial scrubbers as 

they will be installed in warm conditions in the funnel or a similar enclosure. 

3.13 Corrosion tests 

The purpose of the coating test was to determine the tank coating’s resistance to 

corrosion. Coating samples from three different suppliers were installed in bleedoff water and in Sodium Hydroxide for three months. After the test period, the 

samples were delivered to coating manufactures for evaluation. 

All coating samples endured bleed-off water and Sodium Hydroxide and no 

corrosion in the samples was detected. 
Page 26 (30) PUBLIC TEST REPORT © Wärtsilä 

Figure 19. Coating test piece before (left) and after (right) the test. 

3.14 Health and safety aspects 

Wärtsilä scrubber tests onboard the MT Suula did not reveal any potential 

negative consequences on human health. Several different kind of testing were 

performed and no dangerous situations or accidents happened thanks to a safety 

programme. The fresh water exhaust gas scrubber uses a NaOH (Caustic Soda) 

solution with a maximum concentration of 50 %. Alternatively, a 20 % NaOH 

solution can be used. NaOH was present in the NaOH bunkering, storage and 

NaOH feed system on the Suula. During the tests, NaOH was stored and handled 

safely and no dangerous situations occurred. 

Scrubbing water is the water circulating in the system. Water is circulated from 

the scrubber or a separate process tank through a seawater cooler and back to 

the scrubber. Scrubbing water is not a health hazard. Also the applicability of the 

effluent from an Advanced Water Purification (AWP)-type sewage water 

treatment system as a water source to a SOx-scrubber was tested in June 2009. 

The test run in this field test revealed no negative findings for human health or 

comfort. 

Particles can be harmful for health. The size of the particles is directly linked to 

their potential for causing health problems. Small particles of less than 10 

micrometers in diameter cause problems because they can get deep into the 

respiratory system and affect the lungs and heart. The tests confirmed that 

scrubbed exhaust gases contain less particles than normal exhaust gases. 

3.15 Energy consumption 

The tests confirmed required water pressure and flow rates. Thus it was 

confirmed that the pumping power requirement of commercial scrubber 

installations in nominal conditions will be around 0.3 % of the engine power, 

regardless of the vertical position of the scrubber in the vessel. Additionally, 

miscellaneous control systems and other devices consume insignificant amounts 

of electric power in commercial applications. 
© Wärtsilä PUBLIC TEST REPORT Page 27 (30) 

4 LEGISLATION DEVELOPMENT 

4.1 General 

In this project, the regulations with regards documentation, performance 

demonstration, onboard verification and certification were thoroughly and 

successfully tested on the scrubber installed on the MT “Suula”. 

4.2 IMO Resolution MEPC.185(59) 

Continuous PAH monitoring 

Continuous measurement of the PAHphe equivalence onboard is challenging. This 

is due to the small concentrations and limited selectivity of available 

measurement methods. There are furthermore no existing international 

standards for measuring PAH compounds on-line. 

Traditional PAH measurement methodology 

Traditional sampling and laboratory analyses onshore is a more reliable 

approach to monitor the PAH content in effluent. The effluent samples should be 

taken for analysis to a laboratory accredited according to the standard EN 

ISO/IEC 17025. 

The traditional tested and standardized method for aqueous PAH determination 

is a manual analytical laboratory method. In this method, a representative 

effluent water sample is first extracted with dichloromethane or diethylether 

(liquid/liquid extraction), then exchanged with hexane over a steam bath and 

fractionated and purified by alumina/silica gel chromatography. 

After the sample preparation described above, PAH compounds are measured by 

gas chromatography using an ion trap mass selective detector (GC/MS). Method 

detection limit is about 1- 8 ng/l in water. The calibration of analysis system is 

done by known concentrations of PAH (internal standards). In this method both 

gaseous (dissolved) PAH compounds as well as PAH in particles are transferred 

into extraction solution from which the Total PAH (TPAH) is analyzed by a GC/MS 

system. 

This method is standardized internationally including e.g. the following 

standards: EPA 3510 (Separatory funnel liquid-liquid extraction), EPA 8310 

(Polynuclear aromatic hydrocarbons - analysis and result calculations) and 

NS9810 (Water analysis - Clean up procedure of water samples for the 

determination of polycyclic aromatic hydrocarbons (PAH). 

Proposal 

It is proposed to offer sampling and onshore analysis as a part of certification as 

an alternative to continuous PAH monitoring in section 10 of Resolution 

MEPC.184(59), similar to the demonstration procedure for nitrate concentration. 

 
Page 28 (30) PUBLIC TEST REPORT © Wärtsilä 

4.3 EU Directive 2005/33/EC 

The following is worth considering when updating the Directive: 

Article 4c, §4, second bullet, “...are fitted with continuous emission 

monitoring equipment”: When this text was written originally more than five 

years ago, it was to some extent justified for the reasons mentioned below. Now 

there is reason to consider making amendments: 

1. At that time, the discussion about emission abatement technology 

focussed purely on sea water (SW) scrubbing. Since then also fresh water 

(FW) scrubbing (existing technology in many applications, including 

stationary diesel power plants) has been introduced to the marine market. 

2. Emission monitoring can help in determining SW scrubber performance 

considering variations of sea water composition in different sea areas. In 

contrast to SW scrubbing, FW scrubbing is completely independent of the 

sea water composition (alkalinity) and therefore shows no variations in 

SOx-reduction performance. 

3. Since the Directive was written, the IMO has adopted procedures for 

certifying (type approval) the performance, documentation and 

verification procedures of a scrubber without continuous emission 

monitoring systems. This is known as Scheme A in IMO Resolution 

MEPC.184(59), adopted in July 2009 in MEPC 59. Therefore emission 

monitoring is no longer necessary to verify the performance of a scrubber. 

4. In addition to a robust type approval procedure, scheme A under 

Resolution MEPC.184(59) also requires a range of parameters to be 

continuously recorded in a tamper-proof recording device during operation 

throughout the life-time of the ship. These parameters are listed in 

§4.4.7, and include a range of scrubbing water and gas pressures and 

pressure drops, temperatures and flow rates, and combustion equipment 

load. Additionally §4.4.8 requires daily spot checks of the exhaust gas 

quality in terms of SOx-emissions. All these together can be considered at 

least as reliable as a continuous emission monitoring system. 

5. Although continuous emission monitoring systems are frequently used in 

the process industry, monitoring systems of SOx in exhaust gases of a 

diesel engine is technically a complication. This is well documented in a 

CIMAC report Number 23 / 2005, Appendix 4, clearly explaining the 

technical challenges, which also were confirmed in Wärtsilä pilot scrubber 

tests. 

Article 4c, §4, second bullet could e.g. be expanded by adding “...equipment, 

or can demonstrate required performance documented in an IMO certificate, 

and...” 
© Wärtsilä PUBLIC TEST REPORT Page 29 (30) 

5 SUMMARY 

5.1 Test target 

In this project, a new product for ships, a fresh water scrubber, was installed on 

the MT “Suula”. This scrubber type is capable of working in any sea area 

regardless of water composition, including brackish waters and harbour areas. 

The targets of the tests were a demonstration of performance and functionality 

in marine environment, and to obtain operational experience and certification. 

5.2 Test results 

All test targets were achieved. The measured SOx-reduction was excellent, 

complying with the most stringent IMO and EU regulations. The effluent fulfilled 

IMO wash water discharge criteria with good margins. 

The test demonstrated that exhaust gas cleaning systems are capable of safe 

operation and efficient performance onboard a ship in a marine environment, 

including rolling and pitching at open sea, vibrations, load variations, seasonal 

changes, etc. No condensation of the exhaust gas plume occurred outside the 

stack. 

The scrubber sludge can be disposed of safely. 

5.3 Recommendations 

Based on the “Suula” tests, the following actions are recommended: 

 Development of IMO Resolution MEPC.184(59) to include effluent PAHphe

monitoring based on sampling and laboratory analysis as an alternative to 

continuous monitoring. 

 Harmonization of EU Directive 2005/33/EC regulations with IMO Marpol. 

Under Marpol, verification of performance and operation can be carried 

out either with type approval in combination with recording of process 

parameters, or alternatively with a CEMS. 

Product training for ship designers, shipowners and ship staff will be important in 

the scrubber introduction phase. 

5.4 Conclusions 

The marine exhaust gas fresh water scrubber is ready for introduction onto the 

market. 
WÄRTSILÄ® is a registered trademark. Copyright © 2010 Wärtsilä Corporation.

Wärtsilä is a global leader in complete lifecycle power solutions for the 

marine and energy markets. By emphasising technological innovation 

and total efficiency, Wärtsilä maximises the environmental and economic 

performance of the vessels and power plants of its customers.