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ANNEX 26

RESOLUTION MEPC.159(55)

Adopted on 13 October 2006

REVISED GUIDELINES ON IMPLEMENTATION OF EFFLUENT STANDARDS

AND PERFORMANCE TESTS FOR SEWAGE TREATMENT PLANTS

THE MARINE ENVIRONMENT PROTECTION COMMITTEE,

RECALLING Article 38(a) of the Convention on the International Maritime Organization 

concerning the functions of the Marine Environment Protection Committee (the Committee)

conferred upon it by international conventions for the prevention and control of marine pollution,

NOTING resolution MEPC.2(VI) adopted on 3 December 1976 by which the Marine

Environment Protection Committee adopted, at its sixth session, the Recommendation on

International Effluent Standards and Guidelines for Performance Tests for Sewage Treatment 

Plants and invited Governments to apply the Effluent Standards and Guidelines for approving

sewage treatment plants; to take steps to establish testing programmes in accordance with the

Guidelines for Performance Tests; and provide the Organization with a list of sewage treatment

plants meeting the standards,

NOTING ALSO resolution MEPC.115(51) adopted on 1 April 2004 by which the Marine 

Environment Protection Committee adopted, at its fifty-first session, the revised MARPOL

Annex IV and which entered into force on 1 August 2005,

NOTING FURTHER the provisions of regulation 9.1.1 of MARPOL Annex IV, in which 

reference is made to the above-mentioned guidelines,

RECOGNIZING that resolution MEPC.2(VI) should be amended in order that current

trends for the protection of the marine environment and developments in the design and

effectiveness of commercially available sewage treatment plants be reflected; and the 

proliferation of differing unilateral more stringent standards that might be imposed worldwide be 

avoided,

HAVING CONSIDERED the recommendation made by the Sub-Committee on Bulk

Liquids and Gases, at its tenth session,

1. ADOPTS the Revised Guidelines on Implementation of Effluent Standards and

Performance Tests for Sewage Treatment Plants, the text of which is set out in the Annex to this

resolution;

2. INVITES Governments to:

(a) implement the Revised Guidelines on Implementation of Effluent Standards and

Performance Tests for Sewage Treatment Plants and apply them so that all

equipment installed on board on or after 1 January 2010 meets the Revised 

Guidelines in so far as is reasonable and practicable; and 
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(b) provide the Organization with information on experiences gained from their

application and, in particular, on successful testing of equipment against the

Standards;

3. FURTHER INVITES Governments to issue an appropriate “Certificate of type approval

for Sewage Treatment Plants” as referred to in paragraph 5.4.2 and the annex of the Revised 

Guidelines and to recognize such certificates issued under the authority of other Governments as 

having the same validity as certificates issued by them; and

4. SUPERSEDES the Recommendation on International Effluent Standards and Guidelines 

for Performance Tests for Sewage Treatment Plants contained in resolution MEPC.2(VI).
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ANNEX

REVISED GUIDELINES ON IMPLEMENTATION OF EFFLUENT STANDARDS

AND PERFORMANCE TESTS FOR SEWAGE TREATMENT PLANTS

TABLE OF CONTENTS

1 Introduction

2 Definitions

3 General

4 Standards

5 Testing considerations

6 Renewal and additional surveys

7 Familiarization of ship personnel in the use of the sewage treatment plant

ANNEX

Form of Certificate of Type Approval for Sewage Treatment Plants and Appendix
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REVISED GUIDELINES ON IMPLEMENTATION OF EFFLUENT STANDARDS

AND PERFORMANCE TESTS FOR SEWAGE TREATMENT PLANTS 

1 INTRODUCTION

1.1 The Marine Environment Protection Committee (MEPC) of the International Maritime

Organization (IMO) adopted resolution MEPC.2(VI) Recommendation on International Effluent

Standards and Guidelines for Performance Tests for Sewage Treatment Plants in 1976. 

1.2 This document contains the Revised Guidelines on Implementation of Effluent Standards 

and Performance Tests for Sewage Treatment Plants (Guidelines). These Guidelines are intended 

to assist Administrations in establishing operational performance testing programmes for sewage 

treatment plants for the purpose of type approval under regulation 9.1.1 of Annex IV of the

Convention.

1.3 These Guidelines apply to sewage treatment plants installed on board on or after 1 January 

2010.

2 DEFINITIONS

Annex IV – the revised Annex IV of the International Convention for the Prevention of Pollution 

from Ships (MARPOL 73/78) as amended by resolution MEPC.115(51).

Convention – the International Convention for the Prevention of Pollution from Ships 1973/1978 

(MARPOL 73/78).

Geometric mean – the nth root of the product of n numbers.

Greywater – is drainage from dishwater, shower, laundry, bath and washbasin drains.

Testing onboard – testing carried out on a sewage treatment plant that has been installed upon a

ship.

Testing ashore – testing carried out on a sewage treatment plant prior to installation e.g. in the

factory.

Thermotolerant coliforms – the group of coliform bacteria which produce gas from lactose 

in 48 hours at 44.5oC. These organisms are sometimes referred to as “faecal coliforms”; however, 

the term “thermotolerant coliforms” is now accepted as more appropriate, since not all of these

organisms are of faecal origin.

3 GENERAL

3.1 An approved sewage treatment plant must meet the standards in section 4 and the tests

outlined in these Guidelines. It should also be noted that, when ships are operating approved

sewage treatment plants, Annex IV also provides that the effluent shall not produce visible

floating solids or cause discolouration of the surrounding water.
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3.2 It is acknowledged that the performance of sewage treatment plants may vary

considerably when the system is tested ashore under simulated shipboard conditions or onboard a 

ship under actual operating conditions. Where testing ashore demonstrates that a system

complies with the standards, but subsequent onboard testing does not meet the standards, the 

Administration should determine the reason and take it into account when deciding whether to

type approve the plant. 

3.3 It is recognized that Administrations may wish to modify the specific details outlined in

these Guidelines to take account of very large, very small or unique sewage treatment plants.

4 STANDARDS

4.1 For the purpose of regulation 4.1 of Annex IV, a sewage treatment plant should satisfy the 

following effluent standards when tested for its Certificate of Type Approval by the

Administration:

.1 Thermotolerant Coliform Standard

The geometric mean of the thermotolerant coliform count of the samples of

effluent taken during the test period should not exceed 100 thermotolerant

coliforms/100 ml as determined by membrane filter, multiple tube fermentation or

an equivalent analytical procedure.

.2 Total Suspended Solids (TSS) Standard

(a) The geometric mean of the total suspended solids content of the

samples of effluent taken during the test period shall not

exceed 35 mg/l.

(b) Where the sewage treatment plant is tested onboard ship, the

maximum total suspended solids content of the samples of effluent 

taken during the test period may be adjusted to take account of the 

total suspended solid content of the flushing water. In allowing

this adjustment in maximum TSS, Administrations shall ensure

sufficient tests of TSS are taken of the flushing water throughout

the testing period to establish an accurate geometric mean to be

used as the adjustment figure (defined as x). In no cases shall the

maximum allowed TSS be greater than 35 plus x mg/l. 

Method of testing should be by:

.1 filtration of representative sample through a 0.45 μm filter

membrane, drying at 105°C and weighing; or

.2 centrifuging of a representative sample (for at least five minutes

with mean acceleration of 2,800-3,200 g), drying at least 105°C 

and weighing; or

.3 other internationally accepted equivalent test standard.

.3 Biochemical Oxygen Demand and Chemical Oxygen Demand
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Administrations should satisfy themselves that the sewage treatment plant is

designed to reduce both soluble and insoluble organic substances to meet the

requirement that, the geometric mean of 5-day Biochemical Oxygen Demand

(BOD5) of the samples of effluent taken during the test period does not exceed

25 mg/l and the Chemical Oxygen Demand (COD) does not exceed 125 mg/l. 

The test method standard should be ISO 15705:2002 for COD and

ISO 5815-1:2003 for BOD5, or other internationally accepted equivalent test

standards.

.4 pH

The pH of the samples of effluent taken during the test period shall be

between 6 and 8.5.

.5 Zero or non-detected values

For thermolerant coliforms, zero values should be replaced with a value

of 1 thermotolerant coliform/100 ml to allow the calculation of the geometric

mean. For total suspended solids, biochemical oxygen demand and chemical

oxygen demand, values below the limit of detection should be replaced with one

half the limit of detection to allow the calculation of the geometric mean.

4.2 Where the sewage treatment plant has been tested ashore, the initial survey should include 

installation and commissioning of the sewage treatment plant.

5 TESTING CONSIDERATIONS

5.1 Testing of the operational performance of a sewage treatment plant should be conducted

in accordance with the following subparagraphs. Unless otherwise noted, the subparagraphs

apply to testing both onboard and ashore.

5.2 Raw sewage quality

5.2.1 Sewage treatment plants tested ashore - the influent should be fresh sewage consisting of 

faecal matter, urine, toilet paper and flush water to which, for testing purposes primary sewage

sludge has been added as necessary to attain a minimum total suspended solids concentration

appropriate for the number of persons and hydraulic loading for which the sewage treatment

plant will be certified. The testing should take into account the type of system (for example

vacuum or gravity toilets) and any water or greywater that may be added for flushing to the

sewage before treatment. In any case the influent concentration of total suspended solids should

be no less than 500 mg/l.

5.2.2 Sewage treatment plants tested onboard - the influent may consist of the sewage

generated under normal operational conditions. In any case the average influent concentration of 

total suspended solids should be no less than 500 mg/l.
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5.3 Duration and timing of test

5.3.1 The duration of the test period should be a minimum of 10 days and should be timed to

capture normal operational conditions, taking into account the type of system and the number of

persons and hydraulic loading for which the sewage treatment plant will be type approved. The

test should commence after steady-state conditions have been reached by the sewage treatment

plant under test.

5.4 Loading factors

5.4.1 During the test period the sewage treatment plant should be tested under conditions of

minimum, average and maximum volumetric loadings.

.1 For testing ashore, these loadings will be as laid down in the manufacturer’s 

specifications. Figure 1 shows suggested timings for sampling each loading factor.

.2 For testing onboard, minimum loading will represent that generated by the number 

of persons on the ship when it is alongside in port, and average and maximum

loadings will represent those generated by the number of persons on the ship at

sea and will take account of meal times and watch rotations.

5.4.2 The Administration should undertake to assess the capability of the sewage treatment

plant to produce an effluent in accordance with the standards prescribed by section 4 following 

minimum, average and maximum volumetric loadings. The range of conditions under which the 

effluent standards were met should be recorded on the Certificate of Type Approval. The form of 

the Certificate of Type Approval and appendix is set out in the annex to these Guidelines.

5.5 Sampling methods and frequency

5.5.1 Administrations should ensure that the sewage treatment plant is installed in a manner

which facilitates the collection of samples. Sampling should be carried out in a manner and at a

frequency which is representative of the effluent quality. Figure 1 provides a suggested

frequency for sampling, however, the frequency should take account of the residence time of the

influent in the sewage treatment plant. A minimum of 40 effluent samples should be collected to 

allow a statistical analysis of the testing data (e.g. geometric mean, maximum, minimum, variance).

5.5.2 An influent sample should be taken and analyzed for every effluent sample taken and the

results recorded to ensure compliance with section 4. If possible, additional influent and effluent 

samples should be taken to allow for a margin of error. Samples should be appropriately

preserved prior to analysis particularly if there is to be a significant delay between collection and 

analysis or during times of high ambient temperature.

5.5.3 Any disinfectant residual in samples should be neutralized when the sample is collected to 

prevent unrealistic bacteria kill or chemical oxidation of organic matter by the disinfectant

brought about by artificially extended contact times. Chlorine (if used) concentration and pH

should be measured prior to neutralization.
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Figure 1: Suggested hydraulic loading factors and sampling frequency for testing sewage

treatment plants. May be modified as necessary to take account of characteristics of

individual sewage treatment plants

5.6 Analytical testing of effluent

5.6.1 The Administration should give consideration to the recording of other parameters in

addition to those required (thermotolerant coliforms, total suspended solids, BOD5, COD, pH and 

residual chlorine) with a view to future technological development. Parameters which might be

considered include total solids, volatile solids, settlable solids, volatile suspended solids, turbidity, 

total phosphorus, total organic carbon, total coliforms and faecal streptococci.

5.7 Disinfectant residual

5.7.1 The potential adverse environmental effects of many disinfectant residuals and

by-products, such as those associated with the use of chlorine or its compounds, are well

recognized. It is, therefore, recommended that Administrations encourage the use of ozone,

ultra-violet irradiation or any other disinfectants which minimize adverse environmental effects,

whilst pursuing the thermotolerant coliform standard. When chlorine is used as a disinfectant,

the Administration should be satisfied that the best technical practice is used to keep the

disinfectant residual in the effluent below 0.5 mg/l.

5.8 Scaling considerations

5.8.1 Only full-scale marine sewage treatment plants should be accepted for testing purposes. 

The Administration may certify a range of the manufacturer’s equipment sizes employing the

same principles and technology, but due consideration must be given to limitations on

performance which might arise from scaling up or scaling down. In the case of very large, very

small or unique sewage treatment plants, certification may be based on results of prototype tests. 

Where possible, confirmatory tests should be performed on the final installation of such sewage

treatment plants.
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5.9 Environmental testing of the sewage treatment plant

5.9.1 The Administration should be satisfied that the sewage treatment plant can operate under 

conditions of tilt consistent with internationally acceptable shipboard practice.

5.9.2 Tests for certification should be carried out over the range of temperature and salinity

specified by the manufacturer, and the Administration should be satisfied that such specifications 

are adequate for the conditions under which the equipment must operate.

5.9.3 Control and sensor components should be subjected to environmental testing to verify

their suitability for marine use. The Test Specifications section in part 3 of the annex to

resolution MEPC.107(49) provides guidance in this respect.

5.9.4 Any limitation on the conditions of operation should be recorded on the Certificate.

5.9.5 The Administration should also consider requiring the manufacturer to include in the

operating and maintenance manuals, a list of chemicals and materials suitable for use in the 

operation of the sewage treatment plant.

5.10 Other considerations

5.10.1 The type and model of the sewage treatment plant and the name of the manufacturer

should be noted by means of a durable label firmly affixed directly to the sewage treatment plant. 

This label should include the date of manufacture and any operational or installation limits

considered necessary by the manufacturer or the Administration.

5.10.2 Administrations should examine the manufacturer’s installation, operating and

maintenance manuals for adequacy and completeness. The ship should have on board at all times 

a manual detailing the operational and maintenance procedures for the sewage treatment plant.

5.10.3 Qualifications of testing facilities should be carefully examined by the Administration as 

a prerequisite to their participation in the testing programme. Every attempt should be made to

assure uniformity among the various facilities.

6 RENEWAL AND ADDITIONAL SURVEYS

6.1 Administrations should endeavour to ensure, when conducting renewal or additional 

surveys in accordance with regulations 4.1.2 and 4.1.3 of Annex IV, that the sewage treatment

plant continues to perform in accordance with the conditions outlined in regulation 4.1.1 of

Annex IV.

7 FAMILIARIZATION OF SHIP PERSONNEL IN THE USE OF THE SEWAGE

TREATMENT PLANT

7.1 Recognizing that the appropriate regulations relating to familiarization are contained

within the Ships Safety Management Systems under the International Safety Management Code,

Administrations are reminded that ship staff training should include familiarization in the

operation and maintenance of the sewage treatment plant.
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ANNEX

FORM OF CERTIFICATE OF TYPE APPROVAL

FOR SEWAGE TREATMENT PLANTS AND APPENDIX

NAME OF ADMINISTRATION

CERTIFICATE OF TYPE APPROVAL 

FOR SEWAGE TREATMENT PLANTS

This is to certify that the Sewage Treatment Plant, Type .............................................................................. ,

having a designed hydraulic loading of ............ cubic metres per day, (m3/day), an organic loading

of ............ kg per day Biochemical Oxygen Demand (BOD) and of the design shown on Drawings Nos. ..

manufactured by .............................................................................................................................................

has been examined and satisfactorily tested in accordance with the International Maritime Organization

resolution MEPC.159(55) to meet the operational requirements referred to in regulation 9.1.1 of Annex IV 

of the International Convention for the Prevention of Pollution from Ships, 1973/78 as modified by

resolution MEPC.115(51).

The tests on the sewage treatment plant were carried out

ashore at∗........................................................................................................................................................

onboard at∗......................................................................................................................................................

and completed on ...........................................................................................................................................

The sewage treatment plant was tested and produced an effluent which, on analysis, produces:

(i) a geometric mean of no more than 100 thermotolerant coliforms/100 ml;

(ii) a geometric mean of total suspended solids of 35 mg/l if tested ashore or the maximum total

suspended solids not exceeding 35 plus x mg/l for the ambient water used for flushing purposes if 

tested on board;

(iii) a geometric mean of 5-day Biochemical Oxygen Demand (BOD5) of no more than 25 mg/l;

(iv) a geometric mean of Chemical Oxygen Demand of no more than 125 mg/l;

(v) pH of the effluent is between 6 and 8.5.

The Administration is satisfied that the sewage treatment plant can operate at angles of inclination

of 22.5° in any plane from the normal operating position.

Details of the tests and the results obtained are shown on the Appendix to this Certificate.

A plate or durable label containing data of the manufacturer's name, type and serial numbers, hydraulic

loading and date of manufacture is to be fitted on each sewage treatment plant.

A copy of this Certificate shall be carried on board any ship equipped with the above described sewage

treatment plant.

Official stamp Signed ...........................................................

Administration of .............................................

Dated this.................day...........of..........20....

 

∗ Delete as appropriate.

BADGE

OR

CIPHER
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 APPENDIX TO

 CERTIFICATE OF TYPE APPROVAL FOR SEWAGE TREATMENT PLANTS

Test results and details of tests conducted on samples from the Sewage Treatment Plant in accordance with

resolution MEPC.159(55):

Sewage Treatment Plant, Type .......................................................................................................................................

Manufactured by .............................................................................................................................................................

Organization conducting the test ....................................................................................................................................

Designed hydraulic loading ................................................................................................... m3/day

Designed organic loading ............................................................................................. kg/day BOD

Number of effluent samples tested ....................................................................................................

Number of influent samples tested ....................................................................................................

Raw sewage (influent) quality ..............................................................mg/l Total Suspended Solids

Maximum hydraulic loading ...................................................................................................m

3

/day

Minimum hydraulic loading ...................................................................................................m

3

/day

Average hydraulic loading ......................................................................................................m

3

/day

Geometric Mean of Total

Suspended Solids ........................................................................................................................mg/l

Geometric Mean of the thermotolerant

coliform count ................................................................................................ coliforms/100 ml

Geometric Mean of BOD5 ......................................................................................................... mg/l

Type of disinfectant used ...................................................................................................................

If Chlorine - residual Chlorine:

Maximum ............................................................................................................. mg/l

Minimum .............................................................................................................. mg/l

Geometric Mean ................................................................................................... mg/l

Was the sewage treatment plant tested with:

Fresh Water flushing? .................................................................................... Yes/No∗

Salt Water flushing? ....................................................................................... Yes/No∗

Fresh and Salt Water flushing? ...................................................................... Yes/No∗

Greywater added? ..............................................................Yes – proportion: /No*

Was the sewage treatment plant tested against the environmental conditions specified in section 5.9 of

resolution MEPC.159(55):

Temperature ....................................................................................................Yes/No*

Humidity .........................................................................................................Yes/No*

Inclination .......................................................................................................Yes/No*

Vibration .........................................................................................................Yes/No*

Reliability of Electrical and Electronic Equipment .........................................Yes/No*

Limitations and the conditions of operation are imposed:

Salinity .........................................................................................................................

Temperature .................................................................................................................

Humidity ......................................................................................................................

Inclination .....................................................................................................................

Vibration ......................................................................................................................

Results of other parameters tested .....................................................................................................

Official stamp Signed ...........................................................................................

Administration of ...................................................Dated this .................... day of ..................... 20 ....

***

 

∗ Delete as appropriate.

BADGE

OR

CIPHER