Bsi bs en 14701 1 2006 (2007)

BRITISH STANDARD

Characterization of
sludges — Filtration
properties —
Part 1: Capillary suction time (CST)

The European Standard EN 14701-1:2006 has the status of a
British Standard

ICS 13.030.20

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BS EN
14701-1:2006


BS EN 14701-1:2006

National foreword
This British Standard was published by BSI. It is the UK implementation of
EN 14701-1:2006.
The UK participation in its preparation was entrusted to Technical Committee
EH/5, Sludge characterization.
A list of organizations represented on EH/5 can be obtained on request to its
secretary.
The UK committee has never seen the need to standardize this method at a
European level and, as a consequence, has not been actively involved in the
development of this standard. However, the UK committee is pleased that a
classic British method was selected. The method has long been used as a

valuable operational-control method and is available in existing technical
literature (see reference [1] in the bibliography of this standard). Due to the
difficulty and cost of sending liquid sludge samples (in such a manner that
their properties do not change) to laboratories for international interlaboratory
trials of the performance of this method, interested parties convened at a
workshop to assess the test. Their conclusion was that the results are
operationally defined (e.g. by the filter paper used) and, as the document does
not specify all such operational details, the performance data are not really
applicable outside the context of the workshop. As a result, the members of
EH/5 have no information to offer on the reproducibility of the results.
This publication does not purport to include all the necessary provisions of a
contract. Users are responsible for its correct application.
Compliance with a British Standard cannot confer immunity from
legal obligations.

This British Standard was
published under the authority
of the Standards Policy and
Strategy Committee
on 30 April 2007

© BSI 2007

ISBN 978 0 580 50510 2

Amendments issued since publication
Amd. No.

Date

Comments


EN 14701-1

EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM

March 2006

ICS 13.030.20

English Version

Characterization of sludges - Filtration properties - Part 1:
Capillary suction time (CST)
Caractérisation des boues - Propriétés de filtration - Partie
1: Détermination du temps de succion capillaire

Charakterisierung von Schlämmen Filtrationseigenschaften - Teil 1: Bestimmung der kapillaren
Fließzeit

This European Standard was approved by CEN on 3 February 2006.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.

CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,
Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: rue de Stassart, 36

© 2006 CEN

All rights of exploitation in any form and by any means reserved
worldwide for CEN national Members.

B-1050 Brussels

Ref. No. EN 14701-1:2006: E


EN 14701-1:2006 (E)

Contents
Page
Foreword......................................................................................................................................................................3
1

Scope ..............................................................................................................................................................5

2

Normative references ....................................................................................................................................5

3

Terms and definitions ...................................................................................................................................5

4

Principle..........................................................................................................................................................5

5
5.1
5.2
5.3

Apparatus .......................................................................................................................................................6
Standard apparatus .......................................................................................................................................6
Filter paper .....................................................................................................................................................6
Beakers ...........................................................................................................................................................6

6

Procedure .......................................................................................................................................................6

7

Expression of results ....................................................................................................................................6

8

Precision .........................................................................................................................................................7

9

Test report ......................................................................................................................................................7

Annex A (informative) Simple automatic instrument for determining the filterability of sewage
sludge .............................................................................................................................................................8
Annex B (informative) Relation between CST and the specific resistance to filtration .......................................9
Annex C (informative) Relation between CST and solids content .......................................................................10
Annex D (informative) Table of dynamic viscosity ................................................................................................11
Annex E (informative) Results of validation trials .................................................................................................12
Bibliography ..............................................................................................................................................................15

2


EN 14701-1:2006 (E)

Foreword
This document (EN 14701-1:2006) has been prepared by Technical
“Characterization of sludges”, the secretariat of which is held by AFNOR.

Committee

CEN/TC 308

This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by September 2006, and conflicting national standards shall be

withdrawn at the latest by September 2006.
Other parts of this European Standard are:


Part 2: Determination of the specific resistance to filtration;



Part 3: Determination of the compressibility.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.

3


EN 14701-1:2006 (E)

Introduction
The capillary suction time (CST) is a fast and simple way to evaluate the sludge dewaterability by filtration.
This method gives no information on the obtainable solids content in a dewatering process.
The measurement of CST should also make possible the evaluation, although only qualitatively, of other
sludge characteristics, including dewaterability by centrifugation.

4

EN 14701-1:2006 (E)

1

Scope

This document specifies a method for the determination of the capillary suction time. This document is
applicable to sludge and sludge suspensions from:


storm water handling;



urban wastewater collecting systems;



urban wastewater treatment plants;



treating industrial wastewater similar to urban wastewater (as defined in Directive 91/271/EEC);



water supply treatment plants.

This method is also applicable to sludge suspensions from other origin.

2

Normative references

The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 12832:1999, Characterization of sludges — Utilization and disposal of sludges — Vocabulary

3

Terms and definitions

For the purposes of this document, the terms and definitions given in EN 12832:1999 and the following apply.
3.1
filterability
property indicating the amenability of a sludge to be dewatered by a filtration process
3.2
capillary suction time (CST)
measurement of the time for a wetting front in a filter paper to travel between two fixed points

4

Principle

The principle of the method is that dewatering is achieved by the suction applied to the sludge by the capillary
action of an absorbent filter paper.
A part of the absorbent paper area is exposed to the sludge, while the remaining area is free for absorbing the
filtrate. The rate at which the paper becomes wetted with filtrate is a measure correlated to sludge
dewaterability: it is measured by the time necessary for the filtrate to cover the space between two probes

which detect the advancement of the liquid front on the paper (Annex A informative).
The CST measurements are strongly affected by many factors, such as properties of the paper, surface
tension, temperature, suspended solids concentration, so they give only qualitative and comparative
evaluations which can be correlated to the specific resistance to filtration (prEN 14701-2) for a given type of
sludge (Annex B informative).

5


EN 14701-1:2006 (E)

5

Apparatus

5.1

Standard apparatus

Device consisting of:
a)

filtration apparatus, including base for supporting the absorbent paper, sludge reservoir and probes;

b)

automatic time recording unit, including amplifier and digital electric stop-clock recording in seconds (see
Annex A informative).

5.2

Filter paper

Paper suitable for chromatography with grain parallel with the longer side (for instance, Whatman n. 17 or
Wickam CST Papers 7 cm x 9 cm code 8680841) ).
NOTE

5.3

For comparable results the same filter paper type should be used.

Beakers

Conventional beakers, 50 ml minimum.

6

Procedure

6.1

Place a filter paper in the apparatus. The filter paper shall always be placed with the same side up.

6.2

Mix the sludge to be tested by pouring it off from a beaker to another for 4 times.

6.3 Pour immediately the mixed sludge into the reservoir until it is completely full. Great attention shall be
paid in performing measurements immediately after the sludge mixing to avoid any result unreliability due to
sludge settling into the beaker (especially for conditioned sludges).

6.4

When the clock stops, register the time which has been automatically measured.

6.5

Repeat steps 6.1 to 6.4 in order to have at least 3 significant values, as stated in Clause 7.

7

Expression of results

The CST value is given by arithmetically averaging the measured values. If one or more values differ of more
than 20% from the calculated mean value, they must not be considered and the average shall be calculated
again with remaining values: in any case valid values shall be, at least, 3.
The influence of the temperature may be evaluated through the relationship:
CST1 = (µ1/µ2) CST2
where
µ1 and µ2 are the dynamic viscosities of water at the two considered temperatures.

1) This information is given for the convenience of users of this document and does not constitute an endorsement by
CEN of this product. Equivalent products may be used if they can be shown to lead to the same results.

6

(1)


EN 14701-1:2006 (E)

If the room temperature is between 12 °C and 30 °C, the influence of the temperature can be neglected.
Water viscosities as a function of temperature are reported in the table in Annex D (informative).

8

Precision

Results of validation trials are summarized in Annex E (informative).
The repeatability standard deviation ranges from 0,411 s (3,6 %) for activated/thickened sewage sludge, to
0,463 s (4,4 %) for activated sewage sludge, to 1,560 s (3,4 %) for waterworks sludge, and to 7,856 s (5,3 %)
for digested sewage sludge.
Mean value is 2,573 s (4,9 %). Minimum precision is 5,3 %.
The reproducibility standard deviation ranges from 0,643 s (5,6 %) for activated/thickened sewage sludge, to
1,043 s (9,9 %) for activated sewage sludge, to 2,023 s (4,4 %) for waterworks sludge, and to 20,01 s
(14,0 %) for digested sewage sludge.
Mean value is 5,929 s (11,3 %). Minimum precision is 14,0 %.

9

Test report

The test report shall contain the following information:
a)

reference to this document;

b)

all information necessary for the complete identification of the sludge sample;

c)

details of sample pre-treatment, if carried out;

d)

information about the size of the reservoir used;

e)

results of the determination according to Clause 7;

f)

any detail not specified in this document or which are optional and any other factor which may have
affected the results.

7


EN 14701-1:2006 (E)

Annex A
(informative)
Simple automatic instrument for determining the filterability of sewage
sludge

The CST apparatus by Triton as described in [1] consists of a base supporting a rectangular piece of
7 cm x 9 cm of absorbent filter paper and a block holding probes above it; in the centre of the upper block
(which stands clear of the paper by resting on five stainless steel supports) there is a circular hole in which a

stainless steel reservoir (18 mm bore/25 mm high or 10 mm bore/50 mm high) loosely fit. On the under side of
the upper block there are two engraved circles, of 3,2 cm and 4,5 cm in diameter, concentric with the
reservoir; two of the supports are specially machined probes in line with the first concentric circle and one with
the second circle. Both probes are electrically connected to the recording unit.
For this apparatus, the CST values of raw sewage sludge generally range 60 s to 300 s, using the 18 mm
reservoir and the kind of papers reported before (see 5.2).
The 18 mm reservoir is more suitable for low-dewaterable sludges: significant values range 10 s to 900 s.
The use of the 10 mm reservoir is necessary for easily filterable sludges: significant values range 20 s to
1 200 s.
For high filterable sludges, having very low CST, 2 overlapped filter papers could be used.
The 10 mm reservoir can be difficult to fill, especially with thick sludges. The 18 mm reservoir has been found
to be suitable for use with most sewage sludges, but other dimensions may be more suitable for other types of
suspension.

8


EN 14701-1:2006 (E)

Annex B
(informative)
Relation between CST and the specific resistance to filtration

The variation of CST with specific resistance to filtration for 18 mm and 10 mm diameter reservoirs for sewage
sludges is reported in Baskerville and Gale (1968) [1].
The relationship between CST and the specific resistance, measured through the Buchner procedure, was
also studied by Smollen (1986) [2], and Spinosa et al. (1991) [3].

9

EN 14701-1:2006 (E)

Annex C
(informative)
Relation between CST and solids content

The variation of CST with solids content is discussed in Vesilind (1988) [4].

10


EN 14701-1:2006 (E)

Annex D
(informative)
Table of dynamic viscosity
Table D.1 — Dynamic viscosity of water from 0 °C to 40 °C

-3

T
(°C)

Viscosity
-3
(10 Pa · s)

T
(°C)

Viscosity
-3
(10 Pa · s)

0

1,7921

26

0,8737

1

1,7313

27

0,8545

2

1,6728

28

0,8360

3

1,6191

29

0,8180

4

1,5674

30

0,8007

5

1,5188

31

0,7840

6

1,4728

32

0,7679

7

1,4284

33

0,7523

8

1,3860

34

0,7371

9

1,3462

35

0,7225

10

1,3077

36

0,7085

11

1,2713

37

0,6947

12

1.2663

38

0,6814

13

1,2028

39

0,6685

14

1,1709

40

0,6560

15

1,1404

16

1,1111

17

1,0828

18

1,0559

19

1,0299

20

1,0050

20,2

1,0000

21

0,9810

22

0,9579

23

0,9358

24

0,9142

25

0,8937

-2

NOTE 1

10 Pa · s = 10 g/cm · s = 1 centipoise.

NOTE 2

It is assumed that filtrate viscosity is equal to water viscosity.

11


EN 14701-1:2006 (E)

Annex E
(informative)
Results of validation trials

Because the circulation of samples of real sludge high in organic content is not possible due to problems
associated to changes in their physical characteristics during handling and transportation, the “Modified
Round Robin Tests” procedure, developed by TG 3 of CEN/TC 308/WG 1, and reported in doc CEN/TC 308
N 822, was followed. With this procedure, the round robin tests are carried out through “circulation of
analysts”, i. e. operators coming from the laboratories participating to the exercise meet in a common location,
close to the place where samples are collected, and work there on same samples, each using own apparatus.
Validation trials were carried out at LUA, Düsseldorf, on 28 September 2004.
Trials involved a total of 11 Operators from the following 9 Laboratories/Institutions in 3 Countries: ARPA
Puglia (Bari, I), CEMAGREF (Montaldre, F), CNR-IRSA (Bari, I), Comm. Env. Emerg. in Puglia Region (Bari,
I), DIN (Berlin, D), LUA-NRW (Düsseldorf, D), STUA (Lippstadt, D), UBA (Berlin, D), University of Lecce (I).
The following 4 different sludge types were tested:


Sample 1:

Sewage sludge – activated
Solids concentration (g/l): 2,81



Sample 2:

Sewage sludge – digested
Dry residue (%): 2,22



Sample 3:

Waterworks sludge
Dry residue (%): 3,62



Sample 4:

Sewage sludge – activated/thickened
Dry residue (%): 0,71

(analyses for measuring solids concentration and/or dry residue were carried out at the Chemical-biological
Laboratory of Landeshauptstadt in Düsseldorf)
Test results have been statistically analysed for the evaluation of precision according to ISO 5725-2. In
particular, the repeatability standard deviation sr (for cells containing more than one figure), and the
reproducibility standard deviation sR were calculated.
The tables of results which follow contain the following symbols:

12

i

is the operator number;

j

is the level (sample) number;

k

(= 1, 2, ..., n) is the test number;

n

are the replicates;

nij

is the number of test results in the cell for operator (i) at level (j);

p

is the total number of operators (i) (i = 1, 2, …, p);

q

are the total testing levels (batches of materials) (j) (j = 1, 2, …, q);


EN 14701-1:2006 (E)

sr

is the repeatability standard deviation;

sR

is the reproducibility standard deviation;

ūij

is the cell means;

y

is the test result;

yijk is the result of the test number (k) for operator (i) at level/sample (j).
Table E.1 — Readings
Operator
number (i)

Level (j)
Sample 1

Level
Sample 3

Level
Sample 4 (= q)

values
(yijk)

mean
(ūij)

values
(yijk)

mean
(ūij)

values
(yijk)

mean
(ūij)

values
(yijk)

mean
(ūij)

s

s

s

s

s

s

s

s

1

10,1
10,8
11,0

10,6

126,5
131,3
141,2

133,0

48,4
45,5
45,3

46,4

11,7
11,3
11,4

11,5

2

10,4
10,3
11,3

10,7

142,5
153,9
145,9

147,4

40,5
43,8
43,1

42,5

11,4
11,3
12,3

11,7

3

11,3
11,3
11,5

11,4

132,3
146,7
152,2

143,7

42,4
44,7
45,2

44,1

11,9
11,8
12,3

12,0

4

11,3
11,5
11,4

11,4

137,3
147,8
148,9

144,7

45,8
45,6
44,7

45,4

11,9
11,8
12,4

12,1

5

8,7
9,3
9,5

9,2

117,6
128,0
131,4

125,7

46,1
44,7
46,1

45,6

11,5
11,3
11,4

11,4

6

10,6
11,6
10,8

11,0

159,1

144,5
157,9

153,8

47,7
48,7
43,8

46,7

11,1
11,7
12,3

11,7

7

11,1
11,6
11,5

11,4

180,0
175,7
163,9

173,2a

47,5
43,9
45,0

45,5

11,3
11,7
11,9

11,6

8

9,1
9,0
8,9

9,0

120,3
112,5
113,0

115,3

48,9
47,9
47,9

48,2

10,4
10,4
10,5

10,4

9

11,0
9,8
10,6

10,5

119,9
121,0
126,5

122,5

48,0
46,3
44,5

46,3

12,1

10,7
11,7

11,5

10 (= p)

9,3
9,2
9,6

9,4

152,9
176,5
172,9

167,4a

45,8
46,4
48,2

46,8

11,0
10,2
10,5

10,6

Mean at level (j)
a

Level
Sample 2

10,5

142,7

45,8

11,4

These results show the possible influence of which side of filter paper is placed up.

13


EN 14701-1:2006 (E)

NOTE
CST apparatuses used for tests were of the standard Type 304 produced by Triton Electronics, Dunmow,
Essex (UK).

Table E.2 — Repeatability standard deviation, sr
Sample

sr

sr

s

%

1) Sewage sludge, activated

0,463

4,4

2) Sewage sludge, digested

7,856

5,3

3) Waterworks sludge

1,560

3,4

4) Sewage sludge, activated/thickened

0,411

3,6

Mean value

2,573

4,9

Table E.3 — Reproducibility standard deviation, sR
Sample

14

sR

sR

s

%

1) Sewage sludge, activated

1,043

9,9

2) Sewage sludge, digested

20,01

14,0

3) Waterworks sludge

2,023

4,4

4) Sewage sludge, activated/thickened

0,643

5,6

Mean value

5,929

11,3


EN 14701-1:2006 (E)

Bibliography

[1]

Baskerville R.C. and Gale R.S. (1968), A Simple Automatic Instrument for Determining the Filtrability
of Sewage Sludge. J. of The Inst. Of Water Poll. Control, vol. 67, n. 2, 233-241.

[2]

Smollen M. (1986), Dewaterability of municipal sludges 1: A comparative study of specific resistance
to filtration and capillary suction time as dewaterability parameters. Water SA, vol. 12, n. 3, 127-132.

[3]

Spinosa L., Lotito V. and Infusino E. (1991), Relationships between sludge rheology and dewaterability
parameters. Fluid/Particle Sep. J., vol. 4, n. 3, 176-179.

[4]

Vesilind P.A. (1988). Capillary suction time as a fundamental measure of sludge dewaterability,
Journal WPCF, vol. 60, n. 2, 215-220.

[5]

ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic
method for the determination of repeatability and reproducibility of a standard measurement method

[6]

prEN 14701-2, Characterization of sludges — Filtration properties — Part 2: Determination of the
specific resistance to filtration

15


BS EN
14701-1:2006

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