ASTM D4189 - 23

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Designation: D4189 −23
Standard Test Method for
Silt Density Index (SDI) of Water
1
This standard is issued under the ﬁxed designation D4189; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the determination of the silt
density index (SDI) of water. This test method can be used to
indicate the quantity of particulate matter in water and is
applicable to relatively low (<1.0 NTU) turbidity waters such
as well water, ﬁltered water, or clariﬁed effluent samples. Since
the size, shape, and nature of particulate matter in water may
vary, this test method is not an absolute measurement of the
quantity of particulate matter.
1.2 This test method is not applicable for reagent grade
water Types I, II, and III of Speciﬁcation D1193, or effluents
from most reverse osmosis and ultraﬁltration systems.
1.3 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
2
D1129 Terminology Relating to Water
D1193 Speciﬁcation for Reagent Water
D3370 Practices for Sampling Water from Flowing Process
Streams
E1 Speciﬁcation for ASTM Liquid-in-Glass Thermometers
3. Terminology
3.1 Deﬁnitions—For deﬁnitions of terms used in this test
method, refer to Terminology D1129.
3.2 Deﬁnitions:
3.2.1 silt density index (SDI), n—an index calculated from
the rate of plugging of a 0.45 µm membrane ﬁlter.
4. Summary of Test Method
4.1 Water is passed through a 0.45 µm membrane ﬁlter at a
constant applied gauge pressure of 207 kPa (30 psi), and the
rate of plugging of the ﬁlter is measured.
4.2 The SDI is calculated from the rate of plugging.
5. Signiﬁcance and Use
5.1 The SDI can serve as a useful indication of the quantity
of particulate matter in water.
5.2 The SDI can be used to determine effectiveness of
various processes such as ﬁltration or clariﬁcation used to
remove particulate matter.
5.3 The SDI has been empirically correlated with the
fouling tendency of some water treatment equipment such as
reverse osmosis devices.
5.4 The SDI may vary as a function of water temperature,
and values obtained at different temperatures may not neces-
sarily be comparable.
5.5 The SDI can vary with the membrane ﬁlter manufac-
turer. Thus, SDI values obtained with ﬁlters from different
membrane manufacturers might not be comparable.
6. Apparatus
6.1 SDI Assembly, as schematically described in Fig. 1. All
wetted parts should be made of high-quality stainless steel or
plastic to prevent contamination by corrosion products. Do not
use reactive materials such as carbon steel or cast iron. Suitable
ﬁlter holders, designed to withstand an operating gauge pres-
sure of 350 kPa (50 psi) can be obtained from suppliers of
membrane ﬁlters.
6.2 Membrane Filter:
6.2.1 Membrane—White hydrophilic, mixed cellulose ni-
trate (50 % to 75 %) and cellulose acetate (MCE).
6.2.2 Mean Pore Size—0.45 µm.
1
This test method is under the jurisdiction of ASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.08 on Membranes and Ion
Exchange Materials.
Current edition approved Nov. 1, 2023. Published November 2023. Originally
approved in 1982. Last previous edition approved in 2014 as D4189 – 07 (2014)
which was withdrawn July 2023 and reinstated in November 2023. DOI: 10.1520/
D4189-23.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
1

6.2.3 Diameter—47 mm nominal, plain.
6.2.4 Thickness—115 µm to 180 µm.
6.2.5 Pure Water Flow Time—25 s to 50 s ⁄500 mL.
6.2.6 Pressure—91.4 kPa to 94.7 kPa (13.3 psi to 13.8 psi).
6.2.7 Bubble Point—179 kPa to 248 kPa (26.0 psi to
36.0 psi).
6.2.8 Use only ﬁlters that are packaged in the same orien-
tation.
6.3 Graduated Cylinder, 500 mL capacity.
6.4 Stopwatch, graduated in hundredths of a minute.
6.5 Thermometer, liquid-in-glass, suitable for measuring the
temperature of the water sample; capable of being read to
within 61 °C and conforming to the requirements as pre-
scribed in Speciﬁcation E1.
7. Procedure
7.1 Assemble the apparatus as shown in Fig. 1 and set the
pressure regulator at 207 kPa (30 psi).
7.2 Before installing the membrane ﬁlter, ﬂush the water to
be tested through the apparatus to remove entrained contami-
nants. For sampling, follow the procedure given in Practices
D3370. Discrete samples can be used with appropriate pres-
surizing apparatus such as a booster pump to obtain a feed
supply gauge pressure of >276 kPa (>40 psi).
7.3 Measure the temperature of the water.
7.4 Open the membrane ﬁlter holder and place a 0.45 µm
membrane ﬁlter (47 mm in diameter) on the support plate of
the holder. Some ﬁlter holders include a foam support pad,
which should be used. Place the ﬁlter grid side up. Handle the
membrane ﬁlter only with dull tweezers to avoid puncturing.
Avoid touching the membrane ﬁlter with the ﬁngers.
NOTE 1—Other membrane ﬁlter sizes, that is, 25 mm or 90 mm
diameter, can be used.
NOTE 2—Record the manufacturer of the membrane ﬁlter and the
manufacturer’s identiﬁcation for the membrane ﬁlter.
7.5 Make sure the O-ring is in good condition and properly
placed. Replace the top half of the ﬁlter holder and close
loosely.
7.6 Bleed out trapped air by cracking the ball valve. Close
the valve and tighten the ﬁlter holder.
7.7 Open the ball valve. Simultaneously, using a stopwatch,
begin measuring the time required for the ﬂow of 500 mL.
Adjust the pressure regulator as necessary to maintain a
constant feed pressure of 207 kPa 67 kPa (30 psi 61 psi)
throughout the test. Record the time (t
i
). Leave the valve open
for continued ﬂow.
NOTE 3—Time (t
i
) to collect 500 mL should be within 610 % of the
time to collect 500 mL using nonplugging reference water at the same
water temperature. The nonplugging reference water can be obtained by
ﬁltering distilled water through a 0.2 µm pore size membrane ﬁlter.
NOTE 4—If t
i
is less than 90 % of the nonplugging time, the ﬁlter may
be cracked and a new ﬁlter should be used. If t
i
is more than 110 % of the
nonplugging time, then a smaller sample size, that is, 250 mL or 100 mL
should be used.
NOTE 5—The 500 mL sample size is based on a 47 mm diameter ﬁlter.
If a different ﬁlter size is used, adjust the sample size in direct proportion
to the ﬁlter area.
7.8 Measure and record the times to collect additional
500 mL (Note 6) volumes of sample, starting the collection at
5 min, 10 min, and 15 min of total elapsed ﬂow time. Measure
the water temperature as each sample is collected (Note 7).
NOTE 6—If the initial size was not 500 mL, use the same sample size
as used in 7.7.
NOTE 7—To obtain accurate results, the water temperature must remain
constant (61 °C) throughout the test. This is because ﬂow rate changes by
about 3 % ⁄°C.
7.9 After completion of the test, the membrane ﬁlter may be
retained for future reference.
8. Calculation
8.1 Calculate the silt density index (SDI
T
) as follows:
SDI
T
5%P
30
T5
F
12t
i
t
f
G
100
T
where:
% P
30
= percent pluggage at 207 kPa (30 psi) feed pressure,
T= total elapsed ﬂow time, min (usually 15 min, see
Note 8),
t
i
= initial time required to collect 500 mL of sample, s,
and
tf = time required to collect 500 mL of sample after test
time T(usually 15 min, see Note 8), s.
NOTE 8—For this test method, best results are obtained when % P
30
is
≤75 %. If % P
30
exceeds this value, repeat the test using a shorter time for
T; that is, 5-min or 10-min measurements in 7.8. If % P
30
exceeds 75 %
after 5 min, the rate of plugging is too high for this method to be reliable.
9. Report
9.1 Report the following information:
9.1.1 The SDI, with a subscript indicating the total elapsed
ﬂow time (T) in minutes,
9.1.2 The water temperature before and after the test, and
FIG. 1 Apparatus for Measuring the Silt Density Index
D4189 − 23
2

9.1.3 The manufacturer of the 0.45 µm membrane ﬁlter used

for the test, as well as the manufacturer’s identiﬁcation for the

membrane ﬁlter.

10. Precision and Bias

10.1 The interlaboratory test was performed by nine opera-

tors from ﬁve laboratories using test waters of their choice,

whose SDI values varied from 0.4 to 15. Waters used included

RO permeate, deionized water, tap water, and undeﬁned

process water. The pooled single operator precision is 0.43.

10.2 Only pooled single operator precision was determined

for this test method. The test method is very sensitive to both

quantity and size of suspended particles, which contribute to

the plugging of the membrane ﬁlter. Maintenance of the

integrity of the samples cannot be guaranteed through prepa-

ration of the bulk mix, subsampling for testing, shipping, and

holding. Moreover, approximately 5 gal of sample are required

for each SDI test run. Thus, if large stock solutions exhibiting

different SDI values could be prepared and if representative

30-gal to 55-gal subsamples could be drawn, shipping two or

three of these samples to each of six or more laboratories for

full-scale testing was not considered to be practical.

10.3 The bias of this test method cannot be determined

because the test method is based upon waters of choice, which

may differ with each source.

10.4 It is the user’s responsibility to ensure the validity of

this test method for waters of untested matrices.

11. Keywords

11.1 reverse osmosis; RO; SDI; silt density index

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D4189 − 23

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摘要：

ASTM D4189 - 23 是 ASTM International 发布的最新版本标准，专门用于通过测定水的淤泥密度指数（SDI）来评估水中有机物、胶体及颗粒物对反渗透（RO）和纳滤（NF）膜系统污堵的潜力。该标准提供统一的测试方法，通过规定压力、过滤时间及膜孔径（0.45微米），测量水样在标准条件下堵塞膜片的速度，从而量化水中悬浮颗粒的污染倾向。SDI值越低，表示水质越清洁，对膜系统的运行风险越小。本标准广泛应用于海水淡化、工业水处理、电力、制药及半导体等行业，是膜系统设计、运行维护和水

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