A1110D T1474b

NBS

publications

NBSIR 81-2307

Dependence of Model Waste Solid

Transport Characteristics in

Geometry, Mass and Pipe System

Parameters

Dr. J. A. Swaffield

National Engineering Laboratory

Center for Building Technology

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

Drainage Research Group

Department of Building Technology

Brunei University

Uxbridge

U.K.

July 1981

Drainage Solid

and

-QC100

. Ub>6

)EPARTMENT OF COMMERCE

81-2307

MAL BUREAU OF STANDARDS

NATtOMAL BUBKA l OF FTAVDAKU8

LIBRA *T

NBSIR 81-2307

DEPENDENCE OF MODEL WASTE SOLID

TRANSPORT CHARACTERISTICS IN

DRAINAGE SYSTEMS ON SOLID

GEOMETRY, MASS AND PIPE SYSTEM

PARAMETERS

JUL * 0 1981

nu cue -

Dr. J. A. Swaffield

National Engineering Laboratory

Center for Building Technology

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

and

Drainage Research Group

Department of Building Technology

Brunei University

Uxbridge

U.K.

July 1981

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
X, V

- V? • .fr. V

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ABSTRACT

Test results are presented for the transport characteristics of an extensive

range of geometrically similar model solids in a 100 mm diameter UPVC drain

pipe. Model solids were based on commercially available sanitary towels

(napkins) discharged into the pipe system via a series of U.K. standard water

closet types.

Following a data fit analysis, relationships are presented linking solid

transport characteristics to solid, pipe and water closet (w.c.) parameters.

These relationships, linked to observation of installed hospital drainage

systems in the U.K., will allow laboratory test methods to be utilized in

predicting the effect of design changes on system performance.

iii
PREFACE

This report is one of a group documenting National Bureau of Standards (NBS)

research and analysis efforts in developing water conservation test methods,

analysis, economics, and strategies for implementation and acceptance. This

work is sponsored by the Department of Housing and Urban Development /Of f ice of

Policy Development and Research, Division of Energy Building Technology and

Standards, under HUD Interagency Agreement H48-78.

The report was prepared by Dr. J. A. Swaffield, guest research worker at

NBS-Stevens Institute of Technology from Brunei University, U.K.

The test results included in this report were compiled from published work

from the Drainage Research Group, Department of Building Technology, Brunei

University, U.K.

The test programs were funded by the U.K. Department of Health, the U.K.

Association of Sanitary Protection Manufacturers and Brunei University.

iv
Table of Contents

Page

ABSTRACT Ill

PREFACE lv

NOTATION vll

1. INTRODUCTION 1

2. BACKGROUND TO LABORATORY TEST PROGRAM 2

3. ANALYSIS OF THE VARIABLES GOVERNING SOLID TRANSPORT 4

4. EXPERIMENTAL AND MEASUREMENT TECHNIQUES 6

5. PRESENTATION OF RESULTS 7

6. DISCUSSION OF RESULTS 8

7. CONCLUSIONS 11

8. REFERENCES 12

Appendix 1. Reprint of Reference 5, Flushability Criteria Development

for Sanitary Towels, Diapers, and Tampons 18

v
List of Tables

Page

Table 1. Summary of Solid Geometry and Mass Measurements Together

With System Parameters and Test Results 13

List of Figures

Page

Figure 1. Dependance of solid velocity on / (L/G) 14

Figure 2. Relationship between extrapolated solid velocity at pipe

entry and pipe and solid parameters 15

Figure 3. Relationship between solid deceleration with respect to

pipe distance traversed and pipe and solid parameters 16

Figure 4. Predicted solid deposition position based on zero velocity .. 17
NOTATION

Ci Extrapolated solid velocity at pipe entry

C2 Solid deceleration with respect to distance

D Pipe diameter

F Total flush volume available

Fg Volume discharged behind solid

G Pipe slope

g Accleration due to gravity

Ki Non dimensional solid velocity term at pipe entry

K2 Non dimensional solid deceleration with respect to L/D

K Constant in calibration equation

L Pipe length traversed from entry

H Solid length

ms Solid mass (saturated)

q Index in calibration equation

t Solid thickness

V* Non dimensional solid velocity term

v Solid velocity at point L

w Solid width

x Characteristic lengths

y Characteristic lengths

Water density

UPVC Unplasticized polyvinyl chloride (pipe material)

vii

1

INTRODUCTION

Little use has been made in the past of laboratory based studies to model the

waste solid transport characteristics of building drainage systems. This has

been due to a lack of understanding of the transport mechanisms involved and

the difficulty of producing a suitable model solid for laboratory usage. The

test solids utilized for water closet (w.c.) evaluation and type acceptance

tests cannot be used to model system transport. The solids commonly used, for

example, the European 50 x 20 mm diameter ball test, the British single 43 mm

diameter ball test and the Dutch sponge tests, have been designed to reproduce

w.c. discharge criteria and would not be representative of system transport.

Early transport tests by the Japanese utilizing PVC sponge solids were subject

to problems arising from the specific gravity variations of the models that

appeared to be dependent on the solid soaking time prior to usage.

A number of criteria need to be satisfied if a laboratory test solid is to be

successful in modeling system transport mechanisms:

1. The solid must be cheap and available in bulk to repeatable dimensions

and mass. Reusable solids are discounted on the grounds that water

soaking time may become an important factor, as may deterioration of the

model surface, although impermeable solids with sealed voids could be

reused.

2. A sufficient range of geometrically similar solids meeting criterion 1 above should be available if the full range of system loading is to be

represented in the laboratory.

3. The solid must be acceptable in the laboratory environment.

4. The transport characteristics of each solid must be documented in terms

of its geometry and mass, or be capable of being interpolated from tests on similar solids.

5. The transport characteristics of installed systems should have been

monitored to present a range of typical waste transport characteristics.

The range of system loading would then be modeled by choosing the appropriate model solids from the documented transport characteristics mentioned in criterion 4 above.

If these points can be met then laboratory tests may be utilized to assess the

effect of design changes on the performance of the system. Such modifications

as reduced water usage or reductions in pipe slope or diameter could be evaluated. Similarly, the effect of introducing new w.c. designs having lower water

usage could be evaluated.

This brief report summarizes a series of laboratory investigations designed to

determine the dependence of solid transport on pipe geometry, water usage and

solid dimensions and mass.

1
2 BACKGROUND TO THE LABORATORY TEST PROGRAM

During an extensive laboratory test program undertaken at Brunei University,

U.K., as a component of a hospital drainage system study for the U.K. Department

of Health, it was apparent that the transport characteristics of a maternity

pad solid in a 100 mm diameter UPVC, glass or cast iron waste pipe could be

expressed in the form

V = c

x - c

2

1 /lTcF ( 1 )

where

V = solid velocity at distance L from pipe entry

G = pipe gradient

Ci = extrapolated solid velocity at L=0 from equation (1), the units of this

constant being m/s.

C 2 = solid deceleration coefficient with respect to distance L, the units of

this constant being

These results are represented in figure 1 and are more fully explained in [1,2],

together with an analysis of the flow mechanisms observed.

The model solid employed was a commercially available maternity pad, or heavy

duty sanitary napkin, dimensions 270 mm x 60 mm x 20 mm, water saturated weight

250 gms, currently supplied to U.K. hospitals, an acceptable, cheap model

solid for the very large number of tests carried out.

Observation of fecal and other waste materials in hospital installed drainage

systems also displayed this solid transport characteristic equation, the values

of Ci and C2 varying with the solid type [3]. This reproduction in practice of

the observed laboratory results indicated the possibility of representing

typical system loading by a suitable choice of model solids of a type similar

to the maternity pad. It was decided to undertake an analysis of the factors

determining the values of C^ and C 2 , this survey to include both pipe size, w.c. flush volume and solid geometry and mass parameters.

The maternity pad solid was also employed for a series of tests designed to

illustrate the effect of pipe diameter and w.c. flush volume, the test results

confirming the relationships illustrated in figure 1, but displaying a more

rapid deceleration as flush volume decreased [4].

The extension of this program to geometry and mass effects was made possible

by a request from the U.K. Association of Sanitary Protection Manufacturers for

assistance in developing a flushability criterion for w.c. disposal of sanitary

towels (napkins), diapers and tampons. Appendix 1 reproduces a recent paper

[5] describing this test program.

2
At the culmination of the test programs, a total of some 30 solid geometry/mass

combinations had been tested with corresponding data for 100 mm and 75 mm pipe

diameters and w.c. flush volumes ranging from the U.K. standard of 9.1 liters

down to 4 liters. This body of data was considered sufficient to test the

dimensional analysis based on the solid/system parameters presented below.

3
3. ANALYSIS OF THE VARIABLES GOVERNING SOLID TRANSPORT

As shown by figure 1 and equation (1) the velocity profile against distance

travelled along a waste pipe may be expressed as:

v = c

l - c

2

/l7g

Non dimensionally this may be expressed as

_V_ = v^x

v'y/gx /L/yG ( 2 )

where

g

= acceleration due to gravity

x,y = suitable characteristic lengths

Equation (2) may be written as

V* - K

x - K2

v'iTyG (3)

where

V* = is a non dimensional group having the same form as Froude Number.

The terms K^, K2 may be expressed as functions of the solid and pipe system as follows:

Kl> k2 = f l

fc » w » Ps» D * F > fB» Pw> ( 4 )

where

i = solid length

w = solid width

t = solid thickness

p s = solid density

4
D = pipe diameter

F = total flush volume

Fg = flush discharge behind the solid

= water density

Excluded from (4) is the pipe roughness effect as the bulk of the data available

refers to UPVC pipe systems.

Thus, the nine variables involved yield six dimensionless groups:

The solid width w may be used as the length characteristic x in equation (2)

while the pipe diameter D would be appropriate as the y length term.

Approved test methodology would require the study of the dependence of K]_ t K2 on each group in turn, requiring the other four to be held constant.

Unfortunately, this was not possible as the model geometry terms were dictated by human anatomy and fashion. Similarly, the mass terms were dictated

by physiology. Within these limits the various contributing manufacturers

produce a range of towels as shown by table 1.

A general equation of the form

p Jlwt w t F s (5)

D

’ D’ f

b’

n m p ilwt (__

e„FB

)

( 6 )

was postulated and data fit tested by means of a computer program run on the

NBS Center for Building Technology’s Perkin Elmer 732 Computer. The results

of the data fit trials are discussed below.
4. EXPERIMENTAL AND MEASUREMENT TECHNIQUES

Appendix 1 describes the test installation employed for the flushability

criteria development work at Brunei University. The rig consisted of 14 m

length of 100 mm diameter transparent UPVC waste pipe set at a gradient of

1/80. Solid velocity was recorded over six 300 mm lengths at 2 m intervals

along the test pipe by means of photoelectric cells and electronic timers.

The water volume vs. time profile at discharge from the 14 m pipe length was recorded via a linear displacement transducer driven by a surface float in the

collection tank. Sensitivity was sufficient to record solid entry into the

collection tank, yielding the relative volumes of water discharged ahead and

behind the solid.

This basic system was also employed in the variation of flush volume and pipe

diameter tests as well as being based on the original test system used for the

maternity pad investigation represented by figure 1.

Solid dimensions were recorded dry by means of vernier caliper gauge, the

average of 20 measurements being taken.

Similarly, dry weight values were based on the average of 20 measurements from

a random sample chosen from at least 100 solids. This avoided batch inconsistencies in manufacture.

Saturated weight values were recorded based on an initial study for each

product to determine time to achieve full saturation. In most cases saturated

weight became a constant at about 30 seconds soaking time.

The effect of varying degrees of presoaking administered to each product is

described in appendix 1. For the purposes of this study, this effect is

included in the variation in flush water volume discharged behind the solid.

6
5. PRESENTATION OF RESULTS

Table 1 summarizes the test measurements described above for all the products

tested for the Association of Sanitary Protection Manufacturers as well as the Department of Health maternity pad tests and the Brunei University funded

reduced water volume and pipe size study.

The derived relationships linking the transport characteristics, and K2 are presented in figures 2 and 3. It will be noted that the groups:

w , t

D D

have been rewritten as:

wt and

ttD2 /4 D3

for the purpose of presenting these relationships. Although this is not strictly

necessary, it was felt that this term led to a practical blockage factor that

could have a physical interpretation.

It will be seen from table 1 that all products tested are referred to by a code

AB. In this code A refers to the manufacturer and B is a number allocated to

each product tested. Code 34 indicates the maternity pad solid.

7
6. DISCUSSION OF RESULTS

A general format for a possible relationship based on the analysis presented

may be represented by

i j k m m n «i. k2 * (p q) (f-) ( D D D

Z

where ms = p g £tw - the solid mass.

Due to an inability to deal with each group in isolation it was decided to

investigate the dependence of the measured transport characteristics on

pipe blockage factor, as defined above, and w.c. performance, as defined

by the ratio of water discharged behind the solid to the total volume

available, Fg/F.

Referring to the w.c. efficiency, as defined by Fg/F it was found that the

ratio was dependent on the total flush volume available as might be expected

from an analysis of the forces acting to discharge the solid initially at rest

in the pan from the w.c. bowl.

Equation 6 was therefore restructured as:

*1.2 •($)• (fKf)-

and a series of computer trial fits were

form for the relationship.

investigated to determine a suitable

Inspection of equation 7 would suggest that the relationship tends to infinity

as the x or y ordinate tends to zero, as shown by figures 2 and 3.

A number of characteristic points may be identified:

1.

Table 1 indicates that the available spread of terms D/ A and D/w is

much less than that of the term D/t. This is a result of product

design criteria as described previously.

2. As the blockage factor decreases and tends to zero so the values of

the or K2 multiplier terms increase resulting in the y ordinate

tending to infinity.

wt . F_

3. As pipe diameter decreased the value of the ttD^/ 4 F term

B

increases, a group of points representing 75 mm pipe diameter results

in figures 2 and 3 illustrate this.

8
4 At values of x ordinate below 0.1 the 2 multiplied y ordinate term

increases rapidly and hence is more susceptible to measurement errors.

As shown by table 1 the products represented by these results, Codes 41,

61, and 75 had thin profiles, 2 to 7 mm, so that measurement errors have

the potential for multiplication. Similarly, the true blockage within

the pipe could be underestimated due to the solid taking up the local

water surface profile slope, hence increasing its projected area in the

flow direction.

5. Model solid dimensions were recorded dry for practical reasons. The true

thickness of the solid could vary in the saturated state in the pipe. This

would only be a serious source of measurement error for the thinner solids.

6 . Saturated weights were recorded following some 30-40 records soaking in

all cases. It was felt that these figures could be used with confidence

in the data fit trials described.

As shown in figures 2 and 3, the transport characteristics of the chosen model

solids may be represented by equations of the form

K is a positive constant

q is a negative index

and i=j=k=l;n= 2 .

It should be noted that the flush volume behind the solid included in these

relationships was recorded at discharge from the 14 m pipe at a gradient of

1/80. Strictly, this figure should be appropriate to the solid discharge

from the w.c. to be truly independent of pipe slope. However, as these

relationships are to be used as calibration coefficients to model known system

loading, this is acceptable.

The results presented are limited to UPVC waste pipe at this stage. Although

tests with cast iron pipe were included in [ 1 ], these results applied only

to the maternity pad solid. Tests comparing glass, UPVC and cast iron 100 mm

diameter pipe transport indicated that surface roughness alone was not sufficient to explain transport variations as the smooth bore glass yielded transport results between UPVC and cast iron.

Figure 4 represents the waste solid deposit positions as predicted by writing

V=0 in equation 3, i.e.,

(9)

where

/L7DG = K1 /K2 . K3

9
and from figures 2 and 3

K. = 0.8 *£.( _L_ ) ( 'fl I_ ) D

3 pFB *D2 /4 FB'

-2.77

K9 - 1.04 ***( 1_ ) f

wt F_

)

D

3 pFB

' '*ttD2 /4 FB/

-2.3

hence

k3 = 0.77 ( wt F_

) > ttD2 ^ 4 Ffi/

-0.47

In practice the solid deposition may occur from any velocity below about 0.2

m/s due to its retardation by any pipe discontinuity, such as a coupling or

joint. At velocities in this range the solid motion is entirely due to the

water head differential across the solid and any retardation of the solid allows

the driving water to leak past the solid, thus, destroying the driving hydrostatic force.

10
7 . CONCLUSIONS

The test results presented for a wide range of geometrically similar solids

allow their transport characteristics to be expressed in terms of solid

geometry and mass and drainage system parameters including pipe diameter and

w.c. flush volume.

These relationships confirm the dependence of solid transport on the /l/G

term during the deceleration phase. Experimental work has identified this

phase as being predominant in the internal building branch drain situation.

The ability to predict model solid performance from these relationships in

combination with the observation currently being undertaken in installed

drainage systems will allow laboratory based test programs to both model system

loading and predict the effect of design changes on system performance.

11
8. REFERENCES

1. Swaf field, J. A. and Wakelin, R. H. M., Observation and Analysis of the

Parameters Affecting the Transport of Waste Solids in Internal Drainage

Systems, Journal Institution Public Health Engineers, U.K., November 1976.

2. Swaf field, J. A. and Wakelin, R. H. M., A Study of the Transport of

Solids in Internal Drainage Systems, CIBW62 Seminar, Oslo, May 1977.

3. Bokor, S. D. and Swaffield, J. A., Application of Laboratory Test

Techniques to Building Drainage Design, IPHE Seminar, Brunei University,

U.K., June 1980.

4. Marriot, B. S. T. and Swaffield, J. A., Effect of Reduced Volume w.c. Flush on Internal Drainage Performance, CIBW62 Seminar, Brussels,

October 1978.

5. Howarth, G., Wakelin, R. H. M., and Swaffield, J. A., Development of a Flushability Criterion for Sanitary Products, CIBW62 Meeting, Brunei

University, June 1980.

12
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APPENDIX I

Flushability Criteria for U.K. Sanitary Product

Reprint of Reference 5
DRAINAGE AND WATER SUPPLY FOR BUILDINGS

A TWO DAY SEMINAR ON CURRENT RESEARCH

AND FUTURE NEEDS AND OBJECTIVES

BRUNEL UNIVERSITY, UXBRIDGE, ENGLAND

JUNE 3 AND 4 1980

DEVELOPMENT OF A FLUSHABI LITY CRITERION FOR

SANITARY PRODUCTS

DR. G. HOWARTH

TECHNICAL DIRECTOR, SOUTHALLS (BIRMINGHAM) LTD

DR. R.H.M. WAKELIN

DR. J . A

SWAFFIELD

LECTURER AND SENIOR LECTURER RESPECTIVELY

DRAINAGE RESEARCH GROUP

DEPARTMENT OF BUILDING TECHNOLOGY

BRUNEL UNIVERSITY

ORGANISED BY

DRAINAGE RESEARCH GROUP

DEPARTMENT OF BUILDING TECHNOLOGY

BRUNEL UNIVERSITY

18
DEVELOPMENT OF A FLUSHABILITY CRITERION FOR SANITARY

PRODUCTS

by

Dr. G. Howarth, Technical Director,

Southalls (Birmingham) Ltd

Dr. R.H.M. Wakelin

and

Dr. J.A. Swaffield

Lecturer and Senior Lecturer respectively

Drainage Research Group

Department of Building Technology, Brunei University.

SUMMARY

The development of a set of flushability criteria for

sanitary protection products is described. The need for a criterion is stated and the initial test work undertaken

to establish the required pass levels is fully described.

The results show that the form of earlier empirical relations

developed at Brunei to link waste solid velocity to pipe

length and gradient apply to a wide range of solid size and

shape parameters.

Finally the agreed test specification is presented together

with a view of future development work in this area. The

results collected over the test period are to be analysed

further to identify any correlation between transport

characteristics and size and shape parameters.

19
INTRODUCTION

1

The Association of Sanitary Protection Manufacturers (ASPM) is a body formed to represent the views of, and set agreed standards

amongst, all members of the industry. One of these standards to

be examined was the term "flushable" which is printed on nearly

all the packages of sanitary protection products.

These sanitary protection products can vary widely in size,

construction and weight, as follows :-

(a) Tampons 2 to 5 grammes and 5 cms long

(b) Towels (Napkins) - Mini 4 to 8 grammes 15 cms long

Towels 6 to 20 grammes 20 cms long

(c) Panty Shields 2 to 4 grammes 15 cms long

The towel raw materials are basically " cellulose" - fillings of

tissue, fluffing pulp with a non-woven cover. There is sometimes

a plastic film inside the towel as a fluid barrier. Plastic can

also be used as a release tape to cover the pressure sensitive

adhesive on the back of the towel. The non-woven cover can be

very specialised - either completely non-absorbent polyesters or

a "flushable" cover which disperses after some time in water.

Rayon or a rayon/cotton mixture is the usual fibre for tampons.

The actual number of products used per day is estimated as follows :

PRODUCT NO. OF PADS

MILLIONS/DAY

TAMPONS 2.49

TOWELS

Mini 0.62

Looped 1.06

Self Adhesive 2.28

20
2

Our own surveys have shown that approximately 80% of the ladies

dispose of these products by flushing down the toilet i.e. five

million products per day. There are various flushability

instructions given on the packs.

"Simply flush It away - all in one piece"

"Just remove the cover and flush away separately"

"Completely flushable (no need to pull apart)

just flush the

whole towel away"

"Remove outer covering, empty contents and flush away. Then

flush cover separately"

"Do not flush"

These instructions support the general public's view that

"flushable" means it will disappear down the toilet. However the

ASPM wanted to be more specific in its definition of "flushable".

Flushability Definition

The Technical Committe of the ASPM considered that the definition

was really in two parts - the product should flush from the pan but

also cause no problems in the subsequent drainage system. Various

Research Establishments were contacted, with the following general

conclusions

(a) Drain blockages were in fact due in the main to a drain

fault i.e. poor joints or faulty pipework.

(b) Although the BSI minimum flush volume is 9 litres, in the

majority of WC systems the volume is 12 litres. However

there are moves to reduce this minimum standard and in

addition dual flush and controlled flush systems could be

introduced.

(c) If the towels managed to get into the main sewage pipe

trunking system no problems should occur.

(d) The amount of plastic in the products is unlikely to cause a problem at the sewage farm.

Therefore it seemed reasonable to concentrate on a method of

measuring the failure of the product to leave the WC and also the

"state" of the product after travelling some distance in the pipework. ASPM member companies had already simple WC systems plus a collection device for evaluating flushability. Unfortunately these

were non-standard methods with no scientific measurements.

However it was possible using the test rig developed by the

Drainage Research Group at Brunei University to define both a test

method and specification. In summary they have: •

21
3 -

(a) A test rig available consisting of a WC pan, connected to

a short vertical section and then 14 metres of horizontal

pipe. The velocity of the solid can be measured at various

points along the pipe length and the volume of water ahead

of the solid measured.

(b) Developed a theory of solid transport which will allow them

to predict the drainage performance of a solid at any

gradient of pipe and various types of pipe.

Flushability Specification

A 100 samples should be tested on the BRUNEL rig and the following

criteria must be satisfied.

(a) WC failures: A maximum of six WC failures plus pipe stoppages

below 10 metres are allowed i.e. 3 WC failures + 3 stoppages

below 10 metres.

(b) If a WC failure occurs then the product must flush greater

than 10 metres along the pipework on the second flush.

Flushability Rig and Method

TEST EQUIPMENT

A. The test pipe consisted of 7 x 2 m lengths of 100 mm bore UPVC

discharge pipe connected at its upstream end to a vented discharge Twy fords P-trap WC via a Terrain UPVC 104° junction and 92*j

UPVC bend. The centre line of the UPVC pipe was 300mm below

simulated floor level at this connection.

The pipe is supported over its whole length by means of two 7 m

long lightweight aluminium ladders. Initial level setting by

use of a surveyor's level ensured later gradient adjustments to an accuracy of 0.5 mm. A gradient of 1/80 was used for all the

reported tests. The performance of the test pipe was monitored

by recording the velocity of the waste solids at six points along

the pipe length. Table 1 indicated the positions chosen. The

discharge was collected at the downstream end of the test pipe by

a tank equipped with a depth recording linear displacement

transducer linked to a pen recorder. From the volume vs time

output of this system the quantity of water entering the collection

tank ahead of the solid could be accurately measured.

Table 1 SUMMARY OF VELOCITY MEASURING POSITIONS

Test Code

B. Velocity Position

Distance from WC (m)

Separation photocells

1 2

3.05 5.08

-0.3ra

3 4 5

7.11 9.15 11.18

6

13.21

22
- 4 -

C. Velocity Position 1

Distance from WC (m) 3.05

Velocity measuring length

2 3

5.08 7.11

-1.0m

4 5 6

9.15 11.18 13.21

SAMPLE PREPARATION

D. (a) If an adhesive backed towel is tested, the release strip

must be taken off and towel placed on a clean, fresh section

of "pantie" cloth. (The cloth to be defined and sample at

Brunei) . A 2 kilogramme weight (3cm wide x 20cm long) is

placed on towel for 90 seconds. The towel to be then peeled

longitudinally from the cloth. If however on dropping the

towel into the pan it sticks to the side of pan due to the

adhesive then these results should be ignored.

E. (b) The product should be pre-soaked with water

Tampons

Panty shields

Mini towel

Towel

no pre-soak

2cc

6cc

20cc

The water should be applied over the middle third of the product

and to avoid excess running off the surface it should take

1 minute to apply the fluid.

F. (c) The product must be torn, if necessary, as defined on the

package.

SAMPLE PLACEMENT

G. (a) The product should be held vertically and the bottom of the

pad (not loops) should be level with the rim of the toilet

and in the centre of the basin.

H. (b) The product is dropped into the pan and 20 seconds later the

toilet is flushed.

MEASUREMENT

I (a) WC FAILURE: If the product fails to leave the toilet, this

is noted plus the number of flushes required to remove the

product.

J. (b) VELOCITY: The velocity is recorded at various points along

the pipework system as defined in the test equipment. It

may be necessary to change the method of measuring the

velocity if the solid disperses.

K. (c) STOPPAGE DISTANCE: If the product stops in the pipework

the distance from the WC is recorded.

L. (d) rn VOLUME OF FLUID AHEAD: This is recorded as it should

confirm a satisfactory flush. It is measured by a signal

from the depth recorder in the collection tank at the end

of the pipework.

NUMBER OF TESTS:

A minimum of a lOO tests should be completed.

23
KLUSKAJttllTY REPORT

DRAINAGE RESEARCH GRCUF,

DEPARTMENT OF BUILDING TECHNOLOGY,

brunel university,

UXBRIDGE, MIDDLESEX. (Tel: Uxbridge 37188 ext. 344 & 359)

The attached test specification details the test rig and methods used to

determine the acceptance of the towel for disposal by VC flushing. The

operative paragraphs of the specification are listed where appropriate:

Towel type

Dr. White's Panty Pads Super Plus

Test equipment

Velocity measurement

positions

Sample preparation

Sample placement

Measurements

A

C

D,E,F

G,H

I,J,K,L

Number of V/C flushes

WC flush failures

WC 2nd flush failures

Theoretical zero velocity pipelength

based on V = C-j - C2 J~\>/

Stoppage distances recorded Mean

Number of stoppages in pipe

/l/g = 62.44

L = 48.7m at 1/80

- Max = - Min = - STD =

0

Volume discharged ahead

of solid Mean = 1.96 Max = 3*94 Min = 0.9^ STD = 0.59 1 21.6$ 43 .2% 10.8$ 6.43?:

Comments on test performance £jp problems encountered during V/C tests.

This, product passes the test specif ication

24
FLUSHABILITY ASSUMPTIONS

6 -

In carrying out this investigation to determine a flushability

method various assumptions have been made and certain facts found:

(1) WC Pan: A BSI P-trap WC was used as the majority of

U.K. houses would have this type of toilet. At this stage

siphonic systems have not been investigated.

(2) Flush Volume: The current British Standard stipulates a minimum flushing volume of 9 litres, and this was used in the

test method. However it is more likely that the volume is

11/12 litres in the home. There are available reduced volume

flush systems and controlled flush systems, none of these

have been investigated.

(3) Cover Flushing: In the past it has been recommended on those

towels which have the cover torn that the cover is flushed

separately. It was found better to flush cover and contents

together.

(4) Air Entrapment: One of the major factors in poor performance

was air entrapment in the product which forced the product

to float.

(5) Product Placement: It was decided to specify the position

from which the product is dropped so as to try to eliminate

any product falling onto the sides of the pan, and prevent

any bridging effect on long products.

(6) Pre-soak: It was found that the product performance in

general deteriorated if water was added to the product

before flushing. Various levels of pre-soaking have been

defined.

(7) Product Shape: At this stage it was felt better to ignore

the fact the product could be shaped after use. This was

due to the difficulty of reproducing a standard shape, and

some evidence that it did not affect the performance.

(8) Sample size: A lOO samples were tested as typical of 6 months

usage and it was felt that a 1 in 15 first failure would be

acceptable. Care should be taken not to refer the specification

as "6% of towels can fail to leave the WC"

(9) Stoppage Distance 10 metres: There are no British Standards

for pipework distances, but it was considered by Brunei that

the majority of systems would be less than 10 metres even

taking into consideration the twists and turns that sometimes

occur.

Tampons

Panty shield

Mini

Towels

O

2cc

6cc

20cc

25
- 7 -

In conclusion we do have an industry agreed specification and test

method of flushability of sanitary protection products, and

hopefully the number of complaints we have from our customers due

to flushability problems will reduce from the present one complaint

in 100 million products used!

Background to the flushability test work at Brunei

The Drainage Research Group at Brunei have been involved in a fundamental study of the mechanisms of solid transport in above

ground drainage systems for a number of years. The initial

research, funded by the U.K. Department of Health and Social

Security, had led to the establishment for the first time in 1976

of an empirical relationship linking solid velocity to both pipe

length travelled and to pipe gradient. Initially (1) this was limited in its application to tests involving maternity pad model

solids w.c. flushed under laboratory conditions into a 14 m length

of drainage pipework set at gradients from 1/40 to 1/200. Pipe

material was initially transparent UPVC although glass and cast

iron pipes were also tested. In 1977 further funding from DHSS

allowed this programme to continue and to include, in its current

stage, the monitoring of installed systems as a means of demonstrating

the application of the empirical relationship mentioned above to the

wide range of waste transported along a typical drainage system.

The initial relationship linking solid velocity, and hence the

probability of deposition, to pipe length and gradient was found

to have a form -

V = C, - C2 J~T - (1)

where L is the distance travelled along the pipe set at a gradient G, over the main length section of w.c. fed branch drain pipe runs. This basic equation was found to apply in the same format to pipes of

various materials, e.g. glass, UPVC or cast iron, or to pipes of

various cross sectional dimensions and shapes, e.g. 100 mm and 75 mm

diameter and elliptical. Similarly the relationship for various

flush volumes with the standard maternity pad solids was found to

have a form -

where

^ are empirical constants.

Thus when the group was approached by ASPM to aid in the development

of a set of flushability criteria for sanitary products that would

include solid transport as well as w.c. discharge targets it was

clear that the test work envisaged would fit conveniently into the

research programme. The Association of Sanitary Protection

26
~ 8 -

Manufacturers are to be thanked both for entering fully into this

co-operation with Brunei and for allowing the test results to be

published in an anonymous form.

Development of the test rig

As the proposed work fitted so closely into the group's programme

it was possible to modify one of the existing test pipe runs to

form the basis of a flushability test rig. A P-trap w.c. was

chosen as the standard input device based on enquiries on market

penetration of various w.c. types. The pipe chosen was 14 m of

100 mm diameter transparent UPVC to facilitate the use of standard

photo-electric cell and light source instrumentation developed

at Brunei to record solid passage along the pipe and hence velocity.

Choice of pipe length and gradient were more difficult. After

much discussion a gradient of 1/80 and a successful transport

length of 10 m was chosen as reasonable to represent both the more

convoluted pipe networks to be found in domestic installation and

also the possible worst case formed by an isolated branch w.c.,

possible in a large building toilet area or a downstairs second

w.c. in the domestic sector.

Test programme and results

The initial objective in 1978 was the confirmation of the

application of a' relationship of the form of equation 1 to the

range of products to be tested, not only in the complete form

compatible with the single maternity pad test but also in the

torn state compatible with the manufacturer's instructions.

Figures 1 and 2 illustrate typical test results from this initial

test series where dry untorn and tom towels were flushed from the

w.c. In all cases the form of equation 1 is confirmed. Under

the normal untorn towel test condition the photo-electric cell/

light source pair separation was 0.3 m. However, due to the

interaction between multiple solids transported along the pipe,

the setting employed for the torn towel tests was increased to 1 m. Although this yields average rather than point velocities the^L/G

dependence holds, although the gradient of the data equation is

much reduced, indicating an improved travel capability.

Figure 3 illustrates the mechanism of multiple solid transport

in the drainage pipe, the successive accelerations, both positive

and negative, being referred to as the "push me - pull you" effect.

At this stage it is perhaps useful to introduce two other

measurement terms, namely the flush volume ahead of the solid

and the theoretical zero solid velocity value of ,/l/G.

Throughout the tests, and the earlier DHSS work, values of the

quantity of water collected at the drain discharge ahead of the

solid were recorded by a simple float driven level sensing device

in the collection tank. It had been observed that the transport

27
- 9 -

characteristics of a solid depend largely on its position in the

flush and this is borne out by the ASPM results. Solids that

fail the test specification on w.c. failure rate may be shown

to have a wide spread of volume ahead results; indeed a w.c,

failure may be regarded as a limiting value to these results.

In the test rig described values Of volume ahead above 30%

of the 9 litre flush volume generally lead to problems in

satisfying the test specification.

The theoretical zero velocity point from equation 1 is of

course given by -

In practice deposition may occur from any velocity below about

0.2 m/s. At these low solid velocities the continuing transport

is entirely dependent on the retention of a water volume behind

the solid. Any irregularity in the pipe can then retard the

solid sufficiently to allow excessive water leakage past and

deposition will then occur.

At this stage in the testing programme it was decided to investigate

the effect of pre-soaking the towel prior to placing in the w.c. bowl. Available literature would suggest (2) that the volume

range of menstrual fluid, consisting of blood, mucin and

epithelial cells, should be 8 - 20 g. It was decided to employ

pre-soak water volumes in this range. Figure 4 and Table 2

illustrate the results of these tests. It is apparent that the

addition of pre-soak water to the pad resulted in a deterioration

in both the w.c. discharge and solid transport properties of the

five pads investigated initially. This result at first seemed to

be contradictory to the expected mechanism. However, a series of

films taken of the pad sinking action in the w.c. bowl prior to

flushing led to an acceptable explanation of these results. With

an initially dry towel dropped into the bowl the saturation of the

towel material occurs by capillary action so that the level of the

water in the saturated towel is always above the bowl water level.

This results in a force which draws the towel down into the bowl

water.

If the central area of the towel is pre-soaked then two effects

are noticeable, firstly the saturated towel tends to cling to the

ceramic side of the bowl, and this prevents its immersion in the

bowl water, and secondly the presence of a saturated strip across

the towel seems to prevent the capillary action and bowl water

does not move up inside the towel past this area.

28
10 -

Both these effects lead to a later discharge from the w.c. and

hence to deterioration of the transport performance in the

drainage system. Any tendency to retain air within the towel

cover is naturally exacerbated by this failure to totally sink,

again leading to late w.c. discharge.

The final simulation considered was a controlled degradation

of the adhesive now used on many towels due to the lessening

popularity of looped towels. Although this was not a major

problem in terms of the number of towel types affected it is

obviously necessary to simulate the loss of adhesive if for no other reason than to be able to state that any failures to

pass the test specification were not due to uncharacteristic

towel adhesion to the w.c. bowl or to the pipe invert.

After much discussion, and some tests involving preheating of

towels to degrade the adhesive, a test procedure involving

compressing the towel onto representative commercially available

female underwear material was developed.

In parallel to the work reported, similar tests were undertaken

on tampons and disposable diaper materials. Figure 5 illustrates

these investigations and again confirms the VL/G group

predominance. One effect that was noticeable with all tom

products but more pronounced with diapers was the random discharge

from the w.c. In some cases the material was discharged as a continuous, well' spread out stream of pulp with no deposition

problems. However in some cases the w.c. action resulted in

the diaper pulp being discharged in a concentrated mass with

rapid deceleration and deposition in the waste pipe.

29
- 11 -

CONCLUSIONS

The tests reported involving sanitary towel products have contributed

to the development of the flushability specification presented earlier

in this paper. This specification has now been approved by ASPM as the basis for future product testing.

In developing the specification, the decisions taken were based on

the widest possible application of the test findings, hence the choice

of a relatively cheap and common domestic w.c. type. It may be

necessary to investigate further the effects of other w.c. types on

the flushability of sanitary products, in particular siphonic w.c. designs may well be a topic for future investigation.

The test results will be analysed further to investigate whether there

is a correlation between values of C, , C2 , and C3 and the geometry

of the solids and their position in the w.c. flush, as represented

by the volume ahead of solid data.

ACKNOWLEDGMENTS

The Association of Sanitary Protection Manufacturers are to be thanked

for making available test results from a programme of work carried out

by the Drainage Research Group at Brunei on a consultancy basis.

REFERENCES

1. Swaffield J.A.

and

Wakelin R.H.M.

"Observation and analysis of the

parameters affecting the transport

of waste solids in internal drainage

systems"

Journal IPHE 1976.

2. Sears W.G. "Anatomy and Physiology for Nurses"

Edward Arnold 1958.

30
ffble

2

t

COMPARISON

OF

THE

W.C.

PERFORMANCE

AND

TRANSPORT

CHARACTERISTICS

OF

THE

TOWELS

TESTED

WITH

AND

WITHOUT

ADDITION

OF

PRESOAK

WATER

PRIOR

TO

PLACING

IN

THE

W.C.

(Note

value

of

C,

represents

*/l/G

at

V=0,

a

theoretical

stoppage

position

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31

Note

that

the

presoaXed

towels

have

worse

transport

characteristics

under

each

of

the

measurement

criteria

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volume

ahead

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waste

pipe.
32
33
34
35
36
NBS-114A (REV. 2-80

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

. PUBLICATION OR

REPORT NO.

NBSIR 81-2307

2. Performing Organ. Report No. 3. Publication Date

July 1981

4.

TITLE AND SUBTITLE

DEPENDENCE OF MODEL WASTE SOLID TRANSPORT CHARACTERISTICS IN DRAINAGE SYSTEMS

ON SOLID GEOMETRY, MASS AND PIPE SYSTEM PARAMETERS

5. AUTHOR(S)

John A. Swaffield

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Department of Housing and Urban Development

451 7th Street, SW

Washington, D.C. 20410

10.

SUPPLEMENTARY NOTES

I | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11.

ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here

Test results are presented for the transport characteristics of an extensive

range of geometrically similar model solids in a 100 mm diameter UPVC drain

pipe. Model solids were based on commercially available sanitary towels (napkins)

discharged into the pipe system via a series of U.K. standard watercloset (w.c.)

types

Following a data fit analysis, relationships are presented linking solid transport

characteristics to solid, pipe and w.c. parameters.

These relationships, linked to observation of installed hospital drainage systems

in the U.K., will allow laboratory test methods to be utilized in predicting the

effect of design changes on system performance.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) building drainage; waste solid transportation; water conservation; W.C. efficiency

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

|~X~1 Unlimited

| | For Official Distribution. Do Not Release to NTIS 44

”1] O rder From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. 15. Price

[x] 0rder From National Technical Information Service (NTIS), Springfield, VA. 22161 $6.50

USCOMM-DC 6043-P80


d