CEN/TR 15463:2007

Characterization of sludges - Physical consistency - Thixotropic behaviour and piling behaviour

This CEN-Report "Physical Consistency" derives from the Desk Studies "Physical Properties -Flowability"(HORIZONTAL Report No. 21 [60]) and "Physical Properties - Solidity, Thixotropic Behaviour andPiling Behaviour" (HORIZONTAL Report No. 22 [61]) of the Horizontal Project. The "Horizontal" project hasthe objective to develop horizontal and harmonised European standards in the fields of sludge, bio-waste andsoil to facilitate regulation of these major streams in the multiple decisions related to different uses anddisposal governed by EU Directives. The Horizontal Project includes the Work Package 7 "Mechanicalproperties" consisting in the development of Desk Studies on physical consistency, because it is recognizedthat this property is very important for the characterization of sludge, since it affects almost all treatment,utilization and disposal operations, such as storage, pumping, transportation, handling, land-spreading,dewatering, drying, landfilling. The importance of the physical consistency is also true for the characterizationof bio-waste and soil. Also handling and utilization of many other materials, such as cement and asphalt arestrictly depending on their physical consistency. The needs for control of operations and also materialcharacteristics are described.

Charakterisierung von Schlämmen - Bestimmung der physikalischen Konsistenz, thixotropes und Aufschüttverhalten

Caractérisation des boues - Consistance physique - Comportement thixotrope et comportement au tassement

Karakterizacija blata - Fizikalna konzistenca - Tiksotropija (časovna spremenljivost viskoznosti) in luščenje

General Information

• Status: Published
• Publication Date: 17-Apr-2007
• ICS: 13.030.20 - Liquid wastes. Sludge
• Technical Committee: CEN/TC 308 - Characterization of sludges
• Drafting Committee: CEN/TC 308/WG 1 - Characterization methods
• Current Stage: 6060 - Definitive text made available (DAV) - Publishing
• Start Date: 18-Apr-2007
• Due Date: 12-Jul-2007
• Completion Date: 18-Apr-2007
• Ref Project: SIST-TP CEN/TR 15463:2008 - Characterization of sludges - Physical consistency - Thixotropic behaviour and piling behaviour

Overview

CEN/TR 15463:2007 - "Characterization of sludges - Physical consistency - Thixotropic behaviour and piling behaviour" is a CEN Technical Report produced by CEN/TC 308 as part of the HORIZONTAL project. It reviews methods to assess the physical consistency of sludges, bio-waste and soils because consistency (flowability, solidity, thixotropy, piling behaviour) strongly influences treatment, handling and disposal under EU Directives (e.g., Sewage Sludge Directive 86/278/EEC and Landfill Directive 1999/31/EC).

Key topics and technical coverage

• Summary and evaluation of existing test methods and standards (more than 250 methods reviewed) for consistency assessment.
• Definitions and basic concepts: flowability, solidity, thixotropic behaviour, and piling behaviour.
• Grouping of measurement techniques by instrument type:
  • Flowability: capillary viscometers, rotational viscometers (coaxial cylinder), penetrometers, and field flow apparatus (flow cone, magnesium penetration cone, extrusion tube viscometer).
  • Solidity: shearing apparatus, vane shear (laboratory vane shear apparatus), Vicat needle, and portable penetrometers (pocket penetrometers).
  • Thixotropy: combined solidity tests (e.g., penetration) plus energy input simulations (vibrating table, hammer) to quantify structural breakdown and recovery.
  • Piling behaviour: Cubic Piling Box (CPB), oedometer, slump and compaction tests (CPB suitable for lab and field).
• Recommendations: preferred laboratory and field methods for each property, and identification of research needs (precision, repeatability, applicability to a wide range of materials).

Practical applications

CEN/TR 15463:2007 supports operational and regulatory decision-making by providing guidance on measuring consistency parameters that affect:

• Storage, pumping and transportation of sludge
• Dewatering, drying and land-spreading operations
• Composting and landfilling stability assessments
• Equipment selection (pumps, extrusion/handling machinery) and process control
• Regulatory compliance and classification of wastes (liquid vs. non-liquid)

Who should use this report

• Wastewater treatment plant operators and process engineers
• Environmental laboratories and technical testing services
• Landfill and site engineers assessing stability and acceptability
• Regulators, standards developers and consultants working on sludge, bio-waste and soil management
• Equipment manufacturers (viscometers, penetrometers, vane shear apparatus, CPB)

Related standards and next steps

• Prepared by CEN/TC 308 as part of the Horizontal project; the report compiles many referenced standards and proposes draft standards for further validation.
• Identifies the need for harmonized test procedures and additional research to optimize method design and ensure repeatability across sludge, bio-waste and soil materials.

Keywords: CEN/TR 15463:2007, physical consistency, sludge characterization, thixotropic behaviour, piling behaviour, flowability, solids testing, penetrometer, vane shear, CPB.

Standards Content (Sample)

SLOVENSKI STANDARD
01-julij-2008
.DUDNWHUL]DFLMDEODWD)L]LNDOQDNRQ]LVWHQFD7LNVRWURSLMDþDVRYQDVSUHPHQOMLYRVW
YLVNR]QRVWLLQOXãþHQMH
Characterization of sludges - Physical consistency - Thixotropic behaviour and piling
behaviour
Charakterisierung von Schlämmen - Bestimmung der physikalischen Konsistenz,
thixotropes und Aufschüttverhalten
Caractérisation des boues - Consistance physique - Comportement thixotrope et
comportement au tassement
Ta slovenski standard je istoveten z: CEN/TR 15463:2007
ICS:
13.030.20 7HNRþLRGSDGNL%ODWR Liquid wastes. Sludge
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL REPORT
CEN/TR 15463
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
April 2007
ICS 13.030.20
English Version
Characterization of sludges - Physical consistency - Thixotropic
behaviour and piling behaviour
Caractérisation des boues - Consistance physique - Charakterisierung von Schlämmen - Physikalische
Comportement thixotrope et comportement au tassement Beschaffenheit - Thixotropes und Schüttverhalten
This Technical Report was approved by CEN on 4 August 2006. It has been drawn up by the Technical Committee CEN/TC 308.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, 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  B-1050 Brussels
© 2007 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TR 15463:2007: E
worldwide for CEN national Members.

Contents Page
Foreword.4
1 Introduction.6
1.1 The Horizontal project and the Work Package 7 .6
1.2 Desk study subject .7
1.3 Evaluation of needs for control of operations and material characteristics.7
1.3.1 Evaluation of needs for control of operation.7
1.3.2 Material characteristics.8
1.4 Search for existing standards and methods.15
1.5 Basic information.16
1.5.1 Flowability .16
1.5.2 Solidity .18
1.5.3 Thixotropic behaviour of solid materials .19
1.5.4 Piling behaviour.21
2 Existing standards or draft standards.22
2.1 Flowability .22
2.2 Solidity .22
2.3 Thixotropic behaviour .23
2.4 Piling behaviour.23
3 Evaluation of drafting a Horizontal standard.24
3.1 Flowability .24
3.1.1 Capillary viscometers.24
3.1.2 Penetrometer.28
3.1.3 Rotational viscometers .33
3.1.4 “Flow” apparatus.37
3.2 Solidity .43
3.2.1 Shearing apparatus .43
3.2.2 Vane testing apparatus .45
3.2.3 Penetrometer.49
3.3 Thixotropic behaviour of solid materials .57
3.3.1 Laboratory or field test feasibility.57
3.3.2 Apparatus .57
3.3.3 What is measured and how .62
3.3.4 Material to be examined .63
3.3.5 Feasibility of the methods to the materials of investigation.63
3.4 Piling behaviour.63
3.4.1 Laboratory or field test feasibility.63
3.4.2 Apparatus .64
3.4.3 What is measured and how .67
3.4.4 Material to be examined .68
3.4.5 Feasibility of the methods to the materials of investigation.68
4 Critical point and recommendations .69
4.1 Flowability .69
4.1.1 Comparison (discussion: pro/contra).69
4.1.2 Recommendations.70
4.2 Solidity .71
4.2.1 Comparison (discussion: pro/contra).71
4.2.2 Recommendations.75
4.3 Thixotropic behaviour of solid materials .75
4.3.1 Comparison (discussion: pro/contra).75
4.3.2 Recommendations.76
4.4 Piling behaviour.76
4.4.1 Comparison (discussion: pro/contra) .76
4.4.2 Recommendation .77
4.5 Summary of recommended methods .77
4.5.1 Flowability .77
4.5.2 Solidity, thixotropic behaviour and piling behaviour .77
4.6 Research needs .78
4.6.1 Basics of methods.78
4.6.2 Applicability of methods to the materials of investigation .79
4.6.3 Questions to be answered.80
4.6.4 Route, how to answer them.80
4.6.5 Steps to be taken.80
Bibliography.81

Foreword
This document (CEN/TR 15463:2007) has been prepared by Technical Committee CEN/TC 308
“Characterization of sludges”, the secretariat of which is held by AFNOR.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

This CEN-Report “Physical Consistency” derives from the Desk Studies “Physical Properties – Flowability”
(HORIZONTAL Report No. 21 [60]) and “Physical Properties – Solidity, Thixotropic Behaviour and Piling
Behaviour” (HORIZONTAL Report No. 22 [61]) of the Horizontal Project. The “Horizontal” project has the
objective to develop horizontal and harmonised European Standards in the fields of sludge, bio-waste and soil
to facilitate regulation of these major streams in the multiple decisions related to different uses and disposal
governed by EU Directives. The Horizontal Project includes the Work Package 7 “Mechanical properties”
consisting in the development of Desk Studies on physical consistency, because it is recognized that this
property is very important for the characterization of sludge, since it affects almost all treatment, utilization and
disposal operations, such as storage, pumping, transportation, handling, land-spreading, dewatering, drying,
landfilling. The importance of the physical consistency is also true for the characterization of bio-waste and
soil. Also handling and utilization of many other materials, such as cement and asphalt are strictly depending
on their physical consistency. The needs for control of operations and also material characteristics are
described.
The first action carried out is consisted in searching for existing standards to be possibly used or adapted for
utilisation in the specific field of consistency evaluation. The complete list of standards is reported in Annex 1
of the HORIZONTAL Reports No. 21 [60] and No. 22 [61], from which it can be seen that more than 250
standards and non-standardised methods are potentially applicable to consistency evaluation. On the basis of
the selected list of standards and non-standardised methods for further consideration the methods for the
determination of flowability, solidity, thixotropic behaviour and piling behaviour of sludge, bio-waste and soil
have been divided into several groups, according to the instruments used for measuring:
 Flowability: Capillary viscometers, Penetrometers, Rotational viscometers and Flow apparatus.
 Solidity: Shearing apparatus, Vane testing apparatus and Penetrometers.
 Thixotropic behaviour: It should be investigated a combination of methods for determination of the solidity
like penetration, etc. and an energy-input in terms of "flow" apparatus to simulate the shear stress.
 Piling behaviour: Slump test apparatus, Compacting apparatus, Cubic Piling Box (CPB) and "Turned Box".
For each group was evaluated the laboratory or field test feasibility. Apparatuses of the measuring procedures
and existing applications to different materials were described. On this basis the applicability of the described
methods to the materials of investigation was evaluated and documented in the lists of analysed standards.
The recommended methods are for flowability the coaxial cylinder viscometer as laboratory apparatus, while
field apparatus are flow cone, magnesium penetration cone and extrusion tube viscometer. The
recommended methods are for solidity the “Laboratory vane shear apparatus” and “Vicat needle” as
laboratory reference and the pocket penetrometers for field test. The penetrometers in general could be used
for both laboratory reference method and field test. Also for determination of the thixotropic behaviour the
penetrometer is together with an energy-input in terms of a vibrating table or a hammer a suitable instrument.
For measuring the piling behaviour the Cubic Piling Box (CPB) and the Oedometer are the recommended
methods, whereby the CPB could be used in both laboratory and field while the Oedometer could be used
only in the laboratory. All methods should be tested and optimized to adapt design and part dimensions to the
materials in a future experimental activity.
For the research needs first the basics of methods are explicated and the applicability of methods to the
materials is clarified. The questions to be answered (precision, repeatability, reliability, etc.), the route, how to
answer them and finally the steps to be taken are important for following procedures.
In the Horizontal Report No. 21 a total of 6 proposals for draft standards are given, whereby one laboratory
method and five field tests exist. In the Horizontal-Report No. 22 a total of 11 proposals for draft standards are
given, consisting of six laboratory methods and five field tests.
1 Introduction
1.1 The Horizontal project and the Work Package 7
The revision of the Sewage Sludge Directive 86/278/EEC, the upcoming Composting Directive on the
biological treatment of biodegradable waste and the Soil Monitoring Directive call for standards on sampling,
hygienic and biological parameters, methods for inorganic and organic contaminants, and for mechanical
properties of these materials.
In addition, when materials cannot be utilized, landfilling becomes important, in which case leaching becomes
an issue as stipulated by the Council Directive 1999/31/EC on the landfill of waste. More recently, a Council
Decision establishing criteria and procedures for the acceptance of waste at landfills, pursuant to Article 16
and Annex II of mentioned Directive on the landfill of waste was issued (16/12/02) with physical consistency
being one basic parameter of interest.
The “Horizontal” project has the objective to develop horizontal and harmonised European Standards in the
fields of sludge, bio-waste and soil to facilitate regulation of these major streams in the multiple decisions
related to different uses and disposal governed by EU Directives.
Part of the work to be carried out will focus on co-normative work with an emphasis on horizontal
standardization starting from existing standards developed for the same parameter in the fields of sludge, bio-
waste and soil. Another part of the work will focus on pre-normative research required to develop standards
lacking at this point and needed in the next revision of the regulations in these fields.
The work within the HORIZONTAL Project was coordinated in the Work Package 7 “Mechanical properties”
and done in cooperation of the involved teams. It consists in the development of the Desk Studies on physical
consistency mentioned above, because it is recognized that this property is very important for the
characterization of sludge e.g., since it affects almost all treatment, utilization and disposal operations, such
as storage, pumping, transportation, handling, land-spreading, dewatering, drying, landfilling. In fact, the
selection of the most suitable equipment and procedure for land application, storage and transportation of
sludge e.g. is strongly connected to its consistency. Similarly, compacting sludge in a landfill or forming a pile
in composting is depending on sludge shear strength rather than on its solids concentration. In particular, with
reference to the regulations requirements, according to the Sludge Directive 278/86, agricultural reused
sludge should have agronomic interest, be healthy and easily usable, i.e. easily stored, transported, handled,
and spread.
In Council Directive 1999/31/EC (Landfill Directive), Article 2 (q) gives a definition of “liquid waste”, and Article
5 (3.a) does not allow a liquid waste to be landfilled, but a standardized method for this evaluation has to be
developed yet. Further, Annex II (2. General principles) requires that “The composition, … and general
properties of a waste to be landfilled must be known as precisely as possible”, and Annex I (6. Stability) is
referring to “. ensure stability of the mass of waste . particularly in respect of avoidance of slippage”, so the
shear strength and piling behaviour should be known. Article 2 (h) says, that “treatment means . processes .
in order to … facilitate its handling”. Finally, Article 11 (1.b) asks for: “ – visual inspection of the waste at the
entrance and at the point of deposit and, as appropriate, verification of conformity with the description
provided in the document submitted by the holder”, so simple and easy tests to be carried out on the field and
followed by the operators should be defined. Further, the Council Directive establishing criteria and
procedures for the acceptance of waste at landfills, pursuant to Article 16 and Annex II of mentioned Directive
on waste landfilling included “consistency” among the basic parameters to be evaluated for waste
characterization before landfilling; for specific cases it is also demanded, that EU Member States must set
criteria to ensure a sufficient physical stability and bearing capacity of waste. It is also to be pointed out that in
many analytical methods for sludge characterization (e.g. pH, dry matter, leachability, etc.) different
procedures are indicated depending on whether the sample to be examined is liquid or not, is solid or not, but
no procedures are given for evaluating such properties. The importance of the physical consistency is also
true for the characterization of bio-waste and soil.
1.2 Desk study subject
The Task Group 3 (TG3) of CEN/TC308/WG1 defined 3 physical states for sludge (CEN/TC308/WG1/TG3,
2000):
a) Liquid: sludge flowing under the effect of gravity or pressure below a certain threshold.
b) Paste-like: sludge capable of continuous flow under the effect of pressure above a certain threshold
and having a shear resistance below a certain threshold.
c) Solid: sludge having a shear resistance above a certain threshold.
This firstly involves the necessity to set up methods to measure values in the range of the boundary area
between liquid and paste-like behaviours (limit of flowability) and that between solid and paste-like (limit of
solidity). Further, the thixotropic behaviour of solid materials (from “the solid to the liquid state and vice versa”)
should be evaluated, together with the piling behaviour referred both to “compaction and physical stability”.
Also the CEN/TC292/WG2, in the method EN 12457 for the characterisation of waste included in Annex B
(Informative) the description of a test for determining whether waste is in the liquid state (CEN/TC292/WG2,
2002).
Although the methods to be developed are partly known and used in other technology fields, e.g. soil
mechanics, materials for construction works (concrete, suspensions), etc., widely accepted methodologies for
the evaluation of above properties, able to give comparable and reliable results, are not available yet. It
therefore follows the necessity to define simple and reliable measurement procedures to be applied in the field,
together with those to be used as reference in laboratory. Standardisation procedures for the material
examination will consist of
 Sampling, transport, preservation, storage
 Pre-treatment
 Measurement and evaluation of results.
In the report “Globally Harmonized system of Classification and Labelling of Chemicals (GHS)” other
definitions of liquid and solid are given [59]:
Liquid means a substance or mixture which at 50 °C has a vapour pressure of not more than 300 kPa (3 bar),
which is not completely gaseous at 20 °C and at a standard pressure of 101.3 kPa, and which has a melting
point or initial melting point of 20 °C or less at a standard pressure of 101.3 kPa. A viscous substance or
mixture for which a specific melting point cannot be determined shall be subjected to the ASTM D 4359-90
test [56]; or to the test for determining fluidity (penetrometer test) prescribed in section 2.3.4 of Annex A of the
European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR) [55];
Solid means a substance or mixture which does not meet the definitions of liquid or gas.
1.3 Evaluation of needs for control of operations and material characteristics
1.3.1 Evaluation of needs for control of operation
The purpose of using characterisation standards is to control and ascertain the material amenability to
handling and different operations. Materials considered are
 Sewage sludge
 Waterworks sludge
 Bio-waste and
 Soil
Materials, which cannot be utilised, are subjected as waste to the Landfill Directive (Council Directive
1999/31/EC), respectively the ordinances of the member states. The member states had to translate this
directive into national law. In Germany e.g., there is the landfill ordinance [58], which became operative on
24.07.2002. Furthermore there does exist the waste disposal ordinance, it is a kind of adjustment respectively
update of the German “TA Siedlungsabfall”. By this regulation among other things the limit value of ≥ 25 kN/m²
for vane shear strength – termed also in the HORIZONTAL Report No.22 [61] - was set. For this regulation it
is not important, from where the materials come from. It is valid for different respectively all kinds of wastes.
For handling and operating these materials many parameters should have to be known; they include
homogeneity, particles sizes and shape, solids (total, suspended, volatile) that, if available, could define the
range of variation of variable considerations (i.e. viscosity, etc.).
The parameters flowability is an overall parameter taking into account all above mentioned material properties
or characteristics. In particular, the flowability evaluation for sludges, including wastewater, waterworks and
similar sludges, is of fundamental importance in many operations such as pumping, transportation, storage,
dewatering, stabilisation, spreading, etc. also considering the possible formation from a gel to a liquid (sol)
and vice versa. Similarly, for bio-waste, including the shredded organic fraction of municipal solid waste
(OFMSW), in operations such as handling, digestion, reuse, etc. the measure of the parameter flowability
have to be considered. Finally, for fine-grained soils, the water content (and therefore consistency and
flowability) has always been considered an important indication of their mechanical properties. Moreover in
case of soil slurries it is very important to verify flowability as a measurement of their workability and time of
setting.
The solidity is also a parameter, which concerns all the material properties or characteristics mentioned above.
The determination of this parameter is getting more important for handling of solid materials like dewatered
sludge, other bio-waste – e.g. in terms of pieces (compost) – and soil, where the grain size distribution and
water content have to be considered, during operations like pumping, transportation, storage, etc.
The measurement of thixotropic behaviour for solid materials is relevant especially for dewatered sludge like
sewage, waterworks and related sludge. By dewatering and storage the sludge becomes solid. During
operations such as transportation the sludge gets in a liquid state due to the vibration of a truck.
The piling behaviour evaluation is also for dewatered sludge, particular bio-waste and soil of importance. The
determination of the piling angle is a useful instrument to characterise the storage properties and calculate the
space, which is needed for e.g. storage and transportation. Together with the thixotropic behaviour the piling
behaviour refers to the compaction and stability.
However, the development of reliable measurement procedures of all parameters is not a simple matter,
because measurements are influenced by below described properties or characteristics. This means that
those factors must be considered with great attention and methods defined by avoiding any negative
interference with them during measuring procedures. For this reason, it is first essential to select, if any, the
most adapted standards or non-standardised methods applicable to sludge, bio-waste and soil or to develop a
new one, and then to carry out parallel tests to evaluate how they are affected by the other specific
characteristics. In addition, these aspects require to be investigated for both laboratory methods, to be
adopted as a reference, and simple tests to be applied in the field.
1.3.2 Material characteristics
1.3.2.1 Sewage sludge
Sewage sludge can be produced from several processes (primary sedimentation, activated sludge process,
aerobic or anaerobic digestion etc.). Their solid content cover a wide range from 1 % to 30%, while different
total volatile solids percentage on dry matter can vary from 75% to 45%. The presence of coarse particles is
strongly related to the sieve adopted in head-works or external material used in some processes (anaerobic
co-digestion, etc.). Sewage sludge covers a wide range of physical state from liquid to solid. Bibliography
does not offer a characterization of particle size distribution of sewage sludge, a wide range of these
characteristics is forecasting in relation to the process adopted (opening of sieves etc.) and different type of
sewage sludge treated. Some indications are found for sewage sludge (see Table 1 [1]).
Table 1 — Particle size distribution of sewage sludges
Material Process TS basis TVS basis
% cumulative retained % cumulative retained w.w.
w.w.
5 mm 2 mm 0,84 mm 5 mm 2 mm 0,84 mm
Sewage sludges Aerobic 0 3,7 9,4 0 4,7 8,4
WTS process
Mixed primary Mesophilic 0 10,5 18,5 0 15,5 30,5
sludges anaerobic
ADS digestion
Each kind of sludge was analysed for its particle size distribution by wet sieving, using three sieves with
openings of 5,2 mm and 0,82 mm. According to these data the samples can be divided into four conventional
classes: coarse (>5 mm), medium (from 5 mm to 2 mm), medium-fine (from 2 mm to 0,84 mm) and fine (<0.84
mm). It can be noted that the sewage sludges have no coarse particles but a different percentage of medium
and fine particles.
The most diffuse sludge characterization is that rheological, beside CST – capillary suction time, R specific
resistance to filtration etc. Rheological parameters (yield stress, viscosity and thixotropy) were originally
applied to calculation of the head losses in sludge pumping operations, recently it has been shown that they
can affect filtration, thickening [2], pumping [3, 4] and constitute useful on line control parameters for sludge
conditioning and dewatering [5, 6, 7].
Rheological measurements of sewage sludges have been performed using commercial rotational viscometer.
The rheological properties normally determined by using the Bingham plastic model are the yield stress (YS)
(that is the stress required to start the material flowing) the plastic viscosity (that is the internal resistance to
flow under defined shear rate). The Thixotropy, determined by the hysteresis area, is only sometimes
observed (Table 2) [8].
Table 2 — Rheological properties of sewage sludges
Sludge Process TS range TVS/TS YS Plastic
viscosity
% Pa
mPa · s
Mixed 3,0-14 0,52 1,90-185 30-630
Primary 7,0-16 0,43 1,0-49 20-320
Activated 3,0-9 0,73 5,0-214 70-1110
Mixed Sludges Aerobically stabilized 4,0-10 0,53 0,07-58 10-410
Mixed Sludges Anaerobically digested 4,0-9 0,59 1,0-112 20-390
Mixed sludges Mesophilic anaerobic digestion 3,5-5,0 0,5-0,6 0,4-1,6 8,0-24
Mixed sludges Thermophilic anaerobic digestion 3,5-5,0 0,5-0,6 0,1-0,5 11,0-17

Mechanical properties of sewage sludge in solid state were studied with the aim to define the feasibility of
landfill disposal; a correlation between shear strength and dry solid matter for sewage sludge was done using
a Vane apparatus (Figure 1) [9], sludges are suitable for landfilling if their shear strength is of 10 kN/m² at
least (limit value in Italy).
Number of values taken into consideration: 292
Key
X dry solid matter (%) 1 minimum strength 10 kN/m³
Y shearing strength (kN/m³) 2 35 %
Figure 1 — Collation between shearing strength and dry solid method [9]
1.3.2.2 Waterworks sludge
In DVGW W221-1 [10] sludges are defined as solid-water suspensions capable of flowing after sedimentation,
flotation or thickening. Dewatered sludges are sludges, which were dewatered by natural or mechanical
treatments until they are no longer able to flow.
Sludges from water treatment contain several phases differing by their physical state and/or chemical nature.
The space distribution of these phases, as well as the physical-chemical interactions between them, gives to
sludges their cohesion. A too low cohesion of sludges and/or its high fluctuation in the time commonly
generates handling (shovelling- and spreading- ability) and storing difficulties.
An orderly utilisation and disposal of waterworks sludges need the control of the mechanical properties in
order to ensure a quality that is demanded for storage, transport and handling. The mechanical
measurements should be seen and done in connection with other measurements that have been or will be
standardised. There should be mentioned methods for chemical and physical parameters (chemical elements,
dry solids, loss on ignition, pH-value) and operational methods (capillary suction time CST, specific filtration
resistance). The different composition of waterworks sludges with inorganic (Fe, Ca, Al etc.) and organic
(Algae, humid substances, powdered activated carbon etc.) substances depending on the source of raw water
and water treatment processes should be considered. An inquiry from Wichmann et al (2002) [17] showed,
that the waterworks sludges of different types in Germany amounted in 1998 to ca. 181.000 t DS (Lime sludge
40%, Iron sludge 14%, Fe-/Al-Flocculation sludge 13% and other 33%). The composition of the sludge can be
determined after [11] (10 parameters) in Table 3.
Table 3 — Determination of the composition of sludge
Parameter Fraction Conversion in: Fraction
[g/kg DS] [g/kg DS]
(Fictive value)
Acid insoluble 40 Insoluble components 40
(= HCl ) (e.g. sand, activated carbon)
ins.
TOC 30 Total organ. content 60
(Factor: 2)
Mn 20 MnO 31,6
(Factor: 1.58)
Mg 5 Mn(OH) 12,0
(Factor: 2.,4)
Al 20 Al O x H O 44,4
2 3 2
(Factor: 2.22)
SO 5 CaSO 7,1
4 4
(Factor: 1.42) (Ca: 2,1)
CO (= TIC) 80 CaSO 138,6
3 3
(Factor: 1.67) (Ca: 57,6)
Ca –total- 65 -
Residual-Ca 5.3 Ca (PO ) 13,7
3 4 2
(Factor: 2.58) (PO : 8,4)
PO –total- 10 -
Residual-PO 1,6 Fe(PO ) 2,5
4 4
(Factor: 1.59) (Fe: 0,94)
Fe –total- 415,7 -
Residual-Fe 414.8 Fe O x 1,5 H O 692,6
2 3 2
(Factor: 1.67)
Total  1042,5
The range of 0,2 % to 80 % dry solids contents of waterworks sludge to be utilized is quiet wide, so that
several different mechanical properties have to be measured. Possible measuring methods are coming mainly
from the soil mechanical or rheological working fields. There are only few data on mechanical properties of
waterworks sludge published. In Figure 2 after Mc Tigue et al. (1990) [12] e.g. the result of 72 measurement
data of different waterworks sludge types and dewatering processes are shown. A laboratory vane shear
apparatus was used. The vertical line marks the dry solids concentration of 35 % that was given from LAGA
(1979) [13] as a minimum value for disposal of wastes in landfills. Sludge with more than 35 % DS were than
be considered to be qualified for landfilling. The horizontal line marks the minimum value of 25 kN/m
concerning the vane shear strength that is now demanded in new regulations in the TA Siedlungsabfall (1993)
[14]. Approximately 90 % of the waterworks sludges tested after mechanical dewatering could not fulfil the
required minimum value.
Key
X dry solid [% w/w]
Y vane shear strength [kN/m²]
Figure 2 — Comparison dry solid contents vs. laboratory vane shear strength [12]
1.3.2.3 Bio-waste
Organic fraction of municipal solid waste (OFMSW) is utilized for anaerobic and composting treatment.
Anaerobic digestion or co-digestion with sewage sludges is a well-known process where rheological
parameters have been studied to control process.
Table 4 — Particle size distribution of OFMSW
Material Process TS basis TSV basis
% cumulative retained w.w % cumulative retained w.w
5 mm 2 mm 0,84 mm 5 mm 2 mm 0,84 mm
Fresh mechanically Mesophilic 8,2 11,1 18,3 6,7 21 23,5
sorted (F) OFMSW anaerobic
digestion
Pre-composted Mesophilic  19,7  26,1
mechanically sorted anaerobic
(P) OFMSW digestion
Blend of source sorted Mesophilic 6,6 11,5 18,3 12,7 16,8 24,2
and mechanically anaerobic
sorted OFMSW digestion
The OFMSW was analysed for its particle size distribution by wet sieving, using three sieves with openings of
5, 2 mm and 0,82 mm. According to these data the samples can be divided into four conventional classes:
coarse (>5 mm), medium (from 5 mm to 2 mm), medium-fine (from 2 mm to 0,84 mm) and fine (<0,84 mm).
The fresh mechanical sorted OFMSW show up to 18 % and 24% of particles greater than fines for TS and
TVS, respectively. The coarse particles are mainly extraneous materials (plastics, baggage, etc.), which have
no influence on digester fluid-dynamic [21, 22].
Rheological measurements of OFMSW aerobically and anaerobically treated have been performed using
commercial rotational viscometer. The rheological properties normally determined by using the Bingham
plastic model are the yield stress (YS) (that is the stress required to start the material flowing) the plastic
viscosity (that is the internal resistance to flow under defined shear rate). The Thixotropy, determined by the
hysteresis area, is only sometimes observed (Table 5) [21, 22].
Table 5 — Rheological properties of OFMSW aerobically or anaerobically treated
Sludge Process TS range TVS/TS YS Plastic Thixo-
viscosity tropy
% Pa
mPa · s Pa/s
4,8-32,7 0,43-0,49 0,4-63 9-840
OFMSW Thermophilic
mechanically anaerobic
sorted and pre- digestion
composted
6,8-25,2 0,47-0,50 0,1-102 17-1660
Fresh OFMSW Thermophilic
mechanically anaerobic
sorted digestion
5,8-35,1 0,46-0,56 0,2-61 6-560
OFMSW Thermophilic
mechanically anaerobic
sorted enriched digestion
with source
sorted fraction
4,4-18 0,52 0,25-1,2 8,0-54 12-125
OFMSW Anaerobically
digested under
mesophilic and
semi-dry
conditions
5,0-32,7 0,48 0,26-37,7 10-420 36-161
OFMSW Anaerobically
digested under
thermophilic
and semi-dry
conditions
Bio-waste includes also compost, which is derived from aerobic decomposition of recycled plant waste, bio-
solids, fish or other organic material. It is a mixture of decaying organic matter, as from leaves and manure,
used to improve soil structure and provide nutrients.
The sizes of compost pieces can vary within a wide range according to the type of compost e.g. organic
municipal waste. From there the sampling and especially the pre-treatment are of great importance. For
reliable measurements the grain size should be uniform. If needed, the material has to be also compacted in
order to avoid voids of higher dimensions, which could influence the results.
1.3.2.4 Soil
Soils are particulate systems and can cover a wide range of physical state from liquid to solid, depending
mainly on the size and mineralogy of the particles and on the water content. In particular, soils are divided into
coarse-grained soils and fine-grained soils. The surface of the particles has a negative electrical charge,
whose intensity depends on the soil mineral. These surface forces exist in addition to the volume forces of the
particles and in fine-grained soils they play a dominant role in the mechanical and rheological behaviour. The
surface forces strongly depend on the water content and more in general on the chemical composition of the
interstitial fluid.
For this reason, it is very important to set up standards that can define different physical states considering not
only the water content but also the chemical composition of the pore fluid.
The classification of a granular soil is completely defined by the grain distribution curve, the shape of particle
and its specific volume. Whereas the procedure for particle size analysis is well defined and easy to perform
(by a simple sieve analysis), a procedure for characterising the particle shape is not available and it should be
defined as the particle shape strongly influences the mechanical behaviour of these type of soils.
The behaviour of cohesive soils depends on its mineral composition, the water content, the degree of
saturation and its structure. A fine-grained soil can be in a liquid, plastic, semi-solid or solid state, depending
on its water content and this physical state is called consistency. The upper and lower limits of water content
within which a clay element exhibits plastic behaviour are defined as liquid limit and plastic limit. The
procedure is standardised (ASTM D4318) but it is recognised to be strongly affected by the operator
experience. Typical values of liquid limit for natural fine-grained soils range from 40% up to 90% of water
content and the plastic limit from 10% to 50%. Many correlations have been proposed relating the mechanical
characteristics of cohesive soils and the consistency limit; each of them is valid for the specific type of soil for
which it was verified. Table 6 gives an overview of several grain distributions of different standards. The last
one (British Standard) is also valid for Germany e.g. and other European countries.
Table 6 — Grain size of soil according to different classification systems

1.4 Search for existing standards and methods
The first action carried out consisted in searching for existing standards and non-standardised methods to be
possibly used or adapted for utilisation in the specific field of consistency evaluation.
To this purpose, the following standardisation organisations were contacted:
• ISO at www.iso.ch
• ASTM at www.astm.org
• CEN at www.cen.eu
• UNI at www.uni.com
• DIN at www.beuth.de
• AFNOR at www.afnor.fr/portail.asp
• BSI at www.bsi.org.uk
• ASAE at http://webstore.ansi.org/ansidocstore/default.asp
Other information was obtained through personal contacts with experts in the field. In addition, to obtain
selected information, the following keywords were used for research in each web site (among other things):
consistency, viscosity, flowability, shearing, sludge, soil, physical properties, flow properties, suspensions, and
compactibility. The different materials resulted from the research were resins, plastic, lubricant, cement,
asphalts/bitumen, etc.
The complete list of standards is reported in Annex 1 of the HORIZONTAL Reports No. 21 [60] and No. 22
[61], from which it can be seen that more than 250 standards and non-standardised methods are potentially
applicable to consistency evaluation.
1.5 Basic information
1.5.1 Flowability
Flowability and rheology
Flowability is the state in which a material is able to “flow”, i.e. it behaves as a liquid. This characteristics is,
therefore, strictly connected to rheological properties, as rheology is the science of deformation studying the
relationship between shear stress (internal stress) and shear rate (velocity of deformation) which can be
depicted in a rheogram. The rheological behaviour of very thin sludge is Newtonian, like water, i.e. the
viscosity is independent of the flow rate (shear rate) and no initial resistance is shown if a force is applied at
rest (yield stress). This is shown in Figure 3, as T=µ D, where T is the shear stress, D the shear rate and µ the
viscosity. Instead, the behaviour of more concentrated suspensions is described as non-Newtonian: they may
exhibit a yield stress and the viscosity may vary with the shear rate. As shown in Figure 3, many models are
n
applicable: a general equation is T=T +µ D , where T0 is the yield stress, µ the plastic viscosity or fluid
consistency index, and n the fluid behaviour index. The Bingham plastic model, with n=1, so n
...