CEN ISO/TR 20736:2023

SLOVENSKI STANDARD
01-junij-2024
Predelava, recikliranje, obdelava in odlaganje blata - Navodilo za toplotno
obdelavo blata (ISO/TR 20736:2021)
Sludge recovery, recycling, treatment and disposal - Guidance on thermal treatment of
sludge (ISO/TR 20736:2021)
Schlammgewinnung, -verwertung, -behandlung und -beseitigung - Leitfaden für die
thermische Behandlung von Schlamm (ISO/TR 20736:2021)
Valorisation, recyclage, traitement et élimination des boues - Lignes directrices pour le
traitement thermique des boues (ISO/TR 20736:2021)
Ta slovenski standard je istoveten z: CEN ISO/TR 20736:2023
ICS:
13.030.20 Tekoči odpadki. Blato Liquid wastes. Sludge
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN ISO/TR 20736
TECHNICAL REPORT
RAPPORT TECHNIQUE
June 2023
TECHNISCHER REPORT
ICS 13.030.20
English Version
Sludge recovery, recycling, treatment and disposal -
Guidance on thermal treatment of sludge (ISO/TR
20736:2021)
Valorisation, recyclage, traitement et élimination des Schlammgewinnung, -verwertung, -behandlung und -
boues - Lignes directrices pour le traitement beseitigung - Leitfaden für die thermische Behandlung
thermique des boues (ISO/TR 20736:2021) von Schlamm (ISO/TR 20736:2021)

This Technical Report was approved by CEN on 26 June 2023. It has been drawn up by the Technical Committee CEN/TC 308.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TR 20736:2023 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO/TR 20736:2021 has been prepared by Technical Committee ISO/TC 275 "Sludge
recovery, recycling, treatment and disposal” of the International Organization for Standardization (ISO)
and has been taken over as CEN ISO/TR 20736:2023 by Technical Committee CEN/TC 308
“Characterization and management of sludge” 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 shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
Endorsement notice
The text of ISO/TR 20736:2021 has been approved by CEN as CEN ISO/TR 20736:2023 without any
modification.
TECHNICAL ISO/TR
REPORT 20736
First edition
2021-07
Sludge recovery, recycling, treatment
and disposal — Guidance on thermal
treatment of sludge
Valorisation, recyclage, traitement et élimination des boues — Lignes
directrices pour le traitement thermique des boues
Reference number
ISO/TR 20736:2021(E)
©
ISO 2021
ISO/TR 20736:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved

ISO/TR 20736:2021(E)
Contents Page
Foreword .vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 3
5 Sludge properties. 4
5.1 General . 4
5.2 Physico-chemical characteristics . 4
5.2.1 General. 4
5.2.2 Dry matter . 4
5.2.3 Loss on ignition . 4
5.2.4 Calorific value . 5
5.2.5 Grease, scum and screening . 5
5.2.6 Physical consistency and others . 6
5.3 Chemical and microbiological characteristics . 6
5.3.1 General. 6
5.3.2 Sulfur . 6
5.3.3 Phosphorus . 7
5.3.4 Nitrogen . 7
5.3.5 Chlorine and other halogens . 7
5.3.6 Organic micro pollutants . 7
5.3.7 Trace elements. 8
5.3.8 Pathogens . 8
6 Thermal processes fundamentals . 8
6.1 General . 8
6.2 Drying . 9
6.3 Hydrolysis .10
6.4 Incineration .11
6.5 Pyrolysis.12
6.6 Gasification .13
6.7 Thermolysis .14
6.8 Carbonization .14
6.9 Wet oxidation .14
6.10 Melting .15
6.11 Pasteurization .15
7 Technologies .16
7.1 General .16
7.2 Drying .16
7.2.1 Direct dryers .16
7.2.2 Indirect dryers .20
7.2.3 Solar dryers .22
7.3 Hydrolysis .23
7.4 Incineration .24
7.4.1 Fluidized bed furnace .24
7.4.2 Multiple hearth furnace (MHF) .28
7.4.3 Hybrid furnace .31
7.4.4 Others .32
7.5 Pyrolysis.33
7.6 Gasification .33
7.7 Thermolysis .35
7.8 Carbonization .36
ISO/TR 20736:2021(E)
7.9 Wet oxidation .36
7.10 Melting .37
7.11 Pasteurization .39
7.12 Emerging technologies .40
7.12.1 General.40
7.12.2 Oxidation technologies .40
7.12.3 Enzymatic sludge hydrolysis .41
7.12.4 Plasma gasification .41
7.12.5 Ultrasound pretreatment .41
7.12.6 Microwave irradiation .41
7.12.7 Infrared radiation .42
7.13 Design aspects .42
7.14 Auxiliary equipment .42
7.14.1 General.42
7.14.2 Transport, receiving area, storage and feeding systems .43
7.14.3 Heat supply and recovery . .43
7.14.4 Gas cleaning .44
7.14.5 Ash and other residues handling .44
7.14.6 Wastewater treatment .44
7.14.7 Process monitoring .44
7.14.8 Safety systems .45
8 Operational aspects .45
8.1 General .45
8.2 Drying .46
8.3 Hydrolysis .46
8.4 Incineration .46
8.4.1 General.46
8.4.2 Fluidized bed furnace .47
8.4.3 Multiple hearth furnace .48
8.5 Pyrolysis.49
8.6 Gasification .49
8.7 Thermolysis .49
8.8 Carbonization .49
8.9 Wet oxidation .49
8.10 Melting .50
8.11 Pasteurization .50
8.12 Hazards .50
9 Management of energy and secondary resources .50
9.1 General .50
9.2 Drying .51
9.3 Hydrolysis .51
9.4 Incineration .51
9.5 Pyrolysis.52
9.6 Gasification .53
9.7 Thermolysis .54
9.8 Carbonization .54
9.9 Wet oxidation .54
9.10 Melting .54
9.11 Pasteurization .54
9.12 Thermal treatments and circular economy .55
10 Management of residues .55
10.1 General .55
10.2 Flue gas .55
10.2.1 Characteristics and parameters .55
10.2.2 Equipment .57
10.3 Ashes .59
10.3.1 Composition/parameters .59
iv © ISO 2021 – All rights reserved

ISO/TR 20736:2021(E)
10.3.2 Processes and equipment .60
10.4 Wastewater .61
11 Decommissioning of installations .61
11.1 General .61
11.2 Specific considerations .61
12 Co-management with other organic wastes .62
12.1 General .62
12.2 Specific considerations .63
12.3 Additional storage and transport aspects .65
12.3.1 General.65
12.3.2 Storage .65
12.3.3 Transport .66
13 Assessment of sustainability .66
13.1 General .66
13.2 Environmental aspects .67
13.3 Economical aspects .67
13.4 Social aspects.67
Annex A (informative) Calorific values calculations .69
Annex B (informative) Various systems to input sludge into a household waste incineration
plant .70
Annex C (informative) Case studies .72
Annex D (informative) Regulatory aspects .86
Bibliography .89
ISO/TR 20736:2021(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 275, Sludge recovery, recycling, treatment
and disposal.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
vi © ISO 2021 – All rights reserved

ISO/TR 20736:2021(E)
Introduction
Sludge treatment and management is globally a growing challenge for most countries:
— sludge is a by-product of water treatment process produced in large quantities as new wastewater
treatment facilities are built and the existing ones are upgraded to keep up with the population
growth;
— sludge treatment and disposal constitutes one of the most significant costs associated with water
and wastewater treatment;
— stricter regulations on conventional outlets such as beneficial agricultural land, composting,
landfilling require more treatment due to concerns about the long-term impacts on public health
and environment;
— sludge is now being considered as a source of renewable energy, and also a source of valuable
components such as carbon and nutrients.
The growing trend to recover energy and resources from waste sludge and stricter regulations on
outlets have created interest in a number of thermal treatments and may meet, under certain conditions,
the circular economy principles.
The objective of this document is to pragmatically present the methods for thermal treatment of sludge
by covering the different process fundamentals, the associated technologies and operational aspects,
the management of energy, valuables and residues, the aspects related to impacts and integration of
installations referring to them.
Figure 1 highlights the thermal processes covered according to their main function and operating
temperature.
NOTE The processes listed in the right column and connected to conversion and drying as main functions
also achieve the sludge stabilization.
Figure 1 — Thermal processes covered by this document
TECHNICAL REPORT ISO/TR 20736:2021(E)
Sludge recovery, recycling, treatment and disposal —
Guidance on thermal treatment of sludge
1 Scope
This document describes good practices for the incineration and other organic matter treatment by
thermal processes of sludges.
Thermal conditioning is excluded.
This document applies to sludges specifically derived from:
— storm water handling;
— night soil;
— urban wastewater collecting systems;
— urban wastewater treatment plants;
— treating industrial wastewater similar to urban wastewater.
It includes all sludge that may have similar environmental and/or health impacts but excludes hazardous
sludge from industry and dredged sludge.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
melting
thermal treatment which makes sludge or ash temperature raising over melting point of sludge
inorganic substances
3.2
drying
thermal treatment for evaporating water from dewatered sludge to control water content by heating
3.3
carbonization
part of pyrolysis (3.4), focusing on production of a solid secondary resource so-called bio-charcoal
ISO/TR 20736:2021(E)
3.4
pyrolysis
thermal treatment without supply of oxygen
[SOURCE: CEN/TR 16788, 3.4]
3.5
gasification
thermal treatment with less than the stoichiometric supply of oxygen or air (partial combustion)
3.6
char
combination of non-combustible materials and carbon produced from devolatization, gasification (3.5),
pyrolysis (3.4) or carbonization (3.3) process
3.7
bio-charcoal
biochar
solid secondary resource, generated from carbonization (or pyrolysis) process
3.8
thermal treatment
treatment in which heat is applied to remove moisture, microbial content and organic compounds
3.9
thermal process
technique for the application of thermal treatment (3.8)
3.10
combined treatment
treatment of sludge and other waste in the same device
3.11
furnace
enclosed chamber where combustion of organic matter takes place
3.12
boiler
specific part of the thermal treatment plant where heat exchange takes place in view of recovering heat
and energy
3.13
flue gas treatment
any physical or chemical process aimed at cleaning the gas emission resulting from the thermal
treatment (3.8) with regard to their discharge into the atmosphere
3.14
bottom ash
combustion residue collected at the bottom of a combustion furnace
3.15
fly ash
solid material that is entrained in a flue gas stream
3.16
energy recovery
use of combustible waste as a means to generate energy through thermal treatment with recovery of
heat
2 © ISO 2021 – All rights reserved

ISO/TR 20736:2021(E)
3.17
recycling
activity in a production process to process waste materials for the original purpose or for other
purposes, excluding energy recovery (3.16)
3.18
slag
partially glassy by-product obtained by cooling a mineral liquid phase
3.19
energy efficiency
amount of energy and/or heat recovery in relation to the energy content of input material
3.20
wet oxidation
wet air oxidation
aqueous-phase oxidation of organics under pressure, using either air or oxygen as the oxidant
3.21
syngas
mixture of gases (including carbon monoxide, hydrogen, methane, etc.) produced from gasification (3.5)
or pyrolysis (3.4) process
3.22
combustion
chemical and exothermic reaction with full oxidation of combustible materials
3.23
autothermal conditions
conditions that keep combustion without auxiliary fuel and/or other external energy
3.24
paste-like sludge
sludge capable of continuous flow under the effect of pressure above a certain threshold and having a
shear resistance below a certain threshold
[SOURCE: CEN/TR 15463, 1.2.b]
3.25
solid sludge
sludge having a shear resistance above a certain threshold
[SOURCE: CEN/TR 15463, 1.2.c]
4 Abbreviated terms
BAT Best available technology
CFBF Circulating fluidized bed furnace
DM Dry matter
FBF Fluidized bed furnace
GCV Greater (or gross) calorific value
LCV Lower (or net) calorific value
LOI Loss on ignition
ISO/TR 20736:2021(E)
MHF Multiple hearth furnace
MSW Municipal solid waste
PFBF Pressurized fluidized-bed furnace
SCR Selective catalytic reduction
SNCR Selective not catalytic reduction
3T Temperature, turbulence and (residence) time
5 Sludge properties
5.1 General
Sludge characterization for the assessment of thermal processes involves the evaluation of both
technical and economic parameters. The main technical characteristics to evaluate the suitability
of thermal process are DM or moisture content, calorific value, ash content. The main economic
parameters are cost of processing, collection and transport, and the characteristics of the recovered
materials and by-products.
5.2 Physico-chemical characteristics
5.2.1 General
The main physico-chemical characteristics to be taken into account are:
— DM (or moisture content);
— loss on ignition;
— calorific value;
— amount of grease, scum and screenings.
Physical consistency, together with rheological properties, also play an important role, especially as far
as the design of feeding system is concerned.
5.2.2 Dry matter
The DM, or moisture content, is of primary importance for thermal processes because it strongly affects
the LCV of organic material which decreases when the moisture content increases.
In thermal processing of sewage sludge DM is a parameter affecting both fuel requirement and exhaust
gas production. Generally, any increase in DM is believed to be beneficial in the combustion for the
reduction in fuel requirement. When the condition for autothermal combustion, at a given temperature,
is reached the increase in DM corresponds also to a decrease in combustion gases production. Any
further increase of DM beyond the limit of autothermal combustion involves a more abundant gas
production, due to dilution air or water needed for the control of the combustion chamber temperature
depending on design of incineration plant. However, the use of water, reduces the quantity of recoverable
heat in the boiler.
5.2.3 Loss on ignition
The loss on ignition represents the portion mass escaping as gas as a result of the ignition of the dry
mass of sludge.
4 © ISO 2021 – All rights reserved

ISO/TR 20736:2021(E)
The loss of ignition is generally used as a measure of the volatile matter content but it should be noted
that inorganic substances or decomposition products (e.g. H O, CO , SO , O ) are released or absorbed
2 2 2 2
and some inorganic substances are volatile under the reaction conditions.
It is measured by heating sludge in a furnace at 550 °C ± 25 °C (see Reference [4]) or 600 °C ± 25 °C
(see Reference [18]) and expressed as percent of the dry mass. The loss on ignition can be used as an
assessment of the organic part of the sludge, and is therefore related to its heat value.
The presence in the sludge of iron with oxidation during ignition from iron (II) to iron (III), and of
calcium hydroxide or calcium oxide, when sludge is conditioned with lime, can involve decreasing of the
loss on ignition value (see EN 15935).
5.2.4 Calorific value
Calorific value of sludge is a very important parameter for the evaluation of thermal processes, as
it represents the heat quantity developed in the combustion process by the unit mass of material in
standard conditions.
The calorific value can be expressed as (see EN 15170):
— GCV at constant volume which is absolute value of the specific energy of combustion, in Joules, for
unit mass of a solid sludge burned in oxygen in a calorimetric bomb under the conditions specified.
The products of combustion are assumed to consist of gaseous oxygen, nitrogen, carbon dioxide and
sulfur dioxide, of liquid water (in equilibrium with its vapour) saturated with carbon dioxide under
the conditions of the bomb reaction, and of solid ash, all at the reference temperature;
— LCV obtained by calculation from the gross calorific value provided that either the hydrogen content
of the sludge or the amount of water found in the combustion test can be determined.
Sludge usually contains much water, combustible and incombustible solids. Therefore, their calorific
value, especially on the “as received” basis is quite low.
The calculation of calorific value of sludge can be expressed per LOI (loss on ignition) or DM.
Typical calorific values of municipal wastewater sludge range from 22,1 MJ/kg LOI to 24,4 MJ/kg LOI
(anaerobically digested primary) to 23,3 MJ/kg LOI to 27,9 MJ/kg LOI (raw primary). Secondary sludge
displays values between 20,7 MJ/kg
...