CEN/TS 13714:2013
(Main)Characterization of sludges - Sludge management in relation to use or disposal
Characterization of sludges - Sludge management in relation to use or disposal
This Technical Specification gives guidance for dealing with the production and control of sludge in relation to inputs and treatment and gives a strategic evaluation of recovery, recycling and disposal options for sludge according to its properties and the availability of outlets.
This Technical Specification is applicable for sludges from:
- storm water handling;
- night soil;
- urban wastewater collecting systems;
- urban wastewater treatment plants;
- treating industrial wastewater similar to urban wastewater (as defined in Directive 91/271/EC [1]);
- water supply treatment plants;
but excluding hazardous sludges from industry.
Charakterisierung von Schlämmen - Management von Schlamm zur Verwertung oder Beseitigung
Diese Technische Spezifikation gibt Hinweise, wie mit der Erzeugung und Kontrolle von Schlamm bezüglich der Einleitungen und Behandlung umzugehen ist und vermittelt eine Entwicklungsstrategie der Möglichkeiten für die Wiederverwendung, die Verwertung und Beseitigung von Schlamm entsprechend dessen Eigenschaften und der vorhandenen Entsorgungsmöglichkeiten.
Diese Spezifikation gilt für Schlämme aus:
- Ableitungen von Regenwasser;
- Fäkalien;
- städtischen Abwassersammelsystemen;
- städtischen Abwasserbehandlungsanlagen;
- der Behandlung von industriellen Abwässern vergleichbar mit der Behandlung von städtischen Abwässern (entsprechend den Festlegungen in Richtlinie 91/271/EC [1]);
- Wasserverteilungssystemen;
jedoch mit Ausnahme gefährlicher Industrieschlämme.
Caractérisation des boues - Gestion des boues en vue de leur valorisation ou de leur élimination
La présente spécification technique donne des recommandations pour la gestion de la production et de la maîtrise des boues en relation avec les effluents à traiter et le traitement des boues, et fournit une évaluation stratégique des options de valorisation, de recyclage et d'élimination en fonction de leurs propriétés et de la disponibilité des débouchés.
La présente Spécification Technique est applicable aux boues provenant :
- du traitement des eaux pluviales ;
- des matières de vidange ;
- des systèmes de collecte des eaux usées urbaines ;
- des stations d'épuration des eaux usées urbaines ;
- des stations d'épuration des eaux industrielles assimilées (telles que définies par la Directive européenne 91/271/CE [1]) ;
- des stations de traitement de l'eau potable ;
à l'exclusion des boues industrielles dangereuses.
Karakterizacija blata - Ravnanje z blatom pri uporabi ali odlaganju
To tehnično poročilo podaja smernice za obravnavo proizvodnje in nadzora nad blatom glede na vnose in obdelavo ter podaja strateško vrednotenje možnosti glede predelave, reciklaže in odlaganja za blato v skladu z njegovimi značilnostmi in uporabnostjo za trge. To poročilo velja za blato iz: - ravnanja z vodo ob neurjih; - vsebine greznice; - komunalnih odpadnih vod iz kanalizacijskih sistemov; - čistilnih naprav za komunalno odpadno vodo; - obravnavanja industrijske odpadne vode na podoben način kot komunalne odpadne vode (kot je opredeljeno v Direktivi 91/271/EGS); - čistilnih naprav za sistem oskrbe z vodo; vendar ne iz nevarnega blata iz industrije.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2013
1DGRPHãþD
SIST-TP CEN/TR 13714:2010
Karakterizacija blata - Ravnanje z blatom pri uporabi ali odlaganju
Characterization of sludges - Sludge management in relation to use or disposal
Charakterisierung von Schlämmen - Management von Schlamm zur Verwertung oder
Beseitigung
Caractérisation des boues - Gestion des boues en vue de leur valorisation ou de leur
élimination
Ta slovenski standard je istoveten z: CEN/TS 13714:2013
ICS:
13.030.20 7HNRþLRGSDGNL%ODWR Liquid wastes. Sludge
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
TECHNICAL SPECIFICATION
CEN/TS 13714
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
July 2013
ICS 77.060; 93.140 Supersedes CEN/TR 13714:2010
English Version
Characterization of sludges - Sludge management in relation to
use or disposal
Caractérisation des boues - Gestion des boues en vue de Charakterisierung von Schlämmen - Management von
leur valorisation ou de leur élimination Schlamm zur Verwertung oder Beseitigung
This Technical Specification (CEN/TS) was approved by CEN on 27 August 2012 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available
promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS)
until the final decision about the possible conversion of the CEN/TS into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2013 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 13714:2013: E
worldwide for CEN national Members.
Contents Page
Foreword . 4
Introduction . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 7
4 Waste hierarchy . 8
4.1 General . 8
4.2 Context . 9
5 Management of sludge quality - Upstream processes . 9
5.1 General . 9
5.2 Municipal wastewater sludges . 9
5.3 Setting limits for discharges from industrial and commercial premises to municipal
sewers . 10
5.4 Other factors . 10
5.4.1 General . 10
5.4.2 Protection of biological municipal wastewater treatment processes . 11
5.4.3 Protection of biological sludge treatment processes. 11
5.4.4 Protection of environmental quality in the receiving watercourse . 11
5.4.5 Protection of sewer fabric . 11
5.4.6 Protection of sewer maintenance workers. 11
5.5 Minimising contamination including diffuse sources in municipal wastewater . 11
6 Sludge management . 12
6.1 Measures upstream of water and wastewater treatment facilities . 12
6.1.1 Source prevention . 12
6.1.2 Source reduction . 12
6.2 Measures at sites of sludge production and processing . 12
6.2.1 Water and Wastewater treatment processes . 12
6.2.2 Sludge treatment . 12
6.3 Solutions for recycling recovery and disposal . 14
6.3.1 General . 14
6.3.2 Application to land (see CEN/TR 13097 [16] and CEN/TR 13983 [17]) . 14
6.3.3 Other uses . 14
6.3.4 Energy recovery . 14
6.3.5 Component recovery . 15
6.4 Disposal . 15
7 Operational good practices . 16
7.1 General . 16
7.2 Upstream of the sludge production site . 16
7.2.1 General . 16
7.2.2 Communication process between all participants upstream of the sludge production . 16
7.2.3 Sewerage system structure improvement and maintenance . 16
7.3 At the sludge production site . 17
7.3.1 General . 17
7.3.2 General guidelines for operations . 17
7.3.3 Storage . 17
7.3.4 Site access . 18
8 Strategic evaluation of options and links with the other good practice documents . 18
8.1 General .1 8
8.2 Sludge quantity assessment.1 8
8.3 Sludge quality . 18
8.4 Developing a strategy for sludge use/disposal .1 9
Annex A (informative) Best Practicable Environmental Option for sludges use or disposal . 20
Annex B (informative) Environmental checklist .2 1
Bibliography .2 3
Foreword
This document (CEN/TS 13714:2013) 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 document supersedes CEN/TR 13714:2010.
This document gives recommendations for good practice, but existing national regulations remain in force.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the following
countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria, Croatia, Cyprus,
Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany,
Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Introduction
The purpose of this Technical Specification is to outline the management of sludges both upstream and
downstream of the treatment process to ensure that it is suitable for the outlets available. Sludge is the
inevitable residue of treating raw potable water and municipal and industrial wastewaters. This Technical
Specification refers to all types of sludge covered by CEN/TC 308 including sludges from treating industrial
wastewater similar to urban wastewater and from water supply treatment work plants. In considering the likely
quality of sludges, it should be remembered that municipal wastewater sludges are composed of materials
that have already been disposed of and are consequently likely to be more variable than many industrial
sludges that arise from sourced materials or water treatment sludges arising from surface water or
groundwater.
The quality of the sludge should match the requirements of the outlets whether that be to land, thermal
processing or as a last resort landfill. As a general rule a high quality sludge is likely to be acceptable to a
large range of outlets giving greater operational flexibility. High quality sludges are likely to be suitable for
those outlets associated with maximum sustainability and minimum environmental pollution. The management
of sludges will become increasingly more complex as environmental standards become more stringent and if
outlets become more constrained by legislation and public attitudes.
Sludge quality is central to the development of good practice for sludge production in relation to its destination
(use or disposal). Sludge quality depends on the composition of the upstream materials and the type of
treatment including post treatment storage.
Sludge quality can be characterised by its different properties; biological, chemical and physical:
a) biological properties include the microbiological stability of the organic matter in the sludge, odour and
hygienic characteristics;
b) chemical properties include:
1) content of potentially toxic substances (PTSs) which include inorganic (metals, metalloids, and other
minerals), and organic pollutants;
2) concentrations and form (availability) of plant nutrients and the main components of the sludge;
c) physical properties include whether liquid, semi-solid (pasty-like) or solid, and aesthetic factors
associated for instance with removal of unsightly debris by effective screening. Calorific value is a quality
criterion if the sludge is to be incinerated or used as a fuel. Other physical properties include,
thickenability and dewaterability.
The consistency of these different properties is a critical aspect of the sludge quality and of the ability to
determine its end destination (use or disposal).
Standard methods should be used where these are available to measure the quality parameters of sludge.
There is a continuing need to develop a full set of standardised and harmonised methods which the manager
and operator can use to evaluate the quality of sludge for treatment process design and operational purposes.
This Technical Specification considers the management of sludges against the waste hierarchy, the
management of sludge quality and an option evaluation process to determine the options available.
Figure 1 — A basic scheme for deciding on sewage sludge use/disposal options and the relevant
CEN/TC 308 guidance documents
1 Scope
This Technical Specification gives guidance for dealing with the production and control of sludge in relation
to inputs and treatment and gives a strategic evaluation of recovery, recycling and disposal options for
sludge according to its properties and the availability of outlets.
This Technical Specification is applicable for sludges from:
storm water handling;
night soil;
urban wastewater collecting systems;
urban wastewater treatment plants;
treating industrial wastewater similar to urban wastewater (as defined in Directive 91/271/EC [1]);
water supply treatment plants;
but excluding hazardous sludges from industry.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 1085:2007, Wastewater treatment — Vocabulary
EN 12832:1999, Characterization of sludges — Utilization and disposal of sludges — Vocabulary
3 Terms and definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 1085:2007 and EN 12832:1999 and
the following apply.
3.1.1
industrial wastewater
trade wastewater
trade effluent
wastewater discharge resulting from any industrial or commercial activity
3.1.2
urban wastewater
municipal wastewater
wastewater from municipal areas consisting predominantly of domestic wastewater and which may
additionally contain surface water, infiltration water, trade or industrial wastewater
3.2 Abbreviated terms
The following abbreviated terms, necessary for the understanding of this specification, apply:
BOD: Biochemical Oxygen Demand
BPEO: Best Practicable Environmental Option
COD: Chemical Oxygen Demand
EQO/EQS: Environmental Quality Objectives/Environmental Quality Standards
PTS: Potentially Toxic Substance
4 Waste hierarchy
4.1 General
In order that the management of waste be conducted in an increasingly sustainable manner, the EU
encourages a waste hierarchy as a framework by which Member States should develop their strategy for
waste management (EU Directive 75/442/EEC (see [2]) as amended by 91/156/EEC (see [3])).
Figure 2 — The waste hierarchy — Including sludges
This hierarchy encourages:
a) firstly, the prevention or reduction of waste production and its harmfulness, in particular by:
1) development and implementation of clean technologies more sparing in their use of natural
resources;
2) technical development and marketing of products designed so as to make no contribution or to make
the smallest possible contribution, by the nature of their manufacture, use or final disposal, to
increasing the amount or harmfulness of waste and pollution hazards;
3) development of appropriate techniques for the final disposal of dangerous substances contained in
waste destined for recovery;
b) secondly, the best possible use of waste:
1) recovery of waste by means of recycling, re-use or reclamation or any other process with a view to
extracting secondary raw materials;
2) or the use of waste as a source of energy.
The hierarchy places disposal as the last management choice.
Four of the stages within the hierarchy can be applied to sludges, namely reduction, recycling, recovery and
disposal. Obviously, the latter is the least desirable and efforts should be made to minimise the proportion of
sludge which is disposed of, by the adoption of clean technologies, recycling and recovery strategies.
The waste hierarchy can be applied equally to activities upstream of the sludge production process and to the
processes employed within the treatment process. These are discussed separately below. In considering what
management options should be selected, all stages in the sequence of sludge production and its ultimate fate
should be scrutinised.
4.2 Context
The overall objective of a sludge management strategy should be to find outlets for the sludge which are safe,
environmentally acceptable (carbon foot print), secure and economic. The availability of outlets (see Clause 8)
determines how sludge should be treated.
In order to do this, it is important to address quality (Clause 5) and management processes (Clause 6) and
operational practices (Clause 7).
5 Management of sludge quality - Upstream processes
5.1 General
The significant difference between municipal sludges and industrial sludges and to a certain extent water
treatment sludges is the degree and complexity of control over the inputs.
Industrial sludges usually arise from the processing of sourced materials and control over their content and
consequently the quality of sludge can often be made by analysis of the materials and in many cases by the
imposition of quality standards on them. This may not always be possible for instance in the amount of
bacteriocides and fungicides in paper waste collected for recycling which could vary from batch to batch. River
waters can carry a range of pollutants which could enter the sludge and operators should be aware of the
potential pollutants that could enter the river upstream.
5.2 Municipal wastewater sludges
For municipal wastewater sludges strict limits should be imposed on industrial and commercial discharges to
the sewer so that the sludge produced from wastewater is ‘clean’ or as free as possible of contaminants of
industrial origin.
Industrial point sources of contaminants discharging to the sewer should be identified and restricted or
stopped. Key factors are careful discharge consent settings (see below) monitoring and inspection backed by
enforcement. Quality assurance in support of the consent requires adequate sampling to check compliance.
The extent of sampling of effluent from industrial premises should be decided on a risk assessment basis
taking account for instance of size of operation and quantity of chemicals in use.
The "polluter pays" principle should be used to oblige industries failing to produce acceptable effluents to
investigate and implement remedial measures. This may entail a change in the production process or the
installation on the industrial premises of effluent treatment plant. Often the cost of this is offset by reduced
payments for effluent discharge and the recovery and reuse of valuable chemicals that would otherwise have
been discharged to the sewer. Experience has shown that by progressively identifying and controlling point
source discharges, the quality of sludge can be substantially improved by reducing its content of PTS.
Emergency planning should make provisions to deal with accidental discharges of large amounts of polluting
chemicals to the sewer so that contamination of sludge is minimised, and the biological treatment processes
of wastewater and sludge are protected.
Conventional wastewater treatments remove most of the organic polluting load of the wastewater; this is
measured in terms of BOD or COD. These processes also transfer much of the non-treatable polluting load,
consisting of non-degradable or persistent residues, out of the wastewater and into the sludge. This is
advantageous for the production of clean effluent but if the wastewater contains significant levels of
contaminants of industrial origin then these contaminants are likely to be found in the sludge at levels, which
affect its environmental suitability for use and disposal outlets. Some of the PTS contained in an untreated
wastewater is found in the sludge after treatment. The percentage of the wastewater load of PTS transferred
into sludge depends on many parameters, such as the wastewater and sludge treatment process, pH, solids
content, and PTS content.
5.3 Setting limits for discharges from industrial and commercial premises to municipal
sewers
The use of public wastewater systems is regulated by the operators according to the relevant legislation in
place in all the EU Member States and through by-laws, public law agreement or private law operating
conditions.
The EU legislation covering the control of potentially toxic substances in discharges to the aquatic
environment is Directive 2006/11/EC [4] and Directive 2000/60/EC [5] known as the Water Framework
Directive (WFD). These directives should therefore be the springboard for controlling the discharge of toxic
and harmful materials from industry and commercial activities. There should be an effective control of the
discharge from the wastewater treatment process and the quality of the sludge emanating from it.
Directive 2006/11/EC [4] introduces two lists of 132 dangerous substances to limit discharges from industrial
and commercial premises:
List 1 Substances (e.g. mercury, cadmium, organophosphorus compounds and organochlorine
compounds) should be removed as completely as possible from all industrial wastewater discharges
using the best available technology (BAT). Whenever possible, List 1 substances should be replaced by
more benign and less toxic alternatives.
List 2 Substances (e.g. copper, chromium, zinc, and nickel) should be reduced in discharges by the
application of the "Best Available Technology Not Entailing Excessive Cost" with respect to the level of
environmental risks. A cost/benefit analysis is therefore an essential element in deciding the appropriate
level of treatment.
Annex 10 of Directive 2000/60/EC [5] sets out a list of 33 priority substances or group of substances selected
amongst those which present a significant risk to or via the aquatic environment. For those pollutants, specific
control measures are required that aim for the progressive reduction and for 11 priority hazardous substances
the cessation or phasing-out of discharges, emissions and losses.
Directive 2008/105/EC [6] amending the Water Framework Directive 2000/60/EC (WFD) establishes
environmental quality standards for priority substances and other substances from Directive 2006/11/EC [4].
Reduction of the pollution by these substances shall be assessed through inventories of their discharges,
emissions and losses. This text also proposes a list of 13 substances for their identification as priority or
hazardous priority substances. Directive 2006/11/EC [4] is repealed by the WFD as from the end of 2013.
Requirements for these dangerous substances are the subject of varying national regulations. In all cases,
dangerous substances should be reduced at source as far as possible by suitable pre-treatment of the
industrial waste stream prior to discharge to sewer.
Improvements in environmental protection as regards both sludge recycling or disposal, and discharges from
treatment plants to the watercourse, require the periodic review of industrial and commercial discharge permit
conditions.
5.4 Other factors
5.4.1 General
Factors additional to sludge quality have to be considered in setting limits for chemicals in industrial
discharges to the sewer. These are given below.
5.4.2 Protection of biological municipal wastewater treatment processes
Biological processes depending on the action of bacteria and other micro-organisms include biofilm processes
and activated sludge. The chosen threshold values for individual contaminants from industrial and commercial
discharges should be protective enough to avoid damage to the biota with the consequent failure of the
biological wastewater processes.
5.4.3 Protection of biological sludge treatment processes
This normally applies to anaerobic digestion but also to sludge treated by aerobic processes such as
composting. Heavy metals and organic contaminants such as pentachlorophenol have been found to inhibit
anaerobic digestion of sludge.
It is not easy to designate threshold values for individual contaminants above which biological wastewater or
sludge treatment processes may fail because this depends also on the composition of the wastewater,
operating conditions and whether the plant is acclimatised to the contaminant. It is now the case that in order
to meet sludge quality requirements for use or disposal, concentrations of PTS in wastewater shall be
restricted to levels below those which would be expected to adversely affect biological wastewater, sludge
treatment processes or subsequent use of the liquid.
5.4.4 Protection of environmental quality in the receiving watercourse
The maximum permissible concentrations of substances discharged to the wastewater given by the national
regulations have to be related to the standards set for the final discharge effluent from the wastewater
treatment works including storm water overflows from the sewerage system, and those for the receiving
watercourse.
5.4.5 Protection of sewer fabric
This is usually controlled by limits for the acidity, alkalinity and temperature of discharges and their content of
sulphate and sulphide.
5.4.6 Protection of sewer maintenance workers
Personnel should observe the normal rules of hygiene and it is necessary that chemicals which could
generate toxic fumes in the sewer are strictly controlled.
5.5 Minimising contamination including diffuse sources in municipal wastewater
There are sources of contamination of municipal wastewater and sludge other than industrial and commercial
discharges to the sewer. These are inputs among others from domestic sources and from runoff from roads,
etc. and they are diffuse and less readily controlled than point source inputs.
A programme of public education to minimise discharge of unsuitable substances and materials into domestic
wastewater can be advantageous.
The public should be advised of those substances, which are not permitted for discharge down drains or the
lavatory and be given instructions as to how they can be safely disposed of. Such substances include waste
oil, solvents, paint residues, medicines and pesticides.
The public should be encouraged not to put non-degradable litter items down the lavatory; some countries
have instigated campaigns therefore (e.g. ‘bag it and bin it’ campaign in the UK). The message should be that
collective individual action can make a major impact on the environmental problems.
Organic contaminants in sludge include detergent-derived compounds and other compounds that are widely
used by industry or in the home. It is important to test chemicals before they are put into products for
widespread domestic and other use to ensure that they do not cause a hazard to the environment or man with
respect to sludge use or disposal and to receiving waters. Whether this is done or not is usually beyond the
control of those responsible for sludge quality and safe disposal. There should be more accountability of the
manufacturers of these compounds to ensure treatability. This would be in accordance with the "polluter pays"
principle. To some extent this problem is addressed by Directives 67/548/EEC [7] and 82/242/EEC [8] and
82/243/EEC [9].
6 Sludge management
6.1 Measures upstream of water and wastewater treatment facilities
6.1.1 Source prevention
Prevention at source of contaminants and quantity of discharges to sewer is a preferable policy when new
industrial or commercial premises are being connected to the sewer or when processes are being redesigned.
6.1.2 Source reduction
Reduction of sludge by reducing the input to treatment processes is the most difficult of the hierarchy levels to
achieve. This often requires industry and commercial activities to pre-treat their effluents often producing their
own sludge but reducing the amount and/or pollutants at the municipal wastewater treatment works. A large
proportion of the sludge from municipal wastewaters is derived from domestic wastewater and this is difficult
to control although a public relations programme to indicate to the public what should not be put down the
sewer is advisable.
Sludge quantities from industry and water treatment are related to the rate of production and demand. Potable
water sludge can be reduced by ensuring that water is not taken from rivers when they are carrying large
loads of silt.
6.2 Measures at sites of sludge production and processing
6.2.1 Water and Wastewater treatment processes
When selecting water and wastewater treatment processes, consideration should be given to the quantity and
type of sludge that is produced and its characteristics relative to the proposed ultimate use or disposal of the
sludge.
Proper operating procedures can help to keep sludge production at a low level (e.g. operation at high sludge
residence time in biological processes, optimisation of chemical dosages).
Volumes of industrial sludges have been reduced by reducing inputs into the process. In the Tannery industry,
average chemical consumption has been reduced from 400 kg/t hide to 250 kg and lime input from 5 % to 2 %
to 3 % of hide weight.
Water treatment sludges can be reduced by choosing the optimum flocculant, pH, energy input and retention
time in the mixing and flocculation steps. Where iron and manganese are to be removed, the amount of
sludge produced may be minimised by consideration of the oxidant used. There is also an opportunity to
reduce the amount of dry solids in sludges (Tons of Dry Solids, tDS), if chemical softening is employed by
using caustic soda instead of calcium hydroxide though in this last case there are other drawbacks related to
the drinking water quality and to the dewatering of sludge.
6.2.2 Sludge treatment
6.2.2.1 General
All recommendations have to be adapted to the local context and constraints associated to the outlets.
Appropriate treatment practice should be used to control the pathogen risks. More information on hygienic
aspects is given in CEN/TR 15809 [10].
6.2.2.2 Water content reduction
The reduction in the volume of water present in a sludge by thickening, dewatering and drying is the primary
route by which sludge quantity may be reduced following treatment.
All sludge concentration processes in water and wastewater treatment generate a liquor requiring treatment
by a separate process or with wastewater sludge by recirculation through the wastewater treatment works.
There is a limit to the amount of water that can be removed from sludge by mechanical means, and most
dewatered sludges (for instance by belt press, filter press, centrifuge, etc., see prCEN/TR 16456 on sludge
dewatering [11]) have a dry solids content in the range 15 % to 40 %.
Thermal drying of sludge (see CEN/TR 15473 [12]) reduces the volume of sludge by evaporating water that
cannot be removed mechanically to as high as 95 % dry solids. However, considerable energy is used to dry
sludge to this degree and local circumstances dictate whether any environmental benefit is gained from
thermal drying over the transport of large volumes of wet sludge for recycling or disposal purposes. It is
essential for such factors to be appraised in the strategic evaluation of options (Clause 8).
6.2.2.3 Biological treatment
Anaerobic digestion typically achieves a 40 % to 50 % volatile matter reduction and aerobic stabilisation
achieves a volatile matter reduction of 30 % to 40 %. These processes partly reduce the pathogen content of
the sludge (if present) and importantly its odour potential. Centralised digestion units can be considered for
receiving various industrial wastes, for instance olive oil, tomato and wine wastes in the Mediterranean
regions. Centralisation for municipal wastewater sludges is a common feature with sludges brought in for
treatment from a number of different catchments and this should always be considered where a regional
strategy is being examined.
Composting is an aerobic controlled process (biological oxidation of organic matters with heat generation) to
produce a stable and disinfected product of value as soil amendment. A composting process can be
characterised by the maximum temperature and duration. The composting of most sludges can be optimised
by the addition of bulking agent such as straw, wood chips, bark or garden and park wastes. The Carbon to
Nitrogen ration (C/N) has to be around 25:1 and the air pore volume around 35 % for optimal composting.
Selection of the bulking agent should avoid any negative impact in the quality of the composted product due to
the presence of any contaminants in the bulking agent. Sludge criteria which should be considered for the
composting process include sludge fermentability, sludge type and treatment prior to composting, and sludge
rheology. Factors which should be considered in the design of a composting plant are listed in EN 12255-8
[13].
6.2.2.4 Thermal treatment
Incineration (see CEN/TR 13767 [14]) is a reduction of the organics in the sludge by combustion at high
temperature. It produces an ash (about 20 % to 50 % of sludge dry weight) which has to be disposed of
unless a use can be found for it. Vitrification is a technique for reducing the volume of incinerator ash to make
an environmentally inert material. Landfill disposal can be avoided since it is possible to use this technique to
make environmentally inert construction materials. The temperature required for vitrification is much higher
than for incineration and consequently has a high energy cost.
A positive aspect is the opportunity for some energy recovery through waste-to-energy facilities and these
should preferentially be employed over incineration with no energy recovery. With the improvement in sludge
dewatering and incineration techniques, modern fluidised bed incinerators are autothermic in operation, only
requiring support fuel at start-up, and when coupled with gas cleaning systems, have very low emissions to
the atmosphere. Co-incineration (see CEN/TR 13768 [15]) with other organic wastes, such as municipal solid
waste, may also be an option under some circumstances.
Wet oxidation is a reduction of the organics in the sludge by thermal degradation, hydrolysis and oxidation of
sludge organic matter in aqueous phase in a single-stage reaction at high temperature and pressure. The
technique does not require the complex gas cleaning equipment which is needed in many combustion
processes. During the process, some of the organic matter is made soluble and it produces ashes and high
COD and BOD liquors that are to be treated.
6.3 Solutions for recycling recovery and disposal
6.3.1 General
There are opportunities for recovery of the resource value of sludges at the site of sludge production
(e.g. biogas) or downstream of the site of sludge production (e.g. nutrient content of the sludge).
Sludges can be used in liquid, dewatered, dried or incinerated form. The level of processing employed should
be the optimum necessary to ensure the quality of the sludge for the selected end use.
All these activities should be conducted according to the relevant legislation in place in the relevant Member
States, and other CEN guidance documents.
6.3.2 Application to land (see CEN/TR 13097 [16] and CEN/TR 13983 [17])
The most common method of sludge recycling is application to land. For this application, the levels of PTS
have to be verified against national requirements. There is an existing legal framework for the utilisation of
sludges in agriculture in the European Union [18].
Recycling to land involves the processing of waste materials to produce a usable, secondary raw material.
Sludge may be recycled in a range of ways which vary in the degree of processing and energy required. The
potential to cause an odour nuisance shall be assessed for any sludge being applied to land.
Sludge may be beneficially used to supply plant nutrients and add organic matter and/or lime to soil in
agriculture, land reclamation, forestry operations, landscaping, amenity horticulture and horticulture. Apart
from municipal sludge, many industrial sludges are applied to land including those from paper recycling,
brewing and fruit and vegetable processing. Some waterworks sludges can be beneficially applied to land to
utilise their organic matter and/or lime content such as in the improvement of acid mine spoils. However they
generally have a low N,P,K content and some have negligible soil enhancement value. Waterworks sludges
can be used in topsoil manufacture in some circumstances.
Detailed information on quality should ensure that each type and source of sludge is used appropriately
according to its quality. Maximum benefit and maximum fertiliser replacement value will be achieved if the
nutrient values and release characteristics are matched to the crop needs including the timing of applications.
For example, the nitrogen release characteristics of a digested liquid municipal sludge differ from those of a
digested dewatered cake, and the manner of their use should reflect this to minimise the risk of nitrate
leaching losses. Digested liquids should not be used in the autumn as available nitrogen will leach and not be
taken up by crops.
There are several sludge processing techniques that involve the addition of materials in order to produce a
more stable, easily handled material for land application. One such technique is lime addition for stabilisation,
disinfection, dewatering and storage purposes.
6.3.3 Other uses
Municipal wastewater sludge incinerator ash and some waterworks sludges where they contain iron,
manganese and aluminium can be used in the production of construction materials, such as fibre board,
bricks, ceramic lightweight blocks, paving blocks, etc. Water works sludges with high calcium carbonate
content can be used in the filling material industry and in the paper industry for surface processing. Paper
waste sludge can be used for the production of ethanol and lactic acid. Such processes are high cost but may
be the Best Practicable Environmental Option (BPEO) in some circumstances.
6.3.4 Energy recovery
Useful energy can be recovered from:
a) Methane from anaerobic digestion of sludge.
Gas from anaerobic digestion of municipal sludge contains about 2/3 CH by volume, 1/3 CO by volume and
4 2
small amounts of N , H , H S, water vapour and other gases. Total gas production can fluctuate over a wide
2 2 2
range, depending on the volatile solids content of the sludge feed and the biological activity of the digester.
3 3
Typical values vary from 0,75 m /kg to 1,12 m /kg of volatile solids destroyed. Because digester gas is
typically about 65 % methane, the calorific value of digester gas is about 22 400 kJ/m (by comparison,
methane has a low calorific value of approximately 37 300) kJ/m ). Combined heat and power plants make
efficient use of methane for digester heating, air compression, and electrical power for use on the treatment
plant or for export. Digester gas can be burned directly to provide heat for sludge drying or it can also be
upgraded to vehicle fuel. As digester gas contains hydrogen sulphide, particulates, and water vapour, the gas
has to be cleaned in dry or wet scrubbers before it is used in internal combustion engines.
Anaerobic digestion is increasingly being used for industrial sludges including those from food and beverage
production, meat, dairy and wool processing with the biogas being used to offset energy requirements and
reduce the carbon footprint of the process.
b) Combustion techniques applied to dried and dewatered sludges.
The calorific value of sludges depends on the concentration of water and organic material content.
1) Dedicated or co-incineration with other wastes (see CEN/TR 13767 [14] and CEN/TR 13768 [15]).
Energy may be recovered as heat to be used for space heating or raising steam for power generation. For
municipal wastewater sludge, the calorific value of the dry matter of untreated primary sludge is the
highest.
2) Co-combustion with other fuels in power stations.
3) Use in an industrial process, such as cement and asphalt production. Conventional fuel can be
supplemented by substituting sludge to fuel.
4) Other high temperature treatment opt
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