SIST EN 12255-16:2021
(Main)Wastewater treatment plants - Part 16: Physical (mechanical) filtration
Wastewater treatment plants - Part 16: Physical (mechanical) filtration
This European Standard specifies design principles and performance requirements for tertiary clarification (receiving effluent from secondary treatment) by physical filtration plant at wastewater treatment plants serving more than 50 PT.
NOTE 1 Ultrafiltration, nanofiltration and reverse osmosis are not covered within the scope of this standard as they are not considered to be used for tertiary clarification.
NOTE 2 Soil filtration is not covered in this standard.
NOTE 3 Activated carbon filtration is excluded from the scope of this standard as it is not considered to be a form of mechanical filtration.
Kläranlagen - Teil 16: Abwasserfiltration
Dieses Dokument legt Grundsätze der Planung und Leistungsanforderungen für die Abwasserfiltration als dritte Reinigungsstufe (Ablauf der zweiten Reinigungsstufe) auf Kläranlagen über 50 EW fest.
ANMERKUNG 1 Ultrafiltration, Nanofiltration und Umkehrosmose liegen außerhalb des Anwendungsbereichs dieser Norm, da sie nicht als für die dritte Reinigungsstufe in Frage kommend betrachtet werden.
ANMERKUNG 2 Fragen der Bodenfiltration werden in dieser Norm nicht berührt.
ANMERKUNG 3 Die Filtration mit Aktivkohlefilter liegt außerhalb des Anwendungsbereichs dieser Norm, da sie nicht als eine Form der mechanischen Filtration betrachtet wird.
Stations d’épuration - Partie 16 : Filtration physique (mécanique)
Le présent document spécifie les principes de conception et les exigences de performance relatives à la
clarification tertiaire (recevant des effluents provenant du traitement secondaire) effectuée dans une
installation de filtration physique d’une station d’épuration desservant plus de 50 EH.
NOTE 1 L’ultrafiltration, la nanofiltration et l’osmose inverse ne sont pas couvertes par le domaine d’application
de la présente norme, car elles ne sont pas considérées comme étant utilisées pour la clarification tertiaire.
NOTE 2 La filtration par le sol n’est pas couverte par la présente norme.
NOTE 3 La filtration sur charbon actif est exclue du domaine d’application de la présente norme, car elle n’est
pas considérée comme étant une forme de filtration mécanique.
Čistilne naprave za odpadno vodo - 16. del: Fizična (mehanska) filtracija
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 12255-16:2021
01-oktober-2021
Nadomešča:
SIST EN 12255-16:2005
Čistilne naprave za odpadno vodo - 16. del: Fizična (mehanska) filtracija
Wastewater treatment plants - Part 16: Physical (mechanical) filtration
Kläranlagen - Teil 16: Abwasserfiltration
Stations d’épuration - Partie 16 : Filtration physique (mécanique)
Ta slovenski standard je istoveten z: EN 12255-16:2021
ICS:
13.060.30 Odpadna voda Sewage water
SIST EN 12255-16:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 12255-16:2021
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SIST EN 12255-16:2021
EN 12255-16
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2021
EUROPÄISCHE NORM
ICS 13.060.30 Supersedes EN 12255-16:2005
English Version
Wastewater treatment plants - Part 16: Physical
(mechanical) filtration
Stations d'épuration - Partie 16 : Filtration physique Kläranlagen - Teil 16: Abwasserfiltration
(mécanique)
This European Standard was approved by CEN on 21 June 2021.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
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, Turkey 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
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12255-16:2021 E
worldwide for CEN national Members.
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SIST EN 12255-16:2021
EN 12255-16:2021 (E)
Contents Page
European foreword . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Symbols and abbreviations . 7
5 Requirements . 8
5.1 General. 8
5.2 Process types . 8
5.2.1 Deep bed filtration . 8
5.2.2 Surface filtration . 9
5.2.3 Pilecloth filtration . 9
6 Planning . 9
7 Process design . 10
7.1 Design factors . 10
7.2 Selection of filter media . 10
7.2.1 General. 10
7.2.2 Deep bed filters. 11
7.2.3 Surface filters . 11
7.3 Cleaning systems . 11
7.3.1 General. 11
7.3.2 Deep bed filters. 12
7.3.3 Surface filters . 12
7.4 Dimensions. 12
7.4.1 General. 12
7.4.2 Deep bed filters. 13
7.4.3 Surface Filters . 13
7.5 Flow distribution . 13
7.5.1 General. 13
7.5.2 Deep bed filters. 13
7.5.3 Surface filters . 13
7.6 Construction principles . 14
7.6.1 General. 14
7.6.2 Deep bed filters. 14
7.6.3 Surface filters . 14
7.6.4 Materials . 15
7.7 Mechanical and electrical equipment . 15
7.7.1 General. 15
7.7.2 Deep bed filters. 15
7.7.3 Surface filters . 16
7.7.4 System controls . 16
7.7.5 Performance monitoring . 16
7.8 Additional considerations . 17
7.8.1 Maintenance . 17
7.8.2 Protection of the equipment . 17
7.9 Hazard protection . 17
Annex A (informative) Filter dimensioning table . 18
Bibliography . 22
2
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SIST EN 12255-16:2021
EN 12255-16:202 1 (E)
European foreword
This document (EN 12255-16:2021) has been prepared by Technical Committee CEN/TC 165 “Waste
water engineering”, the secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by January 2022, and conflicting national standards shall
be withdrawn at the latest by January 2022.
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.
This is the sixteenth part prepared by Working Group CEN/TC 165/WG 40 relating to the general
requirements and processes for treatment plants for a total number of inhabitants and population
equivalents (PT) over 50.
EN 12255 with the generic title “Wastewater treatment plants” consists of the following parts:
• Part 1: General construction principles
• Part 2: Storm management systems
• Part 3: Preliminary treatment
• Part 4: Primary settlement
• Part 5: Lagooning processes
• Part 6: Activated sludge process
• Part 7: Biological fixed-film reactors
• Part 8: Sludge treatment and storage
• Part 9: Odour control and ventilation
• Part 10: Safety principles
• Part 11: General data required
• Part 12: Control and automation
• Part 13: Chemical treatment — Treatment of wastewater by precipitation/flocculation
• Part 14: Disinfection
• Part 15: Measurement of the oxygen transfer in clean water in aeration tanks of activated sludge plants
• Part 16: Physical (mechanical) filtration
NOTE For requirements on pumping installations at wastewater treatment plants see EN 752 “Drain and sewer
systems outside buildings - Sewer system management” and EN 16932 (all parts) “Drain and sewer systems outside
buildings – Pumping systems”.
Differences in wastewater treatment throughout Europe have led to a variety of systems being developed.
This document gives fundamental information about the systems; this document has not attempted to
specify all available systems. A generic arrangement of wastewater treatment plants is illustrated in
Figure 1.
3
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SIST EN 12255-16:2021
EN 12255-16:2021 (E)
Key
1 preliminary treatment
2 primary treatment
3 secondary treatment
4 tertiary treatment
5 additional treatment (e.g. disinfection or removal of micropollutants)
6 sludge treatment
7 lagoons (as an alternative)
A raw wastewater
B effluent for re-use (e.g. irrigation)
C discharged effluent
D screenings and grit
E primary sludge
F secondary sludge
G tertiary sludge
H digested sludge
I digester gas
J returned water from dewatering
Figure 1 — Schematic diagram of wastewater treatment plants
Detailed information additional to that contained in this document may be obtained by referring to the
bibliography.
The primary application is for wastewater treatment plants designed for the treatment of domestic and
municipal wastewater.
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.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: 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, Turkey and the United
Kingdom.
4
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SIST EN 12255-16:2021
EN 12255-16:202 1 (E)
1 Scope
This document specifies design principles and performance requirements for tertiary clarification
(receiving effluent from secondary treatment) by physical filtration plant at wastewater treatment plants
serving more than 50 PT.
NOTE 1 Ultrafiltration, nanofiltration and reverse osmosis are not covered within the scope of this document as
they are not considered to be used for tertiary clarification.
NOTE 2 Soil filtration is not covered in this document.
NOTE 3 Activated carbon filtration is excluded from the scope of this document as it is not considered to be a
form of mechanical filtration.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 16323:2014, Glossary of wastewater engineering terms
EN 12255-1, Wastewater treatment plants - Part 1: General construction principles
EN 12255-10, Wastewater treatment plants - Part 10: Safety principles
EN 12255-12, Wastewater treatment plants - Part 12: Control and automation
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 16323:2014 and the following
apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
filtration
process of retention of matter on or in a filter medium when passed by a fluid
Note 1 to entry: The filter medium can be a porous bed or a surface whereon a filter cake is building up.
[SOURCE: EN 16323:2014, 2.3.5.17, modified, to reflect that dissolved matter can also be removed by
some filter types (e.g. granular activated carbon)]
3.2
deep bed filtration
process for the removal of solids from a fluid whereby the fluid flows through a filter medium consisting
of a porous bed
3.3
surface filtration
process for the removal of solids from a fluid whereby the fluid flows through a filter cake building up on
an essentially two dimensional filter medium
5
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SIST EN 12255-16:2021
EN 12255-16:2021 (E)
3.4
granular medium filter
deep bed filter with a granular filter medium
[SOURCE: EN 16323:2014, 2.3.5.22, modified, so as not to exclude crossflow and activated carbon]
3.5
sand filter
deep bed filter using natural or artificial fine particles as filter medium
[SOURCE: EN 16323:2014, 2.3.3.12, modified, to not exclude purpose made manufactured media]
3.6
cloth filter
filter with textile fabric as filter medium
3.7
disc filter
surface filter with rotating discs that are covered with a mesh or cloth as filter medium
3.8
drum filter
surface filter with a rotating drum that is covered with a mesh or cloth as filter medium
[SOURCE: EN 16323:2014, 2.3.8.8, modified, to not exclude materials other than cloth and remove
limitation on axis orientation]
3.9
microstrainer
type of rotating filter with a fine mesh
Note 1 to entry: Microstrainers can be drum or disc filters.
[SOURCE: EN 16323:2014, 2.3.8.15, modified, so as not to exclude rotation about any axis]
3.10
fuzzy filter
deep bed upstream filter with a filter medium consisting of porous and compressible plastic components
3.11
filter medium
material through which a fluid flows and on which matter contained in the fluid is retained
Note 1 to entry: The filter medium of surface filters is the mesh or cloth on which a filter cake is building up. Most
of the solids are retained on or within the filter cake.
[SOURCE: EN 16323:2014, 2.3.8.10]
3.12
particle size ratio
PSR
characteristic of a granular filter medium by means of a sieve analysis and the resulting sieving diagram
whereby the ratio of the two mesh sizes, permitting passage of 60 % and 10 % of the granular mass, is
determined
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SIST EN 12255-16:2021
EN 12255-16:202 1 (E)
4 Symbols and abbreviations
2
A Effective filter area m
eff
2
AL Area load kg/(m ∙ h)
C Concentration of SS in the inflow mg/l
SS,in
2
g Acceleration due to gravity m/s
H Filter bed height m
Ṁ Load due to addition of powdered activated carbon kg /h
AC
Ṁ SS influent load kg /h
in
Ṁ SS effluent load kg /h
out
Ṁ SS load due to precipitation kg /h
prec
NH -N Ammonium nitrogen
4
NO -N Nitrate nitrogen
3
PT Total Phosphorous
3
Q Filtrate flow m /h
SS Suspended solids
3
VL Volumetric Load kg/(m ∙ h)
v Filtration Rate m/h
Δh Head Loss m
Δp Required air pressure for backwashing kPa
3
ρ Water density kg/m
7
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SIST EN 12255-16:2021
EN 12255-16:2021 (E)
5 Requirements
5.1 General
Filtering according to this document is used to remove suspended solids from biologically treated
wastewater by mechanical filtration. Mechanical filters may also be used for further removal of
phosphorous, micro-plastics and micro-pollutants. Mechanical filters may also be used for biological
treatment.
Filters take a number of forms. These are summarized in Table 1.
Table 1 — Effluent filter classification
Filter medium Deep bed Surface
Downflow
Filter type Moving bed filter Upflow filter Pilecloth filter Mesh filter
filter
Granulate (e.g.
Granulate (e.g. Sand or Stainless steel
sand or activated
Filter material activated carbon), beads or Pilecloth or plastic
carbon) or small
plastic foam fibre mesh
beads
Retention of Retention of
solids on solids on
Filter effect Retention of solids in pores or adsorption
surface and in mesh and
pores filter cake
Filtration Continuous Batch Continuous
Filtration flow
Up Down Up In Out
direction
Continuous or
Backwashing Intermittent Continuous or intermittent
intermittent
Filter medium Single or
Single Single Single
layer(s) dual
Biological effect Possible No
5.2 Process types
5.2.1 Deep bed filtration
5.2.1.1 General
Deep bed filters include:
— Moving filters;
— Downflow filters;
— Upflow filters.
The filter material can include granulate (e.g. sand or activated carbon), beads or plastic pieces. Solids
are retained mechanically or by surface adsorption.
Under certain circumstances deep bed filters can be used for biological processes.
Depending on the type of filter, the filtration process is either continuous or batched (intermittent).
8
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SIST EN 12255-16:2021
EN 12255-16:202 1 (E)
5.2.1.2 Batch filtration
An upflow or downflow of effluent percolates through a bed of filter media trapping solids within the bed.
During filtration solids accumulate in the bed and increase the head loss. At intervals, the bed shall be
taken out of service and washed using filtered effluent with or without air scouring to remove
accumulated solids. Washing can be effected by either a pumped or siphonic upflow of filtered effluent
through the entire bed or by a travelling bridge washing individual compartments.
Downflow filters can have one or more layers in addition to a support layer. Upflow filters can only have
a single layer.
Fuzzy filters are batch upflow filters with a filter medium of plastic foam pieces. During filtration the foam
layer is compressed. For filter cleaning the pressure is released and then the filter is backwashed with
water and air. After the cleaning the foam is compressed again.
Because of the intermittent nature of batch filtration several units shall be provided.
5.2.1.3 Continuous filtration
In this style of filter, an upflow of effluent passes continuously through a bed of granular media to remove
solids. An air lift raises granular media from the bottom of the bed for washing and returns cleaned media
to the top of the bed, enabling continuous filtration. This backwashing can be undertaken continuously
or intermittently. Where intermittent backwashing is possible there may be an energy saving.
5.2.2 Surface filtration
Disc filters and drum filters are covered with mesh and rotate horizontally about their longitudinal axis.
The filters are partially submerged. The filtration flow is continuous from inside to out. The backwashing
with spray water occurs continuously or intermittently from outside to in by using the filtered water.
Disc and drum filters have a lower head loss than deep bed filters, but their solids removal efficiency is
usually lower. Disc filters are more compact than drum filters.
5.2.3 Pilecloth filtration
Pilecloth filters can be disc filters or drum filters that are covered with pilecloth and rotate horizontally
about the longitudinal axis. The filters are entirely submerged. A filtration flow is continuous from outside
to inside. The backwashing is undertaken by forcing water under pressure from the inside to outside.
6 Planning
The choice of physical filtration process depends on the size of the treatment plant, space available, the
type, quality, quantity and variability of effluent to be treated, the final quality of effluent required, and
the frequency of maintenance that is required for the process.
Physical filtration can be used to supplement secondary clarification. The following primary factors shall
be considered during design:
— flow to be treated, including return flows;
— type and efficacy of secondary treatment and clarification processes;
— nature and concentration of solids to be removed;
— required quality of treated effluent;
— ranges of hydraulic or suspended solids loads;
— available head;
— available space (e.g. footprint);
— environmental conditions (e.g. climate).
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SIST EN 12255-16:2021
EN 12255-16:2021 (E)
The following secondary factors shall be considered:
— redundancy;
— washwater management;
— the need for chemical cleaning and chemicals management;
— insect management.
7 Process design
7.1 Design factors
The following design parameters shall be considered and values shall be selected which are appropriate
for the required level of treatment:
3 2
— surface loading rate required m /(m ∙h);
2
— suspended solids load kg/(m ∙h);
— pore or media size;
— maximum wash water requirement as a percentage of the treated flow rate;
— frequency of backwashing to maintain filtration rate;
— disposal route for backwash liquors;
— control of influent flows to the treatment process during washing;
— control of excessive instantaneous wash water flow rates.
Informative Annex A, Table A.1 describes typical parameters to use in the design of granular deep bed
filters and surface filtration.
Pilot tests should be carried out under local conditions e.g. when very tight (<0,5 mg/l) phosphorous
consents apply or where the solids are very fine.
7.2 Selection of filter media
7.2.1 General
Filter media should have an extensive surface to allow effluent flow with minimum head loss. It shall be
possible to cleanse the filter medium.
Selection of the filter medium depends on inflow characteristics and the required effluent quality. For
example, if coagulants have been added directly upstream for phosphorus removal, then a fine filter
medium is required.
10
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SIST EN 12255-16:2021
EN 12255-16:202 1 (E)
The following factors shall also be considered in choice of media:
— influent quality;
— pore or particle size;
— ease of cleaning by backwashing;
— resistance to abrasion during backwashing;
— durability to withstand corrosion and chemical or biochemical attack;
— design life;
— ease of replacement.
7.2.2 Deep bed filters
Filter media can be made from the following materials:
— graded mineral (e.g. sand);
— plastics of regular size and shape and randomly arranged;
— glass beads.
The filter media should have a narrow size distribution to form a bed with a high porosity.
The particle size distribution, shape for the materials constituting the bed and also the depth of the bed
shall be selected taking account of the effluent to be treated and the filtrate quality requirements. For
shallow static single layer filters (with a layer depth of 0,3 m to 0,5 m), the granular medium size shall be
between 0,5 mm and 0,8 mm, or between 0,6 mm and 1,2 mm. For both static two-layer filters and
moving bed (continuous) filters (both with a layer depth of 1 m to 3 m), typical particle sizes are between
1,0 mm and 2,0 mm or between 2,0 mm and 4,0 mm. For deep single layer beds, typical particle size
distribution is between 1,7 mm and 3,2 mm.
For filters constructed with a bed of multilayer media, the types of media shall have sufficient difference
in specific gravity to ensure stratification into distinct layers during backwashing. Multilayer filters
permit solids penetration throughout the upper layer and thus increase their loading capacity and the
period of operation before backwashing is needed.
7.2.3 Surface filters
Filter media can be made of stainless steel, synthetic mesh or cloth. Mesh is available in mesh sizes
ranging from 100 µm to 10 µm.
7.3 Cleaning systems
7.3.1 General
During physical filtration, the bed or surface becomes laden with retained solids which improves the
filtrate quality but increases the head loss. Backwashing is undertaken when the head loss becomes too
high or on a time basis. Affected media shall be washed to restore the original filtration properties of the
filter.
Backwash systems should use less than 10 % of the average daily flow to avoid imposing an excessive
additional hydraulic load on the treatment works.
11
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SIST EN 12255-16:2021
EN 12255-16:2021 (E)
When a treatment unit is taken out of service or backwashed, the other units should be capable of taking
the extra load and be capable of maintaining the required operational efficiency. Where backwashing is
not continuous a balancing tank for sludge liquors should be provided.
7.3.2 Deep bed filters
Backwashing is carried out using treated effluent often assisted with air to scour the bed. Treated effluent
for backwashing batch filters should be stored in a tank. Backwashing is carried out continuously at a
certain head loss or on a time basis.
Backwashing programmes are necessary as air and backwash water may be used separately or in
combination during separate phases of the backwashing process. The programmes for a multi-layer filter
shall achieve both the cleaning of the bed and stratification of individual filter layers.
The intensity of washing used for static and moving-bed filters shall be sufficient to minimize the growth
of biological slime on elements of media which would reduce their effective specific gravity and cause
their loss in the filtered effluent overflow.
7.3.3 Surface filters
Disk and drum filters with a mesh are backwashed using spray nozzles. Some of the filtrate is sprayed
from the outside in through the mesh while it is above the water, thus dislodging trapped solids into a
trough within the filter.
Factors which shall be considered in the design of the backwash system include the following:
— start of a backwash cycle, depending on head loss or time; duration of a backwash cycle;
— rotational speed during backwashing;
— spray water pressure and flow;
— percentage of filtrate needed for backwashing;
— type and design of backwash pump, spray nozzles and pipework to avoid clogging and minimize
power consumption;
— need for intensive cleaning, e.g. with high pressure steam or chemicals;
— type, amount a
...
SLOVENSKI STANDARD
oSIST prEN 12255-16:2019
01-september-2019
Čistilne naprave za odpadno vodo - 16. del: Fizična (mehanska) filtracija
Wastewater treatment plants - Part 16: Physical (mechanical) filtration
Kläranlagen - Teil 16: Abwasserfiltration
Stations d'épuration - Partie 16: Filtration physique (mécanique)
Ta slovenski standard je istoveten z: prEN 12255-16
ICS:
13.060.30 Odpadna voda Sewage water
oSIST prEN 12255-16:2019 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 12255-16:2019
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oSIST prEN 12255-16:2019
DRAFT
EUROPEAN STANDARD
prEN 12255-16
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2019
ICS 13.060.30 Will supersede EN 12255-16:2005
English Version
Wastewater treatment plants - Part 16: Physical
(mechanical) filtration
Stations d'épuration - Partie 16: Filtration physique Kläranlagen - Teil 16: Abwasserfiltration
(mécanique)
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 165.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.
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, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 12255-16:2019 E
worldwide for CEN national Members.
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oSIST prEN 12255-16:2019
prEN 12255-16:2019 (E)
Contents Page
European foreword . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Requirements . 6
4.1 General. 6
4.2 Process types . 7
4.2.1 Deep bed filtration . 7
4.2.2 Pilecloth filtration . 8
4.2.3 Surface filtration . 8
5 Planning . 8
6 Process design . 9
6.1 Design factors . 9
6.2 Selection of filter media . 9
6.2.1 General. 9
6.2.2 Deep bed filters. 10
6.2.3 Surface filters . 10
6.3 Cleaning systems . 10
6.3.1 General. 10
6.3.2 Deep bed filters. 11
6.3.3 Surface filters . 11
6.4 Dimensions. 11
6.4.1 General. 11
6.4.2 Deep bed filters. 12
6.4.3 Surface Filters . 12
6.5 Flow distribution . 12
6.5.1 General. 12
6.5.2 Deep bed filters. 12
6.5.3 Surface filters . 13
6.6 Construction principles . 13
6.6.1 General. 13
6.6.2 Deep bed filters. 13
6.6.3 Surface filters . 13
6.7 Mechanical and electrical equipment . 14
6.7.1 General. 14
6.7.2 Deep bed filters. 14
6.7.3 Surface filters . 15
6.7.4 System controls . 15
6.7.5 Performance monitoring . 15
6.8 Additional considerations . 16
6.8.1 Maintenance . 16
6.8.2 Protection of the equipment . 16
6.9 Hazard protection . 16
Annex A (informative) Filter Dimensioning Table. 17
Bibliography . 21
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European foreword
This document (prEN 12255-16:2019) has been prepared by Technical Committee CEN/TC 165 “Waste
water engineering”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document has been prepared under a mandate given to CEN by the European Commission and the
European Free Trade Association, and supports essential requirements of EU Directive(s).
It is the sixteenth part prepared by Working Group CEN/TC 165/WG 40 relating to the general
requirements and processes for treatment plants for a total number of inhabitants and population
equivalents (PT) over 50. EN 12255 with the generic title “Wastewater treatment plants” consists of the
following Parts:
• Part 1: General construction principles
• Part 2: Pumping Stations
• Part 3: Preliminary treatment
• Part 4: Primary settlement
• Part 5: Lagooning processes
• Part 6: Activated sludge process
• Part 7: Biological fixed-film reactors
• Part 8: Sludge treatment and storage
• Part 9: Odour control and ventilation
• Part 10: Safety principles
• Part 11: General data required
• Part 12: Control and automation
• Part 13: Chemical treatment — Treatment of wastewater by precipitation/flocculation
• Part 14: Disinfection
• Part 15: Measurement of the oxygen transfer in clean water in aeration tanks of activated sludge
plants
• Part 16: Physical (mechanical) filtration
• Part 17: Storm Tanks
NOTE For requirements on pumping installations at wastewater treatment plants see EN 752-6 “Drain and
sewer systems outside buildings — Part 6: Pumping installations”.
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Differences in wastewater treatment throughout Europe have led to a variety of systems being
developed. This document gives fundamental information about the systems; this document has not
attempted to specify all available systems. Detailed information additional to that contained in this
European Standard may be obtained by referring to the bibliography.
The primary application is for wastewater treatment plants designed for the treatment of domestic and
municipal wastewater.
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1 Scope
This document specifies design principles and performance requirements for tertiary clarification
(receiving effluent from secondary treatment) by physical filtration plant at wastewater treatment
plants serving more than 50 PT.
NOTE 1 Ultrafiltration, nanofiltration and reverse osmosis are not covered within the scope of this standard as
they are not considered to be used for tertiary clarification.
NOTE 2 Soil filtration is not covered in this standard.
NOTE 3 Activated carbon filtration is excluded from the scope of this standard as it is not considered to be a
form of mechanical filtration.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 16323:2014, Glossary of wastewater engineering terms
EN 12255-1, Wastewater treatment plants - Part 1: General construction principles
EN 12255-10, Wastewater treatment plants - Part 10: Safety principles
EN 12255-12, Wastewater treatment plants - Part 12: Control and automation
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 16323:2014 and the following
apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
deep bed filtration
process for the removal of solids from a fluid whereby the fluid flows through a filter medium
consisting of a porous bed
3.2
surface filtration
process for the removal of solids from a fluid whereby the fluid flows through a filter cake building up
on an essentially two dimensional filter medium
3.3
cloth filter
filter with textile fabric as filter medium
3.4
disc filter
surface filter with rotating disks that are covered with a mesh or cloth as filter medium
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3.5
drum filter
surface filter with a rotating drum that is covered with a mesh or cloth as filter medium
3.6
filter medium
material through which a fluid flows and on which matter contained in the fluid is retained
Note 1 to entry: The filter medium of surface filters is the mesh or cloth on which a filter cake is building up. Most
of the solids are retained on or within the filter cake.
3.7
filtration
process for retention of matter on or in a filter medium when passed by a fluid
Note 1 to entry: The filter medium can be a porous bed or a surface whereon a filter cake is building up
3.8
granular medium filter
deep bed filter with a granular filter medium
3.9
microstrainer
type of cylindrical sieve with a fine mesh
Note 1 to entry: Microstrainers can be drum or disc filters.
3.10
sand filter
deep bed filter using natural or artificial sand as filter medium
3.11
fuzzy filter
deep bed upstream filter with a filter medium consisting of porous and compressible plastic
components
4 Requirements
4.1 General
Filtering according to this standard is used to remove suspended solids from biologically treated
wastewater by mechanical filtration. Mechanical filters may also be used for further removal of
phosphorous, micro-plastics and micro-pollutants. Mechanical filters may also be used for biological
treatment.
Filters take a number of forms. These are summarized in Table 1.
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Table 1 — Effluent filter classification
Filter Medium Deep Bed Surface
Moving Bed Downflow Pilecloth
Filter Type Upflow Filter Mesh Filter
Filter Filter Filter
Granulate (e.g.
Granulate (e.g. Sand or
Sand or Activated SS or Plastic
Filter Material Activated Carbon), Beads or Pilecloth
Carbon) or Small Fibre Mesh
Plastic Foam
Beads
Retention of Retention of
Solids on Solids on
Filter Effect Retention of Solids in Pores or Adsorption
Surface and in Mesh and
Pores Filter Cake
Filtration Continuous Batch Continuous
Filtration Flow
Up Down Up In Out
Direction
Continuous or
Backwashing Intermittent Continuous or Intermittent
Intermittent
Filter Medium Single or
Single Single Single
Layer(s) Dual
Biological Effect Possible No
4.2 Process types
4.2.1 Deep bed filtration
4.2.1.1 General
Deep bed filters include:
— Moving filters
— Downflow filters
— Upflow filters
The filter material can include granulate (e.g. sand or activated carbon), beads or plastic pieces. Solids
are retained mechanically or by surface adsorption.
Under certain circumstances deep bed filters can be used for biological processes.
Depending on the type of filter, the filtration process is either continuous or batched (intermittent).
4.2.1.2 Batch filtration
An upflow or downflow of effluent percolates through a bed of filter media trapping solids within the
bed. During filtration solids accumulate in the bed and increase the head loss. At intervals, the bed shall
be taken out of service and washed using filtered effluent with or without air scouring to remove
accumulated solids. Washing can be effected by either a pumped or siphonic upflow of filtered effluent
through the entire bed or by a travelling bridge washing individual compartments.
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Downflow filters can have one or more layers in addition to a support layer. Upflow filters can only have
a single layer.
Fuzzy filters are batch upflow filters with a filter medium of plastic foam pieces. During filtration the
foam layer is compressed. For filter cleaning the pressure is released and then the filter is backwashed
with water and air. After the cleaning the foam is compressed again.
Because of the intermittent nature of batch filtration several units shall be provided.
4.2.1.3 Continuous filtration
In this style of filter, an upflow of effluent passes continuously through a bed of granular media to
remove solids. An air lift raises granular media from the bottom of the bed for washing and returns
cleaned media to the top of the bed, enabling continuous filtration. This backwashing can be undertaken
continuously or intermittently. Where intermittent backwashing is possible there may be an energy
saving.
4.2.2 Pilecloth filtration
Pilecloth filters can be disc filters or drum filters that are covered with pilecloth and rotate horizontally
about the longitudinal axis. The filters are entirely submerged. A filtration flow is continuous from
outside to inside. The backwashing is undertaken by forcing water under pressure from the inside to
outside.
4.2.3 Surface filtration
Disc filters and drum filters are covered with mesh and rotate horizontally about their longitudinal axis.
The filters are partially submerged. The filtration flow is continuous from inside to out. The
backwashing with spray water occurs continuously or intermittently from outside to in by using the
filtered water.
Disc and drum filters have a lower head loss than deep bed filters, but their solids removal efficiency is
usually lower. Disc filters are more compact than drum filters.
5 Planning
The choice of physical filtration process depends on the size of the treatment plant, space available, the
type, quality, quantity and variability of effluent to be treated, the final quality of effluent required, and
the frequency of maintenance that is required for the process.
Physical filtration can be used to supplement secondary clarification. The following primary factors
shall be considered during design:
— flow to be treated, including return flows;
— type and efficacy of secondary treatment and clarification processes;
— nature and concentration of solids to be removed;
— required quality of treated effluent;
— ranges of hydraulic or suspended solids loads;
— available head;
— available space (e.g. footprint);
— environmental conditions (e.g. climate).
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The following secondary factor shall be considered:
— redundancy;
— washwater management;
— the need for chemical cleaning and chemicals management;
— insect management.
6 Process design
6.1 Design factors
The following design parameters shall be considered and values shall be selected which are appropriate
for the required level of treatment:
3 2
— surface loading rate required m /(m ∙h);
2
— suspended solids load kg/(m ∙h);
— pore or media size;
— maximum wash water requirement as a percentage of the treated flow rate;
— frequency of backwashing to maintain filtration rate;
— disposal route for backwash liquors;
— control of influent flows to the treatment process during washing;
— control of excessive instantaneous wash water flow rates.
Informative Annex A describes typical parameters to use in the design of granular deep bed filters and
surface filtration.
Pilot tests should be carried out under local conditions e.g. when very tight (<0,5 mg/l) phosphorous
consents apply or where the solids are very fine.
6.2 Selection of filter media
6.2.1 General
Filter media
...
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