EN 12255-6:2023

SLOVENSKI STANDARD
01-september-2023
Nadomešča:
SIST EN 12255-6:2002
Čistilne naprave za odpadno vodo - 6. del: Postopek z aktivnim blatom
Wastewater treatment plants - Part 6: Activated sludge process
Kläranlagen - Teil 6: Belebungsverfahren
Stations d'épuration - Partie 6: Procédé à boues activées
Ta slovenski standard je istoveten z: EN 12255-6:2023
ICS:
13.060.30 Odpadna voda Sewage water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 12255-6
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2023
EUROPÄISCHE NORM
ICS 13.060.30 Supersedes EN 12255-6:2002
English Version
Wastewater treatment plants - Part 6: Activated sludge
process
Stations d'épuration - Partie 6: Procédé à boues Kläranlagen - Teil 6: Belebungsverfahren
activées
This European Standard was approved by CEN on 28 May 2023.

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, 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. EN 12255-6:2023 E
worldwide for CEN national Members.

Contents
Page
European foreword . 4
Introduction . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Symbols and abbreviations . 8
4.1 Symbols . 8
4.2 Indices (not included in the symbols or abbreviations below). 10
4.3 Abbreviations . 11
5 Requirements . 12
5.1 General. 12
5.2 Planning . 13
5.2.1 Basic information. 13
5.2.2 System selection . 14
5.2.3 Biological reactors . 18
5.2.4 Clarifiers . 18
5.2.5 Environmental impact . 19
5.3 Detailed Design . 19
5.3.1 Flow-splitting . 19
5.3.2 Biological reactors . 19
5.3.3 Mixing . 20
5.3.4 Aeration . 22
5.3.5 Secondary clarifiers . 26
5.3.6 Return and surplus sludge systems . 28
5.3.7 Internal recirculation . 28
5.3.8 Control and automation . 28
6 Test methods . 30
Annex A (informative) Design of biological reactors . 31
Annex B (informative) Raw wastewater characteristics . 32
Annex C (informative) Removal efficiency of primary clarifiers . 33
Annex D (informative) External carbon sources . 34
Annex E (informative) Sludge age (MSRT) and aerobic sludge age (MASRT) . 35
Annex F (informative) Surplus sludge production . 37
Annex G (informative) Denitrification capacity . 39
Annex H (informative) Oxygen Consumption . 40
Annex I (informative) Iterative calculation of the volumetric ratio of denitrification reactors
(V /V ) . 42
Den R
) . 43
Annex J (informative) Reactor volume (VR
Annex K (informative) Internal recirculation ratio (IRR) . 44
Annex L (informative) Alkalinity . 45
Annex M (informative) Aerobic selectors . 47
Annex N (informative) Design based on F/M-ratio . 48
Annex O (informative) Sludge volume index (SVI) . 49
Annex P (informative) Solids concentration of the return sludge (C ) . 50
TSS,RS
Annex Q (informative) Return sludge flow (Q ) and total suspended solids concentration in
RS
the biological reactor (C ) . 51
TSS,R
Annex R (informative) Surface area (A ) of final clarifiers . 53
Cla
Annex S (informative) Depth (hCla) of final clarifiers . 54
Annex T (informative) Scraper Design. 55
Annex U (informative) Return sludge balance . 57
Annex V (informative) Influent structures . 58
Annex W (informative) Design of a fine bubble aeration system . 59
Bibliography . 62
European foreword
This document (EN 12255-6:2023) 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 2024, and conflicting national standards shall
be withdrawn at the latest by January 2024.
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 document supersedes EN 12255-6:2002.
This is the sixth 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.
The EN 12255 series 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 treatment
• 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 Part 2 is under preparation.
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.
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, Türkiye and the United
Kingdom
Introduction
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:
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
The primary application is for wastewater treatment plants designed for the treatment of domestic and
municipal wastewater.
NOTE For requirements on pumping installations at wastewater treatment plants see EN 752, Drain and sewer
systems outside buildings, and EN 16932, Drain and sewer systems outside buildings — Pumping systems:
—  Part 1: General requirements;
—  Part 2: Positive pressure systems;
—  Part 3: Vacuum systems.
1 Scope
This document specifies performance requirements for treatment of wastewater using the activated
sludge process for plants over 50 PT.
The informative Annexes A to W provide design information.
2 Normative references
The following documents are referred to in the
...