SIST EN 12255-6:2002

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Wastewater treatment plants - Part 6: Activated sludge processDWRPStations d'épuration - Partie 6: Procédé a boues activéesKläranlagen - Teil 6: Belebungsverfahren13.060.30Odpadna vodaSewage waterICS:SIST EN 12255-6:2002enTa slovenski standard je istoveten z:EN 12255-6:200201-december-2002SIST EN 12255-6:2002SLOVENSKI
STANDARD







EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12255-6January 2002ICS 13.060.30English versionWastewater treatment plants - Part 6: Activated sludge processStations d'épuration - Partie 6: Procédé à boues activéesKläranlagen - Teil 6: BelebungsverfahrenThis European Standard was approved by CEN on 9 November 2001.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the 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 translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2002 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12255-6:2002 E



EN 12255-6:2001 (E)2ContentspageForeword.31Scope.52Normative references.53Terms and definitions.54Requirements.54.1General.54.2Planning.54.3Flow-splitting structure.64.4Biological reactor.64.4.1Design.64.4.2Operational parameters.74.4.3Mixing.74.4.4Aeration.74.4.5Additional considerations.94.5Clarifiers.104.5.1General.104.5.2Design.104.6Return and surplus sludge systems.11Annex A (informative)
Design-Technical process characteristics.12Bibliography.13



EN 12255-6:2001 (E)3ForewordThis European Standard has been prepared by Technical Committee CEN/TC 165 "Wastewater engineering", thesecretariat 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 orby endorsement, at the latest by July 2002, and conflicting national standards shall be withdrawn at the latest byDecember 2002.In this standard the annex A is informative.It is the sixth part prepared by the Working Groups CEN/TC 165/WG 42 and 43 relating to the generalrequirements and processes for treatment plants for a total number of inhabitants and population equivalents (PT)over 50. The Parts of the series are as follows: Part 1: General construction principles Part 3: Preliminary treatment Part 4: Primary settlement Part 5: Lagooning processes Part 6: Activated sludge processes 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) filtration1)NOTEFor requirements on pumping installations at wastewater treatment plants, provided initially as Part 2 "Pumpinginstallations for wastewater treatment plants", see EN 752-6 "Drain and sewer systems outside buildings — Part 6: Pumpinginstallations”.EN 12255-1, EN 12255-3 to EN 12255-8 and EN 12255-10 and EN 12255-11 were implemented together as aEuropean package (Resolution BT 152/1998).
1) In preparation.



EN 12255-6:2001 (E)4According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain,Sweden, Switzerland and the United Kingdom.



EN 12255-6:2001 (E)51 ScopeThis European Standard specifies the performance requirements for treatment of wastewater using the activatedsludge process for plants over 50 PT.Differences in wastewater treatment throughout Europe have led to a variety of systems being developed. Thisstandard gives fundamental information about the systems; this standard has not attempted to specify all availablesystems.Detailed information additional to that contained in this standard may be obtained by referring to the bibliography.2 Normative referencesThis European Standard incorporates by dated or undated reference, provisions from other publications. Thesenormative references are cited at the appropriate places in the text, and the publications are listed hereafter. Fordated references, subsequent amendments to or revisions of any of these publications apply to this EuropeanStandard only when incorporated in it by amendment or revision. For undated references the latest edition of thepublication referred to applies (including amendments).EN 1085, Wastewater treatment — Vocabulary.EN 12255-1, Wastewater treatment plants — Part 1: General construction principles.EN 12255-10, Wastewater treatment plants — Part 10: Safety principles.EN 12255-11, Wastewater treatment plants — Part 11: General data required.prEN 12255-12, Wastewater treatment plants — Part 12: Control and automation.3 Terms and definitionsFor the purposes of this European Standard the terms and definitions given in EN 1085 apply.4 Requirements4.1 GeneralThe biological reactors and the clarifiers connected by the return sludge recirculation form a unit process - theactivated sludge process. The performance of the process depends on the biological and chemical reactions in theactivated sludge tanks as well as the separation of the activated sludge in the final clarifiers.NOTE
Biological treatment and clarification may be combined in the same tank e.g. a sequencing batch reactor (SBR).The design shall take account of the requirements specified in EN 12255-1, EN 12255-10, EN 12255-11 and prEN12255-12.4.2 PlanningThe following factors shall be considered in the design of an activated sludge treatment plant: the capacity and dimensions of the biological reactors; the prevention of dead zones and detrimental deposition in tanks/channels;



EN 12255-6:2001 (E)6 the establishment of multiple lines/units or other technical means to ensure maintenance of required finaleffluent quality if one or more line/unit is out of operation; the aeration and/or mixing equipment; the surface area , volume and depth of the clarifiers ; sludge removal system within the clarifier; the sludge recirculation
and excess sludge wasting equipment; the treatment and
final destination of the sludge produced; measurement and control; the head loss to be minimised.The structures shall be designed to allow emptying either by gravity flow or by pumping. Emptying shall not affectthe stability of structures, irrespective of the groundwater level. All necessary measures shall be taken such asballast concrete, floor check valve or provision for temporary lowering of the groundwater.It can be useful to design the floor to slightly incline towards the lowest points.When a pump is used for emptying a drain pit may be built into these low points.4.3 Flow-splitting structureWhen the process involves multiple lines or parallel units, the incoming flow shall be distributed by an adjustabledistribution device (e.g. valve, gate, stop-log) that can also be used to isolate each treatment unit.This device shall provide the required flow distribution over the range of flow rates considered.NOTEThe accumulation and removal of floating matter can be considered at this stage.4.4 Biological reactor4.4.1 DesignThe number, shape and capacity of the reactors achieving the main biological reactions can vary considerablyaccording to: the size of plant; the level of treatment to be achieved e.g. carbonaceous removal, nitrification, denitrification and phosphorusremoval; the anoxic stage, with respect to nitrogen removal; the dosage of precipitant and/or the anaerobic stage with respect to phosphate removal.The hydraulic design shall minimise short-circuiting. The reactor flow pattern depends on the process selected. Inthe case of multipoint feed (e.g. step-aeration), appropriate devices (e.g. valves, gates, stop-logs) shall be providedto allow modification of the original flow-splitting arrangement.When the plant is designed for one or more reactors to be taken out of service for routine maintenance, thereactors remaining in operation and their associated pipework, channels, etc., shall have the hydraulic andtreatment capacity to accommodate all the incoming flow.



EN 12255-6:2001 (E)7A selector where return sludge and wastewater are brought into a short period of contact can reduce the growth offilamentous bacteria and improve the growth of flocculant bacteria. Owing to the short contact time, the contentshall be mixed efficiently. Where intermittent pumping exist the influent and return sludge shall arrive at the sametime.4.4.2 Operational parametersThe following operational parameters shall be considered and should be appropriate for the level of treatmentrequired: the mixed liquor suspended solids concentration (MLSS) or the mixed liquor volatile suspended solids(MLVSS); the sludge age; the sludge loading (F/M); the sludge volume index (SVI) e.g. stirred (SSVI) or diluted.NOTE
Further information is available in the references listed in the Bibliography.4.4.3 MixingMixing can be performed by the aeration devices themselves (e.g. surface aerators, air-diffusers), by separatemixing devices or by the two together. Individual mixing devices should be capable of being removed withoutemptying the tank. The contents of the aeration tank shall be mixed to prevent activated sludge from settling orforming detrimental deposits.If aeration is not continuous, the devices shall have the capacity to maintain or resuspend the mixed liquor.Mixers should be designed to minimise fouling by fibrous materials.The choice of device depends on the characteristics of the wastewater to be treated and the mixed liquorconcentration required. More powerful devices can be required in cases where the activated sludge process is notpreceded by primary settlement.4.4.4 AerationIn the absence of complementary mixing devices, aeration devices shall have the capacity to provide sufficientagitation to thoroughly mix the biomass, the pollutants and the dissolved oxygen.The dimensioning of the aeration devices and the tanks should ensure both the adequacy of mixing of the activatedsludge mixed liquor and the energy efficiency of the process.If pure oxygen is used in aeration: all necessary safety precautions shall be taken; explosive gas monitoring and explosion proof equipment shall be provided; specific safety signs shall be displayed.It shall be verified that the power input of the aeration device, derived from aeration requirements, is not lower thanthe power required to ensure adequate mixing conditions at all times (unless alternative arrangements are in placefor the mixing process).Air diffusers shall be installed to ensure a uniform depth of immersion.



EN 12255-6:2001 (E)8The aeration system shall have the capacity to supply sufficient oxygen to ensure carbonaceous oxidation,endogenous respiration and oxidation of nitrogen compounds (if these are required) under all operating conditions.The basis of the design is clean water oxygen transfer capacity which shall
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