Unknown BRITISH STANDARD BS EN 12255 4 2002 Incorporating Corrigendum No 1 Wastewater treatment plants — Part 4 Primary settlement The European Standard EN 12255 4 2002 has the status of a British Sta[.]
BRITISH STANDARD BS EN 12255-4:2002 Incorporating Corrigendum No Wastewater treatment plants — Part 4: Primary settlement The European Standard EN 12255-4:2002 has the status of a British Standard ICS 13.060.30 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN 12255-4:2002 National foreword This British Standard is the official English language version of EN 12255-4:2002 The UK participation in its preparation was entrusted to Technical Committee B/505, Wastewater engineering, which has the responsibility to: — aid enquirers to understand the text; — present to the responsible European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; — monitor related international and European developments and promulgate them in the UK A list of organizations represented on this committee can be obtained on request to its secretary Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online This publication does not purport to include all the necessary provisions of a contract Users of this publication are responsible for their correct application Compliance with a British Standard does not of itself confer immunity from legal obligations This British Standard, having been prepared under the direction of the Building and Civil Engineering Sector Policy and Strategy Committee, was published under the authority of the Standards Policy and Strategy Committee on April 2002 Summary of pages This document comprises a front cover, an inside front cover, the EN title page, pages to 8, the annex NA page and a back cover The BSI copyright date displayed in this document indicates when the document was last issued Amendments issued since publication © BSI 21 June 2002 ISBN 580 39426 Amd No Date 13961 21 June 2002 Insertion of clause numbering for Clauses 1, 2, Corrigendum No Comments EN 12255-4 EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM January 2002 ICS 13.060.30 English version Wastewater treatment plants — Part 4: Primary settlement Stations d'épuration — Partie 4: Décantation primaire Kläranlagen — Teil 4: Vorklärung This European Standard was approved by CEN on November 2001 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 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 Management Centre has the same status as the official versions 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 STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG Management Centre: rue de Stassart, 36 © 2002 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members B-1050 Brussels Ref No EN 12255-4:2002 E EN 12255-4:2002 (E) Contents Page Foreword Scope Normative references Terms and definitions 4 4.1 4.2 4.3 4.3.1 4.3.2 4.3.3 4.3.4 4.3.5 4.3.6 4.3.7 4.4 4.5 Requirements .5 General Planning Process General Required Capacity .6 Upward Flow Tanks (including Imhoff Tanks) Horizontal Flow Tanks .6 Lamella Separator Sludge Collection and Removal .7 Scum Removal .7 Maintenance Health and Safety .7 Bibliography EN 12255-4:2002 (E) Foreword This European Standard has been prepared by Technical Committee CEN/TC 165, Wastewater 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 July 2002, and conflicting national standards shall be withdrawn at the latest by December 2002 It is the fourth part prepared by the Working Groups CEN/TC 165/WG 42 and 43 relating to the general requirements 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: ¾ Part 1: General construction principles ¾ Part 3: Preliminary treatment ¾ Part 4: Primary settlement ¾ Part 5: Lagooning processes ¾ Part 6: Activated sludge processes ¾ Part 7: Biological fixed-film reactors ¾ Part 8: Sludge treatment and storage ¾ Part 9: Odour control and ventilation ¾ Part 10: Safety principles ¾ Part 11: General data required ¾ Part 12: Control and automation ¾ Part 13: Chemical treatment — Treatment of wastewater by precipitation/flocculation ¾ Part 14: Disinfection ¾ Part 15: Measurement of the oxygen transfer in clean water in aeration tanks of activated sludge plants ¾ Part 16: Physical (mechanical) filtration2 ) NOTE For requirements on pumping installations at wastewater treatment plants, provided initially as Part 2, Pumping installations for wastewater treatment plants, see EN 752-6, Drain and sewer systems outside buildings — Part 6: Pumping installations EN 12255-1, EN 12255-3 to EN 12255-8 and EN 12255-10 and EN 12255-11 were implemented together as a European package (Resolution BT 152/1998) According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries 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 2) In preparation EN 12255-4:2002 (E) Scope This European Standard specifies the performance requirements for the primary settlement of wastewater at wastewater treatment plants for over 50 PT The primary application is for wastewater treatment plants designed for the treatment of domestic and municipal wastewater Differences in wastewater treatment throughout Europe have led to a variety of systems being developed This standard gives fundamental information about the systems; this standard has not attempted to specify all available systems Detailed information additional to that contained in this standard may be obtained by referring to the Bibliography Normative references This European Standard incorporates by dated or undated reference, provisions from other publications These normative references are cited at the appropriate places in the text, and the publications are listed hereafter For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision For undated references the latest edition of the publication referred to applies (including amendments) EN 1085, Wastewater treatment — Vocabulary EN 12255-1, Wastewater treatment plants — Part 1: General construction principles EN 12255-3, Wastewater treatment plants — Part 3: Preliminary treatment EN 12255-10, Wastewater treatment plants — Part 10: Safety principles EN 12255-11, Wastewater treatment plants — Part 11: General data required EN 12566-1, Small wastewater treatment systems for up to 50 PT — Part 1: Prefabricated septic tanks Terms and definitions For the purposes of this European Standard, the following terms and definitions given in EN 1085 and the following apply 3.1 lamella separator system of regularly spaced, inclined plates or tubes, designed to increase the effective settling area in a settlement tank EN 12255-4:2002 (E) Requirements 4.1 General Primary settlement serves the purpose of separating settleable solids, which are removed on a regular basis in the form of raw sludge Grease and other floating materials which can cause malfunction of a wastewater treatment plant can also be separated and removed during this process Where large quantities of grease are expected a separate grease separation step is recommended prior to primary settlement (see EN 12255-3) The type and size of unit(s) will depend on the overall system, PT, sludge removal and ground conditions prevailing on the construction site Primary treatment may include the following types of settlement tank: ¾ upward flow (including Imhoff) — generally square or circular in plan; ¾ horizontal flow — generally rectangular in plan; ¾ lamella separator Primary settlement may not be required e.g where biological treatment is by lagooning or by certain activated sludge processes The consequences for subsequent processes of omitting this step shall be considered Septic tanks can be used for the function of primary settlement NOTE 4.2 The design, construction and operation of septic tanks is specified in EN 12566-1 Planning The requirements for the performance of primary settlement should be determined after consideration of the following factors: ¾ the quality and quantity of sludge produced; ¾ the effect of the residual loads on the subsequent treatment processes; ¾ the need to limit retention time in order to avoid septicity Those requirements specific to the performance of the primary settlement plant that are specified in EN 12255-11 shall be applied Additional requirements are specified in EN 12255-1 and EN 12255-10 EN 12255-4:2002 (E) 4.3 Process 4.3.1 General Solids removal and detention times at maximum and minimum flows shall be in accordance with the requirements of any downstream process Where applicable, peak flow shall take into account pumped inflow and/or return flow rates Wastewater shall enter the tank via a stilling device which shall be capable of dissipating the input energy and ensuring even distribution over the entire settlement zone or lamella plate pack The procedure for effluent draw-off shall be designed to minimize disturbance to the settling zone and allow removal of floating matter 4.3.2 Required Capacity The total primary settlement tank capacity required shall take into account the PT and the dry weather peak hourly flow to the plant 4.3.3 Upward Flow Tanks (including Imhoff Tanks) Upward flow tanks may be square or circular in plan Tanks without mechanical scrapers shall have a hopper bottom for sludge collection NOTE Tanks square in plan are not usually employed for populations in excess of 000 PT The tank should be so designed that the upward flow velocity is restricted to within a typical range of 3 1,0 m /(m ·h) to 2,0 m /(m ·h) surface area at dry weather peak hourly flow The minimum sidewall height between the top of the hopper and top water level shall be from 0,3 m to 1,5 m for individual tanks serving populations > 50 PT to 000 PT 4.3.4 Horizontal Flow Tanks Horizontal flow tanks are typically rectangular in plan with a sludge hopper situated at the inlet end of the tank They shall conform to the following minimum values: ¾ 1,5 m water depth at outlet; ¾ 3:1 length to breadth ratio; ¾ 0,3 m freeboard in uncovered tanks Maximum weir overflow rate shall not exceed 30 m /(m·h) at dry weather peak hourly flow EN 12255-4:2002 (E) 4.3.5 Lamella Separator Where these tanks are used they should be equipped with inclined settling plates or tubes, typically forming a counter current system by water circulating from the bottom to top and sludge moving from top to bottom The lamellae shall be so spaced as to avoid clogging and shall be determined by the effectiveness of upstream screening and grease removal The angle of plates/tubes shall be within a range between 55° and 65° measured from the horizontal The space between lamellae and the bottom of the tank shall be designed to ensure an even distribution of wastewater and a sufficient space for the settled sludge Sludge should be collected in one or more hoppers and in larger tanks a scraper mechanism may be used to move the sludge to hopper(s) at one end of the tank The design should allow ease of cleaning of settling plates or tubes on a regular basis 4.3.6 Sludge Collection and Removal 4.3.6.1 Upward Flow Tanks Small tanks typically not have a scraper mechanism to assist sludge removal, and therefore shall have a hopper with smooth sides The angle of slope of the sides of the hopper measured from the horizontal, shall not be less than 50º for conical and 60º for pyramidal hoppers As tank size increases (typically for those serving above 000 PT) a hopper with a 50° respectively 60° floor slope becomes impractical due to the depth of excavation required In these cases a shallow sloping floor is required to collect sludge and allow it to be scraped to the central hopper for removal The floor slope should be between 3º and 30º measured from the horizontal, depending on the size of tank and the type of scraper to be used NOTE Where sludge removal is by suction a floor slope may not be required 4.3.6.2 Horizontal Flow Tanks Very small tanks without a mechanical scraper to assist sludge removal shall have a floor slope of not less than 1:100 to permit emptying to the sludge hopper at the inlet end of the tank These tanks should be completely emptied for sludge removal A minimum of two tanks is required to ensure continuity of treatment Large tanks should have a scraper and/or suction mechanisms installed and a sloping floor may not be required 4.3.7 Scum Removal All tanks shall be designed with a baffle (scum board) to retain floating matter The design of the tank shall enable the retained matter to be removed 4.4 Maintenance The requirements for access, spare parts and maintenance of plants are given in EN 12255-1 4.5 Health and Safety The generality of health and safety requirements for plants are given in EN 12255-10 EN 12255-4:2002 (E) Bibliography The following documents contain details which can be used within the framework of this standard This list of documents which are published and used by the members of CEN was correct at the time of publication of this European Standard but should not be considered to be exhaustive Austria [1] OENorm B 2502-1, Domestic sewage treatment plants for buildings up to 50 inhabitants — Appliance, dimensioning, erection and operation [2] OENorm B 2502-2, Small sewage treatment plants — Installations for buildings of 51 to 500 population equivalents — Application, dimensions, construction and operation [3] OENorm B 2505, Subsurface flow constructed wetlands (constructed wetlands) — Application, dimensioning, installation and operation France [4] Ministére de l’équipement, du logement et des transports (96-7 TO); Conception et exécution o d’installations d’épuration d’eaux usées — Fascicule n 81 titre II Germany [5] DIN 4261-2, Small sewage treatment plants — Part 2: Plants with sewage aeration; application, design, construction and testing [6] E DIN 19551-1, Wastewater treatment plants — Rectangular tanks — Part 1: Settlement tanks with sludge scraper, suction type sludge remover and chain scraper; types, main dimensions, equipment [7] E DIN 19552, Wastewater treatment plants — Circular tanks — Settlement tanks with sludge scraper, suction type sludge remover and thickener; main dimensions, equipment [8] E DIN 19558, Wastewater treatment plants — Outlet installations, weir and scum baffle, submerged effluent pipes in tanks; construction principles, main dimensions, layout [9] DIN 19569-2, Sewage treatment plants — Principles for the design of structures and technical equipment — Part 2: Specific principles for the equipment for separating and thickening of solid material [10] ATV-Handbuch: Mechanische Abwasserreinigung (only in German), Verlag Ernst & Sohn, Berlin; Auflage 1997 Portugal [11] Direcỗóo general da qualidade ambiente Manual de tecnologias de saneamento basico apropriadas a pequenos aglomerados, SEARN, rua de O Século 51 - 1200 Lisboa Portugal Switzerland [12] VSA-Richtlinie, Kleinkläranlagen — Richtlinie für den Einsatz, die Auswahl und die Bemessung von Kleinkläranlagen United Kingdom [13] BS 6297:1983 (amended 1990), Code of practice for the design and installation of a small sewage treatment works and cesspools [14] Manual of British Practice in Water Pollution Control, Primary Sedimentation 1973, reprinted 1980 National Annex NA (informative) Design and Loading Data NA.1 Introduction Clause of the standard gives guidance on upward-flow tanks, horizontal-flow tanks and lamella separators so as to highlight the main design considerations for each type of tank This annex gives more detailed information on the typical surface loading rates, retention times and floor slopes used for design of each type of tank Further information may be obtained from the Manual of UK British Practice on Primary Sedimentation [1] The design of primary treatment plant to serve population equivalents of 000 or less and septic tanks is considered in more detail by the British Standard for the design and installation of small sewage treatment works [2] The surface loading rates and retention times are based on treatment of typical domestic wastewater Additional treatment or extra capacity may be required, if wastewater: — contains high proportion of colloidal or poorly-settling solids (e.g from tanning); — contains readily putrescible solids (e.g from abattoir) which may cause rising sludge; — contains excessive grease (e.g from restaurants); — has warm temperature which generates density gradients within the tank; — has significant saline intrusion generating density gradients within the tank; — receives nitrified activated sludge which denitrifies and forms nitrogen gas buoying solids; — is subject to wide variations in diurnal flow, e.g at small works [2] NA.2 Horizontal-flow tanks Such tanks should be designed to operate at a maximum surface loading rate of between 1.2 to 1.9 m³/m²·h At the tank inlet, the velocity of the wastewater flow should be reduced to about 0.005 m/s to avoid shortcircuiting through the tank Floor slopes should be between 0.3º (1 in 200) and 3º (1 in 20) with a gradient of 1.5º (1 in 40) being commonly used List of references [1] Manuals of British Practice in water Pollution Control Unit Processes Primary Sedimentation 1980 The Institute of Water Pollution Control [2] BS 6297 (amended 1990), Code of practice for design and installation of small sewage and treatment works and cesspools BS EN 12255-4:2002 BSI — British Standards Institution BSI is the independent national body responsible for preparing British Standards It presents the UK view on standards in Europe and at the international level It is incorporated by Royal Charter 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