Bsi bs en 12255 8 2001 (2004)

Unknown BRITISH STANDARD BS EN 12255 8 2001 Incorporating Corrigendum No 1 Wastewater treatment plants — Part 8 Sludge treatment and storage The European Standard EN 12255 8 2001 has the status of a B[.]

Incorporating Corrigendum No 1

Wastewater treatment

plants —

Part 8: Sludge treatment and storage

The European Standard EN 12255-8:2001 has the status of a

British Standard

ICS 13.060.30

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This British Standard, having

been prepared under the

direction of the Sector

Committee for Building and

Civil Engineering, was

published under the authority

of the Standards Committee

and comes into effect on

15 July 2001

© BSI 13 December 2004

ISBN 0 580 37451 3

National foreword

This British Standard is the official English language version of

EN 12255-8:2001

The UK participation in its preparation was entrusted to Technical Committee B/505, Wastewater engineering, which has the responsibility to:

National annex NA provides further guidance on design and loading data for use 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 are responsible for its correct application

Compliance with a British Standard does not of itself confer immunity from legal obligations.

— 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

Summary of pages

This document comprises a front cover, an inside front cover, the EN title page, pages 2 to 16, an inside back cover and a back cover

The BSI copyright date displayed in this document indicates when the document was last issued

Amendments issued since publication

15294

Corrigendum No 1

13 December 2004 Addition of National annex NA

NORME EUROPÉENNE

ICS 13.060.30

English version

Wastewater treatment plants — Part 8: Sludge treatment and

storage

Stations d'épuration — Partie 8: Stockage et traitement des

boues

Kläranlagen — Teil 8: Schlammbehandlung und -lagerung

This European Standard was approved by CEN on 8 March 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, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION

C O M I T É E U R O P É E N D E N O R M A L I S A T I O N

E U R O P Ä I S C H E S K O M I T E E FÜ R N O R M U N G

Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2001 CEN All rights of exploitation in any form and by any means reserved

worldwide for CEN national Members. Ref No EN 12255-8:2001 E

Page

Foreword 3

1 Scope 3

2 Normative references 4

3 Terms and definitions 4

4 Planning 4

5 Process requirements 5

5.1 General 5

5.2 Thickening 5

5.3 Disinfection 6

5.4 Stabilization and pseudo stabilization 7

5.5 Sludge dewatering 10

5.6 Composting 11

5.7 Handling and storage 12

6 Construction principles 12

6.1 Service life 12

6.2 Pipelines 13

6.3 Sludge pumps 13

7 Safety 13

Bibliography 14

This European Standard 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 November 2001, and conflicting national standards shall be withdrawn at the latest by December 2001

It is the eighth part prepared by the Working Groups CEN/TC 165/WG 42 and WG 43 relating to the general requirements and processes for treatment plants for over 50 PT The parts of the series are as follows:

Part 7: Biological fixed-film reactors;

Part 10: Safety principles;

Part 11: General data required;

Part 12: Control and automation1);

Part 13: Chemical treatment;

Part 14: Disinfection1);

Part 15: Measurement of the oxygen transfer in clean water in aeration tanks of activated sludge plants;

Part 16: Physical (mechanical) filtration1)

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.

The parts EN 12255-1, EN 12255-3 to EN 12255-8 and EN 12255-10 and EN 12255-11 became implemented together as a European package (Resolution BT 152/1998) The date of withdrawal (dow) of all conflicting national standards is 2001-12-31 Until the date of withdrawal is reached, the national and the already published European standards both coexist

This standard includes a Bibliography

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, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom

1 Scope

This European Standard gives design principles and specifies construction requirements for sludge treatment and storage facilities in wastewater treatment plants for more than 50 PT

Other sludges and organic wastes may be treated together with the municipal sewage sludge

Differences in wastewater treatment throughout Europe have led to a variety of systems being developed This standard gives fundamental informations 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

1) In preparation

2 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 12176, Characterization of sludge — Determination of pH-value.

prEN 12255-1:1996, Wastewater treatment plants — Part 1: General construction principles.

prEN 12255-4:1997, Wastewater treatment plants — Part 4: Primary settlement.

EN 12255-5, Wastewater treatment plants — Part 5: Lagooning processes.

prEN 12255-6:1997, Wastewater treatment plants — Part 6: Activated sludge processes.

prEN 12255-9:1999, Wastewater treatment plants — Part 9: Odour control and ventilation.

EN 12255-10, Wastewater treatment plants — Part 10: Safety principles for the construction of wastewater

treatment plants.

EN 12880, Characterization of sludges — Determination of dry residue and water content.

EN ISO 5667-13, Water quality — Sampling — Part 13: Guidance on sampling of sludges from sewage and

water treatment works (ISO 5667-13:1997).

3 Terms and definitions

For the purposes of this European Standard the terms and definitions given in EN 1085 and the following apply

3.1

psychrophilic

process conditions for organisms which are active below 30 °C

3.2 mesophilic

process conditions for organisms which are active at temperatures between 30 °C and 45 °C, with an optimum of

32 °C to 37 °C

3.3

thermophilic

process conditions for organisms which are active at temperatures between 45 °C and 80 °C, and have an optimum of 55 °C to 65 °C

3.4

pseudo stabilization

process which prevents organic degradation so long as particular conditions (such as pH value or dryness) are maintained, but for which degradation recommences when the conditions are no longer met

4 Planning

Sludge treatment and storage influences subsequent utilization It may be subject to a variety of regulations dependent upon the site of the treatment plant and the proposed routes for use or disposal For new works or major upgrading, an environmental impact assessment should be carried out

The choice of the sludge treatment process depends on the size of the treatment plant, the type, origin and characteristics of the sludge to be treated and the final method of utilization or disposal Processes which allow for more than one sludge utilization or disposal option are preferable

Consideration should be given to the possibility of centralized sludge treatment facilities which allow a wider range

of treatment techniques Special care is needed in respect of extra loads, e.g of nitrogen generated from sludge liquors at centralized facilities

Sufficient storage capacity shall be available on the source site for raw or treated sludge to prevent sludge overflow under all likely conditions

The following factors shall be considered in planning sludge treatment:

— the utilization or disposal route and related quality requirements, e.g nutrients, harmful substances and calorific value;

— sludge characteristics;

— import of sludges and other organic wastes;

— minimum and maximum daily sludge production (volume and mass);

— future sludge production;

— range of solids concentrations (total and volatile solids);

— physical characteristics (viscosity, temperature);

— biological properties (degradability, inhibitors and toxicants);

— aggressive or corrosive conditions;

— likely emissions including greenhouse gases, and odours (see also prEN 12255-9:1999);

— removal or disintegration of gross solids which may cause blockage or malfunction;

— effect of abrasive or deposit forming solids such as grit;

— effect of additives used in wastewater treatment, such as precipitants, coagulants and flocculants and their influence on utilization;

— impact of return liquors on the wastewater treatment process, e.g peak loads of ammonia and phosphorus resolubilization from sludge processing;

— health and safety of operators and the general public (see also EN 12255-10), e.g the generation of toxic and/or explosive atmospheres;

— nuisance, e.g smell and visual intrusion;

— environment, e.g effect of leakage

5 Process requirements

5.1 General

Provision shall be made to allow the sampling of input and output for each unit process (see EN ISO 5667-13)

Flow measurement for each unit process should be considered

The design shall take account of any requirements for control of odour, noise, vibration and explosive atmospheres in accordance with prEN 12255-9:1999 and EN 12255-10

5.2 Thickening

5.2.1 General

Sludge thickening is carried out in a continuous or batch mode of operation, using gravity thickeners, mechanical thickening equipment such as filters or centrifuges, or dissolved air flotation

The selection of the thickening method and its design shall take account of the following factors:

— the sludge solids concentration required by subsequent processes;

— the solids recovery from the process;

— resolubilization of phosphorus in gravity thickeners;

— retention times, which when exceeding one day can result in anaerobic degradation, causing odour emission, foaming, bulking and impaired dewaterability;

— control of the sludge feed and liquor removal rates;

— the storage and controlled return of sludge liquor where nitrification or nitrogen removal is required

Due to enhanced viscosity, positive displacement pumps should be used for transferring the thickened sludge

A programme of sludge testing and analysis shall be considered where practicable to assist in the design of gravity thickeners

5.2.2 Gravity thickening

Gravity thickeners should have a depth of at least 3 m, have a bottom slope of at least 50° (conical) or 60° (pyramidal) to the horizontal or be equipped with either an agitator or a rake which includes a bottom scraper (e.g picket fence) Other features which shall be considered include:

— retention and removal of scum;

— supernatant withdrawal at different levels (e.g using a vertically moveable device);

— observing the quality of the supernatant liquor during removal;

— ventilation and exhaust air deodorization if thickeners are covered

Factors which affect the design of gravity thickeners include:

— the surface loading rate;

— the mass surface loading rate;

— the solids detention time;

— the total depth of the consolidation zone

5.2.3 Mechanical thickening

Where thickening equipment is similar to that used for mechanical dewatering, the relevant construction principles apply The most common machines for mechanical thickening are:

— drum filters;

— belt filters;

— centrifuges

Mechanical sludge thickening equipment should:

— normally operate automatically with the facility for manual override;

— include all equipment required for storage, preparation and dosage of any necessary flocculant;

— be enclosed or located in adequately ventilated rooms to reduce corrosion and for the health and safety of the operator

The requirements and guidelines for mechanical sludge dewatering equipment in 5.5.2 are also appropriate to mechanical sludge thickening

5.2.4 Air flotation

Waste activated sludge or backwash water from biofilters can be thickened by dissolved air flotation with or without chemical flocculation

Dimensioning of a dissolved air flotation unit shall take account of the following:

— the surface loading rate;

— the mass surface loading rate;

— the air/solids ratio

5.3 Disinfection

Sludge disinfection may be achieved chemically (see 5.4.4) or thermally

Processes which can achieve disinfection include:

— thermophilic aerobic digestion;

— thermic processes, e.g heat treatment, thermal drying;

— thermophilic aerobic digestion as a pre-treatment before mesophilic anaerobic digestion;

— thermophilic anaerobic digestion as a pre-treatment before mesophilic anaerobic digestion;

— composting;

— addition of lime to liquid sludge or sludge cake;

— mesophilic anaerobic digestion in combination with long term storage

NOTE Pasteurization is time/temperature dependent It may take place before or simultaneously with any stabilization process used

5.4 Stabilization and pseudo stabilization

5.4.1 General

Stabilization is a process for transformation of readily degradable organic substances into mineral or slowly degradable organic substances Treatment of sludge with lime or thermal drying is known as

“pseudo stabilization” It can prevent organic degradation so long as particular conditions (pH value or dryness) are maintained, but degradation recommences when the conditions are no longer met

Pseudo stabilization processes may be used to reduce odour emission during storage, to improve sludge handling

as well as to achieve disinfection They remain an option for treatment before land application, but they do not reduce the long-term potential for gas production which shall be considered if the sludges are to be landfilled

Methods which measure degradability may be used to characterize the quality of stabilization

Methods which measure sulfide evolution may be used to characterize septicity (or the potential for odour formation and emission)

A degree of sludge stabilization can be achieved by the extended aeration process (see prEN 12255-6:1997)

5.4.2 Anaerobic digestion

5.4.2.1 Design considerations

When designing an anaerobic digestion plant, the following factors shall be considered depending upon whether the plant is heated:

— the required volatile solids reduction;

— degradability;

— operating temperature;

— temperature control;

— hydraulic retention time;

— average and peak loads;

— dimensions of the digester;

— one- or two-stage processes;

— gas production (average and peak);

— gas storage and use;

— limitation on gas emissions;

— limits and controls on odour emissions;

— frequency of feeding;

— scum and foam control and removal;

— seeding;

— mixing;

— short-circuiting and dead-space;

— mixing energy (Wh/m3 d) and mixing intensity (W/m3);

— thermal insulation;

— generation of aggressive components in sludge or gas;

— corrosion protection to the interior surface in contact with biogas;

— corrosion protection for gas holders, or means of adding inhibitors to water seals;

— the sum of the maximum hydrostatic pressure plus the maximum gas pressure;

— effect of static and dynamic forces (for example, due to mixers, recirculation, pumps, or temperature variations);

— equipment repair or replacement without emptying the digester;

— overflow routes shall not be obstructed by any valve arrangement;

— provision of a view port with external and internal wiper on top of the digester;

— pressure relief mechanisms;

— equipment for dosing, e.g alkali or anti-foam agents

The average influent solids concentration should be greater than 4 % total dry solids by mass (see EN 12880)

Pipelines connected to the digester below the minimum sludge level should have a section between the isolation valve and the digester which can be isolated by freezing

Gas filters, desulfurizers and gas measurement equipment arranged between digesters and gas holders shall be provided with by-passes Where digester gas is collected, it should be used or burnt and not vented

NOTE Processes for gas treatment storage and utilization are not included in this standard

For heated digestion as a minimum, equipment should be provided to monitor or record the following as a minimum:

— temperature;

— sludge level;

— sludge input and gas production;

— the volume of gas in gas holders;

— pressure loss in the gas system

All sensors shall be removable without emptying the digester Means for sampling raw sludge, sludge in the digester, digested sludge and biogas shall be considered

5.4.2.2 Cold digestion

This may be carried out in open digesters, such as lagoons, open tanks, in enclosed vessels and Imhoff tanks Open digestion of raw sludge should be used only at wastewater treatment plants of less than 1 000 PT, and only where odour and other volatile emissions including methane, are environmentally acceptable

The following factors shall be considered:

— minimum of two anaerobic lagoons or vessels;

— operation in parallel;

— sludge removal;

— the need for scum boards at the overflow

For details about Imhoff tanks and lagoons see prEN 12255-4:1997 and EN 12255-5 respectively

5.4.2.3 Heated digestion

Heated digestion is preferable to cold digestion for sewage sludge, as stabilization and process control are more reliable Imported wastes should be screened or disintegrated as appropriate, and either fed directly or in admixture into digesters

Factors which shall be considered in design of heating systems and heat exchangers include:

— installation of equipment external to digesters;

— condensate hammer (in the case of steam injection);

— removal of precipitates and deposits;

— minimum flow velocity in pipework (if less than 1 m/s, then a regular flushing procedure is required);

— head loss;

— thermal insulation and heat balance

Factors which shall be considered in design of mixing systems include:

— external or internal sludge recirculation;

— digester size and shape;

— completely mixed digesters or digesters with simultaneous thickening and supernatant liquor removal;

— prevention of dead spaces and short-circuits

Efficient mixing by recirculation requires at least five times the digester volume/day

Scum, foam and bottom deposits lead to severe disturbances during the process of digestion The following factors shall be considered:

— means to prevent formation of scum layers and bottom deposits;

— scum removal without emptying tanks;

— health and safety measures during maintenance;

— prevention of foam entry to gas lines, e.g by foam traps;

— grit removal during normal digester operation

5.4.3 Aerobic digestion

Aerobic digestion is usually thermophilic and carried out in closed tanks