Small Sewage Treatment Plants

CE Marking and Regulations

Introduction

• Small sewage treatments plants are characterised as plants serving 50 Population Equivalents (PE) or less

• There has been a large number of changes in the regulation and standards that these systems are now expected to comply with.

History – British Standards

Standards often quoted with regards to Small Plants are:

•BS6297:1983 Design of installation of small sewage treatment works and cesspools – REPLACED WITH BS6297:2007 Cope of practice for the design installation of drainage fields for use in wastewater treatment

•BS7781:1994 Procedure for type testing of small biological domestic wastewater treatment plants – NOW WITHDRAWN

Current ‘UK’ Standard – BS EN 12566EN 12566 “Small wastewater treatment systems up to 50PT” contains the following British Standards:

•BS EN 12566-1:2000 Prefabricated septic tanks

•BS EN 12566-3:2005 Packaged and/or site assembled domestic wastewater treatment plants

•BS EN 12566-4:2007 Septic tanks assembled in situ from prefabricated kits

Current ‘UK’ Standard – BS EN 12566Code of Practice:

•TR 12566-2 Code of Practice for in-situ constructed soil infiltration systems

and Standards in preparation:

•EN 12566-5 Pre-treated Effluent Filtration systems

•EN 12566-6 Prefabricated treatment units used for septic tank effluent

•EN 12566-7 Prefabricated tertiary treatment units

BS EN 12566-3:2005 – Confusion over Status

The EN standard includes for a period of “co-existence” of national standards, however there are no existing/conflicting standards in the UK.

Therefore, BS EN 12566-3 is the ONLY standard that all small treatment plants up to 50PE MUST comply to.

Key Points of BS EN 12566-3

BS EN 12566-3:2005 specifies:

• Requirements (e.g. design, structural loads)

• Test methods

• Evaluation of conformity and marking of plants

• Installation, operation and maintenance instructions

Requirement of Small Plants

• Robust, watertight and corrosion resistant

• Equipped with alarm function

• Inlet/outlet pipe: 100mm ID ≤ 4m3/d

150mm ID > 4m3/d

• Sized in accordance with national regulations (EA and BW CoP, Flow and Loads)

Test Methods for Small Plants

• Watertightness Test (different test methods)

• Treatment Efficiency Test (38-week) incl:

o Normal, under and over loading periods

o Power breakdown

o Low occupation stress (holiday simulation)

• Structural Test (different methods, incl. physical and calculations)

Compliance and Marking of Plants

• Compliance of plants is tested and certified by independent test facilities in Europe (none in the UK)

• Manufacturers shall affix CE-certificate stating:

o Name and construction material of plant

o Watertightness and structural test results

o removal efficiencies for BOD, SS and Ammonia

o Energy consumption

UK Foreword of BS EN 12566-3

• UK foreword was amended in May 2007

• Plants shall demonstrate a minimum effluent quality of 20/30/20 (BOD/SS/Ammonia), e.g. achieve removal efficiencies of

o BOD > 93% (based on 300mg/l influent conc.)

o SS > 88% (based on 250mg/l influent conc.)

o Ammonia > 50% (based on 40mg/l influent conc.)

Marsh Sewage Treatment Plants

• Have been tested and certified to BSEN12566-3

• They have passed with a BOD level below 15mg/litre

• Test certificates are available