Category: Information

Sewage Treatment Systems Code of Practice
Flows and loads (sizing criteria)

This code of practice was prepared by the British Water Package Sewage Treatment Plant Focus Group comprising manufacturers, suppliers and service companies of all types of small wastewater treatment systems.

The Environment Agency, the Northern Ireland Environment Agency and the Scottish Environment Protection Agency support the use of this code of practice, but the Agencies do not specifically endorse any particular manufacturer’s product.

This code of practice provides a table of loadings which allows the total daily sewage load from properties to be calculated and it is recommended that all designers should use this table when sizing and designing non-mains sewage treatment systems.

The flows and loads values given represent current best knowledge within the UK but may change with time in line with per capita water use.

Where proposed alternative usage rates or methods of sizing might be more appropriate for a particular application this should be supported by the collection of data or additional site specific evidence to validatethe proposal. Professional judgment is required and may be used to compare alternatives especially when assessing sewage strengths and treatability.

Guidance is provided to assist the user to identify the various sources of sewage, to consider the nature of the sewage to be treated and to make users aware of issues which may affect treatability and system performance. Each manufacturer is aware of the capabilities of their own systems with respect to different situations.

The table of loadings may be used to design all sizes of sewage treatment systems serving up to 1000 population.

Use of this code of practice by all UK manufacturers and system designers will:

• Help to clearly define site activity and sewage sources
• Promote a consistent approach to collecting accurate and complete loading information
• Provide consistent information about problem effluents and treatability
• Promote the design and installation of appropriate treatment systems and so reduce the problem of undersized systems causing environmental contamination

The loadings in this code of practice are more comprehensive than in previously published guidance, they are generally higher and include values for ammonia.

The owner of the treatment system holds the permit, consentor authorisation to discharge and should be aware that he is responsible for the effluent quality discharged. Thus all sources of discharge into the system must be declared. It is an offence if the effluent fails to comply with the regulators requirements.

Full details of the guidelines are enclosed on the attached PDF, but please do not hesitate to call us on 01773 767611 should you require any further assistance.

British Water Flows and Loads 4

Drainstore hold copies of the most up to date Building Regulations part H, Drainage and waste disposal, both in hard copy and PDF to assist customers with their drainage queries. Please call on 01773 767611 for further details.

What are the Part H Building Regs?

The Building Regulations Part H is an approved document that provides guidance on how to achieve compliance with the laws surrounding drainage and waste disposal, both above and below ground. It covers a wide range of topics, including sanitary pipework, foul drainage, waste collection, testing and inspection, and more.

Installing and maintaining drainage are hazardous operations and should only be attempted in line with safety codes, including procedures relating to working in confined spaces.

If you will need to apply for building regulations approval or need help with installation or inspection of your drains, you can call us on 01773 767611 and we will help make sure that your application is up to the necessary standards.

Pollution prevention guidelines

Treatment and disposal of sewage where no foul sewer is available: PPG4

These guidelines are jointly produced by the Environment Agency for England and Wales, the Scottish Environment Protection Agency, and the Environment and Heritage Service for Northern Ireland (referred to here as ‘we’ or ‘us’). You should consider all sites individually and we advise you to consult one of our local offices as early as possible. You can find contact details at the end of these guidelines.

Following the good practice described does not remove your obligation to comply with relevant legislation and to prevent pollution from your site. Pollution of the environment is a criminal offence and compliance with one or more Guidance Note is not a defence to such offences. It is recommended that you check the references to other sources of guidance to ensure they are still current.

In this document sewage is defined as the water borne wastes of a community or household. The Construction Products Regulations 1991 dictate the essential requirements that a sewage treatment system must fulfil to be legally supplied in the UK. Where we use the word ‘must’ in this guidance, compliance with that particular part of the guidance is a legal requirement under these regulations. The Trading Standards Authorities enforce these regulations.

1. Introduction

Choosing the right sewage treatment and disposal method for your site is essential to ensure value for money, effective long-term performance, protection of public health and the environment, and compliance with relevant legislation.

This guidance will help you choose the correct option for your circumstances by telling you about; ¨ the sewage treatment and disposal methods available. ¨ the maintenance requirements of the system you choose. ¨ the basic legal requirements.

Sewage treatment and disposal can be provided by a sewer provider (that is the public ‘foul’ sewer) or by a private sewage treatment system. Developments proposing the use of private sewage treatment systems are usually only acceptable where connection to the public sewer is not possible. Although if a treatment system is proposed that offers a more sustainable solution to the overall water management of the site, that might be acceptable.

2. Sewage treatment and disposal – Selecting the best option

Use the flowchart and questions below to help you choose the best system for your site. When you have selected an option you should continue to read the relevant section in this guidance. You should always seek expert advice before making your final decision. (See reference 2 for more information on selecting the best option)

Septic tanks and small sewage treatment plants

The requirement to register small domestic sewage discharges from septic tanks and small sewage treatment plants, has changed in England.

The requirement to register was a result of regulations made in 2010 by the Department for Environment, Food and Rural Affairs (Defra) and the Welsh Government, as part of the implementation of the European Union Water Framework Directive. Registration was considered to provide the lightest touch approach to meet legal obligations.

However, we are now undertaking a joint review with Government on the requirement to register small domestic sewage discharges in England, details of which will be announced in the next few weeks.

While the review is underway, we will not require the registration of small domestic sewage discharges, including septic tanks, in England – although householders can still register if they wish. If you would still like to register a small domestic sewage discharge please visit these pages.

Registering your septic tank and small sewage treatment plant discharges in England

Registering your septic tank and small sewage treatment plant discharges in Wales

Environmental permitting for small sewage discharges

Environment Agency Home Page