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Sewage Treatment

Background

Before the wastewater generated by society can be returned as effluent to a stream, river, or the sea it first needs to receive treatment to ensure the receptor is not significantly polluted.

In England and Wales the Environment Agency is responsible for setting Effluent Quality Standards and does so by issuing Site Specific Environmental Permits (formally Discharge Consents).  This does not apply to discharges of less than 5m3 per day which are exempt from the Permitting Regulations. 

If an Environmental Permit is required MHE Associates can complete all of the necessary forms on your behalf and submit to the Environment Agency, but please note that the Permit Holder is legally responsible for ensuring the discharge meets the requirements of the Permit.

Treatment Methods

Methods of treatment can be grouped together to provide various levels of treatment:

  • Preliminary – Removal of Solids
  • Primary – Removal of a percentage of suspended solids and organic matter
  • Secondary – Removal of biodegradable matter and suspended solids
  • Tertiary – Removal of residual suspended solids, usually by granular filtration.

To remove the constituents of concern physical, biological and chemical methods are used such as:

  • Physical – Screening, Mixing, Filtration
  • Biological – Activated Sludge and Trickling Filter processes
  • Chemical – Disinfection, Oxidation

Whilst the type of treatment facility required will depend upon the particular circumstances the above methods are generic across all facilities from large municipal works to smaller scale package sewage treatment plants.

Packaged Treatment Plants

There are numerous manufacturers offering packaged sewage treatment plants but care must be taken to ensure the treatment process is suitable for the intended use.

The following are an example of typical processes:

  • Activated Sludge Plants (ASP)
  • Rotating Biological Contactors (RBC’s)
  • Submerged Aerated Filters (SAF)
  • Biofilters