Sewerage Treatment Plants & Residential Property

The rules differ for England & Wales and also depending on whether discharging to ground or surface water.

Read requirements here ...

https://www.gov.uk/permits-you-need-for-septic-tanks/you-have-a-septic-tank-or-small-sewage-treatment-plant

England is controlled by Environmsnt Agency

Wales by Natural Resource Wales

See my related articles on this subject.