How A Septic Tank Works

A septic tank is a common wastewater treatment system in areas without access to main sewers, particularly in rural parts of the UK. Here’s how it works:

  1. Wastewater enters the tank: The wastewater from your house, including toilets, sinks, showers, dishwashers, and washing machines, flows into the septic tank through an inlet pipe.
  2. Separation into layers: Inside the tank, the wastewater separates into three layers due to density differences:
    • Top Layer (Scum): Fats, oils, and lighter solids float to the top, forming a layer called scum.
    • Middle Layer (Effluent): The bulk of the wastewater clarifies in the middle. This liquid effluent is what undergoes further treatment.
    • Bottom Layer (Sludge): Heavier solids sink to the bottom, forming a layer of sludge. Bacteria in the tank anaerobically decompose the sludge, slowly reducing its volume.
  3. Effluent exits the tank: The clarified effluent in the middle layer flows out of the tank through an outlet pipe into a drainage field or soakaway.
  4. Treatment in the drainage field: The drainage field is an underground network of perforated pipes surrounded by gravel. The effluent trickles through the gravel, where aerobic bacteria in the soil further purify the water. The treated wastewater then percolates into the ground.

Here are some additional points to note:

  • Septic tanks require regular maintenance, including pumping out the accumulated sludge and scum every few years.
  • It’s crucial to avoid putting harmful substances down the drain that can kill the bacteria essential for breakdown in the tank.
  • The effectiveness of a septic tank depends on the permeability of the soil in the drainage field.

How Does a Septic Tank Baffle Work?

  • Purpose: Septic tank baffles are designed to keep the solid waste (sludge) and floating waste (scum) within the tank, preventing them from entering your drainage field. They also help direct the flow of wastewater.
  • Types:
    • Inlet baffle: Located where the wastewater enters the tank. It directs the flow downwards to prevent disturbing the scum layer and allows for initial settling of solids.
    • Outlet baffle: Located where the wastewater exits the tank. It prevents scum from flowing into the drainage field and creates a final barrier to keep solids within the tank.
  • Materials: Modern baffles are usually made of durable PVC, while older tanks may have concrete baffles. Concrete is more susceptible to deterioration over time.
  • Importance: Intact baffles are essential for the proper functioning of your septic system. Damaged or missing baffles can result in solids entering your drainage field, leading to clogging, backups, and expensive repairs.

How Does a 2 Chamber Septic Tank Work?

  1. Wastewater Entry: Wastewater from your home flows into the first chamber of the septic tank via the inlet pipe and inlet baffle.
  2. Primary Settlement: Solids begin to settle to the bottom, forming a sludge layer. Lighter materials like grease and oils float to the top, creating the scum layer.
  3. Partial Breakdown: Bacteria in the tank start to break down the organic matter in the sludge layer.
  4. Chamber Transfer: The partially treated liquid (effluent) flows into the second chamber through an opening between the chambers.
  5. Further Settlement: More solids settle out in the second chamber, adding to the sludge layer.
  6. Drainage Field: The clarified effluent leaves the second chamber through the outlet pipe and outlet baffle, heading towards your drainage field for final treatment and dispersal into the soil.

How Does a 3 Chamber Septic Tank Work?

  1. First Two Chambers: The first two chambers function similarly to a 2-chamber septic tank, with the initial settling and partial breakdown of waste.
  2. Third Chamber: The third chamber provides an additional stage of settling and clarification. This results in even cleaner effluent entering the drainage field.
  3. Advanced Treatment (Optional): Some 3-chamber tanks may incorporate features like filters or aeration systems in the final chamber for further improved treatment of effluent.

Key Points for UK Septic Tank Owners:

  • Have your septic tank emptied regularly by a registered waste carrier to prevent solids from building up and potentially damaging the system.
  • During emptying, ask the technician to inspect the condition of your baffles.
  • Avoid flushing anything down the toilet or sink that doesn’t break down, as this can clog the tank and drainage field.
Get Access To Septic Tank Kits
Get Access To Septic Tank Kits

UK Building Control Approved: https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-the-ground

Environment Agency Certified: https://www.planningportal.co.uk/applications/building-control-applications/building-control/approved-documents/part-h-drainage-and-waste-disposal/approved-document-h

Compliant with General Binding Rules: https://www.generalbindingrules.co.uk/general-binding-rules
British Water Approved: https://www.britishwater.co.uk/page/Accreditation-Certificationcertified-small-wastewater-treatment-systems-for-up-to-50-pt

UK Building Regulations Approved: https://www.planningportal.co.uk/applications/building-control-applications/building-control/approved-documents/part-h-drainage-and-waste-disposal/approved-document-h

https://www.gov.uk/guidance/general-binding-rules-small-sewage-discharge-to-the-ground

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