WWT/Process Areas/TBT-WWT-008

Activated Sludge Plant (ASP) Safety

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Activated Sludge Plant (ASP) Safety

Toolbox Talk Record

Ref: TBT-WWT-008  |  Issue: 1  |  Date: March 2026
PresenterProject
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What?

  • Activated sludge plants use aeration tanks to biologically treat wastewater.
  • Main hazards are drowning, biological agents, toxic gases, and rotating equipment.
  • ASP tanks are typically open-topped containing deep aerated liquor with no visible bottom.
  • A person falling into an aerated tank will not float — buoyancy is reduced.
  • Hydrogen sulphide and ammonia can be released from the mixed liquor surface.
  • Aerators, mixers, and return sludge pumps present entanglement hazards.
  • Walkways and handrails must be maintained and kept free of slippery biofilm.
  • COSHH 2002 applies to biological hazards at wastewater treatment works.
  • Leptospirosis, hepatitis, and gastro-intestinal infections are occupational risks.
  • All work on ASP tanks must follow the site safe system of work and permits.

Why?

Drowning riskAerated liquor reduces buoyancy — a person entering an ASP tank will sink.
Biological hazardsSewage contains bacteria and viruses causing serious infections.
Toxic gas exposureH2S and ammonia cause illness and death at high concentrations.
Rotating equipmentAerators and mixers create entanglement hazards near tanks.
Do Don't
  • Maintain guardrails and edge protection around all ASP tanks at all times.
  • Wear a personal flotation device within 2 metres of tank edges.
  • Ensure rescue equipment including life rings and throw lines is in place.
  • Isolate and lock out aerators and mixers before work near moving parts.
  • Wash hands thoroughly before eating or drinking after sewage contact.
  • Cover all cuts with waterproof dressings before starting work.
  • Monitor for H2S and ammonia when working on or near ASP tanks.
  • Keep walkways and handrails clean and free of slippery biofilm.
  • Follow the permit to work system for all ASP maintenance tasks.
  • Ensure tetanus and hepatitis vaccinations are up to date.
  • DON'T remove guardrails around ASP tanks without a permit.
  • DON'T lean over tank edges or stand on non-designated surfaces.
  • DON'T enter an ASP tank without a confined space procedure.
  • DON'T work near aerators or mixers without confirmed isolation.
  • DON'T eat, drink, or smoke near ASP tanks without washing first.
  • DON'T ignore cuts or abrasions — cover them to prevent infection.
  • DON'T assume walkways are non-slip — biofilm builds up rapidly.
  • DON'T attempt rescue from an aerated tank without specialist equipment.
  • DON'T ignore symptoms of illness after sewage exposure — seek medical advice.
  • DON'T bypass the permit to work system for any ASP task.

See also: Wastewater Treatment Works Safety Awareness | Drowning Prevention and Water Safety
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