The activated sludge plant is the biological heart of most wastewater treatment works. Construction and maintenance work in this area involves exposure to open aeration tanks, rotating mechanical equipment, and toxic gases including hydrogen sulphide. Falling into an ASP lane is extremely dangerous because the aerated mixed liquor makes it almost impossible to stay afloat.
Key Hazards
Drowning in aerated mixed liquor that cannot support a person's buoyancy
Hydrogen sulphide gas accumulating in enclosed channels and distribution chambers
Entanglement with rotating aerators, mixers, or return sludge equipment
Biological infection from contact with activated sludge and wastewater
Control Measures
Install edge protection around all open ASP lanes and channels before starting construction work.
Wear an auto-inflating personal flotation device when working within two metres of open tank edges.
Ensure all rotating equipment including aerators and mixers is isolated and locked out before access.
Carry out atmospheric monitoring for H2S in enclosed distribution chambers and inlet channels.
Cover all cuts and wounds with waterproof dressings before entering the ASP work area.
Wear waterproof gloves and overalls when there is any risk of contact with mixed liquor.
Brief operatives on the man overboard procedure and the location of rescue equipment at the ASP.
Position lifebuoys and throw lines at intervals along the tank edges within reach of all work areas.
Wash hands with antibacterial soap before eating, drinking, or smoking after leaving the area.
Emergency / Rescue
If a person falls into an ASP lane, throw a lifebuoy immediately and raise the alarm. Do not enter the tank — the aerated water will not support your weight. Call 999 and shut down aeration if safe to do so.
Remember
Aerated mixed liquor cannot support a person's buoyancy — falling in is extremely dangerous
Wear an auto-inflating PFD within two metres of any open ASP lane or tank edge
All rotating equipment must be isolated and locked out before any work access is permitted
Atmospheric monitoring for H2S is required in enclosed distribution chambers and channels
Lifebuoys and throw lines must be positioned at intervals along all open tank edges
Applicable Legislation: Confined Spaces Regulations 1997 · PUWER 1998 · CDM Regulations 2015 · Health and Safety at Work etc. Act 1974