Trickling Filter Safety

Trickling filters are biological treatment units where wastewater is distributed over a bed of media.
The filter surface is wet, slimy, and extremely slippery, creating a serious slip and fall hazard.
Rotating distributor arms sweep across the filter surface and can strike workers without warning.
The filter media bed may be several metres deep; falling into an uncovered filter is potentially fatal.
Hydrogen sulphide and other odorous gases accumulate around trickling filters, especially in warm weather.
Filter flies (Psychoda) breed in the media and can cause respiratory irritation in large numbers.
Access onto the filter surface requires a permit and must only be done when the distributor arm is isolated.
Guardrails and covers protect the filter perimeter, but these are sometimes removed for maintenance access.
Working on filter media involves biological hazards from sewage contact requiring appropriate PPE and hygiene.
The Confined Spaces Regulations 1997 may apply if the filter has restricted access and poor ventilation.

Slip and fall	The wet, slimy filter surface and rotating arms cause slips, trips, and falls resulting in fractures and head injuries.
Rotating arm strike	Distributor arms rotate continuously and silently. Being struck causes serious injuries including broken bones.
Biological hazards	Sewage contact on trickling filters exposes workers to bacteria, viruses, and parasites causing serious illness.

Do

Don't

Isolate and lock off the rotating distributor arm before accessing the filter surface.
Wear non-slip footwear with aggressive tread pattern when walking on filter surrounds.
Use a permit to work system before anyone accesses the trickling filter surface.
Monitor for hydrogen sulphide gas around the filter, especially in warm weather.
Wear waterproof gloves and wash hands thoroughly after any sewage contact.
Maintain guardrails and covers around the filter perimeter at all times.
Brief the team on the biological hazards and hygiene requirements before access.
Ensure the distributor arm isolation is verified before anyone steps onto the filter.
Use temporary barriers to prevent falls into open sections during maintenance.
Report any missing or damaged guardrails around the filter immediately.

DON'T step onto the filter surface while the distributor arm is rotating.
DON'T walk on the slippery filter surround without appropriate non-slip footwear.
DON'T remove perimeter guardrails without installing temporary edge protection.
DON'T ignore hydrogen sulphide odour around filters; monitor gas levels.
DON'T eat, drink, or smoke near the trickling filter work area.
DON'T lean over the filter edge without fall protection in place.
DON'T access the filter without a completed permit to work.
DON'T touch your face while working on or near the filter without clean hands.
DON'T assume the distributor arm has stopped; verify isolation before access.
DON'T work on filter media without waterproof PPE and biological hazard controls.

See also: Wastewater Treatment Works Safety Awareness | Slips, Trips and Falls Awareness

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