Trade Waste in Residential Plumbing

What it is

Trade waste is liquid waste discharged to the sewer that is not ordinary domestic sewage. In Australia, ordinary domestic sewage is the waste produced from normal living activities in a household: toilets, showers, baths, basins, sinks and laundries used by the residents.

Anything beyond that, even from a residential property, can be classified as trade waste by the water authority. This means the discharge needs an approval and may need pre-treatment before it can enter the sewer. NCC Volume Three covers this under Section C, and Tasmania has a specific Part C4 for on-site liquid trade waste systems.

When residential becomes trade waste

A standard family home with no business or industrial activity does not produce trade waste. But several common residential scenarios do trigger trade waste classification or pre-treatment requirements.

Home-based food businesses

The most common residential trigger is a home-based food business. Catering from home, a home bakery, a coffee cart rinsed in the garage, or a food truck cleaned on the driveway can all generate grease-bearing wastewater that the water authority will treat as trade waste. A grease arrestor is usually required.

Pool and spa discharge

Backwash from pool filters and spa drain-downs contain chlorinated water and accumulated solids. Most water authorities require pool backwash to be discharged either to the sewer through a sediment trap, to the stormwater system if local rules allow, or controlled on-site. Discharging chlorinated water straight to a garden or gutter can breach local trade waste rules.

Workshop and hobby activities

A residential garage used for vehicle servicing, paint mixing, photographic developing or similar activities generates wastewater the water authority can classify as trade waste. Any chemical other than ordinary domestic cleaning is the trigger.

Subfloor and ducted air conditioner condensate

Some authorities treat condensate from large or commercial-style air conditioners as trade waste when discharged to the sewer. Standard residential split-system condensate is usually exempt.

Pre-treatment requirements

Where trade waste is generated, the water authority will set conditions on the connection. The most common condition is a pre-treatment device sized for the expected discharge.

Grease arrestor

A grease arrestor is a sealed underground or floor-mounted tank that detains wastewater long enough for fats and oils to rise and solids to settle. The clarified water in the middle layer is what is discharged to the sewer. Sizes start at 1,000 litres and go up to 5,000 litres or larger for commercial sites. Home-based food operations typically need a 1,000 to 1,500 litre grease arrestor.

Other pre-treatment

• Oil arrestors and oil separators for workshop runoff
• Cooling pits for hot discharges
• Lint traps for commercial laundry
• Dilution pits for chemical or pH balancing

Most pre-treatment products must carry WaterMark approval and be installed by a licensed plumber. The plumber lodges the installation with the water authority and the discharge is permitted under a trade waste agreement.

Approval process

A trade waste classification needs an approval from the water authority before the connection is made or before the activity starts. The steps generally follow this sequence.

1. The owner or occupier applies to the water authority for a trade waste agreement
2. The water authority assesses the type and volume of waste
3. The authority specifies pre-treatment, sampling and reporting conditions
4. A licensed plumber installs the pre-treatment device and lodges the work
5. The trade waste agreement is issued, often with annual or quarterly inspection
6. The discharge is metered or sampled by the authority

Each water authority has its own application form and fee structure. In Sydney this is handled by Sydney Water, in Melbourne by City West Water or South East Water depending on suburb, in Brisbane by Queensland Urban Utilities and in Perth by Water Corporation.

Maintenance

A grease arrestor must be pumped out regularly to keep working. Service intervals depend on the volume of fats discharged and range from fortnightly for busy food sites to quarterly or annually for low-volume residential operations. Servicing must be performed by a registered liquid waste contractor and the manifest kept on record.

Failure to maintain the device, or discharging trade waste without an approval, is a breach of the trade waste agreement and can result in fines, shutdown of the activity and disconnection of the sewer connection.

Where the rules sit

The high-level requirement that liquid trade waste must be managed sits in NCC Volume Three Section C. Detailed device design and installation come from the AS/NZS 3500.2 sanitary plumbing and drainage standard. The trade waste agreement itself is a contract between the property owner and the water authority and is regulated under state water industry law.