Pretreatment Requirements

When a building or structure is designed for a commercial occupier and the building has trade waste drainage, there may be a requirement for basic basic pretreatment infrastructure as detailed in Appendix A3-1 of the Queensland Urban Utilities TWEMP.

Where basic pretreatment is required, the pretreatment infrastructure installed must be of a type listed in Queensland Urban Utilities’ Register of Authorised Basic Trade Waste Pretreatment Products.

Where business types listed in TWEMP Appendix A3-1 install and properly maintain pretreatment infrastructure, their discharge is usually deemed to comply with sewer acceptance criteria, provided the discharge does not exceed a flow of 10kL/day or contaminant load of 20kg/day BOD (or 40kg/day COD).

Approval holders must ensure that:

trade waste pretreatment infrastructure detailed on the approved hydraulic plans is installed and used
trade waste pretreatment infrastructure is properly operated and maintained in accordance with the manufacturer’sguidelines and the trade waste approval conditions.

Basic pretreatment requirements for nominated business types

Register of authorised basic pretreatment products

Business types that are compliant without pretreatment

Pretreatment infrastructure will not normally be required for the business types listed below:

Business types deemed to comply without pretreatment

For clarity, business types listed in TWEMP Appendix A3-2 with discharge less than 10 kL/day and less than 20kg BOD/day (or 40kg/day COD) are deemed to comply with sewer acceptance criteria without pretreatment infrastructure, unless otherwise specified in the relevant trade waste approval.

Sizing of basic pretreatment infrastructure

The following sizing requirements for basic pretreatment infrastructure (mainly grease silt or oil silt arrestors) apply to all new or replacement equipment installed after 1 July 2011. Existing non-compliant pretreatment infrastructure may not need to be replaced retrospectively, except where the system is negatively affecting the sewerage system (at the sole discretion of Queensland Urban Utilities).

For new or replacement basic pretreatment infrastructure (grease silt traps and oil silt traps) the minimum size is 1000L
Where unusual circumstances exist, Queensland Urban Utilities may provide written consent for smaller pretreatment infrastructure if a request and justification is made in writing by a qualified hydraulic consultant representing the applicant.
Grease silt traps and oil silt traps must be sized to provide a minimum of one hour retention at peak hourly trade waste flow.
The peak hourly trade waste flow should be calculated using the total of the guideline flows attributable to each trade waste generating fixture. Guideline flows are provided below.
Alternative peak hourly flow estimates will be accepted where a qualified hydraulic engineer attests to the peak flow and design (thereby providing a performance guarantee for the system design and taking responsibility for any failure to meet sewer acceptance criteria).
The maximum allowable capacity of any one grease silt trap is 5000L, unless Queensland Urban Utilities provides written consent for other sizing (consideration must be given to the adequacy of the applied flow rate at the time of installation).
Where tenancy occupiers are unknown (i.e. new set of shops), the minimum grease silt arrestor sizing requirements are as follows:
- minimum grease silt trap capacity allocation for the 1st connected tenancy is 1000L, and
- minimum grease silt trap capacity allocation for each additional tenancy shown as connected to trade waste is 500L, unless -the applicant provides documentation with submitted hydraulic plans justifying an alternative pretreatment allowance.

Sizing for pretreatment devices

Pretreatment maintenance requirements

Approval holders must ensure proper maintenance of trade waste pretreatment infrastructure in accordance with trade waste approval conditions.

Adequately sized basic pretreatment infrastructure must be serviced in accordance with the manufacturer’s recommendations or as described below:

Grease silt arrestors: At least once every 13 weeks unless otherwise specified by Queensland Urban Utilities within the trade waste approval.
Oil silt arrestors: Triple interceptor types - at least once every 12 months unless otherwise specified by Queensland Urban Utilities within the trade waste approval.
Plate separator types – at the frequency specified by the manufacturer (as a minimum) unless otherwise specified by Queensland Urban Utilities within the trade waste approval.

More frequent servicing may be a condition of the Trade Waste Approval.

Owners of under-sized or inadequate basic pretreatment infrastructure, such as pre-existing grease silt arrestors with a treatment capacity less than 550 litres, may be required to:

service the device at an increased frequency
install dry basket arrestors (strainers), with a fixed screen or an automatic closing mechanism that prevents discharge to sewer when the basket/strainer is removed, in all connected sink and floor drains.

If failure to maintain trade waste pretreatment infrastructure results in interference to Queensland Urban Utilities’ sewerage infrastructure (e.g. sewer blockage) or causes a public health risk, the approval holder responsible for the infrastructure may be subject to enforcement action and possible cost recovery claims.

Grease, fat, mineral oil, hydrocarbon products, residual wastes and regulated wastes that are removed from trade waste pretreatment infrastructure must not be discharged into Queensland Urban Utilities’ sewerage infrastructure unless specifically approved by Queensland Urban Utilities.

The use of authorised trade waste additives, such as bacterial cultures and enzymes, in pretreatment infrastructure and sewer pipes cannot be used as a substitute for pretreatment infrastructure maintenance. Pretreatment infrastructure under this form of treatment must continue to be regularly serviced by the complete evacuation method at a frequency determined by negotiation.

Pretreatment considerations for business types

Queensland Urban Utilities TWEMP provides details of pretreatment requirements according to business type. Relevant information is provided in relation to the following businesses:

Food retailing/processing and hospitality industry

Motor trades industry

Photographic and Imaging Industry

Metal Finishing Industry

Laboratories

Commercial and Institutional Swimming Pools

Evaporative Cooling Towers

Commercial and Institutional Laundries

Other Commerce and Industry

Trade Waste Environmental Management Plan

Stormwater considerations

The discharge of uncontaminated stormwater into Queensland Urban Utilities’ sewerage infrastructure is prohibited. However, contaminated first flush water collected from trade waste generating areas may be approved for discharge to sewer. The use of harvested stormwater in trade waste generating activities (e.g. vehicle washing) may also be approved.

Trade Waste/Stormwater Diversion and First Flush Systems
A rain-sensor linked trade waste/stormwater diversion system will only be approved to allow connection of an external trade waste generating area to Queensland Urban Utilities’ sewerage infrastructure in situations where:

adequately roofing such an area is not possible; and
the catchment area for the system is confined to such an area (e.g. wash pad).

Specific conditions and design requirements apply to the acceptance of stormwater diversion and first flush systems, including the requirement for a Queensland Urban Utilities trade waste consent prior to submission of plans to council for plumbing compliance assessment. Specific conditions related to such systems are detailed in the section 4.6 of the Queensland Urban Utilities TWEMP.

Stormwater pretreatment considerations

Collecting Stormwater for Use in Trade Waste Generating Activities
In systems where stormwater/roofwater is used as an alternative water supply to trade waste generating activities, the system must employ:

an approved trade waste effluent flowmeter to directly measure the volume of trade waste discharged to Queensland Urban Utilities’ sewerage infrastructure, or
include sub-metering of all input water supplied to trade waste generating areas.

Excess stormwater collected during major rain events (i.e. stormwater that cannot be stored for later use or directly used in trade waste generating activities) cannot be disposed to sewer under any circumstances. Where stormwater/roofwater is used in trade waste generating activities, diversion, treatment and disposal options for excess stormwater will need to be detailed in the trade waste approval application (e.g. treatment and diversion to council stormwater infrastructure either directly or via ponds and/or wetlands).