Our wastewater system is designed primarily to treat domestic wastewater however compatible trade waste is accepted where system capacity is available.
We individually assess your business when you apply for a trade waste permit. We identify what you need to do to make sure your trade waste is suitable for discharge to the wastewater system and we incorporate these requirements into your permit conditions.
To meet our acceptance criteria we may require you to pre-treat your wastewater before it is discharged to sewer.
Non-compliant discharges can result in:
The types of wastewater contaminants that we must limit in the system, their potential impacts and our general approach to controlling them are summarised below.
BOD is a measure of organic content. Wastewater with high organic content can overload our treatment plants. Wastewater with excessive BOD can lead to hydrogen sulphide gas within the sewers. This toxic gas is dangerous for our workers and creates odour problems. It also causes corrosion of the fabric of our sewers, pump stations and treatment plants.
Suspended solids can accumulate within sewers and pump stations, leading to blockages, failures and overflows. Suspended solids also result in excessive loading at treatment plants. Pretreatment can range from simple gravity settling to chemically assisted removal using dissolved air flotation (DAF) units.
Fats, oil and grease merge and solidify in the sewer as it cools and causes blockages and overflows. Oily residues can affect water level sensors and pump switches and cause them to fail. This can cause wastewater overflows. Large amounts of FOG can also interfere with wastewater treatment processes. We control FOG wastes by pre-treatment at the source. This means a grease trap for commercial kitchens or an oil separator in automotive trades. More complex pre-treatment may be required for larger businesses.
Metals entering our system are not destroyed and will ultimately re-enter the environment. Excessive amounts of heavy metals can inhibit our biological treatment processes and can affect reuse options.
Excessive acidity or alkalinity cause corrosion of our sewer system and pump stations, resulting in extensive damage across a wide area. High levels also pose a danger to our wastewater system workers. We require neutralisation of extremes of pH prior to discharge.
Hot water can flush grease and other deposits into the wastewater collection system, where it cools, precipitates and causes blockages.
Flammable or volatile liquids can cause fires or explosions in wastewater systems and are a danger to our workers. Discharge into the sewer system is not permitted.
Disposal of radioactive wastes is regulated by the Radiological Council of WA. Discharges are only accepted once approval is first obtained from the Radiological Council.
Infectious Substances, Pharmaceuticals and Cytotoxic Wastes are subject to strict supervision and controls. Guidelines for the disposal of clinical and related wastes, are available at the Department of Health. With the exception of blood and body fluids, these wastes are not to be discharged to sewer.
Discharging storm water to the sewer is not permitted. Storm water flow is often high and exceeds the design capacity of urban sewer systems. Increasing the capacity to accommodate these high flows is uneconomic. It is standard practice to keep municipal storm water and sewerage systems separate and prohibit the discharge of storm water to sewers. Proposals for discharge to storm water should be referred to the relevant local government authority or the Department of Water and Environmental Regulation
The acceptance criteria are based on technical considerations of wastewater collection, treatment, disposal and reuse. Water Corporation exercises some flexibility in applying the criteria – relaxing or tightening the requirements in particular cases as the need arises.
The acceptance criteria include common substances present in trade waste. Contact us for information on acceptability of other substances.
Units
For the purposes of this document, mg/L is equivalent to 'parts per million' (ppm).
100 mg/L
Mass limits determined by system capacity
1. Mass limits determined by system capacity
2. Maximum concentration 3,000 mg/L
3. Discharge not to change overall C:N:P ratio of system
1. 3 mg/L weak acid dissociable cyanide
2. Limits on dissociable cyanide may be varied depending on composition of waste
3. Mass limits on total cyanide determined by system capacity
1. 1000 mg/L
2. Mass limits determined by system capacity
1. Organic liquids immiscible with water will not be accepted
2. Limits to water-miscible compounds will be set on a case-by-case basis
3. Only dilute solutions which pose no threat to the wastewater system will be accepted
1. No readily settleable solids which are likely to accumulate in the wastewater collection system
2. Mass limits determined by system capacity
3. Maximum concentration 1500 mg/L
| Metal | Mass treatment threshold (g/d) | Concentration limit for daily mass load above the mass treatment threshold (mg/L) |
|---|---|---|
| arsenic | 1 | 1 |
| cadmium | 1 | 1 |
| chromium | 30 | 3 |
| copper | 30 | 5 |
| lead | 30 | 1 |
| mercury | 0.1 | 0.01 |
| molybdenum | 1 | 5 |
| nickel | 6 | 3 |
| selenium | 1 | 1 |
| silver | 2 | 5 |
| zinc | 50 | 3 |
Discharges to wastewater treatment plants other than Beenyup, Subiaco and Woodman Point:
Limits shall be determined on a case by case basis.