Portable vs permanent wash bays

Cleanawater on 26 August 2019

Wash bays are used for any kind of equipment or vehicle wash down ranging in size from wheelchair cleaning to large busses and trucks.

They are essential for the purposes of preventing contaminated water from entering the trade effluent system. This is because equipment and vehicles often have oil and grease mixed with the dirt, which is harmful if released into the environment. In addition, the chemicals and detergents used for cleaning may also be detrimental to the environment and must be removed prior to discharge.

Cleanawater has more than 20-years experience in wash bays and trade waste requirements. Get advice and recommendations from our expert team.

Portable vs permanent wash bays: choosing the right solution

There are two main types of wash bay—permanent and portable:

  • Permanent wash bays have underground tanks and require civil construction to install. They are meant for established sites where there is no prospect of moving in the short to medium term.
  • Portable wash bays are installed without much civil construction. They are designed to be dismantled, moved and reassembled in another location. These solutions are ideal for growing companies which may move to bigger premises or rearrange their worksite in the short to medium term.

Permanent wash bays have the advantage of being designed for the application so that they can be sized to meet your exact requirement. Portable wash bays are also customisable because of their modular design. They can be expanded to suit any size.

Managing wash bay wastewater

aitkin cranes wash bay

The most important aspect of managing wastewater from wash bays is the removal of free oils. This is a requirement stipulated by local councils and water authorities, and it forms part of a company’s trade waste agreement. Wastewater generated by a wash bay goes through a number of phases of cleaning and treatment before discharging to the wastewater sewer network:

1. Filtering in a silt trap

The first line of defence is a silt trap filter, which removes large particles, dirt and even bits of rubbish like plastic. These filters must be cleaned regularly to prevent blockages from building up in the system.

2. Settling in a retention tank

Water collects in a tank where it is allowed to settle so that oils can separate from the water. This settling time is important because detergents actually allow oil and water molecules to bind together for effective washing. Quick break detergents allow the oil molecules to begin separating from the water within 15 minutes of washing.

A typical retention tank design allows for one hour of settling time, before the water passes on to an oil water separator. If oil and water do not begin to separate in the retention tank, the oil water separator will be ineffective and oily water will escape into the discharge. This is why the use of quick break detergents is so important.

3. Oil water separators

Oil water separators assist the process of separating oil from water. They facilitate the process of oil molecules connecting together into bigger droplets. Oil rises to the top of an oil water separator where it collects in a tank for disposal. Clean water is discharged from the bottom of the separator for further treatment, recycling or disposal to a wastewater sewer.

The problem of rain water

wash bays gallery truck wash bay

Rainwater is clean water and should be processed via the stormwater system. The volume of rainwater is too large to be processed by oil water separators on site and will also overload effluent treatment plants downstream.

Some regions in Australia require wash bays above 20 square metres to be roofed. This keeps the rainwater out of the wash bay, and it can be routed directly to stormwater. First flush diversion systems can also be used to divert rainwater to stormwater after the wash bay has been flushed. The first flush cleans the wash bay surface from oils and contaminants.


There are two main requirements for wash bays in terms of their construction:

  • The wash bay area must be bunded, meaning that the area must be contained with a low barrier similar to a speed bump. This prevents contaminated water from escaping to stormwater.
  • The wash bay must be impermeable, meaning that no water may seep through the floor of the wash bay into the surrounding groundwater.

Get expert advice from Cleanawater

Contact Cleanawater for all your wash bay needs, whether they are permanent or portable. We have more than 20 years experience in the Australian market and have all the expertise to help you implement a compliant wash bay system.

Contact Cleanawater for advice on the right wash bay for your business. We can recommend and supply a compliant solution.