Why “oil water separator” performance is won or lost in the specification
On Australian worksites, wash water rarely arrives as a neat, predictable stream. It changes with weather, fleet mix, maintenance activities, detergents, and the solids load tracked in on tyres and underbodies. If we treat an oil water separator as a standalone “box”, the site typically pays for it later—through unstable discharge quality, accelerated filter fouling, sludge handling issues, and avoidable downtime. Our approach is different: we specify the separator as one stage in a complete treatment train, matched to the discharge pathway and the wastewater reality.
We build Domino oil and water separator solutions for businesses producing hydrocarbon wastewater containing oil and grease, suspended solids and other pollutants—particularly where trade waste discharge, reuse, or a mix of both is required.
What an oil-water separator must remove (and what it must protect downstream from)
An oil-water separator stage is typically responsible for removing bulk hydrocarbons and reducing the load on downstream polishing steps. In practice, the separator stage must also help protect later filtration and disinfection systems by stabilising the incoming wastewater conditions. That is why we design from the front end: solids management, predictable hydraulics, and staged separation—before we talk about “final quality”.
Free oil vs difficult hydrocarbons
Domino VGS systems focus on separating non‑emulsified impurities using controlled fluid velocity and pressure. This gentle hydraulic control allows higher‑density contaminants to fall into a sludge retaining area while oil droplets and low‑density suspended solids rise and drain into a waste tank.
Where the wastewater requires more than free‑oil separation, we specify additional hydrocarbon polishing (for example, pairing separation with oil removal cartridges designed for persistent hydrocarbons and emulsified oils, based on the wastewater conditions and pathway).
Domino VGS systems: how vertical gravity separation is engineered for wash water
Domino VGS systems use controlled fluid dynamics—velocity and pressure—to coax separation without aggressive mixing that can worsen emulsions. We build this stage to be practical to operate, with system options such as automated cleaning and automated sludge removal designed to support consistent operation and manageable servicing.
From a specification perspective, the key point is this: a VGS stage is a separation workhorse, but it still depends on the wastewater presented to it. So we protect it with sensible pre‑treatment and stable feed design, then choose polishing steps based on the contaminants we confirm on site.
Skimmers: how we stabilise our pretreated water and improve separator outcomes
An oil water separator performs best when the feed water is consistent. Skimmers are one of the most practical tools for this. Our skimmers are designed to skim the surface of contaminated catchments, removing hydrocarbon pollutants and supporting a balanced oil/water feed ratio for delivery to above‑ground oil separators and waste recyclers. Skimmers also create a floating suction which stays in the oil layer to ensure removal of all free oil and prevent entry of sludge into the pumping system.
In Domino systems, the skimmer is installed in the primary treatment tank so contaminated water can be transferred to the Domino system during operation, and it is supplied as part of the Domino system purchased as an additional option. We also supply, install and commission larger skimmers for settling ponds and evaporation ponds where required.
Staged treatment: where the oil water separator sits in the real train
Wash water is rarely solved by one component. The most robust outcomes come from staged treatment, where each stage does a specific job and protects the next stage from being overloaded.
Stage one: pre‑treatment for solids and stable hydraulics
If solids are not managed up front, everything downstream becomes harder: separation efficiency drops, sludge handling becomes unpredictable, and polishing filtration becomes expensive. We use practical pre‑treatment measures (screens, weirs, and settlement where appropriate) to manage solids and stabilise inflow conditions before the separator stage.
Stage two: primary oil water separation (VGS) and control features
This is where we remove free oil, grease and a portion of suspended solids using the controlled velocity/pressure separation approach described above, with automated features that support maintainability.
Stage three: polishing (when the wastewater requires it)
When hydrocarbons are more persistent (including emulsified oils), we specify polishing stages appropriate to the wastewater and pathway—often by combining separation with targeted cartridge polishing and/or other process stages as needed. Other polishing stages can be provided for other contaminates eg. heavy metals removal.
Stage four: recycle/reuse operations (storage + water quality management)
Where the goal is reuse, we treat, store and manage water quality as an operating model—not an afterthought. Domino wastewater recycling systems preserve and reuse water, with monitoring of recycled tank water quality with pH control and disinfection dosing to maintain quality and support Work Health and Safety requirements.
Case study lens: why the “train” matters (Fulton Hogan upgrade)
A clear example of staged design is the Fulton Hogan asphalt/bitumen plant wash bay upgrade. Contaminants were no longer being removed to an acceptable level due to changes in equipment entering the wash bay, and pump‑out costs were escalating—so a major upgrade was required. The accepted solution retrofitted the pre‑treatment system with a silt screen, proper draining and an oil retention weir, then added staged upgrades including flocculation, pH adjustment, dissolved air flotation treatment, an oil water separator fitted with skimmer, secondary filtration down to 5 micron, recycled water storage, and disinfection dosing.
The lesson is straightforward: when you specify the oil water separator as one part of the system—and protect it with upstream solids control and downstream polishing—you reduce operational surprises and improve whole‑of‑system reliability.
Specification checklist: how we lock in performance before fabrication
Use this checklist to brief your team and accelerate engineering scoping.
Confirm the discharge pathway and approvals early
Our Oil/Water systems have Water Authority approval for discharge to Trade Waste. If the system is intended to recycle and reuse wastewater, Water Authorities may require additional information (including the intended use), and recycled water is not potable.
We also deliver wash water treatment systems that are approved by various Water Authorities throughout Australia either as a single‑pass system for discharge to sewer or as a recycled and reuse system (site and authority dependent).
Characterise the wastewater you actually generate
Capture the likely contaminant mix: oils/grease, solids/silt, detergents, and any special contaminants relevant to your operation. This drives whether a basic separation stage is sufficient or whether polishing is required.
Define volumes, peaks, and “worst‑day” conditions
Design for peaks (shutdown washdowns, wet‑weather impacts, changed fleet mix), not averages. This prevents undersized containment and unstable operation at the times you most need control.
Confirm site constraints (power, space, access, maintainability)
All EWA systems are designed and built in Brendale, QLD to current Australian plumbing and electrical standards. VGS systems can be configured with single or three‑phase components depending on the installation site; larger systems use three‑phase components.
We also assess access for maintenance (sludge waste handling logistics, filter change access, safe isolation points) and the practicality of operating the system with the resources available on site.
Choose the delivery model: equipment supply vs total project management
When scope, schedule and documentation need to be tightly controlled, Total Project Management allows delivery on a firm schedule and integrates design, upgrades and commissioning requirements into one accountable pathway.
Next steps
If you are reviewing an existing wash bay, planning a new bay, or experiencing rising pump‑out costs and inconsistent performance, start with a pathway decision and a staged train. We will assess your wastewater, confirm the discharge/reuse intent, and specify the separator, skimming and polishing steps required to make the system practical to operate.
