Case study
Removing Compressor Oil from Rainwater with an Above-Ground Oil-Water Separator
A case study for handling low-volume rainwater collected from portable air compressors.
A Florida industrial facility asked Ecologix to evaluate a practical treatment approach for rainwater drained from eight portable air-compressor belly pans. The reported wastewater contained low concentrations of predominantly free-floating compressor oil and was expected to be introduced manually in small batches.
Application Snapshot
| Source | Rainwater drained from portable compressor belly pans |
|---|---|
| Equipment population | Eight portable air compressors |
| Estimated peak volume | Approximately 20-25 gallons after heavy rain |
| Anticipated feed rate | Up to approximately 5 GPM, introduced in batches |
| Reported oil condition | Low-concentration, predominantly free-floating compressor oil |
| Treatment objective | Remove free oil before any authorized discharge or water-management step |
Why Oil Characterization Matters
Whether oil is free-floating or emulsified determines whether gravity separation is likely to be appropriate. Free-floating and larger dispersed, non-emulsified droplets can rise through water under sufficiently calm hydraulic conditions. Stable emulsions contain much smaller droplets that may remain suspended instead.
The facility reported primarily free-floating oil, low oil concentration and no significant solids. On that basis, Ecologix evaluated an above-ground oil-water separator as the initial treatment approach rather than automatically adding filtration and adsorption.
Recommended Treatment Approach
Ecologix evaluated an AGS-2SS above-ground oil-water separator and supplied information for 5 GPM and 10 GPM configurations. The 10 GPM package considered for the application used a 12-gauge, 304 stainless-steel vessel with parallel corrugated coalescing plates and gravity discharge.
Within a coalescing-plate separator, velocity is reduced and available separation area is increased. Oil droplets contact plate surfaces, combine into larger droplets and rise to the surface for removal. Maintaining laminar flow is important because turbulence can keep droplets suspended or break them into smaller droplets.
When Additional Polishing May Be Needed
An oil-water separator is a primary separation device, not a universal hydrocarbon-removal system. If testing or observation identifies emulsified oil, dissolved hydrocarbons, fine solids or detergent mixtures, additional treatment may be appropriate.
| Observed condition | Potential treatment role |
|---|---|
| Visible free oil; droplets readily rise | Coalescing oil-water separator |
| Fine suspended solids | Bag filtration before polishing |
| Persistent sheen or emulsified oil | OrganoClay cartridge polishing |
| Oil mixed with detergents or unknown chemistry | Bench testing or wastewater characterization |
| Regulated discharge or reuse target | Sampling and compliance verification |
Sizing and Operating Considerations
The small daily volume alone does not determine separator selection. The instantaneous bucket-pour rate, surge behavior, water and oil properties, temperature, influent oil concentration, droplet size, solids content, specific gravity and pH can all influence separation. Sizing should confirm adequate projected plate area at the design overflow rate while maintaining laminar-flow conditions.
Before discharge, the receiving location, applicable federal, state and local requirements, sampling method and any required permits should be confirmed with the relevant authority. Visually clear water is not by itself evidence that discharge is authorized.
Engineering Takeaways
- Characterize the oil before selecting equipment; free oil and emulsified oil need different treatment strategies.
- Size for the instantaneous hydraulic load, not only the daily wastewater volume.
- Account for how wastewater enters the system, including short surge flows from bucket-fed batches.
- Add solids filtration and polishing when influent conditions or discharge targets require them.
Explore industrial oil-water separation solutions and learn more about above-ground oil-water separators.
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