What Is an Oil Water Separator? A Complete UK Guide

An oil-water separator is a legal requirement for UK businesses that use oil-lubricated air compressors. But why? Well, compressed air systems are a known cause of the unavoidable, legally controlled byproduct of oily condensate. Managing this environmental hazard is a core business activity when you operate a compressed air system, and the responsible way to do it is defined by rigorous UK law.

So, what’s the solution? An oil-water separator; it works by filtering the contaminated condensate to separate the nasty oil from the harmless water. That means the water can be disposed of safely, and your business can stay on the right side of the law, penalty-free, and responsible.

Why Oily Condensate is a Concern for UK Businesses

A standard 200 CFM compressor will generate a quantity of oily condensate each week that is noteworthy in itself: 60 to 160 gallons, depending on environmental factors. That water/lubricant mixture must be treated, and any inappropriate discharge can result in serious ecological, legal, and operational ramifications

UK Legal and Compliance Requirements

The oily condensate air compressors produce is classed as trade effluent and hazardous waste by UK law. In the UK, plant operators must be fully aware of their responsibilities and obtain trade effluent consent from the relevant local water authority before discharging this waste, and failure to do so is a criminal offence

Key legislation to be aware of:

• Water Industry Act 1991: It is against the law to discharge trade effluent to a public sewer without appropriate consent in writing.
• Environmental Protection Act 1990: This Act places a “Duty of Care” on any person undertaking a business activity that produces waste, which is legally enforceable.
• Hazardous Waste Regulations 2005: Oily water must be kept separate, stored securely, and delivered to a licensed carrier for disposal.

The risks associated with failing to comply with UK regulations are far-reaching and include potential imprisonment. The Environment Agency can impose unlimited fines, and company directors can be held personally criminally liable if adequate steps are not taken to prevent illegal discharges. An effective oil-water separator is the obvious solution to avoid all such risks.

The Environmental Impact

Oil, when released into a watercourse, quickly spreads over the water’s surface, reducing the oxygen content in the water, suffocating fish and aquatic plants, as well as smothering wildlife and blocking out sunlight. And, as it is commonly accepted that one litre of oil could pollute one million litres of groundwater, it’s clear to see why responsible Compressed Air Condensate and Its Disposal is a simple but vital environmental obligation.

How Oil-Water Separators Work

Typical modern oil-water separators operate through multi-stage filtration to achieve a significantly higher level of water purity than previous iterations. Our separators leave condensate with oil content levels below 10 ppm, achieving ISO 8573-1 and Environment Agency-compliant limits, which can be discharged safely. 

The Oil-Water Separation Process:

1. Depressurisation and Gravity Separation: Oily condensate is discharged from the pressurised air system into an expansion chamber. There is then a settling time here, which allows the largest, free-floating oil droplets to separate naturally due to their lower density.
2. Absorption and Coalescence: The condensate is then passed through a filter medium composed of oleophilic (oil-attracting) polypropylene fibres. These fibres absorb the bulk of the dispersed oil, and millions of tiny oil droplets coalesce (merge) to form larger droplets which can easily be separated.
3. Adsorption (Polishing): In the final stage, the water passes through a bed of activated carbon. The vast, porous surface area of the carbon adsorbs the final microscopic traces of oil, ensuring the discharged water meets legal limits.

Lubricant Type and its Critical Impact on Separator Performance

A common cause of compliance failure is a mismatch between the compressor lubricant and the separator’s filter media. Traditional mineral-based oils form emulsions that are relatively easy to break, while modern high-performance synthetic lubricants form very stable, tightly emulsified systems. 

The more stubborn emulsions formed by synthetic lubricants can pass straight through standard polypropylene and carbon filters, without the oil and water being separated. This challenge requires advanced adsorbent media specifically engineered to break these emulsions, such as Atlas Copco’s Organoclay cartridges, which provide an effective solution for capturing synthetic oil and ensuring regulatory compliance.

Choosing the Right Oil-Water Separator

Selecting the correct separator is crucial for ensuring reliable performance and compliance with legal requirements, but sizing your separator is more complex than simply finding something that fits.

Key Sizing Factors

• Compressor Capacity (CFM): The most critical sizing variable is your compressor’s airflow, as a higher CFM will generate more condensate and therefore require a much larger capacity.
• Site Conditions: Compressors operating in a hot and humid environment, like a UK Summer, will produce significantly more water than in a cold, dry winter environment. The separator must be sized for this worst-case scenario.
• Operating Hours: Facilities that operate 24/7 will require a larger model or more frequent filter changes than those that operate in a single shift.
• Lubricant Type: Your lubricant type will determine whether standard or advanced filter media is required.

Leading Technology from Atlas Copco

As an Atlas Copco Premier Distributor, Anglian Compressors offers the full range of OSC, OSS, and OSD separators, and can expertly specify the correct model to meet your business’s specific needs.

• OSC Series: A versatile, heavy-duty range for most industrial applications, featuring highly effective multi-stage filtration with the option of using Organoclay cartridges for synthetic lubricants.
• OSS Series: A compact and economical solution ideal for smaller systems, such as piston compressors or the small rotary screw units often found in workshops.
• OSD Series: A unique, fully integrated separator built directly into Atlas Copco’s GA series compressors, requiring zero additional floor space and eliminating installation piping.

Maintenance and Troubleshooting for Lasting Compliance

Oil-water separators require regular maintenance to function correctly, and following a schedule for proper air compressor maintenance is essential.

Routine Maintenance and Disposal

Visual water quality tests of the discharged water should be performed regularly to monitor separator performance. Filters are consumable items and must be replaced at the manufacturer’s recommended service interval (typically 4,000 hours) or annually, but sites with 24/7 operations or high humidity may require more frequent service intervals.

Spent filter cartridges and collected oil are hazardous waste and must be disposed of according to UK regulations.

• A licensed waste carrier is required to collect them.
• A Hazardous Waste Consignment Note must be completed to provide a full paper trail for compliance.

Common Problems and Solutions

• High Oil Content in Discharge: This is a compliance issue, and the most likely causes are saturated filters or a mismatch between your compressor lubricant and your filter media.
• Clogged or Blocked Unit: Clogs and blockages are often caused by high levels of dirt from your compressor’s environment or by degraded compressor oil forming sludge.
• Separator Overflowing: An overflowing separator is an indicator of either a severe blockage in the outlet pipe or completely clogged filters, or a failed drain valve upstream.

The Business Case: Beyond Legal Compliance

The value of a high-performance oil-water separator extends far beyond mere compliance and avoiding fines.

• Drastic Cost Savings: The alternative to an oil-water separator is paying a specialist company to haul away all your condensate as liquid hazardous waste. By separating the oil on-site, the volume of hazardous waste is reduced by over 98%, so you can enjoy savings of up to 90% on your annual disposal costs.
• Protecting Your Equipment: Acidic, oily condensate can corrode air receivers, pipework, and downstream pneumatic equipment. You can maximise the life of your entire compressed air system by effectively removing this hazard with a separator.
• Enhancing Your Corporate Reputation: Proactive waste management supports ISO 14001 environmental management systems and ensures air quality meets ISO 8573-1 standards for oil content. And, for operations where oil contamination is not an option, oil-free air compressors offer an alternative solution.

Failing to manage your condensate is a failure of your business’s duty of care. Correctly specifying, installing, and servicing this equipment requires specialist knowledge of the entire compressed air system, including proper handling and disposal, as well as the correct disposal of condensate from the system.

Consult with the experts at Anglian Compressors to discuss condensate handling systems and compliance requirements. We can audit your current system and help by offering expert advice on finding the right solution for you.