What Are the Key Differences Between Oil Interceptors and Oil Separators?

Are you trying to figure out whether an oil interceptor or an oil separator is the right choice for your project in Ireland? It’s a common question, especially when you’re dealing with managing oil in water. Both systems have their own roles and work in different ways. 

This guide aims to simplify these concepts for you. We’ll explain what oil interceptors and oil separators are, how they work, and where they’re best used, helping you make an informed decision for your project. Let’s get into the details of these systems and figure out the best fit for your needs.

What is an Oil Interceptor?

An oil interceptor, often found in drain lines, is designed to trap oils, sediment, and other liquids before they enter the sewage system. These are typically used in areas with low flow rates and small quantities of contaminants, such as parking garages, machine shops, and service stations.

Oil interceptors are usually made of steel, fibreglass, or plastic and include components like a baffle plate, a solid bucket, and a separation area. The baffle plate slows down the flow, helping in sediment and sludge settlement. The low flow rate allows oils and light-density liquids to separate and rise to the top, leaving relatively clean water to be discharged.

What is an Oil Separator?

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Oil separators are more sophisticated systems used in higher volume applications like industrial wash operations and re-fueling facilities. They are designed to handle a greater volume of water, oil, and contaminants.

Standard oil separators are constructed from materials like steel or stainless steel and consist of various compartments, including an inlet, baffles, a sludge chamber, a separation chamber with coalescing media, and a clean water outlet chamber

The process begins in the inlet compartment, where baffles reduce water flow, allowing solids to settle. The coalescing media in the separation chamber then causes oil droplets to combine and separate from the water.

Differences Between Oil Interceptors and Oil Separators

Understanding the differences between these two systems is essential for choosing the right solution for your needs.

Design and Structural Complexity

Oil interceptors are typically simpler in design and smaller in size. They are suited for lower volume applications and are easier to install and maintain. Their design is straightforward, focusing on trapping oil using gravity and simple separation techniques.

In contrast, oil separators are more complex and larger. They are designed to handle higher volumes of water and more significant amounts of oil. Their complexity allows for more efficient separation and treatment of contaminated water.

Efficiency and Capacity

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While oil interceptors are effective for small-scale applications, their efficiency decreases as the volume of oil increases. They are ideal for situations where oil presence is relatively low and consistent.

Oil separators, however, are designed for high efficiency in large-scale operations. They can handle fluctuating volumes of oil with greater effectiveness, making them suitable for industrial applications where oil contamination levels are higher and more variable.

Suitability for Different Applications

Oil interceptors are most suitable for commercial settings like restaurants or small garages. They work well in environments where oil contamination is moderate and not the primary concern.

However, for larger industrial settings where the volume of oil is higher, oil separators are more effective due to their higher efficiency and capacity.

Maintenance and Operational Demands

The maintenance of oil interceptors is generally simpler due to their less complex design. They require regular cleaning and inspection but are easier to manage, especially in smaller installations.

While oil separators demand more rigorous maintenance routines. Their complex systems require regular checks and professional servicing to ensure optimal operation. This can involve more technical expertise and resources.

Cost Implications

Oil interceptors are typically more cost-effective in terms of both installation and maintenance. They are a practical choice for small businesses or facilities with limited budgets.

On the other hand, the initial investment and ongoing maintenance costs for oil separators are higher. However, their efficiency and capacity to handle large volumes make them a worthwhile investment for larger operations.

Environmental Compliance

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Oil interceptors are suitable for meeting basic environmental compliance requirements in low-risk areas. They provide a fundamental level of protection against oil contamination.

Oil separators are designed to meet more rigorous environmental regulations. Their high efficiency and advanced design make them suitable for areas where compliance with strict environmental standards is a priority.

Conclusion: Choose the Right System for Your Needs

Deciding whether to use an oil interceptor or an oil separator comes down to what you need for your project. Each one has its own strengths and is better for certain situations. Understanding these differences is key to making a smart choice.If you’re looking for expert guidance in selecting the right oil management system in Ireland, Resolute Civils is here to help. Contact us today to ensure your project not only meets but exceeds environmental standards with the most suitable oil management system.


What is the main difference between oil interceptors and oil separators?

Oil interceptors are simpler systems designed for low flow drain lines and small quantities of contaminants, while oil separators are more sophisticated and efficient, used in higher volume applications with a potential for a larger volume of water, oil, and contaminants.

Where are oil interceptors typically used?

Oil interceptors are commonly used in areas like parking garages, machine shops, service stations, and manufacturing facilities where there is a lower risk of oil contamination.

What are the typical applications for oil separators?

Oil separators are used in high-volume applications such as industrial wash operations, parking lots, re-fueling facilities, and military installations where there is a higher risk of significant oil contamination.

What is the efficiency level of oil separators compared to oil interceptors?

Oil separators are generally more efficient than oil interceptors, capable of removing almost all free and dispersed non-emulsified oils to a concentration of less than 5 ppm, which is suitable for most municipal sewer systems.

What are the different types of oil interceptors?

The two main types of oil interceptors are Full Retention Interceptors, designed to treat the full flow from a drainage system, and Bypass Interceptors, which treat flows up to a lower limit and are used in areas with infrequent light contamination risks.

What is the difference between Class 1 and Class 2 Separators?

Class 1 Separators are designed to achieve a concentration of 5 mg/l of petrol/oil at discharge and usually include a coalescer, while Class 2 Separators aim for a concentration of 100 mg/l and are typically used when discharge is to a foul sewer.

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