Grease traps are one of the most popular FOG (fats, oils and grease) management solutions, with passive (manual) and automatic traps being the most popular options for commercial kitchen operators looking to prevent grease related issues.
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They both do essentially the same job of separating FOG from wastewater though at a glance, automatic grease traps seem very expensive compared to manual grease traps, there are more factors to consider than just the initial cost of the unit.
This article will compare the two system types, explaining the main differences and the pros and cons of each system so you can make an informed buying decision and select the right system for your requirements.
Firstly, lets cover what each system does so you can understand what to expect from each type of unit.
Traditional passive grease traps simply slow the flow of wastewater to allow it to cool and separate into 3 layers; FOG, solids and clear water. The FOG forms a &#;grease mat&#; at the top of the unit and solids either accumulate at the bottom of the unit or collect inside a strainer which is located just after the inlet. The clear water escapes via the outlet.
Automatic systems, also known as AGRU&#;s (automatic grease removal units), perform many of the same operations as a manual grease trap. Much like a manual system the flow of wastewater is slowed to allow it to cool and separate though automatic systems almost always feature the addition of a removable strainer basket for solids collection. This means the wastewater inside the unit will mainly contain FOG with only small amounts of solid waste escaping the strainer and settling at the bottom of the unit.
The similarities between the automatic and passive models stop once the FOG separates and rises to the top inside the unit. Rather than letting the FOG form a &#;grease mat&#;, automatic system re-heat and skim out the FOG automatically on a programmed schedule. The skimmed FOG is then transferred into a collector bin for easy removal and recycling.
For a more detailed insight on exactly how grease traps work, check out our article What is a Grease Trap & How Do They Work?
So now you know what each system does, lets delve into some comparison between the 2 systems, which may help with your buying decision. The 4 main area&#;s covered are:
There is a direct correlation between how efficient a grease trap is and the amount of grease inside the system. The more kilograms of grease inside the unit, the less efficient the trap becomes, which impacts overall performance.
For this reason, manual grease traps are less efficient than automatic ones as the grease accumulates inside them until its either pumped out or emptied manually. As automatic traps skim and remove FOG on a scheduled basis, grease doesn&#;t build-up inside the unit meaning the system will maintain maximum efficiency and perform at a consistent level.
The graphs below give a visual representation of performance vs kilograms of grease based on 25kg traps connected to equipment producing 2.5kg of grease per day:
As you can see the overall performance of the manual trap drops quickly once the amount of grease gets to a certain level, while the automatic trap maintains consistent performance.
Both systems are kind to the environment as they help prevent FOG entering the sewerage system but what happens to the recovered and pumped out waste?
With manual traps, the grease management service company who pump out the trap will dispose of all substances removed from the trap. The grease will often be recycled into biodiesel and any solids will be disposed of in the correct manner, helping to keep our environment clean.
Automatic traps remove grease and deposit it into a container in liquid form. This can then be collected along with other used cooking and waste oil by your relevant service provider. Potentially, if enough is produced, the removed grease from automatic traps can be sold as an additional revenue stream.
So, while both systems are eco-friendly, automatic traps edge ahead due to the potential of adding an extra source of income via selling removed grease.
Purchase price is usually the deciding factor between choosing a manual or automatic grease trap, however there are other costs which need to be considered when buying any type of grease trap. All the costs to consider are:
The purchase cost of an automatic grease trap can be 5 times more than the purchase cost of its manual equivalent. Manual traps also have no moving parts meaning they need no daily maintenance and require no electricity to run, unlike automatic traps which need around 10 minutes of maintenance a day and require an electricity supply to function.
It looks like manual traps come out on top but the final consideration of pump out costs swing the comparison in the favour of automatic grease traps. Manual traps require pumping out every 2-4 weeks at a cost of between £150 and £200, whereas automatic traps only require pumping out every 3-6 months at the same cost. While you can increase the time between pump outs of manual traps to up to 8 weeks by adding a biological grease treatment fluid into the system or &#;dosing&#;, this adds to the purchase / install costs and to running costs. So, over the course of 3 years, automatic traps will be much cheaper overall.
Let&#;s compare 2 similar automatic and manual Grease Guardian grease traps, the GGX15 (automatic) and GT1 (manual), so you can see which one will cost you less over a 3-year period.
The figures below are based on the following:
Evidently, in the first year the GGX15 automatic unit works out more expensive than the manual GT1, mainly due to the high purchase price. However, by the end of year 2, the much higher pump out costs of the manual unit mean the overall cost is higher its automatic counterpart. After 3 years, the cost difference between the 2 units is nearly £3,000 in favour of the automatic GGX15. If you also add potential income from selling recovered oil from the automatic unit, the cost difference increases even more.
Although automatic grease traps require a higher initial investment, the additional features gained by the extra investment offer increased performance, potential for additional revenue and reduced long term costs, making automatic grease removal units the best choice for grease management.
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If you are in the market for a FOG management solution, check out our great range of grease traps or contact us to discuss your requirements.
Nearly half a million tonnes of grease and fat enter the UK sewerage system every year. Grease sticks to pipe walls, which can eventually lead to blockages while fats and oils damage waste water treatment equipment, costing municipalities millions in repairs every year. If allowed to enter a natural water course, fats, oils and grease (FOG) can cause serious damage to the environment.
For these reasons, legislation ensuring that the correct FOG management is used by food service operators is now being heavily enforced. Polluters can face large fines or even closure if FOG waste isn't managed effectively. FOG also causes big problems within commercial kitchens, with FOG from wastewater causing blockages in internal pipes leading to expensive repairs and potential equipment downtime.
Fortunately, grease management systems such as grease traps are readily available. They're often the first-choice FOG management solution for kitchen operators but what are they and how do they work?
Grease traps have been around for more than 100 years and are also known as grease interceptors, converters, catchers, grease recovery / management devices or FOG traps. They're used in in a wide range of environments including:
To put it simply, a grease trap is a receptacle into which wastewater containing FOG flows through before entering a drainage system. The receptacle is designed to intercept or "trap" the FOG while allowing clear water to escape.
Grease traps work on the basis that animal fats and vegetable oils (grease) are 10 to 15 percent less dense than water and that grease won&#;t mix with water. Thus, fats and oils float on top of water.
When wastewater enters a grease trap, the flow rate is reduced enough so the wastewater is given enough time to cool and separate into 3 layers. The grease rises to the top inside the interceptor and is trapped using a system of baffles. Solids settle at the bottom and the separated clear water escapes under an outlet baffle. Many grease traps also have strainers for collecting solid debris, which reduces the amount of solids that settle at the bottom of the trap.
Over time, solids and grease build-up, and if left to accumulate for long enough they can start to escape through the outlet and in some circumstances, they can back-up through the inlet. For this reason, the trap must be cleaned / pumped out on a regular basis.
The time between cleaning / pumping out the trap will depend on the amount of wastewater produced and the size of the grease trap but it is usually every 2-4 weeks. This time-period can be lengthened to up to 8 weeks by adding a biological grease treatment fluid into the system. The solution combines non-pathogenic bacteria with nutrients and enzymes to break down FOG, aiding grease trap performance. This process is commonly referred to as &#;dosing&#;.
Dosing can also be implemented at the outlet stage as a further method of preventing FOG build-up in internal piping.
There are 3 main types of grease trap; passive hydromechanical (manual), automatic and gravity.
Traditional passive systems are one of the most common systems used in smaller establishments. This is due to the low initial investment cost required to purchase one and the variety of sizes available, meaning they can be easily installed under most sinks while larger units are available to accommodate bigger wastewater production requirements.
Designs of manual grease traps date back to when the first U.S. patent was issued. Even today grease interceptors use the same basic operating design as the model. They&#;re usually constructed from plastic or stainless steel and must be cleaned manually and on a regular basis.
Automatic systems, also known as AGRU&#;s (automatic grease removal units), use some of the same principals as a traditional passive trap but re-heat and skim out the FOG automatically on a programmed schedule. The skimmed FOG is then transferred into a collector bin for easy removal and recycling. The programmed schedule is based on the amount of FOG produced and means operators don&#;t have to measure or check grease levels.
Much like passive systems they&#;re available in a variety of sizes to accommodate a range of requirements. While they have a higher initial investment cost, they are more efficient and have lower long term running and servicing costs.
For a more detailed insight on the differences between automatic and passive grease traps, check out our Automatic vs Manual Grease Traps article.
Gravity systems are usually large in-ground tanks constructed from concrete, fibreglass or steel. They work in a similar way to a passive hydromechanical trap but have a much larger capacity and are better for high-flow applications.
Gravity traps must be pumped out on a scheduled basis, usually by a specialist grease management service company.
With public awareness of environmental issues increasing, looking into your FOG management now is potentially a wise investment and effectively future-proofs your business against future legislation which some are predicting will become more stringent in this area in years to come.
We compare Automatic Grease traps with Passive or Manual grease traps for efficiency, sustainability and cost over a three year period, view our results.
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