History of the Grease Trap
Grease Traps are not a recent invention. In fact, grease interceptors have been around for nearly 150 years. Even in the Victorian era, blockages as a result of the build up of fats, oils and grease were problematic enough to merit the inclusion of a grease trap. This prompted Nathaniel T. Whiting of California to patent the first ever grease trap in 1883/4.
Whiting’s design was similar in concept to the modern grease separator. Basically, a tank that contains liquid with an inlet and outlet and separation baffle is used to allow the separation of water from oil. Oil, if given enough time, should quickly separate from water as they do not bond. Oil is lighter/less dense than water. Oil has a lower specific gravity value than water. In simple terms this means it will float. How quickly oil and grease separates in a grease trap depends on the velocity of the waste entering the tank, the size/liquids volume of the tank and the specific gravity of the oil. The bigger the tank and the lower the flow the more easily grease will separate. A 100-litre grease trap with a flow rate entering it of 1 litre/second will perform far better than a 50 litre grease trap with a flow entering of around 2 litres/second.
Though this is rudimentary physics early manufacturers of grease traps may have often undersized their separators allowing too much flow into small tanks. It wasn’t until World War 2 that grease trap sizes became regulated better. The Construction Division of the US Army is said to be the first body to regulate the size of grease traps. Over time these regulations evolved into the modern plumbing and drainage standards seen across America today.
In Europe grease traps were developed largely following German standards. The main difference between the US standards and European grease trap standards were in relation to size. The European grease trap needed to provide sufficient volume for the highest level of effluent quality whereas the US standards focused on the percentage of grease removed. As a result, approved grease traps in the US are more compact than the European equivalently rated unit.
The other factor that Whiting would have noticed in those early grease trap designs would have been the fact that efficiency soon dropped as grease and food waste built up inside the unit. In a trap that has yet to accumulate any grease, the full liquids volume of the tank is utilised for grease to separate. When grease builds up from the surface and solids from the bottom, that “free” volume of water is reduced, resulting in less room for incoming grease waste to separate. If grease is allowed to build up, the tank would get to a stage where there would be no more space for grease to separate and this would result in grease escaping to drain.
This meant that, somehow, the grease needed to be removed. In the early days of grease traps there would not have been the infrastructure in place for pumping companies to empty the traps on time. Many traps would have had to have been emptied manually by hand. However, knowing when to empty the trap was unclear. In the US in the 1940s the Plumbing and Drainage Manufacturers Association investigated how grease traps should be sized and maintained.
Eventually, the Drainage Institutions in the US were able to develop a standard that worked out how much waste the trap could handle before it lost efficiency.
Today in the US every grease trap is given a flow rating (such as 15 GPM, 20, 35) and a grease capacity which is usually double that of the flow rate but in pounds (30 pounds, 40, 70). When a grease trap reaches capacity, it needs to be emptied. This can be difficult to work out by simply looking at a grease trap so many authorities settled on mandating a monthly emptying of the grease trap. This is the same in Europe where the recommendation is that a grease trap should be emptied at least once a month.
As cities grew there were more and more restaurants. Each grease trap needed to be emptied once a month. That’s a lot of pumping activity. Those that followed the advice incurred monthly emptying fees and those who ignored it risked being fined or having blockages.
In the modern era of grease traps a system for automatically removing the grease has been introduced as a bolt on feature. The combination of grease trap and recovery system is generically referred to as a grease recovery device (GRD) In a GRD, the traditional grease trap may be equipped with a skimming device that lifts the grease off on a daily bases. This ensures that the grease capacity of the trap is seldom reached, therefore removing the need for monthly emptying.
In today’s greener cities grease removal devices are used instead of traditional “manual” grease traps not just to ensure a better performing network of traps but to remove the need of pumper trucks constantly moving between restaurants every month.
Back in World War Two grease and fat was used to produce explosives, hence the interest of the army in recuperating it. Today, the removed grease is put to much safer use. Grease can be recycled into biofuel, paints, and soaps. In the modern city every outlet with a grease recovery device is preventing blockages and pollution without the need for hundreds of pump trucks and the recovered grease can be used to power any vehicles that do make it on to the roads.
In the cities of the future, the grease trap and removal device may very well help power the building they are housed in while preventing drains and sewers from filling up with grease. Some even believe we will soon fly in planes that are fuelled by grease. Maybe Nathaile Whiting was a head of his time but even he surely couldn’t imagine that his humble grease trap could be a means to harvesting fuel for magnificent flying machines.