Grease Trap Pumping Variance
To understand the variance program you need to firstly understand the process for pollution prevention by municipal waste water authorities.
The purpose of fitting a grease trap/interceptor is to prevent particles of solids and or grease from entering the public or private sewer system.
A grease trap is normally sized to allow waste water to achieve satisfactory separation time that allows particles lighter than water, such as grease to float to the surface, for particles heavier than water to fall to the bottom such as solids and clarified water to pass on through the system into the public sewer. Without sufficient retention time, turbulence occurs within the trap allowing particles pass through causing issues down stream.
The key components that cause issues for waste water operations are:
- TSS (Total Suspended Solids) are different sized particles in the waste stream which can act as a food source for bacteria including corrosion causing strains which increase Hydrogen Sulfide levels. It also creates excess sludge levels at the sewer treatment works requiring higher processing activity.
- BOD (Biological Oxygen Demand) this is a rate at which organisms use oxygen in waste water, under aerobic conditions. Bacterial growth depletes oxygen levels in the waste water stream effectively poisoning the water thus requiring additional treatment at the sewer treatment works.
- FOG (Fats, Oils and Grease). The culmination of these components restrict the size and flow of the sewer system causing SSO’s (Sanitary Sewer Overflows)
- Hydrogen Sulfide. Grease traps which are not maintained effectively create anaerobic bacteria. These bacteria utilize sulfate molecules for growth, the by product of this process is H2S which causes bad odors and corrosion in grease traps and the main sewer system.
In order to prevent these issues waste water authorities frequently require larger grease traps or higher frequency pumping schedule. What they are looking to achieve is maximum performance of the grease trap to ensure floating grease and settled particles don’t build up to a level where the trap is inhibited.
Requirements vary across the country but many authorities utilize the 25% measurement rule (a reduced capacity measurement) and others set a maximum limit of inches of grease or inches of solids which must not be exceeded.
The 25% rule example: If a grease trap is 6 ft deep (To the water line) and has 12 inches of grease and 6 inches of solids equaling a total of 18 inches, then utilizing the 25% rule the trap capacity has been reduced by 25%.
Solution
Fat and grease deposits from milk and cream do build up in Starbucks traps and drain lines. However the main issue is build up of solids particles from rinsing of coffee pots and bakery trays etc.
In an initial pilot trial at Store 11706 Venetia Plaza Orlando, solids particles were captured and weighed every day over a 7 day period. The average daily volume of solids was 0.895lbs per day. The internal store grease trap was also measured and solids built up at a rate of 2” per week.
The store was required by the local waste water authority to check and clean the trap weekly which equated to the pumping 52 times per years at a cost $9100.
Having implemented the process detailed below, solids levels reduced to less than 3/16th of an inch a week. Following consultation with the local waste water officials, a new extended pumping frequency was granted at 90 days The cost saving on this store was approximately $6500 in year 1 and $7500 in year 2
The process
Two Fine Particle Strainers (FPS) are installed per store. One connected to the three compartment sink and the other to the front of house single rinse sink. The unit works by gravity and has no moving parts but contains a daily disposable filter made from expandable nylon. The filter captures nearly 100% of solids particles and collects particles as small as 300 microns (smaller than a used grain of coffee). The system thus collects nearly all coffee, bakery and fruit pulp particles. Both FPS devices are fitted above ground and remove waste prior to it flowing into the grease trap.
The filter expands during the course of the day and is changed over in the evening and disposed of directly into the trash.
Once installed, every 3 or 4 weeks a B Environmental service technicians visit on site to carry out a service call for four primary reasons.
- Ensure device is working correctly and there are no other drainage related issues that need addressing related to the system.
- To carry out a detailed inspection of the grease trap / interceptor to inspect its condition, measure the pH for waste water purposes and also measure levels of grease trap solids, clear water and floating grease to ensure the system is compliant with the city or municipality. All service information and details are fully documented for audit purposes.
- Ensure that allocated contractors for grease trap cleaning are carrying out their work to a suitable standard as required by Starbucks Facility Managers and local waste water departments. Failures or problems identified are reported to FSM’s.
- The final component is ensuring onsite partners are maintaining the system daily and work with them to ensure best management practices are being attained.
When the system has been installed and B Environmental is satisfied with reduced solids levels being achieved within the trap/interceptor B Environmental contacts the local municipality to understand the compliance codes and work to gain an amended pumping schedule. B Environmental check the system monthly and maintain a data log/record of site visits and the condition of the system. Because the waste is being disposed of daily municipal water authorities are approving or confirming it meets within their requirements and so allowing a reduced pumping schedule to be implemented.
Sites with lift stations normally are effected by: H2S, Corrosion, Reduced performance and odor problems caused by solids build up. This problem is reduced significantly with the above system installation and pumping/cleanout / maintenance and repair schedules can be adjusted. Some Grease may be present but this can be dealt with through a different process.
Justin Price
VP Business Development
