“Fatbergs” was the term used to refer to the masses of FOG (fats, oils and grease) found in the sanitary sewer lines surrounding the second oldest residential dining facility operated by the Housing Dining Services at the University of Illinois at Urbana-Champaign. Five years ago the University’s Facilities and Services department asked us: What are you going to do about it? The Housing Maintenance department already had a contractor jetting out the sanitary sewer ejector system with ever increasing frequency. But it wasn’t enough. We couldn’t allow the sanitary sewer system to back up into the dining and residence hall.
We knew we weren’t alone in battling this problem and also knew we had to remedy the situation. Soon. The solution was simple: keep the food out of the sanitary sewer system. Execution, though, posed a different set of challenges. Pulpers can be a smelly maintenance nightmare. Composting was not an option on our campus and sending it to a landfill was not even a consideration.
Enter food waste digesters. They seemed to provide the answer but much research needed to be done.
I began educating myself about the different types of digesters available. Some digesters required the addition of enzymes, bacteria, pellets, etc. to the food waste as it was beat in a tank by rotating paddles. I went to visit one of these units in person. You had to open the door and dump the food waste in the tank. It smelled, you couldn’t add any bones, and it had to be plumbed to a grease trap. As I researched other types of digesters, I was finding the same common theme: yes, they kept the food waste out of the landfill, and it was turned into grey water, but they weren’t able to digest the FOG.
Enter aerobic digesters. I found out about this technology from a manufacturer’s rep that I had been working with for many years and made arrangements to go see the unit in person. The rep warned me before the visit that I wasn’t going to see much. It’s just a big box, he said. He was right: it was just a big box, eight or nine feet tall and six or seven feet wide.
Staff dump the food waste into a disposal that pumps it to the digester tank. It wasn’t an open tank, like the other type of digesters; this one was enclosed. Since the tank was enclosed, we could not smell the food waste. The unit could digest bones, shells, meat, dairy, produce and, best of all, FOG. The effluent produced by this unit is basically lipid free, and I was told the effluent would continue to work in digesting the FOG as it travelled through the sanitary sewer system. The technology uses a proprietary bio-mix, not enzymes or bacteria, to aid in the digestion, along with air and water. Sounded simple enough.
After reviewing side by side documentation weighing the pros and cons of the different types of digesters, it was a no-brainer to try the aerobic digester. In the fall of 2012 we decided to start out with two units, one in the residential dining building with the “fatbergs” in the sewer, and the other at our catering production facility. I invited the manufacturer’s rep to review the locations we had selected. We had to locate three utilities for the units: power, water supply and drain. One of the units can digest 480 pounds of food in a 24-hour period. The other, larger unit, can digest 720 pounds of food in a 24-hour period. Because of the size of the units, the rep had to get careful dimensions of doorways and hallways that would need to be navigated during delivery of the equipment.
Delivery and installation day came and we had no surprises getting any of the large pieces into the facilities. The installation team trained the dining staff on how to operate the hammermill, and load it without overfilling it.
One of the most important training lessons was the cleaning of the hammermill. Staff can use absolutely nothing but water and a scrub brush when doing this. If an over-ambitious employee decides to put a cleaning agent into the hammermill, it would render the biomix useless. Then you end up with a very large tank of rotting food waste. Not a pretty picture. One other key to keeping the hammermill fresh is to leave the door open overnight after it has been cleaned for the day. If one ever does smell an odor, it is because the hammermill hasn’t been properly cleaned, and not because of the digestion process.
Other than the daily hammermill cleaning, the unit requires very little maintenance. Every couple of weeks, depending on volume, staff change the internal biomix container. During regular operation, the unit automatically dispenses biomix into the tank. Annually, we completely drain and empty the tank. When this happens, we clean the tank and provide the necessary planned maintenance to the pumps and other mechanical components.
Silverware, serving utensils and other non-food items will somehow manage to find their way into the hammermill, despite everyone’s best efforts. So the installation team trained our in-house plumbers and electricians on how to solve this common problem.
Our third unit, another one that can process 720 pounds of food waste in 24 hours, was installed in the spring of 2013, and a fourth, processing up to 600 pounds of waste in 24 hours, in the fall of 2014. And we are exploring options for installing two more units.
Since our last installation, a few new changes have been made by the manufacturer. A new type of hammermill can literally shred that pesky silverware that gets into the grinder. Second, a method for significantly reducing the amount of fresh water needed is available. This system takes the grey water effluent and sends it through a process where it is ozonated and recirculated back to the grinder as needed.
We are confident we made the right choice with this anaerobic digester. It is truly a safe, sanitary, effective and environmentally responsible method of food waste disposal. We no longer spend thousands of dollars to have the sewer lift pumps jetted. And the fatbergs? They’re history.