For years, restaurant wastewater has caused problems with sewage systems because of the accumulation of fat, oil and grease (FOG) that can clog pipes. These “fatbergs” can damage water sewage networks resulting in increased costs because of the need for declogging and repair operations.
A group of researchers from North Carolina State University are focusing their efforts in developing a method for converting sewage sludge and restaurant grease into methane. Although the process is not new, the group is trying to determine if they can optimize the production of methane from biosolids treatment and what factors to focus on to maximize its output.
They observed that biosolids, the by-product of wastewater treatment, have been used for extracting methane from biosolids through microbial digestion. Their research indicates that adding grease interceptor waste (GIW) can potentially increase the methane from biosolids yield making it more viable as a sustainable energy solution.
Grease interceptors are utilized for capturing fat, oil and grease from the wastewater that comes from dining establishments to prevent clog build up in the sewers. The fatty waste that is collected makes it an ideal medium for bacteria to produce methane from biosolids which can provide energy for the treatment process making it more efficient.
Francis de los Reyes, a Professor of Civil, Construction and Environmental Engineering at NC State, is the lead author of the research. He believes that the conversion of biosolids and GIW into a renewable source of clean energy is a commendable achievement.
His team is determining the best ratio for the biosolids and GIW that would produce the most methane. If too much GIW is added during the anaerobic digestion phase of biosolids treatment, the amount of methane produced falls dramatically.
“Our goal with this work was to figure out the best balance of biosolids and GIW for maximising production of methane from biosolids. And we were able to make significant advances,” said de los Reyes.
They discovered that gradual increases of GIW added into the digester improved the output of methane from biosolids until it eventually comprised 75% of the overall volatile solids. This is significantly more than the amount of GIW that is added in other wastewater treatment facilities, according to de los Reyes.
With this method, the research team was able to reach a maximum yield rate of 0.785 litres of methane per gram of volatile wastes during the digestion process. This is approximately twice the amount of what is typically found in other systems.
With this much methane, it would be easy to bring it up to commercial scale making it an excellent energy alternative for many industries because it is more affordable and is also renewable. This would create an extra income stream for wastewater plants and would discourage them from just burning off the excess methane from their site.
In their pursuit to further refine their method, the researchers are looking into identifying the micro-organisms that play a major role in converting fats, oil and grease into methane. They are also investigating other varieties of food waste for methane potential, such as fruits and vegetables.
If you are a municipality in Ontario and in need of a biosolids management solution, please feel free to contact us at 1 (877) 479-1388.