Tackling Urban Sewer Blockages: Evaluating the Effectiveness of Grease Interceptors in Managing FOG Waste

A recent study from the School of Engineering, RMIT University, Melbourne, Australia, Cranfield Water Science Institute, Cranfield University, Bedfordshire, and South East Water, Frankston, Australia explored the effectiveness of grease interceptors (GIs) in managing fat, oil, and grease (FOG) deposition in sewer systems. Despite claims that commercial GIs can remove up to 99 percent of FOG, the study revealed that these devices still allow significant amounts of FOG to enter the sewer network, contributing to blockages and the formation of fatbergs.

Investigating the Role of Grease Interceptors

The study was conducted at three food service establishments (FSEs) in Melbourne, Australia, each employing different cleaning methods: handwashing sinks, dishwashers, or a combination of both. Researchers collected samples from the GIs at these sites, as well as from a household kitchen, and analyzed them for FOG particle size, fatty acid (FA) profiles, and metal content. The findings indicated that GIs are more effective at removing larger FOG particles, typically those over 150 micrometers. However, the use of dishwashers in FSEs resulted in the production of a higher proportion of smaller particles, which are harder to separate by gravity and more likely to pass through GIs into the sewer system.

Unmasking Fatty Acid Profiles

One of the key insights from the study was the variation in FA profiles between different sampling points within the GIs. Common FAs like palmitic, oleic, and linoleic acids were prevalent in the scum, but the effluents contained higher proportions of extra-long-chain FAs such as behenic and lignoceric acids. These long-chain FAs, along with metals like calcium and magnesium, contribute to the solidification of FOG in the sewer, exacerbating the formation of fatbergs.

Chemical Complications in Effluents

Chemical analyses revealed that the scum accumulated in GIs had high concentrations of FOG, up to 309.8 grams per liter in some cases. Effluent samples, however, still contained FOG concentrations well above allowable limits, with GI-3 (a BBQ restaurant) discharging up to 9.6 grams per liter. This indicates that despite the presence of GIs, significant amounts of FOG are still making their way into the sewer system. The presence of metals in the effluents, particularly sodium from detergents and calcium from food residues, further complicates the issue. These metals can interact with FAs to form soaps, which adhere to sewer walls and promote FOG deposition.

Towards Better Grease Management

The study found that while GIs play a role in managing FOG, they are not entirely effective in preventing FOG-related sewer blockages. Improvements in GI design, such as the addition of baffles and longer hydraulic retention times, are necessary to enhance their performance. Additionally, better management practices at the source, including the use of less aggressive detergents and regular maintenance of GIs, could help mitigate the problem. The study emphasized that controlling FOG at the source is crucial for reducing its impact on sewer systems. Regular maintenance and proper use of GIs, combined with improved designs, can significantly reduce the amount of FOG that enters the sewer network. This is important not only for preventing blockages and fatbergs but also for minimizing the environmental and economic impacts associated with FOG deposition.

Overall, this research underscores the need for more effective strategies and technologies to address the ongoing challenges posed by FOG in sewer systems. As urbanization and dining trends continue to increase the pressure on sewer infrastructure, tackling FOG deposition remains a critical issue for maintaining efficient and sustainable wastewater management. Upgrading existing GI systems and implementing better FOG management practices at FSEs and households are essential steps toward achieving this goal.