A new study by engineers at the University of Hawaii at Manoa indicates that traps designed to keep fat, oil and grease from entering sewer lines may indirectly contribute to more damaging problems for sewer systems.

The study, by associate professor of civil and environmental engineering Tao Yan and postdoctoral student Xia He, was published in the journal Environmental Science, Water Research and Technology.

“We are interested in the biological processes that contribute to sewer systems deteriorating and in developing engineering solutions that can improve the sustainability of sewer infrastructure and help protect public health and the environment,” Yan said in a news release.

According to Yan and He, the traps, typically installed between a kitchen wastewater drain and sewer pipelines, may be effective in keeping fat, oil and grease from continuing on through the sewer system, but they can also foster the growth of microorganisms that produce long-chain fatty acids, which in turn form hardened deposits along sewer pipes.

These hardened deposits — called “fatbergs” — are composed of calcium salts of long-chain fatty acids and can cause severe problems, including overflows and sewer system degradation, according to the authors.

Duplicating conditions within grease traps in their laboratory, Yan and He found that the microorganisms increased the concentration of fatty acids both within the trap and in the water that would flow through the sewer system.

These fatty acids were mainly unsaturated, thereby producing stickier deposits that are harder to dislodge and which can corrode concrete pipes.

Yan said that designing grease traps to include greater microbial activity could be effective in minimizing the formation of such deposits.