Bacterial behaviour a slippery slope to sewer fatbergs

Researchers in the US have discovered that microorganisms in wastewater grease traps may aggravate fat, oil and grease deposits in sewers – a problem that these traps are designed to reduce.

Researchers in the US have discovered that microorganisms in wastewater grease traps may aggravate fat, oil and grease deposits in sewers – a problem that these traps are designed to reduce.

The deposits, often known as fatbergs, are caused by fats and cooking oils entering wastewater pipelines. They cause severe problems for those maintaining the sewers and in the worst cases, lead to overflows and flooding.

Businesses can install grease interceptors between their kitchen wastewater drain and the sewer pipeline to trap and remove the fat, oil and grease. Now a study by Tao Yan at the University of Hawaii indicates that microorganisms within these grease traps could have an impact on their efficiency. ‘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,’ explains Yan.

Salts of free, long-chain fatty acids are a major component of sewer deposits but we did not fully understand how they got there. Yan and postdoctoral researcher Xia He replicated the conditions within grease interceptors – where microorganisms from food waste can thrive – in their laboratory. Bacteria produce enzymes that hydrolyse oils and grease in wastewater, forming fatty acids. Yan and He found this process increased the concentration of fatty acids within the traps and in the water that would flow into a sewer pipeline. Furthermore, the fatty acids generated by the microorganisms were mainly unsaturated. Unsaturated fatty acids produce stickier deposits so are a menace for sewer upkeep as they are harder to dislodge and corrode concrete pipes even more. ‘The majority [of the fatty acids] remain in the reactors under normal operational conditions but disturbing grease interceptors could lead to a discharge and increase the risk of deposit formation in sewer systems,’ comments Yan.

In light of this research, Yan advises grease interceptor designers to consider microbial activity to maximise their effectiveness. Raffaella Villa, an expert in waste management at the Cranfield Water Sciences Institute, UK, however urges readers not to misinterpret the findings: ‘Although the results could be very helpful in designing separation processes … grease interceptors, if well designed and regularly maintained, are a very effective way of reducing the total deposit load in sewers.’