When fat, oils and grease (FOG) enter the wastewater system from both domestic and food-establishment sources they can lead, in conjunction with non-flushables such as wet wipes, to the formation of blockages, coined ‘fatbergs’ by Thames Water.
When fat, oils and grease (FOG) enter the wastewater system from both domestic and food-establishment sources they can lead, in conjunction with non-flushables such as wet wipes, to the formation of blockages, coined ‘fatbergs’ by Thames Water. These fatbergs have come into the national consciousness with the discovery of several high-profile mega-fatbergs, such as the Whitechapel Fatberg (now named by the public as ‘Fatty McFatberg,’), which is on display at the Museum of London and was made famous in the Channel 4 Fatberg autopsy documentary. This example reportedly weighed over 130 tonnes and was longer than Tower Bridge, measuring 250 m. In fact, Thames Water estimates that physical FOG removal costs over £1 million per month. In addition, blockages can cause flooding and release of sewage into the environment and thus pose public health and environmental risks – alongside incurring extra costs and inconvenience to consumers.
The process by which fatbergs form after entering the sewer is still relatively poorly understood, but involves a dual process of solidification and saponification that results in deposits on sewer walls at water–air interfaces. Saponification is the process in which free fatty acids (FFAs) in the wastewater react, along with calcium and other minerals, to produce metal soaps that act as nucleation points for FOG, with further FFAs and minerals, alongside non-flushables such as wet-wipes and sanitary products, to cause blockages.
Current treatment and recycling regimes
When fatberg blockages form, the main procedure for removal and remediation is manual excavation, which essentially involves sending people into the sewers with a hose and a shovel to manually clear the blockage. This is dangerous, costly and time consuming; for example, trapped gas is a constant risk. The FOG material excavated from the sewers is usually discharged to landfill. However, Thames Water is currently collaborating with Argent Energy to process fatbergs to generate biodiesel as a new use for this otherwise waste product.
Clearly, a preferred solution would be to manage and reduce the FOG entering the sewer system and thereby stop the cause of the blockage at source. One solution is the use of grease traps or separators used by food service establishments (FSEs) to catch the FOG before they enter the sewers. These are containers, inside or outside the FSE premises, where the FOG are allowed to separate from the wastewater by gravity. The waste FOG collected from grease traps, and used cooking oil from fryers, are already used in many countries as renewable feedstocks for biodiesel production. In addition, some water companies have started social outreach and public education programmes to increase awareness of the detrimental effects of FOG on the sewer system and, potentially, their water bills.
Microbiology: life at the tip of the fatberg
It will be no surprise to this readership that microbes may play a key role in the process of FOG deposition and may provide some solutions to the prevention and eradication of fatbergs in the future. It has been suggested that microbes play a part in the formation of the fatbergs, as it is the microbial production of FFAs and their leaching of calcium from the sewer pipe walls that provide the building blocks required for saponification to occur in the system. Isolates from sewer systems have been observed to form solid fat deposits when cultured with oil, suggesting some microbial activity may be involved in the formation of fatbergs.
Bacteria are able to degrade fats via the action of lipase enzymes that are secreted or present on the surface of the bacteria and cleave the fatty acids from the glycerol backbone. These released fatty acids are then transported into the bacterial cell via specific transporters and used in the cell metabolic processes. Inefficient or incomplete degradation of lipids can lead to the release of FFAs, which can contribute to FOG deposit formation.
However, the potential application of bacteria that degrade and completely remove FFAs from wastewater has great potential for bioaddition treatment. Numerous bacterial-based products have been used for FOG management, with many based on proprietary cocktails of bacteria used for other applications, such as lipase production or hydrocarbon degradation in the oil industry. These cocktails used by wastewater companies are largely based on environmental or type strains such as Bacillus and Pseudomonas species. Other products also exist that contain enzyme preparations but, since they may have short retention times and release FFAs with no onward degradation, their use has been limited. Many FSEs regularly use microbial additions for keeping their kitchen drains free from deposits. In addition, bioadditives for FSE grease traps have been reportedly used successfully to increase the time between emptying.
Bioadditives have also been also used in sewers to keep the pipes clean and to tackle the deposits, with mixed success, possibly due to inconsistent information on management, lack of stability in the environment in which they are to be deployed, and also a lack of technology transfer, that is, translation from lab ‘ideal’ conditions to a range of different and complex sewer environments. The main challenge is in translating bacteria’s laboratory performances into predictions of efficacy in the wastewater system for how, when and where to use them; this is in need of more focused and in-depth research and development.
Bioadditives have been utilised in sewer systems for many years, where a variety of different products and application methods, including regular manual and automatic dosing in liquid and dry formats, have been used in the system and have been shown to be effective in reducing FOG in wastewater. However, so far, consistent prediction of the microbial activity of these products in different environments in the wastewater network remains a struggle and knowledge of how these products work in different sewer environments, such as pumping stations versus sewer pipework, is needed. One other factor is that there is very little information regarding the microbiology of this environment; nor have products been developed using bacteria actually sourced from FOG deposits.
Our work has begun to characterise the microbiome of fatbergs using next-generation sequencing techniques, uncovering a plethora of environmental bacteria residing at the fatberg surface, including Ferruginibacteria, Xanthomonas, Rhodobacter, Klebsiella and Acinetobacter. Combining this information with a range of novel fat-degrading bacteria that our team has isolated from FOG deposits in London, including novel Klebsiella and Serratia species, we have also begun preliminarily testing the performance and efficacy of a FOG-degrading consortium in domestic wastewater rigs. This proof of concept highlights that a more targeted and tailored consortium approach to address the FOG problem might yield greater success.
FOG detection: an oily issue
Finally, one aspect of FOG management in wastewater systems is in the detection of increased FOG in effluents. Surprisingly, accurate and easy detection of FOG is not simple, with specialised laboratories being needed to carry out these assays off-site. Again, bacteria may hold the answer, with many bacteria harbouring sensitive and accurate FOG detection systems, such as the Fad system of Escherichia coli. Given recent advances in biosensor and synthetic biology applications, it is possible that biological-based fat sensors with colorimetric outputs may have the potential for simple ‘sewer-side’ tests for levels of FOG in the environment. However, the challenge of translating these results from the laboratory to the real world still remains.
The potential for bacterial applications to FOG degradation and/or detection and the management or removal of fatbergs is great, offering exciting research, development and commercial opportunities. Further knowledge and investigation into fatberg (micro)biology alongside engineering translation in a real-world context, would greatly increase the likelihood of a tailored product designed specifically for the different and complex environments in which it would be used.