Pipe up: Jacob Tompkins, Waterwise

“More bioremediation field ­trials are needed, otherwise we will be digging fatbergs for the foreseeable future”

Around 150,000 sewer blockages a year in the UK are caused by fats, oils and greases (FOG), which cause a major headache for water utilities.

The combination of commercial fats and a growth in domestic (un)flushable wipes has led to a recent surge in the fatberg phenomenon.

There has been a lot of activity to try to solve the problem. Southern Water has recently prosecuted some food service establishments (FSEs) for repeated sewer blockages. Thames Water is using fat removed from the sewers to produce power in Beckton. The key actions seem to be the introduction of standards, collaboration with FSEs, catching the fat at source, behaviour change programmes, and the development of alternative uses for FOG. But how about in-situ bioremediation?

There are commercially available bioremediation approaches and there have been some successful trials of these. However, there is very little scientific and/or engineering knowledge in this area and the trials have generally been localised.

There are some key issues that need to be resolved. Bacteria can have a major impact on reducing FOG blockages, but they have to be the right bacteria and unfortunately the bacteria commonly found in wastewater tend to make things worse by degrading unsaturated fatty acids in a way that leads to deposition of semi-solid fatbergs rather than the digestion of the fat.

There is some academic evidence that introducing multi-species microbial additives can degrade FOG without forming solids and could keep sewers flowing, but these have not been tested widely. Likewise, there are microbial inocula that could tackle sewer blockages, but these are mainly used for commercial FOG treatment.

So why is bioremediation used extensively by utilities in sewage treatment but rarely used in sewers? The difficulties of upscaling from trials to widescale use seem to be threefold: the logistics of mass dosing; the type of bacteria used; and the timing and location of dosing.

The best ways to solve this could be to combine bioremediation with predictive sewer modelling so that sewers can be regularly dosed at critical times and locations, or to find alternative ways to regularly dose sewers (such as toilet tissues impregnated with bacterial spores that activate when wet); or to introduce materials that can develop biofilms able to host the right type of bacteria.

The problem of FOG is set to continue and ­possibly get worse; more field trials of bioremediation are needed, otherwise we are going to be digging fatbergs for the foreseeable future.

Jacob Tompkins, managing director, Waterwise