Avoiding the dreaded 'fatbergs' (Day 110)

Avoiding the dreaded 'fatbergs' (Day 110)

14th September 2014

A FOG blocking a sewage pipe - Image courtesy of Severn Trent Water
Fatbergs recently received some news coverage in the UK, with a giant fatberg - 80 metres in length - being found in a west London sewer by Thames Water. So, to put that in perspective, 80 metres is the length of a commercial plane.

For those of you who don’t know exactly what a fatberg is, it is the term given to the solidified lump of fat that can cause blockages in sewer systems.

The problem stems from people pouring hot cooking oil down the sink, and when the oil hits the cold temperature of the sewers, it solidifies to fat. Wet wipes, food, cotton buds and litter can easily cling to this fat and form congealed masses or fatbergs.

Another phrase used in the water industry, for example at Severn Trent Water, to describe these unpleasant wastewater blockers are 'FOGs' – fats, oil and grease.

These fatbergs or FOGs cause major headaches for water companies by blocking the sewers, which can often lead to flooding. It’s definitely not a pretty thought - imagining sewage being flooded back up into our roads, gardens and even our homes.

And this means that to tackle the problem, it costs the water companies around £79 million per year.

To help break-up the fatbergs, workers have to use high-powered jets so that wastewater can pass through the sewers again, but by this point they are already a serious problem.

A manhole cover full of fat - Image courtesy of Severn Trent Water.

Prevention is always the best cure for fatbergs and chemical engineers, as well as fixing the problems in the sewers, are working towards this aim.

Instead of pouring fats and oils down the drain, the idea is to use this waste to generate renewable energy by feeding it into a specialist power plant, usually Combined Heat and Power (CHP).

Thames Water will feed the fatbergs, collected from restaurants around London, into a Combined Heat and intelligent Power plant to generate energy for their Beckton sewage works .

Another such example is at the Davyhulme Wastewater Treatment Works in Manchester, UK, run by United Utilities, and their sludge recycling centre. Designed by process engineers at Black & Veatch, and awarded IChemE's Energy Award last year, this project uses thermal hydrolysis technology to generate energy from sewage.

Sewage, containing human waste and fatbergs is heated to a high temperature, which causes the harmful bacteria to be destroyed and biogas to be produced. The biogas then gets fed into CHP units to generate electricity.

And the sludge that is left over can then be used as a fertiliser for farmers, which will inevitably make the cows happier.

It's a win-win situation. And it's even more of a win that chemical engineers have been at the helm of a this 'titanic' task of tackling 'fatbergs'.