If you have ever eaten at the National Exhibition Centre (NEC) in Birmingham, there is every chance your leftovers – potato peelings and more – could be powering Severn Trent’s sewage treatment works (STW) nearby at Coleshill, claims Chris Jellett in the Water & Sewerage Journal.

The NEC has become one of the first local businesses to send its food waste to Severn Trent Green Power’s £13m food waste anaerobic digestion (AD) plant on the Coleshill site.

Whether it’s a fine dining experience or a fast food outlet, food waste from the NEC site, which includes both the NEC and Genting Arena, will be powering sewage treatment at Coleshill.

Severn Trent started constructing the plant in 2014. Rather than food waste going to landfill, which is costing businesses more and more, we will be stopping around 8,000 tonnes of CO₂ from being released into the local environment – that's equivalent to taking 3,300 cars off UK roads. To add to that, every year we expect to generate around 17,000 megawatt hours (MWh) of electricity from the food waste AD plant, which is enough to power around 4,000 homes, or the whole of Coleshill STW and more.

This means that the site will be totally self-sufficient for its electricity needs. Brian Pell, the NEC’s director of operations, explained: “We are continually looking for new ways to make our venue more environmentally friendly. Thanks to our on-site waste pre-treatment centre, we send zero waste to landfill and are committed to ensuring that any waste that travels off site for further processing never travels more than 30 miles – this helps to save CO₂ emissions during travel and keeps our costs down too.

“Severn Trent’s site is right on our doorstep, so it provides us with the perfect location to send our food waste. This year, we expect to send around 120 tonnes of food waste to Coleshill to help generate power for the site.”

Severn Trent expects to generate around 17GWe per year from its new food waste AD plant at Coleshill sewage treatment works.

Giant stomach

Food waste is packed with energy, which – with a bit of ingenuity – can be unlocked and turned into power. The process works in a similar way to us eating food. Trucks full of food waste deliver food into the ‘mouth’ of the plant, which is contained in a sealed building – acting like ‘lips’.Within the ‘mouth’, food is unwrapped by a machine. This removes the plastic, which goes for recycling. The waste food is then ‘chewed up’ by another machine and sent straight into the anaerobic digestion tanks, the ‘stomachs’, for digestion.

As that happens, methane gas is produced in two Jenbacher 4 Series engines, supplied by Clarke Energy with a capacity of 1.2MWe each, and collected on the top of the tank without being released into the air. It is then sent over to a combined heat and power (CHP) unit, which turns it into green energy to power the works. Heat from the facility is used in the digesters to maintain them at a temperature of around 40ºC, as well as pasteurising the digested food waste, which is used as an agricultural fertiliser.

The whole digestion process takes around 90 days from the plant ‘mouth’ to field. The AD plant has the capacity to process 48,500 tonnes of food waste per year and the site is totally self-sufficient for its electricity and heat needs.