THE wind rips across the saltplains, tearing at the words on Donna Rawlinson’s lips and whistling them out into the North Sea, where the container ships, vivid red against the blustery blue sky, wait for the tide to turn.

From atop a gantry in Bran Sands, Dr Rawlinson is explaining the extraordinary digestive process that will soon be going on below in the shiny new chemical plant.

She points across to a trio of 20-metre high silos that dominate the works and block out the mouth of the Tees behind.

“In those digesters,” shouts Dr Rawlinson above the wind, "the natural bacteria feed on the sewage. This process produces biogas which rises up through the sludge to the top of the tanks for collection.”

Not only do the bugs reduce the amount of sludge by about half, but their gassy by-product – a methane belch – is converted into electricity which powers the whole process.

Treating human sewage has improved markedly since 1995 when a European directive banned dumping at sea. Since then, Northumbrian Water has been cleaning it up, drying it off and converting it into pellets, which are used as fuel in the cement industry and fertiliser on the farm.

“Our existing sludgedrying process relies upon putting energy in to allow energy to be taken out further down the line,” says David Charlton, the Bran Sands manager. “Moving to this new process is a completely different way of looking at sewage sludge treatment.”

To take the green aspect of cleaning up our natural waste to the next level, Northumbrian Water has spent £33m creating the largest thermal hydrolysis advanced anaerobic digestion plant in the country. It has been built by Aker Solutions, of Stockton, and will start work in July. It puts energy into the cleaning-up process, but it is the energy that the bugs, in the style of Blue Peter, have made earlier.

Let’s start at the beginning.

Flush… The sewage produced by the humans who live between the Tees and the Wear comes in the form of a liquid sludge at the Bran Sands treatment works on the windswept flats near Redcar. From July, this sludge will be pumped into eight reactors where it will be heated to 165C and held under six bars of steam pressure for 45 minutes. This destroys the dangerous bacteria, such as e-coli and salmonella, and begins to break down the biological cell structure within the sludge.

It is then cooled and fed into the three large digesters, each with a capacity of 7,000 cubic metres, where it is kept at 37 degrees for 18 days.

Now the good bacteria get to work, chomping away at the sludge.

“They are naturally occurring organisms which are in the sludge already," says Mr Charlton.

Humans use bacteria in their digestive process. The bugs in the sludge have come along for the ride from your bowels to Bran Sands and now get their reward.

“We are accelerating the natural process by keeping them in these ideal conditions,” says Mr Charlton. “We are just encouraging them to grow and multiply.”

The more bacteria, the more they eat through the sludge.

And the more they eat through the sludge, the more they burp. They also emit from the other end, but we shan’t go into that – there is something so inherently comic about the digestive process that even the cleverest of chemists is reduced to sniggering at bottom gags.

Whichever end it comes out of, the bugs produce methane which rises to the top of the digester. It is collected and then fed into gas engines which produce electricity which heats water to create steam which treats the sludge when it first arrives and so begins the process of breaking down the cell structure and releasing the energy.

“It is a complex biological system that needs to be maintained and nurtured,” says Mr Charlton.

Meanwhile, any solids remaining in the sludge are removed from the digester and “de-watered”.

“It ends up as a cake,” says Dr Rawlinson. “Because everything has been biologically broken down, there’s negligible odour and it has a very earthy texture.

It’s an excellent product that’s been welcomed by agriculture.”

It has also been welcomed by accountants, as the gas engines will create 4.7 megawatts of electricity and the Bran Sands site uses eight megawatts – so this process will meet more than half of the demands of the whole site.

Those sewage-munching methane-belching bugs will not only be kinder to the environment, but will also cut Northumbrian Water’s annual energy bill by about ten per cent, proving that where there’s muck there really may well be brass.