Inverted Phase Fermentation

An ambitious two-year programme linked to United Utilities' award-winning Enzymic Hydrolysis technology.

How does it work?

Inverted Phase Fermentation (IPF) substantially cuts the amount of chemicals used in conventional sludge-thickening, and as a result could be a significant cost-saver.
Most companies use a chemical called poly as a coagulant to thicken sludge, combined with Gravity Belt Thickener (GBT) machines - but it's an expensive and relatively inefficient solution.

With our IPF project we're looking at a different way of doing things.The process heats sludge to body temperature, before being allowed to settle for a couple of days. The sludge in the IPF tank separates into layers using the natural carbon dioxide produced from the fermentation process. These bubbles of gas rise to the surface and the organic material in the sludge sticks to those gas bubbles.

What is left is a thick layer of sludge on top, and a watery layer of liquor underneath. This simple process produces thicker sludge - 10 per cent dry solids, as opposed to the six or seven you get with a GBT. When the volumes involved are hundreds of tonnes of sludge every day, those are significant numbers.
Our IPF process also creates more gas. More gas means that we can create more of our own electricity using our combined heat and power engines.

There's another great spin-off: the watery layer mentioned above is much thinner and rich in volatile fatty acids. These acids are ideal for the biological nutrient removal that could become a key part of wastewater treatment in the future, and reduce our dependence on chemicals. With increasing pressure on companies like us to reduce phosphates, we can use these volatile fatty acids as a carbon source to aid the process of nutrient removal from the sewage. Currently the only way to get rid of these phosphates is by using large amounts of ferric chloride. Like poly, ferric chloride is an expensive chemical. So with IPF, we're reducing our reliance on chemicals, while cutting our power consumption - a sustainable solution that's good for the environment and our customers' bills.

Who's behind it?

Ruyi Hu is working for us through a Knowledge Transfer Partnership (KTP) with Cranfield University that allows him to get industry experience and enables us to make the most of his skills and expertise. After obtaining his Bachelors degree in pharmaceutical engineering in his native China, Ruyi completed a Masters in the same subject at Loughborough University before joining us.