Waste not want not: Wastewater wattage!

Words by Joe Crutwell, Edited by Nicola Simcock

This month’s SciBar was presented by Dr Elizabeth Heidrich, an environmental engineer from Newcastle University. The subject was something that travels below our feet every day, produced by everyone without a second thought: wastewater.

The crowd in the Old George was notably reserved when asked to name what made up wastewater, perhaps out of politeness. Dr Heidrich quickly convinced us why this flow ─ that many of us think of as merely sewage ─ could be much more than a reason to turn your nose up, and even one of our most neglected resources.

Wastewater does not solely emanate from our bathrooms, it also includes excess rainwater, and the run-off from production facilities such as factories. These components mix together in our sewer systems, with a varying balance of water, oxygen content and microbiology. Sewage often has much higher levels of microbes and lower levels of oxygen that what is in our rivers and seas. To fix this imbalance and avoid causing damage to our waterways, this flow must first go through a water treatment facility.

Water treatment facilities process wastewater so it is safe enough to return to the ocean. They are not, as Dr Heidrich explained, used to produce drinkable water. Wastewater is classed as unsafe if there are too many bacteria or too little oxygen. Such imbalances will damage subsequent ecosystems, creating a toxic environment for the animals and plants that live there, making water treatment a very important process.

Treatment facilities have two main methods to create safe water: trickling filters and activated sludge. Trickling filters work by spraying the wastewater onto gravel. The trickling filter gravel is covered in a film of bacteria, and the bacteria and gravel are carefully maintained to ensure they increase the oxygen level to the correct amount by eating the biological matter found in the wastewater. Alternatively, the activated sludge process works by collecting wastewater in huge tanks, into which oxygen and sewage-digesting bacteria are injected. Once digested, the sludge settles on the bottom of the tank and the resulting treated water is drained from the top. While effective, both processes require a lot of space, and importantly, are very expensive to power.

 

In the UK, this process costs 1-2% of GDP, which could be reduced with increased efficiency. However, for less developed countries these costs are unmanageable, which leads to over 80% of untreated wastewater returning to rivers, severely increasing the risk of disease and contamination.

The big problem is technology. Over the last 80 years we’ve seen phones become supercomputers and wooden planes advance to supersonic machines, but sludge tank technology has not changed.

Dr Heidrich asks, is the science just not sexy enough?

Luckily, she has devised an ingenious solution to this problem, and it relies on one simple fact: the energy to power water treatment is locked within the wastewater itself, over ten times over!  The bacteria and microbes stored in the water could potentially be used to generate power, requiring only a battery to store the harvested energy. It could allow countries like the UK to ‘break even’ on water treatment, and provide solutions to less energy-rich countries by making wastewater an energy source, rather than an energy sink.

In a world first, Dr Heidrich and her lab managed to create a battery that harnessed the energy locked in the wastewater, the same way chemical energy is locked in coal or oil. But instead of combustion, this energy is obtained through using specific bacteria. These bacteria digest wastewater, using it as fuel. These bacteria then act like ‘wires’ within the battery, producing an electric current. Whilst still in the prototype stage, the potential of this technology ─ if the battery can be scaled up from lab-use to commercial range ─ is monumental.

Issues still remain however, such as the need to keep the various battery parts clean, whilst maintaining functionality in the many different water treatment centres and types of water around the world. For instance, the fat content of water is an issue known to affect the efficiency of this process.

After fielding many questions, the Old George agreed that far from being a waste, Dr Heidrich has treated us to an enlightening talk on a very important topic for our future.

If you want to attend the next SciBar, please keep an eye on the upcoming events page.

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