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Aarhus burns sewage waste to provide fresh water to its citizens

Fresh drinking water is not usually something that you would want to associate with sewage waste.

But a city in Denmark is bringing the two together, to become the world’s first city to provide fresh water using only the energy from household wastewater.

The water treatment plant in Aarhus, Denmark’s second biggest city, is now generating so much excess electricity, the surplus is being used to pump drinking water around the city.

The water treatment plant in Aarhus, Denmark's second biggest city, is now generating so much excess electricity, the surplus is being used to pump drinking water around the cityThe water treatment plant in Aarhus, Denmark's second biggest city, is now generating so much excess electricity, the surplus is being used to pump drinking water around the city

The water treatment plant in Aarhus, Denmark’s second biggest city, is now generating so much excess electricity, the surplus is being used to pump drinking water around the city

The plant pumps household waste into huge digesters kept at 38°C and filled with bacteria.

These produce biogas – a mixture of different gases produced by the breakdown of organic matter.

The biogas is then burned to make energy in the form of heat and electricity.

In addition to powering the city’s water system, excess electricity could also be sold to the local grid.

The plant pumps household waste into huge digesters kept at 38°C and filled with bacteria.

These produce biogas – a mixture of different gases produced by the breakdown of organic matter – that is then burned to make energy in the form of heat and electricity.

Speaking to New Scientist, Lars Schrøder, general manager of Aarhus Water, said: ‘We don’t add any extra organic material like from restaurants or energy from wind turbines or solar panels.’

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      The technology comes at quite a price, with an upfront investment of nearly €3 million (£2.5 million/$3.2 million).

      But Aarhus Water expects the investment will be made back in five years, from maintenance savings and the sale of excess energy into the grid.

      The plant is the first in the world to produce more than 50 per cent more energy than it consumes, according to Denmark’s Ministry of Environment and Food.

      Environment Minister Eva Kjer Hansen told the Local: ‘Treatment plants must move forward from being energy guzzlers to being energy producers, and we have a really good example of this here.’

      The plant is the first anywhere to produce more than 50 per cent more energy than it consumes, claimed the country's Ministry of Environment and FoodThe plant is the first anywhere to produce more than 50 per cent more energy than it consumes, claimed the country's Ministry of Environment and Food

      The plant is the first anywhere to produce more than 50 per cent more energy than it consumes, claimed the country’s Ministry of Environment and Food

      Other cities around the world, including Chicago and San Francisco, are now showing interest in replicating Aarhus’ water system.

      But Molly Walton, an energy analyst at the International Energy Agency, told New Scientist: ‘Replicating Denmark’s experience and performance will not be easy.

      For the system to be successful, the wastewater plant needs to be big enough to generate enough biogas.

      And if the wastewater becomes diluted, for example by storm or grounwater, it will be even harder to generate energy.

      COCKROACHES COMMUNICATE THROUGH POO

      Researchers found that cockroaches may communicate through their poo.

      Gut bacteria in the poo may hold ‘aggregation pheramones’ that helps the insects band together in large social groups.

      The team sterilised a group of German cockroaches, and raised them in germ-free cages, which then led to germ-free faeces.

      The roaches tended to avoid the faeces when it didn’t have the gut microbes in it.

      Entomologists also tracked the roaches’ reactions when given the option of sterile water, or normal poop.

      They found that 80 to 100 per cent of young roaches preferred the poo.

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