Sorry, but this doesn't make sense to me. In the first instance, every wastewater treatment plant operator and process designer knows that wastewater temperatures vary throughout the year. In the UK the range is typically 10-22°C and colder in Scotland (not a constant 21°C as reported). Second, if you use wastewater as a source for a heat pump, you cool the wastewater. All biological processes such as nitrification (the oxidation of ammonia) are temperature-sensitive so they won't work as well (if at all) during winter. The result will be polluted rivers or a massive spend to build larger treatment works. Third, a daily flow of 921 million litres per day (that's ALL the wastewater in Scotland), cooled from 10°C to 5°C at 100% efficiency (impossible!) Would yield about 50MW of power. I know the Scots are a hardy bunch but I think even they would want a bit more than 50 MW to heat a city in a Scottish winter.  Energy recovery from wastewater has its place, but let's be realistic about it rather than trying to create fanciful headline-grabbing stories.

Published June 17, 2017 22:20 by Jeremy Biddle, Engineering Director at Bluewater Bio