Biosolids are a natural by-product of wastewater treatment. Finding a beneficial and sustainable option for re-using these biosolids has been a challenge for the water industry for many years.
Melbourne Water has undertaken a number of staged studies into hydrothermal liquefaction (HTL) technology and is now supporting a trial with Southern Oil Refining which has received a grant of $4 million from the Australian Renewable Energy Agency (ARENA) to take HTL technology to a commercial scale.
So, what is hydrothermal liquefaction?
HTL utilises elevated temperature and pressure to break the carbon bonds in the biosolids and reform them into long chain molecules that take the form of a bio-crude oil. This can be refined into transport fuels such as diesel. If successful, this technology has the potential to remove the need for sludge drying pans, reducing future capital costs. It can also use existing stockpiles of biosolids which have not had an appropriate beneficial use option to date.