PROCESSING HEAVY METALS

Heavy metals exist naturally in our oceans, but what happens when we process them?

Sargassum -Mexico (Photo: Becky Dowell)

We are using Hydrothermal processes to convert problematic seaweed, Sargassum, into useful fertilisers, biofuels and stock chemicals. Although the resulting products are useful to different industries, there are also added benefits to the environment. Hydrothermal liquefaction (HTL) and hydrothermal carbonisation (HTC) have the ability to deal with wet biomass, salt and even plastic pollution, incorporating them into the eventual outputs.

Recent studies have also demonstrated the ability of HTL and HTC to remediate heavy metals which are absorbed by seaweed and stored in their tissues.

Overview of heavy metals (@amy_pilsbury)

Heavy metals are naturally occurring in the earth's crust and enter the oceans through river run-off and atmospheric deposition. Human impact is increasing the amount heavy metals in the oceans with wastewater run-off, factories and transportation. Heavy metals are stable and cannot be broken down meaning they accumulate in the environment and can become toxic causing growth inhibition and damage to DNA. Current methods of dealing with contaminated biomass include composting and mulching which lead to accumulation of heavy metals in soils.

There are a few heavy metals which are of concern here including; cadmium, mercury, lead and arsenic. HTL/HTC can process these metals in the Sargassum tissue and partition them into the solid char phase output. As an example, this means that 1 tonne of metal contaminated Sargassum can be processed and produce around 100kg of metal contaminated solids, condensing the problem into more manageable volumes. Hydrothermal processes are proving promising as a method of remediating metals from the environment. Stay tuned as we find out more!

Follow our work @PhycoMExUK and visit our website www.phycomex.uk to keep up to date with the latest developments.

Find links to relevant papers from our partners below:

'A synergistic use of microalgae and macroalgae for heavy metal bioremediation and bioenergy production through hydrothermal liquefaction'

'Assessing hydrothermal liquefaction for the production of bio-oil and enhanced metal recovery from microalgae cultivated on acid mine drainage'

'Making light work of heavy metal contamination: the potential for coupling bioremediation with bioenergy production'