Manufacturing of algal biochar for combined water treatment and CO2 sequestration

Climate change and the need to minimise/reverse CO2 emissions represent a serious global problem requiring urgent solutions. Global warming also impacts on the quality of water resources and water contamination with algae is known to be a significant problem in the UK as well as in Brazil and in particular in the state of Ceara, especially in the summer months when algae blooms occur. Cyanobacteria, associated with algae, is known to produce toxic and/or noxious secondary metabolites, which could render large quantities of water unsuitable for drinking.
Biochar (a charcoal material) provides an effective and innovative solution for long-term CO2 capture while reducing soil/water contamination. Biochar adjusts soil structure and improves its physicochemical properties to boost the uptake of soil nutrients for plant growth. Biochar is a high-value product with low remediation costs. Biochar’s projected annual growth rate is 14.5% (global biochar market size was $1.48billion in 2018 and is expected to reach $3.82billion by 2025). While efforts in manufacturing biochar have increased in the last decade there is still need for advancing the manufacturing processes (pyrolysis) to improve biochar quality and product quantity based on locally available feedstock.

Here we propose a novel technique based on the use of algae as feedstock for biochar manufacturing with the aim of applying the produced biochar in treatment of contaminated water. Essentially, the produced biochar will replace the activated carbon material which is currently used. Activated carbon is produced by burning available organic waste, but in this process significant CO2 is released. Use of algal biochar instead of activated carbon not only reduces carbon emissions but also allows creating a circular economy where the unwanted algae will be regarded as a feedstock for production of biochar which is a high value product. The produced biochar will partly be used in the water treatment process and the excess will be used for soil regeneration and enrichment by carbon.