The final step in wastewater treatment, sometimes called polishing, often uses a process called photocatalysis, which may be about to get cheaper and more environmentally friendlier, thanks to a waste byproduct from the seafood industry.
When treating wastewater, there are typically at least three stages in the process, with the first stage removing solids and oils, the second stage filtering the water, and the third stage improving the quality of the treated water before it gets released from the treatment plant. The third, or tertiary, treatment often uses a process called photocatalysis, which requires titanium dioxide to remove any final contaminants, such as fertilizers or pharmaceuticals, from the water.
But an alternative material could be used instead of titanium dioxide, which is an expensive component of the process, due to the recent work of Dr Darrell Patterson of the University of Bath's Department of Chemical Engineering.
Dr Patterson's process uses waste mussel shells, which are created by the ton by the shellfish industry, and which are just as effective, but much cheaper and more eco-friendly in the long run.
"Shells are a calcium rich resource that can be used to produce calcium oxide (lime). This lime can be used in several different ways in environmental technologies, and our study has shown that the hydroxyapatite formed from them is an effective, green and potentially cost-efficient alternative photocatalyst for waste water treatment." - Dr Patterson
According to Dr Patterson, his research used mussel shells, but other types of seashells could be used to reproduce the process just about anywhere in the world where shells are easy to come by. The next phase of his research is to look at other applications for the process, as well as pursue methods for scaling it up to level that would be necessary if used on a large scale. The results of his research are available here: Greener photocatalysts: Hydroxyapatite derived from waste mussel shells for the photocatalytic degradation of a model azo dye wastewater.