The accumulation, in the environment and in human food supply chain, of organic micropollutants, highly toxic substances such as drugs, hormones or endocrine disruptors found at very low concentrations in water, represents today one of the biggest challenges to public health and the environment in the UK and other developed countries. As a large number of compounds, including common anti-inflammatories, antibiotics, hormones, pesticides and and herbicides, is added to the priority substances watch list for future regulation, there is an urgent need for novel technologies capable of degrading micropollutants safely and without generating significant increases in carbon emissions of the water industry, already accounting for about 5% of UK emissions.
Legacy technology comprising the majority of water treatment plants in the UK and other developed countries cannot remove micropollutants, requiring an additional treatment step to be added to the water treatment train. Alternative technologies currently being tested in the UK and abroad all have limitations, in terms of high energy costs or high capital costs or production of toxic by-products, which require further removal. The urgency of addressing this issue is witnessed by estimates of multi-billion pound capital investments and £B/year operating costs faced by the UK water industry, to address impending legislation mandating the removal of micropollutants. In fact, the European Water Industry Platform has concluded that the chance of removing micropollutants without significant increases in energy consumption with current technology is 'very low', and that this can be achieved only by 'leapfrogging traditional, polluting and resource-intensive technologies', a view shared by the UK government.
Photocatalysis, considered the leading technology to treat micropollutants, suffers from a twin-set of limitations that have hindered more widespread adoption so far. Slurry reactors, where wastewater is mixed with a slurr of photocatalytic nanoparticles under UV illumination, can effectively degrade micropollutants but require costly downstream retention of the particles to avoid their leaching into the environment. Reactors with immobilised catalysts, on the other hand, have significantly lower activity due to lower contact area and higher light scattering. Furthermore, preliminary evidence of potential adverse health effects arising from the accumulation of nanoparticles in the environment, has convinced UK's Environment Agency, DEFRA and health authorities to block their use in water treatment.
My vision as an EPSRC Established Career Fellow in Water Engineering is to safely degrade micropollutants without significantly increasing carbon emissions or producing toxic by-products. I will achieve this by creating novel photocatalytic nanoporous anodic metal foams, combining the high surface area of slurries and the stability of immobilised systems requiring no downstream removal. The combination of a metallic core and a metal oxide coating will enable boosting photocatalytic activity by using a small electrical potential, decreasing the need for low-efficiency electricity-to-light conversion.
My ambition is to address the twin challenges that have so-far hindered the use of photocatalysis in water treatment: the potential leaching of photocatalytic slurries in the environment and the low efficiency of UV light illumination, which translates in low activity, for immobilised photocatalysts.