IAS Fellows' Public Lecture - New Filtration Materials for Passive Water Treatment: dephosphatisation and denitrification (Professor Christian Ruby - Universite de Lorraine, France)
The protection of the water resource is among the major issues of the twenty-first century due to the population growth, the rapid industrialization and the intensification of agriculture. Among the various pollutants that threaten the water quality, phosphate species (PO4) are of upmost importance since the excess of PO4 is mainly responsible of the water eutrophication phenomena. It leads to strong perturbation of the biodiversity and important economic losses, e.g. closing of fisheries and groundwater production wells (an annual cost of 1.75 milliard € was estimated for the freshwater of USA only).
For a better prevention of the excessive release of PO4 in natural environment, it is crucial to be able to perform PO4 water treatments in critical zones such as the outfall pipes of waste water treatment plants (WWTP). It is particularly problematic for small and middle size WWTP situated in ecologically more sensitive rural areas where shortage of permanent human limits the possibility to perform classical chemical treatments, e.g. precipitation of PO4 by coagulants (FeIII or AlIII salts). In rural areas, reed bed filters are often preferred due to their good fit with the landscape and their low maintenance and infrastructure costs. Such filters are very efficient for removing the organic matter from waste water, but the filtration materials generally used do not retain PO4.
In this lecture, the advantages and the drawbacks of various filtration materials used for passive waste water treatments will be presented. Some of them, such as commercially available granules of calcium phosphate, were implemented in several WWTP in France. Wastes of the steel industry, e.g. blast furnace slag, were used at the pilot scale. Finally, more sophisticated materials such as ferrihydrite coated pozzolana, a volcanic rock from Puy de Domes in Auvergne, were recently developed in the laboratory. Important parameters of choice of the filtration materials are obviously their PO4 removal efficiency, but also their alkalinity and their cost of production.
This lecture is free and open to all.
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