The use of Pd catalysts for treating compounds susceptible to reduction in natural water and wastewater effluent matrices is being explored. A factor currently limiting the adoption of these catalysts for water treatment is poor understanding of catalyst interactions with non-target water constituents, including dissolved organic matter that potentially inhibit and deactivate catalyst materials. In this study, we evaluated the hydro(dehalo)genation activity of alumina-supported Pd catalysts during the reduction of two different compounds, diclofenac (negatively charged, faster reacting) and N-nitrosodimethylamine (NDMA, neutral compound, slower reacting) in the absence and presence of natural organic matter. We utilized organic fractions of natural waters (Suwannee River NOM, humic acid, fulvic acid) and wastewater effluent (EfOM, isolated from a treatment plant in Jeddah, Saudi Arabia), as well as model surrogates for proteinaceous and polysaccharides. Some catalyst inhibition was observed in the presence of all organic foulants tested. The inhibition observed was reversible as catalyst activity was restored on promoting desorption of organic matter at higher pH conditions. Effluent organic matter showed the strongest inhibition of the Pd catalyst activity for the same carbon loading (mg C/L) in comparison to all other organic mixtures/compounds tested. The observed inhibition does not appear to be caused by catalyst poisoning by sulfur containing organic fractions, since pre-treatment of EfOM with strong oxidants (free chlorine, permanganate) did not produce any gains in catalyst activity. The strong EfOM inhibition trend is consistent between diclofenac and NDMA degradation. These results suggest a strong interaction of effluent organic matter constituents with Pd domains on the catalysts rather than pore blocking to slow mass transfer of the target contaminants to reactive sites.

Inhibition of alumina-supported Pd hydro(dehalo)genation catalysts by dissolved organic matter and hydrophobic fractions of effluent organic matter

246th National Meeting (2013)

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