Valorization of biomass-derived compounds using residual sludge from water treatment as a catalytic support

Residual sludges from both a wastewater treatment plant and a drinking water treatment plant have been used as catalytic supports of ruthenium for reactions of biomass valorization employing very low reaction temperatures. The biomass derived substrates used for the catalytic reactions have been levulinic acid and furfural. Interestingly, Ru catalysts deposited on the sludges are far more efficient for this reactions than analogous Ru catalysts deposited on the pure oxides that constitute the sludges and also than Ru supported on a HY zeolite. The sludge obtained from the drinking water treatment plant proved to be the most effective support, primarily due to its high capacity to disperse ruthenium on its surface while maintaining a high proportion of ruthenium in its metallic state. Notably, a yield of 93 % to furfuryl alcohol from furfural was obtained at 30 °C in just 5 h using the most efficient catalyst. Moreover, the ruthenium is highly anchored on the support resulting in high stability and minimal metal leaching. The slight decline in the catalytic performance observed after several catalytic uses is mainly due to the formation of residual carbon deposits on the catalyst surface. Overall, this work offers a dual environmental interest, as the catalyst material is derived from waste sludge, and the studied catalytic reaction focuses on the valorization of biomass. • Sludges from water drinking treatment plants as supports for ruthenium. • Ru on sludge better than Ru on single metal oxides components of the sludge. • Ru/sludge selectively activates levulinic acid and furfural at low temperature. • Gamma-valerolactone yields of 90% from levulinic acid at room temperature. • Furfuryl alcohol yields of 90% from furfural at almost room temperature.