Conversion of waste-activated sludge from wastewater treatment plants to 5-hydroxymethylfurfural by microwave hydrothermal treatment

Waste-activated sludge (WAS) is a common renewable biomass resource rich in organics. In this study, microwave hydrothermal treatment (MHT) was used to produce 5-hydroxymethylfurfural (HMF) from WAS. The key MHT process parameters of holding temperature, holding time, and pH value were optimized by a Box–Behnken design and response surface methodology. The highest HMF yield (1.58%) was obtained with a holding temperature of 225 °C, holding time of 5 min, and pH value of 1.7. Economic evaluation showed that a profit of $4640 can be made from one ton of WAS by HMF production. This economical and feasible waste recycling method can produce HMF from WAS with considerable output under suitable MHT conditions and provides a new concept for WAS valorization. Graphical abstract