Biodiesel production from wastewater sludge using exchange resins as heterogeneous acid catalyst: Catalyst selection and sludge pre-treatments

Abstract

Three different ion-exchange resins (Amberlyst 15, 36 and IR120) were used as heterogeneous catalysts for the transesterification of the secondary sludge lipids. Catalyst performance was evaluated based on the biodiesel yield and quality; the best biodiesel yield, with the best properties was obtained with Amberlyst IR120. Microwaves (MW) and ultrasounds (US) were studied as a pre-treatment step to increase lipid extraction. US treatment shows the highest biodiesel yield, providing a biodiesel that fulfils the current regulations. The sludge particle size effect was also studied obtaining the best results using the smallest one. However, in these conditions, ultrasound damage the lipids, decreasing the biodiesel yield. Temperature and catalyst/sludge ratio have been optimized. The maximum biodiesel yield (32.9% FAMEs/lipids) was obtained with Amberlyst IR120, catalyst/sludge ratio 1:2, MeOH/sludge ratio 33:1, 120 °C, 21 h reaction time and US as pre-treatment. The catalyst was also reused for six times under the optimal reaction conditions with negligible catalytic activity loss.