Removal of urea from wastewater by heterogeneous catalysis

In order to find an effective method for urea removal from wastewater, a number of experiments were conducted in a batch reactor with α-Al2O3 and η-Al2O3 as catalysts, respectively. The results indicate that η-Al2O3 catalyst shows significantly higher urea removal rate than α-Al2O3 catalyst or the thermal hydrolysis, and the removal rate increases with increasing temperature, catalyst dosage and reaction time. Using η-Al2O3 catalyst, the urea concentration in wastewater is reduced to less than 1 mg/L at 165°C after 150 min. The reaction kinetics study shows that the hydrolysis of urea behaves as a pseudo-first-order reaction. From the calculated rate constants, η-Al2O3 exhibits an excellent catalytic activity for urea hydrolysis, whereas the activity of α-Al2O3 is considerably weak. In addition, the η-Al2O3 catalyst possesses good recycling ability. The slight loss of activity of η-Al2O3 should be attributed to the generation of a small amount of hydrated aluminas, and the activity can be recovered by calcination.