Background andpurpose:Currently, leachate production and its management are major environmental problems associated with the operation of solid waste landfill. The aim of this study was to evaluate the efficiency of combined processes of coagulation, ozonation, and advanced oxidation using UV-activated oxone in treatment of landfill leachate of Zahedan, Iran.

Materials andmethods: This experimental-laboratory study included chemical coagulation using poly aluminum chloride (PAC), ozonation, and chemical oxidation using potassium peroxymonosulfate (oxone). For the purpose of this study, the effect of critical operating parameters on treatment of landfill leachate was investigated. These operating parameteres included: pH (3-8) and concentration of PAC (50-250 mg/l) in chemical coagulation process,time of ozonation (5-20 min), pH of solution (2-10), concentration of oxone reactant (150-750 mg/l), contact time with oxone (60-360 min), temperature (20-45ºC), and intensity of UV lamp in oxidation process using oxone (8, 15, 30 W).

Results: According to the results, the overall efficiency rates of this process in removal of total coliform, fecal coliform, total phosphorus, total nitrogen, biochemical oxygen demand (BOD), and chemical oxygen demand (COD)were 99%, 99%, 97%, 100%, 91.1%, and 85.62%, respectively, with optimum
PAC concentration= 250 mg/L, pH= 6 at the chemical coagulation phase, ozonation duration= 20 min,
reactiontime= 180 min during oxone-based oxidation process, oxone concentration= 750 mg/L, pH= 5, temperature= 25ºC, and UV lamp intensity= 8 W. Furthermore, the BOD₅/COD ratio increased from 0.42 to 0.72 after completion of the treatment process.

Conclusion:Current study showed that application of combined processes of chemical coagulation, ozonation, and advanced oxidation using UV-activated oxone are highlyefficient in removing major pollutants from waste landfill leachate.