Abstract: Environmental damages and pollution induced by the leachate of landfills are a source of concern for citizens. The present empirical study explored the anaerobic treatment of mature leachate of Saravan-Rasht in Guilan province, Iran and the efficiency of the Fenton process at pH 3-8 under different Fe2+ and H2O2 rates and oxidation retention time of 15-135 minutes using the Bench-scale method in laboratory conditions. In addition, the impact of nanosilica absorbent at the rates of 0.25-6.5 g L−1 was examined at retention times of 15-75 minutes and pH 3-11. BOD, COD and TSS removal efficiency was measured at all stages. It was found that BOD, COD and TSS removal efficiency at leachate anaerobic treatment stage was 63.7, 37.95 and 21% in the sample containing seed. BOD, COD and TSS removal efficiency exhibited an ascending trend in nanosilica absorbent as retention time was increased from 15 to 75 minutes, reaching 73, 70 and 58% at the retention time of 75 minutes, respectively. The results revealed that to treat mature leachate, anaerobic treatment should be first applied to remove biodegradable organic matter, and then the Fenton process and nanosilica absorbent should be used to remove resistant organic matter.
