Abstract
Advanced oxidation processes like Fenton and photo-Fenton have been effectively applied to oxidize the persistent organic compounds in solid waste leachate and convert them to unharmful materials and products. However, there are limited data about application of Fenton-like process in leachate treatment. Therefore, this study was designed with the objective of treating municipal landfill leachate by Fenton, Fenton-like and photo–Fenton processes to determine the effect of different variables, by setting up a pilot system. The used leachate was collected from a municipal unsanitary landfill in Qaem-Shahr in the north of Iran. Fenton and Fenton-like processes were conducted by Jar-test method. Photo-Fenton process was performed in a glass photo-reactor. In all processes, H2O2 was used as the oxidant. FeSO4.7H2O and FeCl3.6H2O were used as reagents. All parameters were measured based on standard methods. The results showed that the optimum concentration of H2O2 was equal to 5 g/L for the Fenton-like process and 3 g/L for the Fenton and photo-Fenton processes. The optimum ratio of H2O2: Fe+2/Fe+3 were equal to 8:1 in all processes. At optimum conditions, the amount of COD removal was 69.6%, 65.9% and 83.2% in Fenton, Fenton-like and photo–Fenton processes, respectively. In addition, optimum pH were 3, 5 and 3 and the optimum contact time were 150, 90 and 120 minutes, for Fenton, Fenton-like and photo–Fenton processes, respectively. After all processes, the biodegradability (BOD5/COD ratio) of the treated leachate was increased compared to that of the raw leachate and the highest increase in BOD5/COD ratio was observed in the photo-Fenton process. The efficiency of the Fenton-like process was overally less than Fenton and photo-Fenton processes, meanwhile the Fenton-like process was at higher pH and did not show problems.
Highlights
Deposition of municipal and industrial wastes in landfills is considered as the most widespread and economical method for waste disposal
The results showed that the optimum ratio of H2O2 to Fe2+ in the Fenton and photo-Fenton processes and H2O2 to Fe3+ ratio in Fenton-like process was 8:1(Figure 3)
The low BOD5/COD ratio of the leachate indicated that the biological treatment was difficult; advanced oxidation processes (AOPs) were studied as alternative treatment options
Summary
Deposition of municipal and industrial wastes in landfills is considered as the most widespread and economical method for waste disposal. To remove the readily biodegradable organic pollutants in young leachate, the biological treatments are usually preferred over physico-chemical. In the case of "old" leachates, biological process cannot successfully treat the leachate because it contains a higher proportion of the organic matter and consists of relatively refractory compounds or nonbiodegradable matters and these pollutants inhibit biomass activity and/or are recalcitrant to biological treatments. In such instances, leachate must usually be treated by more expensive physico-chemical treatments such as chemical precipitation, adsorption on activated carbon, chemical oxidation and etc., to obtain satisfactory treatment efficiencies. Among them, growing interest has been focused on advanced oxidation processes (AOPs) [1,7]
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