Abstract
Advanced oxidation processes (AOPs) such as H2O2/UV, O3/H2O2, modified Fenton, and modified photo-Fenton processes have been investigated in terms of the treatment of landfill leachate with ratio of BOD5/COD in the range of 0.22 to 0.24. The modification of Fenton and photo-Fenton processes consisted in the inclusion of precipitation and separation of humic substances at pH 3. Due to the precipitation, the value of COD decreased by 39% and BOD5by 7.1%. The modification of the processes allowed us to improve the efficiency and to decrease the doses of reagents necessary to continue the process. Modified photo-Fenton process proved to be the most effective (92.7% COD removal) of all processes investigated. Additionally, modified-Fenton process was much more effective than the other two processes when compared up to 120 min, while after longer times it gave the least satisfactory results. After 30 min of modified-Fenton process BOD5/COD ratio increased to 0.43. The parameter referred to as “efficiency of oxidants” was used to estimate the efficiency of all the processes—its value varied from 178 to 239%. Various substances including phthalates, hydrocarbons, silanes, and siloxanes were identified in raw and treated leachate.
Highlights
In advanced oxidation processes (AOPs) the hydroxyl radical HO characterized by high redox potential (2,8 V) is produced
Due to the fact that the leachates come from an old, medium-stabilized landfill site, they have BOD5/COD values of 0.22–0.24
For the above-mentioned optimal doses and after Fenton reaction period of 15 min the ratio increased to 0.42–0.45
Summary
In advanced oxidation processes (AOPs) the hydroxyl radical HO characterized by high redox potential (2,8 V) is produced. The number of studies referring to more than two methods is limited. Another reason is a wide range of concentrations of organics in leachate varying from a few hundreds to more than ten thousand mg/L COD [1]. According to the review published by Kurniawan et al [1] photo-Fenton and H2O2/O3/UV processes are the most effective. The efficiency of O3/H2O2 and H2O2/UV processes is comparable, while Fenton and O3/OH− processes are less effective. In one of the recently published papers [4] O3/OH−, O3/H2O2, and Fenton processes have been compared. It has been shown that Fenton process yielding 46% COD removal is far less effective than the two remaining processes, in which efficiency is approximately 72%. They classified the methods according to their efficiency in the following order: photo-Fenton, Fenton-like > Fenton > H2O2/UV > UV
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