The Application of Ozonation Process for the Treatment of Landfill Leachate

In the past decade, the municipal and industrial solid waste production has become one of the main environmental challenges. Municipal Solid Waste (MSW) generation continues to grow both in per capita and overall terms [1]. Overall, the liquid generated due to the agglomeration, pressured and chemically interacted intosolid waste is called leachate [2]. The characteristics of landfill leachates depend on a number of complex factors, including the nature of the deposited wastes, soil characteristics, the “age” of the landfill, weather conditions such as rainfall patterns, the design and the means of operation of the landfill [3-5]. By considering the leachate characteristics, operation and capital costs as well as regulations, various site-specific treatment techniques can be used to treat these hazardous wastewaters (e.g. coagulation/ flocculation, biological, oxidation, membrane, leachate recirculation through the landfill, grassland spray irrigation, etc.) [6]. Therefore, treatment of hazardous liquidwastes by oxidation processes such as ozonation (due to high oxidative power of the ozone) has gained popularity. It has been shown that ozone is capable of destroying recalcitrant compounds in effluents and bringing about alterations to biodegradability. Mainly, Biodegradability of high molecular weight of organic compound is low, so that they cannot be removed simply through biological treatment [7]. In this study, the leachate was sampled from landfill in Anakhatoon region situated in Tabriz city. This landfill mainly is used for the disposal of municipal solid wastes. Samples were transported to the laboratory for Analyzing. Before any processing, samples were exposed to ambient temperature for 3 to 5 days to settle mud and coarse particles. The COD and BOD5 analyses were performed according to the standard methodology [8]. Absorbance of samples at wavelength of 254 nm was determined by means of UV–visible spectrophotometry (Spectroquant Pharo 300 (Merck, Germany)). Also, the absorbance value at 455 nm was measured by Spectroquant Pharo 300 using visible spectrophotometry. Some of the characteristics of the two samples of landfill leachate used in this work are presented in Table 1. 3.1. COD removal, color removal and aromatic compounds removal The reduction of COD content, the percentage of color removal and the percentage of aromatic compounds removal is shown as a function of reaction time in Fig. 2. It is clear that the maximum removal for leachates with COD0 =22000 mg/L and COD0 =1900 mg/L obtained 57.99% and 59.27%, respectively. On the other hand, in this work, ozonation effect on color change was determined by measuring absorption of samples at wavelength of 455 nm as an index. It is clear that a major part of decolonization occurred during ozonation [9]. During the current study, the initial dark brown color of the leachate sample, which can be attributed to the presence of humicsubstances, became light yellow as the oxidation reaction by ozone was preceded. Discoloration of landfill leachates is evidence of the transformation of recalcitrant organic matter by ozone [10]. Also, the absorbance of samples at wavelength of 254 nm can be directly related to the presence of aromatic and unsaturated structures of organicsubstances and it is considered as an additional quality parameter of most wastewaters. Similarly to the decolorization reactions, the reduction of UV absorbance took place by a high rate during the initial stages of ozone treatment. In this paper, by using a new reactor system contained a centrifuge pump and a venture tube, the capability of ozonation in treatment of the leachate generated in the landfill was indicated. The influences of initial COD value was studied on the COD, color and aromatic compounds removal. For leachates with COD0 =22000 mg/L and COD0 =1900 mg/L, 57.99% and 59.27% percent of COD removal, 85.15% and 94.94% percent of color removal and 39.65% and 82.71% percent of aromatic compounds removal was obtained, respectively. The changes of pH during the ozonation process were minimal because of buffering effect of bicarbonates present in the system.