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Treatment of stabilised anaerobic landfill leachate by ozonation process with zirconium and tin tetrachlorides

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Date
2020-04-01
Authors
Zakaria, Siti Nor Farhana
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Leachate is a crucial problem in sanitary landfills which threatens the environment due to hazardous pollutants. However, most of the current results are unable to comply with the discharge limit of effluent. Therefore, an advanced oxidation process (AOP) using ozone and coagulation was applied during stabilised anaerobic landfill leachate (SAL) treatment in this study since this method promises high degradation of pollutants. Stabilised anaerobic leachate containing high concentrations of colour (14,984 PtCo), COD (3852 mg/L), and NH3-N (1241 mg/L). The sample was taken from Alor Pongsu Landfill Site (APLS), Kerian Perak for a duration of 1 year. Colour, COD and NH3-N were investigated as a target parameter to see the performance of each method in removing pollutant. Whilst, 3 critical factors such as dosage, pH and reaction time were studied their influences on performance of all batch studies and RSM tests. The experiment started with a batch study of zirconium tetrachloride (ZrCl4) and tin tetrachloride (SnCl4) as coagulants in the coagulation-flocculation process. Results for both coagulants were recorded and compared. Next, the performance of ozonation (O3) in a semi-batch ozone reactor was also examined. Based on the results, O3 alone could only remove 85.4%, 50% and 15% of colour, COD and NH3-N, respectively. However, these concentrations still exceeded the standard discharge limits. To improve the results, O3 was combined with two chemicals which are ZrCl4 and SnCl4. An optimisation process was designed for both (O3/ZrCl4 and O3/SnCl4) using the response surface methodology software (RSM). O3/ZrCl4 improved reduction in colour, COD and NH3-N by 99.8%, 93.5% and 46%, respectively. Meanwhile, O3/SnCl4 removed 98.8%, 85.5% and 26% of colour, COD and NH3-N accordingly. An integrated treatment method consisting of ozonation and a jar test (as ZrCl4 and SnCl4 function as coagulants) was studied. Treatment using ozonation followed a jar test yielded good results compared to the treatment which started with a jar test and ended with ozonation. However, there was only a small improvement in the biodegradability (BOD5/COD) of the sample compared to other methods. On the other hand, the improvement of BOD5/COD ratio by O3/ZrCl4 from 0.02 (raw) up to 0.43 was significant. The kinetic constant reaction rate (k’) of O3/ZrCl4 was calculated and this resulted in a value of 0.1173 min-1 based on the pseudo first-order kinetic model. Another oxidation method involving O3 and O3/SnCl4 also fit the pseudo first-order kinetic model. It can be concluded from the research that, the combination of O3 and ZrCl4 presents an effective treatment method for remediating high concentrations of containing high concentrations of colour, COD, and NH3-N in SAL.
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