BOD removal in leachate by free water surface flow constructed wetland with vetiver and colocasia

Abstract

The study was conducted to determine the efficiency of Free Water Surface (FWS) constructed wetlands in removal of Biochemical Oxygen Demand (BOD), Total Kjedahl Nitrogen (TKN), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), and Total Dissolved Solids (TDS) of leachate from a sanitary landfill. Three water levels were 0.2, 0.4, and 0.6 meters, which yielded flow rates of 0.075, 0.150, and 0.225 cubicmeters per day respectively. Also, the efficiency in removal was compared among two plants (Vetiveria zizanioides Nash and Colocasia esculenta) and no plant in the system. The growth of the two plants was studied. The studied period was 100 days with 11 sample collection every 10 days from the beginning to the end of the experiment. The constructed wetland with Vetiveria zizanioides Nash at the 0.2 meter water level was the most efficient model in BOD removal. The average efficiency was 66.04 +- 19.02 percent. This result is true to the SPSS analysis of the efficiency of significant difference statistically. The second most efficient model was the wetland with Vetiveria zizanioides Nash at 0.4 meter water level. The average efficiency was 63.15 +- 14.37 percent. However, the wetlands with Colocasia esculenta do not give the contemptible efficiency in BOD removal. At the water level of 0.2 meter and 0.4 meter, Colocasia esculenta gave the BOD removal for 58.96 +-16.62 percent and 58.42 +-15.45 percent. The shallower depth, the greater removal quality. The constructed wetland with Vetiveria zizanioides Nash at the 0.2 meter water level was the most efficient model in COD removal too. The average efficiency was 53.76 +- 30.07 percent. The second most efficient model was the wetland with Vetiveria zizanioides Nash at 0.4 meter water level. The average efficiency was 53.45 +- 30.28 percent. But by SPSS analysis, the best in COD removal is the constructed wetland with Vetiveria zizanioides Nash at 0.2 and 0.4 meter water level of significant difference statistically. However, the wetlands with Colocasia esculenta do not give the contemptible efficiency in COD removal. At the water level of 0.2 meter and 0.4 meter, Colocasia esculenta give the COD removal for 42.18+-34.02 percent and 39.02+-32.55 percent. The shallower depth, the greater quality of removal again. The constructed wetland with Vetiveria zizanioides Nash at the 0.2 meter water level was the most efficient model in TKN removal. The average efficiency was 79.37+-11.46 percent. By the SPSS analysis of the TKN removal efficiency, the constructed wetland with Vetiveria zizanioides Nash at the 0.2 meter water level was the most efficient model in TKN removal of significant difference statistically. The second most efficient model was the wetland with Vetiveria zizanioides Nash at 0.4 meter water level. The average efficiency was 77.95 ±13.43 percent. However, the wetlands with Colocasia esculenta do not give the contemptible efficiency in TKN removal. At the water level of 0.2 meter and 0.4 meter, Colocasia esculenta gave the TKN removal for 77.85+-15.69 percent and 77.73+-14.34 percent. The most average efficiency of TSS removal is 76.14 +- 28.00 percent at 0.6 m with Vetiveria zizanioides Nash. The second most efficient model was the wetland with Vetiveria zizanioides Nash at 0.2 meter water level. The average efficiency was 64.39 ± 38.86 percent. And by the SPSS analysis by One-way ANOVA, the greatest efficient constructed wetland was Vetiveria zizanioides at 0.6 meter depth in TSS removal with significant difference statistically. However, the wetlands with Colocasia esculenta do not give the contemptible efficiency in TSS removal. At the water level of 0.6 meter and 0.4 meter, Colocasia esculenta give the TSS removal for 56.85 ± 41.53 percent and 38.42 +- 58.27 percent. And the lowest average TSS removal is -70.08 +- 201.52 percent at 0.6 m without plants due to the hydraulic loading rate reason and algae bloom in the pond. Generally, TDS decreases in the same direction as TSS. So the most average efficiency of TDS removal is 55.71 +- 34.33 percent at 0.2 m with Vetiveria zizanioides Nash. The second most efficient model was the wetland with Vetiveria zizanioides Nash at 0.4 meter water level. The average efficiency was 49.76 +- 26.28 percent. But by the SPSS analysis by One-way ANOVA, the most efficient constructed wetland with Vetiveria zizanioides at 0.2 meter depth becomes the best in TDS removal with significant difference statistically. However, the wetlands with Colocasia esculenta do not have the contemptible efficiency in TDS removal. At the water level of 0.2 meter and 0.4 meter, Colocasia esculenta give the TDS removal for 35.88 +- 50.72 percent and 39.17 +- 30.51 percent. And the lowest average TDS removal is 9.83 +- 46.78 percent at 0.6 m without plants. Conclusively, the FWS constructed wetland worked well with both plants in BOD and other factors removal but the limitation is the water level in the units. If it is over 0.4 meter, the plants will decrease the removal efficiency and die more than the shallower ones. And the best between both plants is Vetiveria zizanioides when the results were analyzed by SPSS program. And the uses are up to the specific purposes.