# Analysis of the Landfill Leachate Treatment System Using Arima Models: A Case Study in a Megacity
## 3 Results and Discussion
### Untreated Leachate
However, an analysis of principal components showed the following four groups in order of importance (determinant \(<\) 0.001): component 1 = Zn, Pb, Ni, and Fe (variance = 27.9%); component 2 = Cu and Cr (variance = 16.0%); component 3 = Cd and As (variance = 12.4%); and component 4 = Co and Hg (variance = 9.82%). Thus, Zn was also selected as a possible indicator of HMs in untreated leachate. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{8}{c}{Untreated Leachate} \\ \hline  & MSW & Flow & BOD\({}_{5}\) & COD & NH\({}_{4}\) & Cd & Zn & Hg \\ \hline \(\mu\) & 179,765 & 15.3 & 8034 & 14,657 & 2707 & 0.014 & 0.790 & 0.015 \\ \(\hat{\rm u}\) & 182,157 & 14.9 & 7688 & 14,003 & 2733 & 0.010 & 0.530 & 0.008 \\ Mi & 139,798 & 6.91 & 32.8 & 2198 & 1959 & 0.003 & 0.120 & 0.001 \\ Ma & 217,386 & 26.0 & 19,402 & 32,358 & 3967 & 0.200 & 4.830 & 0.500 \\ SD & 16168 & 4.33 & 5403 & 8445 & 287 & 0.021 & 0.662 & 0.043 \\  & As & Cu & Fe & Pb & Co & Cr & Ni & pH \\ \(\mu\) & 0.029 & 0.303 & 97.2 & 0.236 & 0.096 & 0.717 & 0.488 & 8.29 \\ \(\hat{\rm u}\) & 0.020 & 0.090 & 20.3 & 0.190 & 0.080 & 0.700 & 0.450 & 8.34 \\ Mi & 0.001 & 0.010 & 0.260 & 0.010 & 0.030 & 0.020 & 0.058 & 7.49 \\ Ma & 0.110 & 30.0 & 10,900 & 8.280 & 0.680 & 3.075 & 1.510 & 9.38 \\ SD & 0.031 & 2.413 & 888 & 0.658 & 0.063 & 0.358 & 0.194 & 0.31 \\ \hline \multicolumn{8}{c}{Treated Leachate} \\ \hline  & MSW & Flow & BOD\({}_{5}\) & COD & NH\({}_{4}\) & Cd & Zn & Hg \\ \hline \(\mu\) & 179,765 & 15.1 & 503 & 2521 & 465 & 0.011 & 0.404 & 0.005 \\ \(\hat{\rm u}\) & 182,157 & 14.9 & 99.0 & 2281 & 250 & 0.010 & 0.370 & 0.004 \\ Mi & 139,798 & 5.71 & 14.0 & 25.0 & 31.0 & 0.005 & 0.100 & 0.001 \\ Ma & 217,386 & 25.5 & 5750 & 11,074 & 2152 & 0.041 & 1.360 & 0.029 \\ SD & 16,168 & 4.36 & 868 & 1601 & 565 & 0.008 & 0.207 & 0.004 \\  & As & Cu & Fe & Pb & Co & Cr & Ni & pH \\ \(\mu\) & 0.014 & 0.080 & 7.78 & 0.121 & 0.060 & 0.455 & 0.390 & 8.19 \\ \(\hat{\rm u}\) & 0.010 & 0.050 & 4.78 & 0.100 & 0.050 & 0.400 & 0.384 & 8.35 \\ Mi & 0.000 & 0.010 & 1.60 & 0.005 & 0.020 & 0.030 & 0.020 & 7.00 \\ Ma & 0.065 & 0.200 & 38.4 & 0.417 & 0.188 & 1.500 & 0.700 & 9.00 \\ SD & 0.014 & 0.068 & 6.63 & 0.066 & 0.029 & 0.237 & 0.119 & 0.46 \\ \hline \multicolumn{8}{c}{ Removal (\%)} \\ \hline  & MSW & Flow & BOD\({}_{5}\) & COD & NH\({}_{4}\) & Cd & Zn & Hg \\ \hline \(\mu\) & - & - & 86.3 & 63.8 & 88.7 & 17.0 & 26.8 & 19.3 \\ \(\hat{\rm u}\) & - & - & 87.0 & 67.5 & 89.0 & 17.0 & 27.5 & 18.0 \\ Mi & - & - & 78.0 & 34.0 & 85.0 & 15.0 & 4.00 & 0.00 \\ Ma & - & - & 89.0 & 76.0 & 94.0 & 19.0 & 41.0 & 52.0 \\ SD & - & - & 3.17 & 11.4 & 2.74 & 2.83 & 11.1 & 14.8 \\  & As & Cu & Fe & Pb & Co & Cr & Ni & pH \\ \(\mu\) & 27.4 & 26.0 & 52.4 & 23.5 & 22.5 & 33.5 & 12.8 & - \\ \(\hat{\rm u}\) & 27.5 & 29.5 & 53.0 & 22.5 & 26.5 & 35.0 & 12.0 & - \\ Mi & 20.0 & 2.00 & 42.0 & 12.0 & 8.00 & 18.0 & 9.0 & - \\ Ma & 39.0 & 33.0 & 59.0 & 37.0 & 31.0 & 43.0 & 18.0 & - \\ SD & 5.21 & 8.54 & 5.22 & 10.3 & 8.57 & 8.67 & 3.31 & - \\ \hline \end{tabular} Note: \(\mu\) = Mean, \(\hat{\rm u}\) = Median, Mi = Minimum, Ma = Maximum, and SD = Standard deviation. MSW in Ton/month, Flow in L/s, HM concentration in mg/L, and BOD\({}_{5}\) and COD concentration in mg/L.  
\end{table} 
Table 1: Quantity of MSWs disposed, chemical characteristics of leachate, and removal efficiency from the treatment plant during the study period. Additionally, BOD\({}_{5}\) and COD concentrations had no significant correlations with the Cu and Pb concentrations (Figure 2). However, an analysis of principal components between the BOD\({}_{5}\) and COD concentrations, and the concentrations of all HMs allowed visualizing a first component of four consisting of the following parameters and metallic elements (determinant < 0.001): COD, BOD\({}_{5}\), Zn, Ni, Fe, Pb, and Cu (variance = 33.9%). Thus, it was observed that Zn was the metallic element of best correlation with the DBO\({}_{5}\) and DQO concentrations in untreated leachate (BOD\({}_{5}\)-r = 0.516, \(p\)-value < 0.001; COD-r = 0.519, \(p\)-value < 0.001).