# Quantifying Total Phosphorus and Heavy Metals in Residential Septage
## 3 Results and Discussion
### Total Phosphorus and Metal in Septage
#### 3.2.2 Metal Concentrations and Masses  
Zinc, copper, and lead were the most prominent metals observed across all septage layers (Table 2). The median concentration of zinc was greatest in the liquid layer, which was approximately 2.5 and 3 times greater than the scum and sludge layers, respectively. This difference was not statistically significant (\(p\) = 0.13). The scum layer contained the greatest median value of copper and lead relative to the other septage layers (Table 2). Copper concentrations between the scum and liquid layers were statistically different (\(p\) = 0.05). There were no significant differences found in copper concentrations when comparing the sludge to the scum (\(p\) = 0.13) or liquid (\(p\) = 0.27) layers. While slight differences in the median concentrations of lead between septage layers were observed, there was no statistically significant difference (\(p\) = 0.56). Median concentrations of nickel were similar across all septage layers (Table 2). Cadmium concentrations were routinely below the detection limit in all septage layers, thus the median concentrations were \(<\)0.01 mg L\({}^{-1}\) (Table 2). The concentrations of these metals were not statistically significant between the septage layers for both nickel (\(p\) = 0.79) and cadmium (\(p\) = 0.99). Liquid and sludge layers exhibited similar trends in metal masses as those observed in the concentration data (Table 2). Similar to the TP data, scum layers exhibited a decline in median masses of metals, and since there were 12 septic tanks without a measurable scum layer, the metal mass was 0 g. Median masses for both zinc and lead were the greatest in the liquid layer (Table 2). The median mass of zinc in the liquid layer was approximately \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Metal**}} & \multicolumn{3}{c}{**Median (Range)**} & \multicolumn{3}{c}{**Mean (SD)**} \\ \cline{2-7}  & **Scum** & **Liquid** & **Sludge** & **Scum** & **Liquid** & **Sludge** \\ \hline Cadmium & & & & & & \\ Conc (mg L\({}^{-1}\)) & \(<\)0.01 & \(<\)0.01 & \(<\)0.01 & \(<\)0.01 & 0.09 (0.27) & 0.03 (0.08) & 0.07 (0.20) \\ Conc (mg L\({}^{-1}\)) & (\(<\)0.01–0.80) & (\(<\)0.01–0.30) & (\(<\)0.01–0.60) & 0.14 (0.66) & 0.11 (0.32) & 0.24 (0.72) \\ Mass (g) & (\(<\)0.01–3.03) & (\(<\)0.01–1.14) & (\(<\)0.01–2.27) & & & \\ \hline Copper & & & & & & \\ Conc (mg L\({}^{-1}\)) & 1.15 & 0.40 & 0.60 & 18.21 (56.53) & 0.85 (1.28) & 11.63 (43.87) \\  & (0.06–206.00) & (0.04–4.80) & (0.05–222.00) & 18.21 (56.53) & 0.85 (1.28) & 11.63 (43.87) \\ Mass (g) & 0.23 & 1.51 & 1.89 & 35.86 (155.43) & 3.24 (4.85) & 41.39 (161.22) \\ Mass (g) & (\(<\)0.01–780.22) & (0.15–18.18) & (\(<\)0.01–840.82) & & & \\ \hline Lead & & & & & \\ Conc (mg L\({}^{-1}\)) & 0.60 & 0.50 & 0.40 & 3.19 (8.00) & 0.79 (1.17) & 1.61 (3.51) \\  & (\(<\)0.01–24.50) & (\(<\)0.01–4.30) & (\(<\)0.01–12.50) & 3.18 (20.11) & 2.99 (4.43) & 5.44 (12.66) \\ Mass (g) & (\(<\)0.01–92.79) & (\(<\)0.01–16.29) & (\(<\)0.01–47.34) & & & \\ \hline Nickel & & & & & \\ Conc (mg L\({}^{-1}\)) & 0.20 & 0.20 & 0.20 & 0.20 & 0.79 (1.27) & 0.31 (0.39) & 0.52 (0.94) \\ Conc (mg L\({}^{-1}\)) & (\(<\)0.01–3.70) & (\(<\)0.01–1.50) & (\(<\)0.01–4.00) & & & \\ Mass (g) & (\(<\)0.01–13.01) & 0.76 & 0.76 & 1.28 (3.40) & 1.16 (1.46) & 1.77 (3.43) \\ Mass (g) & (\(<\)0.01–14.01) & (\(<\)0.01–5.68) & (\(<\)0.01–15.15) & & & \\ \hline Zinc & & & & & \\ Conc (mg L\({}^{-1}\)) & 3.00 & 7.92 & 2.14 & 33.90 (97.65) & 13.50 (16.86) & 18.62 (55.88) \\  & (0.60–358.00) & (\(<\)0.01–76.80) & (0.30–256.00) & & & \\ Mass (g) & 2.27 & 30.00 & 7.76 & 66.76 (269.60) & 51.15 (63.87) & 66.25 (205.64) \\ Mass (g) & (\(<\)0.01–1355.92) & (\(<\)0.01–290.88) & (\(<\)0.01–969.60) & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Median (range) and mean (standard deviation (SD)) of trace metal concentration (Conc) and mass in each septage layer.