# Quantifying Total Phosphorus and Heavy Metals in Residential Septage
## 3 Results and Discussion
### Total Phosphorus and Metal in Septage
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{2}{c}{pH} & \multicolumn{2}{c}{Temperature (C)} & \multicolumn{2}{c}{**DO (mg L\({}^{-1}\))**} & \multicolumn{2}{c}{**ORF (mV)**} & \multicolumn{2}{c}{**SC (sig cm\({}^{-1}\))**} \\ \cline{2-10}
**Task Layer** & **Median** & **Mean (SD)** & **Median** & **Mean (SD)** & **Median** & **Mean (SD)** & **Median** & **Mean (SD)** & **Median** \\  & **(Range)** & & **(Range)** & & **(Range)** & & **(Range)** & & **(Range)** & **(Range)** \\ \hline \multirow{2}{*}{Scum} & 6.79 & 6.45 & 27.12 & 24.14 & 1.47 & 2.72 & \(-\)174 & \(-\)184 & 1038 & 1193 \\  & (391-74.0) & (1.06) & (12.40-30.20) & _(6.72)_ & (0.45-9.31) & (2.90) & (\(-\)91\(-\)15) & (154) & (226-2426) & (855) \\ \multirow{2}{*}{Liquid} & 6.87 & 6.89 & 26.79 & 25.05 & 0.85 & 1.75 & \(-\)296 & \(-\)278 & 1380 & 1414 \\  & (5.36-80.0) & (0.52) & (11.36-34.90) & (5.83) & (0.17-10.07) & (2.43) & (\(-\)554-14) & (227) & (129-2742) & (718) \\ \multirow{2}{*}{Sludge} & 6.69 & 6.68 & 25.07 & 23.26 & 0.63 & 1.60 & \(-\)275 & \(-\)262 & 1797 & 1810 \\  & (5.66-77.7) & (0.44) & (12.39-32.07) & (5.53) & (0.17-8.8) & (2.37) & (\(-\)508--1) & (121) & (184-3325) & (981) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean \(\pm\) standard deviation of layer thickness and environmental readings for domestic septage. DO = dissolved oxygen; ORF = oxidation-reduction potential; SC = specific conductance. Concentrations of TP in the scum and sludge layers exhibited high variability and tended to have greater TP concentrations relative to the liquid wastewater. Municipal wastewater treatment facilities also contained TP concentrations in sludge that exhibited large variability [53; 54]. Few studies have quantified the concentrations or masses of TP in domestic septage from septic systems [35], but more information is available from septage collected from municipal wastewater treatment facilities [55; 56]. [PERSON] [35] reported mean TP concentrations of 281, 100, and 96 mg L\({}^{-1}\) across 3 sites. Septage from municipal wastewater treatment facilities contained similar TP concentrations. The US EPA [56] reported a mean TP concentration of 210 mg L\({}^{-1}\), and [PERSON] et al. [55] found a mean TP concentration of 77 mg L\({}^{-1}\). The reported range of TP values was 7-760 mg L\({}^{-1}\) across both studies. Assuming the range of TP concentrations was representative of septage from a 3785-L tank, the TP masses ranged from 18.94 to 2878.50 g. [PERSON] [35] reported mean TP masses of 957.86 g, 454.50 g, and 872.64 g across 3 different septic systems, which were  
Figure 3: Boxplots of total phosphorus (TP) concentrations (**A**) and masses (**B**) for scum, liquid, and sludge layers from septic tanks. Mass values of “0 g” were coded as “0.01 g” to represent values that were below detection or layers that were absent at time of sampling. Asterisks (*) represent outliers. similar to the TP masses estimated from septage collected from municipal wastewater facilities. In the current study, the median septic tank contained a TP mass of 46.09 g, which was within the range reported by these studies.