# Quantifying Total Phosphorus and Heavy Metals in Residential Septage
## 3 Results and Discussion
### Mass and Watershed Mass of Pollutants from Domestic Septage  
The total masses for TP, zinc, and copper were elevated relative to the other measured pollutants (Figure 4). The median septic tank contained masses of TP, cadmium, copper, lead, nickel, and zinc of 20 g, <0.01 g, 2 g, 2 g, 2 g, and 14 g, respectively (Table 4). Total masses for all pollutants (except cadmium) contained a range that spanned several orders of magnitude. The estimates of the total pollutant mass in the studied sub-watershed are summarized in Table 5. The pollutant mass estimates based on median concentrations show that TP and zinc could have an excess of 1 kg in septic tanks throughout the watershed. The estimates of the sub-watershed masses based on the mean values suggest that there was 5.8 kg, 4.8 kg, and 1.7 kg of TP, zinc, and copper, respectively, in all septic tanks throughout the studied sub-watershed, which discharges to the Lick Creek Watershed. The difference between the median and mean values and the variability of the pollutant masses were likely due to individual differences across septic systems. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Total Phosphorus**} & \multicolumn{2}{c}{**Cadmium**} & \multicolumn{2}{c}{**Copper**} \\ \cline{2-7}
**Source** & **Conc (mg L\({}^{-1}\))** & **Mass (g)** & **Conc (mg L\({}^{-1}\))** & **Mass (g)** & **Conc (mg L\({}^{-1}\))** & **Mass (g)** \\ \hline Septic, liquid \({}^{1}\) & 1.20–39.5 & 4.54–149.61 \({}^{\rm a}\) & \(<\)0.01–0.04 & \(<\)0.03–0.15 \({}^{\rm b}\) & 0.01–0.12 & 0.03–0.45 \({}^{\rm b}\) \\ Septic, sludge \({}^{2}\) & 18–610 & 61.36–2079.33 \({}^{\rm a}\) & 0.06–0.35 & 0.23–1.33 \({}^{\rm a}\) & - & - \\ Sewer, liquid \({}^{3}\) & 4–180 & - & 0.56–11 & - & 52.2–102 & - \\ Sewer, sludge \({}^{4}\) & 8000–59,500 & - & 0.49–30 & - & 0.66–1160 & - \\ Septage, composite \({}^{5}\) & 5–760 & 75.75–2879 \({}^{\rm a}\) & 0.005–11 & 0.07–42 \({}^{\rm a}\) & 0.01–640 & 2.18–2424 \({}^{\rm a}\) \\ Ceiling cone \({}^{6}\) & & & 85 & 39 & 4300 & 1500 \\ \hline  & \multicolumn{2}{c}{**Lead**} & \multicolumn{2}{c}{**Nickel**} & \multicolumn{2}{c}{**Zinc**} \\ \cline{2-7}
**Source** & **Conc (mg L\({}^{-1}\))** & **Mass (g)** & **Conc (mg L\({}^{-1}\))** & **Mass (g)** & **Conc (mg L\({}^{-1}\))** & **Mass (g)** \\ \hline Septic, liquid \({}^{1}\) & 0.01–0.19 & 0.04–0.72 \({}^{\rm a}\) & \(<\)0.02 & \(<\)0.06 & 0.04–0.18 & 0.12–0.68 \({}^{\rm b}\) \\ Septic, sludge \({}^{2}\) & 1.01–7.70 & 3.83–29.16 \({}^{\rm a}\) & - & - & - & - \\ Sewer, liquid \({}^{3}\) & 28.6–98 & - & 32.2–191 & - & 0.46–182 & - \\ Sewer, sludge \({}^{4}\) & 2.72–1600 & - & 3.37–177 & - & 79–1980 & - \\ Septage, composite \({}^{5}\) & \(<\)0.025–791 & \(<\)0.09–2996 \({}^{\rm a}\) & 0.01–37 & 0.04–140.14 \({}^{\rm a}\) & \(<\)0.01–1273 & \(<\)0.01–4821 \({}^{\rm a}\) \\ Ceiling cone \({}^{6}\) & 840 & 300 & 420 & 420 & 7500 & 2800 \\ \hline  & \multicolumn{2}{c}{\({}^{\rm a}\) Entire range estimated assuming a 3785-L tank. \({}^{\rm b}\) Upper endmember estimated assuming a 3785-L tank. \({}^{\rm a}\) Values of phosphorus [3, 24, 25, 26, 31, 35, 49, 50, 51, 52] and trace metals [34, 50, 61, 62] in liquid layer of septic tank. \({}^{\rm 2}\) Values of phosphorus [35] and trace metals [34] and trace metals [34, 63] in primary effluent. \({}^{\rm a}\) Values of phosphorus [53, 54] and trace metals [53, 54, 60, 66, 67] in sludge or biosolids. \({}^{\rm 5}\) Values of phosphorus [55, 56] and trace metals [55, 56, 68] in composited septage samples from Sewer. \({}^{\rm 6}\) Trace metals [69], with masses reported as cumulative mass (kg ha\({}^{-1}\)).} \\ \hline \end{tabular}
\end{table} 
Table 3: Ranges of concentrations (mg L\({}^{-1}\)) and masses (g) of phosphorus and trace metals from past studies. The ceiling concentration refers to the maximum concentration of a trace metal at the biosolids application site. Figure 4: Boxplot of total masses for total phosphorus, cadmium, copper, lead, nickel, and zinc in the studied septic tanks (\(n=37\)). Asterisks (*) represent outliers.