Neco 2021 Chemistry Question 50

A lake with a volume of \(5.0\times10^{6}\) L receives runoff containing nitrate at 2 mg/L (as N) and ammonium at 1 mg/L (as N). A biological treatment first nitrifies 80 % of the ammonium to nitrate, then denitrifies 60 % of the total nitrate present. Additionally, a constructed wetland containing 5000 kg of substrate adsorbs phosphate (\( \mathrm{PO_4^{3-}} \)) according to the Langmuir isotherm \( q = \frac{Q_{\text{max}} K C}{1 + K C} \) with \( Q_{\text{max}} = 10\) mg kg⁻¹ and \( K = 0.5\) L mg⁻¹. The initial phosphate concentration in the lake is 0.5 mg/L. Assuming the lake water passes through the wetland once and becomes fully mixed, calculate (a) the final total nitrogen concentration (mg/L) and (b) the final phosphate concentration (mg/L) after equilibrium adsorption. Give answers to two decimal places.