Question

An industry discharges 2 million liters per day (MLD) of wastewater with a temperature of 45°C and a pH of 2, whereas the neighboring industry produces 3 MLD of wastewater with a temperature of 30°C and pH of 8. If both the wastewaters are mixed and carried through a pipeline, then the resultant pH of mixed wastewater is ___________ (rounded off to 2 decimal places).
Neglect buffering capacity of the system and the temperature effect on pH.

Answer 1

Correct Answer: 2.38

Step 1: Convert pH values to hydrogen ion concentrations. \[ [H^+]_{\text{pH 2}} = 10^{-2} \, \text{mol/L}, \quad [H^+]_{\text{pH 8}} = 10^{-8} \, \text{mol/L} \] Step 2: Calculate the volume-weighted average of the hydrogen ion concentration. \[ [H^+]_{\text{avg}} = \frac{(2 \times 10^{-2}) + (3 \times 10^{-8})}{5} \approx 4 \times 10^{-3} \, \text{mol/L} \] Step 3: Convert the average hydrogen ion concentration back to pH. \[ \text{pH} = -\log(4 \times 10^{-3}) \approx 2.40 \]