#### A reverse osmosis plant is designed to produce $100 \ \text{L/h}$ of drinking water from seawatercontaining 35,000 ppm of dissolved salts. The applied pressure is 35 atm and the membranehas a rejection coefficient of 0.95 for salt. What is the flow rate of the feedwater required for this plant?Option: 1 $128.9 \ \text{L/h}$Option: 2 $109.5 \ \text{L/h}$Option: 3 $92.3 \ \text{L/h}$Option: 4 $74.7 \ \text{L/h}$

The flow rate of the feedwater required can be calculated using the equation:

$\frac{\text{permeate flow rate}}{\text{rejection coefficient}}=\text{feed flow rate}$

Given, $\text{permeate flow rate } = 100 \ \text{L/h}, \text{ rejection coefficient }= 0.95,\text{ and applied\ pressure }= 35\ \text{atm}.$

The osmotic pressure of seawater at 35,000 ppm  is approximately 27.5 atm. The effective pressure applied for reverse osmosis can be calculated as:$P_\text{eff} = P_\text{applied} - \pi$

where $\pi$ is the osmotic pressure.

$P_\text{eff} = 35 \ \text{atm} - 27.5 \ \text{atm} = 7.5 \ \text{atm}$

The flow rate of the feedwater required is:

$\text{feed flow rate} = \frac{\text{permeate flow rate}}{\text{rejection coefficient}} = \frac{100 \ \text{L/h}}{0.95} = 105.26 \ \text{L/h} \approx 109.5 \ \text{L/h}$

Therefore, the correct answer is option (b).