Question 57 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is C ### Explanation of Why Option C is Correct Option C states: "The freshwater production rate would be lower than normal, and the feed pressure would be higher than normal." This accurately describes the effects of membrane fouling in a reverse-osmosis (RO) system. 1. **Lower Freshwater Production Rate (Permeate Flow):** Fouling refers to the accumulation of scale, organic material, or particulates on the surface of the RO membrane. This accumulation creates a physical barrier, increasing the resistance to water flow across the membrane. Since the system must overcome this increased resistance, the amount of pure water (permeate) that can pass through the membrane per unit of time decreases, leading to a **lower freshwater production rate**. 2. **Higher Feed Pressure:** As the membrane fouls, the flow channels between the membrane sheets narrow, and the flow resistance on the feedwater side increases (often measured as an increase in the pressure drop across the entire module). To maintain a minimum standard permeate flow (or simply to push the required volume of feed water through the constricted system), the high-pressure pump must work harder, requiring a **higher feed pressure** delivered to the membrane modules compared to a clean system. ### Explanation of Why Other Options are Incorrect **A) The freshwater production rate would be higher than normal, and the feed pressure would be higher than normal.** * **Incorrect:** While the pressure (or differential pressure) is higher, the entire point of fouling is to restrict flow, which makes the production rate **lower**, not higher. A higher production rate would only occur if the membrane degraded severely (allowing salt through) or the pressure was increased drastically beyond normal operating limits on a clean membrane. **B) The freshwater production rate would be lower than normal, and the feed pressure would be lower than normal.** * **Incorrect:** While the production rate is indeed lower (correct), the feed pressure is generally **higher** because the system must overcome the resistance caused by the fouling layer. Lower feed pressure would indicate pump failure or a clean, highly efficient system operating under reduced load. **D) The freshwater production rate would be higher than normal, and the feed pressure would be lower than normal.** * **Incorrect:** Both parts are incorrect. Fouling restricts flow, leading to **lower** production. Fouling increases resistance, requiring **higher** feed pressure.