Question 15 1AE01 - First Assistant Engineer

The Correct Answer is A. **Explanation of why option A ("Entering harbors.") is correct:** The pre-treatment section of a reverse osmosis (RO) freshwater generator is designed to remove suspended solids, colloids, and biological matter to protect the delicate RO membranes. Harbors are high-risk environments for water intake due to significantly increased levels of contaminants compared to open seas. These contaminants include: 1. **High Turbidity/Suspended Solids:** Propeller wash, dredging, and general port activities stir up sediment. 2. **Biological Fouling:** Increased concentrations of algae, bacteria, and plankton due to nutrient runoff and warmer, shallower water. 3. **Chemical Pollutants:** Oil spills, sewage discharge, and industrial waste are common in harbors. When the intake water has a very high load of these contaminants, the filters (e.g., cartridge filters, media filters) and chemical dosing systems in the pre-treatment stage become saturated or exhausted rapidly. This overloads the system, leading to frequent backwashing, filter replacement, decreased performance, and ultimately, accelerated fouling and damage to the expensive RO membranes. Therefore, taking in water in harbors should generally be avoided. **Explanation of why the other options are incorrect:** * **B) Entering open seas:** This condition offers the cleanest and most stable water quality. Suspended solids and biological load are minimal compared to coastal areas. This is the optimal condition for RO intake, not a scenario leading to pre-treatment overload. * **C) Entering low temperature seas:** Low water temperature generally improves RO performance efficiency (though it requires slightly higher pressure) and significantly reduces biological activity and fouling potential. Low temperature does not typically overload the filtration section; in fact, it often reduces the load. * **D) Entering high temperature seas:** While high temperatures increase the risk of biological growth and require careful biocide management, the primary issue is focused on the post-treatment biological control and the RO membrane flux rate, not necessarily a catastrophic overload of the *pre-treatment* mechanical filtration systems (solids/turbidity) in the same way that entering a harbor does. The contaminant load in terms of solids is typically much lower than in a confined port area.