Question 14 1AE01 - First Assistant Engineer

The Correct Answer is A **Why Option A is Correct:** A high salinity alarm at the freshwater (permeate) outlet of a Reverse Osmosis (RO) unit indicates that the RO membranes are failing to adequately reject salts, allowing too many dissolved solids to pass into the treated water. This is usually caused by one of two primary issues related to the membranes: 1. **Membrane Scaling/Fouling:** The accumulation of salts, organic matter, or particulates on the membrane surface significantly reduces the efficiency and effective surface area of the membrane, leading to increased salt passage. 2. **Membrane Degradation/Damage:** While outright damage requires replacement, initial high salinity due to fouling requires intervention. Cleaning and flushing the membrane modules (A) is the standard and immediate corrective action taken when performance drops due to fouling, aiming to restore the membrane's rejection capabilities and reduce the permeate salinity. **Why the Other Options are Incorrect:** * **B) The post-treatment sterilizer should be serviced:** The sterilizer (such as UV or chlorination) is responsible for killing microorganisms *after* the RO process. It has no impact whatsoever on the removal of dissolved salts (salinity). Therefore, servicing it will not address the high salinity alarm. * **C) The pre-treatment chemical doser should be serviced:** Pre-treatment chemicals (like antiscalants or coagulants) are used to protect the membranes from fouling and scaling. While a malfunctioning doser might *cause* future fouling, the high salinity alarm indicates that the fouling or performance drop has *already occurred*. Servicing the doser addresses the preventive maintenance, not the immediate corrective action needed to fix the current high salinity resulting from the fouled membranes. * **D) The pre-filters should be serviced by cleaning or replacement:** Pre-filters (like cartridge or multimedia filters) remove large suspended solids and sediment. While clogged pre-filters can affect the flow and pressure into the RO unit, they do not directly regulate the passage of dissolved salts across the RO membrane. High salinity is a membrane performance issue, not a pre-filtration issue.