🔍 Key Concepts

• Reverse osmosis (RO) flow path: sea water inlet → pre‑treatment → RO membranes → product (fresh) water → possible post‑treatment • Difference between mechanical filtration (screens, cartridge filters) and chemical treatment (chlorine/biocides, antiscalants, etc.) • Difference between pre‑treatment (before the RO membranes) and post‑treatment (after the fresh water is produced)

💭 Think About

• Ask yourself: At what point in the system does pre‑treatment act – on the incoming seawater or on the outgoing fresh water? • Which option is describing something that would more likely be done by filters/strainers rather than by chemicals? • Which options clearly refer to sterilizing (killing microorganisms) and which to removing solids – and where in the flow path would each of those make the most sense as a chemical step before the RO membranes?

✅ Before You Answer

• Identify whether pre‑treatment should be applied to the feed seawater or the product freshwater. • Decide which process (removing particles vs. sterilizing) is more realistically achieved chemically rather than just by physical filters. • Eliminate any choice that clearly describes a step that would logically be called post‑treatment, i.e., something done after the RO unit, just before storage or distribution.