Step 1: Understanding the Concept:
Wastewater treatment plants operate using continuous flow systems.
Specific terminologies are used to define the fluid streams based on their direction of flow relative to a treatment unit or process tank.
Step 2: Detailed Explanation:
- Influent: This refers to raw, untreated water or wastewater that flows into a treatment plant, chamber, or individual process unit (e.g., settling tank, aeration basin).
- Effluent: This refers to the treated or processed wastewater that flows out of a treatment unit or is discharged into the environment.
Step 3: Final Answer:
Therefore, influent means water flowing in, which corresponds to option (A).