In trickling filters used for secondary wastewater treatment, the filtering medium becomes coated with a microbial community known as the ________. (Identify the correct technical term for this biofilm layer.)

Introduction:
Trickling filters rely on a microbial biofilm growing on a medium (rocks or plastic media) to oxidize organic matter. This question focuses on the proper term for that slime layer and its role in treatment performance.

Given Data / Assumptions:

• Media are wetted by wastewater as it trickles over the surface.
• Biofilm includes bacteria, protozoa, fungi, and extracellular polymeric substances (EPS).
• As biofilm grows and sloughs, it is separated downstream for clarification.

Concept / Approach:
The correct term “zoogloeal film” describes the EPS-rich biofilm matrix that supports heterotrophs and nitrifiers. Oxygen is supplied by natural draft or forced aeration, enabling biological oxidation of biochemical oxygen demand (BOD) and partial nitrification depending on loading and temperature.

Step-by-Step Solution:
Recall that trickling filters are attached-growth systems. Identify the biofilm layer critical to carbon removal. Match the technical name: zoogloeal film (biofilm/EPS matrix). Choose the option that uses the correct terminology.

Verification / Alternative check:
Process descriptions and microscopy of filter media consistently show EPS-bound microbial aggregates—zoogloeae—responsible for treatment.

Why Other Options Are Wrong:

• Zoological film: Not a technical process term.
• Geological film: Refers to minerals/rocks; not microbiology.
• None of these: Incorrect because “zoogloeal film” is correct.

Common Pitfalls:
Misspelling or misreading “zoogloeal” as “zooglocal” or “zoogleal.” Correct spelling matters in technical contexts.

Final Answer:
zoogloeal film is the proper term for the biofilm on trickling filter media.