Wastewater Treatment Plant Wwtp

Step 1: Understanding the Concept:
Slow sand filtration is a type of centralized water purification system. The question asks for its primary role in the water treatment process.
Step 2: Detailed Explanation:


A slow sand filter works by passing water slowly through a bed of fine sand.

The primary mechanism of purification is not just physical straining. A complex biological layer, called the schmutzdecke, forms on the surface of the sand.

This schmutzdecke is a gelatinous matrix of bacteria, fungi, protozoa, rotifera, and algae. It is this biological layer that is responsible for most of the purification.

The microorganisms in the schmutzdecke trap, prey upon, and outcompete pathogenic microbes (bacteria, viruses, and protozoan cysts) in the water.

As a result, slow sand filters are extremely effective at removing waterborne microbes, often reducing turbidity and microbial counts by over 99\%. This brings the water quality up to a safe, potable standard.

While some ammonia removal can occur through nitrification, it is not the primary role (B). Filters are a treatment step, not an evaluation method (C). They do not significantly neutralize pH (D).

Step 3: Final Answer:
The main role of slow sand filters is to remove waterborne microbes to a standard safe for consumption.

Step 1: Understanding the Concept:
This question asks for the correct hydrogeological term for a rock formation that can store and transmit a significant quantity of groundwater.
Step 2: Detailed Explanation:
Let's define the given terms:


Lake: A large body of fresh water on the Earth's surface. It is surface water, not groundwater within a rock body.

Artesian well: A well in which water flows upward under its own pressure. It is a structure used to access water from an aquifer, not the rock body itself.

Springs: A location where groundwater naturally emerges from the Earth's surface. It is a feature resulting from an aquifer, not the aquifer itself.

Aquifer: A body of porous and permeable rock, sand, or gravel that can store and transmit groundwater. This definition directly matches the description in the question. Aquifers are the sources for wells and springs.

Step 3: Final Answer:
A rock body through which groundwater flows is called an aquifer.