Question

The grown algae are useful in the operation of

• A. oxidation pond.
• B. slow sand filter.
• C. cyclone separator.
• D. septic tank.

Hint:

Think about which treatment unit is shallow, sunlit, and depends on a natural relationship between algae and bacteria to stay aerobic.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks which treatment unit relies on algae growing in the water to do useful work, rather than treating algae as a nuisance or contaminant.

Step 2: Key Formula or Approach:
An oxidation pond (also called a waste stabilization pond) is a shallow basin that treats sewage using natural sunlight, algae, and bacteria acting together. Algae growing near the surface use sunlight to carry out photosynthesis, releasing oxygen into the water.

Step 3: Detailed Explanation:
Bacteria in the pond use this oxygen to break down the organic matter present in the sewage. As the bacteria break down the organic matter, they release carbon dioxide and nutrients, which the algae then use to grow further. This algae-bacteria relationship keeps the pond aerobic without any mechanical aerators, which is what makes an oxidation pond a low cost, low energy treatment method.
Now check the other options. A slow sand filter treats water by passing it through a fine sand bed where a biological layer called the schmutzdecke, formed mostly of bacteria and other microorganisms on top of the sand, removes impurities. Algae growth on a slow sand filter is not wanted since it can clog the filter and shorten the filter run. A cyclone separator is a mechanical device that removes grit or coarse particles from air or water using centrifugal force, it has nothing to do with algae growth. A septic tank is an anaerobic underground unit used for onsite sewage treatment in small setups, algae cannot grow in it since no sunlight reaches the tank.

Step 4: Final Answer:
Algae growing in sunlight and providing oxygen to bacteria is the working principle of an oxidation pond, so the grown algae are useful in the operation of an oxidation pond. This corresponds to option (A).