107. Which one of the following method can be used to treat crude sewage and nitrify secondary
effluent?
A. Duck weed ponds
B. Reed beds
C. Algal fish ponds
D. Water hyacinth pond

Detailed Explanation:

Among the various ecological methods for wastewater treatment, algal fish ponds stand out as an efficient option for both crude sewage treatment and nitrification of secondary effluent. This method leverages a symbiotic relationship between algae and fish, offering a sustainable, low-cost solution, particularly in rural and peri-urban settings.

How Algal Fish Ponds Work:

1. Algae in the pond use nutrients (like nitrogen and phosphorus) from the sewage to grow, carrying out photosynthesis, which releases oxygen.

2. The oxygen supports aerobic bacteria that break down organic waste.

3. Fish feed on algae and organic matter, helping to reduce biomass and control algal overgrowth.

4. The system promotes nitrification, converting ammonia into nitrates, and can also remove pathogens through natural UV exposure and competition.

Comparison with Other Methods:

• Duckweed ponds are good for nutrient uptake but less effective for complete nitrification.

• Reed beds are used in constructed wetlands, mostly for polishing and solid removal, not crude sewage.

• Water hyacinth ponds help in nutrient uptake but can become invasive and are harder to manage.

Correct Answer:

C. Algal fish ponds

Conclusion:

Algal fish ponds offer an eco-friendly and effective solution for treating wastewater, combining natural biological processes with aquaculture. Their ability to handle both crude sewage and secondary effluent nitrification makes them a valuable component of decentralized wastewater management systems.