65. To enhance biodegradation process efficiently it is required to vary the design and operation of
activated sludge system. Which of the following variations in design and operation of this system is
NOT correct?
1. Step aeration
2. Contact stabilization
3. Anaerobic fermentation
4. Tapered aeration

 

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Correct Answer: 3. Anaerobic fermentation

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Explanation:

The activated sludge system is a widely used process in wastewater treatment that relies on aerobic microorganisms to degrade organic matter. To enhance its efficiency, several modifications in design and operation have been developed. Let’s break down each option:

1. Step Aeration

   • Correct Design Variation

   • Oxygen is added at multiple stages rather than at a single point. This improves oxygen transfer and distribution, enhancing microbial activity and degradation efficiency.

2. Contact Stabilization

   • Correct Design Variation

   • Involves separating the contact (where the biomass contacts incoming wastewater) and stabilization (where the biomass is aerated separately), helping to handle shock loads and variable wastewater quality.

3. Anaerobic Fermentation

   • Not Applicable to Activated Sludge Systems

   • This process occurs in the absence of oxygen, which is the opposite of the aerobic conditions required for activated sludge systems. While anaerobic processes are used in sludge digestion, they are not part of the activated sludge process used for initial wastewater treatment.

4. Tapered Aeration

   • Correct Design Variation

   • In this approach, more aeration is applied at the beginning of the tank where oxygen demand is highest, and less is applied further downstream. This optimizes oxygen use and improves treatment efficiency.

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Conclusion:

The design variation not suitable for enhancing the biodegradation process in an activated sludge system is Option 3: Anaerobic fermentation, because it contradicts the core aerobic nature of the process.