Question

The two stage anaerobic process of dairy effluent treatment allows _________

• A. higher retention times and shorter loading rates
• B. shorter loading rates and nil retention
• C. higher loading rates and shorter retention times
• D. nil loading and shorter retention times

Hint:

To remember the benefits of two-stage anaerobic systems:
Separating acid-formers from methane-formers allows each to work at peak efficiency.
This maximizes throughput (higher loading rates) and minimizes processing time (shorter retention times).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Dairy effluents contain high organic loads (high BOD and COD) due to milk solids and cleaning chemical residues.
Anaerobic digestion is widely used to treat these effluents, breaking down organic pollutants to produce biogas.
In a two-stage anaerobic system, the digestion process is split into two distinct reactors to optimize processing efficiency.

Step 2: Detailed Explanation:
Let us analyze how splitting anaerobic digestion into two stages improves treatment efficiency:
- Anaerobic digestion consists of two primary biochemical phases:
1. Acidogenesis (acid-forming phase): Fast-growing acidogenic bacteria convert complex organics into volatile fatty acids (VFAs). They thrive at a lower optimal pH (5.5 to 6.5).
2. Methanogenesis (methane-forming phase): Slow-growing methanogenic archaea convert VFAs into methane and carbon dioxide. They are highly sensitive and require a neutral pH (7.0 to 7.5).
- In a single-stage reactor, these two groups must coexist in a single vessel, which compromises their growth rates and overall efficiency.
- By separating these phases into a two-stage system:
- Each stage can operate under its optimal pH, temperature, and loading conditions.
- This optimization allows the system to process a much higher organic loading rate (OLR) without risk of overloading or souring the reactor.
- Additionally, it significantly accelerates the digestion process, reducing the required hydraulic retention time (HRT).
- This allows for smaller reactor sizes and a footprint compared to single-stage systems.
Therefore, the two-stage process allows for higher loading rates and shorter retention times.

Step 3: Final Answer:
The two-stage anaerobic process of dairy effluent treatment allows for higher organic loading rates and shorter hydraulic retention times.