Question

What gases are produced in anaerobic sludge digester?
A. Methane and Carbon dioxide
B. Methane, Hydrogen sulphide and Carbon dioxide
C. Methane, Hydrogen sulphide and oxygen
D. Hydrogen sulphide and carbon dioxide

Answer 1

Hint: Anaerobic sludge digestion is a sequence of processes by which microorganisms breakdown biodegradable material in the absence of oxygen releasing mainly, methane and carbon dioxide along with other contaminant gases.

Complete answer:
Aerobic sludge digestion is the process of reduction of sludge in the absence of oxygen. In this process, organic pollutants are converted to a gaseous product that has a potential use by an anaerobic microorganism. It’s a “two-phase” reaction. It is an integrated part of the waste management system and hence it reduces the emission of landfill gas into the atmosphere. This process is conducted in four steps, namely, hydrolysis, acidogenesis, acetogenesis and methanogenesis.
> Hydrolysis: Insoluble organic polymers like carbohydrates are broken down into smaller soluble derivatives.
> Acidogenesis: It leads to breakdown of the remaining components into simpler elements by fermentative (acidogenic) bacteria. In this step, the sugar is converted and amino acids are converted into carbon dioxide, ammonia, hydrogen and organic acids.
> Acetogenesis: Simpler molecules are produced in this step. Acetogens act on the organic acid and produce acetic acid (largely) along with ammonia, carbon dioxide and hydrogen.
> Methanogenesis: The final step involves release of methane, carbon dioxide and water by digestion with the help of methanogens. The methanogenic archaea-bacteria population plays a major role in this process.

So, the correct answer is option (B) Methane, Hydrogen sulphide and carbon dioxide.

Note:
The major products of anaerobic are methane (50%-75%) and carbon dioxide (25%-50%). However, traces of Hydrogen sulphide (0%-3%) are also produced.