Question

The primary effluent in the treatment of sewage is sent to tanks for secondary treatment in the presence of aerobic bacteria. 

(a) How would the BOD of the effluent be affected if anaerobic bacteria are used for secondary treatment? 

(b) Name one condition that should be maintained in a sludge digester where biogas is produced. 

(c) The slurry formed after biogas production is recommended as manure for plants. Which nutrients will the slurry be rich in and why?

Answer 1

(a) Anaerobic bacteria would not use the oxygen in the wastewater, thus the BOD would not reduce.

(b) Anaerobic conditions need to be maintained as biogas-producing bacteria are strict anaerobes.

(c) The slurry will mainly be rich in nitrogen and phosphorus as the carbon in the sludge would be used in the formation of methane and carbon dioxide.