Which one of the following method can be used to treat crude sewage and nitrify secondary effluent?
Which one of the following method can be used to treat crude sewage and nitrify secondary effluent?
Select an option to attempt
Correct Answer: Option B
Explanation
Reed beds for sewage treatment and nitrification:Constructed wetlands using macrophytes (especially Phragmites australis, common reed) treat wastewater through:• Physical: sedimentation, filtration through root/gravel matrix.• Chemical: adsorption, photodegradation.• Biological: complex microbial communities exploiting oxygen gradients.Zone structure around reed roots:• Aerobic rhizosphere: O₂ released by roots → nitrification () by Nitrosomonas and Nitrobacter.• Anaerobic zones: denitrification (), anaerobic degradation.Capabilities:• Can treat CRUDE SEWAGE (primary effluent) — handles high BOD loads.• Can NITRIFY secondary effluent — converting residual ammonium to nitrate.• Remove BOD, suspended solids, pathogens, some heavy metals.Other options:• Duckweed/algal/water hyacinth ponds: used for secondary treatment but primarily as stabilisation ponds; less effective for crude sewage.Answer: Reed beds (Phragmites-based constructed wetlands) can treat crude sewage AND nitrify secondary effluent through their diverse aerobic/anaerobic microbial zones.