Final answer:
An excessive amount of filamentous bacteria in a wastewater treatment system leads to sludge bulking and poor settling, disrupting the separation of clear effluent and compromising treatment efficiency. The correct option is D.
Step-by-step explanation:
The consequence of having an excessive amount of filamentous bacteria in wastewater treatment, particularly relating to the settling of activated sludge in the secondary clarifier, is sludge bulking and poor settling. Excessive growth of filamentous bacteria causes a phenomenon known as 'sludge bulking.'
This happens during the secondary treatment phase when the activated sludge fails to settle properly, which can lead to operational issues in the clarifier. Instead of forming compact, heavy particles that settle quickly, sludge bulking involves the formation of fluffy and voluminous masses of bacteria that settle slowly, if at all.
This can hinder the separation of clear water from the sludge and result in poor treatment efficiency. As filamentous bacteria overgrow, they trap air and other particles, making the sludge lighter and more resistant to settling. Efficient wastewater treatment relies on the ability of the sludge to settle out of the water, and sludge bulking disrupts this critical process, compromising the quality of the treated effluent.