Question

what is sludge? where it is used?

Answer 1

a sluge is a thick and soft substance which is used for made pots

Answer 2

Sludge is a semi-solid slurry that can be produced from a range of industrial processes, from water treatment, wastewater treatment or on-site sanitation systems. ... In the activated sludge process for wastewater treatment, the terms "waste activated sludge" and "return activated sludge" are used.