Daily sludge production of a wastewater treatment plant is measured as 12.000kg dry solid/day. This mixed sludge (raw primary and waste activated sludge) will be thickened in a gravity thickener. Solid flux chosen for the design is 50kg/m2, day. It is known that sludge mixture has a solid content of 2% and retention time in the thickener is 32 hours. If the volume of thickener is 667,2cm2; a) What is the solid content of sludge removed from thickener (underflow)? (16 Points) b) Calculate the volume of supernatant returned to the treatment process. (8 Points)