Consider an activated sludge treatment plant with an average daily flow rate of 20,000 m3/day. The untreated
Question:
Consider an activated sludge treatment plant with an average daily flow rate of 20,000 m3/day. The untreated wastewater contains 200 mg/L suspended solids and 250 mg/L COD. The plant provides 60% removal of suspended solids and 30% removal of BOD5 in the primary clarifier. The primary sludge contains 5% solids and is 65% volatile. The activated sludge process achieves 90% BOD5 removal and is operated at a C of 5 days. The values of kd and Y are known to be 0.05 day-1 and 0.4, respectively. Gravity clarification is used and the effluent TSS is quite low and insignificant. The waste activated sludge (WAS) is taken from the underflow of the secondary clarifier, contains 0.8% solids and is 75% volatile.
Assume: (BOD5/COD)influent = 0.86, (BOD5/COD)primary effluent = 0.78 and (BOD5/COD)secondary effluent = 0.43
a) Draw a process flow schematic that includes information given in the problem, and information determined as the problem is solved.
b) Calculate the kg/day of solids and liters per day (lpd) of sludge removed from the primary clarifier and activated sludge system.
c) Calculate the specific gravity of the dry solids in the primary sludge and the WAS.
d) Determine the quantity of sludge in lpd and the combined % solids if the two sludge streams are combined.
e) The waste activated sludge can be thickened using dissolved air flotation to 4% solids (no chemical addition). If this is done prior to combining the WAS with the primary sludge, calculate the quantity of combined sludge produced in lpd.
f) Assuming the WAS is thickened by DAF prior to combining it with the primary sludge (as determined in (e) above), what will be the percent reduction in the daily volume of sludge produced compared to part (d).
g) Determine the composition and quantity of sludge produced from a single stage, high rate anaerobic digester assuming the WAS is thickened by DAF prior to being combined with primary sludge. Make (and state) reasonable assumptions.
h) Determine the quantity of sludge that ultimately leaves the solids handling part of the treatment process, assuming the digested sludge is dewatered using a belt filter press.
Chemistry The Central Science
ISBN: 978-0321696724
12th edition
Authors: Theodore Brown, Eugene LeMay, Bruce Bursten, Catherine Murphy, Patrick Woodward