Structural Analysis
6th Edition
ISBN: 9781337630931
Author: KASSIMALI, Aslam.
Publisher: Cengage,
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Please answer parts c, d, and e
Transcribed Image Text:Design three solids handling unit processes: (a) an anaerobic digester to treat a plant's
primary sludge, (b) a thickener to increase the solids concentration in a plant's
secondary sludge (activated sludge), and then (c) an aerobic digester to stabilize these
secondary solids. The plant has an average day flow of 120mgd.
1. Anaerobic Digester – Assume a sludge temperature of 60° with 72% volatile matter
in the settled solids and a digester solids retention time (SRT) of 17 days. You have
decided to provide 8 cylindrical, anaerobic digesters.
a. Calculate the mass of sludge wasted (lb/day) that each digester will have to
stabilize if the TSS removed by the primary clarifier is 150 mg/l, producing sludge
with 95% water content.
(Ans: 375,621 lb/day)
b. If the specific gravity of the fixed solids is 2.60 and the specific gravity of the
volatile solids is 1.30, calculate the specific gravity (S) of the TSS in the primary
treatment and then the specific gravity (Ss¹) of the sludge (Eq. 14-1, p.1456(ed4)
or Eq. 13-1, p.1459(ed5))
(Ss = 1.51 & Ssl = 1.02)
c.
Calculate the sludge volume (ft³/day) that the digesters must stabilize each day.
d. If the h:D = 2 for each digester, calculate the volume (ft³) of each.
e. Determine the diameter and height of each digester.
Ans: D=15ft, H=29ft
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