Environmental Engineering FOURTH EDITION

Sludge Treatment and Disposal 23 1

PROBLEMS

10.1 Using reasonable values, estimate the sludge production in a 10-mgd
wastewater treatment plant. Estimate both sludge volume per time and dry solids
per time.
10.2 A 1-L cylinder is used to measure the settleability of 0.5% suspended solids
sludge. After 30 min, the settled sludge solids occupy 600 mL,. Calculate the SVI.
10.3 What measures of “stability” would you need if a sludge from a wastewater
treatment plant were to be

a. placed on the White House lawn?

b. dumped into a trout stream?

c. sprayed on a playground?

d. sprayed on a vegetable garden?

10.4 A sludge is thickened from 2000 to 17,000 mg/L. What is the reduction in

10.5 A laboratory batch thickening test produces the following results:

volume, in percent?

Solids concentration Settling velocity

(%I (cdmin)

0.6

1 .o

1.4

1.8

2.2

0.83

0.25

0.11

0.067

0.041

Calculate the required thickener area if the desired underflow concentration (C,) is to
be 3% solids and the feed to the thickener is 0.5 m3/min at a solids concentration of
2000 mgL.
10.6 A Biichner funnel test for specific resistance to filtration, conducted at a
vacuum pressure of 6 x lo4 N/m2, with an area of 40 cm2, and a solids concentration
of 60,000 mg/L, yields the following data:

Time Filtrate volume

11

20

29

37

43

Calculate the specific resistance to filtration. Use ,u = 0.011 N-s/m2. Is this sludge
amenable to dewatering by vacuum filtration?