TM 5-814-8
CHAPTER 7
SOLIDS HANDLING AND DISPOSAL
material which require solids handling. For sec-
7-1. Introduction
ondary sludges, all of the activated sludge sys-
a. Most treatment processes normally em-
tems generate the higher values except extended
ployed in water pollution control yield a sludge
aeration which produces very low quantities.
from a solids-liquid separation process or pro-
Most treatment plants at military installations
duce a sludge as a result of a chemical or
are trickling filters and sludge from the final
biological reaction. Solids handling and disposal
clarifiers is routinely returned to the primary
represent 30 to 50 percent of the total cost of
settling tanks for subsequent solids withdrawal.
treatment. Cost-effective treatment requires effi-
Thus, the combined primary-secondary sludge
cient solids handling and disposal along with
quantities in table 7-1 are most appropriate and
liquid treatment procedures. Process use is lim-
should be used for planning purposes. When
ited by sensitivity to the quantity handled, clima-
chemical precipitation methods are employed for
tological effects, land area and soil constraints,
phosphorus removal or other purposes, the solids
and technological development. Information on
shown in table 7-1 will increase to a level
proven processes applicable to handling domestic
dependent on the type and quantity of chemical
sewage sludge from military installations is pre-
addition and the chemical characteristics of the
sented herein. Industrial wastes may place con-
raw wastewater. The quantity of chemical sludge
straints on the use of some sludge processes and
must be estimated for each application and, in
must be evaluated on a case-by-case basis.
most instances, will warrant bench testing prior
b. The ultimate objective in solids handling and
to facility design.
disposal methods is to reduce the water and
Table 7-1. Typical raw sludge quantities
organic content of sludges. These methods in-
clude:
Dry Solids Per Day
lb/capita
Sludge Type
Thickening.
Primary Sludge
Digestion.
0.12-0.20
0.05-0.20
Secondary Sludge
Conditioning.
Combined Primary & Secondary
0.17-0.40
Dewatering and drying.
Incineration.
b. Volatility. The volatile solids content of
undigested primary and/or secondary sludges is
Digestion and incineration are primarily used for
60 to 80 percent. The volatile solids loading is
.
the removal of organic matter in sludge while
particularly important for sizing digesters.
thickening, conditioning and dewatering are pri-
c. Specific gravity. The specific gravity of the
marily used for the removal of water from the
dry volatile solids is about 1.0 and dry fixed
sludge. This chapter discusses these methods and
solids about 2.5. The specific gravity of a particu-
describes the application in which they should be
lar mixture of sludges depends upon the relative
used.
fraction of volatile solids. Most wet raw sludges
have a specific gravity ranging from about 1.01
7-2. Sludge characteristics
to 1.03.
All evaluations of sludge systems should include
d. Solids content. The percent dry solids of
a detailed mass balance of solids in the system.
fresh sludges drawn from clarifiers range as
The mass balance defines the sludge quantities,
shown in table 7-2. Sludges can be efficiently
dry solids content, volatile solids content and
pumped when the dry solids content is under 5 to
extent of recycle or supernatant flow back to the
6 percent. Most sludges over 10 percent dry
liquid treatment processes, and thus identifies the
solids content must be transported as a semi-solid
basis for evaluating different sludge systems.
using such equipment as conveyor belts.
a. Quantity. The quantity of dry solids pro-
Table 7-2. Typical raw sludge solids content
duced per day from domestic sewage at military
Solids Content
facilities will generally range as shown in table
(percent dry solids
Sludge Type
by weight)
7-1. Variations in primary sludge quantities are
due to the type of collection system, i.e. combined
2.5-5.0
Primary
Trickling Filter
5.0-8.0
systems yield more grit and other suspended
7-1
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