Solids Handling - Wastewater Operators - page 364

Table 10.1 TyPiCal WaTer
ConTenT of sludges

% Moisture
of sludge

lb Water/lb sludge
solids generated

Water Treatment Process

Primary sedimentation 95 19

Trickling filter
Humus, low rate 93 13.3

Humus, high rate 97 32.3

Activated sludge 99 99

Source: USEPA, operational manual: Sludge handling and
Conditioning , EPA-430/9-78-002, U.S. Environmental
Protection Agency, Washington, D.C., 1978.

• free water— Water that is not attached to sludge solids in any way.
This can be removed by simple gravitational settling.

• floc water— Water that is trapped within the floc and travels with
it; its removal is possible by mechanical dewatering.

• Capillary water— Water that adheres to the individual particles and
can be squeezed out of shape and compacted.

• Particle water— Water that is chemically bound to the individual
particles and cannot be removed without inclination.

From a public health view, the second and probably more important
component of sludge is the solids matter. Representing from 1 to 8% of
the total mixture, these solids are extremely unstable. Wastewater solids
can be classified into two categories based on their origin—organic and
inorganic. organic solids in wastewater, simply put, are materials that
were at one time alive and that will burn or volatilize at 550°C after 15
minutes in a muffle furnace. The percent organic solids within a sludge
will determine how unstable it is.

The inorganic material within sludge will determine how stable it
is. The inorganic solids are those solids that were never alive and will
not burn or volatilize at 550°C after 15 minutes in a muffle furnace.
Inorganic solids are generally not subject to breakdown by biological
action and are considered stable. Certain inorganic solids, however, can
create problems when related to the environment—for example, heavy
metals such as copper, lead, zinc, mercury, and others. These can be
extremely harmful if discharged.

Organic solids may be subject to biological decomposition in aerobic
or anaerobic environments. Decomposition of organic matter (with its pro-
duction of objectionable byproducts) and the possibility of toxic organic
solids within the sludge compound the problems of sludge disposal.

Before moving on to a discussion of the fundamentals of sludge
treatment methods, we must first cover sludge pumping calculations. It
is difficult (if not impossible) to treat the sludge unless it is pumped to
the specific sludge treatment process.