Environmental Engineering Reference
In-Depth Information
and disposal or reuse. The difference between sludge and biosolids lies
is in the way they are managed. Sludge is typically considered to be
wastewater solids that are disposed of, whereas biosolids is the same
substance managed for beneficial reuse (e.g., for land application as a
soil amendment, such as biosolids compost). As wastewater treatment
standards have become more stringent because of increasing environ-
mental regulations, the volume of wastewater sludge has increased. Note
also that, before sludge can be disposed of or reused, it requires some
form of treatment to reduce its volume, to stabilize it, and to inactivate
pathogenic organisms.
Note:
The task of disposing of, treating, or reusing wastewater solids is
called
sludge
or
biosolids management.
Sludge forms initially as a 3 to 7% suspension of solids; with each
person typically generating about 4 gallons of sludge per week, the
total quantity generated each day, week, month, and year is significant.
Because of the volume and nature of the material, sludge management is
a major factor in the design and operation of all water pollution control
plants.
Note:
Wastewater solids account for more than half of the total costs in
a typical secondary treatment plant.
10.1.2 a note about sludge Treatment
The release of wastewater solids without proper treatment could
result in severe damage to the environment. Obviously, we must have
a system to treat the volume of material removed as sludge throughout
the system. Release without treatment would defeat the purpose of envi-
ronmental protection. A design engineer can choose from many pro-
cesses when developing sludge treatment systems. No matter what the
system or combination of systems chosen, the ultimate purpose will be
the same: the conversion of wastewater sludges into a form that can be
handled economically and disposed of without damage to the environ-
ment or creating nuisance conditions. Leaving either condition unmet
will require further treatment. The degree of treatment will generally
depend on the proposed method of disposal. Sludge treatment pro-
cesses can be classified into a number of major categories. In this chap-
ter, we discuss the processes of thickening, digestion (or stabilization),
dewatering, incineration, and land application. Each of these categories
has then been further subdivided according to the specific processes
that are used to accomplish sludge treatment. As mentioned, the impor-
tance of adequate, efficient sludge treatment cannot be overlooked when
designing wastewater treatment facilities. The inadequacies of a sludge
treatment system can severely affect a plant's overall performance capa-
bilities. The inability to remove and process solids as fast as they accu-
mulate in the process can lead to the discharge of large quantities of
solids to receiving waters. Even with proper design and capabilities in
place, no system can be effective unless it is properly operated. Proper
operation requires proper operator performance. Proper operator perfor-
mance begins and ends with proper training.
