includes moisture, density, color, texture,
fluidity and plasticity etc.
includes organic matter, volatile solids,
Nitrogen, phosphate, fats etc.
Main objectives Digestion of organic matter by Common
Destruction of pathogenic organisms.
Safe and aesthetically acceptable disposal of
By product of methane is used as fuel & and
helps in controlling temperature and also
Thickening or concentration
Reduction of moisture content of raw sludge.
Helps in reducing capacity of digestion tank and
provides control of digestion condition.
It can produce sludge of less than 10% solid
Units of thickening are gravity thickener,
floatation thickener, elutriation thickener.
Digestion or Stabilization
Results in reduction of organic content.
Improved drain ability.
Greatly reduces odor of the pollutant matter
Overall reduction in the volume of the sludge
finally to be deposed.
Units of digestion are– anaerobic & aerobic
converts sludge into liquid & gases and also
reduces odor, volume, putrescence & produces
Bacteria like saprophytic organisms are present
that react on complex organic matter and
Temperature of anaerobic digestion
produces sludge of greater than 10% solid content and
is used after digestion process.
sludge drying beds.
mechanical methods by
Drying beds are generally used for dewatering
of well digested sludges. Attempts to air dry
raw sludge usually result in odor problems.
Sludge drying beds consist of perforated or
open joint drainage pipe laid within a gravel
Incineration—sludge burnt in incinerator.
disposal by crops land
disposal by oceans
unimportant additional operation, increase in total cost
of waste water treatment.
represents SS and BOD loads, impact of biological
processes, stabilized sludge considers hygienic and
aesthetic requirements, aerobic digestion contains
lower BOD value than anaerobic digestion.