Semisolid materials that are produced during the
wastewater treatment. These materials are oftenly infected with organic
or inorganic compound and hence should be treated well before they are
discharged in an environment.
Sludge is treated with a motive to reduce the amount of organic matter
and the microorganism which are the causative agents of many diseases.
Sludge can be treated following processes:
Anaerobic digestion
This is a bacterial process carried out in the absence of oxygen. There
are two methods used in this process - Thermophilic digestion or
Mesophilic digestion. In thermophilic digestion fermentation of sludge
takes place in tanks at a temperature of 55°C whereas in mesophilic
digestion fermentation takes place at a temperature of around 36°C.
The process generates biogas that is used not only for heating the tanks
but also to generate electricity.
Aerobic digestion
Aerobic digestion takes place in the presence of oxygen. Organic matter
is consumed by bacteria and convert it into carbon dioxide. The lack of
organic matter leads to the death of bacteria. Once the bacteria dies
they are used as food by other bacteria. Thus through this process solid
reduction takes place. The cost of aerobic digestion is low with
compared to anaerobic digestion as it consumes bacteria faster.
