30
A. A. Inyinbor et al.
of crops not consumable by man or for wetting vineyards. Secondary treatments
are required in countries where problems associated with food storage are usually
avoided. This is applicable to non-food crop irrigation as well. Small portions of
the primary effluent may be used for irrigation in cases where off-line storage is
available.
Anaerobic digestion is a type of biological treatment that is usually adopted
for primary sludge treatment in large sewage treatment plant (7600 m
3 /d) in the
United States. The volume of wastewater that requires ultimate disposal is reduced
by the metabolic action of anaerobic and facultative bacteria on it [2]. This results in
the stability of the sludge and improvement of its dewatering properties. Digestion
usually takes place in anaerobic digesters. These are tanks with a cover that has its
depth ranging from 7 to 14 m. The duration of wastewater in a digester takes about
10 days and 60 days for a high—rate digester and standard—rate digester, respectively. This enhances the mixing and heating of the wastewater. There is the possibility of generating gas during digestion. The gas generated usually has a methane
content of about 60–65%. This can be harnessed as an energy source. Sludge can
be processed in various ways in the small sewage. This includes land application,
in-process storage, direct application to sludge drying beds, and aerobic digestion.
(c) Secondary treatment
Effluents are usually subjected to further treatments. The third phase of wastewater
treatment is characterized by the secondary treatment process. This stage enhances
the removal of suspended solids as well as organic matters. Secondary treatment
of wastewater is usually subsequent to primary treatment. Removal of colloidal
dissolved and biodegradable organic matters usually occur during this treatment
phase. Biological treatment that occurs in the presence of oxygen is referred to
as aerobic biological treatment. Wastewater is usually subjected to the action of
aerobic microbes (majorly bacteria). The bacteria usually initiate the metabolism of
the organic matter present in the wastewater [153]. Hence, inorganic end–products,
such as CO 2 , NH 3 , and H 2 O as well as other microorganisms are usually produced.
Aerobic biological methods which are employed for secondary treatment of effluent
differ in the transport of oxygen to the microorganisms and the rate organic matter
is broken down by these organisms.
High-rate biological reactors possess relatively small volume reactors and highly
concentrated microbes when compared with low-rate reactors. Therefore, the pace
of growth of new organisms in systems of high rate is quite more due to adequate
environmental control. Clarified secondary effluent is produced when there is a separation of the microorganisms from treated wastewater by sedimentation. Secondary
clarifiers are the sedimentation tanks that are utilized in secondary effluent treatment.
Their mode of operation is similar to that of the primary clarifiers. Solids that are
biological in nature which is removed during secondary sedimentation are referred
to as either biological sludge or secondary sludge. These are usually combined with
primary sludge and are subjected to sludge processing.
A. A. Inyinbor et al.
of crops not consumable by man or for wetting vineyards. Secondary treatments
are required in countries where problems associated with food storage are usually
avoided. This is applicable to non-food crop irrigation as well. Small portions of
the primary effluent may be used for irrigation in cases where off-line storage is
available.
Anaerobic digestion is a type of biological treatment that is usually adopted
for primary sludge treatment in large sewage treatment plant (7600 m
3 /d) in the
United States. The volume of wastewater that requires ultimate disposal is reduced
by the metabolic action of anaerobic and facultative bacteria on it [2]. This results in
the stability of the sludge and improvement of its dewatering properties. Digestion
usually takes place in anaerobic digesters. These are tanks with a cover that has its
depth ranging from 7 to 14 m. The duration of wastewater in a digester takes about
10 days and 60 days for a high—rate digester and standard—rate digester, respectively. This enhances the mixing and heating of the wastewater. There is the possibility of generating gas during digestion. The gas generated usually has a methane
content of about 60–65%. This can be harnessed as an energy source. Sludge can
be processed in various ways in the small sewage. This includes land application,
in-process storage, direct application to sludge drying beds, and aerobic digestion.
(c) Secondary treatment
Effluents are usually subjected to further treatments. The third phase of wastewater
treatment is characterized by the secondary treatment process. This stage enhances
the removal of suspended solids as well as organic matters. Secondary treatment
of wastewater is usually subsequent to primary treatment. Removal of colloidal
dissolved and biodegradable organic matters usually occur during this treatment
phase. Biological treatment that occurs in the presence of oxygen is referred to
as aerobic biological treatment. Wastewater is usually subjected to the action of
aerobic microbes (majorly bacteria). The bacteria usually initiate the metabolism of
the organic matter present in the wastewater [153]. Hence, inorganic end–products,
such as CO 2 , NH 3 , and H 2 O as well as other microorganisms are usually produced.
Aerobic biological methods which are employed for secondary treatment of effluent
differ in the transport of oxygen to the microorganisms and the rate organic matter
is broken down by these organisms.
High-rate biological reactors possess relatively small volume reactors and highly
concentrated microbes when compared with low-rate reactors. Therefore, the pace
of growth of new organisms in systems of high rate is quite more due to adequate
environmental control. Clarified secondary effluent is produced when there is a separation of the microorganisms from treated wastewater by sedimentation. Secondary
clarifiers are the sedimentation tanks that are utilized in secondary effluent treatment.
Their mode of operation is similar to that of the primary clarifiers. Solids that are
biological in nature which is removed during secondary sedimentation are referred
to as either biological sludge or secondary sludge. These are usually combined with
primary sludge and are subjected to sludge processing.