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A. A. Inyinbor et al.
(a) Activated sludge
This method typically employs the use of biological floc containing protozoans and
bacteria for the treatment of industrial effluents or sewage. In this method, a mixed
liquor of microorganism and wastewater suspension is contained in an aeration basin
or tank which is the dispersed-growth reactor. The components in the aeration basin
are thoroughly mixed by devices that also aerate (i.e. oxygen supplies) the biological
suspension. Common devices used for aeration are surface mechanical aerators which
input air by shaking the surface of the liquid and submerged diffusers which liberate
compressed air. The holding time of hydraulics in aeration basins is between 3 and
8 h. which can be more with wastewaters containing high BODs. Sequel to the
aeration phase, separation by sedimentation of microorganisms from liquid occurs
and the secondary effluent is obtained as clarified. To have a sustained high level of
mixed-liquor suspended solids (MLSS), recycling of aliquots of the biological sludge
to the aeration tank is employed. The remaining portion of the sludge is taken off the
process and transferred to sludge processing to ensure a consistent microorganism
concentration within the system. A different variation of the fundamental activated
sludge process, but similar in principle, such as oxidation ditches and extended
aeration, are commonly employed.
(b) Trickling filters
A trickling filter is a type of treatment system for wastewater. In this system, sewage or
wastewater in a downward delivery passes over a filter system consisting of sphagnum
peat moss, polyurethane foam, slag, gravel, coke, fixed bed of rocks, ceramic, or
plastic media, causing the growth of a layer of microbial slime (biofilm) which
covers the media bed. Metabolism of organic components presents in the wastewater
occurs as they diffuse into the biofilm. The film is usually supplied by oxygen as
unhindered air flows across the media as determined by the wastewater temperature
and atmospheric air. On rare occasions, blowers may be needed to supply forced air
to the system. An increase in the growth of new organisms consequently leads to an
increase in film thickness and at intervals, aliquots of the biofilm slide away from
the media. The discarded substances are in the secondary clarifier separated from
the liquid and deposited in the sludge processing unit. A portion of the secondary
effluent (liquid clarified from the second clarifier) is usually recycled to the biofilter.
This is to ensure better wastewater hydraulic spread over the filter.
(c) Rotating Biological Contactors (RBC)
This is a biological fixed-film reactor process employed in wastewater treatment.
During RBC process, the wastewater is contacted with a biological film so as to
remove contaminants in the wastewater. This is done before the remediated wastewater is discharged into water bodies, such as river, lakes and oceans etc. A rotating
biological contactor consists of a series of parallel discs that are spaced closely
and half-way submerged in the reactor containing flowing wastewater. Biological
degradation of the effluents contaminants takes place on the surface of the disc.
A. A. Inyinbor et al.
(a) Activated sludge
This method typically employs the use of biological floc containing protozoans and
bacteria for the treatment of industrial effluents or sewage. In this method, a mixed
liquor of microorganism and wastewater suspension is contained in an aeration basin
or tank which is the dispersed-growth reactor. The components in the aeration basin
are thoroughly mixed by devices that also aerate (i.e. oxygen supplies) the biological
suspension. Common devices used for aeration are surface mechanical aerators which
input air by shaking the surface of the liquid and submerged diffusers which liberate
compressed air. The holding time of hydraulics in aeration basins is between 3 and
8 h. which can be more with wastewaters containing high BODs. Sequel to the
aeration phase, separation by sedimentation of microorganisms from liquid occurs
and the secondary effluent is obtained as clarified. To have a sustained high level of
mixed-liquor suspended solids (MLSS), recycling of aliquots of the biological sludge
to the aeration tank is employed. The remaining portion of the sludge is taken off the
process and transferred to sludge processing to ensure a consistent microorganism
concentration within the system. A different variation of the fundamental activated
sludge process, but similar in principle, such as oxidation ditches and extended
aeration, are commonly employed.
(b) Trickling filters
A trickling filter is a type of treatment system for wastewater. In this system, sewage or
wastewater in a downward delivery passes over a filter system consisting of sphagnum
peat moss, polyurethane foam, slag, gravel, coke, fixed bed of rocks, ceramic, or
plastic media, causing the growth of a layer of microbial slime (biofilm) which
covers the media bed. Metabolism of organic components presents in the wastewater
occurs as they diffuse into the biofilm. The film is usually supplied by oxygen as
unhindered air flows across the media as determined by the wastewater temperature
and atmospheric air. On rare occasions, blowers may be needed to supply forced air
to the system. An increase in the growth of new organisms consequently leads to an
increase in film thickness and at intervals, aliquots of the biofilm slide away from
the media. The discarded substances are in the secondary clarifier separated from
the liquid and deposited in the sludge processing unit. A portion of the secondary
effluent (liquid clarified from the second clarifier) is usually recycled to the biofilter.
This is to ensure better wastewater hydraulic spread over the filter.
(c) Rotating Biological Contactors (RBC)
This is a biological fixed-film reactor process employed in wastewater treatment.
During RBC process, the wastewater is contacted with a biological film so as to
remove contaminants in the wastewater. This is done before the remediated wastewater is discharged into water bodies, such as river, lakes and oceans etc. A rotating
biological contactor consists of a series of parallel discs that are spaced closely
and half-way submerged in the reactor containing flowing wastewater. Biological
degradation of the effluents contaminants takes place on the surface of the disc.