Emerging Water Pollutants and Wastewater Treatments
29
be included. Listing the different forms of available treatment in the order in which
they are executed: preliminary, primary, secondary and tertiary otherwise referred to
as advanced wastewater treatment [152]. Furthermore, a disinfection method may be
included in order to make the wastewater free from some pathogenic microbes such
as bacteria and viruses.
(a) Preliminary treatment
This primarily involves the uptake of large particle and coarse solids materials that
may be present in wastewater or discharged from industries. This is necessary so
as to enhance the efficiency of the subsequent water treatment units and to avoid
blockage of pipes of some of the equipment. The preliminary treatment process can
be grouped into the following: coarse screening, grit removal, commination of large
objects. Preliminary treatment is relatively cheap to operate, that is, manually cleared
screens to require either little or no maintenance of equipment. The automated cleared
screen requires a lower workforce than manually cleared screen. Similarly, it is easy
to operate. Grit removal reduces damages and downstream processes of maintenance.
Screening, handling and disposal are eliminated which may help in reducing odors,
flies associated with screening. However, a manually cleaned screen requires frequent
scraping in order to prevent clogging blocking and elevated backwater level that
causes accumulation of a solid on the surface. It is relatively costly to operate. The
efficiency of solid capturing by downstream units may be reduced. High equipment
maintenance costs. There may be the accumulation of rag on air diffuse. There may
be an increase in the plastic build-up in the digestion tank. During the digestion
process, solids from comminutors and grinders will not decompose.
Note: Coarse Screening is seldom supplemented by the use of comminutors. This
usually reduces the particles with large size to a smaller size. The size reduction will
enhance the removal of the particles in other treatment processes in sludge form.
Treatment of wastewater at the preliminary stage often requires the inclusion of
devices measuring flow; usually, standing-wave flumes are always included at the
preliminary treatment stage.
(b) Primary treatment
This treatment involves the use of sedimentation and skimming process for the uptake
of organic and inorganic solid that is capable of settling. The percentages of materials
removed during primary treatment are: suspended solids (SS): 55–75%, biochemical oxygen demand (BOD): 25–50% fat and oil: 60–65%. During these stages, it
should be noted that some organic compounds containing phosphorus, nitrogen, and
heavy metals connected with solids wastes are also sequestrated in the process of
primary sedimentation. This treatment doesn’t interfere with the constituents that
are dissolved and those that are colloidal in nature [144]. The effluent that is generated as a result of primary sedimentation is known as the primary effluent. The least
wastewater irrigation pre-treatment required is the primary treatment. The level of
treatment depends on the objectives of the need. Primary treatment may be described
as sufficient for wastewater remediation if the water is intended for use in irrigation
29
be included. Listing the different forms of available treatment in the order in which
they are executed: preliminary, primary, secondary and tertiary otherwise referred to
as advanced wastewater treatment [152]. Furthermore, a disinfection method may be
included in order to make the wastewater free from some pathogenic microbes such
as bacteria and viruses.
(a) Preliminary treatment
This primarily involves the uptake of large particle and coarse solids materials that
may be present in wastewater or discharged from industries. This is necessary so
as to enhance the efficiency of the subsequent water treatment units and to avoid
blockage of pipes of some of the equipment. The preliminary treatment process can
be grouped into the following: coarse screening, grit removal, commination of large
objects. Preliminary treatment is relatively cheap to operate, that is, manually cleared
screens to require either little or no maintenance of equipment. The automated cleared
screen requires a lower workforce than manually cleared screen. Similarly, it is easy
to operate. Grit removal reduces damages and downstream processes of maintenance.
Screening, handling and disposal are eliminated which may help in reducing odors,
flies associated with screening. However, a manually cleaned screen requires frequent
scraping in order to prevent clogging blocking and elevated backwater level that
causes accumulation of a solid on the surface. It is relatively costly to operate. The
efficiency of solid capturing by downstream units may be reduced. High equipment
maintenance costs. There may be the accumulation of rag on air diffuse. There may
be an increase in the plastic build-up in the digestion tank. During the digestion
process, solids from comminutors and grinders will not decompose.
Note: Coarse Screening is seldom supplemented by the use of comminutors. This
usually reduces the particles with large size to a smaller size. The size reduction will
enhance the removal of the particles in other treatment processes in sludge form.
Treatment of wastewater at the preliminary stage often requires the inclusion of
devices measuring flow; usually, standing-wave flumes are always included at the
preliminary treatment stage.
(b) Primary treatment
This treatment involves the use of sedimentation and skimming process for the uptake
of organic and inorganic solid that is capable of settling. The percentages of materials
removed during primary treatment are: suspended solids (SS): 55–75%, biochemical oxygen demand (BOD): 25–50% fat and oil: 60–65%. During these stages, it
should be noted that some organic compounds containing phosphorus, nitrogen, and
heavy metals connected with solids wastes are also sequestrated in the process of
primary sedimentation. This treatment doesn’t interfere with the constituents that
are dissolved and those that are colloidal in nature [144]. The effluent that is generated as a result of primary sedimentation is known as the primary effluent. The least
wastewater irrigation pre-treatment required is the primary treatment. The level of
treatment depends on the objectives of the need. Primary treatment may be described
as sufficient for wastewater remediation if the water is intended for use in irrigation