100
4 Nitrogen and Phosphorous Recovery from Municipal Wastewater …
presence of sunlight, microorganisms and algae. The algae grow through the photosynthesis process and release the oxygen by the microorganisms. The microorganisms use the organic matter in wastewater as food for energy production for their
growth and reproduction, and finally produce stabilized products as carbon dioxide
and water. Thus, the process is to stabilize the organic matter and the lagoons are
also known as stabilization ponds [4].
Rotating Biological Contactors: This system consists of large plastic disks
installed on a horizontal shaft. It is partially submerged in the primary effluent,
and rotated while in operation, allowing a layer of microorganisms to grow on the
disks in the presence of air to metabolize the organics in wastewater [4].
4.1.4 Tertiary Treatment
Tertiary treatment is the final treatment step in order to improve the wastewater
quality before it is discharged to the receiving environment. It aims to substantially
reduce the number of microorganisms and trace concentrations of organics in water.
The most common tertiary treatments include disinfection or effluent polishing using
chorine, UV or ozone and filtration for additional removal of suspended solids. In
most of the sewage treatment plants, chlorine is used at the tertiary stage due to its
low cost and effectiveness. Chlorine is added to the wastewater in chlorine contact
tanks, to remove the microorganisms such as bacteria, viruses and parasites [5].
Ozone is also used for bacterial disinfection. It is more effective in deactivating
viruses and bacteria and requires lower contact time [6], and ozone is considered
safer than chlorine as it produces fewer disinfection by-products. UV treatment is an
advanced chemical-free process that can replace the chlorination system and it has
the advantage of producing lower carcinogenic disinfection by-products [7].
Filtration in tertiary treatment is most often performed using granular media filters
such as sand and activated carbon. The most important factors for pollutant removal
are the amount of media in the column and the contact time [6].
4.1.5 Advanced Treatment Processes
Biological nutrient removal (BNR) is considered as the advanced treatment process
(or tertiary treatment) and sometimes as a part of the secondary treatment process.
Wastewater contains a large number of nutrients such as nitrogen, phosphorous,
potassium and trace metals that can be recovered and reused accordingly. Excessive
release of these nutrients to the environment can result in eutrophication, an increased
growth of plant life such as algae, oxygen depletion of the water body and death of
animal life from the lack of oxygen. Moreover, some algal species produce toxins
that can contaminate the drinking water supplies. Thus, these nutrients are required
to be removed from the wastewater. On the other hand, these nutrients if recovered
4 Nitrogen and Phosphorous Recovery from Municipal Wastewater …
presence of sunlight, microorganisms and algae. The algae grow through the photosynthesis process and release the oxygen by the microorganisms. The microorganisms use the organic matter in wastewater as food for energy production for their
growth and reproduction, and finally produce stabilized products as carbon dioxide
and water. Thus, the process is to stabilize the organic matter and the lagoons are
also known as stabilization ponds [4].
Rotating Biological Contactors: This system consists of large plastic disks
installed on a horizontal shaft. It is partially submerged in the primary effluent,
and rotated while in operation, allowing a layer of microorganisms to grow on the
disks in the presence of air to metabolize the organics in wastewater [4].
4.1.4 Tertiary Treatment
Tertiary treatment is the final treatment step in order to improve the wastewater
quality before it is discharged to the receiving environment. It aims to substantially
reduce the number of microorganisms and trace concentrations of organics in water.
The most common tertiary treatments include disinfection or effluent polishing using
chorine, UV or ozone and filtration for additional removal of suspended solids. In
most of the sewage treatment plants, chlorine is used at the tertiary stage due to its
low cost and effectiveness. Chlorine is added to the wastewater in chlorine contact
tanks, to remove the microorganisms such as bacteria, viruses and parasites [5].
Ozone is also used for bacterial disinfection. It is more effective in deactivating
viruses and bacteria and requires lower contact time [6], and ozone is considered
safer than chlorine as it produces fewer disinfection by-products. UV treatment is an
advanced chemical-free process that can replace the chlorination system and it has
the advantage of producing lower carcinogenic disinfection by-products [7].
Filtration in tertiary treatment is most often performed using granular media filters
such as sand and activated carbon. The most important factors for pollutant removal
are the amount of media in the column and the contact time [6].
4.1.5 Advanced Treatment Processes
Biological nutrient removal (BNR) is considered as the advanced treatment process
(or tertiary treatment) and sometimes as a part of the secondary treatment process.
Wastewater contains a large number of nutrients such as nitrogen, phosphorous,
potassium and trace metals that can be recovered and reused accordingly. Excessive
release of these nutrients to the environment can result in eutrophication, an increased
growth of plant life such as algae, oxygen depletion of the water body and death of
animal life from the lack of oxygen. Moreover, some algal species produce toxins
that can contaminate the drinking water supplies. Thus, these nutrients are required
to be removed from the wastewater. On the other hand, these nutrients if recovered