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A mathematical model for the biological treatment of industrial wastewaters in a cascade of four reactors

Conference Paper


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Abstract


  • Many industrial processes, particularly in the food industry, produce slurries

    or wastewaters containing high concentrations of biodegradable organic

    materials. Before these contaminated wastewaters can be discharged

    the concentration of these pollutants must be reduced. A method which has been

    extensively employed to remove biodegradable organic matter is biological

    treatment. In this process the wastewater (or slurry) is passed through a

    bioreactor containing biomass which grows through consumption of the

    pollutants.

    The industrial treatment of wastewaters typically employs a reactor cascade.

    In a reactor cascade of n reactors the effluent stream from the ith reactor in

    the cascade acts as the feed stream for the (i+1)th reactor, i.e. the next

    reactor. The efficiency of the reactor cascade may be improved by using a

    settling unit. The settling unit `captures' and concentrates the

    microorganisms in the effluent stream of reactor (i) and recycles it into the

    influent stream of reactor (j, j≤i). The benefit of using the settling unit

    is that it increases the concentration of microorganisms in reactor j,

    hopefully leading to an improvement in the performance of the cascade. When

    i=j the operation of the settling unit is characterised by a single parameter,

    the dimensionless recycle parameter, which can take values between zero

    (no recycle) and one (perfect recycle). When i<j

    the operation of the settling

    unit is characterised by two parameters: a concentrating factor (C) and a

    recycle parameter (R). The maximum value of the concentrating factor that be

    achieved in a specific settling unit is related to the value of the recycle

    parameter.

    We investigate how recycle affects the performance of a reactor cascade with

    four reactors. We consider the use of one settling unit. Steady state analysis

    is used to study and compare the performance for the various reactor

    configurations.

    In the first configuration we consider the scenario in which the

    effluent stream leaving a settling unit placed around the ith reactor enters

    the feed stream for the ith reactor. With even one settling unit various

    configurations can be utilized. For instance, the settling unit can be placed

    after the first, second, third or fourth reactor. We find that if the settling

    unit is placed around the final reactor the performance of the cascade is

    optimised when the settling unit operates with perfect recycle. If the

    settling unit is placed around one of the other reactors the performance is

    optimised with a value of the dimensionless recycle parameter less than one.

    For the second configuration we consider the scenario in which the settling

    unit is placed after the fourth reactor and the effluent stream from the

    settling unit is recycled back into the first reactor. We find that there is a

    critical value of the residence time. If the residence time is below the

    critical value then the settling unit improves the performance of the reactor

    cascade whereas if the residence time is above the critical value the

    performance of the cascade is reduced compared to that of a cascade without a

    settling unit.

    We conclude by noting that the first configuration outperforms the second

    configuration at high residence time.

    This is noteworthy as the latter is often used in industry.

Publication Date


  • 2011

Citation


  • Alqahtani, R., Nelson, M. I. & Worthy, A. L. (2011). A mathematical model for the biological treatment of industrial wastewaters in a cascade of four reactors. 19th International Congress on Modelling and Simulation (pp. 256-262). Australia: Modelling and Simulation Society of Australia and New Zealand (MSSANZ).

Scopus Eid


  • 2-s2.0-84858820548

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=2543&context=infopapers

Ro Metadata Url


  • http://ro.uow.edu.au/infopapers/1523

Start Page


  • 256

End Page


  • 262

Abstract


  • Many industrial processes, particularly in the food industry, produce slurries

    or wastewaters containing high concentrations of biodegradable organic

    materials. Before these contaminated wastewaters can be discharged

    the concentration of these pollutants must be reduced. A method which has been

    extensively employed to remove biodegradable organic matter is biological

    treatment. In this process the wastewater (or slurry) is passed through a

    bioreactor containing biomass which grows through consumption of the

    pollutants.

    The industrial treatment of wastewaters typically employs a reactor cascade.

    In a reactor cascade of n reactors the effluent stream from the ith reactor in

    the cascade acts as the feed stream for the (i+1)th reactor, i.e. the next

    reactor. The efficiency of the reactor cascade may be improved by using a

    settling unit. The settling unit `captures' and concentrates the

    microorganisms in the effluent stream of reactor (i) and recycles it into the

    influent stream of reactor (j, j≤i). The benefit of using the settling unit

    is that it increases the concentration of microorganisms in reactor j,

    hopefully leading to an improvement in the performance of the cascade. When

    i=j the operation of the settling unit is characterised by a single parameter,

    the dimensionless recycle parameter, which can take values between zero

    (no recycle) and one (perfect recycle). When i<j

    the operation of the settling

    unit is characterised by two parameters: a concentrating factor (C) and a

    recycle parameter (R). The maximum value of the concentrating factor that be

    achieved in a specific settling unit is related to the value of the recycle

    parameter.

    We investigate how recycle affects the performance of a reactor cascade with

    four reactors. We consider the use of one settling unit. Steady state analysis

    is used to study and compare the performance for the various reactor

    configurations.

    In the first configuration we consider the scenario in which the

    effluent stream leaving a settling unit placed around the ith reactor enters

    the feed stream for the ith reactor. With even one settling unit various

    configurations can be utilized. For instance, the settling unit can be placed

    after the first, second, third or fourth reactor. We find that if the settling

    unit is placed around the final reactor the performance of the cascade is

    optimised when the settling unit operates with perfect recycle. If the

    settling unit is placed around one of the other reactors the performance is

    optimised with a value of the dimensionless recycle parameter less than one.

    For the second configuration we consider the scenario in which the settling

    unit is placed after the fourth reactor and the effluent stream from the

    settling unit is recycled back into the first reactor. We find that there is a

    critical value of the residence time. If the residence time is below the

    critical value then the settling unit improves the performance of the reactor

    cascade whereas if the residence time is above the critical value the

    performance of the cascade is reduced compared to that of a cascade without a

    settling unit.

    We conclude by noting that the first configuration outperforms the second

    configuration at high residence time.

    This is noteworthy as the latter is often used in industry.

Publication Date


  • 2011

Citation


  • Alqahtani, R., Nelson, M. I. & Worthy, A. L. (2011). A mathematical model for the biological treatment of industrial wastewaters in a cascade of four reactors. 19th International Congress on Modelling and Simulation (pp. 256-262). Australia: Modelling and Simulation Society of Australia and New Zealand (MSSANZ).

Scopus Eid


  • 2-s2.0-84858820548

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=2543&context=infopapers

Ro Metadata Url


  • http://ro.uow.edu.au/infopapers/1523

Start Page


  • 256

End Page


  • 262