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An analysis of an activated sludge process containing a sludge disintegration system

Conference Paper


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Abstract


  • A continuous flow bioreactor is a well-stirred vessel containing

    microorganisms (X) through which a substrate (S)

    flows at a continuous rate.

    The microorganisms grow through the consumption of the substrate,

    producing more microorganisms and products.

    The products will typically contain carbon dioxide, nitrogen,

    water and other

    species, including biological compounds, specific to the process

    under consideration. The nature of these products is unimportant in this study.

    Unused substrate, microorganisms,

    and products flow out of the reactor. The use of a continuous flow

    bioreactor to treat sewage or industrial wastewaters is known as the

    activated sludge process.

    One drawback associated with the activated sludge process is the

    production of `sludge'.

    Traditional methods for disposing of excess

    sludge, which include incineration, the use of landfill sites and

    dumping at sea, are becoming increasingly regulated in many countries

    due to environmental concerns about the presence of potentially toxic

    elements in the sewage sludge. Furthermore, a combination of

    the limited amount of land available for landfill, particularly

    in urban areas, with stringent legislation has seen the economic costs of using

    landfill sites to increase sharply. It should be noted that incineration

    does not eliminate the need for landfill sites as

    a product of incineration is an ash containing high heavy materials content

    and general toxicity.

    Thus there is a pressing need, and growing interest,

    in methods that reduce the volume and mass of excess sludge

    produced as part of biological wastewater treatment processes.

    A promising method to reduce excess sludge production is to

    increase the biodegradability of the sludge by

    disintegrating it within the reactor.

    This approach works primarily by causing the disintegration of

    bacterial cell walls.

    Among the many techniques that have been

    reported for application to the activated sludge process,

    chemical treatments and ozone treatments have been the most

    widely adopted commercially [Oh et al, 2007].

    In processes involving ozonation

    a part of the sludge is removed from the

    reactor and treated with ozone in a sludge disintegrator. This ozonation

    stage converts the live sludge into a mixture of soluble substrate

    and particulates.

    The liquidized sludge is then returned to the bioreactor as a feed solution

    where the soluble substrate is biodegraded by live sludge.

    These techniques have shown to lead to much lower levels of

    MLSS (mixed liquor suspended solids).

    A simple model is considered for a reactor cascade in which each reactor

    may be connected to both a settling unit and a sludge disintegration

    unit (SDU). The sludge disintegration unit is not modelled per se. Instead

    sludge disintegration terms are added to a conventional activated sludge model.

    These terms assume that the disintegrator unit destroys the biochemical

    activity of the sludge, converting a fraction, α, directly into usable

    substrate and the remainder, (1-α), into organic particulates. We obtain aqualitative understanding of the performance of the process

    by finding the steady-state solutions of

    the model and determining their stability.

    For a specified mixed liquor suspended solids

    (MLSS) content the values of the dimensionless

    residence time and the sludge disintegration factor are determined

    that ensure zero excess sludge production. We show that if the

    sludge disintegration factor is sufficiently high then

    the MLSS content is guaranteed to be below the target value

    provided that the residence time is higher than the washout value.

Publication Date


  • 2011

Citation


  • Nelson, M. I. & Balakrishnan, E. (2011). An analysis of an activated sludge process containing a sludge disintegration system. MODSIM 2011: 19th International Congress on Modelling and Simulation (pp. 331-337). Australia: Modelling and Simulation Society of Australia and New Zealand.

Scopus Eid


  • 2-s2.0-84858820228

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=9957&context=infopapers

Ro Metadata Url


  • http://ro.uow.edu.au/infopapers/2621

Start Page


  • 331

End Page


  • 337

Abstract


  • A continuous flow bioreactor is a well-stirred vessel containing

    microorganisms (X) through which a substrate (S)

    flows at a continuous rate.

    The microorganisms grow through the consumption of the substrate,

    producing more microorganisms and products.

    The products will typically contain carbon dioxide, nitrogen,

    water and other

    species, including biological compounds, specific to the process

    under consideration. The nature of these products is unimportant in this study.

    Unused substrate, microorganisms,

    and products flow out of the reactor. The use of a continuous flow

    bioreactor to treat sewage or industrial wastewaters is known as the

    activated sludge process.

    One drawback associated with the activated sludge process is the

    production of `sludge'.

    Traditional methods for disposing of excess

    sludge, which include incineration, the use of landfill sites and

    dumping at sea, are becoming increasingly regulated in many countries

    due to environmental concerns about the presence of potentially toxic

    elements in the sewage sludge. Furthermore, a combination of

    the limited amount of land available for landfill, particularly

    in urban areas, with stringent legislation has seen the economic costs of using

    landfill sites to increase sharply. It should be noted that incineration

    does not eliminate the need for landfill sites as

    a product of incineration is an ash containing high heavy materials content

    and general toxicity.

    Thus there is a pressing need, and growing interest,

    in methods that reduce the volume and mass of excess sludge

    produced as part of biological wastewater treatment processes.

    A promising method to reduce excess sludge production is to

    increase the biodegradability of the sludge by

    disintegrating it within the reactor.

    This approach works primarily by causing the disintegration of

    bacterial cell walls.

    Among the many techniques that have been

    reported for application to the activated sludge process,

    chemical treatments and ozone treatments have been the most

    widely adopted commercially [Oh et al, 2007].

    In processes involving ozonation

    a part of the sludge is removed from the

    reactor and treated with ozone in a sludge disintegrator. This ozonation

    stage converts the live sludge into a mixture of soluble substrate

    and particulates.

    The liquidized sludge is then returned to the bioreactor as a feed solution

    where the soluble substrate is biodegraded by live sludge.

    These techniques have shown to lead to much lower levels of

    MLSS (mixed liquor suspended solids).

    A simple model is considered for a reactor cascade in which each reactor

    may be connected to both a settling unit and a sludge disintegration

    unit (SDU). The sludge disintegration unit is not modelled per se. Instead

    sludge disintegration terms are added to a conventional activated sludge model.

    These terms assume that the disintegrator unit destroys the biochemical

    activity of the sludge, converting a fraction, α, directly into usable

    substrate and the remainder, (1-α), into organic particulates. We obtain aqualitative understanding of the performance of the process

    by finding the steady-state solutions of

    the model and determining their stability.

    For a specified mixed liquor suspended solids

    (MLSS) content the values of the dimensionless

    residence time and the sludge disintegration factor are determined

    that ensure zero excess sludge production. We show that if the

    sludge disintegration factor is sufficiently high then

    the MLSS content is guaranteed to be below the target value

    provided that the residence time is higher than the washout value.

Publication Date


  • 2011

Citation


  • Nelson, M. I. & Balakrishnan, E. (2011). An analysis of an activated sludge process containing a sludge disintegration system. MODSIM 2011: 19th International Congress on Modelling and Simulation (pp. 331-337). Australia: Modelling and Simulation Society of Australia and New Zealand.

Scopus Eid


  • 2-s2.0-84858820228

Ro Full-text Url


  • http://ro.uow.edu.au/cgi/viewcontent.cgi?article=9957&context=infopapers

Ro Metadata Url


  • http://ro.uow.edu.au/infopapers/2621

Start Page


  • 331

End Page


  • 337