Activated sludge model
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Activated sludge model is a generic name for a group of mathematical methods to model
activated sludge The activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. It uses air (or oxygen) and microorganism ...
systems. The research in this area is coordinated by a task group of the
International Water Association The International Water Association (IWA) is a nonprofit organization and knowledge hub for the water sector, connecting water professionals and companies to find solutions to the world's water challenges. The IWA is headquartered in London, UK, ...
(IWA). Activated sludge models are used in scientific research to study biological processes in hypothetical systems. They can also be applied on full scale wastewater treatment plants for optimisation, when carefully calibrated with reference data for sludge production and nutrients in the effluent. Around 1983 a task group of the International Association on Water Quality (one of the associations that formed IWA) was formed. They started creating on a generalised framework for mathematical models that could be used to model activated sludge for nitrogen removal.Modelling using ASM1
/ref> One of the main goals was to develop a model of which the complexity was as low as possible and simple to represent, though still able to accurately predict the biological processes. After four years, the first IAWQ model, named ASM1 was ready and incorporated a basic model taking into account
chemical oxygen demand In environmental chemistry, the chemical oxygen demand (COD) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution. It is commonly expressed in mass of oxygen consumed over volume of solution whic ...
(COD),
bacterial growth 250px, Growth is shown as ''L'' = log(numbers) where numbers is the number of colony forming units per ml, versus ''T'' (time.) Bacterial growth is proliferation of bacterium into two daughter cells, in a process called binary fission. Providing ...
, and biomass degradation. An activated sludge model consists of: * ''state variables'': these include the different fractions of COD, biomass and different types of nutrients, both organic and inorganic * a description of the ''dynamic processes'': lists the different biological processes that are modelled, together with their formulae * ''parameters'': variables that describe the circumstances of the biological system, such as growth and decay rate, half-saturation coefficient for hydrolysis, etc.


History

Before work on ASM1 started in 1983, there was already some 15 years of experience in activated sludge modelling, although every research group that worked on mathematical systems of activated sludge created its own model framework, incompatible to all others. ASM1 therefore catalysed the research and had a major impact on activated sludge modelling . ASM1 was the foundation for numerous extensions. These extensions include for example better prediction of nitrogen and phosphorus removal. Widely used extended models include ASM2, ASM2d, and ASM3P. At the time of publication of the ASM1 model, biological phosphorus removal was already used although this process was not completely understood at that time. Basic knowledge of phosphorus removing bacteria was included in the ASM1 model and parameters were adjusted accordingly. Hence after 8 years, ASM2 was published in 1995. ASM1 does not include the role of '' phosphorus accumulating organisms'' nor the relationship between
biological phosphorus removal Enhanced biological phosphorus removal (EBPR) is a sewage treatment configuration applied to activated sludge systems for the removal of phosphate. The common element in EBPR implementations is the presence of an anaerobic tank ( nitrate and oxyge ...
and removal of nitrogen. An enhanced version of ASM1, simply named ASM2, was developed to include biological and
chemical phosphorus removal Chemical phosphorus removal is a wastewater treatment method, where phosphorus is removed using salts of aluminum (e.g. alum or polyaluminum chloride), iron (e.g. ferric chloride), or calcium (e.g. lime). Phosphate forms precipitates with the metal ...
. As scientific understanding grew in the late 1990s, ASM2 was extended into ASM2d, principally by the addition of anoxic as well as aerobic uptake of phosphorus.


Availability

The IWA activated sludge models are commonly used in existing programs. The most common ar
BiowinGPS-XWESTSTOATSIMBA#
an
SUMO
In addition there are Matlab implementations available to university researchers, Fortran code in th
COST 682 Benchmarking report
an
Modelica
code in the
Modelica WasteWater library


See also

*
Activated sludge The activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa. It uses air (or oxygen) and microorganism ...
*
Bacterial growth 250px, Growth is shown as ''L'' = log(numbers) where numbers is the number of colony forming units per ml, versus ''T'' (time.) Bacterial growth is proliferation of bacterium into two daughter cells, in a process called binary fission. Providing ...
*
Membrane bioreactors Membrane bioreactor (MBR) is a combination of membrane processes like microfiltration or ultrafiltration with a biological wastewater treatment process, the activated sludge process. It is now widely used for municipal and industrial wastewate ...
* Michaelis-Menten kinetics *
Monod equation The Monod equation is a mathematical model for the growth of microorganisms. It is named for Jacques Monod (1910 – 1976, a French biochemist, Nobel Prize in Physiology or Medicine in 1965), who proposed using an equation of this form to relate mi ...


References

{{Reflist


External links


Various PhD theses on modelling activated sludge systems

Detailed algorithms for ASM1 and Takacs settling tank model
Sewerage