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GPS-X Technical Reference

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Suspended Growth Models 142<br />

14. Growth on propionate (spro) using NO 2 as electron acceptor: The process<br />

of heterotrophic growth on acetate using NO 2-N is similar to the process #12<br />

except that the growth rate is proportional to the ratio of propionate<br />

concentration to the total soluble substrate (ss+sac+spro) available to<br />

heterotrophic biomass.<br />

15. Decay of heterotrophs: The process rate of heterotrophic decay is modeled<br />

similar to that in ASM2d model. The main difference in the stoichiometry of<br />

decay reaction is the production of N, P, Ca, Mg, K, anion and cation<br />

according to the biomass composition<br />

Processes mediated by autotrophic organisms<br />

The model considers two-step conversion of NH 3-N to NO 3-N. The two steps are<br />

mediated by ammonia oxidizer and nitrite oxidizer sequentially.<br />

16. Growth of ammonia oxidizer: The process of growth of ammonia oxidizer<br />

oxidizes NH3-N to NO2-N in the presence of oxygen. The reaction rate uses<br />

ammonia and oxygen saturation terms. The stoichiometry of the process is<br />

developed based on the conversion of NH3-N to NO2-N.<br />

17. Growth of nitrite oxidizer: The process of growth of ammonia oxidizer<br />

oxidizes NO 2-N to NO 3-N in the presence of oxygen. The reaction rate uses<br />

NO 2-N and oxygen saturation terms. The stoichiometry of the process is<br />

developed based on the conversion of NO 2-N to NO 3-N.<br />

18. Decay of ammonia oxidizer: The process rate of ammonia oxidizer decay is<br />

modelled similar to that in the ASM2d model.<br />

19. Decay of nitrite oxidizer: The process rate of nitrite oxidizer decay is<br />

modelled similar to that in the ASM2d model.<br />

Processes mediated by phosphate accumulating organisms (PAO)<br />

The processes mediated by PAO are based on the ASM2D model. Three new processes<br />

describing the storage of PHA on propionate, growth of PAO on PHA using NO 2 as<br />

electron acceptor and anoxic storage of XPP using NO 2 are added to the processes<br />

mediated by PAO.<br />

20. Storage of PHA by PAO using acetate: The rate expression for PHA<br />

storage by PAO using acetate as used in ASM2d is modified to include the<br />

effect of propionate, another VFA used by PAO. The rate expression is<br />

modified by assuming that PAO can utilize acetate and propionate<br />

simultaneous in proportion to the availability of each substrate<br />

<strong>GPS</strong>-X <strong>Technical</strong> <strong>Reference</strong>

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