Two-sludge technology is a representative of denitrifying phosphorus removal technologies and has potential advantage in treating municipal wastewater with low carbon source. There have a large number of reports about the technology

but few concerned with the modeling of it. So this paper was aim to develop a mathematical model which can be used to simulate the processes of Two-sludge system. A series of kinetic models which were simplified to linear form basing on some assumption and referencing to ASM2D were adopted to represent the main biochemical processes including phosphorus release（organic storing under anaerobic condition）

nitrating

aerobic biodegradability of organic and denitrifying phosphorus uptake. Then the model of Two-sludge technology was developed on the base of material balance and the principal components of the model were a set of linear equations. The input variables of the model include water quality parameters

HRT of each reactor

MLSS of anaerobic tank

MLSS of nitrifying tank

reflux ratio and transfluence ratio.The kinetic parameters and stoichiometry parameter of the model can be estimated base on experiment data. In this paper

the values of the reaction rate constants of organic storing under anaerobic condition

aerobic biodegradability of organic in nitrifying tank

nitrating in nitrifying tank

aerobic biodegradability of organic in postpositional aeration tank and phosphorus uptake in postpositional aeration tank were estimated from the run datum of a Two-sludge system pilot and the values were respectively 0.29 L/(g.h)

0.26 L/(g.h)

0.64 L/(g.h)

0.31 L/(g.h)

0.20 L/(g.h)

2.326 L/(g.h).The stoichiometry parameters were also estimated from experiment. The stoichiometry relation between the organic consumption and denitrification is 10.03g(COD)/g(N)

the stoichiometry relation between phosphorus release and organic storing is 0.2g(P)/g(COD) and that between denitrification and phosphorus uptake is 0.98g(N)/g(P).It is worthy of special mention that

the reaction rate denitrifying phosphorus uptake is expressed as the product of the duration of the phosphorus uptake and the average rate of denitrifying phosphorus uptake per MLSS（ KP-upt） reflect the effect of phosphorus release on denitrifying phosphorus uptake because it was shown by the former experiment that the value of KP-upt is related with the amount of phosphorus release per MLSS and duration of the phosphorus uptake. The value of KP-upt can be got from a table which reflect the KP-upt relation of

the amount of phosphorus release per MLSS and duration of the phosphorus uptake. The table can be drawn from denitrifying phosphorus uptake. But not as other parameters

the value of KP-upt can’t be ascertained before the model being solved

for the amount of phosphorus release is unknown

so the solution of the model can’t be obtained by solving linear equations in on time. For that problem

trial balance method was adopted. The model was verified by experiment

and it was proved that the model can simulate the variation of the concentration of each kind of pollutant of every unit of Two-sludge system well

but the high accuracy was possibly benefit from the mutual offset of difference partially，So further study is still needed.