Following the format of conventional Activated Sludge Models, 36 the structure of PM 2 is presented using the Gujer (Petersen) stoichiometric and composition matrix (Table ). The PM 2 is composed of 13 state variables (columns in the matrix; 𝑖, Table ) and 30 kinetic rate equations from 30 biological processes (rows in the matrix; 𝑗 , Table ). The rate of production or consumption of the state variable 𝑖 (𝑟 ! ) can be expressed as follows: