This research intends to develop the mathematical model of forward osmosis process during the filtration of a single carboxylic acid and a mixture of two carboxylic acids by investigating and compiling each single logical phenomenon to formulate simultaneous equation models of the associated process variables in the operation of forward osmosis system (Dynamic Modelling). The developed model demonstrates that the permeating CO2 from NaCl draw solution performs the major role in sequentially generating the true carbonic acid (Pk(a) = 3.45), causing the substantial impact on the pH reduction in acid feed solution. Based on inverse problems techniques, the dynamic model, which takes into account the presence of true carbonic acid formation, was fitted to experimental pH profiles. The unobserved membrane CO2 permeability (0.0025 L/m(2)/h) could directly be obtained. Referred to Levenberg-Marquardt algorithm, all time-dependent process variables could be defined by the dynamic simulation model at any point in simulating time. (C) 2016 Elsevier Ltd. All rights reserved.