In order to enhance retention of particulate and colloidal (organic) matter, chemical coagulation (CC) is often used prior to pressure-driven membrane filtration. This combined hybrid membrane system may be a potential solution for environmental problems dealing with drinking water treatment, water reuse, and rational waste management. In this study, an EC reactor with spiral electrodes was investigated numerically, focusing on modeling with a given design/geometry configuration and boundary conditions. Two-phase flow interactions between water and hydrogen were modeled via computational fluid dynamics (CFD). Different flow rates (Q = 1 − 1000 l/h) through two batches of the watering stage (Case 1–3) and the degassing stage (Case 4–6) were sim-ulated. The results provided information about flow characteristics such as sufficient retention time, water circulation, undesirable gas penetration into the water inlet channel, gas holdup during watering and degassing, and finally the optimal period for the degasification. Retention time decreases with increasing water velocity and thirty seconds seemed to be the optimal time with gas holdup of 0.020%, 0.028%, and 0.027%, respectively, for Case 4, Case 5, and Case 6. Another finding is that the consideration for the most abundant gas holdup for the typical BC was the smallest ratio of water to gas flow.