| abstract |
A separation membrane element capable of realizing excellent fouling resistance over a long period of time is provided. SOLUTION: A permeation-side channel material having a specific structure, a square average surface roughness of a separation functional layer of a separation membrane, a dissociated carboxyl group amount, and a hydrophilic polymer possessed by a separation functional layer are represented by the following chemical formula ( When the separation functional layer side of the composite semipermeable membrane is measured using time-of-flight secondary ion mass spectrometry, including the structure shown in 1), negative secondary ions m / z = 71.02, 103.02 , 107.06, 133.04 satisfy a / (b + c + d) ≧ 1, where a, b, c, and d are respectively set. [Selection] Figure 1 |