A method of sewage treatment includes: immersing a separation membrane module into sewage, wherein the separation membrane module has a plurality of separation membrane elements, each having a supporting plate, a separation membrane and a filtered water outlet; separating water into filtered water and suspended solids by having the water permeated through the separation membrane; and having the filtered water flow toward the exterior from the filtered water outlet; wherein the separation membrane has a nonwoven fabric and a porous resin layer on at least one surface of the nonwoven fabric; and a part of the resin permeates into the nonwoven fabric to form a composite layer with the nonwoven fabric.