This is a project of an aquaculture wastewater treatment, with the biochemical secondary sedimentation tank mixed with part of the biogas slurry and biogas residue. The process is composed of submerged MBR membrane system and nanofiltration membrane system. and the nanofiltration membranes are used. The orange liquid in this figure is the water produced by the MBR system, and the colorless liquid is the water produced by the nanofiltration system. The COD before entering the nanofiltration system was 497.5 mg/l, and the COD after being treated by the nanofiltration membranes was 8.5 mg/l. The COD removal rate of the nanofiltration system was 98.3%, and the water production was stable.