It is injection-molded from plastic into two semi-circular, fishnet-like spherical halves. The center is filled with plastic woven filaments or small pieces of sponge. In the biochemical treatment of sewage, it features a fully three-dimensional structure, a large specific surface area, direct placement without fixation, easy biofilm formation, and no clogging. The all-plastic structural unit filler possesses A/O and A2/O hydrolysis–aerobic functions, produces minimal residual sludge, and has a long service life.