Abstract: An apparatus for the biological treatment of waste fluid from the coating process is presented in the present invention. Said apparatus comprises a biological treatment vessel filled with carriers immobilizing microorganism useful for the treatment of waste fluid from the coating process, a tank in which said biological treatment vessel is set, a heating means to heat said waste fluid in said tank, a stirrer to stir said waste fluid, an aeration means to blow air into said waste fluid, a filter for filtration of said waste fluid having been treated, and a return pass to return filtrate of said waste fluid to said tank.

Abstract: A new grinding medium consisting essentially of a synthetic resin matrix in which small-sized foam, coarse powdery abrasives and fine powdery abrasives are dispersed is provided. A powder having a low electric resistance is added to the medium to form relatively large-sized foam around the powder. The medium is preferably produced by softening and blocking a synthetic resin powder by high-frequency dielectric heating to form a matrix of the synthetic resin and dispersing small-sized foam, coarse powdery abrasives, fine powdery abrasives and powder having a low electic resistance in the synthetic resin matrix wherein relatively large-sized foam is formed around the powder. The medium has a high ability of abrasion and the surface of the medium is smoothly renewed during the grinding process so that the medium has an excellent grinding effectiveness.