1.1 This specification establishes the criteria for acceptance, prior to installation, of vitrified clay filter block used in trickling filters for the treatment of sewage and industrial wastes. 1.2 The values stated in i This specification establishes the criteria for acceptance, prior to installation, of vitrified clay filter block used in trickling filters for the treatment of sewage and industrial wastes. Filter block shall be formed from fire clay, shale, surface c