Based on a survey which showed that seven of eight conventional trickling filter (CFT) plants exceeded the U.S. Environmental Protection Agency secondary treatment regulatory requirements, a new design procedure is proposed. It recognizes that bioflocculation within CTFs is poor and that most of the effluent violations seen in the survey could be related directly or indirectly to the level of effluent suspended solids. In past practice, process design focus has been on soluble or settled effluent biochemical oxygen demand BOD5 rather than the effluent suspended solids. The principal focus in CTF process design should be on predicting effluent suspended solids (SS) after secondary clarification, rather than effluent carbonaceous BOD5. If the total organic loading TOL is set in the proper range, the effluent carbonaceous BOD5 is primarily determined by the effluent SS. A new design procedure has been developed that identifies the highest TOL that can be sustained without posing a constraint on effluent SS due to effluent CBOD5 limitations. This is coupled with the incorporation of additional design features that can control effluent SS.