Over the past 50 years extensive research has been conducted by universities, equipment manufacturers, and governmental agencies to delineate the physical, chemical, and biological relationships which govern the operation of wastewater treatment processes. The literature on the performance of the individual processes is voluminous but the techniques for calculating the performance of groups of processes working together as a system are limited. The report is an effort to bring together in one computational scheme the significant cost and performance relationships for the processes and to attempt to calculate the performance and cost of the system as a whole, based on relationships which have been developed for the processes individually. (Author)