A digital computer program which can be used to compute the quasi-steady-state performance and cost of groups of conventional wastewater treatment processes arranged in any configuration has been developed. This executive or calling program contains a main program and ten subroutines, each of which computes the performance and cost of a single wastewater treatment process. Two additional subroutines are provided. The first, entitled COST sums the cost of the individual processes, adds engineering cost, contractor's profit, contingencies and omissions, and cost of land. The second subroutine entitle PRINT simply prints all pertinent data. The ten processes included in the program are: Preliminary treatment; Primary settler; Aerator-final settler; Mixer; Splitter; Digester; Vacuum filter; Sludge thickener; Sludge elutriation; and Sludge drying beds. A listing of the entire FORTRAN IV program, a sample printout, and coding forms designed for preparing input to the program are included in the Appendix. (Author)