The treatment of a segregated textile wastewater containing reactive dyes was investigated in two continuous-flow process trains using ozonation and biological processes. The degree of decolorization and dissolved organic carbon (DOC) removal achieved by ozonation followed by aerobic treatment (two-stage) was compared with that found when an anaerobic and aerobic pretreatment was added (four-stage). Although the biological pretreatment reduced color by similar to70%, similar amounts of ozone were required in both trains to achieve high degrees of overall removal of color and DOC. In both trains, ozonation increased biodegradability in the following aerobic reactor, however, in order to reach similar to80% overall DOC removal, a specific ozone absorption (A*) of similar to6 gO(3) gDOC(0)(-1) was required and >50% of the DOC was mineralized in the ozone reactor. A comparison of cost estimates based on investment and operating costs for the process alternatives showed that a four-stage train would reduce costs only if it enabled a decrease in A* to less than 2 903 gDOC(0)(-1). Difficulties in comparing treatment processes for segregated vs full-stream wastewaters are discussed. (C) 2003 Society of Chemical Industry.