Waste is generated in a chemical process mainly because of its chemistry. Technological decisions, like type of reactors and separators also play a major role. At the stage of preliminary design, bounds (targets) on waste generation can be established (Flower el al., 1994) through a modular approach. The process is represented by a simple, generic reactor-separator-recycle structure with purge streams (discharges to environment) and waste streams (destructive treatment of waste) and a limiting version of the reactor and separator systems is employed for targeting purposes. This paper reports on the insights that help moving away from targets towards realistic processes.