This work addresses the problem of optimal synthesis and operation of wastewater treatment processes considering multiscenario influent streams under different discharge standards and penalty rates of noncompliant emissions. We develop a general disjunctive programming model to address this problem, which is then reformulated as a multiperiod mixed-integer nonlinear programming model using hull reformulation for the disjunctions. To solve the resulting model to global optimality, we propose a Lagrangean-based decomposition algorithm. Numerical studies verify the effectiveness of the algorithm, and comparison studies provide useful management insights for policy makers.