A fuzzy optimization model was implemented in this study as a decision-making approach to optimize pollutant degradation processes in facultative ponds of domestic wastewater treatment plants. The fuzzy parameters are due to uncertain situations, which eliminate the need for managers to collect data, particularly when the data are no longer represent the real situation. The managers formulate the fuzzy parameters in the problem based on their intuition and experience in using the provided decision-making tool. Also, the fuzzy optimization model proposed in this study was solved using the fuzzy-based programming approach with the generalized gradient algorithm performed in LINGO 19.0 optimization software. In addition, the numerical experiment was conducted with secondary and generated data for the certain and fuzzy parameters, respectively. The results showed that optimal decisions were achieved and the manager can then use the proposed model in managing domestic wastewater treatment plants.