The wastewater industry is critical for both current and future human life. At the same time, competitive conditions of market spaces lead to technology evolution reaching continuously new frontiers. While many wastewater treatment plants are designed identically in different global loci, wastewater characteristics are unique and therefore decisions related to wastewater treatment technologies are very critical. Wastewater characteristics vary due to cultural and climate factors, among other things and thus, each wastewater treatment technology must be studied independently. Hence, decision analysis and decision making are an integral part of the industry. A multi criteria decision analysis (MCDA) has been applied in this thesis, including a fictional decision-making problem. Furthermore, this thesis describes an analytic approach to a complex decision-making problem in wastewater treatment by using multi attribute utility theory (MAUT). This thesis assigns utility values, applies Swing Weighting (SW) which is not commonly used in the wastewater industry and assesses weight coefficients for the utility functions for each criterion. The goal is to illustrate how proportional scoring can be used to assign utility values in different aspects related to wastewater treatment, how SW can be performed to assess weight coefficients that are related to wastewater treatment and finally how the additive utility can be applied to deliver the total utility. For this reason, a hypothetical decision problem was developed, in which, the decision maker can select amongst three different wastewater treatment technologies using sustainability criteria. This is a multi-dimensional problem that requires the use of a structured approach to analyze the options accordingly. More, six criteria are used to rank three different wastewater treatment technologies with respect to sustainability. Finally, the MCDA results from this hypothetical decision problem show how proportional scoring, SW, and the additive utility could be used in the selection of a wastewater treatment technology however it should be tested with real life decision problems.