Polycyclic aromatic hydrocarbons (PAHs) are among the most persistent and hazardous organic pollutants found in natural ecosystems, and phenanthrene, a three-ring PAH, has received particular attention because of its toxicity, environmental persistence, and ability to accumulate in soil and aquatic environments. The contamination of wastewater with phenanthrene is largely the result of incomplete combustion of fossil fuels, leakage from petroleum refining processes, and a range of industrial and urban activities. Once released, phenanthrene exhibits strong hydrophobicity and chemical stability, characteristics that make it difficult to degrade naturally and that promote its long-term accumulation in sediments, soils, and aquatic environments. Numerous studies have shown that phenanthrene is both carcinogenic and mutagenic, while also contributing to cardiovascular disease, reproductive disorders, and developmental abnormalities in humans and other organisms. Its ability to bioaccumulate and biomagnify through food chains, coupled with its persistence in the environment, makes phenanthrene a serious ecological and public health hazard. For this reason, the development and implementation of effective treatment methods for wastewater contaminated with phenanthrene is an urgent priority in environmental engineering and pollution management.

The selection of an optimal remediation strategy for phenanthrene-contaminated wastewater is a complex task because it requires balancing multiple and often conflicting factors. Technical effectiveness alone is not sufficient; a treatment method must also be economically feasible, technologically accessible, and compatible with existing social and regulatory conditions. This challenge is particularly acute in developing countries such as Iran, where financial resources are limited, advanced remediation technologies are not always accessible, and institutional frameworks for environmental management may lack consistency. Therefore, decision-making in this context must account for not only pollutant removal efficiency but also broader considerations such as cost of implementation, availability of suitable technologies, time required for treatment, and the potential to recover or reuse pollutants in order to offset remediation costs.

In this study, a hybrid multi-criteria decision-making (MCDM) model was employed to address these challenges and to identify the most suitable method for treating wastewater contaminated with phenanthrene. The research combined the fuzzy analytic hierarchy process (FAHP) with the fuzzy VIKOR (FVIKOR) model to evaluate alternative remediation techniques under uncertainty and with multiple decision criteria. This integrated approach was designed to reduce subjectivity in expert judgments, handle conflicting criteria, and provide a transparent framework for ranking options. The evaluation criteria were first identified through a comprehensive review of the literature and by consulting experts in petroleum pollution management and environmental remediation. Four main indicators were selected: cost, technology availability, pollutant recovery potential, and time. Expert opinions gathered through structured questionnaires were analyzed using FAHP to assign weights to these indicators. The results revealed that cost was the most influential factor, accounting for 46% of the decision-making weight, followed by technology availability with 39%, pollutant recovery potential with 9%, and time with only 6%. These findings reflect the reality that in developing regions, economic feasibility and accessibility of technologies dominate environmental decision-making, often outweighing other considerations such as pollutant recovery or treatment speed.

Five remediation methods were shortlisted for evaluation: reverse osmosis membrane treatment, potassium salt-assisted membrane treatment, chemical oxidation, photocatalytic oxidation, and biological degradation using microorganisms. Each method was assessed using FVIKOR, which calculates three parameters—S (group utility, reflecting the overall performance of an option across criteria), R (individual regret, reflecting the worst performance across criteria), and Q (the compromise solution index that combines S and R into a single ranking measure). The results demonstrated clear differences in the performance of these methods. The reverse osmosis membrane technique achieved the best overall ranking with values of R = 0.205, S = 0.274, and Q = 0.002. The potassium salt membrane technique followed closely, with R = 0.214, S = 0.271, and Q = 0.005. Chemical oxidation ranked third with R = 0.207, S = 0.331, and Q = 0.028, while biological degradation and photocatalytic oxidation were less favorable, with higher costs, longer treatment times, or limited technological feasibility leading to R, S, and Q values that placed them at the bottom of the ranking.

The dominance of membrane-based technologies in this analysis highlights their effectiveness and adaptability for treating phenanthrene-contaminated wastewater. Reverse osmosis is widely recognized for its ability to remove a broad range of organic and inorganic pollutants with high efficiency and reliability. Its relatively short treatment time and compatibility with different wastewater compositions make it particularly suitable for urgent remediation needs. The potassium salt membrane method, while slightly less efficient than reverse osmosis in the model, remains attractive because of its lower operational costs, its ability to recover pollutants during the treatment process, and its strong compatibility with local conditions. Chemical oxidation methods, although capable of degrading phenanthrene, are less practical in the Iranian context due to the high costs of chemicals, risks of secondary pollution, and complex operational requirements. Biological degradation, though environmentally sustainable and theoretically appealing, is constrained by slow treatment times and sensitivity to environmental conditions, which reduces its feasibility for large-scale applications. Photocatalytic oxidation, despite its promise in laboratory settings, suffers from high costs and scalability issues, making it less suitable for immediate implementation in resource-limited settings.

The results of this study have broader implications for environmental policy and management. The high weighting of cost and technology availability suggests that without investment in infrastructure and technology transfer, even highly effective remediation methods may remain impractical in many developing countries. This underscores the importance of policies that reduce the financial barriers to advanced remediation technologies, such as subsidies, international cooperation, or technology-sharing agreements. Furthermore, the incorporation of pollutant recovery into the decision-making model points to the potential benefits of integrating circular economy principles into wastewater management. By designing treatment methods that not only remove but also recover valuable by-products, countries can offset some of the costs associated with remediation, making advanced technologies more economically viable. This approach could also create new opportunities for resource efficiency and sustainability, turning waste into a potential source of value rather than solely a liability.

Another key contribution of this study is the demonstration of the value of hybrid MCDM approaches in environmental engineering. Traditional decision-making models often struggle with uncertainty and subjectivity, particularly when expert opinions differ or when data is incomplete. By applying FAHP to weight the criteria and FVIKOR to rank the alternatives, this study was able to incorporate fuzzy logic and triangular fuzzy sets to manage uncertainty more effectively. The integration of expert knowledge with quantitative modeling enhanced the robustness and credibility of the findings, offering a replicable framework for future studies in other contexts or with other pollutants. Moreover, the transparency of the model provides a structured basis for dialogue among stakeholders, facilitating consensus-building and more informed decision-making in environmental management.

In conclusion, this study identified reverse osmosis membrane treatment and potassium salt-assisted membrane treatment as the most suitable technologies for the remediation of wastewater contaminated with phenanthrene under the specific economic, technological, and social conditions of Iran. These findings are not only supported by the mathematical modeling but also consistent with experimental evidence reported in the literature, which confirms the high efficiency of membrane technologies in removing PAHs from wastewater. More broadly, the research underscores the need to approach environmental remediation holistically, balancing technical efficiency with cost-effectiveness, technological feasibility, and opportunities for pollutant recovery. For policy-makers, engineers, and industry stakeholders, the results highlight the importance of investing in accessible and affordable remediation technologies, particularly in developing countries where constraints are most acute. For researchers, the study provides a methodological framework that can be applied to other pollutants and contexts, helping to bridge the gap between theoretical solutions and practical implementation. Ultimately, the integration of advanced decision-making tools with practical environmental engineering offers a pathway toward more sustainable and effective management of persistent pollutants such as phenanthrene, supporting both environmental protection and public health in the face of growing industrial challenges.