Site Suitability Analysis for Natural Systems for Wastewater Treatment with Spatial Fuzzy Analytic Hierarchy Process Konstantinos Anagnostopoulos 1 , Athanasios Vavatsikos 2 Abstract When decentralized strategies are considered for managing wastewater, natural systems for wastewater treatment (NSWT) (constructed wetlands) seem to be strongly preferred in comparison with the conventional activated sludge wastewater treatment systems. However, because of their high land requirements, land-use suitability analysis should be conducted to specify adequate areas for their accommodation. Multicriteria spatial decision support systems have emerged as the technology that takes into account both decision criteria and constraints in complex land-use planning problems. This study presents a multiattribute decision analysis approach called the spatial fuzzy Analytic Hierarchy Process (SFAHP) to support raster-based land-use suitability studies for the implementation of NSWT. The SFAHP enables decision makers to circumvent vagueness when they perform evaluations using linguistic variables. Its application in a region of Northeastern Greece using a two-level criteria hierarchical model demonstrates its potential use for suitability analyses. Subject headings: Decision support systems, Fuzzy sets, Geographic information systems, Multiple objective analysis, Spatial analysis, Wastewater management 1 Professor, Dept. of Production and Management Engineering, Democritus University of Thrace, Vas. Sofias 12, 67100 Xanthi, Greece. E-mail: kanagn@civil.duth.gr (corresponding author) 2 Civil Engineer, Ph.D., Brokoumi 30B, 67100 Xanthi, Greece. E-mail: avavatsi@pme.duth.gr