Adaptive grey water management in tropical coastal settlements: A modular wetland approach for kinship-based communities

Grey water mismanagement in tropical coastal settlements poses significant environmental and public health risks, particularly in dense informal fishing communities with limited sanitation infrastructure. This study aims to develop a spatially informed and socially grounded planning framework for decentralized grey water management through a Modular Wetland System (MWS), using Desa Biringkassi, South Sulawesi, as a case study. A mixed spatial and participatory approach was employed, integrating GIS-based spatial overlay and suitability analysis (including elevation, tidal flood exposure, drainage conditions, and settlement density), hydrodynamic modeling, space syntax, field surveys, and community engagement to identify key drivers of grey water pollution. An Analytical Hierarchy Process (AHP) was applied to prioritize potential MWS locations based on weighted spatial, environmental, and socio-technical criteria, resulting in a ranked set of feasible installation sites within kinship-based residential clusters. The study produces pollution risk maps, spatial suitability zoning, and site prioritization outcomes that inform the conceptual design of a modular, nature-based grey water treatment system. Rather than evaluating treatment performance, the findings demonstrate how integrated spatial analysis and multi-criteria decision support can guide context-sensitive placement of decentralized sanitation systems. The proposed framework offers a replicable planning-level model for grey water management in space-constrained tropical coastal settlements facing similar environmental and socio-spatial challenges.