Eutrophication control and wastewater management through nature-based solutions in Mwanza City, Tanzania, for sustainable Lake Victoria

Integrates eutrophication drivers, wastewater pathways, and NBS-based treatment within the Mwanza-Lake Victoria system for nutrient mitigation. Urban expansion, population growth, and inadequate wastewater management have accelerated eutrophication and impaired water quality in Lake Victoria, Africa's largest freshwater lake. Mwanza City, a major urban center on its shores, contributes substantially through discharges of untreated and poorly treated effluents. Conventional wastewater treatment technologies are limited by high capital and energy demands, raising sustainability concerns. This study evaluates nature-based solutions as context-appropriate, low-energy alternatives for wastewater treatment in Mwanza's hilly terrain to mitigate nutrient loading and protect lake health. Constructed wetlands (CWs), waste stabilization ponds, anaerobic baffled reactors, and communal septic systems were analyzed for their technical and economic suitability. About 10 wastewater hotspots were identified using integrated assessments of inflows, nutrient fluxes, and contamination levels. Hydrological, environmental, and cost-based feasibility analyses were conducted to determine their effectiveness. Results demonstrate that CWs achieved over 70% nitrogen and phosphorus removal, while decentralized wastewater treatment systems, low-energy, localized treatment systems that function near the source, provided efficient organic matter degradation with minimal operational costs. The study proposes a scalable framework for urban wastewater management in resource-constrained settings, offering policymakers actionable strategies to curb eutrophication and enhance Lake Victoria's ecological resilience.