Beyond Removal Efficiency
A Critical Review of the Long-Term Sustainability of Constructed Wetlands for Wastewater Treatment
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Abstract
Constructed wetlands (CWs) have become important nature-based systems for wastewater treatment because of their relatively low external energy requirements, operational simplicity, potential for decentralized application, and capacity to provide additional ecosystem services. However, portraying CWs as fundamentally sustainable may be misleading when treatment efficacy is assessed without accounting for the associated land requirements, hydraulic deterioration, greenhouse gas emissions, building materials, maintenance, and life-cycle costs. This review critically examines CW sustainability beyond conventional pollutant-removal efficiency, emphasising treatment performance, long-term hydraulic reliability, clogging, greenhouse gas emissions, land, energy, materials, economics, and resource recovery. Evidence from free-water-surface, horizontal subsurface-flow, vertical subsurface-flow, hybrid, and aerated systems indicates that CWs generally remove suspended solids and organic matter effectively, whereas nitrogen and phosphorus removal depend more strongly on hydraulic conditions, substrate characteristics, redox environment, carbon availability, and configuration. Long-term reliability is constrained principally by hydraulic deterioration and solids accumulation in subsurface systems, although pretreatment, modular design, and hydraulic management can extend service life. The sustainability advantage of CWs is further complicated by direct methane and nitrous oxide emissions and by environmental burdens associated with construction and, in intensified systems, aeration. Recent life-cycle research confirms that construction, energy use, system boundaries, and methodological assumptions can materially change environmental and economic conclusions. The review therefore argues that CW sustainability is a multidimensional, context-dependent property rather than a direct consequence of low electricity use or high removal efficiency. A practical framework is proposed that considers treatment performance, reliability, land, energy, greenhouse gases, materials, life-cycle cost, and resource recovery together. Priority needs are long-term full-scale monitoring, harmonized reporting and context-specific life-cycle evaluation, particularly in underrepresented tropical, arid and developing-country settings.
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Copyright (c) 2026 Nura Hassan, Bukar Alhaji Aji (Author)
This work is licensed under a Creative Commons Attribution 4.0 International License.
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