Harnessing water hyacinth potential in hydroponic systems for sustainable sewage treatment

Rapid urbanization and population growth have increased sewage generation, creating major environmental and public health challenges, particularly in regions lacking centralized treatment. Conventional systems are effective but costly and energy-intensive, limiting decentralized deployment. Integrating water hyacinth ( Eichhornia crassipes ) into hydroponic systems offers a low-cost, nature-based alternative for nutrient and organic removal. This review makes three key contributions: (i) it defines a quantitative design–performance envelope linking hydraulic retention time, plant density, and harvesting frequency to treatment efficiency; (ii) it reframes biomass harvesting as a core process control governing net nitrogen and phosphorus removal and root-zone oxygen dynamics; and (iii) it integrates reactor design, biosecurity, and biomass valorization into a unified framework for decentralized sewage treatment. Synthesis of 220 studies shows that controlled floating hydroponic systems typically achieve 50–90% total nitrogen, 60–95% total phosphorus, and 60–95% BOD removal at 7–30 days HRT, driven by coupled plant uptake, rhizosphere nitrification–denitrification, and biofilm adsorption. Pathogen removal is generally limited to 0.5–2 log reductions for indicator bacteria (total and faecal coliforms/ Escherichia coli ), indicating that post-treatment polishing (UV, chlorination, maturation ponds, or wetlands) is required depending on the intended reuse or discharge standard. Performance declines below 15°C without greenhouse protection or hybridization with conventional biological units. Key constraints include seasonal metabolic limitations, hydraulic sensitivity to shock loading, invasive escape risks, and the need for standardized protocols for metal-laden biomass management. Proposed solutions include adaptive harvesting regimes, modular plug-flow layouts, hybrid treatment trains, and biochar production to stabilize contaminants and enable carbon sequestration. Positioned between passive wetlands and energy-intensive membrane systems, water hyacinth hydroponics offers moderate land demand, low energy use (0.02–0.1 kWh m⁻³), and circular bioeconomy potential for scalable decentralized sewage treatment.