Nutrient and colour removal from healthcare wastewater: using gravel/ignimbrite bed constructed wetlands with <i>Cyperus alternifolius</i>

Healthcare wastewater (HCWW) is often rich in nutrients and pollutants that cause colour, posing serious environmental and public health risks if untreated. This study evaluated the effectiveness of horizontal subsurface flow constructed wetlands (HSSFCWs) for removing nutrients and colour from HCWW, using locally available substrate materials, with and without <i>Cyperus alternifolius</i>. Four pilot-scale wetland systems were installed in parallel at the Jimma Institute of Technology to treat wastewater discharged from the Jimma Institute of Health, with hydraulic retention times (HRT) of 4, 8, 12, and 24 days. Systems with an ignimbrite substrate planted with <i>Cyperus alternifolius</i> showed the highest removal rates: 96.33% for nitrate, 94.19% for phosphate, and 98.82% for colour at a 24-day HRT. The statistical analysis indicated that both substrate type and HRT significantly affect waste removal performance of the CW units (<i>p</i> < 0.0001). FTIR and XRD analysis of substrates before and after treatment revealed changes in functional groups and adsorption properties, supporting the treatment results. The findings indicate that Horizontal subsurface flow constructed wetlands, which utilize ignimbrite beds and <i>Cyperus alternifolius</i>, offer a sustainable and eco-friendly approach for mitigating the risks associated with healthcare wastewater, aligning with the Sustainable Development Goals (SDGs) and directly targeting SDG 6, specifically 6.3 and 6.6. This approach is particularly beneficial in resource-limited areas.