Nature based solutions for sewage treatment-lessons from two constructed wetland systems

Pollution is one of the three planetary crises, the other two being climate change and biodiversity loss. To mitigate against the negative impacts of landbased pollution, governments and stakeholders have invested in wastewater treatment infrastructure. To cut construction costs and ensure sustainability, there is a shift towards the use of more comprehensive and nature-based solutions in form of constructed wetlands systems (CWS). Constructed wetlands (Green infrastructure) are man-made engineered systems that use natural functions such as vegetation soil, and organisms to treat municipal or industrial wastewater, greywater. Constructed wetlands emerge as a promising approach, offering not only effective treatment but also offer environmental and economic benefits. This technology was applied for sewage/wastewater treatment in Shimo la Tewa prison and in Runyu and Giriamani villages in Mikindani, Mombasa County. The CWS were effective in the removal of many pollutants associated with municipal and industrial wastewater including significantly reducing chemical oxygen demand (COD) with 77% efficiency, biological oxygen demand (BOD) with 66% efficiency, dissolved inorganic nutrients (ammonium, nitrites and phosphates) with about 88% efficiency and indicators of microbial contamination (faecal coliforms and Escherichia coli) with over 98% efficiency. Using NEMA standards (maximum levels permissible), effluent water from the systems was certified as safe for discharge into the marine environment, fit for reuse and in greening the environment and irrigation. For the CWS implemented at both sites, the key lessons learnt from the concept development, implementation, operation and maintenance is the need for intensive stakeholder engagement and buy in, professional designs and construction and capacity building of the recipient stakeholders to ensure system efficiency and sustainability.