7. A Two-Stage Constructed Wetland Design Integrating Artificial Aeration and Sludge Mineralization for Municipal Wastewater Treatment

The technology of constructed wetlands is well known for its multiple benefits in terms of cost-efficiency and environmental performance. The main advantage arises during the operational phase for which the related costs can be significantly lower compared to common conventional/mechanical solutions. One of the main limitations is, however, the higher area demand, which usually limits the application range of these systems to areas where adequate land is available. Over the last years, various modifications have been tested towards the optimization of the system design in terms of both pollutant removal efficiency and reducing area demands. The introduction of air using artificial means has gained significant attraction among researchers and engineers mainly due to the reduced area requirements. Furthermore, the implementation of such systems in arid and dry climates is always a technical and operational challenge. Bauer Nimr LLC designed and constructed in 2017–2018 a new constructed wetland facility in Oman using a novel combination of different wetland designs. The first stage is a vertical flow constructed wetland with integrated sludge accumulation and dewatering, and the second stage is an aerated horizontal subsurface flow constructed wetland. This hybrid system is designed to treat 350 m³/day of domestic wastewater from a nearby residential area with approx. 1800 persons equivalent. This facility introduces not only an innovative design with minimum footprint (1.6 m²/PE), but it is also designed to provide a treated effluent quality that meets the strict national standards for irrigation reuse. This is the first hybrid wetland system of that design implemented in the GCC region under desert climatic conditions, which also acts as a first full-scale demonstration of the aerated wetland technology and the feasibility of these systems even in harsh environments.