Ecological engineering and circular solutions: constructed wetland case studies for wastewater treatment and reuse

Wetland systems are known for their capacity to transform and/or remove various pollutants (organics, nutrients, trace elements, etc.) via various physical, biological, and chemical processes. As wetlands provide a wide range of economic and ecological benefits, they stimulated the development of constructed wetlands (CW) to exploit this water purification capacity for wastewater treatment purposes under controlled conditions. Constructed wetland ecosystems have been used for the treatment of domestic, municipal and industrial wastewater effluents for many years. CWs are nature-based solutions designed in such a way to mimic and enhance the functions of natural wetlands, but further to provide an added value to the known values and functions of natural wetlands, and a wider range of ecosystem services that include flood and stormwater control, habitat creation, reduced carbon footprint and biodiversity restoration. This is why CWs represent a key development in the field of ecological engineering. The modern view of ecological engineering, as outlined by the International Ecological Engineering Society in their Manifesto, dictates that a circular approach should be adopted across the various engineering solutions, in this case in the water and wastewater sector. Adopting green technologies such as CW is the first crucial step towards circularity and overall reduced carbon and material footprint, which should further be integrated with interventions such as treated effluent valorization for irrigation of crops and plant biomass conversion to valuable organic materials. This study will present different case studies of CW from around the world where this modern approach has already been applied in the field. Focus is given on different wastewater effluents to demonstrate the treatment capacity of this green technology, as well as on different facility scales (small and large) to showcase the feasibility of building such systems even at the largest scale and the large potential to upscale CW technology. The following CW case studies will be presented:   Country Flow rate (m³/day) CW area (m²) Water source Circularity aspect Czech Republic 16.5 319 Mixed wastewater from a hotel, a restaurant and a brewery Effluent reuse for irrigation of crops Iran 10 250 Glass manufacturing industry Effluent recycled in the manufacturing process Saudi Arabia 16,000 135,000 Municipal wastewater Effluent reused for landscape irrigation Mexico 8,640 34,000 Municipal WWTP effuent Effluent reused for potable water production Oman 175,000 4.9 million Oily produced water Effluent reused for irrigation of commercial crops, Biomass used for compost and energy production   Keywords: constructed wetlands; wastewater treatment; ecological engineering; nature-based solutions; circularity; water reuse; organic waste; systems thinking; resilience; ecosystem services