Bosque de San Juan de Aragón is a Public Park, located in the Gustavo A. Madero City Hall of Mexico City, it receives approximately 4.2 million visitors a year. One of its main attractions is its artificial lake. This lake is fed with the effluent of a municipal wastewater treatment plant, conventional activated sludge type, with the following quality: 6.2 X 103 NMP/100 mL Fecal Coliforms; 180 mg/L TSS; 170 BOD5 mg/L; 170 mg/L Total Nitrogen; 3 mg/L Total Phosphorus and pH 8.2. The concentration of nutrients, together with the excreta of fishes and birds that inhabit it, promote their eutrophication. To improve the quality of the water contained in the lake and obtain additional environmental benefits, an interdisciplinary work team was formed, which designed a Double Spiral Artificial Wetland System (SHADE) between February and April 2019. It was inaugurated on February 2, 2020. The spiral geometry allows treating more volume of water in less area and also is a symbol of water and movement for the ancient people of Mexico (Fig. 1 and 2).
The construction material used was concrete (cement, sand, gravel and water) reinforcing steel, wood, galvanized iron (Fig. 3). Gravels and grits of different diameters, used as packing material. Geomembrane to cover cells and prevent leaks. Submersible pump 1 HP, 120V, Timmer. Photovoltaic pole, with solar panel and 32 W led lamp.
The wetland SHADE has a total area of 3108 m2, with an average treatment capacity of 140 m3 per day. Structurally, the cells that make it up contain, separately, different packing means, which will allow the removal of carbonaceous, phosphorous and nitrogenous compounds preferentially and in successive stages. The operation is in batches, with vertical and horizontal flow (Fig. 4). Currently, it receives 100 m3 per day and as it stabilizes, the cost will be progressively increased until reaching 140 m3.
The water to be treated is pumped to the highest point of the system, promoting its aeration. From that point on, the flow is by gravity. It passes through a limestone-based dephosphating filter, followed by subsurface and surface wetland cells, which facilitates the process of degradation of carbonaceous compounds and nitrification. The architectural arrangement allows easy access for travel and maintenance. The water quality is expected to have concentrations below 1mg/L of N and P, which will reduce the degree of eutrophication of the lake.
It is expected to obtain environmental benefits associated with the increase in vegetation cover, as well as a habitat for local and migratory birds; improvement of the landscape environment and a space for environmental education, integrating a marginal area of Mexico City (Fig. 5).
Vascular plants of various species, both purifiers such as reeds and typhus, as well as ornamental plants such as papyrus and calla lilies, allow an aesthetic according to the vocation of the site and usable raw material for handicrafts or biodegradable paper.
Location: Gustavo A. Madero
City: Mexico City
Project Size: Total area 3,108 m2, phosphate removal 270 m2; subsurface wetland 1,025 m2; surface wetland 337 m2; stabilization 168 m2; spillway and sump 85 m2; walkers 1,223 m2
Wetland Type (System/Cells): Mixed with subsurface and surface flow cells
Company/Organization: Government of Mexico City
YouTube video: https://www.youtube.com/watch?v=RKlMWi1H8J0