Technological Development of Artificial Wetlands. Water Purification Experiences at UNAM

ARTIFICIAL WETLANDS
Among the various wastewater treatment alternatives, in the 1970s a technology called rhizosphere zone method emerged, known today as artificial wetlands (AW) or treatment wetlands. AW operation is based on that of natural wetlands and is part of the so-called nature-based solutions. AW are ecosystems created by humans, following the characteristics of natural wetlands (see box). Its main function is to remove pollutants in wastewater. Natural and artificial wetlands share common elements such as water (with different degrees of pollution), vascular plants (aquatic or terrestrial), a support medium (sand, stone, gravel), and microorganisms (bacteria, protozoa, microscopic fungi, micrometazoans, and algae).

Figure 1. Comparing natural and artifical wetlands

 Elaboración propia

A BIT OF HISTORY
The origin of AW in Mexico can be traced back to pre-Hispanic times. They were a type of ecotechnics applied on a large scale in the time of the Toltecs, around the 10th century, to produce food for human consumption. For example, the photo on p. 312 shows a system of improved water use to obtain aquatic, semi-aquatic, and terrestrial crops in the southeast of Veracruz.

Remains of raised fields in a wetland in Veracruz.

 Alfred H. Siemens (tomada de Siemens, 1983)

Thus, it can be said that the presence of wetlands has accompanied the history of the Mexican people since before the very foundation of Mexico-Tenochtitlan; an example of artificial ecosystems are the chinampas that still exist today.

Xochimilco canals and chinampas today.

 Mónica Rodríguez

PRINCIPLES OF OPERATION OF ARTIFICIAL WETLANDS 
The structure of an AW is designed to reduce organic, inorganic, and microbiological contaminants contained in water through physical, chemical, biochemical, and biological processes. A packaging material is used that works as a filter and precipitant, as well as a support for the growth of microorganisms and plant roots. Plants take nitrogenated compounds and provide oxygen through roots and rhizomes, while microorganisms carry out the transformation and mineralization of carbonaceous, nitrogenated, and phosphorated compounds, along with processes of elimination of enteric bacteria by bacterivorous microorganisms.

Among the benefits of AW are their low cost of operation and maintenance, the increase in vegetation cover, the creation of habitats for birds, the improvement of the landscape, the promotion of social awareness around the care of water, and others (see infographic).

Figure 2. Purification processes in an artificial wetland

 Modificada de Luna Pabello y Aburto Castañeda, 2014

AW can be classified by the type of water they receive, the type of water flow they are fed with, and the type of vegetation they contain, as shown in the classification diagram.

DESIGN AND CONSTRUCTION 
The design and construction of AW must be undertaken in an interdisciplinary manner, with the participation of specialists in engineering (civil, chemical, forestry), biology, architecture, and pharmaceuticals among other disciplines. Amid the main activities to be carried out are the selection and conditioning of the site, construction, start-up, and operation and maintenance of the system. The stage of abandonment or rehabilitation of AW or the site it occupies must also be considered. Studies of soil mechanics, existing vegetation, and the environmental benefits provided by the site should also be incorporated.

ARTIFICIAL WETLANDS AT UNAM
AW technology allows the human and social environment in which they are installed to be transformed in a favorable way and to different measures. The development of this technology at UNAM can be divided into the three stages described below and in the timeline included in this article.

First Stage 
In 1991, an AW was designed and built in the Faculty of Chemistry (FQ, Spanish initials), with the collaboration of other university entities and of international universities. It is among the first functional models for testing, in the laboratory and in the field, with municipal wastewater; for purification of water bodies such as urban rivers and canals; for reuse in irrigation of green areas and hydroponic crops, and for wildlife protection.

Second Stage 
Between 2012 and 2019, interdisciplinary work teams from different UNAM entities and dependencies were formed with independent specialists: the Interdisciplinary Environmental Academic Group (GAIA, Spanish initials) of the FQ was born for large-scale executive AW projects.

Third Stage 
From 2019 to date, alliances have been formed with the Comprehensive Multidisciplinary Group (GMI, Spanish initials) to offer conceptualization, design, and engineering alternatives, support in the supervision and construction of medium-scale AW systems, as well as their start-up and monitoring (see https://gaia.quimica.unam.mx/). GAIA-FQ serves as a technologist, GMI as a company, and local governments provide financial support, in interaction with the recipients of the technology (schools, parks, communities), which has turned out to be an excellent formula to address different problems.

Figure 3. Classification of artificial wetlands

 Adaptado de Wallace & Knight, 2006

Thus, technologies have been successfully transferred to communities of chinamperos (chinampa farmers), public schools, and urban parks, and have been shared with authorities and students and their families through recreational activities and workshops. Added to this is the dissemination of advances through publications and presentations at scientific conferences, and human resources training in undergraduate and postgraduate programs. As a result of all this, two patents have been obtained and in June 2026 the first Mexican Conference of Wetland Systems will be held at the FQ (see box).

PROSPECTIVE
The development and technological innovation of AW is oriented towards its implementation on a larger scale in Mexico, in a context that requires strategies and solutions capable of promoting, in the medium- and long-term, wastewater sanitation, the restoration of aquatic ecosystems, and the sustainable use of water resources.

Current design efforts focus on promoting the removal of nitrogen, phosphorus, and emerging organic compounds, as well as on the synthesis and use of materials to optimize purification processes. Likewise, work is being done on the intensification of AW through aeration and on the incorporation of artificial intelligence in the analysis and design processes.

El Caracol, artificial wetland at Bosque de San Juan de Aragón

 Cortesía de GAIA-FQ

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