Wastewaters at the University. Treatment Plants in UNAM Fields

WASTEWATER TREATMENT PLANT IN UNIVERSITY CITY
The idea of a wastewater treatment plant (WWTP) arose since the construction of University City (CU) in the 1950s, although the project was not carried out then. It was not until the 1970s that the university authorities, through UNAM’s General Direction of Construction and General Services (today General Direction of Construction and Conservation, DGOC), entrusted the Institute of Engineering with the project of the WWTP of CU, today called Cerro del Agua WWTP or PTAR-CU (Spanish initials for Wastewater Treatment Plant). Construction began in 1979 and was completed in 1982; in October of that year it began its operation.

The WWTP-CU was designed to meet three objectives:

1. To treat the wastewater generated in CU for reuse in the irrigation of green areas.
2. To support research by providing facilities and physical spaces for the installation of experimental units.
3. To support teaching by operating—with didactic and research objectives—three aerobic biological systems: trickling filter, rotating biological discs, and activated sludge.

The WWTP-CU was designed to treat 40 liters per second, but the decrease in wastewater during the night made operation difficult. The solution to equilibrate the changes in day and night flows was the design and construction of a homogenization tank—with technology by researchers from the Institute of Engineering—to collect the discharges at a low-elevation site in the area of the institutes of Geophysics, Geology, and Geography, adjacent to the Faculty of Veterinary Medicine and Animal Science (FMVZ), in an arrangement consisting of a regulating tank and a biofiltration system for the elimination of gases and odors, known as a GEOS tank (“Único en su tipo…,” 2004). This allowed pumping wastewater accumulated during the day to the WWTP-CU at night; the plant operated in a more stable manner, complying with the quality required for the use of treated wastewater in the irrigation of CU’s green areas.

University City Wastewater Treatment Plant Reactor - MBR System.

 Juan Hilario García Gil

However, towards the end of the 1990s, having a growing consumption of drinking water in CU, UNAM carried out various actions aimed at a more rational use, replacing sanitary furniture with more efficient models, as well as through an intensive campaign to locate and repair leaks in the water distribution network.

As a result, the characteristics of the wastewater changed, which impacted the operating conditions of the treatment plant. From the wastewater records in the laboratory of the WWTP-CU, the average concentrations of organic matter grew 2.75 times between the years 2001-2002 and 2007-2008, because of the decrease in water consumption per capita. Thus, a higher concentration of organic matter forced the adjustment of the operating conditions of the WWTP-CU, and the production capacity was reduced from 40 to a range between 18 and 20 liters per second. 2008 was also an important year because UNAM’s Water Management, Use, and Reuse Program was initiated (PUMAGUA, 2008).

In 2009, the DGOC and the Institute of Engineering made modifications to the WWTP-CU: a modernization of the activated sludge system that included the replacement of the aeration mechanism with fine bubble membrane diffusers and the change of the secondary settling tank for microfiltration equipment to separate activated sludge. Thus, the previous process, which can be described as conventional, was replaced by a membrane biological reactor (MBR). The modifications were made during 2010 (the bio-discs systems were taken out of operation due to advanced mechanical wear and the trickling filter due to the low capacity for treatment). When the MBR system came into operation in 2011, a better quality of the water treated for reuse was achieved in sports, recreation, and emblematic green areas of the university.

The modified activated sludge process operated efficiently until 2022, producing an average flow of between 12 and 16 liters per second of treated wastewater with a much higher quality than that required by the Official Mexican Standard (NOM-003-ECOL-1997). However, membranes worn out allowing solids to pass, and it was not possible to replace them. A temporary solution was to recondition the conventional activated sludge process. Again, in 2024, the rehabilitation of the MBR-type process was carried out, with the replacement of the filtration membranes to achieve an average treatment capacity of 18 liters per second and recover the quality of the water treated with microfiltration. The DGOC is currently working on the project to treat all the wastewater (24 liters per second) that reaches the WWTP-CU through three collectors. 

Processes at PTAR - CU.

 Juan Hilario García Gil

WWTP IN THE FACULTY OF POLITICAL AND SOCIAL SCIENCES
In 1997 UNAM built a second treatment plant within CU to serve the Faculty of Political and Social Sciences (FCPyS), surrounding administrative offices, and the institutes of the Coordination of Humanities. The original design of the WWTP-FCPyS included a process composed of two aerobic reactors in series with suspended biofilm. Due to the low average flow (1.2 liters per second) that the plant received, the aerobic biological system installed was unstable due to the drastic variations in quality and quantity of wastewater received. In search of a solution, the DGOC sought advice from the Institute of Engineering, who proposed to incorporate, at the beginning of the treatment, an anaerobic biological process that would allow more uniform concentrations of organic matter to be delivered to a second stage with an aerobic biological process. Thus, in 2017 the WWTP-FCPyS was transformed into an anaerobic reactor scheme followed by two sequential aerobic batch reactors.

Currently, DGOC is completing drainage coverage in the Cultural Zone and in the Administrative Zone of CU, which will discharge into the WWTP-FCPyS. The treatment capacity of the plant will be exceeded with the new sewerage connections, so a project has been launched to increase its capacity, which includes microfiltration to achieve the same quality of the wastewater treated in the WWTP-CU, for reuse in green areas.

Wetland, Faculty of Political and Social Sciences.

 Mónica Rodríguez

WWTP OF THE FACULTY OF HIGHER STUDIES ACATLÁN
The WWTP of the Faculty of Higher Studies Acatlán (FES Acatlán), in the State of Mexico, was built in 2014 to support the proposal of the PUMAGUA program with the goal of a 50 percent reduction in the use of drinking water on campus, through reuse for irrigation of green areas and sanitary services (“Acatlán trata sus aguas residuals,” 2016).

The WWTP-FES Acatlán is a model university system with the incorporation of technologies developed at the Institute of Engineering, a biological system that includes an anaerobic reactor and a biofilter system for odor control. It has been launched thanks to the financing considered in the Institutional Development Plan of FES Acatlán (Sustainable University chapter) to comply with the PUMAGUA program, through joint efforts with UNAM Foundation and the Central Administration (“Wastewater treatment plant for the campus,” 2016; “ Wastewater treatment plant of the FES ACATLÁN is presented,” 2016). The participation of academics from FES Acatlán was essential to achieve a project that complied with the efficient use of energy. Thus, the university raises awareness among its community for the development of knowledge and the implementation of sustainable technologies for wastewater treatment, its use in irrigation of green areas, and obtaining by-products (sludge and biogas). With an average installed capacity of 7.5 liters per second, the WWTP-FES Acatlán achieves the purpose of reducing water consumption and accommodates new lines of research related to wastewater treatment.

THE PARTICIPATION OF ACADEMICS FROM FES ACATLÁN WAS ESSENTIAL TO ACHIEVE A PRO JECT THAT COMPLIED WITH THE EFFICIENT USE OF ENERGY

MICROPLANTS AT THE INSTITUTE OF ENGINEERING
The Institute of Engineering implemented a model system for the biological treatment of wastewater for reuse in its toilets (Rodríguez González, 2013). The system, located at the back of the Bernardo Quintana Arrioja and Hermanos Chicurel Uziel buildings, is composed of four distinctive stages:

1. Septic tank for sedimentation and decomposition of solids. 
2. Two types of biological processes, one of them with the institute’s own technology that uses oxygen-free processes, with oxygen and recirculation between them. 
3. Ultraviolet light for disinfection before pumping treated water to toilets. 
4. Elimination of odors from the septic tank in a biofilter with compost (also with technology from the institute). 

The project has allowed an 80 percent saving of drinking water (“Operará planta de tratamiento…,” 2010). The Institute of Engineering has continued with the installation of micro-plants in CU and in foreign academic units. 

PTAR Building 12 and 18 of the Engineering Institute.

 Roberto Briones

MICROPLANTS WITH ARTIFICIAL WETLANDS
Research on artificial wetlands in the Faculty of Chemistry (FQ) began in the 1990s. From there the Interdisciplinary Environmental Academic Group (GAIA) emerged, composed of academics and students from the faculties of Architecture, Sciences, Engineering, and Chemistry, as well as postgraduate degrees in biology, engineering, and biochemical sciences (Suárez Sánchez & Ramírez Venancio, 2024). The GAIA provides opportunities for its graduates in the design and construction of artificial wetlands, such as the construction of micro-plants within university facilities, useful in the dissemination of technologies for environmental care, teaching, research, and reuse of treated water in irrigation of green areas. Support from the Deputy Directorate of Sustainable Campuses of the University Coordination for Sustainability (COUS) stands out here, which has accompanied academic entities in gray wastewater and urine projects, including the College of Sciences and Humanities (CCH) Eastern campus, the National School of Earth Sciences (ENCiT), and FQ and FCPyS. Some of these projects have the endorsement of the Ministry of Education, Science, Technology, and Innovation (SECTEI) of Mexico City’s government.

CCH Oriente Wetland.

 Mónica Rodríguez

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