FA info icon.svgAngle down icon.svgProject data
Authors Carrie Schaden
Tressie Word
Location Mexico, Oaxaca
Status Deployed
Completed 2010
Instance of Waste water treatment project
OKH Manifest Download

In 2006, the University of Benito Juarez in Oaxaca, Mexico (UABJO) implemented a natural wastewater treatment, reuse, demonstration and outreach program. This program continues to grow and has yielded many measurable successes, as depicted by following three elements:

  • Applied Bachelor's and Master's Chemistry Academic Programs. These water quality focused, service-learning programs are providing surrounding communities assesments of potable water and treated wastewater quality. In addition, coursework evaluates levels of contamination in the major waterways of the Oaxaca Valley, such as the Rio Salado and Rio Atoyac. Although water quality analyses are conducted in the University laboratory by students, and are not nationally certified, this data is helping to fill in largely non-existent environmental water quality inforation within the region.
  • An on-campus demonstration wetland wastewater treatment system that treats a portion of campus wastewater and reuses this treated wastewater for on-campus landscaping. This systems also serves as a living laboratory for UABJO Chemistry Department students.
  • An outreach program that consists of an ongoing conference series; demonstration system workshops; local community outreach; wastewater quality monitoring and analysis; and international exchange opportunities

Background[edit | edit source]

Venn Diagram of the PLANTAR UABJO Program by Tressie Word.
Logo Plantar UABJO.jpg
The UABJO Emblem

Oaxaca City, the Oaxaca State capital comprised of approximately 265,000 inhabitants, is about 5000 feet above sea level in the Sierra Madre de Sur Mountains. The rainy season in Oaxaca is normally June to August. Oaxaca City recently installed an activated sludge wastewater treatment plant, prior to which no wastewater treatment measures were in place. In addition, in surrounding communities, subsurface wetlands and other treatment technologies have been implemented to varying levels of success.

The UABJO Demonstration Wetland Wastewater Treatment, Reclamation and Outreach program is located in Oaxaca City and aims to provide these surrounding communities with the tools necessary to potentially improve their water conditions. The UABJO project is unusual, as it is a collaborative effort between two international universities, international engineering firms, government agencies, and residents of Oaxaca. The University of Benito Juarez in Oaxaca, Oaxaca (UABJO) and Cal Poly Humboldt in Arcata, California (HSU) have a long standing relationship as sister campuses that catalyzed this project. HSU provides project expertise and conducted the demonstration plant design; HSU, Fall Creek Engineering and Tressie Word (an International Technical Consultant) provide ongoing project technical support; UABJO is administering this service-learning curriculum, funding, managing, operating and providing outreach on the project; and the State of Oaxaca constructed the demonstration system under the supervision of the UABJO and participates in program conferences.

Contamination of Surface Water and Drinking Water[edit | edit source]

Latin America and the Caribbean are the most urbanized regions in the developing world. However, less than 10 percent of the waste water is treated properly, creating dangerous environmental, health, social and economic problems.[1] In the state of Oaxaca there are 12,081 localities and only 57 of them (0.47%) have a system of domestic waste water treatment and services. Out of these 57 systems 34 (60%) are in operation and 23 (40%) are out of operation.[2]

Insufficiencies in wastewater treatment in the Oaxaca Valley contribute to contamination of surface water within the Oaxaca Valley. The primary watercourses affected by untreated municipal and industrial contamination are the Rio Salado and Rio Atoyac. Contamination includes, but is not limited to: severely decreased dissolved oxygen levels in water; blooms in algae, pathogens and vectors; increased sediment and nitrogen concentrations.

Vision[edit | edit source]

The Plantar UABJO Project vision entails three tiers:

  1. Academics
  2. Outreach
  3. Pilot Natural Wastewater Treatment and Reuse System

These elements are depicted in the sections below.

Academics[edit | edit source]

The service learning nature of the UABJO Chemistry Department to provide much needed services to surrounding communities while students gain applied skills in water quality analysis is a leading-edge concept in academe. In addition, the international nature of this project may provide opportunities for students and faculty, beyond UABJO and HSU, to become more internationally engaged with the watershed management, health, sanitation and treatment technology represented on-campus.

Research and Publications[edit | edit source]

  • Erik Martinez Torres`s thesis on the wastewater treatment plant assessment in Tlacolula is available in Spanish online.
  • UABJO published an in-depth water quality analysis at five locations along the Rio Salado
  • UABJO is currently conducting research on improving natural wastewater treatment systems using filter fish

Outreach[edit | edit source]

Outreach programs include service learning projects via the Chemistry Department; an ongoing series of watershed management, wastewater treatment and reuse conferences; and hands-on workshops and site visits at the pilot wastewater treatment plant.

Service Learning[edit | edit source]

Communities that have worked or are currently working with the Plantar UABJO program to assess their water conditions are as follows:

  • Tlacolula
  • Etla
  • Zautla
  • San Sebastián Tutla
  • Ocotlán de Morelos
  • Matatlan
  • Mitla
  • Santa Ana del Valle
  • Teotitlan del Valle
  • Tlacochahuaya
  • Community Site Visits Conducted in August of 2010:
    • Zautla: System not functioning. Future workshop and collaboration planned between UABJO and Zautla community to revise plans. Currently the waste water is not reused, but flows back into the river next to the community.
    • Etla: System not functioning. Quickly filled with sediment 3 months after placing in system, since rapid population growth out sized the system. Cleaning out sediment has not occurred for financial reasons. Half of the system is has been drained and shut off from more waste water. Waste water now inundates the land around the facility and flows around it. Future collaboration is planned between Water for Humans, an engineering company from the US, as well as a local engineering company to help build capacity here for fixing, maintaining, and installing these waste water treatment plants. Currently Water for Humans does not have much land to be able to extend the system and the land they do have includes a landfill that is not lined and has leaching issues. Thus alternative treatment systems requiring less land, the remediation of the current landfill, or the purchase of more land are three possibilities for getting the treatment system functioning.

Conferences[edit | edit source]

Conferences vary in focus depending on invited participants but generally involve connecting resources and needs to improve water quality within the Oaxaca Valley. Historically, conference topics have addressed community specific water issues such as the context of wastewater treatment in the Oaxaca Valley, funding sources, design processes, treatment technology alternatives, water reclamation, other beneficial uses, and challenges/opportunities for system operation and maintenance.

  • HSU and UABJO collaborated to conduct three wastewater treatment design and watershed management conferences at the UABJO campus in March 2006, Februrary 2008, and August 2009.
  • The next conference is tentatively scheduled for March 2011 at the UABJO campus.

Presentations[edit | edit source]

Demonstration Facility[edit | edit source]

The UABJO hosts applied workshops and site visits for leaders from surrounding communities, government organizations, operators, academics and NGOs. This natural pilot system has received international attention from representatives for various projects based in California, Oregon, Washington, and Houston.

Pilot Natural Wastewater Treatment and Reuse System[edit | edit source]

The UABJO Chemistry Department conducts site visits to surrounding communities, NGOs and government agencies to showcase a functioning natural wastewater treatment and reuse system. In addition, the plant acts as a living laboratory to teach chemistry students applied water quality analyses while supporting system monitoring, operation and maintenance. Please see the section below for more details on the UABJO campus treatment and reuse system.

Design[edit | edit source]

The Plantar UABJO pilot plant naturally treats 10,000 cubic meter per day of sewage generated on-campus. The pilot-scale treatment system is comprised of an upflow anaerobic sludge blanket, a facultative lagoon, two free surface wetlands, a disk filter, storage, and subsurface irrigation for on-campus landscaping. System construction was complete in March 2008, and system is currently functioning well.

Overall Treatment Goals:

  • Reduce total nitrogen by 15%
  • Reduce the biochemical oxygen demand and suspended solids to at least 20 mg/l
  • Improve habitat for waterfowl
  • Reuse wastewater for irrigation
  • Prevent the generation of foul odors

Typical Influent Loading Rate and Effluent Goals for Nutrient and Pollutant Rates by EPA Standards

Constituent Typical Influent Concentration mg/L Target Effluent Concentration mg/L
Hydraulic Load (in/d) .4-4
BOD 5-100 5-30
TSS 5-100 5-30
NH3 & NH4 as N 2-20 1-10
NO3 as N 2-20 1-10
TN 2-20 1-10
TP 1-10 .5-3


Upflow Anaerobic Sludge Blanket[edit | edit source]


  • To improve public health conditions by breaking down pathogenic organisms
  • To reduce the organic load of the wastewater
  • To separate the liquids from the solid waste
  • Possibility of reusing settled sludge biosolids for use in land application
  • Possibility of capturing and using methane from digester for powering plant operations or in direct use for heating or cooking


  • The inlet of the waste water comes in at the bottom
  • Sludge granulation occurs from flow conditions that only allow microorganisms capable of attaching to each other are able to survive and proliferate, these aggregates are known as "granules".
  • Granules resist washout and thus permit high hydraulic loading into the UASB and thus allowing waste water with low concentration of substrate material.
  • Granules are also compact with high microbial activity allowing for increased organic loading. One gram of granular sludge (dry weight) can catalyze the conversion of 0.5 g of COD per day into 1g of methane.
  • Rapid settling occurs from the large particle sizes of granules, with water clarifying faster than the dispersed sludge from a regular anaerobic treatment system. See a picture of settled sludge[4]
  • Methane is produced as well as some CO2 from the break down of organic materials, this methane can be utilized to power the system, produce heat, or used for off system applications like cooking. The design for this system initially wanted to put soil and establish plants above were the methane escapes so that the plants could capture the methane for growth, however these plans were never finished and methane is not currently being used or burned off.
  • Settled sludge has most pathogens reduced and these solids go to the sludge drying beds
  • The wastewater outlet flows out the top and has a reduced organic content, reduced Total Suspended Solids (TSS), and reduced pathogens.

Sludge Drying Beds[edit | edit source]

Digested sludge, or biosolids, generated in the UASB will be land applied applying on campus for landscaping fertilizer, as long as they meet health standard requirements. Currently, tomato plants that stemmed from seeds in the waste stream are thriving in the drying beds. Land applying biosolids is an established solids management strategy implemented at other facilities, including the Arcata Marsh and wastewater treatment facility for the city of Arcata.

Purpose of Sludge Drying Beds:

  1. Temporary containment area for removal of settled sludge from UASB
  2. Dewatering sludge for increased ease in transport either for land application or other disposal methods


  • Sludge is manually released from the UASB preferably at times when UASB is not in session so that odors are not problematic,
  • The beds are open so that sludge dewatering may occur, reducing the weight of the bio-soilds before being transported for re-use or disposal

Advantages of Fertilizer Application of Biosolids:

  • Nitrogen is slowly released in comparison to inorganic fertilizers
  • Less water soluble and thus less likely to leach into the ground water or surface runoff
  • Improves soil texture and water holding capacity, making it great for root growth and drought tolerance
  • After the UASB many pathogens and odors have been reduced rendering this fertilizer much safer

Disadvantages of Biosolids Reuse

  • Though application requires less capital then disposal it requires more labor for oversight
  • Weather can prevent application thus requiring some way to properly store excess bio-solids
  • Without effective communication with the public there might be a lot of opposition that has the power to stop the operation

Facultative Lagoon[edit | edit source]


  1. To continue to remove pathogens, solids and organic load from the wastewater


  • Aerobic organisms and facultative organisms live on the surface layer of water, where there is increased amounts of dissolved oxygen due to atmospheric aeration and algal respiration.
  • Anearobic organisms live in the bottom layer where sludge settles
  • The middle anoxic layer (or layer of depleted oxygen) supports a range from aerobic and anearobic organisms and is termed the facultative zone.
  • These layers are not stagnant, but are maintained due to temperature dependent density variations.
  • Algae living within the aerobic and falcultative zone are an essential factor for success in the system. When the sun is out, algae use CO2 from the waste water and release O2 from photosynthesis into the surface waters. From the intense use of CO2 by the algae the ph rises above 10 and encourages conditions where dissolved ammonia vaporizes out of the water.
  • Oxygen produced by algae is used to stabilize organic material in the upper layer.


  • Removes settleable solids, organic load, pathogens, fecal coliform and ammonia
  • Cheaper than other treatment systems commonly used
  • Easy to operate
  • Requires little energy if using gravity flow


  • Requires lots of land
  • Settled sludge needs to be removed periodically
  • Mosquitoes and other insects may be problematic without ecosystem support like bird or fish populations or without vegetation control, like cutting back overgrowth where mosquito larvae live
  • Difficult to control or predict ammonia levels
  • Can become smelly if aerobic algae are removed from surface[5]

Free Surface Wetlands[edit | edit source]


  1. Reduction of suspended sediments
  2. Reduction of nitrogen
  3. Reduction of organic load


  • Plant canopy of reeds and bulrush in water used to prevent growth and persistence of algae and reduces wind turbulence in water.
  • Submerged portions of the live plants, dead plants, and litter accumulation act as the physical substrate for the microorganisms breaking down nutrients and pollutants
  • The low velocity and smooth, mostly undisturbed, laminar flow allows for effective sedimentation of suspended solids.
  • Sedimentation allows for the removal of some metals and other pollutants
  • Oxidation of organic materials as well as oxidation of fixed forms of nitrogen (TN) and phosphorous (TP) can release soluble forms of BOD, TN, and TP that are then available to be absorbed by the soil or taken up by the wetland microbes and plants.
  • Oxygen available at the water surface as well as on wetland roots and rhizomes allows for some aerobic activity that can remove ammonia nitrogen from the waste water[6]


  • Low maintenance and operation needs
  • Low energy needs
  • Provision of habitat for wildlife including acting as a bird migratory pathway
  • Provision of "green space" for recreational activities and can contribute to a park system
  • Water treatment with particular regard to suspended sediment, nitrogen, and organic load reductions


  • Requires large amounts of land
  • Phosphorous, metals, and some organics build up in the sediment over time and must be periodically removed
  • The lack of available oxygen can reduce the nitrification and removal of ammonium
  • Mosquito problems may persist if there is not a completed ecosystem including mosquito predators like frogs, fish, birds, and other insects[7]

Storage[edit | edit source]


  • Store treated wastewater for landscaping irrigation

Subsurface Irrigation[edit | edit source]


  • Reclaim treated wastewater
  • Water landscaping
  • Demonstrate reuse methods of wastewater

Construction[edit | edit source]

Next steps[edit | edit source]

  • Another wastewater treatment and watershed management conference is anticipated for March 2011, with the support of the UABJO, HSU, Secretary of Health of Oaxaca (SSO), the Institute of Nature and Society of Oaxaca (INSO) and the Mexico National Water Commission (CONAGUA).
  • UABJO, Tressie Word, and Peter Haase of Fall Creek Engineering are working on a book to document the Plantar UABJO Program. The book will have detailed information on the academics, outreach and pilot plant that stemmed from this program. The book should be coming out in March of 2011 in Spanish, after it is published in Spanish, an English version will follow.

References[edit | edit source]

  1. Haase,Peter H. ABSTRACT FIELD ASSESSMENT OF WASTEWATER TREATMENT FACILITIES IN THE OAXACA VALLEY, MEXICO. http://humboldt-dspace.calstate.edu/xmlui/bitstream/handle/2148/625/Field%20Assessment%20of%20Wastewater%20Treatment%20Facilities%20in%20the%20Oaxaca%20Valley,%20Mexico.pdf?sequence=1
  3. EPA, Waste Water Technology Fact Sheet, September, 2000. http://water.epa.gov/scitech/wastetech/upload/2002_06_28_mtb_free_water_surface_wetlands.pdf
  4. Jim Field, jimfield@email.arizona.edu, September 20th, 2002, http://www.uasb.org/discover/granules.htm
  5. United States Environmental Protection Agency, Waste water Technology Fact Sheet, http://water.epa.gov/scitech/wastetech/upload/2002_10_15_mtb_faclagon.pdf
  6. EPA, Wastewater Technology Fact Sheet, Free Water Surface Wetlands. http://water.epa.gov/scitech/wastetech/upload/2002_06_28_mtb_free_water_surface_wetlands.pdf
  7. Aquatic plant systems and wetlands have natural treatment functions that can be mimiced and utilized as a much cheaper way to treat human waste water.
FA info icon.svgAngle down icon.svgPage data
Keywords wastewater
SDG SDG06 Clean water and sanitation, SDG10 Reduced inequalities
Authors Carrie Schaden, Tressie Word
License CC-BY-SA-3.0
Organizations Autonomous University of Benito Juarez
Language English (en)
Related 0 subpages, 18 pages link here
Impact 562 page views
Created April 27, 2008 by Tressie Word
Modified February 28, 2024 by Felipe Schenone
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