Waste Water Treatment in Mexico

Hugo Fernando Palacios González

IntroductionHydrologic resources in Mexico

780 mm of pluvial precipitation (1 532 million m3)

Superficial runoffs of an annual average volume of 410,164 million m3.

Runoffs distributed in 320 drainage basinsSome of the most important rivers: Yaqui,

Lerma-Santiago, Balsas, Bravo, Pánuco, Grijalva, Usumacinta.

Yaqui Bravo

Lerma Grijalva

Water distribution problem- 80% of hydrological resources under 500 m (over sea level). 70% of total population over this level, 80% of industrial activity as well.

55% of industrial activity is developed in the valley of Mexico at more than 2000 m over sea level.

Water Quality3 main pollution sources classified as follows:Social sector. Mexico 23%, Monterrey 4.1%,

Guadalajara 4%. Only 50% of the population has sewerage infrastructure.

Industrial sector. Generates 43% of waste water in the country.

Agricultural sector. 92 500 million m3 are used in this sector. Produces 12% of waste water. Water with high levels of particles in eutrophication state.

Waste Water Treatment361 municipal WWT plants. Installed capacity

of 25 m3/s. (Unfortunately they only have capacity to treat 24%)

282 industrial WWT plants. Capacity of 20 m3/s. (Only treats 25%)

It’s been estimated that only 50% of these plants operate regularly

There’s an index of water quality used by scientists to classify treated water.

It’s known as the ICARen (Índice de Calidad de Agua Renovada) which would literally mean Quality Index of Renewed Water

ICARen of 0- drinkable waterICARen >38- useless water

ICaren Uses

<3 Drinkable water

16 Industrial: vapor production

22 Industrial: Cooling

25 Fishing

26 Recreation: swimming

26 Commerce, Services, industrial processes

27 Livestock

28 Agriculture

30 Municipal, undrinkable

34 Agriculture: plantations and vines

35 Agriculture: Industrial crops/ Green areas

36 Recreation with secondary contact: navigation

38 Not recommended for use

Water Purification StationsConventional treatment methodsBasic Physical and chemical procedures, such

as decantation, sedimentation and coagulation

Elimination of wastes, oils, greases, sandElimination of inorganic and organic

materials by decantationElimination of biodegradable organic matterStabilization and disposition of sludge

extracted in the processes

Reverse OsmosisMembranes made out of synthetic materials

CoagulationAddition of electrolytes (Alum or Lime)Charged particles of waste water combine

with ions neutralizing the chargesThe neutral particles combine to form greater

particles E.G. Ca(OH)2 -> Ca(aq)

2+ + 2 OH- (causing pH change)

FlocculationUse of starch or multiply charged ions to

attract or trap the particles and settle down together.

Other salts such as iron sulfates Fe2(SO4)3 and FeSO4, chromium sulfate Cr2(SO4)3, and some special polymers are also useful

SedimentationUsed after coagulation and flocculationA settling tank with inlets and outlets is usedThe settled particles and sludge must be

removed

Settling tank

FiltrationRemoval of solids from water, passing them

by a porous mediumArtificial membranes, nets, sand filter and

high technological filter systems

AerationMain purpose: OxygenationRemoval of volatile organic substances , hydrogen

sulfide, ammonia and volatile compoundsDiffused aeration- air bubbles through waterSpray aerationMultiple tray aeration- water flows through many

trays to mix with airCascade aerationAir stripping- combination of multiple tray and

cascade techniques

BioaugmentationIntroduction of a group of natural microbial

strains or a genetically engineered variant

KB-1 Dechlorinator.Used to introduce Dehalococcoides to sites where they are absent

Activated SludgeAtmospheric air or pure oxygen is bubbled

through sewage combined with organisms to develop a sludge, which reduces the organic content of sewage.

Industrial Effluent RecyclingClonal poplar as recycling engineTranspiration function driven by weather

characteristicsPlantation supplied with water according to needsMonitoring of parameters every 10 minutes:1. Solar radiation2. Air temperature3. Air relative humidity4. Wind speed5. Rainfall

Parameters monitored by a station equipped with a micrologger (environmental data logger)

Data is retrieved and evapotranspiration is calculated for every 10 min. interval

These amounts are summed until they reach the amount of a watering (Pre-established based on soil water)

Poplar plantation

Effluent recycling plant

Sewerage InfrastructureOld infrastructural designsOld facilitiesNew Projects:“Túnel Emisor Oriente” (Mexico city). Interior

diameter of 7 meters. Extension of 62 kilometers at more than 200 meters under ground level. Investment of 13 million pesos (19.5 million Kč approximately). Avoid Future floods.

Present Day ProblemsIn the Valley of Mexico only about 6% of their

waste water is treated (against legislation)Immediate response to the problem:1. Permits for the construction of 6 new WWT

plants in Mexico city2. Investment of 37 million pesos (55.4 million

Kč approx)

Leading WWT companiesACS Medio Ambiente   (Monterrey, NL)Aguas Latinas México S de RL de CV  

(México, DF)Alianza con la Biosfera (AliBio)   (México, DF)Bio-Ingenieria Ingeniería SA de CV   (La Paz,

BCS)

References www.sagan-gea.org/hojared_AGUA/paginas/

8agua.htmlhttp://www.imacmexico.org/ev_es.php?

ID=17461_201&ID2=DO_TOPIC