Etapa “P” Planear

Wastewater reuse is practiced in water stressed countries frequently involving low water quality, but it also exists as an unplanned activity in water rich countries. Both situations arise due to the low level of sanitation in Latin America, only 22% according to WWF (2006). Most of the wastewater is reused, intentionally or unintentionally, for agricultural irrigation (Table 9.1) due to an increasingly high urban population (currently at 81%) that, on one hand produces a large amount of untreated wastewater and, on the other demands food.

0 1000 2000 3000 4000 5000 6000 7000

México Chile Panama Costa Venezuela Argentina Uruguay Brasil Jamaica Cuba Perú Salvador Ecuador Guatemal Colombia República Paraguay Honduras Bolivia Nicaragua Haití

0 1 2 3 4 5 6 7 8 9 10 USD/capita.yr Water Quality Score

Table 9.1 Non-treated wastewater-irrigated areas in Latin American Countries.

Country Description Reference

3,700 ha in direct irrigation⁽¹⁾ Bartone and Arlosoroff, 1987 Argentina

20,000 ha with treated and diluted water Kotlik, 1998 Brazil The practice is acknowledged but there is

no precise data on the total area irrigated with waste or polluted water

Rodrigues-Pimentel et al., 2001

Chile 16,000 ha of direct irrigation Bartone and Arlosoroff, 1987 Colombia 26,000 ha of indirect irrigation Moscoso-Cavallini and

Egocheaga-Young, 2000 Mexico 260,000 ha of direct⁽¹⁾ and indirect⁽²⁾

irrigation with 13.8 Mm³/d (160 m³/s) of wastewater, mainly without treatment

CNA, 2004

Peru 6,800 ha in Lima and 2,546 ha other sites

Bartone and Arlosoroff, 1987 and van der Hoek, 2004

(1) Direct wastewater irrigation: Use of wastewater to irrigate

(2) Indirect wastewater irrigation: Use of wastewater to irrigate after dilution with surface water

Irrigation enables 13% of the arable land to produce 30% of total sector income and is therefore a key factor for most of the economies within the region. This is why the total irrigated area in Latin America continues to increase. In the 30 years to 1995 it grew 96% to reach a value of 9.1 million hectares (World Bank, 2002). Given its water-intensive nature, agriculture very easily incorporates wastewater produced by cities for irrigation either directly (without dilution) or indirectly (after discharge into rivers or lakes that are used for irrigation). Based on the patchy information available it is estimated that more than 510,000 ha are directly irrigated with wastewater and 2,500,000ha are irrigated using polluted water (Bartone, 1990 and WHO, 1989) and overall one third of the total irrigated area uses polluted water.

Besides the lack of “clean” water, reasons for using wastewater for agricultural irrigation are the following:

• seasonal variations in “first use” water availability;

• its fertilizing properties;

• its low or zero cost;

• as part of the historical process of water use, i.e. the consistent use of water from the same source which, due to the lack of sanitation, becomes polluted with time.

Frequently, farmers not only accept the use of wastewater but request it to boost agricultural productivity and hence their income, although frequently they are unaware of the health risks associated. The majority of the irrigated area in Latin America is concentrated in Mexico, Brazil, Peru, Chile and Argentina (79% of the total) and it is these countries which report the greatest area irrigated with wastewater or polluted water. According to Moscoso-Cavallini and Egocheaga-Young (2004) irrigation with wastewater is performed on non-food produce or crops consumed cooked or after industrialization (81%), fruit trees (11%) and vegetables (7%). Mexico is the country with the largest area irrigated with wastewater (see Box 9.1) and, unlike most of the countries where public acceptance of the use of wastewater to irrigate is low, Mexico’s farmers appreciate it. The government has openly recognized this practice as a first step towards controlling the problem. Additionally, it is introducing several programs to progressively control reuse. Following the cholera pandemic of 1989, the government prohibited the use of wastewater to irrigate crops consumed raw and also limited the area that could be irrigated using wastewater, with poor results. Then in 1996 it

developed a regulation to control the quality of the wastewater for irrigation at low cost, combining different methods to control the spread of diseases with the use of feasible and affordable technology. This action reduced the area under irrigation with wastewater by 20%

and increased wastewater treatment for agricultural reuse to 1,728,000m³/d (20m³/s according to Jimenez, 2005).

Even in areas with high water availability where large urban areas dispose of their wastewater into lakes, reuse is becoming an interesting option because of environmental concerns. Secondary treatment plants that were originally designed to control pollution in surface water remove only organic matter, not nutrients, the result being that their effluents are causing eutrophication in lakes. Consequently, agricultural reuse is promoted to remove nutrients from the treated effluents prior to its disposal in surface reservoirs.

Extensive use of wastewater in agriculture has encouraged a lot of research in several Latin American countries. It has been shown that different crops are not polluted in the same way. Some crops, such as garlic and onion, have compounds that limit, at least partially, bacterial growth. Others, such as rice, have been found to possess important wastewater treatment capabilities through soil filtration while still others (such as zucchini, coriander, parsley) are reported to concentrate pathogens and bacteria.

Box 9.1 Wastewater reuse in Mexico: The Mezquital Valley case

In Mexico a total of 17.5 Mm³/d of municipal wastewater is collected of which 30% is treated in 1,360 wastewater treatment plants (40% in activated sludge systems, 20% in stabilization ponds, 20%

using advanced primary treatment, and the rest with aerated ponds, primary settlers, oxidation ditches, biofilters and septic or Imhoff tanks). The volume of treated wastewater has been increasing at a rate of 7% per year since 1996, and by the year 2008 it is expected that 60% of the municipal wastewater produced will be treated. It is estimated that of the total amount of municipal wastewater produced, 16.4 Mm³/d is reused, either directly (3.2 M³/d) or indirectly (13.2 m³/d), and with (4.5 Mm³/d) or without (11.9 Mm³/d) treatment, mainly to irrigate 260,000 ha (CNA, 2004). The majority of the water is reused for agricultural irrigation, while only a small fraction is reused in industries (1.4%) or for urban purposes (0.004%).

The biggest continuous irrigated area using untreated wastewater in the world is located in Mexico, where the practice began in 1896 as a method for disposing of Mexico City’s wastewater. This area is colloquially known as the Mezquital Valley, but its formal name is the Tula Valley. The Mezquital Valley is a semi-arid area, with only 550 mm/yr of rainfall and 1,750 mm/yr of evapotranspiration. The region used to be very poor and agriculture could not be developed due to the lack of water. With the arrival of Mexico City’s wastewater the situation soon changed and economic conditions improved (Jimenez, 2005). Consequently, in 1912, irrigation using wastewater was officially acknowledged.

Currently 73,632 farmers irrigate 76,119 ha (Jimenez, 2005). The main crops are alfalfa and maize (60%), but oats, barley, wheat, beans and some vegetables (chilli, Italian squash and tomatoes) are also grown. In order to irrigate, a complex hydraulic system has gradually been constructed by the government. It consists of three perennial rivers, nine dams (three of fresh water and six of wastewater) and more than 800 km of unlined channels to distribute around 4.5 Mm³/d of untreated wastewater (Jimenez, 2004). Wastewater is greatly appreciated by Mezquital farmers. They know that due to its fertilizing properties, land leasing prices increase (1 ha can be rented at 455 US$/yr where wastewater is available instead of 183 US$/yr for rain-fed agricultural land) and that it is possible to grow two or three crops per year instead of just one (Jimenez, 2005). Wastewater contributes some 2,400 kg of organic matter per hectare, 195 kg/ha of nitrogen and 81 kg/ha of phosphorus to the soil each year, increasing maize productivity by 150%, barley by 100% and tomatoes by 94%.

The disadvantage is the effect on health: a 16-fold increase in morbidity by helminths in children in comparison to unexposed nearby areas has been reported. To date, the WHO has obtained most of its

information used to establish limits on helminth eggs content for agricultural reuse of wastewater from the Mezquital area (Cifuentes et al., 1992; WHO, 1989; Blumenthal et al., 1996 and 2000).

Based on the situation in the Mezquital Valley, it has been recommended that in order to protect farmers’, crops’ and the health of consumers while maintaining short and long-term positive impacts on soil productivity, wastewater must be treated and managed wisely. This management must include an appropriate treatment of Mexico City’s wastewater to remove pathogens while partly preserving nutrients and organic matter (Jimenez and Chavez, 1997). In particular, it is recommended not to reduce the contribution of organic matter to the soil in order to avoid metal mobilization (Siebe and Fisher, 1996; Downs et al., 2000). Also pre-treatment or segregation of industrial discharges to Mexico City’s sewers is recommended because wastewater used to irrigate is infiltrated to an aquifer serving as a water supply in the Mezquital Valley. To meet these demands, treatment methods at one third of the cost of conventional options have been developed (Jimenez and Chavez, 1997).

Examples of industrial reuse in Latin American are still isolated and limited to a few countries. Mexico, with a significant lack of water and a relatively high level of industrialization, reuses almost 240,000 m³/d of wastewater for industrial purposes, with some projects operating since 1956 (in Monterrey and Mexico City). Wastewater is reused mainly for power plant cooling; a single plant reclaims 129,600 m³/d of secondary treated effluent from Mexico City for this purpose (Jiménez-Cisneros, 2003). Sao Paulo in Brazil is a highly industrialized city with an ambitious program to reuse water. The main driving force is economic, as the cost of fresh water is about 17 times the cost of reclaimed water (Rodrigues-Pimentel et al., 2001). In Antofagasta, Chile, 5% of the municipal treated wastewater is reused, mainly for mining. For Latin America as a whole wastewater reuse in industries and in municipalities represents a much smaller volume, estimated at around 345,600 m³/d (4 m³/s), than that used for irrigation. In most countries, industrial reuse potential is considered limited by the subsidized low cost of first use water and a low enforcement capacity in relation to deterring illegal groundwater abstraction.

Municipal reuse data is very scarce for Latin America. Mexico reports a total reclaimed water use for the whole country of 78,000 m³/d and Brazil claims that several municipalities are making extensive use of wastewater without reporting figures (Espanhol, 2006). In both countries wastewater is used for lawn irrigation, public parks, recreational lakes and car washing. Several Brazilian municipalities are distributing treated wastewater by tanker trucks for washing streets and road construction dust control. Reclaimed water is sold at a cost of 0.12 US$/m³ (Espanhol, 2004).

An additional type of reuse is the so-called “non intentional reuse” due to the incidental recharge of aquifers that are being used for municipal supply by the infiltration of wastewater transported in unlined channels and irrigation drains, or due to the infiltration of wastewater used to irrigate. This phenomenon has been documented in Mexico and Peru (Foster et al., 2004). Fortunately, during infiltration, passage of the wastewater through the soil significantly improves its quality (Jimenez and Chavez, 2004); however periodical surveys must be performed to detect potential problems and take required measures. Chapter 23 describes in detail the unintentional use of infiltrated wastewater for drinking purposes.