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Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

5.4 Reuse (Topic d)

As reported in section 5.3 sewage treatment before discharge to the environment is more often than not defective or even non-existent which in turn poses problems for wastewater reuse in the Region. For when these wastewaters are used to help irrigate crops whose products are used for human consumption, especially fresh produce e.g, salad vegetables, the public health risk factors reach intolerable levels. In South and Central America, with important exceptions in Peru5 , Chile and Mexico, wastewater reuse is not widely spread. One one hand, this fact is undoubtedly a pity, economically speaking, but on the other hand it does not contribute to already considerable public health risk factors. Quite often wastewater reuse and treatment are measures that should be implemented simultaneously, unfortunately this is seldom the case in the Region.

The wastewater reuse in South and Central America countries is mainly designated to agricultural lands where it is estimated that about 500,000 ha of these lands have been so irrigated, some 20-25% of the overall worldwide figure.

  • In the outskirts of Mexico City, the Country’s capital, lands irrigated by wastewater reuse comprise nearly 90,000 ha, with a further 275,000 ha spread throughout other areas of the Country. Areas of note are (i) in the Mezquital Valley nearly 70,000 ha of agricultural lands use around 45 cubic meter per second of wastewaters generated in the Country’s capital and (ii) that in the Texcoco Lake Project, in the Eastern Mexico Valley Basin 14,500 ha have been irrigated since 1971 with wastewaters that have made possible the existence of 500,00 trees and a reserve area for endogenous wild fauna;
  • in Santiago, the Chilean Capital, especially in the Mapocho River Basin, around 16,000 ha are wastewater irrigated;
  • in Lima, Peru, the wastewater irrigated areas account for 3,000 ha; and
  • around 4,000 ha of wastewater irrigated areas exist in Argentina.

5The important example from the San Juan Ponds Project in Lima, Peru, that has been conducted by CEPIS (PAHO/WHO) is reported as a case study.

 

5.4.1 Mexico

In the Mezquital Valley wastewater reuse started late last century. Some 43 m3/s of wastewaters out of 53 m3/s generated in the Mexico City enter the Mezquital Valley. It is expected that these figures will increase by 30% as soon as the new sewerage systems are put into full operation. In this valley the wastewater storage capacity is 350 million of m3 split into 6 reservoirs which convey into over 1,800 km of channels and canals. This system lowers the coliform figures from 108/100 ml to acceptable levels of 104/100 ml.

Over 70,000 ha of land was assigned to 45,000 families who grow corn and other vegetables such as oat, bean, wheat, pumpkin, tomato, etc. It is estimated that the economic value of the crops is around US$ 100 million yearly.

5.4.2 Peru

The importance of wastewater reuse is even higher in arid lands. Once again given existing poor sewage treatment the conflict between economic benefit and public health risks do appear in these areas. In the desert Peruvian coast only 700,000 ha out of 13,600,000 ha have been used for agricultural purposes, with the above mentioned 3,000 ha of wastewater irrigated land included here. If these data are compared with the population of 12,000,000 people that live in the area, the demand for a dramatic increase in the amount of wastewater irrigated area is easy to understand.

Lima, in the desert coast, is the Country’s capital and largest city, with about 7.5 million people. It is undisputable that the most efficient use of the scarce water supply in Lima is a top priority as a matter of long term survival. The overexploitation of the local water tables is increasingly depleting the available water resources (the water table level has lowered around 20 meters in the last decades). While over 25 cubic meter per second of the City's raw sewage have been disposed of either to the River Rimac or straight to the Pacific Ocean. Thus a wastewater reuse policy with short term implementation measures is called for. It must also be emphasized that most of the wastewater irrigated area in Lima has been used for vegetable crops, a fact that cause diarrhoeas, intestinal fevers, hepatitis and parasitosis in their people, mostly the poor. In Lima, diarrhoea is the most common infant mortality cause and typhoid fever reaches the highest figures in the Region.

The Peruvian Agriculture Ministry has developed wastewater irrigation projects for approximately a further 10,000 ha of lands in Lima (including San Bartolo (4,300 ha), Ventanilla (550 ha) and Villa El Salvador (475 ha)), as well as in the cities of Trujillo (1,400 ha), Chiclayo (1,300 ha), Piura (1,000 ha) and Ica (450 ha).

 

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