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


5.3 Treatment (Topic c)

It is estimated that nearly 100 million cubic meters of sewage is generated in the Region daily. Previous estimates for the Region, collected by PAHO for the Mid term Decade Review put the level of sewage collected that received treatment at 10% or less, but even worse, the quality of the treatment provided as generally low. Argentina is reportedly treating 10% of this sewage while Colombia reports only 5% treatment; Brazil estimates its coverage in sewage treatment at 20%.

This information is shown in Table 5.5.

Table 5.5: Proportion of urban sewage treated before discharge and associated level of treatment per country.
Country Proportion of
Urban Sewage Treated
Before Discharge
  Proportion of Treated Waste by Level
P S O
Argentina 10 0 100 0
Bolivia 30 33 67 -
Brazil 20 10 68 22
Colombia 5 - 100 -
Costa Rica 3 33 67 -
Ecuador - - - -
El Salvador 1 - - -
Guatemala 9 46 54 -
Mexico 13 14 27 59
Nicaragua 21 46 54 -
Paraguay 1 - 100 -
Peru - - - -
Suriname 1 - 100 -
Uruguay 15 50 28 22
Venezuela - - - -
* P = Primary Treatment
   S = Secondary Treatment
   O = Others

The water pollution problems in Latin America have been well documented and there is no evidence as far as the data show of any substantive effort to change the situation. Another aspect that must be taken into due consideration is the poor level of confidence of data collected as they appear sometimes highly contradictory even when the collecting source (PAHO) is the same.

Nevertheless some of the main efforts made in specific countries are worth mentioning. Country-by-country, some specific information may be reported as follows:

  • Buenos Aires metropolitan area has constructed 20 waste treatment plants and is in the process of building 15 more, with over 80% of the sewage generated there being treated. In Argentina as a whole it is estimated that 10% of all sewage has been treated, with 7 out of the 21 departments treating all their sewage and 2 treating nothing at all. The River Conquista Basin Project for the Greater Buenos Aires is under construction.
  • In Belize, sewage treatment facilities in Belize City comprise two facultative lagoons situated south of the city. Treated effluent is discharged into canals, cut through a mangrove wetland, which discharge into the Sibun Bight. The lagoon cells operate in series and are designed to provide 10 days hydraulic retention time each, although actual retention time could be double this period in the dry season. Early problems in the lagoons included premature corrosion of chambers and weed growth. However, the lagoons are generally in good condition, providing some 80 - 85% biological oxygen demand removal. In Belmopan, the treatment involves sedimentation tanks only, with the effluent discharging into the Belize River. Not all the meters and pumps are working and the treatment plant is partly bypassed, resulting in a biological oxygen demand removal rate of about only 5%. Currently, the plant is a potential health hazard because of fecal contamination of the Belize River and, hence, the improvements should be carried out as soon as possible.
  • In Brazil, of the total amount of wastewater collected, only 20% is treated or discharged to a safe marine point. Less than 30% of the sewage generated in São Paulo and Rio de Janeiro, the Country's largest cities, receive some sort of treatment before final destination. Large sewage treatment projects are under implementation such as the Guanabara Bay Depollution Project for Rio de Janeiro, and the Greater Salvador and Porto Alegre Pollution Control Project. The Tietê Project for the Greater São Paulo, the Country's largest project has been brought to a halt.
  • In Bolivia sewage treatment is virtually non-existent.
  • In Chile 97% of the wastewater is disposed of in waterways without prior treatment. Nonetheless there are underway the Sewage Treatment Project for the Greater Santiago (the Country ’apital), and Projects for Viña del Mar-Valparaiso as well as the Lomalarga Treatment Plant.
  • In Colombia, only 154 out of 1068 municipal districts treat sewage before discharging it to a water body, the amount of total treated sewage being 4.5 m3/s. In the metropolitan areas the proportion is 12 out of 30. Enteritis, hepatitis and typhoid fevers are endemically found. There are in Colombia 202 treatment units comprising 24 percolating and trickling filters, 17 UASB's, 96 stabilization ponds, 17 activated sludge plants, 26 extended aeration plants, 6 compact plants and 16 under other processes. Regular sampling and analysis have been made only in a few selected areas, such as the Cartagena Bay. Very developed environmental legislation is available which sets standards for faecal coliforms, and wastewater effluents for new & existing plants.
  • In Ecuador there are no sewage treatment systems currently available however plans for construction exist for the Cities of Quito, Guayaquil and Cuenca.
  • In Costa Rica it is estimated that a mere 3% of the liquid effluents of the population are treated before reaching final destination. Limon discharges raw sewage into its harbour. No major problems exist except the high coliform count near the Limon discharge although no regular monitoring program is known to exist. Studies of coastal waters have found total coliforms (TC) to be twice that of faecal coliforms (FC). In U.S., more common values of TC:FC are 5:1.
  • In Guatemala out of 27 treatment facilities there are 16 wastewater treatment plants in the metropolitan area, but only 4 of them are in full operation giving a total treated flow below 0.1 m3/s. Only 15 municipalities out of 286 have wastewater treatment plants comprising Imhoff tanks, lagoons, trickling filters, and activated sludge. Many treatment facilities are impaired due to poor design, lack of spares, and shortage of qualified operators.

Table 5.6: Treatment of sewage in Colombia.


  • In El Salvador, sewage treatment is poorly available, with 31 small plants under operation using various treatment systems such as tricking filters, stabilization ponds, activated sludge, Imhoff tanks, and oxidation ditches, for a total flow of 123 l/s.

  • According to SANAA, the operating unit, only 11 of the 55 major sewerage systems of Honduras have wastewater treatment plants.

  • In Panama 6 sewer systems serve 95% of coastal population. 4 of these systems have primary treatment (10% of coastal population); 2 systems discharge raw sewage (85% of coastal population). No information available on monitoring programs. Water quality criteria have been recently adopted based on WHO/PAHO standards.

  • In Paraguay, raw sewage from Asunción, the Country’s capital is discharged from 5 outfalls to the Paraguay River at a rate of 1.5 m3/sec. Improvements in this service are to be implemented soon. In the last years the Itu and San Estanislao sewage treatment systems were remodelled.

  • It is estimated that in Peru 83% of the urban sewage discharges to water bodies, whether coastal areas, rivers, lakes, or even agriculture lands with no control or treatment whatsoever. For the Greater Lima the sewage flow is around 23 m3/s. Only 1.0 m3/s comes from secondary treatment plants and then diverted to agriculture use. After the implementation of the Southern Lima Sewerage Project in the forthcoming years it is expected that an additional 9.6 m3/s will be treated, so increasing the capital’s sewage treatment to about 39%. As a result of the projects to be implemented in the interior of the Country in the coming years, the National coverage for sewage treatment shall increase to a figure of 40%.

  • In Paramaribo, the Suriname’s capital, 15% of the population still use pit latrines and 5% have no facilities at all, so that the level of sewage treatment, estimated at about 1%, is fairly within the overall low level of coverage.

  • In Venezuela the percentage of treated wastes does not exceed 5%, with only 6% out of the 40 m3/s of the sewage collected in the urban areas being treated. The majority of this treatment occurs on Margarita Island, a tourist destination. The remaining untreated flow is diverted into water bodies in and around Caracas, the Country capital, and other major cities. Isolated industrial discharges receive treatment, but residential areas are typically served by gravity sewers leading to outfalls in nearby rivers or streams. In the year 1995 there were in Venezuela 12 sewage treatment plants and 44 sewage treatment ponds serving 11 serving cities, all of them with a population less than 25,000 people with the exception of Nova Esparta, where the sewage flow is around 2,000 m3/s. A set of new plants, including the 2,000 m3/s extended aeration plant to be put into service in Maracaibo, for one million people are to be built. Upon completion, the new facilities will increase the population served by domestic sewage treatment in Venezuela from 3 to 25 percent. There is a significant industrial load as well as oxygen depletion and coliform contamination of rivers. Monitoring and compliance programs are being implemented. National standards for coastal water quality criteria were developed in 1983 based on EEC, WHO, and U.S. EPA guidelines.

The Consultative Meeting on Excreta and Wastewater Disposal in Latin America and the Caribbean in 1991 identified the following critical issues for the subsector which are still to be addressed seriously:

  • Political support. One of the critical aspects of the problem is the low level of political support on the part of governments and relevant national sector institutions due to several factors including a lack of environmental policies. This has led to a general absence of awareness on the part of the population. With the increased resultant pollution and their effect on water quality, in particular the deterioration of water sources, the need for integrated water resources management and waste treatment and disposal will become a major issue in Latin America.

  • Financing of wastewater facilities. Many problems were identified in relation to involving both the international financing agencies and the governments, including the lack of capacity of national institutions and the need to change the methodologies and criteria used for financing wastewater facilities by the international financing agencies.

  • Other main issues identified were the inadequacy and/or non-existence of environmental policies and institutional deficiencies, and the need for developing and applying appropriate technological and engineering standards for waste disposal.

A new initiative to concentrate on the waste treatment needs of the Region through co-operation between the countries and the international financing agencies was recommended. This initiative emphasized the development of projects for collection and treatment of wastewater and the control of water pollution.

Greater participation of professional organizations and pressure groups was seen as an essential element to support the development of appropriate environmental policies and to address environmental issues related to waste treatment pollution. The strengthening of environmental education programs to promote community awareness and participation was also recommended to improve sector policies.

It can be mentioned, as per PAHO documents, that up to 90% of the sewage generated in the Region are discharged under no treatment whatsoever either to the environment or to 500.000 ha of agriculture lands, thus producing serious public health and environmental hazards.

The figures above show undoubtedly how serious the situation of sanitation coverage and sewage treatment is in S&CA. The conventional counter-attack measures would include a detailed survey of the needs with capital and running costs to be incurred using updated technology for collection, treatment and final disposal. Such an exercise has been made many times, though with poor results, because they fall far beyond the available resources, and almost nothing happens. As a result a surge towards concessions for (water and) sewage services to the private sector has swept the Region, along with major support being provided by multilateral agencies such as the World Bank and IDB. But even though the major problem will subsist: the public water and sewerage companies in general are running short of capital which makes it impossible for them to expand investments in sewerage and sewage treatment; and the recently privatised companies will likely have to increase tariffs so as to expand their services. Will this approach prove feasible?

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