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.
| Proportion of
Treated Waste by Level
|* 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
- 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
- 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
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
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
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?