Documento(s) 14 de 19

¹Irrigation and Water Engineering Group, Wageningen University, The Netherlands
²Centro de Aguas y Saneamiento Ambiental (CASA), San Simón University, Cochabamba, Bolivia
³ Centro Andino para la Gestión y Uso del Agua (Centro AGUA), San Simón University, Cochabamba, Bolivia
⁴Sub-Department of Environmental Technology, Wageningen University, The Netherlands

Abstract

In Cochabamba, Bolivia, wastewater is extensively used in urban and peri-urban agriculture. Both vegetable and fodder crops are irrigated with polluted water, i.e. diluted or partly treated municipal and industrial sewage containing high concentrations of pathogens, heavy metals and salts. Specifically in the downstream La Mayca area, where the farmers have an agreement with the municipal water and sewerage company, soil degradation has forced farmers to increasingly replace vegetable crops with more salt-tolerant fodder crops. In other areas around the city, cultivators deny using readily available wastewater, pointing to nearby wells as their water source. However, many wells are probably also polluted and do not yield enough water for the irrigated area served. Farmers state they are not confronted with specific health problems related to the use of polluted water, contradicting reports from local health workers. Low surface water flows and low rainfall, along with high (industrial) pollution and low wastewater treatment capacity mean that most of the water available to the farmers is of poor quality. Reduction of (industrial) pollution, increased treatment capacity and an integrated water management (IWM) approach, in which nearby good-quality groundwater could be used as a water source for blending with wastewater, represent options for improvement. However, strong traditional water rights, lack of urban planning, and weak institutions are constraints to the improvement of wastewater management in Cochabamba.

Introduction

In urban areas of many (developing) countries, urban and peri-urban agriculture depends, at least to some extent, on wastewater as a source of irrigation water. The quality of the water and the conditions under which this water is used vary greatly. In poor countries this water may, in extreme cases, take the form of diluted raw sewage, even if this is considered illegal.

Lack of infrastructure results in uncontrolled wastewater flow. Legislation on wastewater discharge and use is either poorly developed or not enforced. Partial treatment at secondary level, typical of overloaded treatment plants, and natural treatment before agricultural use are more common. In general, irrigation with effluent that has been treated up to secondary level can be considered a cost-effective and environmentally safe way of handling domestic wastewater.

In countries where legislation and control are strict and where the economic conditions allow, industrial wastewater is separated from domestic wastewater. Domestic wastewater may receive secondary and sometimes tertiary treatment before it is made available for crop production. Even then, legislation can restrict the type of crops that are allowed to be grown and the irrigation technology to be used. For vegetable crops that are consumed raw, the most stringent conditions are applied.

Bolivia is a typical example of a country where, due to poverty and lack of planning and management capacity, uncontrolled use of wastewater takes place. Cochabamba, the regional capital of the agricultural centre of the country, is a typical example of untreated wastewater irrigation resulting from a shortage of freshwater resources, high levels of pollution from industrial and domestic origin, and insufficient water treatment capacity.

Bolivia

Bolivia, a land-locked country in Latin America, can be divided into three ecological regions. The western part of the country (the Altiplano) is 3,800 m above sea level, cold and relatively dry (300–600 mm annual rainfall). The capital La Paz (almost 1.6 million inhabitants) is situated in a valley of the Altiplano. The sub-Andean region, with Cochabamba (855,000 population) as a major departmental capital, is situated between the Altiplano and the eastern lowlands. Here, average temperatures are between 15° and 18°C and annual rainfall from 380–700 mm. The eastern lowlands (the Llanos) cover about 57% of Bolivia’s total area. Their average temperature is high at 23^oC and annual rainfall between 1,100–1,900 mm. The biggest city here is fast-growing Santa Cruz (1.5 million).

In the major cities, the urban population has increased by a yearly average of 3–6% in the last 50 years and is estimated now at 62% of the total population of 8.3 million compared to 42% in 1976. For Cochabamba the urbanisation rate rose from 38% in 1976 to 59% in 2001 (Durán et al., 2003).

La Paz discharges all its wastewater, without any treatment, into the Choqueyapu river that runs through the city. Water from this river is used downstream for agriculture, including vegetable production.

Cochabamba is situated in the valleys between the Altiplano and the lowlands. Irrigated agriculture is focused on the production of fodder crops, including fodder maize and alfalfa, although many other crops, including vegetables, are grown for farmers’ own consumption. The city has one central wastewater treatment plant (WWTP) with a capacity of 400 l/s. Its effluent, that is of low quality due to overloading of the plant, is used for irrigation. In housing areas there are a large number of septic tanks and Imhoff tanks for primary treatment. However, few of them are functioning properly.

Santa Cruz, the second largest city of Bolivia after La Paz, has three WWTPs with a total design capacity of about 380 l/s, which is low given the population. The WWTP discharge is not used for irrigation, as the immediate surroundings receive sufficient rainfall to meet farmers’ needs.

In some other cities in Bolivia, the wastewater is of extremely poor quality, due to industrial activities. Such wastewater is discharged, without any treatment, into evaporation ponds, without any form of subsequent use.

Sewerage coverage is limited in Bolivia, particularly in comparison to other Latin American countries (World Bank, 1999). Yet, from Table 12.1 it can be seen that these coverage figures have increased enormously in the last 25 years, even more impressive if population growth in this same period is considered.

Table 12.1. Increase in access to water supply and sanitation in urban and rural Bolivia, 1976–97 (World Bank 1999).

^a Data on sanitation facilities include domestic connections to a sewerage network, latrines and septic tanks.

Actual Use of Wastewater in Bolivia

Wastewater use can be defined as direct or indirect and be characterised as formal or informal:

• In the case of direct use, untreated discharge from the sewer or effluent from the treatment plant is directed to the crops. This includes discharge released by intentional ruptures of the sewer pipelines by farmers. The wastewater, treated or untreated, is not diluted before being used. This is a common phenomenon in the areas where water is scarce, e.g. Cochabamba.
• Indirect use refers to the use of surface water that is polluted with wastewater, raw or partly treated. In this case the wastewater is diluted before use, certainly in the wet season. In Bolivia, indirect use of wastewater takes place in almost all rural and peri-urban areas downstream of the urban centres.
• In the case of formal use a convention or other type of agreement supports the use of (treated) wastewater. There is only one such case known in Bolivia. In Cochabamba, the irrigator’s organisation has an agreement with the municipal water and sewerage company (SEMAPA) for the use of their effluent.
• Informal use is not supported by any agreement. This is the case in most parts of Bolivia.

Table 12.2 gives an overview of the characteristics of wastewater use in Bolivia’s main cities. Most wastewater use is indirect and informal, and is limited to the arid and semi-arid regions: the Altiplano and the Valleys. In the case of the Llanos region, where the rainfall is high, crops do not require irrigation and the wastewater is simply discharged into the rivers that are an important source of fish for indigenous people living downstream in the forests.

When wastewater in Bolivia is used directly the irrigators have at least some insight or opinion about the advantages (availability, nutrients) and disadvantages of such use. In the situation of indirect use, however, the irrigators consider that the pollution of the river damages their agricultural activities.

Table 12.2. Characteristics of wastewater use in peri-urban areas of the main cities in Bolivia (Durán etal., 2003).

Wastewater Use in and Around Cochabamba

The downstream area of Cochabamba known as La Mayca is served by the Sistema Nacional de Riegos No. 1 (SNR-1) Irrigation Scheme. Before 1980, this Scheme received its irrigation water from the Angostura Dam and partly from the small Rocha river that crosses Cochabamba. Since the construction of a new airport, part of SNR-1 was cut off from these supply sources. To solve this, the farmers agreed with SEMAPA to irrigate with effluent from the Alba Rancho facultative stabilisation pond treatment plant, constructed in 1986 that has a design capacity of 400 l/s. Other farmers depend more on the water from the Rocha river and from two smaller rivers, the Tamborada and the Valverde. These rivers, however, have increasingly been polluted due to the growing urban population and the uncontrolled discharge of industrial and domestic wastewater. Actually, in the dry season the natural water flow of the river is virtually zero, which means that almost all the discharge is domestic and industrial wastewater.

The irrigated area downstream of Cochabamba can be divided into several zones, each of which uses a different mix of water, depending on location, season and general water availability (Fig. 12.1 and Table 12.3). Most water flows by gravity, although in some places it is pumped to irrigate fields located higher up the valley. Some farmers have a choice between water sources, including wells, depending on water availability.

In the entire area surface flood irrigation is practised. Average farm size ranges from 1–5 ha. The farms have a relatively high cattle density at 12 animals per family. The milk is mostly delivered to Cochabamba dairies although farmers increasingly process part of their milk production into cheese.

Apart from alfalfa and fodder grass (Lolium sp.), maize, potato and beans are cultivated. However, due to increasing salinisation in the area, farmers are increasingly shifting to Lolium fodder grass that is salt-tolerant. Some plots are no longer cultivated because of soil degradation.

Because all farmers do not use rubber boots and gloves for protection during irrigation, this results in infections. Farmers in this area do not complain about their health, yet 80% of them are known to have skin mycosis (Agreda, 2000).

Fig. 12.1. Map of the La Mayca irrigated area downstream Cochabamba, Bolivia.

Table 12.3. Area irrigated (ha) from different sources depending on water availability in La Mayca, Cochabamba.

Source: Consultora Galindo Ltda., 2001.

Table 12.4. Quality of water from different irrigation sources in La Mayca, Cochabamba.

Source: Agreda, 2000.
^a Samples taken at different dates during the dry season: September–November, 1999.
^b The analyses for heavy metals included those for lead and cadmium. These metals were not detected.
^c No data available.
^d For crops consumed raw.
^e For processed crops and fodder.
^f Data from SEMAPA.

The data in Table 12.3 show that, of a total irrigated area of 1,578 ha almost 50% is wastewater-irrigated in dry years and up to 40% with polluted surface water from small rivers. Only 16% of the area (253 ha) is assured of freshwater from the Angostura Dam in a dry year.

Table 12.4 gives water quality data as measured in this region. Farmers complain about the quality of irrigation water, specifically, about the degradation of their plots through salinisation. The industrial discharge (from tanneries) and the increasing use of wastewater might well be a cause for this, although the effects of the poor internal and external drainage of the area and the excess water applied to the fields should also be considered.

The inflow to the treatment plant exceeds the design capacity by almost 50%. The high inflow load and poor dilution of waste concentrations resulting from the low per capita average daily water consumption of 80 l result in the poor quality of the WWTP effluent.

Even though there are strict by-laws that forbid this, industries discharge their wastewater without treatment into the domestic sewerage system or directly into the surface water. This is an important environmental threat, and has already led to a build up of heavy metals in the soil profile, with extremely high concentrations of cadmium (Cd), chromium (Cr⁶⁺), and lead (Pb) (Table 12.5).

During a field visit in October 2002 it was observed that wastewater is also used in the upstream parts of the city, immediately downstream of some housing areas that have been provided with communal primary treatment facilities (Imhoff tanks) at some distance from the housing. The main objective of an Imhoff tank is to reduce the suspended solids load in the receiving surface water. Because of the design of the Imhoff tank system there is no further treatment of waste at the secondary level. The local community was asked to assign and pay a person to maintain these primary treatment systems. But, the community has no incentive to maintain the systems, and consequently they malfunction. As a result, sewage water is now being discharged into open drains and subsequently used for small-scale irrigation, including vegetables.

Institutional Aspects

The use of (treated) wastewater in (peri-)urban agriculture is directly linked to urban water supply, sanitation and wastewater treatment capacity since water-supply organisations are also usually responsible for sewerage and wastewater treatment. In Bolivia, different institutions have a role to play (Durán et al., 2003):

• The Ministry of Housing and Basic Services (Ministerio de Vivienda y Servicios Básicos) includes among its responsibilities: the definition of sector policies and priorities, formulation of norms and regulations for the sector, planning sector development, promotion of research and human resources development programmes, channelling of financing and investments, the establishment of a sector-wide information system, and the supervision of the Superintendent of Basic Sanitation (see below).
• The Ministry of Sustainable Development and Planning (Ministerio de Planificación y Desarrollo Sostenible), in coordination with the Ministry of Housing and Basic Services, plays a role in the formulation and application of the environmental norms related to water supply and sanitation. It also oversees water quality.
• A Superintendent of Basic Sanitation (Superintendencia de Saneamiento Básico, SIASAB) is mandated to regulate water supply and sanitation services in the urban and rural sectors. In particular, SIASAB oversees the quality of service provision, approves tariffs according to sector regulations, grants concessions from customers, and applies fines.
• The Prefectura, with responsibility at the Department level for formulating investment projects, plans service expansion programmes and projects, supervises works, and provides technical assistance to the service companies. It actually works mainly in the rural areas.
• The Popular Participation Law and the Law of Municipalities transferred ownership and operational responsibility for provision of water supply and sanitation services to municipal governments, enlarging their roles and responsibilities. It is also the Municipal governments’ task to develop plans and programmes for the expansion of water supply and sanitation services, in coordination with the Prefectura.

Table 12.5. Occurrence of heavy metals (mg/kg dry soil) in soil of the La Mayca area, Cochabamba, Bolivia (Agreda, 2000).

Table 12.6. Estimated wastewater production in 2020, based on population data for various Bolivian cities (Durán et al., 2003).

^a Authors’ estimate.
^b Estimated discharge Q = cPD/86400 where: c = discharge coefficient (0.8), P = population, and D = water supply per capita (average value: 80 l/day).

Presently, there are four types of institutional arrangement for the management of water supply and sanitation:

• Cooperatives: of which there are 120, mainly in Santa Cruz and Tarija
• Autonomous municipal companies: the main ones being in Cochabamba (SEMAPA), Sucre, and Potosí
• Concessions with the private sector: which only exist in La Paz and El Alto (Aguas del Illimani). This model provoked great social conflicts in the city of Cochabamba after its introduction in 1999 and the company (Aguas del Tunari) was forced to withdraw in April 2000, handing back the administration to SEMAPA.
• Water committees: formed with contribution and participation at the neighbourhood level.

Costs for wastewater treatment are included in the price of drinking water, which is already high in Cochabamba (US$0.23/m³) compared to the prices charged by other (rural) drinking water suppliers (US$0.10–0.20/m³), who only recover operational costs. The tariff for sewerage and wastewater treatment varies from 40–65% of the drinking water price. Although people seem to be aware and prepared to pay for wastewater treatment, a recent decision to further increase the drinking water price to allow more and better treatment had to be withdrawn, after violent protests by the Cochabamba city population. This is a significant backwards step in improving the water quality for the irrigators, if indeed wastewater treatment were to be made effective.

The general lack of urban planning and management capacity in Cochabamba affects this situation. The municipal authorities have not been capable of steering the rapidly expanding city. Comparing the state of the Rocha river now to its situation in the 1990s reveals major differences in discharge and water quality (A.M. Romero, Cochabamba, 2002, personal communication). Cochabamba has also been confronted with uncontrolled housing construction that has certainly increased water pollution. There is a clear lack of land use planning that should cope with the growth in wastewater and its management. In Bolivia, water is available for those people who have established water rights that are closely linked to irrigation. This automatically means that people and institutions without such traditional rights have limited access to (good quality) water.

Agricultural Potential

A significant area in and around Cochabamba currently depends on untreated and treated wastewater for irrigation, especially in the dry years. In the coming 20 years, the volume of wastewater is expected to double (Table 12.6) and those farmers that have no or insufficient access to other water sources will certainly try to use wastewater. Although wastewater is of inferior quality because of its high salt contents and possibly even contains toxic elements, the farmers will first consider that it is the most reliable source of water. Contrary to supplies of surface water or water from a formal irrigation scheme, wastewater flow is increasing in volume and is available all year round.

Discussion and Conclusions

Treated domestic wastewater should be considered as a valuable source of water for irrigated agriculture. If well managed, such use is productive, cost-effective and environmentally safe. However, the way wastewater is actually used in Cochabamba is far from ideal and poses a number of health risk and environmental pollution problems. To avoid an environmental crisis, several things need immediate action.

The wastewater flow in Cochabamba partly originates from industries, including tanneries. This wastewater contains salts and such toxic elements as chromium (Cr⁶⁺), that are harmful to crop production and/or are polluting the environment. As a first and immediate step, industries should be forced to reduce the contaminant load in their discharge by, for example, pre-treating their wastewater before discharging it. Special attention should be given to industries like the tanneries that discharge high quantities of soluble salts which degrade soils in the downstream irrigated area by rendering them saline.

Investments are required to improve the drainage of lower-lying areas. Observed salinity problems should also be studied in relation to the irrigation techniques used. A change in these techniques (possibly in combination with a change in the types of crops cultivated) might help to reduce this problem. However, such modern irrigation techniques as micro-irrigation, are expensive and do not completely reduce the risks of salinisation. It should be realised that irrigation with moderately saline water is possible so long as there is appropriate drainage for leaching. This would, however, transfer the salts to the drainage water that would undoubtedly be discharged again into the river.

An increase in the city’s water treatment capacity is badly needed. In developing this capacity, care should be taken to invest in appropriate technology that can be managed within the limited available financial and managerial resources. In other countries, like Brazil, Colombia, and India, systems such as the upflow anaerobic sludge blanket (UASB) have been developed; these are not dependent on electricity and can provide adequate contaminant reduction with minimal maintenance (van Lier and Lettinga, 1999).

The present situation calls for a decentralised water treatment approach, given the fact that wastewater is produced and used for irrigation in different areas in and around the city. Decentralised systems can be initiated far more rapidly than large capital-intensive centralised treatment plants. In the Brazilian city of Recife a decentralised approach has been officially included in the sanitation and sewerage master plan of the city (Florencio and Kato, 2001). The Water and Environmental Sanitation Centre, [Centro de Aguas y Saneamiento Ambiental (CASA)], of Cochabamba, could play an important role in technology choice, with specific attention to the requirement for low-maintenance systems If maintenance of the decentralised systems depends on local community initiative, then the community should also benefit from its investment. This means that farmers from the same community that treats the wastewater should be able to use the treated effluent.

An integrated water management (IWM) approach is surely needed to improve the present situation in Cochabamba. Farmers who now have direct access to wastewater flows and those just beyond are irrigating with water of extremely different qualities. An irrigation supply system that would allow mixing of water from different sources to manage the high salt content should be considered. At the same time, sanitation, wastewater treatment, and subsequent agricultural use should be based on a conceptual design framework in which the water flow from source to irrigation and drainage is subject to holistic management that also considers cost-effectiveness and environmental issues (Martijn and Huibers, 2001). An interdisciplinary and participative approach is needed. In common with most of Latin America, the Bolivian irrigators are organised in such a way that they represent themselves well in negotiations and could be partners in a design process.

Creating awareness among actors, building management capacity, extension, and communication are all seen as important ways to improve the present situation and to support future development.

Irrigated farming around Cochabamba presents an example of a degrading agricultural system caused by water pollution particularly that resulting from uncontrolled discharge of industrial liquid waste into surface water, and the use of irrigation techniques without drainage required to effectively manage the poor water quality.

Acknowledgement

We acknowledge support of the Dutch-financed programme Partners for Water. Facts and figures used in this chapter originate mainly from the W4F-Wastewater Project, realised under this programme. Authors and contributors of the original document include Oscar Moscoso and Ana Maria Romero of the Centro de Aguas y Saneamiento Ambiental (CASA) and Elena Villaroel, Martine Jeths and Alfredo Durán of the Centro Andino para la Gestión y Uso del Agua (Centro AGUA), San Simón University Cochabamba, Bolivia.

References

Agreda, E. (2000) The problematics of the use of polluted water in agriculture under irrigation. Case study Rocha River – La Mayca and Caramarca areas. MSc Thesis. Wageningen University, The Netherlands (unpublished).

Consultora Galindo Ltda. (2001) Estudio de Factibilidad del Traspaso del Sistema Nacional de Riegos Nº 1, Cochabamba-Bolivia, pp. 15–16.

Durán, A., Moscoso, O., Romero, A.M., Huibers, F.P., Agodzo, S.K., Chenini, F. and van Lier, J.B. (2003) Use of wastewater in irrigated agriculture. Country studies from Bolivia, Ghana and Tunisia, Volume 1, Bolivia. Water for Food – Wastewater Project, Wageningen University, The Netherlands, 55 pp.

Florencio, L. and Kato, M. T. (2001) Perspectives of anaerobic treatment for domestic sewage in Recife Metropolitan Region. In: van Lier, J.B. and Lexmond, M. (eds) Proceedings of the Gatze Lettinga Farewell Symposium, Anaerobic Digestion for Sustainable Development, Wageningen, 29–30 March 2001. Sub-Department of Environmental Technology, Wageningen, The Netherlands, pp. 17–26.

van Lier, J.B. and Lettinga, G. (1999) Appropriate technologies for effective management of industrial and domestic wastewaters: the decentralised approach. Water Science and Technology 40(7), 171–183.

Martijn, E.J. and Huibers, F.P. (2001) Use of Treated Wastewater in Irrigated Agriculture: A Design Framework. Development of cost-effective reclamation technologies for domestic wastewater and the appropriate agricultural use of the treated effluent under (semi-)arid climate conditions (CORETECH) Working Document WP4-3. Wageningen, The Netherlands, 33 pp.

World Bank. (1999) Cited in Moscoso, O. and Coronado, O. (2002) Proyecto regional de sistemas integrados de tratamiento y uso de aguas residuales en América Latino. Caso de estudio: ciudad de Cochabamba. Viabilidad del uso del agua residual tratada, CEPIS-OPS (Centro Panamericano de Ingeniería Sanitaria y Ciencias del Ambiente-Organizatión Panamericana de la Salud) Lima, Perú. pp. 14–18, 63–66.

Documento(s) 14 de 19