Background | Bogotá River, Colombia

Bogotá is the capital of Colombia. The city is located on la Sabana de Bogotá, a highland plateau at an average of 2,550m above sea level (see Fig. 1). The Sabana is an important agricultural region, owing its productivity to fertile soils and the system of rivers, tributaries, and aquifers. The city of Bogotá has experienced rapid urbanization (see Fig. 2) in the past few decades and has a population of approximately 8 million people today. The relatively unplanned development has resulted in environmental degradation, particularly the contamination of water sources which has led to a substantial deterioration of water quality in the region.

The city of Bogota is bordered by the Eastern Andean Ranges (Cordillera Oriental) to the east, and the Bogotá River (Río Bogotá) to its west (see Fig. 3). The Bogotá River is a major river in the region. The river runs northeast to the southwest, and can be divided into three sub-basins – cuenca alta, cuenca media, cuenca baja –  upper, mid, lower (see Fig. 4). The mid-basin of Río Bogotá consists of various densely populated municipalities, including the city of Bogotá (see Fig. 5).

 

 

 

 

Problem | Pollution of the Bogotá river

 

The Bogotá river is considered one of the most contaminated rivers in the world. Pollution occurs throughout the Rio Bogota watershed. Pollutants include industrial, domestic and agricultural waste (see Fig. 7)

As seen on the map below (Fig. 8), water quality varies across the Río Bogotá watershed – with the mid-basin – where the city of Bogotá is located, having the worst water quality (Class VII and VIII – magenta and black lines in the map) in the entire stretch of the river. For reference, Class I and II water quality corresponds to Human and domestic consumption. Class III water quality is assigned to the untreated water in reservoirs and natural wetlands, Class IV corresponds to water quality suitable for agricultural and livestock use, Class V water quality is suitable for energy generation and industrial use.

Fig. 9 below shows dissolved oxygen levels throughout the Río Bogotá watershed. Dissolved oxygen (DO) is an important indicator of water quality. It is essential for the survival of fish and other aquatic life. As seen on the graph, dissolved oxygen levels drop to zero in the mid-basin of Río Bogotá. Besides the impact on biodiversity and natural habitats, contamination of Río Bogotá also has negative impacts on public health and quality of life (see Fig. 10).

 

 

 

 

 

 

As seen in Fig. 8 above, water pollution reaches its peak (Class VIII) as the river runs through the city of Bogotá. 90% of the pollution of Bogotá river comes from the three main tributaries within the city – Salitre, Fucha, and Tunjuelo (see Fig. 10). The city generates 16,000 liters of wastewater per second, only 25% (4,000 liters) of which is directed and treated at the Salitre PTAR (Planta de Tratamiento de Aguas Residuales, or wastewater treatment plant). The rest is directly discharged without any treatment into the Bogotá river. Within the city of Bogotá, domestic and industrial sources are the main contributors to pollution of Río Bogotá. Domestic pollution accounts for 76% of the total pollution generated by the city that is discharged into the river. Some examples of pollutants include: household wastes (detergents/grease/sewage), industrial chemicals/heavy metals (chromium/lead/mercury/color dyes), and solid waste (construction debris/car tires/scrap wood/trash).

Existing plans to restore the Bogotá river have focused on infrastructural solutions to address the problem of water pollution. There have been calls for the expansion of the existing Salitre WWTP and proposal of a larger treatment plant (see Fig. 11) further downstream since 2004. However, neither has been completed yet, mainly due to the high costs of infrastructure. Financing has only recently been secured for the new treatment plant. Construction is set to begin in 2020 and is expected to begin operation in 2024. Meanwhile, contamination of Rio Bogota continues.

 

 

Potential Strategies

There is no single “silver bullet” solution to water pollution. The pollution of the Bogotá river is a regional problem and will need to be addressed in an integrated manner with cooperation between municipalities across the watershed. However, considering the fact that the city of Bogotá contributes to most of the pollution (90%) of the Bogotá river, this blog post will focus on proposing strategies that are specific to the city. While the city’s existing infrastructural plan of constructing and expanding wastewater treatment capacity is necessary and will definitely help reduce contamination of the Bogotá river, the pollution problem still remains as the plan is undergoing implementation.

Having identified the three tributaries that cut across the city – Salitre, Fucha, and Tunjuelo as the main contributors to the overall contamination of the Bogotá river, this presentation will focus solutions on minimizing pollution in these tributaries in order to mitigate public health risks, improve quality of life, as well as the quality of water feeding into the river. A combination of policy and physical interventions will be needed to decrease pollution in the tributaries, and by extension, the contamination of the Bogotá river.

This blog post will discuss a potential complementary strategy – the installation of constructed wetlands along tributaries for wastewater filtration and treatment – and consider its implementation on a specific site.

 

 

Constructed Wetlands

Constructed wetlands are engineered systems consisting of vegetation, aquatic plants, and organisms, and can be used for storm/wastewater treatment. The treatment process involves natural functions to remove pollutants such as suspended solids, organic matter, and nutrients to improve water quality. They tend to be located adjacent to natural water bodies in order to remove and minimize pollutants entering the receiving waters. Pollutants can be removed through various methods, such as adsorption (aquatic plant uptake), retention (sedimentation), filtration, and microbial decomposition. Removal rates can vary depending on pollutant characteristics and design of the wetland. Constructed wetlands are generally more effective for removing suspended solids/particulate matter than dissolved pollutants (see Fig.13).

 

 

Case Study | Ang Mo Kio-Bishan Park, Singapore

 

 

 

An example of constructed wetlands used to improve the water quality of a waterway is the Ang Mo Kio-Bishan Park in Singapore. What was once a concrete canal was naturalized into a meandering river (see Fig. 14) to provide flood control, water purification and filtration, as well as a recreational space for public use.

The park consists of a network of vegetated swales that provides filtration and a constructed wetland that treats and purifies the runoff through the use of specific aquatic plants. The vegetated swales are effective for removing coarse sediments, which helps to pre-treat the runoff before it enters the constructed wetlands. The runoff is then channeled through various stages of the constructed wetland. The wetland plants were selected for their ability to remove specific contaminants such as phosphorus, nitrogen, or copper. The water is then subjected to UV treatment to remove bacteria before being returned to the river.

It is important to note that the applicability of this case study to Bogotá requires consideration of the various conditions that contributed to the project’s feasibility and success. The success can be attributed, in large part, to Singapore’s political environment, institutional framework, access to financing and technical expertise, environmental and climatic conditions.

 

Constructed wetland strategy in Bogotá | site-specific intervention + barriers to implementation

Fucha tributary has the worst water quality (red line indicates poor quality – see Fig. 16) within the city of Bogotá. The Fucha tributary passes through major industrial zones where most of the city’s industrial waste is produced (see purple area in Fig.17). Industries include breweries, car washes, textile factories (dyeing and garment processing). Besides pollution from industrial chemicals, wastewater and debris, domestic waste, sewage, and stormwater are also drained into Fucha.

A site along the Fucha tributary has been selected – based on the availability of land/open space (allowing for installation of constructed wetlands), proximity to industrial and residential land uses, and presence of substantial pollution. The selected site is primarily low-middle income, and is surrounded by residential, commercial and industrial land uses.

Below are some photos of the site – there is an existing park abutting a polluted stretch of Fucha tributary. The area across Fucha is occupied mostly by commercial and residential uses, with substantial amount of waste piled up along the waterway. The Main Pollutants along this 700m stretch of Fucha include: stormwater runoff (non-point source pollutants), grease/oil/ detergents (restaurants/ residential), organic matter/sewage, residential/ commercial/ industrial wastewater, and solid waste/trash.

 

 

 

The proposed site-specific intervention is to expand the existing park along and across Fucha (see Fig. 19), with the addition of a network of vegetated swales and constructed wetlands lining the tributary. The expected outcome is that there would be a reduction in pollutant loads, improvement in water quality, decreased flood risk (slowing of flow/ water retention) and increased opportunities for public recreational use.

The local institutions that address issues of water in Bogota include the Bogota city government (Alcaldía de Bogotá), the water and sanitation utility (EEAB – Acueducto), and the Department of Environment (Secretaria Distrital de Ambiente). Preliminary technical documents exploring alternative options for sustainable urban drainage systems have been published by Bogotá’s Department of Environment. The documents examined feasibility and design of SUDS (Sistema Urbanos de Drenaje Sostenible), or sustainable urban drainage systems, and included plans for constructed wetlands for the retention and treatment of stormwater in various parts of the city. Moreover, there have been instances of schools installing constructed wetlands as part of an educational program, as well as increasing research being carried out by local universities to evaluate the capacity of constructed wetlands to reduce pollutants in order to improve the water quality of the Bogotá River.

Despite the increasing awareness of constructed wetlands as a potential strategy to address water pollution, there are still barriers to the implementation. These include: lack of institutional support, costs/ lack of financing sources, land ownership issues, resources for maintenance/ monitoring, lack of community buy-in, continued dumping etc. That said, this is a more of an experimental solution/ pilot project proposal- and will need to be implemented with other complementary strategies mentioned earlier in the blog post. Going forward, identification of possible financing mechanisms and feasibility studies will be required to examine the effectiveness, replicability, and scalability of the strategy along other parts of the tributary/ other tributaries.