Wetlands the answer to ‘invisible’ wastewater crisis?

Constructed wetlands are a low-cost alternative to conventional wastewater treatment. Copyright: Courtesy of Green Growth Group Mexico SA de CV.

Speed read

  • Low-cost constructed wetlands technology requires little specialised labour
  • Some developing countries discharge 95 per cent of wastewater without treatment
  • But, wetlands need land, inefficient at eliminating phosphorous

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Developing countries are failing to use nature-based solutions to solve wastewater crises, leaving contaminated water to pollute environments, drinking water sources and urban areas.

Indonesia is suffering an “invisible crisis of wastewater management”, where 95 percent of contaminated water flows into rivers, agricultural fields and groundwater sources through leakage or unsafe disposal, according to The World Bank.

Untreated wastewater is particularly hazardous in mountain areas, where it can rapidly connect between surface water bodies and underground water that moves over large distances, say researchers in Lebanon, a country on the eastern Mediterranean coast where 92 per cent of wastewater is discharged without treatment.

“Conventional [wastewater treatment] systems, which are more expensive to install and operate, have been used more in regions where there is less money for their implementation and operation, which explains the high rate of abandonment.”

Marco Rodríguez, Department of Biology, University of Aarhus

While constructed wetlands have been used to treat wastewater across Europe and the United States since the 1970s, their use remains limited in the global South.

In Denmark, there is one constructed wetland for every 5000 people, but just one for every 1.5 million people in Latin America and the Caribbean — meaning just 0.22 per cent of effluent is processed this way, according to Marco Rodríguez, a researcher at the Danish University of Aarhus’ Department of Biology and lead author of a 10-year review of constructed wetlands use in Latin America and the Caribbean, published in the journal Water (18 June).

Constructed wetlands use natural mechanisms to separate contaminants from households, industry, agriculture and livestock, as well as the liquid that drains to the bottom of landfills and can contaminate groundwater. Effluent is discharged into reservoirs before natural filters, such as gravel or clay, and aquatic plants and microorganisms purify the water.

Vertical Flow Constructed Wetland diagram
Vertical Flow Constructed Wetland diagram.

“With low implementation and operating costs, [wetland] operation requires little specialised labour, without generating technological dependence,” says Rodríguez.

María Alejandra Maine, from the Chemical Engineering School at Argentina’s National University of the Littoral, who did not participate in the review, says constructed wetlands should be used more widely. She says the geography in Latin America and the Caribbean offers ideal conditions for these systems, including warm temperatures, large areas of soil and long periods of light radiation.

Yet, the technology is only used to treat wastewater from university campuses, tourist resorts and small towns in a handful of countries, Maine says. In Latin America and the Caribbean, 60 per cent of wastewater goes untreated.

Climate change is leaving many regions facing water scarcity. Demand for water is making finding water treatment and recycling solutions increasingly urgent.

Nature-based education

Engineering education fails to consider nature-based solutions for water infrastructure in urban contexts, a study to be published next month (20 August) in the Journal of Clean Production argues, adding that this should be a focus in developing countries.

“The alarmingly low rate of wastewater treatment is becoming obvious,” The World Bank said in a 2019 review of Indonesia. “The fetid smell and grey canals in Jakarta’s metropolitan core … are stark and vivid reminders that only two per cent of households in a population of 10 million are connected to public sewers.”

Constructed wetlands could offer an affordable and accessible solution for lower-income countries, says Rodríguez.

“Conventional [wastewater treatment] systems, which are more expensive to install and operate, have been used more in regions where there is less money for their implementation and operation, which explains the high rate of abandonment,” Rodríguez tells SciDev.Net.

About one quarter of the more than 3500 conventional treatment plants in Mexico have been shut down, the review found.

Urban limits

But, wastewater treatment specialist Christoph Platzer says “the wetlands are reaching the limit of their possibilities” in Latin America, where there is a growing need for sanitation solutions.

Platzer, director of private Brazilian sanitary engineering company Rotária and founder of the Global Wetland Technology consortium, says Nicaragua is the only country using this technology on a large scale, to treat municipal wastewater through the public Nicaraguan Water and Sewerage Enterprise (ENACAL).

Wetlands require more land for construction than other systems and are inefficient at eliminating phosphorous, an element present in large quantities in fertilisers, the Water review found.

There is also a lack of a regulation, design guidelines and incentive schemes. “In most countries in the region there is no legislation regulating wetlands, ignoring the important environmental services that these ecosystems provide,” Pablo Filippo, a specialist in natural resources law at the University of Buenos Aires who was not involved in the review, tells SciDev.Net.

While it is technically possible to build constructed wetlands in Latin America, Platzer says, it remains to be seen whether their set-up costs will make them a viable option in the region.

This piece was produced by SciDev.Net’s Latin America & Caribbean desk.