Wastewater crops feeding millions
Thalif DEEN
Vegetables, rice and other cereals in at least 53 cities in Asia,
Africa and Latin America may someday come with warning labels that read
“this is a byproduct of raw sewage”.
Against the backdrop of rising food prices and a shortage of drinking
water worldwide, urban farmers are being forced to use either untreated
wastewater or polluted river water both for their agricultural needs and
for their economic survival.
A 53-city survey finds the practice most common in some of the
world’s poorer nations where wastewater use is critical both to farmer’s
incomes and urban food security while simultaneously raising critical
health risks.
Wastewater treatment |
Wastewater agriculture |
The study conducted by the Sri Lanka-based International Water
Management Institute (IWMI) and released to coincide with World Water
Week in the Swedish capital of Stockholm indicates that about 80 percent
of the cities surveyed are using untreated or partially treated
wastewater for agriculture.
In over 70 percent of the cities studied, more than half of urban
agricultural land is irrigated with wastewater that is either raw or
diluted in streams.
The use of waste water, which usually includes sludge, industrial
effluent, kitchen and bathroom waste, is a widespread phenomenon,
occurring on 20 million hectares across the developing world, according
to the survey.
This is particularly prevalent in Asian countries, including China,
India and Vietnam, but also around nearly every city of sub-Saharan
Africa, as well as in many Latin American cities, including Lima,
Santiago, La Paz, Bogota and Sao Paulo.
The study says that wastewater is most commonly used to produce
vegetables and cereals, especially rice, raising concerns about health
risks for consumers, particularly in vegetables consumed uncooked.
At the same time, wastewater agriculture contributes importantly to
urban food supplies and helps provide a livelihood for the urban poor,
especially women, and recent migrants from the countryside.
As a notable example, the study points out that Accra, Ghana’s
capital city with an urban population of nearly 2.0 million people,
illustrates those tradeoffs particularly well.
An estimated 200,000 of the city’s inhabitants make daily purchases
of vegetables produced on just 100 hectares of urban agricultural land
irrigated with wastewater.
Consumers across the 53 cities said they would prefer to avoid
wastewater produce. But most of the time, they have no way of knowing
the origin of the products they buy.
Farmers too are aware that irrigating with wastewater may pose health
risks both for themselves and the consumers of their produce, but they
simply have little choice, since safe groundwater is seldom an
accessible alternative, according to the IWMI report.
The negative and positive implications of wastewater agriculture have
only recently received attention, says Colin Chartres, director general
of IWMI, which is supported by the Consultative Group on International
Agricultural Research (CGIAR).
This study, he said, offers the first comprehensive, cross-country
analysis of the conditions that account for the practice and the
difficult tradeoffs that arise from it.
Asked if benefits outweigh health risks, Liqa Raschid-Sally of
IWMI-West Africa and lead author of the study, told IPS there are no
comprehensive studies on benefits versus risks.
“But it is abundantly clear that if you put an immediate stop to
this, you will certainly cut off supplies of some types of vegetables to
cities, as almost 75 percent of the cities source at least some of their
vegetables from urban and peri-urban agriculture which uses wastewater.”
Simple economics, she argued, will indicate that this would cause a
rise in vegetable prices in cities.
The health risks can be managed because there are various
interventions on farms, markets and households which can effectively
reduce the health risks.
In Indonesia, Nepal, Ghana and Vietnam, for example, farmers store
wastewater in ponds to allow suspended solids to be eliminated. And
inadvertently, this practice also permits worm eggs to settle out,
possibly reducing bacteria in the water.
In Ouagadougou, Burkina Faso, farmers using water from a brewery
build storage basins for wastewater and fill them only when they judge
the quality of the wastewater to be acceptable (that is, not acidic),
based on its appearance, odour and even taste.
So the message to the poorest nations is that they can apply these
methods to reduce the risks and it just needs to be incorporated within
agriculture extension services, Raschid-Sally said.
“This is not an encouragement to use wastewater but a push to improve
practices,” she added.
Pay Drechsel of IWMI Ghana said the benefit and risk factors can be
at two levels: farmers and society.
In poor nations, where sanitation is not keeping pace with
urbanisation, farmers often have no other choice than to use polluted
water. Discontinuing it by law would threaten thousands of farm
livelihoods, with an individual impact of poverty much higher than the
pathogen exposure, which is manageable.
Moreover, irrigating cash crops near cities in many cases helps the
farmer to jump over the poverty line, allowing them a profit to buy key
inputs, such as pills for de-worming.
If there are alternative, safer water sources available, like
groundwater, or clean surface water in rural areas, combined with cool
transport for leafy vegetables, then this is certainly the preferred
option for a safe supply of perishable vegetables, experts say.
“Wherever this situation is not given, we agree with the World Health
Organisation (WHO) that it is not necessary to stop wastewater
irrigation,” Drechsel told IPS.
To maintain the urban supply with these vegetables, the WHO is
recommending multiple barriers which can easily reduce the pathogen
level on the crop.
“We tested and verified this approach. Its implementation, however,
requires behaviour change and social marketing of food safety, like we
see it in hand-washing campaigns,” he noted.
The situation is different in emerging economies where the chemical
industry is posing an additional threat, Drechsel added.
Asked if the use of wastewater is also part of the problem relating
to the global water crisis, Raschid-Sally told IPS it certainly has to
do with water scarcity in some cases, and the lack of alternative clean
water sources in others.
“This is part of the global water crisis from a water quality
perspective, where uncontrolled discharge of wastewater is polluting
large volumes of fresh water,” she added.
Drechsel said there is a significant water quality dimension which is
interlinked: “On the one hand, where wastewater is not or only partially
treated it is polluting and further diminishing our clean water
resources.
On the other hand, where we are able to make an asset out of
wastewater, we are gaining a valuable resource back.” |