Human Waste Used by 200 Million Farmers, Study Says

Tasha Eichenseher in Stockholm, Sweden
for National Geographic News
August 21, 2008
Facing water shortages and escalating fertilizer costs, farmers in developing countries are using raw sewage to irrigate and fertilize nearly 49 million acres (20 million hectares) of cropland, according to a new report—and it may not be a bad thing.

While the practice carries serious health risks for many, those dangers are eclipsed by the social and economic gains for poor urban farmers and consumers who need affordable food, the study authors say.

Nearly 200 million farmers in China, India, Vietnam, sub-Saharan Africa, and Latin America harvest grains and vegetables from fields that use untreated human waste.

Ten percent of the world's population relies on such foods, according to the World Health Organization (WHO).

"There is a large potential for wastewater agriculture to both help and hurt great numbers of urban consumers," said Liqa Raschid-Sally, who led the study published by the Sri Lanka-based International Water Management Institute (IWMI) and released this week at the World Water Week conference in Stockholm, Sweden.

Health Risks

The report focused on poor urban areas, where farms in or near cities supply relatively inexpensive food. Most of these operations draw irrigation water from local rivers or lakes. Unlike developed cities, however, these areas lack advanced water-treatment facilities, and rivers effectively become sewers.

When this water is used for agricultural irrigation, farmers risk absorbing disease-causing bacteria, as do consumers who eat the produce raw and unwashed. Nearly 2.2 million people die each year because of diarrhea-related diseases, including cholera, according to WHO statistics. More than 80 percent of those cases can be attributed to contact with contaminated water and a lack of proper sanitation. But Pay Drechsel, an IWMI environmental scientist, argues that the social and economic benefits of using untreated human waste to grow food outweigh the health risks.

Those dangers can be addressed with farmer and consumer education, he said, while the free water and nutrients from human wastewater and feces can help urban farmers in developing countries to escape poverty.

Waste Into Water

Agriculture is a water-intensive business, accounting for nearly 70 percent of global fresh water consumption.

In poor, parched regions, untreated wastewater is the only viable irrigation source to keep farmers in business, according to Drechsel. Mark Redwood, a senior program officer with the Canadian International Development Research Centre, said that in some cases, water is so scarce that farmers break open sewage pipes transporting waste to local rivers.

Irrigation is the primary agricultural use of human waste in the developing world. But frequently untreated human feces harvested from latrines is delivered to farms and spread as fertilizer.

In most cases, the excrement is used on cereal or grain crops, which are eventually cooked, minimizing the risk of transmitting water-borne pathogens and diseases, IWMI's Drechsel noted.

With fertilizer prices jumping nearly 50 percent per metric ton over the last year in some places, human waste is an attractive, and often necessary, alternative, Redwood said.

In cases where sewage sludge is used, expensive chemical fertilizer use can be avoided, he said. The sludge contains the same critical nutrients—nitrogen, phosphorous, and potassium.

Wastewater Recycling

It is generally unheard of for untreated wastewater to be used for agriculture in developed countries, simply because farmers there have access to treated water, said Margaret Catley-Carlson of the Global Water Partnership.

Instead, farmers in developed countries use recycled wastewater that often meets drinking-water standards.

To address health risks associated with wastewater agriculture in developing countries, IWMI recommends education programs for both consumers and farmers.

The nonprofit also recommends that such operations adhere to World Health Organization (WHO) standards for safe wastewater usage. WHO, in turn, has made their own standards less stringent.

"Overly strict standards often fail," James Bartram, a WHO water-health expert, said. "We need to accept that across much of the planet, waste with little or no treatment will be applied to agriculture for good reason." According to IWMI's report, few developing countries have official guidelines for the use of wastewater for farming. But the fact that authorities are even acknowledging that wastewater agriculture exists is progress, the report says.

In the city of Kumasi, Ghana, home to 1.6 million people, IWMI estimates that there are about 12,000 families growing food on 27,000 acres (12,000 hectares) using mostly polluted surface water.

Just this year the Ghanaian government began to recognize this type of informal irrigation in its new irrigation policy, according to IWMI's Drechsel, who views the move as a giant breakthrough for addressing related health issues.

There are also low-tech solutions for "treating" human waste. IWMI suggests employing appropriate and time-tested indigenous practices.

The report cites examples in Indonesia, Nepal, and Vietnam. There, farmers store wastewater in ponds to allow solid feces and worm eggs to settle, possibly reducing bacterial content in the residual water.

Composting, in which heat kills much of the bacteria, is another option, according to the report.

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