Urban Agriculture 2: Agri-Sewage

I've written before about the importance of urban agriculture, particularly during the current food-price crisis. That we are also going through serious water shortages in many parts of the globe begs a question that I had wondered about while I was in South Africa: where are urban farmers getting their water? The answer, according to a report by the International Water Management Institute (IWMI), is Sewage. The World Health Organization tells us that 10% of the world's population relies of food grown in fields watered and fertilized with untreated human waste. The IWMI report argues that not only will that be an inevitable reality for the conceivable future, but that it might not be all bad -- if we deal with it constructively.

The Guardian excerpts a section from the report that lays out the situation:
"As long as developing countries lack suitable transport to deliver large quantities of perishable produce to urban areas, urban agriculture will remain important. In the face of water scarcity generally and a lack of access to clean water, urban farmers will have no alternative except to use … polluted water." That polluted water can produce significant yields. In Ghana's capital Accra (pop. close to 2 mil.) 200,000 residents purchase vegetables produced on just 100 hectares of urban agricultural land that is irrigated with sewage. That is a lot of food, but it is also a direct vector for dihoreal diseases and cholera. The pratice, they go on to say, is not limited to Africa but is also found in China, India, Vietnam and Latin America.

So what to do? The IWMI makes clear that outlawing the agricultural use of nutrient rich waste water is simply not an option. Shortages of both clean potable water and affordable food make it a necessary reality. They are happy that cities are finally willing to discuss what had been a tacitly accepted practice. Instead of introducing strict standards or restrictions that will be impossible to enforce, the report recommends promoting practices like drip-irrigation (which keeps bacteria off the edible parts of the crops), creating infrastructure in markets to carefully wash produce before sale, and the use of settling pools and other low-tech forms of water filtration. (Some of these same simple biofiltration technologies are used in Canada and elsewhere to provide low-cost sewage treatment and storm water remediation services from smaller centres like St. Stephen (NB) to larger cities like Edmonton (AB). As search for "wetlands" on The Federation of Canadian Municipalities Green Municipal Fund database turns up a number of examples.)

Distasteful as it may seem, there are multiple advantages to using waste water for irrigation; it relieves stress on fresh water supplies (agriculture currently consumes close to 70% of global fresh water supplies), it is rich in nitrogen, phosphorous, and potassium and provides an alternative to costly chemical fertilizers, and it supports both a needed source of food and the livelihoods of urban (largely female) farmers. It also serves an important ecological function; in the same way that settling pools and wetlands can clean waste water before agricultural use, the fields themselves serve to further filter the water reducing its impact on surrounding rivers and streams.

To rethink cities as productive parts of our ecosystem, not just monstrous consumers of resources, is the challenge that we currently face. We also have to address the pressures placed on our cities by rapid population growth, urban poverty, and deficits in needed or aging infrastructure. Looking for linked solutions to these problems guided by principles like "Zero Waste" is something that we are comfortable with, up to a point. Waste water agriculture might be a bit beyond that point for some of us. (But so might other aspects of "accepted" agri-business practices if we knew about them - case in point, the regular scandals that plague industrial meat manufacture, this time in Canada.) But from the IWMI report it is clear that "sustainable" practices can be born of necessity and test some of our preconceptions about what is possible, practical and safe. It also shows that while necessity may push innovation, careful guidance and support is necessary to minimize risks and maximize returns.

The best summary of the report that I have found is here (although not as easy on the eyes as the National Geo. piece linked above).

UPDATE: Sustainablog has just put up an interesting post, excerpted from Lester Brown's Plan B 3.0: Mobilizing to Save Civilization, on the need to raise the productivity of water used for agriculture. They don't touch on the waste water issue though.


1 Response to "Urban Agriculture 2: Agri-Sewage"

Biogas Plant in Bangalore said... 22 August 2013 at 03:57

Thank you for sharing this article. I love it. Keep on writing this type of great stuff.
Biogas Plant in Kerala
Recycling of Waste in Bangalore


This is a blog for news and views on the future of sustainable cites. A major revamp is in the works. Until then I am keeping this version up as an archive of my past writing.

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