Pros and cons of using wastewater for irrigation

By Sumana Narayanan
Published: Wednesday 31 October 2007

reuse of wastewater for irrigation is touted as an environmentally sound practice. But little is known about its long-term effects. A recent study from Jordan says that the frequent use of treated wastewater can affect plant growth and crop yield. Researchers say the use of wastewater has to be continuously monitored to get optimal results.

While wastewater does contain nutrients and organic matter, the researchers say its effectiveness in irrigation depends on the match beween its composition and the ecology of the soil. The study was published in the journal Desalination (Vol 215, issues 1-3).

The study analysed soil irrigated with treated municipal wastewater for two, five and 10 years. At the first site the acid content was high and salinity and organic content in the soil were found to have increased with the duration of irrigation.

The soil irrigated for a longer duration had increased presence of macronutrients, phosphorus and potassium in the top layer. Micronutrients--manganese, iron, zinc--too tended to accumulate in the top soil while heavy metals like lead, cadmium did not really vary. Earlier research had showed varying results for micronutrients and heavy metals.
Important measures The paper, however, ignores the possible health hazards for people who eat crops irrigated with wastewater. Liqa Raschid-Sally of the Colombo-based International Water Management Institute (iwmi) says the major concern is the pathogens. "It is better to avoid wastewater from industrial sources. Food processing and domestic wastewater is easier to treat and apply for agriculture."

Researchers point to the need for an effective policy on wastewater reuse in agriculture. Raschid-Sally feels, "Countries should consider wastewater recycling as part of the national water policy. Under water-scarce conditions, this is a must. Even under water-rich conditions, wastewater has to be disposed of and put to agricultural use". She adds that who guidelines (2006) for the safe use of wastewater give tips on how such practices can be carried out.

Robert Simmons of iwmi says India does not have a comprehensive policy on wastewater reuse. In the states where reuse of wastewater is part of irrigation policies, specific guidelines are absent. An estimate shows 33,000 million litres per day of wastewater is released in the big cities in India. But 75 per cent of this goes untreated. Simmons says that all kinds of wastewater should be treated and reused for irrigation.

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