Considering wastewater for irrigation

The concept of ‘sustainability’ will be familiar to anyone involved in modern agriculture along with the importance of improving water-use efficiency - we share an insight from the Global Forum for Innovations in Agriculture Conference 2018 in Abu Dhabi

Trying to do ‘more with less’, it’s focused on making more efficient use of the many inputs – energy, fertiliser, plant protection products and other inputs that our growing demand for food necessitates.

Such resources are ultimately finite. Fossil fuels won’t be available forever. That’s why alternatives are emerging: tractors fuelled by methane or batteries, bio-pesticides, ‘smarter’ ways to apply nitrogen, and so on.

But the other huge resource on which agriculture is absolutely dependent has no substitute. It’s water. Seventy per cent of the world’s water is used for agriculture. In some countries, particularly those with arid climates, that figure’s much higher – and, as a result, completely unsustainable.

Searching for a solution is Dr Asad Sarwar Qureshi, a senior scientist at the International Centre for Biosaline Agriculture (ICBA), Dubai. While there’s scope to make water use more efficient, through crop breeding and technological advances in irrigation, he’s been looking at the potential to make use of other, previously unavailable, sources of water.

Wastewater is one such source. Dr Qureshi says 11 billion cubic metres of waste water is produced by Gulf states every year. Less than half of it is currently treated and reused; in the UAE, most of the treated wastewater (TWW) is used only for landscaping or amenity purposes.

Qureshi thinks TWW should be reused for food crop production. Aside from increasing water-use efficiency, it would reduce problems associated with effluent and could – owing to the nutrient content of TWW – reduce fertiliser usage. Moreover, TWW boasts higher marginal economic returns than fresh water.

It’s not without its problems. TWW can contain high levels of heavy metals: zinc, copper, iron and chromium. At high enough concentrations in harvested produce, all can pose health problems. Another concern is microbial loading. Pathogens such as E. coli are the subject of strict controls in the food chain. Any practices that increase the risk of transmission would not be viewed favourably by regulatory authorities.

At ICBA, Dr Qureshi has led a four-year project to examine the uptake of heavy metals and pathogens. Results show that leafy vegetables (such as lettuce and spinach) were more likely to show higher ‘bio-accumulation factors’ than non-leafy, root vegetables such as carrots and radishes. However, while all levels detected in finished produce were within the limits set by the World Health Organization (WHO), some elements – chromium and iron especially – showed cause for concern, especially if children were consuming such produce over an extended period.

Qureshi is delighted with these results. The ICBA has recommended that TWW be used for agricultural production, with the proviso of additional treatment to detect and reduce levels of chromium and iron, and the selection of appropriate crops. 

The UAE currently imports around 85% of its food. Identifying safe, alternative sources of water for crop production could allow the country, neighbouring Gulf states, and other arid or semi-arid countries, to grow and source more home-grown food.

In UAE, the findings are especially valuable. Government has encouraged the development of hydroponic, or ‘indoor’ farming – which itself offers a 90 per cent reduction in water use. The guaranteed availability of TWW, and its endorsement for use in agricultural production, will surely act to stimulate this fledgling industry.
Improving water-use efficiency
Improving water-use efficiency has been the subject of Dr Asad Sarwar Qureshi's research
treated wastewater agricultural production
Over a four-year project, Dr Asad Sarwar Qureshi examined how treated wastewater (TWW) might be used for agricultural production
chromium and iron in crops
By measuring uptake of heavy metals such as chromium and iron in crops such as radish, eggplant and tomato, Dr Asad Sarwar Qureshi has been able to determine which crops are most suited to using TWW
additional treatment
Dr Asad Sarwar Qureshi's project has also revealed how much additional treatment TWW might require