MechChem Africa February 2018

Desalination, brackish water and bio-saline agriculture

IDE’s PROGREEN™ modular, containerised, reverse osmosis desalination plants deliver high quality clean water without the use of chemicals and with reduced energy consumption.

IDTechEx, an independent research and business intelligence advice service, has produced a report entitled Desalination : Off Grid Zero Emission 2018-2028 , which argues the case for producing drinking water from brine or brackish water using integral energy harvesting.

A gricultural use is currently respon- sible for 70% of all fresh water consumption, but fresh water is becoming more expensive and scarce. Fortunately there are many solutions because they are all needed. Desalination ismainly applied to seawater because it constitutes 97 to 98%of thewater on Earth. But it is expensive. There is limited scope for desalinating salty lakes, with 70% of the planet’s salt lake water is in one place, theCaspianSea. Indeed, a cooperativeproject between Israel, Jordan and thePalestinians is to make drinking water from the ocean and put the other 50% of the output – the strong brine – into the Dead Sea to get it back to former levels. Brackishwater (0.5-5g/ ℓ salt, one quarter of the seawater concentration) is muchmore attractive because it is 100 timesmore abun- dant than salt lakes. Desalination of brackish water therefore required less energy than desalination of seawater and higher volumes emerge clean, whereas a much smaller pro- portion of potable water emerges clean from seawater desalination. There are about 325 brackish groundwa- ter desalination plants in the United States. The International Desalination Association (IDA) reports that desalination of brackish water is growing globally, with an increase of 29% in contracted capacity for thefirst half of 2017. The typical brackishwater desalination plant is for smaller utilities and industrial us- ers, meaning small and medium-sized plants.

and intensive fish and shrimp farming. Researchers such as the International Centre for Biosaline Agriculture (ICBA) have worked on key annual conventional crops, such as sorghum, pearl millet and barley. The process of selection for both salt- and drought-tolerant genotypes has led to large- scale adoption in many countries in Central Asia, Middle East, North Africa and sub- Saharan Africa. IDTechExCEORaghuDas says: “Brackish- water irrigation does not have to result in in- creased salinity of the soil, though sometimes farmers must use water from a rainstorm to carry salts back down to below the root zone. Accordingly, perhaps this story can even go full circle. Areas with almost no water, brackish or otherwise, could be irrigated with partially desalinated seawater at much lower cost than full desalination and all those wonderful salt-tolerant crops grown. Cost will be particularly lowwhen the desalination plants used for such purposes produce zero gas emission, making all their electricity from wind, sun and/or water power.” These aspects are covered in the new IDTechEx report, ‘Desalination: Off Grid Zero Emission 2018-2028’, which predicts that, coming from very little in 2018, off grid zero-emission desalination, including plants for brackish water, will be a rapidly grow- ing $35-billion market by 2028. The report looks closely at its roadmap of exciting new desalination and electricity technologies that will boost performance and reduce cost, in

China accounted for a large percentage of growth in these plants, especially during the second half of 2016. The use of desalinated groundwater is expectedtogrowinthefuture.SupplierVeolia estimates that roughly one quarter of all wa- terdesalinationdemandiscurrentlyforinland brackish water desalination technology. Another option for using brackishwater is bio-saline agriculture, a relatively newway of dealingwith salinity inagriculture. It develops cropping systems for saline environments, using the capacity of certain plants, called Halophytes , to grow under saline conditions: quinoa, mustard, sesbania, safflower and triticale, along with appropriate genotypes of sorghum, pearl millet and barley. Sesbania is an alfalfa replacement. Triticale, a hybrid of wheat and rye, is used as a feed crop for cattle, swine and poultry and can be used as an alternative for corn and soybean. Halophytes oftenproducebetter yields under saline circumstances. Vegetables can also be grown in seawater. Examples are salicornia, mangroves, and seawater grasses such as kelp. These are variously used for livestock, pet and human food. Brackishwater is often available far away from the sea in aquifers, marshes and so on. Many arid and semi-arid areas do have sources of water, but brackishwater is often available. Brackishwater also takes the form of drainagewater from irrigated agriculture, excess water from oil production, geo ther- mal plants, wastewater from industrial use

32 ¦ MechChem Africa • February 2018