"Agricultural Oasis" A pilot-scale nanofiltration desalination system for growing in Arid zone
Rami Messalem and Andrea Ghermandi - Zuckerberg Institute for Water Research Ben-Gurion University of the Negev
Shabtai Cohen, Rivka Offenbach, Avi Usherovitz, Dorit Hashmonai, Yuval Barzilai - Central and Northern Arava R&D
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A pilot-scale agricultural facility aimed at the environmentally sustainable production of staple crops in arid environments was built and tested at the Yair agricultural research station in Hatzeva, Israel. The facility relies on a pilot plant utilizing nanofiltration (NF) membranes for the desalination of the local brackish water and production of high-quality irrigation water. During the first project year, the desalination unit was run on grid electricity, but solar photovoltaic (PV) modules were installed in May 2011 with the purpose of achieving full energy autonomy during the second project year. The potential costs for brine disposal in inland desalination are turned to an advantage by growing red beet with the brine waste product, a salt-tolerant crop with a high nutritional value.
Agricultural experiments with different staple crops were conducted over two growing seasons. Experimental plots irrigated with desalinated water and control plots irrigated with brackish water were cultivated with potatoes during the winter cycle, between November 2010 and March 2011. Maize, millet and sorghum were grown during the spring cycle between March and June 2011. During both cycles, crops irrigated with desalinated water consistently received 25% less irrigation volumes than the control plots.
The NF desalination unit operated according to expectations and with only one significant interruption due to a pump malfunction over the whole period. It exceeded the expectations regarding permeate flow (6.5 m3/d) and specific energy consumption (1.37 kWh/m3). It was consistently operated at the low pressure of 4.3 bar. The permeate water produced after blending with a fraction of the feed water has a moderate electrical conductivity (0.86 dS/m) and contains concentrations of the plant micronutrients calcium (45 ppm) and magnesium (23 ppm), which are above the minimum recommended for use of desalinated water in agriculture. The use of NF desalination is shown to provide substantial advantages for agricultural application with respect to reverse osmosis in terms of lower operating pressure and energy consumption.
The analysis of the produce from the cultivation of potatoes during the winter cycle shows no significant differences in terms of total yields and number of tubers produced between experimental and control plots, despite the larger irrigation volume in the former ones. The lack of a predicted positive effect of desalinated water irrigation on the yield of potatoes can be largely attributed to an infestation of Erwinia carotovora, which affected plants grown with desalinated water 1.7-2.7 times more severely than those irrigated with brackish water.
Maize, millet and sorghum plots irrigated with desalinated water were found to produce statistically significant taller crops, higher plant density and – for maize and sorghum – larger wet and dry plant weight per plot. The yield of millet and sorghum was substantially higher in experimental plots, while no statistically significant differences were found for maize plants.
During both growing seasons, red beet plants irrigated with concentrated brine from the desalination plant grew strong, showing no sign of being affected by the salinity of the water and yielding higher quantity of produce than expected.
A preliminary cost-benefit analysis shows that a full-scale agricultural facility using the proposed technological approach may achieve economic viability for the production of relatively high-value crops such as potatoes. Arguably, the most significant environmental benefit of the proposed system would lie however in the substantial reduction of abstraction of groundwater from fossil aquifers for agricultural purposes.
מחבר Rami Messalem, Andrea Ghermandi, Shabtai Cohen, Rivka Offenbach, Avi Usherovitz, Dorit Hashmonai, Yuval Barzilai