Abstract

DEVORA-ISIORDIA, Germán Eduardo et al. Desalination by Reverse Osmosis and Its Use in Agriculture in Valle Del Yaqui, Sonora, Mexico. Tecnol. cienc. agua [online]. 2016, vol.7, n.3, pp.155-169. ISSN 2007-2422.

Sonora, situated in northwest Mexico, ranks second among the country's irrigation crop producing states. The problems of water resource availability in Sonora, particularly for farming, are due to the high concentration of salts in well water, which go from 2 000 to 5 000 mg/l of total dissolved solids (TDS). High salt concentration in groundwater wells is attributed to the effects of saline intrusion related to the excessive exploitation of aquifers (Conagua, 2011). Nonetheless, desalination technologies and process prediction models can allow the optimal use of this resource. This work aims to develop a mathematical simulation model for predicting the performance of an RO desalination plant fed with brackish water, whilst ensuring that the product water achieves the permissible limits for its use in agriculture. In order to validate the model, an RO desalination plant with a nominal capacity of 100 m3/d, consisting of eight commercial SWC4 8"×40" membranes, was used to desalinate groundwater for the irrigation of 0.25 ha of sorghum crop. For a brackish feed water with 6 610 mg/L TDS, the product and rejected flows presented 64.8 and 21,300 mg/l TDS respectively. With the help of a YSI 556 multiparameter measuring unit, the electric conductivity (mS/ cm), TDS (mg/l), pH and temperature (°C) were determined for the permeate, retentate and feed water of the desalination plant. Using data obtained from the pilot plant, a simulation model was developed in MATLAB 2009a using Simulink, which has the function of predicting the behavior of the desalination plant. The model is able to determine the concentration of dissolved solids in the retentate and product water depending of the process configuration and the number of control iterations. Each iteration includes different volumes of brine recirculation. For this study, this model is used to simulate the utilization of the flow of retentate, in order to increase the sustainability of the process. The results of the measurements in the desalination plant show that for a feed water with 6,610 mg/l TDS, the product and retentate flows have 64.8 and 21 300 mg/l TDS respectively. The economic assessment of the process shows that the water production cost without brine recirculation is MX$6.16/m3. This is very similar to the MX$6.70/m3 cost reported by the International Desalination Association. Using the desalinated water, a production increase of 1 ton/ha of sorghum was achieved, compared with brackish water irrigation. Using the data obtained from the pilot plant, the simulation model was developed, validated and calibrated, in order to predict the behavior of the desalination plant in terms of concentrations in the retentate and product water. The model was then used to simulate brine recirculation, in order to increase the sustainability of the process. It was found that, for the conditions of the 100 m3/d plant, it is possible to totally or partially recirculate the brine stream. Recirculation modeling results show several brine recirculation iterations can be carried out without significantly affecting the product water. Further, using a low brine recirculation rate, up to five iterations can be carried out without increasing the concentration in the feed water above 42 000 mg/l. At higher brine recirculation rates, less iterations can be achieved, but brine discharges to the environment would be reduced. Given that desalinated water increased the agricultural productivity, public and private investments in desalination for the rural sector appear viable in the short term.

Keywords : Desalination; reverse osmosis; agriculture; sorghum; yield; simulation; MATLAB.

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