| Under the pressure of the global shortage of water resources,the unconventional water source such as micro-polluted water was tried for irrigation.However,micro-polluted water contains harmful substances such as heavy metal ions,which are easily enriched by plants and cause damage to the environment and human health.The fertilizer-drawn forward osmosis technology has advantages such as good separation effect of harmful substance,and strong anti-pollution ability of membrane.What's more,concentrated fertilizer can be used as draw solution and can be directly used for irrigation after dilution,no further separation is required,which means low energy consumption.Therefore fertilizer-drawn forward osmosis technology has a good potential for application in water treatment and agriculture.In this paper,concentrated fertilizer was used as draw solution of forward osmosis,and the membrane performance under two systems was investigated.System one whose feed solution is micro-polluted water containing heavy metals,and draw solution is biogas slurry.System two whose feed solution is seawater and sewage,draw solution is solid fertilizer.The rejection performance of hollow fiber forward osmosis membranes for heavy metal Cd2+ and Pb2+ was investigated.Water flux and reverse solute flux were used as indexes optimizing the operation parameters of the process.In order to evaluate the feasibility of drawing clean water from unconventional sources for agricultural cultivation via fertilizer-driven forward osmosis process,the diluted fertilizer solution was used for hydroponic experiment(including rice,cotton and leeks),and the plant growth status was examined.The main contents and conclusions are as follows:(1)Biogas slurry was used as draw solution to draw clean water from the micro-polluted water containing heavy metal ions.Water flux and reverse solute flux were used as indicators to optimize the operation parameter including recirculation flow rate,temperature of feed solution and draw solution,etc.Considering factors such as energy consumption,the optimal operating conditions of temperature,recirculation flow rate and composition of draw solution were determined as 25 ?,200 ml/min,1000 ppm,100%biogas slurry,respectively.Under the optimal operating condition,the rejection coefficients of Pb2+ and Cd2+ were high to be 98.5%and 97.0%,respectively.(2)The diluted biogas slurry from the FO process was directly utilized as the hydroponic solutions for cultivating crops:Concentrated biogas slurry was used as draw solution to draw clean water from micro-polluted water with various saltness.And then the diluted biogas slurry was used as culture solution to cultivate crops.The hydroponic results showed that when the salinity of micro-polluted wastewater was 3000 ppm,the difference in growth was obvious.With the FO treatment,the rice height and root length were 20.9 cm and 14.5 cm,and the number of leaves and roots were 4 and 10,respectively.When the rice grown in biogas slurry diluted with micro-polluted water directly,the plant height and root length were only 12.1 cm and 9.8 cm,and the number of leaves and roots were 3 and 5,respectively.The leeks grown in biogas slurry diluted with the clean water drew from the micro-polluted wastewater with FO technology had a better growth conditions than leeks grown in biogas slurry diluted by micro-polluted wastewater directly.Therefore,it can be seen that crops grown in biogas slurry diluted with clean water drew from the micro-pulluted water containing heavy metals had a better growth conditions than crops grown in biogas slurry diluted by micro-polluted water containing heavy metals directly.(3)Solid feitilizer was used as draw solution to draw clean water from the seawater and sewage.Water flux and reverse solute flux were used as indicators to optimize the operation parameter including the recirculation flow rate,temperature of feed solution and draw solution,etc.Considering factors such as energy consumption,the optimal operating conditions of operation mode,feed and draw solution temperature,recirculation flow rate,concentration of draw solution were determined as counter-current,PRO,25 ?,400 ml/min,1M KH2PO4,respectively.And under the optimal operating condition for 120 h,the volume of draw solution increased from the initial 200 ml to 5750 ml,providing 42.3%of the water required to dilute the solid fertilizer.(4)The diluted solid fertilizer from the FO process was directly utilized as the hydroponic solutions to cultivate rice and cotton,and the hydroponic results showed that rice and cotton grown in solid fertilizer diluted with clean water drew from the seawater and sewage had a better growth conditions than crops grown in solid fertilizer diluted by seawater or sewage directly.The sequence of rice height and root length were membrane group(23.22 cm)>sewage group(16.24 cm)>seawater group(12.08 cm)and membrane group(14.36 cm)>sewage group(10.63 cm)>seawater group(9.20 cm),respectively.The sequence of rice leaves and roots number were membrane group(4)>sewage group(3)=seawater group(3)and membrane group(12)>sewage group(5)>seawater group(4).The hydroponic results of cotton were similar to those of rice.The growth of cotton in the membrane group was better than that in the sewage group and was better than that in the seawater group.The results of this study showed that the fertilizer-drawn forward osmosis technology had excellent rejection rates for heavy metal ions.When solid fertilizer was used as daw solution,it could draw considerable amounts of clean water from seawater and sewage.The results of hydroponic proved the feasibility that the fertilizer-draw forward osmosis technology can draw clean water from unconventional sources such as micro-polluted water and seawater for agricultural irrigation.It is believed that with the development of new forward osmosis membrane materials and improved membrane performance,fertilizer-driven forward osmosis technology will have a broader application prospect. |
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