Evaluation of kinetic models in water salinity reduction by phytoremediation method with three halophyte plants

Water scarcity has led to the search for alternative water resources. One solution is the recycling of wastewater for irrigation. Wastewater treatment is often based on biological systems such as activated sludge or other engineered units in urban areas. In rural areas، low-cost، environmentally-friendly alternative treatments such as constructed wetlands (CW)، are more common. CWs are man-made planted systems that utilize natural processes to improve water quality for human benefit. Salinity in treated wastewater is often increased، especially in arid and semi-arid areas. Phytoremediation can be used to remove much of this problem. Phytoremediation is the use of plants for remedying water and soil pollution. This approach is based on plants that are especially tolerant to salt environments. Around 1% of all plant species are halophytes that can complete their life cycle in relatively high saline environments، as much as 200 mM NaCl or more. In the current study، we addressed the problem of soilsalinization due to the use of treated wastewater that is often more saline than fresh water، especially in desert environments. We aimed at testing the potential to recruit halophyte plants for salt phytoremediation in constructed wetlands. Therefore this study was performed to evaluate the ability of reducing salinity of wastewater by three halophyte plant species such as Frankenia، Atriplex and Festuca. The experiments were performed with different concentrations of saltwater. Reducing the electrical conductivity، salt removal and its uptake rate، the concentration of sodium stored in plant tissues at different levels of salinity، were analyzed. Also by matching the data with Michaelis- Menten and Lineweaver- Burk kinetic models، some results were obtained from each plant. The electrical conductivity decreased with increasing salinity levels in all three species. The highest salt absorption amount in Frankenia was in 4500 µs/cm about 20 percent، in Festuca was in 2600 µs/cm about 17 percent and Atriplex was in 5000 µs/cm about 14 percent. Of course reducing of salt uptake in each plant had its own reason for example; Atriplex plants due to having less compatible with wetland situation، Festuca plants due to facing with salinity stress and Frankenia plants because of salt replenishment faced with yield loss and withered state. Based on these results Frankenia، Festuca and Atriplex plants during the treatment with saline water، had the first order of kinetic equation with a correlation coefficient of respectively 97. 7، 95. 9 and 97. 01، gradually with increasing of salinity these plants had the kinetic equations of 2، 0 and 1 order that as this result، Atriplex plants showed more resistance in salt uptaking. In reduction range also Atriplexand Frankenia had a better performance. The highest conformity of data in Frankenia plant related to Lineweaver- Burk and Atriplex plant related to Michaelis- Menten.