Abstract

Lake Urmia is one of the largest saltwater lakes in the world. In recent years, due to the drought conditions and the uncontrolled entry of industrial wastewater into the lake, the amount of some chemical pollutants has been increased dramatically in lake sediments. The most important pollutants in the lake are chemical organic compounds, heavy metals, nitrate, nitrite, among which, nitrite pollution is very important. The aim of this study was to prepare and asses the efficiency of a biodegradable biohydrogel based on isolated soy protein/tragacanth containing mesoporous silica nanoparticles and lycopene pigment (ISP/ TG/MPS/Lyc) in removal of the nitrite from the Lake sediments. The physicochemical characteristics and structure of the biohydrogel are investigated by scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and thermal gravimetry analysis (TGA) techniques. Five optimal biohydrogels including pure ISP, ISP/TG, ISP/MPS, ISP/Lyc, and ISP/ TG/MPS/Lyc are used for chemical treatment of Lake Urmia sediments. For this purpose, biochemical oxygen demand (BOD), chemical oxygen demand (COD), and nitrite of sediments are examined before and after treatment with biohydrogels. According to the FTIR results, there is only physical interaction between lycopene and isolated soy protein. According to the TGA results, adding silica mesoporous to biohydrogel increases its thermal stability. Tragacanth gum and lycopene pigment reduce water solubility and increase the WAC of biohydrogel. The biohydrogel significantly reduces the BOD and COD of the sediments. The biohydrogel reduces nitrite content up to 90%, while reducing nitrate content by almost 30%. The results show that the biohydrogel containing lycopene selectively purifies nitrite from the sediment solution of Lake Urmia.

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