چكيده انگليسي :
This study investigated the effectiveness of a multi-stage wastewater treatment system consisting of a sand media as a pre-treatment, constructed wetland as secondary treatment and advanced treatment with nanofiber membrane reinforced with zeolite. At first, about 500 liters of raw wastewater was transferred from Feyz Company to Isfahan University of Technology. In order to prepare the nylon 6/zeolite membrane, the important parameters of the electrospinning process were optimized and the nanofiber membrane with amounts of 0, 1, 3 and 5% of nanozeolite was prepared using the electrospinning method. After characterization of nylon 6/zeolite nanofibers, the membrane containing 5% zeolite was selected for further experiments, because of the results of the BET analysis which showed that the nanofiber membrane with 5% zeolite had the highest specific surface area (45.7 m2/g), as well as the highest area and volume of pores. Besides, column absorption experiments were conducted to check the removal efficiency of some parameters such as COD and turbidity using the membranes. The results showed that the nanofiber membrane containing 5% zeolite had 82% and 15%removal efficiency of turbidity and COD, respectively, which showed the higher efficiency compared to other membranes. Furthermore, the effect of zeolite on the mechanical properties of the membrane showed that with increasing the zeolite content, the parameters including the diameter of nanofibers, the thickness of the membrane, and the air permeability increased, and on the other hand, the tensile strength of the membrane decreased from 6792 MPa to 1991 MPa, which could be due to the heterogeneous dispersion of zeolite nanoparticles in the membrane structure. Thus, after performing various tests, the membrane with 5% zeolite with the highest removal efficiency and the most favorable properties was used for the integrated system.Constructed wetland cells were prepared by simulating vertical subsurface flow in a greenhouse, and Phragmites australis species were planted at the beginning of September 2020 and irrigated for three months for sufficient growth. In addition to the planted cells, 3 cells were used as control cells (without vegetation). In order to reduce the load of wastewater and prevent the negative effects of direct feeding of wastewater on wetland plants, a large tank with a volume of 300 liters, half of which was filled with four layers of sand with an average diameter of 5-8 mm, 15 - 10 mm, 20-30 mm and 50-60 mm were filled and used as a as a pre-treatment step. After growth and good development of reed roots within 90 days, the sand media was fed with wastewater and after 4 days, the cells of the vertical flow constructed wetland (VFCW) were fed with the effluent passing from the pre-treatment step (sand media). Finally, the effluent from the VFCW was passed through the synthesized nanofiber membrane for additional purification. The samples were taken weekly and regularly during 6 weeks. The values of TOC, BOD5, COD, EC, pH, NH4+, NO3-, PO4-3, phenol and turbidity at the inlet and outlet of each stage of the system were measured. Based on the obtained results, the average removal of COD, BOD5, turbidity, PO4-3, NH4+, NO3- and phenol during the two stages approach (sand media+constructed wetland) was around 82%, 87%, 96 %, 92 %, 94%, 93% and 97%, respectively. After this effluent passes through the nylon 6 nanofiber membrane reinforced with zeolite, the total removal efficiency of the system was achieved to 84% for COD, 90% for BOD, 99% for turbidity, 91% for PO4-3, 96% for NH4+, 89% for NO3- and more than 99.9% for phenol. In general, the integrated system studied in this research showed a good performance in removing pollutants from the wastewater of herbal essences industries, but due to the mismatch of the concentration of some parameters, including COD, considering the standard level for discharging into the environment, the system needs to be improved.
