Investigating the Efficiency of Phosphate Removal from Wastewater from Sugar Cultivation Industry Using Baffled Subsurface-Flow Constructed Wetland

Phosphorus is recognized as a nutrient in aquatic environments, but increasing its concentration in water resources causes the occurrence of eutrophication in water and, as a result, causes the death of aquatic organisms. Therefore, removal of phosphate from water is very important. In this research, in order to remove phosphate from water resources, the baffled subsurface-flow constructed wetland was used. In order to increase the efficiency of the wetland system, experiments were designed in 3 different phases. In the first phase, in the form of batch experiments, the composite performance of cheap materials such as zeolite, bentonite and pumice aggregates (The stabilization of nanoparticles of zeolitebentonite on the surface of Pumice aggregates) to absorb phosphate and select the preferred candidate for placement in the wetland was investigated. In the second phase, in the form of pot experimentation, the performance of native plants of khuzestan province such as salicornia, Typha, and Juncus, In order to uptake phosphate and select the best candidate for cultivation in the bed of the wetland was investigated. Finally, in the third phase, with the placement of the selected bedding and plant (selected from previous experiments) in the wetland system, experiments were carried out to study the effect of parameters such as the percentage of optimum mix of Selected bed with gravel, hydraulic residence time and temperature changes on the phosphate removal efficiency. The results showed that among absorbent materials and candidate plants for placement and cultivation in the wetland, the maximum capacity to absorb and accumulate phosphate by Pumice aggregate coated by zeolite nanoparticles (1.08 mg/g) and salicornia (9.68 mg/g of plant dry weight) was observed. In this experiment, The use of a combination of 10% of the selected bed with 90% of the gravel was obtained as the best and most economical option for removal of phosphate. Also, the efficiency of removal of phosphate in the 1-day hydraulic residence time was achieved at the highest intensity (99.60%) and was selected as the optimum time to remove phosphate. Finally, the results of the effect of temperature changes on the efficiency of the wetland system showed that the removal efficiency from March 2018 (20 °C) to July 2018 (40 °C) increased to about 1 percent, which indicates the effect of temperature changes on the performance of the wetland system. According to the results, in the case of adequate land availability, the use of subsurface-flow constructed wetland systems to wastewater treatment of agricultural and industrial units is very convenient and cost-effective.