Experimental Study and Mathematical Modeling for the Removal of Lead and Cadmium Ions from Wastewater by Reverse Osmosis and Nanofiltration Membranes

Abstract

Many industrial wastewaters that contain heavy metals (HM) lead, cadmium, chromium, and cobalt ions can be produced as toxic pollutants that affect human and animal health. The industrial wastewater ions are treated efficiently with reverse osmosis (RO) membrane and nanofiltration (NF) system technologies so that water consumption can be minimized as well as environmental conservation. Industrial wastewater samples containing Cd⁺² Pb⁺² HMs ions at varying concentrations of 10 ppm to 500 ppm using distilled water at different pressures of (3-11) bar and a common room temperature of 25 ºC and at different pHs of 4, 5, & 7. Many of the water purifiers in use today use RO and NF in the purification process as one of the efficient methods. According to the results, the RO method was one of the best methods to remove heavy metal ions from industrial water, as its efficiency (%R) reached more than 98%. The results revealed that the Rejection efficiency (%R) of the system in removing Pb⁺² ions reached 98.548%, and Cd⁺² 97.974 under these operational conditions: pH = 6±0.2, the pressure of 11 bar, concentration=10 - 500 ppm, time= 90 min, and T=25 °C, so it is higher efficiency Removal (%R) of Pb⁺², then Cd⁺². In the nanofiltration NF system, the highest removal %R of the Pb⁺² ion reached 93.17%, and the Cd⁺² ion reached 92.594%. These results were under operational conditions: pH=6±0.2, pressure= 11, concentration= 10-500 ppm, time= 90 min, and T=25 °C. The CFSD model is good for representing the value of the experiment because it has a higher R2 = (97±2) %. A satisfactory experimental data fit is again achieved using the film theory/Spiegler-Kedem (CFSK) model. The Combined–Film Theory / Finely Porous model (CFFP) model has higher coefficients of determination, as shown in Figures 5.13 and 5.14 for RO and NF, respectively, the CFFP model is suitable to represent the experimental results. The Peclet number is used to see the separation mechanism because of diffusion; diffusion in the boundary layer cannot control the convective flow through the membrane, and the concentration polarization will be high. When the Peclet number is small (J<<K), then the convective flow will easily be tamed by diffusion at the boundary layer.