The path for water molecules transported across a membrane in real porous membranes has been considered to be a constant factor in the membrane distillation (MD) process (i.e., constant tortuosity); as such, its effect on membrane performance at various operating conditions has been ignored by researchers. Therefore, a simultaneous heat and mass transfer model throughout the direct contact membrane distillation (DCMD) module was developed in this study by taking into account the hypothetical path across the membrane as a variable factor within the operating conditions because it exhibits the changes to the mass transfer resistance across the membrane under the DCMD run. The DCMD process was described by the developed model using a system of nonlinear equations and solved numerically by MATLAB software. The performance of the poly-tetra-fluoroethylene (PTFE) membrane was examined to treat 200 g/L NaCl saline at various operating conditions. The simulation results in the present work showed that the hypothetical proposed path across the membrane has a variable value and was affected by changing the feed temperature and feed concentration. The results estimated by the developed model showed an excellent conformity with the experimental results. The salt rejection remained high (greater than 99.9%) in all cases. The temperature polarization coefficient for the DCMD ranged between 0.88 and 0.967, and the gain output ratio (GOR) was 0.893. The maximum thermal efficiency of the system was 84.5%.

The presence of organic compounds such as ciprofloxacin in untreated pharmaceutical wastewater often poses a serious health risk to human and aquatic life when discharged into water bodies. One of the most effective means of removing ciprofloxacin from wastewater is photocatalytic degradation. However, the synthesis of an effective photocatalyst that can degrade the organic pollutant in the wastewater is often a challenge. Hence, this study focuses on the synthesis and application of nitrogen-doped TiO₂ (N-TiO₂) in suspension and coated forms for the photocatalytic degradation of ciprofloxacin in wastewater by applying UV-light irradiation. The nitrogen-doped TiO₂ photocatalyst was prepared by a co-precipitation process and characterized using energy-dispersive X-ray spectroscopy, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The effects of the initial concentration of the ciprofloxacin (6, 12, 18, or 30 ppm), pH (3, 5, 7, or 9), and flow rate (0.4, 0.8, 0.95, or 1.5 L/min) on the degradation of the ciprofloxacin over the N-TiO₂ were investigated. The results showed that the removal efficiency of ciprofloxacin was enhanced by increasing the initial ciprofloxacin concentration, while it was decreased with the increase in the feed flow rate. The best operating conditions were obtained using an initial ciprofloxacin concentration of 30 ppm, pH of 5, and feed flow rate of 0.4 L/min. Under these operating conditions, removal efficiencies of 87.87% and 93.6% were obtained for net TiO₂ and N-TiO₂ of 5 wt% in suspension form, respectively, while 94.5% ciprofloxacin removal efficiency was obtained using coated 5 wt% N-TiO₂ after 2 h of photocatalytic degradation. Based on the response surface optimization strategy, a quadratic model was suggested to obtain mathematical expressions to predict the ciprofloxacin removal efficiency under various studied operational parameters.

Membrane engineering is currently classified as an eco-friendly cleaning technology in various fields, especially for wastewater treatment, and its use is increasing due to the growing interest in water environment protection and preservation. In this study, a new approach to improving membrane performance is proposed by using polyethersulfone (PES) as a polymer blend with polyphenylsulfone (PPSU). PPSU-PES ultrafiltration membranes were prepared using the classical phase inversion method to remove dyes from simulated wastewater of the leather tanning industry. Four concentrations of PES were studied (i.e. 0, 4, 5, and 6 wt.%), while keeping the concentration of PPSU constant at 20%. A scanning electron microscope (SEM) and atomic force microscopy (AFM) were used to characterize the surface structure of the cross-section, top, and bottom membranes. It was found that the structural morphology of the membrane varied with the PES concentration. The addition of PES helped significantly decrease the contact angle and increase the porosity of the PPSU/PES/N-methyl-2-pyrrolidinone (NMP) blend membranes by approximately 15.2% and 280%, respectively, and to decrease the thickness of the membrane compared with neat PPSU. The effects of black dye (i.e. acid black 210, MW = 938.017 g mol⁻¹) concentration (i.e. 35, 45, and 65 ppm), feed temperature, and pH on the permeate flux and dye removal were also investigated in this study. It was found that there is a minor effect of the feed temperature and no effect of pH on the permeation flux. Also, it was discovered that the performance of the membranes improved from 5.77 to 27.7 and 3.46 to 19.62 for distilled water and feed solution of 35 ppm, respectively over those prepared from the neat PPSU membrane, while the dye removal was higher than 99.65% for all of the membranes studied.