Sub-therapeutic levels of antibiotics (ABs) are given to animals and poultry to promote growth and reduce disease. In agricultural environments, ABs reach croplands via animal manure used as fertilizer and/or ABs-contaminated water used for irrigation. The continuous discharge of ABs into the ecosystem raises growing concerns on the ABs contamination of edible crops. Tetracyclines (TCs) are among the most widely used ABs around the world. In this review, we discuss the contamination of irrigation water with TCs, its impact on edible crops, and the potential risks of crop contamination with TCs on human health. We propose solar-mediated photocatalytic degradation using Titania (TiO2) photocatalyst as a promising method to remove TCs from irrigation water. The photocatalytic activity of TiO2 can be enhanced by chemical modification to expand its activity under visible light irradiation. Herein, we aim for providing literature-based guidance on developing a visible light–active TiO2-based system to degrade TCs and other ABs in water streams. We include a summary of recent advances on this topic based on three main modification methods of Titania: metal/non-metal/mixed doping, composite formation, and heterojunction construction. Among the investigated photocatalysts, Fe2O3-TiO2/Fe-zeolite and the N-doped TiO2/rGO immobilized composite catalysts were found to be very efficient in the degradation of TCs under visible light irradiation (i.e., 98% degradation within 60 min). Most immobilized TiO2 based composite systems exhibited improved performances and hence we highlight these as efficient, cost effective and ecofriendly photocatalysts for the degradation of TCs in irrigation water.
In this study, we investigated the photocatalytic degradation as a potential treatment of tetracycline (TC) antibiotic contaminated water using TiO2 semiconductor. To expand the activity of TiO2 into the visible light region and to enhance its adsorption capacity for TC, we explored its modification via sensitization with Fe ions and via immobilization on beta (BEA) zeolite support. The nano-sized beta zeolite, synthesized using the seed-assisted procedure, was used to immobilize TiO2 initially prepared by the sol-gel method. The immobilized TiO2/BEA catalyst was further ion exchanged with Fe3+ ions using FeCl3 precursor. Fe3+ modified TiO2/BEA (Fe-TiO2/BEA) catalyst was characterized using SEM, XRD, BET, UV-VIS DRS, and FTIR. After the immobilization of TiO2 over BEA, the surface area of TiO2 increased from 90 to 530 m2/g and similarly its TC adsorption efficiency increased from 10% to 33%. The photocatalytic performance of the Fe-TiO2/BEA was evaluated under blue LED light for TC degradation. Fe-TiO2/BEA exhibited higher TC removal efficiency (100%) compared to TiO2 (80%) after 90 min of irradiation using 50 W blue LED light for a 250 mg/L initial catalyst concentration and 20 mg/L TC concentration. The enhanced performance of the final catalyst was a result of the expanded surface area due to the immobilization of the TiO2 on the BEA zeolite, which resulted in an improved TC adsorption. Moreover, the presence of Fe3+ ions reduced the band gap energy of the TiO2, hence led to a red shift in its absorption spectrum to the visible light region and minimized the extent of the recombination of the charge carriers.
In this project, an unsupported electrospun poly(vinylidene fluoride)‐co‐hexafluoropropylene (PVDF‐HFP) membrane was used for water desalination using direct contact membrane distillation (DCMD). The membrane was electrospun using a laboratory‐scale machine with multiple nozzles that was developed in‐house. Critical process parameters, including the applied voltage and polymer concentration, were optimized to obtain bead‐free electrospun membranes with fiber diameters less than 300 nm. To improve the membrane thermal stability and performance, the selected electrospun membrane was heat‐pressed at 160°C. The untreated and heat‐pressed membranes were tested in a DCMD setup at different feed temperatures (60, 70, and 80°C) and feed flow rates (0.4, 0.6, and 0.8 L/min), while maintaining the permeate temperature and flow rate at 20°C and 0.2 L/min, respectively. The modified electrospun membrane exhibited a very high permeate flux (>37.5 kg/m2/h) and a salt rejection rate of 99.99% at a feed temperature of 70°C. The performance of the heat‐pressed unsupported PVDF‐HFP electrospun membrane was nearly identical to a commercially available polytetrafluoroethylene (PTFE) supported membrane. These promising results demonstrate that relatively low‐cost electrospun membranes can be easily produced and successfully used in DCMD to minimize the capital cost and increase the energy efficiency of the process.
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