Water is one of the main sources of human pathogenic microorganisms in developing countries. Therefore, new low-cost water treatment technologies are required to prevent public health problems. The main goal of this work was to develop a water purification technology using magnetic nanoparticles, to be applied in a water outlet point where the contact time between the two phases is minimal. For that, six different nanomaterials were synthesised based on iron oxide (FeO): FeO, mixed oxides of Fe with Mn, Co or Cu, a composite of FeO with activated carbon, and FeO subsequently coated with carbon by chemical vapour deposition (CVD). Different techniques were used to characterise these nanomaterials and their ability to remove E. coli (a Gram-negative bacteria) and also S. aureus (a Gram-positive bacteria) cells from a suspension was assessed. CuFeO, FeO, MnFeO and FeO/AC composite MNPs showed high removal efficiencies of Escherichia coli (Gram-negative). For the nanoparticles with higher removal efficiencies in the first tests (FeO and CuFeO), 50 mg mL−1 was the optimal concentration of particles and 1 min of contact time it was enough to obtain high removal efficiencies. The removal efficiency of S. aureus was higher than that of E. coli when FeO particles were used. In contrast, the removal efficiency of E. coli was higher than that of S. aureus for CuFeO particles. For both particles, the removal efficiency of microorganisms for the well water sample was lower when compared with the bacteria suspensions, being 64.1 % for FeO and 91.8 % for CuFeO. The reuse tests showed that these particles could be re-used several times without losing efficiency in bacteria removal. The MNPs used are simple and low-cost and show promising results for the elimination of both types of bacteria (gram-positive and gram-negative) demonstrating that this technology is a promising alternative to the conventionally used processes showing an easy, efficient, and inexpensive method for treating water for human consumption.
The presence of heavy metals and/or harmful bacteria in drinking water represents significant risks to human health. This study aimed to develop a low-cost water treatment technology using synthesized nanocomposites with metal nanoparticles supported on activated carbon (AC) for bacteria and heavy metal removal. In addition, the performance of the developed nanomaterials was compared with that of commercial materials – carbon fibers of three different typologies. The chemical and textural properties of all tested materials were characterized. To simulate a technology to be applied in a water outlet point, removal tests were carried out in a continuous system using suspensions of Escherichia coli and/or Staphylococcus aureus, wherein the contact time with the two phases was minimal (1 min). The obtained results revealed that iron and copper oxides supported on AC with a calcination treatment (CuFeO/AC-C) was the nanocomposite with the best performance, achieving a 6 log reduction for both bacteria in the same suspension up to 9 h operation. A mix of bacteria and heavy metals, simulating a real water, was treated with CuFeO/AC-C obtaining a 6 log reduction of bacteria, a Pb2+ removal >99.9% and Cd2+ removal between 97 and 98% over 180 passage times.
A brief overview about the use of carbon materials as metal free ozonation catalysts is presented. Carbon materials (activated carbons, carbon xerogels, carbon nanofibers and carbon nanotubes) have been shown to be active catalysts in the ozonation of a wide range of organic pollutants. Carbon materials with surface basic properties (i.e. high electron density) and with large pores are the most promising for this process. Resumen En el presente trabajo se resume brevemente el uso de materiales de carbon como catalizadores libres de metales en el proceso de ozonizacion. Los materiales de carbon (carbones activados, xerogeles de carbon, nanofibras y nanotubos de carbono) han mostrado ser catalizadores activos para una gran variedad de contaminantes organicos en dicho proceso, siendo los mas adecuados aquellos con propiedades superficiales basicas (alta densidad electronica) y con mayor tamano de poros. 1. Ozone reactivity in water
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