Iranian Journal of

Background and objective: The conventional chemical and physical methods for water disinfection include the application of ultraviolet (UV), chlorination, and ozonation. Water disinfection by electrochemical methods has been increasingly carried out recently. The goal of this applied - analytical research is to investigate the removal of E. coli bacteria, as the index of water microbial contamination, from drinking water by electrochemistry method.
Materials and Methods: In this study, the contaminated water sample was prepared through adding 102 and 103 E. coli bacteria per ml of drinking water. The contaminated water entered into the electrochemical reactor and different conditions were studied, included pH (6, 7, and 8), number of bacterium (102 and 103 per milliliter), time (5, 10, 20, and 40 min), distance between electrodes (2,2.5, 3, and 3.5 cm), and voltage (10, 20, 30, and 40 volts).
Results: The findings indicated the indirect correlation between bacteria removal efficiency and the variable distances between two electrode. The results indicated the direct correlation between bacteria removal efficiency and the variables voltage and electrolysis times. The results showed that the best conditions for removal of 102 and 103 bacteria per milliliter obtained at pH 7, electrolysis time of 10 min, distance between electrodes 2 cm, in the voltage 20 and 30 volts, respectively.
Conclusion: The results of this study indicate that voltage and electrolysis time have the most significant effect on electrolysis efficiency. Research findings showed that electrolysis is a promising method for removal of E. coli bacterium from drinking water.

Background and Objectives: Toxicity assessment of material related to nanotechnology is necessary before excess development of this industry. On the other hand, specific characteristic of nanomaterials can be used in disinfection of other material. In this study toxicity and antibacterial properties of nano-TiO₂ and nano-CuO were investigated with four bacterial species in solid media.

Material and Methods: Stock suspension of nanoparticles (10g-TSS/L) was diluted using Muller Hinton Agar to achieve 5-6000mg-TSS/L concentration. We prepared three Petri dishes for each concentration and refined bacteria were cultured on these Petri dishes. After culturing of these bacteria on the media containing nanoparticles, growth inhibition was determined. According to this data, 50% growth inhibition (EC₅₀), no observed effect concentration (NOEC) and 100% growth inhibition were determined.

Results: Our results showed that toxicity of TiO₂ is more than CuO in solid media. In this regard, nano-TiO₂ EC₅₀ for Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Pseudomonas aeruginosa was calculated 181, 571, 93 and 933mg-TSS/L respectively. These figures for nano-TiO₂ were 2550, 1609, 946, and 1231mg-TSS/L respectively.

Conclusion: This study showed that compared with other bacteria studied, E. aureus due to high sensitivity and E. coli due to high resistance to both TiO₂ and CuO nanoparticles are more proper as bioindicator in toxicity test and antibacterial test respectively.

Background and Objective: The use of household water filter systems has been widely increasing in recent years because of water pollution.  In water filter systems, bacterial biofilm forms on the surface of the membranes, thereby increasing the possibility of transferring antibiotic resistance among bacteria and allowing their entry into the human body. This study analyzed the types of bacteria that grow in the membranes of water filter systems and their antibiotic resistance.

Materials and Methods: For this study, samples were collected from 80 membranes of household water filter systems. Bacteria grown on these membranes were identified using biochemical and molecular methods. Resistance against antibiotics including penicillin, tetracycline, erythromycin, gentamycin, cephalexin, and trimethoprim-sulfamethoxazole was evaluated by disk diffusion method.

Results: The detected bacteria included Pseudomonas, Rhodococcus, Bacillus, Sphingomonas, Zymomonas, Aeromonas, Klebsiella, Citrobacter, Drexia and Achromobacter. Majority of the isolates were identified as Pseudomonas aeruginosa. The antibiogram test showed that most of these bacteria exhibited multi-drug resistance (MDR). Maximum resistance was observed toward cephalexin and the least resistance was toward gentamicin.

Conclusion: The results revealed that membranes of household water filter systems were suitable environments for the growth of bacteria. In these conditions, MDR bacteria presumably could transfer antibiotic resistance genes to bacteria and microflora of the human body through water. Therefore, membranes should be designed in such a manner that not only they can remove the bacteria from water but also kill them.