Iranian Journal of

Background and objectives: Perchloroethylene (PCE) is categorized as contaminant of concern because of its adverse health effects and persistence in drinking water resources. Permeable reactive barrier with zero valent iron (ZVI-PRB) is a passive zone in which chlorinated ethenes are degraded in situ through the chemical reduction mechanism. The objective of the present investigation was optimization and modelling of ZVI-PRB technology for the elimination of PCE from the aqueous environment using response surface methodology. Materials and methods: In order to simulate ZVI-PRB, a column filled with silica sand and ZVI was used. effects of three variables including pH, column height or barrier thickness and flow on reductive dechlorination efficiency were assessed. Design of experiment, modelling, and data analysis were carried out using response surface method. Results: The dechlorination efficiency was about 93% under optimum conditions (pH=5, 26 cm column height and 2 mL/min flow rate). The ascending trend of pH along the column revealed that the reductive condition was dominant within the column. The R² value of 0.98 also indicated good fitness of the experimental results and model predictions. Conclusion: Based on the results, ZVI-PRB technology has high efficiency in dechlorination of PCE. Likewise, regarding to no need of energy consumption, abundance of iron, no production of harmful by-products and cost-effectiveness, ZVI-PRB is propounded as a stable, green, and environmental friendly technology in groundwater remediation.

Background & Objectives: Cryptosporidium parvum is considered as one of the pathogenic agents transmitted by water, high resistance to conventional disinfection methods, and potency of creating various problems in water resource. Because of various problems in Cryptosporidium parvum studies, Bacillus subtilis spore is recommended as a surrogate organism for studying protozoa inactivation and evaluation of water quality. On the other hand, electrochemical process is presented as an environmental friendly and high efficient method in disinfection in recent years. The aim of this study was to propose a method for promotion of the water quality. Materials & Methods: In this study, the electrochemical system used was consisted of steel electrodes (4×8 cm), 200 mL volume, and 1-4 mg/L sodium chloride. The bacterial suspensions of Bacillus subtilis (ATCC 6633) was prepared according to the McFarland method with 103 to 106 spores/mL concentration. The microbial agent removal was evaluated by sampling and transferring water to the tripticase soy agar medium every 15 min for 60 min. The number of bacteria spores, supporting electrolyte, induced current, and reaction time were evaluated. Results: The proposed electrolysis process could not eliminate Bacillus subtilis spores at 104 to 106 spores mL^-1 rate at lower than 100 mA current for 60 min. Adding sodium chloride supporting electrolyte up to 4 mg/L concentration completely eliminated Bacillus subtilis spores after 60 min. Conclusion: Adding sodium chloride as a supporting electrolyte can increase the spore removal because of increasing direct and indirect oxidation in electrolysis process. Improving water disinfection and spore removal after 60 min could be described by higher oxidant agents in anode electrode.

Background and Objectives: Among the different types of antibiotics, tetracycline antibiotics are the second most common group around the world that their entrance into domestic sewage can result in contamination of water sources. The aim of this study was to investigate the efficacy of the nano-sonocatalytic process on removal of tetracycline antibiotics from aqueous solutions. Materials and Methods: In this study, the effectiveness of ultrasonic irradiation without and with TiO₂ nanoparticles and hydrogen peroxide were studied in tetracycline antibiotics removal. For this purpose, a reactor different concentrations of tetracycline was exposed to two irradiation frequencies of 35 and 130 KHz. Concentration of residual antibiotic was measured using HPLC equipped with a C18 reverse phase column and a UV detector. Results: It was found that the efficacy of ultrasonic irradiation alone in removal of this pollutant was negligible and at the best conditions only 20.3% removal was achieved at the frequency of 35 KHz. Addition of TiO2 nanoparticles improved the removal efficiency the removal rate increased with the increase in TiO₂ concentration until 250 mg/L, after which it remained approximately stable. The best removal efficiency was achieved by adding 100 mg/l hydrogen peroxide to US/TiO₂ process at pH 4 in which 94.3% removal was achieved after 60 minute. Conclusion: The results of this study showed that the sonocatalytic process using TiO₂ nanoparticles and along with adding H₂O₂ as an oxidant is very effective and can be used for removal of tetracycline antibiotics from aqueous solutions.

Background and Objective: Natural organic matters (NOM) are known as precursors to disinfection byproducts. As conventional treatment processes cannot get disinfection by-product standards, novel methods have been increasingly applied for the removal of disinfection by-products precursors. The UV/ZnO process is one of the advanced oxidation processes using photocatalytic technology. The present study aims to investigate the effect of UV/ZnO photocatalytic technology on the NOM removal from aqueous solution. Materials and methods: This study was conducted in a lab-scale batch photocatalytic reactor. The volume of reactor was 1liter and covered with UV lamps. Peristaltic pump was used for complete mixing. Humic acid is a key component of natural organic matter and it was used in this study. Each of the samples taken from the UV/ZnO process and other processes were analyzed for their UV absorbance at 254 nm by spectrophotometric. Initial concentration of Humic acid, contact time, pH, and UV irradiation were investigated. Results: The highest efficiency of the UV/ZnO photocatalytic process for removal of Humic acid from aqueous solution was achieved at initial concentration = 2 mg/L, contact time = 120 min, UV irradiation = 3950 µw/cm², and pH=3. In this process, the removal efficiency for 2 mg/L humic acid was 100 % at 2h retention time. Conclusion: The research showed that performance of system was increased by increasing contact time and UV irradiation and was decreased by increasing HA initial concentration and pH and UV radiation with ZnO agent could not remove NOM lonely. Photocatalytic system using zinc oxide immobilized on glass have high performance to remove humic acid from aqueous solution. The UV/ZnO process was efficient and environmental friendly for natural organic matter removal.

Background and Objective: Natural organic matters (NOMs) are a mixture of chemically complex polyelectrolytes with varying molecular weights, produced mainly from the decomposition of plants and animal residues. Various purification methods are used for removal of NOMs from water. The objective of this study was to remove NOMs from aqueous solution using reformed continuous carbon nanotubes column. Materials and Methods: The removal of NOMs from aqueous solution using reformed continuous carbon nanotubes column was studied. Effect of several variables such as zero point of pH (pH_ZPC), pH, influent concentration of natural organic matters were studied and different isotherms were assessed. Results: Investigation of pH effect showed that the adsorbability of NOMs increased with decreasing of pH. The experiments indicated that carbon nanotubes (CNT) samples exhibit pH_ZPC around 6. Results from Freundlich, Langmuir, and BET isotherm experiments revealed that the correlation coefficient R² in Freundlich model was higher than that of Langmuir. In addition, experiments of continuous flow in different initial concentrations of NOMs showed that the adsorption capacities of CNT were 53.46, 30.40, and 24.75 mg/g for NOMs initial concentrations of 10, 5, and 3 mg/L, respectively. Conclusion: The present study shows that CNTs have high potential for adsorption of NOMs from aqueous solution

Background and Objective: Arsenic is one of the most toxic pollutants in groundwater and surface water. Arsenic could have lots of adverse impacts on human health. Therefore, access to new technologies is required to achieve the arsenic standard.

Materials and Methods: The present study was conducted at laboratory scale in non-continuous batches. The adsorbent of zero-valent iron nanoparticles -Chitosan was produced through reducing ferric iron by sodium borohydride (NaBH₄) in the presence of chitosan as a stabilizer. At first, the effect of various parameters such as contact time (5-120 min), pH (3-10), adsorbent dose (0.3-3.5 g/L) and initial concentration of arsenate (2-10 mg/L) were investigated on process efficiency. Then optimum conditions in terms of contact time, pH, adsorbent dose and initial concentration of arsenate were determined by RSM method. Freundlich and Langmuir isotherm model equilibrium constant, pseudo-first and second order kinetic constants were calculated. The residual arsenate was measured y using ICP-AES.

Results: The optimum values based on RSM for pH, absorbent dose, contact time, and initial concentration of arsenate were 7.16, 3.04 g/L, 91.48 min, and 9.71 mg/L respectively. Langmuir isotherm with R²= 0.9904 for Arsenate was the best graph for the experimental data. According to Langmuir isotherm model, the maximum amount of arsenate adsorption was 135.14mg/g. . The investigation of arsenate adsorption kinetics showed that arsenate adsorption follows the pseudo-second kinetics model.

Conclusion: This research showed that the adsorption process is depended on pH. With increasing pH, the ability of amine groups in chitosan are decreased to protonation, caused to decrease the efficiency of arsenate removal at high pH.

Background and Objective: Dyes are important pollutants that lead to producing serious hazards to human, other animals and organisms. Dyes are not biodegradable by aerobic treatment processes. Therefore, their removal from industrial effluents before discharging into the environment requires extreme and great attention. The aim of this research was to evaluate removal efficacy of methyl orange dye from aqueous solutions using NiFe₂O₄ nanoparticles.

Materials and Methods: This study was an empirical investigation in which NiFe₂O₄ nanoparticles were synthesized by co-precipitation method and were used as an adsorbent for the removal of methyl orange from aqueous solution. NiFe₂O₄ nanoparticles were characterized using X-Ray Diffraction (XRD), Transmission Electronic Microscopy (TEM), pH_pzc and SEM-EDX elemental analysis methods. Experiments were conducted discontinuously using 20 mL methyl orange solution of 40 mg/L. The effect of variables such as pH (2-8), amount of adsorbent (0.009-0.07 g) and contact time (2-70 min) on the efficacy of dye removal was studied. Finally, experimental data were compared by Langmuir, Freundlich, and Temkin isotherms and pseudo-first-order and pseudo-second-order kinetic models.

Results: TEM images showed that the NiFe₂O₄ nanoparticles had spherical shapes with the size of 12 nm. The results indicated that removal efficiency increased up to 0.04 g adsorbent and 20 min contact time. The optimum pH for methyl range removal was 2. Moreover, under these conditions, the adsorption process followed the Langmuir adsorption isotherm with a correlation coefficient of 0.995 and pseudo-second-order kinetic model with a correlation coefficient of 0.999. Also, the maximum adsorption capacity of the prepared adsorbent was 135 (mg/g) for Langmuir isotherm.

Conclusion: The NiFe₂O₄ nanoparticles are effective and available adsorbents for the removal of methyl orange from industrial wastewater.

Background and Objective: Owing to the extended usage in the safekeeping of environments, the photocatalytic materials have been widely applied. The purpose of the present study was to investigate the photocatalytic activity of ZnO and SnO₂ nanoparticles in removal of methyl orange from aqueous media.

Materials and Methods: ZnO and SnO₂ nanoparticles were synthesized through sol-gel and chemical precipitation respectively. Methyl orange was selected as model pollutant. The effect of weight fraction on the removal of pollutant was investigated in the range of 0.25, 0.5, and 1 weight percent. Meanwhile, for investigating the effect of radiation time, the suspension containing pollutant and nanoparticles was irradiated. The obtained results were analyzed by MSTATC, Ver 1.42 software and Duncan’s multiple range test.

Results: The analysis of variance results of removal efficiency of methyl orange showed that in the suspension involving ZnO and SnO₂, radiation time, weight fraction and the combined effect of them have a significant effect on the removal of methyl orange at 5% level of probability. Meanwhile, by increasing irradiation time from 5 to 25 min, the removal efficiency in suspensions containing ZnO and SnO₂ reached 97.42 and 65.55% respectively. Investigation on the effect of concentration on the removal of methyl orange shows that the removal of methyl orange increases with respect to the weight fraction.

Conclusion: According to the obtained results, it was observed that the photocatalytic activity of ZnO is higher than that of SnO₂. Therefore, the application of ZnO is more effective for removal of methyl orange from aqueous media.

Background and Objective: Malachite green dye is used in many industries including textile industries. Disposal of wastewaters containing the dye to the environment, can lead to many environmental problems. Currently, many physico-chemical approaches are used for wastewater treatment. Because of limitations and difficulties of these methods, biological treatment is considered as an economic and effective treatment method. The aim of the present study was to study the feasibility of phytoremediation of malachite green dye using watercress and investigate the effect of some environmental factors in removal efficiency.

Materials and Methods: After collection, the plants were kept in the laboratory, and they were treated with different concentrations of malachite green. During the experiments, decolorization extent was determined by UV-Vis spectrophotometry. Intermediate compounds generated during the biodegradation of the pollutant were identified using GC-MS method.

Results: After 7 days, the ability of watercress in removal and biodegradation of 10 mg/L of malachite green solution was more than 90%. Five intermediate compounds were identified in the biodegradation pathway of the pollutant. It was also found that increasing dye concentration up to 20 mg/L led to the increase of the plant photosynthetic pigment contents and activities of antioxidant enzymes.

Conclusion: Our results showed that watercress has high ability in the dye removal of malachite green. The reusability of the plant for decolorization confirmed the biological degradation process. Moreover, an increase in the plant biomass, temperature and pH led to the increased decolorization efficiency.

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.

Background and Objective: Phosphorus (P), as one of the agricultural, industrial and urban wastewater pollutants, plays an important role in eutrophication of surface waters. Use of cationic sorbents for removal of anions including phosphate from aqueous environments is a well-known and effective method. Meanwhile, layered double hydroxides (LDHs) are known as effective anion exchange sorbents. In this study, the efficiency of Mg-Al layered double hydroxide (Mg-Al-LDH) for P removal from aqueous solutions was investigated.

Methods and Materials: The Mg-Al layered double hydroxide (Mg-Al-LDH) was synthesized by co-precipitation method and used for removing of P from aqueous solutions. The kinetics and equilibrium studies of phosphate adsorption by Mg-Al-LDH were performed using a batch experiment at different contact times, initial phosphate concentrations, pH values, ionic strengths and doses of sorbent.

Results: The results of the kinetics experiments showed that sorption of P with LDH reached equilibrium after 30 min. The highest correlation coefficient was obtained for the pseudo-second order model, indicated that chemical sorption controlled the rate of phosphate sorption by LDH. The results showed that the sorption experiments data were in good agreement with Langmuir model and the maximum adsorption capacity predicted by this model was 37.83 mg P/g LDH.

Conclusion: The current study revealed that P adsorption by LDH was increased by increasing contact time and concentration of LDH, but decreased by increasing initial concentration of P, pH and ionic strength. The optimum conditions for phosphate anion adsorption by Mg-Al-LDH were determined as P initial concentration of 20 mg/L, contact time of 120 min, pH of 3.0, sorbent dose of 10 g/L and ionic strength of 0.03 mol/L.