Iranian Journal of

Backgrounds and Objectives: Nitrate is a water contaminant that can cause health problems in human and animals, in addition to eutrophication of the water body. So, Nitrate-contaminated water may be treated by treatment systems. In this study, hydrogenotrophic denitrification using hydrogen produced by Fe0 as an electron donor to nitrate removal was evaluated to assess the feasibility of employing Fe0 in the biological nitrate treatment.
Materials andMethods : Batch experiments were conducted using 250 ml amber bottles at 20-35oC under anoxic conditions. The nitrate concentration in each reactor was 20 mg N/L and triplicate samples were prepared for the following treatment: Fe0 plus cells, Fe0 only, and control. The effect of Fe+2 and temperature on nitrate reduction was evaluated.
Results : 97 percent of Nitrate was reduced within 2 day in a Fe0-cell reactor, while only 30% of the nitrate was abiotically reduced over 2 day at 30 oC. Fe+2, which is produced during anaerobic iron corrosion in the Fe0-cell system, might act as an electron donor for nitrate. Abiotic reduction and microbial reduction of nitrate was significantly affected by temperature conditions. The reduction rate decreased as the temperature deceased.
Conclusion:This study demonstrated the potential applicability of employing Fe0 as a source of electrons for biological nitrate reduction. Use of Fe0 for microbial nitrate reduction can obviate the disadvantages associated with traditional biological denitrification that relies on the use of organic substrates or explosive hydrogen gas.

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 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.