جستجوی مقالات مرتبط با کلیدواژه « Nitrate Removal » در نشریات گروه « مهندسی آب »

In this paper, the removal of nitrates from urban raw sewage (Tehran) by walnut tree sawdust using the surface absorption method was introduced as an efficient green method, and the effect of various parameters was studied. The results obtained from Langmuir isotherms R2=0.9951 and Freundlich R2 = 0.9936 indicated better absorption in low concentrations, which follows the Langmuir model. To complete the present studies, the adsorption diagram, the effect of pH, thermodynamic and kinetic studies were investigated. Kinetic studies showed that the surface adsorption process of nitrate by walnut tree sawdust follows the pseudo-first order kinetic. The absorption capacity obtained from this equation was 34.2 mg/g (its experimental value of 32 mg/g). The results showed that this process is controlled by reversible physical adsorption. According to the FT-IR spectrum of the absorbent, the phenomenon of nitrate absorption takes place with the help of the cellulose structure of the absorbent. The use of walnut tree sawdust (micro size) without chemical modification as a natural, green, environmentally friendly, efficient, and effective adsorbent in removing nitrates from the raw sewage of Tehran city was one of the important features of this research.

Nitrate removal using biological heterotrophic denitrification is one of the most effective and economical processes to remove nitrate from drinking water. In recent studies, carbon sources such as acetic acid, methanol, ethanol, glucose, etc. have been used as a carbon source for heterotrophic bacteria. Inevitable residues of these carbon sources in effluent water and the cost of them are the key challenges for applying these carbon sources in drinking water, in the operational scales. To overcome these challenges, in this research, citric acid produced from sugar beet is used as a harmless, relatively economical and accessible carbon source. Also, to remove the remaining trace amounts of carbon source in denitrified water and disinfection of treated water, ozonation has been used as a dual-purpose process. Pilot studies of this process during the operation of about one year on natural water of one of the wells of North Khorasan province in Iran with the nitrate concentration of 104±10 ppm ppm as NO3- showed that in four column bioreactor packed with different media such as natural river gravel, polypropylene plastic (PP), polyethylene plastic (PE) and Pumice aggregates and by carbon to nitrogen ratio (C/N) of about stoichiometric amount and HRT of greater than 4 hours and without any other chemical addition, the nitrate removal rate of greater than 85% can be achieved. In the carbon concentrations, about 1.5 times the stoichiometric value and the HRT of about 5 to 7 hours, the removal efficiency can be as high as 95%. Ozonation of treated water in 30 to 60 minutes also showed that the ozone has the capability of the complete removal of carbon residuals in effluent of the process from 15-30 ppm as COD to about zero.

Nitrate contamination in water resources has become an important issue because of the environmental issue and potential risk to human health. The aim of this study is investigating the stabilization of modified bentonite nanoparticles by cationic surfactant on pumice aggregates to remove nitrate from aqueous environments. Bentonite nanoparticles were investigated by XRD, EDAX, and SEM techniques after modification by CTAB surfactant with the thermal method on the substrate of Pumice aggregate stabilization and physical and structural characteristics of the adsorbent. In this research, response surface method based on the Box-Behnken model was used for evaluation of the effects of independent variables such as pH, temperature and the amount of adsorbent on the response function and prediction of the best response value. Langmuir and Freundlich isotherm models were used for calculating the equilibrium constants and pseudo-first and second order constants. According to the results, the optimum nitrate removal efficiency was determined 63.49% based on the Box-Behnken model in pH = 5, the adsorbent concentration of 15 g/L, and temperature 35°C. As well, the nitrate removal rate was increased by increasing the amount of adsorbent and contact time unless the removal efficiency was decreased with an increase in pH and initial nitrate concentration. Isotherm surveying showed that the laboratory data had better agreement with Langmuir isotherm and the best kinetic model of adsorption was determined by the pseudo-second-order kinetic model. Also, the recovery efficiency in 5 cycles of absorption and desorption was observed more than 85%. This study showed that modified Pumice aggregates could be used as an effective and economical adsorbent for pollutants elimination.

The efficiency of modified Phragmites australis nanoparticles for nitrate removal from aqueous solution in batch and continuous conditions was studied. The effect of different operating conditions such as pH, the amount of adsorbent, and initial nitrate concentration were surveyed. Our results showed that, pH 6 could provide better condition for nitrate removal. The increase in the nitrate concentration from 5 to 120mg L-1 reduced the efficiency from 90% to 67%. Kinetics and isotherm data revealed that the nitrate adsorption successfully can be described by pseudo-second order kinetic model (R2 =1) and Longmuir isotherm (R2 =0.99), respectively. At the continuous-flow mode, column were operated at 0.98 L hr-1 and 2.27 L hr-1 with initial nitrate concentration of 15, 50 and 120 mg L-1. At the above mentioned conditions, the adsorption capacities were 13.4, 28.5 and 36.5 mg g -1 at 0.98 L hr-1 and 25.2, 60.9 and 74.3 mg g-1 at 2.27 L hr-1, respectively.

In this research the effect of Sugarcane straw and Phragmites australis anion exchanger nano adsorbents have been investigated for removal of nitrate from aqueous solutions. The effects of operating conditions such as pH, contact time, adsorbent loading, initial anion concentration, and the presence of competitive ions on the adsorption performances were examined. The results showed that the equilibrium time was 2 hours and the pH was 6. With pH of the solution varying from 2 to 10, the nitrate removal efficiency for sugarcane straw and Phragmites australis nano adsorbent increased up to maximum of 45% to 76% and 60% to 86% reached at pH 6. With an increase in the nitrate concentration from 5 to 120 mg/L, the removal efficiency decreased from 86% to 66% and 90% to 67% for sugarcane straw and Phragmites australis nano adsorbent,respectively. For Phragmites australis nano adsorbent, with an increase in the adsorbent dosage from 0.1 to 0.3 grams, the removal efficiency increased from 60% to 85%, but remained almost unchanged when adsorbent dosage ranged from 0.3 to 1grams. For sugarcane straw nano adsorbent as the adsorbent dosage increased from 0.1 to 0.5 grams, the removal efficiency of nitrate increased from 45% to 75%, but remained almost unchanged for the increase of 0.5 to 1 grams. Adsorption kinetics of nitrate ions could most successfully be described by Freundlich isotherm. This study indicated that sugarcane straw and Phragmites australis nano adsorbents could be used for the removal of nitrate ions in water treatment and Phragmites australis nano adsorbent has higher adsorption than sugarcane straw nano adsorbent for nitrate removal.