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Wastewater treatment with microalgae and its reuse is an effective step toward reducing water consumption and preserving water resources. The possibility of growing spirulina microalga on cattle effluents and the possibility of purifying effluents using microalga were investigated. Different concentrations of standard culture medium (Zaruk)-wastewater were used to measure the optimal algal growth on wastewater and to determine the concentration of effluent-Zaruk for optimal algal growth. The treatments were T1 including 100% Zaruk and no wastewater, T2 including 75% Zaruk and 25% wastewater, T3 including 50% Zaruk and 50% wastewater, T4 including 25% Zaruk and 75% effluent and T5 including 100% effluent without Zaruk. Treatments that had more Zaruk, showed more optimal growth, and those that had a higher concentration of effluent often showed a relatively lower growth of algae biomass. The results showed the high growth of algae on the concentrated effluent. T1 with 0.35 and T2 with 0.3 g/liter of dry biomass had the highest biomass of microalgae. T1, T2, T4, T3, and T5 had the highest to the lowest amount of phycocyanin pigment production in microalgae, respectively. The highest removal of nitrate belonged to T5 and T4 with 82.57% and 78.21% removal respectively, and the lowest nitrate removal belonged to T1 and T2 with 57.17% and 70.94%, respectively. The highest removal of phosphate belonged to T1 and T2 with 94% and 92.11% removal, respectively. The lowest removal of phosphate belonged to T4 with 84% removal. Findings indicated the high potential of microalga for treating cattle wastewater. [ABSTRACT FROM AUTHOR]

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.

Introduction and purpose: Nitrate is one of the most important pollutants in surface and groundwater. The present study aimed to evaluate the effect of different parameters on the performance of the electrical coagulation process in the removal of nitrate from contaminated water. Methods: This study was conducted based on an experimental design and the statistical community was urban water. A cylindrical batch reactor with aluminum and zinc electrodes (monopolar arrangement) was used to remove 100 mg/L nitrates. The experiments were performed three times in direct and alternating currents using standard methods. Factors of pH, contact time, and weight of electrodes were evaluated, and the results were reported in tables and graphs. Results: Nitrate removal efficiency (87.4%) was higher in direct current, as compared to that in alternating current (39.1%). The highest nitrate removal efficiency of 87.4% was obtained in direct current, in comparison with 61% for alternating current. As the contact time increased, the pH of the solution increased in two currents, from 7 to 11.21 and 8.47, respectively. Total dissolved solids (TDS) at optimal conditions in alternating and direct current were 79 and 126 mg/L, respectively. After 30 min of settling, the produced sludge was measured as 17.66 and 280 mL/L in direct and alternating current, respectively. The weight of the anode electrode had the greatest decrease in direct current. Conclusion: The results of this study pointed out that the process of electrical coagulation could reduce the concentration of nitrate to less than the standard. Nitrate removal with the direct current was performed with less energy consumption and cost than alternating current. As a result, the use of optimal conditions increases the process efficiency in the electrochemical removal of nitrate.

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.

Background and Objective: Synthetic wetlands are engineering systems that use natural plants, soils and organisms to purify municipal polluted water and remove nitrate. Materials and Methods: In this study, three systems were considerd as soil culture, three systems as plant cultivation on floating plates and three other systems without plant and porous bed as. The experiments were done three times within six months. The hydraulic retention times were 1, 3 and 5 days. The experimental design consisted of a factorial split-plot design. The analysis of variance showed that the efficiency of nitrate removal was affected by the type of constructed wetland, HRT, and temperature changes (p≤0.01). Results: At the HRT of 1 day, the average efficiency of nitrate removal by the soil culture, plant cultivation on floating plates and control were 14.34%, 12.09% and 10.51%, respectively. At the HRT of 3 days, the average efficiencies were 17.62%, 15.76% and 13.54%, respectively. At the HRT of 5 days, the efficiencies were increased and they were 17.75%, 17.66% and 16.08%, respectively. Conclusion: The results showed that the soil culture were more efficinet in removing nitrate .Also, the Cyperus alternifolius plant has the potential of nitrate phytoremediation.

In order to study the capability of microalgea Chlorella vulgaris in removal of nitrate and phosphate from water, the effects of initial concentration of nitrate and phosphate and photoperiod were investigated in 20 experiments proposed by response surface methodology. The most effective factors in nitrate removal include initial nitrate concentration, photoperiod and interaction of phosphate-photoperiod. Highest capability of nitrate removal (49.42%) achieved at the initial nitrate concentration of 1500 mg/l, initial phosphate concentration of 40 mg/l and under 16h of photoperiod. Initial concentration of phosphate, photoperiod and interaction of nitrate-phosphate and phosphate-photoperiod were the main factors affecting phosphate capability of algea. Highest capability of nitrate removal (41.61%) achieved at the initial nitrate concentration of 2250 mg/l, initial phosphate concentration of 60 mg/l and under 24h of photoperiod.

Background and Objective: Synthetic wetlands are engineering systems that use natural plants, soils and organisms to purify municipal polluted water and remove nitrate. Materials and Methods: In this study, three systems were considerd as soil culture, three systems as plant cultivation on floating plates and three other systems without plant and porous bed as. The experiments were done three times within six months. The hydraulic retention times were 1, 3 and 5 days. The experimental design consisted of a factorial split-plot design. The analysis of variance showed that the efficiency of nitrate removal was affected by the type of constructed wetland, HRT, and temperature changes (p≤0.01). Results: At the HRT of 1 day, the average efficiency of nitrate removal by the soil culture, plant cultivation on floating plates and control were 14.34%, 12.09% and 10.51%, respectively. At the HRT of 3 days, the average efficiencies were 17.62%, 15.76% and 13.54%, respectively. At the HRT of 5 days, the efficiencies were increased and they were 17.75%, 17.66% and 16.08%, respectively. Conclusion: The results showed that the soil culture were more efficinet in removing nitrate .Also, the Cyperus alternifolius plant has the potential of nitrate phytoremediation. [ABSTRACT FROM AUTHOR]

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, a system was designed and constructed that included an efficient, economically feasible method for adjustable, in-situ generation of hydrogen and carbon dioxide coupled with a packed bed bioreactor. The system was subsequently tested for its ability to remove nitrate from drinking water. The major objective was to develop an economical technology with a high selectivity for nitrate ions but causing minimum changes in other drinking water quality parameters. Hydrogen (as the electron donor) and carbon dioxide (as the carbon source for autotrophic denitrifier bacteria) were generated in a cost-effective way by applying a very low DC voltage (5-10 volts) in an electrochemical reactor using methanol electrolysis. The gases were injected into a denitrification bioreactor inoculated with denitrifier bacteria which are naturally present in water. Finally, the system was put to a pilot operation to remove nitrate from a nitrate-contaminated well (a typical contamination range of 120 mg/L as NO3-) in Tehran aquifer for a period of 160 days. The results showed that the system was capable of achieving a nitrate removal efficiency of 95% with an HRT of 2-5 hr while its power consumption was minimal and only required the two harmless gases, hydrogen and carbon dioxide, to be injected without any chemical additions.

Zebra mussel (Dreissenidae polymorpha) is capable of filtering great volumes of water due to its high population density. In this study, Nitrate and Phosphate removal capability of 3 shell masses (20, 40, and 60 gr) in urban wastewater was investigated based on filtering rate measurements (using simultaneous phytoplankton, chlorella, and Scenedesmus cultures) and indirect absorption of nitrate and phosphate in open and closed systems with 3 to 10 replications. Open and closed systems showed a positive correlation between shell weights and Nitrate and Phosphate filtration rates (R2 =0.99) but a negative correlation between influent Nitrate and Phosphate concentrations and their filtration rates (R2=0.97). Increasing of shell weights in the open system resulted in absorption rates of 0.08-0.2mg.l-1 of the shell dry weight for Nitrate and 0.02-0.04 mg.l-1 for Phosphate. In the closed system, these rates were 0.03-0.11 mg.l-1 of the shell dry weight for Nitrate absorption and 0.01-0.02 mg.l-1 for Phosphate. These results show that shell masses have a low nitrate and phosphate removal efficiency, especially in the case of phosphate, and they can not be, therefore, recommended for urban wastewater treatment.

Batch experiments were carried out to study chemical reduction of nitrate by metallic iron (Fe0) as a potential technology to remediate nitrate-contaminated water. The effects of different operating conditions such as initial pH of the solution, nitrate concentration, and Fe0 dosage on both nitrate reduction and removal efficiency were investigated. The results showed that the initial pH of the solution was very effective on nitrate removal which was over 95% within two hours at pH=2. However, nitrate removal decreased with increasing pH. Thus, only 18.2% of nitrate was removed at pH=5. It was also found that the ratio of iron to nitrate was important in nitrate removal, and a ratio of 400gFe0/gNO3- had the best efficiency for nitrate removal. The feasibility of using industrial wastes such as iron filings was also studied and it was found that the wastes could be desirable for nitrate removal.