Many communities in the world use groundwater as a source of potable water. The high nitrate concentration is a serious problem in groundwater usage. This study utilizes a biological DENITRIFICATION method to investigate a moving bed biofilm reactor (MBBR) for the case of Tehran's groundwater. One pilot-scale MBBR with a 3 liter volume was designed and used in this research. The DENITRIFICATION reactor operates under anoxic conditions. Methanol was used as a carbon source in the reactor throughout the study, and fifty percent of the reactor volume was occupied with KMT packing (k1). To determine the optimum nitrate loading rate, the concentration of nitrate changed from 100 to 400 mg N/l. It was concluded that heterotrophic denitrifying bacteria converted nitrate to nitrogen. According to obtained results, the removal efficiency and optimum loading rate were estimated during the experiments in different concentrations and different HRTs for this type of reactor. Sodium nitrate was in the feed source in the anoxic reactor. The maximum removal rate of nitrate was measured to be 2. 8 g of NO3N m-2-1 carrier d. Therefore, it was shown that the optimum loading rate of nitrate and the optimum COD/N were equal to 3. 2 g of NO3-N m-2 -1 carrier d and 6 g of COD/g N respectively.

Years ago nitrate pollution in water and soil has been a major concern in the world's environmental issues. Nitrogen-containing compounds in the environment can cause new problems, such as river eutrofication and a dangerous disease called methemoglobinemia and other disorders in human health. One of the most important wastewater treatment goals is the removal of nitrogen, which is carried out by chemical, physical and biological processes that biological methods of nitrogen removal are more efficient and economical. Nitrification is one of the main processes for the removal of nitrate in water, a process that requires no oxygen, in which bacteria use from nitrate as an electron receiver to obtain energy for growth. Solid-phase DENITRIFICATION process is an emerging technology which has received increasing attention in recent years. It uses biodegradable polymers as both the carbon source and biofilm carrier for denitrifying microorganisms this process is a promising technology for the removal of nitrate from water and wastewater. In the future, more attention can be devoted to the simultaneous removal of nitrate and other pollutants from water by Solid-phase DENITRIFICATION, thereby ensuring the health of the environment and human.

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 and Methods: 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 30oC. Fe+2, which are 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.

Increasing nitrate concentration of surface and groundwater resources in different countries is considered as a common environmental problem, which is threatening the water quality all around the world. In Iran the concentration of nitrate in groundwater resources have exceeded the acceptable limits. This is due to the increase of agricultural and industrial activities and the excessive land discharge of treated and untreated wastewaters which mostly occurs in the urban and rural areas like Tehran, Mashhad and Isfahan. The high amount of nitrate causes adverse effects on water ecosystems. Furthermore, high concentration of this contaminant in drinking water may result in health risks like methemoglobinemia in infants and children, childhood diabetes and formation of carcinogenic compounds like nitrosamines.Among different physical, chemical and biological nitrate removal processes, biological DENITRIFICATION is considered as an efficient and inexpensive method. A wide range of heterotrophic and autotrophic bacteria consume nitrate as a final electron acceptor. In the heterotrophic DENITRIFICATION, heterotrophic denitrifying bacteria, like Achromobacter and Pseudomonas consume organic matters as electron donors. While in the autotrophic DENITRIFICATION autotrophic denitrifying bacteria, like Paracoccus denitrificans and Thiobaci/lus denitrificans consume inorganic compounds like sulfide, sulfur, molecular hydrogen, thiosulfate and Fe++ as electron donors. However, both processes may encounter some deficiencies during the treatment process. During t his process, some problems related to Heterotrophic DENITRIFICATION may rise up. These problems are mostly due to the need for an external organic carbon source in the case of wastewaters containing low C/N ratio, need for post treatment of the remained organic carbon removal, excess sludge production and its relevant costs and nitrite accumulation. On the other hand, autotrophic DENITRIFICATION may encounter problems like alkalinity consumption particularly at high-nitrate, low alkalinity of wastewater, high sulfate production and low nitrate removal ratio…..

DENITRIFICATION of high- nitrate high- salinity wastewater is difficult due to plasmolysis and inactivation of denitrifiers at high salinity conditions. In this study, the effects of salinity and empty bed contact time (EBCT) on simultaneous heterotrophic and sulfur based autotrophic DENITRIFICATION of synthetic wastewater were evaluated in an up flow packed bed reactor .The reactor was filled with granular elemental sulfur particles with diameters of 2.8-5.6 mm and porosity of 40%. The initial culture was prepared from sludge of Shahrak-e- ghods domestic wastewater treatment plant. The influent nitrate concentration and EBCT were 600 mg NO3-N/lit and 16 h respectively. First, the stoichiometric fraction of nitrate removed by heterotrophic DENITRIFICATION (with methanol as organic carbon source) supplied enough alkalinity to compensate the autotrophic alkalinity consumption, was determined 60%. Then, salt concentration was gradually increased with NaCl from 0% in the feed. The Process kept high nitrate removal efficiency (>99%) even at 3.5 % NaCl. During these changes the alkalinity variations were insignificant which showed the microbial population ratio of acclimated autotrophic to heterotrophic denitrifiers had no any significant changes with NaCl concentrations up to 3.5% in the feed. At 4 and 5% NaCl, the efficiency drastically decreased to 78% and 48%, respectively. Similar behavior was also observed for methanol removal efficiency, effluent turbidity as an indirect determinant of biological mass and sulfate production. The effects of flow rates on DENITRIFICATION of synthetic high nitrate high salinity wastewater with 3.5 %NaCl under mixotrophic condition were also investigated by increasing the flow rate from 7.06 lit/day to 70.6 lit/day with corresponding EBCT 20 to 2 h. DENITRIFICATION efficiency was close to 100% at EBCT of 20 to 8 hr, but decreased to 79% and 39% when the EBCT was 4 and 2 h, respectively. The decrease in effluent sulfate concentration (as an indicator for autotrophic DENITRIFICATION) and the increase in effluent alkalinity (as an indicator for heterotrophic DENITRIFICATION) and pH at EBCT of 4 and 2 h were considerable correspondingly. These results imply that the population ratio of autotrophic to heterotrophic denitrifiers depends on EBCT.

Nitrate contamination in drinking water can cause methemoglobinemia, which is especially detrimental to infants and nursing mothers. Batch experiments in two units for catalytic reduction of nitrate from groundwater with Zn catalyst and sulfamic acid were conducted. The system includes chemical denitriphication (ChemDen reactor) and electrolytic recovery reactoers. A batch study was conducted to optimize parameters like pH, sulfamic acid concentration, Zn concentration, temperature and reaction time governing the ChemDen process. The concentrations of remained nitrate and Zn were measured at the end of the reactions. Results showed that near to 100% of nitrate decreased and the quantity of remained nitrate was <1 mg/L. pH and agitation had great effect on DENITRIFICATION, and the nitrate removal rate changed rapidly when pH value ranged between 3-4. Two water quality parameters which limit this process were sulfate and chloride ions concentrations in nitrate contaminated water.

Background and Objectives: Contamination of drinking water sources with nitrate may cause adverse effects on human health. Due to operational and maintenance problems of physicochemical nitrate removal processes, using biological DENITRIFICATION processes have been performed. The aim of this study is to evaluate nitrate removal efficiency from drinking water using autotrophic denitrifying bacteria immobilized on sulfur impregnated activated carbon in a fluidized bed bioreactor.Materials and Methods: After impregnating activated carbon by sulfur as a microorganism carriers and enrichment and inoculation of denitrifying bacteria, a laboratory-scale fluidized bed bioreactor was operated. Nitrate removal efficiency, nitrite, turbidity, hardness and TOC in the effluent were examined during the whole experiment under various conditions including constant influent nitrate concentration as 90 mg NO3--N/l corresponding to different HRT ranging from 5.53 to 1.5 hr.Results: We found that the DENITRIFICATION rates was depended on the hydraulic retention time and the nitrate removal efficiency was up to 98% and nitrite concentration was lower than 1mg/l at optimum HRT=2.4 hr respectively. Moreover, there was no difference in hardness between influent and effluent due to supplying sodium bicarbonate as carbon source for denitrifying bacteria. However pH, TOC, hardness, and turbidity of the effluent met the W.H.O guidelines for drinking water.Conclusion: This study demonstrated that an innovative carrier as sulfur impregnated activated carbon could be used as both the biofilm carrier and energy source for treating nitrate contaminated drinking water in the lab-scale fluidized bed bioreactor.