International Research Journal of Environment Sciences________________________________ ISSN 2319–1414Vol. 2(12), 42-51, December (2013) Int. Res. J. Environment Sci. International Science Congress Association 42 Biodenitrification by Fluidized Bed Biofilm ReactorBurghate S.P.1* and Ingole N.W.2 1*Department of Civil Engineering, Government Polytechnic, Amravati, INDIA Department of Civil Engineering, Prof. Ram Meghe Institute of Technology and Research, Badnera, Amravati, INDIA Available online at: www.isca.in, www.isca.me Received 13th November 2013, revised 20th November 2013, accepted 18th December 2013 AbstractNitrate contamination of water resources has been documented worldwide. It has become one of the major environmental issues because of its implications on human and animal health. Therefore for welfare of mankind it is necessary to remove nitrate from water resources. Biological denitrification (biodenitrification) is an attractive treatment option, among the various options available for removal of nitrate. The FBBR (Fluidized Bed Biofilm Reactor) is one of the recent methods which can be used for denitrification. Considering the severity of the problem the present study was carried out with a aim to remove nitrate from synthetic wastewater using denitrification by FBBR. Fine glass granules were used as a biofilm carrier media which were prepared by grinding and sieving the wastage broken glass as a biofilm carrier media. In the study, the maximum average nitrate nitrogen removal efficiency observed was 90.90% at HRT of 30 minutes and optimum as 86.03% at HRT of 10 minutes. For nitrogen loading rates varying from 0.48 kg N m-3-1 to 28.80 kg N m-3-1, the denitrification rates observed were varying from 0.42 kg N m-3-1 to 16.91 kg N m-3-1. The optimum nitrate nitrogen loading rate and denitrification rate observed were 10.08 kg N m-3-1 and 8.67 kg N m-3-1 respectively. This indicates that the denitrification by FBBR has great potential for removal of nitrate. Keywords: Anoxic, denitrification, fluidized bed biofilm reactor (FBBR), methanol, nitrate. Introduction Nitrate is essential for the growth of many plant species, including most of those we eat. It becomes a formidable hazard if it gets into water in excessive concentrations. The excessive application of fertilizers, intensive exploitation of farms and the significant contribution from industry has increased the nitrogen load discharged to receiving waterways. Nitrate contamination of water resources is becoming a serious environmental problem worldwide2-6. A physico-chemical analysis study of groundwater in Sambhar lake city, Rajasthan, India was carried out and researchers have found nitrate concentration levels upto 1100 mg l-1 7. After assessing the water quality of Upper Lake, Bhopal (India), which supplies drinking water to 16 lakh populations, found nitrate concentration as 150–720 mg l-1 5. In a case study carried out for water quality of water sources of Yavatmal district, Maharashtra (India), found nitrate concentration in the range of 100 mg l-1 to 500 mg l-1. Nitrate concentration is above the permissible level of 45 mg l-1 in 11 states, covering 95 districts and 2 blocks of Delhi. Similar high concentrations of nitrate found in an investigation of nitrate content in ground and surface waters in urban and rural areas. Nitrate contamination of groundwater resources is becoming a problem in Europe as well as in the United States and Canada. In many areas the nitrate concentration in groundwater has reached serious levels exceeding the nominal limits of 10.0 mg -1 as NO-N (nitrate nitrogen) set by the U.S. Environmental Protection Agency or 50 mg l-1 as NO(nitrate) set by the World Health Organization, the European Economic Community, and some former East European countries, e.g. Czechoslovakia. Concern over increase in nitrate concentrations is very legitimate due to potential ill effects on health. The toxicity of nitrates for humans is not clearly established. However, their consumption can cause infant methemoglobinemia (blue baby syndrome). Reduction of nitrates into nitrites in saliva may contribute to the formation of nitrosoamines, which are known carcinogens10-13. Accumulation of various forms of nitrogen in surface and ground waters can lead to adverse effects including depletion of dissolved oxygen (DO) in receiving waters, eutrophication, ammonia toxicity to aquatic life, and other health problems like gastric cancer, goiter, birth malformations and hypertension etc, related to the presence of nitrate in drinking water supplies14-17. Thus with the new dimensions of nitrate problems, there is a vital need to identify and develop appropriate treatment to control nitrate in water resources. A survey of literature yielded an abundance of information on the technical treatment to remove nitrate from water including ion exchange, biological denitrification (biodenitrification), chemical denitrification, catalytic denitrification, reverse osmosis and electrodialysis18. Three methods show some potential for full-scale application: ion exchange, reverse osmosis, and biological denitrification. Nitrate from the contaminated water can be removed by ion exchange. Ion exchange is basically a physical/chemical process which requires periodic regeneration to restore its exchange capacity and process efficiency. It is known that periodic International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 2(12), 42-51, December (2013) Int. Res. J. Environment Sci. International Science Congress Association 43 regeneration of exhausted resins with sodium chloride (NaCl) or sodium bicarbonate (NaHCO) results in a spent regenerant or brine waste containing high concentrations of nitrate-N, NaCl and NaHCO. Ion exchange is limited by two problems. The first is that a resin of high selectivity for nitrates over ions that are commonly present in groundwater does not exist. The second problem involves providing an adequate resin regenerant such that regenerant disposal does not become a problem itself. Reverse osmosis results in the removal of many ionic species and significant reduction in the mineral content of the water. The problem of this method is that the membranes used generally do not exhibit high selectivity for nitrates. The degree of salt rejection is directly related to the valency of the ions. That is why the process results in better removal of multivalent ions. The most promising and versatile approach being studied is biological denitrification. This process has been used for years in wastewater treatment. Biological denitrification is highly selective for nitrate removal. The efficiency of the process is very high and can reach nearly 100%, which is not matched by any other methods available for nitrate reduction. The potential bacterial contamination of treated water is the main disadvantage. This risk is very legitimate and subsequent treatment and disinfection is required to meet current drinking water standards. Biological denitrification can be carried out in either fixed film or suspended growth systems with the use of methanol or some equivalent carbon source. The FBBR is one of the methods, which comes under the category of fixed film type of system. It is the recent method and can be used for biological denitrification with great advantages. By considering the severity of the problems, arise due to presence of nitrate in the water resources, the present study was carried out with an aim to remove nitrate from wastewater. The method, biological denitrification was selected by considering its advantages over the other methods available for the removal of nitrate. For carrying out denitrification, the recent novel reactor FBBR was used. The work presented in this paper is related to an experimental work carried out in the laboratory. A setup of FBBR was established in the laboratory to study it potential of biological denitrification. Various researchers have used different medias as a biofilm carrier media in their work. In this study, the biofilm carrier media used was fine glass granules which can be easily prepared from waste broken glass. This will be economical as it was prepared from wastage material. By considering the advantages of FBBR and easily available media, this study was carried out. The FBBR was run for several days to observe denitrification of synthetic wastewater for various concentrations of NO-N, which vary from 10 mg l-1 to 100 mg l-1. The results showed, the FBBR has great potential for denitrification. The scientific contribution of this paper are: i. The potential of FBBR for biological denitrfication was tested. ii. The economical and easily available biofilm carrier media prepared from wastage material was used. iii. The results of the study indicate that the process adopted for the removal of nitrate has a great potential. iv. By considering the various advantages of FBBR, the adopted process can be used to upgrade present existing treatment units without acquiring more space. This is because FBBR requires less space as compare to conventional treatments. Biological Denitrification (Biodenitrification): Biological nitrogen removal involves two successive processes, i.e. nitrification and denitrification. Biological nitrification and denitrification is one of the most economical processes of nitrogen removal from municipal wastewaters19-22. Nitrate removal from wastewaters is commonly achieved by employing the bacterial process of denitrification, in which nitrate is reduced to innocuous nitrogen gas (N). Biological denitrification has been proved to be one of the more advanced high-performance methods and the sole selective method for complete nitrate elimination. The process requires an electron donor to supply electrons (energy) to the bacteria23-27. The condition suitable for denitrification – absence of oxygen but presence of nitrate, is commonly referred as anoxic. The biological denitrification process (dissimilation) involves the conversion of nitrate ions into nitrogen gas by facultative heterotrophic bacteria. Anoxic conditions and an energy source are required for this. Heterotrophic denitrifying bacteria require an organic carbon source for respiration and growth. Carbon source plays an important role in biological nitrogen and phosphorus removal during the wastewater treatment28. A wide variety of organic compounds have been used, such as methanol, ethanol, glucose, acetate, aspartate, or formic acid as well as different industrial wastes including molasses, whey, distillery spillage, and sulfite waste liquor. However, most of the published research regarding denitrification involves the use of methanol, ethanol, and acetic acid. The usefulness of methanol in the denitrification process is determined first of all by economic considerations29. It is a very convenient carbon source for denitrification due to its high solubility in water, high biodegradability and known stoichiometry30,31. It is the most appropriate choice because of its availability, low cost, favorable sludge production, low volatile organic compound (VOC) emissions potential and lack of nitrogen and phosphorus. If methanol is used as a carbon source, the stoichiometric relationships describing bacterial energy reactions in two steps are written as equations 1 and 2 which give the overall (dissimilation) equation 332: 33222 6NO2CHOH6NO2CO4HO --+®++ (1) 23222 6NO3CHOH3N3CO3HO6OH - +®+++ (2) 33222 6NO5CHOH3N5CO7HO6OH - +®+++ (3) International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 2(12), 42-51, December (2013) Int. Res. J. Environment Sci. International Science Congress Association 44 Nitrate assimilation is generally expressed by equation 4: 332722 3NO14CHOHCO4H3CHNO19HO +++®+ (4) The cell formula CNO suggested by Hoover and Porgess32was used. The “overall” (dissimilation + assimilation) process in nitrate-limiting conditions is described by McCarty’s equation 5: 33572222 NO1.08CHOHH0.065CHNO0.467N0.76CO2.44HO -+++®+++ (5) Extension of equation 5 to take also nitrite and oxygen, which often keep company with nitrate in the feed, into account, gives to the empirical relation equation 6 weight basis33. ( ) 322 2.47()1.53()0.87--=-+-+ MgNONgNONgO (6) The data found in the literature significantly differ from those in the above. In spite of 2.47, the value of the coefficient in equation 6 was often found to be 2.65. and the suggested working value is 3.0 (g methanol) /(g NO –N) removed; in spite of the coefficient 0.87 in equation 6, values as large as 1.1-1.2 have been found as well34. This process of biological denitrification depends on environmental conditions such as oxygen content, temperature and pH35. Alkalinity is produced in denitrification reactions and the pH is generally elevated, instead of being depressed as in nitrification reactions. In contrast to nitrifying organisms, there has been less concern about pH influences on denitrification rates. No significant effect of the denitrification rate has been reported for pH between 7.0 and 8.032. Biological Denitrification System: Denitrification is the biological reduction of nitrate and nitrite to nitrous oxide and molecular nitrogen. It can be achieved by providing a zone in which the effluent is brought into contact with a large biomass containing heterotrophic micro-organisms, in an anoxic environment; and in the presence of a suitable exogenous carbon source. Complete denitrification appears feasible with the use of methanol or some equivalent carbon source, in either attached growth (fixed film) or suspended growth system. Fluidized Bed Biofilm Reactor: The Fluidized Bed Biofilm Reactor (FBBR), the attached growth type of reactor (system), is a recent process innovation in wastewater treatment, which utilizes small, fluidized media for cell immobilization and retention. Main application of this reactor is in the field of biological treatment of wastewater. Aerobic as well as anaerobic FBBRs have received increasing attention for being an effective technology to treat water and wastewater36,37,38. Its most important features are - the fixation of microorganisms on the surface of small-sized particles, leading to high content of active microorganisms and large surface area available for reaction with the liquid; the high flow rate (low residence time) which can be achieved, leading to high degree of mixing (decreased external mass transfer resistances) and to large reduction in size of the plant; and the removal of risk of clogging. The basic concept of the process consists of passing wastewater up through a packed bed of particles at a velocity sufficient to impart motion to or fluidize the particles. As the flow of the wastewater passes upward through the biological bed, very dense concentrations of organisms growing on the surface of the bed particles consume the biodegradable waste contaminants in the liquid. Figure-1 is a schematic of the basic unit of the process, showing the entire fluidized bed biofilm reactor with the wastewater flowing upwards through the bed, fluidizing the particles in the liquid. Above the bed is a clear water zone wherein the particles separate from the liquid. InletTankGlass Tube(0.036 M Dia,1.20 M long)FluidizedMediaRegulatorCockPumpInletPipeOutlet Pipe DenitrifyingReactor SyntheticWastewater Figure-1 Experimental Setup of Fluidized Bed Biofilm ReactorFrom a biological point of view, the attached microorganisms on the suspended particles may include any of the aerobic, facultative, or anaerobic organisms typically found in trickling filters and suspended growth type of treatment systems. The predominating species would depend entirely on the waste contaminant being consumed and whether an aerobic or anaerobic environment is maintained, as well as other factors that affect biological growth. Fluidized beds combine the best features of activated sludge and trickling filtration into one process. Offering a fixed film and a large surface area, these systems offer the stability and ease of operation of the trickling filter as well as the greater operating efficiency of the activated sludge process. More importantly, treatment is accomplished in significantly less space and time, which can be translated into less cost than conventional treatment. The primary reason for this savings in space, cost, and treatment time is that the measured concentration of active biomass in the fluidized bed system reported is in the order of 8,000 mg l-1 – 40,000 mg l-1, which is usually greater than International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 2(12), 42-51, December (2013) Int. Res. J. Environment Sci. International Science Congress Association 45 conventional treatment systems such as the complete-mix activated sludge process in which the MLSS (Mixed Liquor Suspended Solids) ranges between 3,000 mg l-1 – 6,000 mg l-1 or the pure oxygen systems where the MLSS ranges from 6,000 mg l-1 – 8,000 mg l-1 37. The reason for this is that the available surface area per unit of volume of reactor for biological growth in the fluidized bed system is much greater than either trickling filters or rotating biological contactors. This area is estimated to be about 3,290 m m-3, which is far greater than that of trickling filter (82.25 m m-3) or of the rotating disc (164.5 m m-3). Fluidized beds with attached microbial growth on carrier particles have been found to be extremely efficient for biodegradation of liquid waste. Both aerobic as well as anaerobic degradation can effectively be obtained. In capital cost including land, tanks, pumps, clarifiers and solid separators, works out at 1/4th the cost of that for the conventional suspended growth process. The operating cost is slightly lower for the same capacity39. In anaerobic fluidized bed biofilm reactor, biomass concentrations exceeding 30,000 mg l-1 have been reported and organic removal efficiencies of 80 percent were achieved at loadings of 4 kg COD m-3 d-1 on dilute wastewaters40. The advantages of FBBR can be summarized as follows. First, higher biomass concentration can be maintained in the process; hence the system has more metabolic activities, compared to that of suspended growth system. Second, the presence of longer food chains in biofilm with abundant microbial species and can provide stability, long retention time of microbes and much less surplus sludge. Third, the coexistence of aerobic and anoxic zones within the biomass film could provide an opportunity for simultaneous nitrification and denitrification to occur. Fourth, the biofilm processes are less sensitive to the toxic condition and other adverse operational conditions, thus making them easy to operate and maintain. Finally, problems caused by poor settling of sludge and sludge bulking would not be encountered during operation41. Material and Methods Fluidized Bed Biofilm Reactor (Denitrifying Unit): The experimental setup used for this study is shown in figure 1. Its main part is 1.22 l reactor made of Plexiglas tube (0.036 m diameter, 1.20 m long), which is fixed to a steel stand. It is filled with uniform size fine glass granules as a biofilm carrier to a settled depth of 0.30 m. At the bottom, a small closed influent tank of 6 l capacity is provided to which pump is fitted which supplies the influent to the reactor. At the top of the reactor an outlet pipe (tube) is joined which collects the effluent from the reactor and discharge again into influent tank. At the inlet of the reactor, a regulator cock is provided to regulate the flow as well as fluidization of media in the reactor. A fine screen is provided at both the ends (bottom and top end) of the reactor to avoid escape of fine glass granules from the reactor and also to distribute the flow uniformly in the reactor. pH, temperature, alkalinity, COD and NO N concentrations were systematically recorded at the end of each run. Biofilm Carrier Media: Various materials have been tried by researchers as biofilm carrier media. e.g. sand, glass beads, activated carbon, cement ball, plastic, etc. In this study fine glass granules was used as biofilm carrier media. It is prepared by crushing and grinding wastage broken glass material. The characteristics found after performing particle size distribution of fine glass granules were – Effective size (D10) 0.148 mm, Coefficient of Uniformity Cu (D60/D10) 3.253, Coefficient of curvature or gradation Cc ((D30/(D60*D10)) 0.024, and Specific gravity 2.00. Feed: A synthetic medium (synthetic wastewater) was prepared using deionized water in addition to the other chemicals. Potassium nitrate (KNO) was added as the nitrogen source at different varying concentrations of NO-N in mg l-1. PO3- (as NaHPO.12HO and KHPO) both as P source and medium buffering agent. Trace mineral constituents essential to the bacterial growth added per liter were : 0.85 mg FeSO.7HO, 0.25 mg NaMoO.2HO, 0.157 mg MnSO.7HO and 33 mg NaHCO. Sodium sulfite and Cobalt chloride were added at concentrations of 20 and 0.55 mg l-1 respectively, to reduce the oxygen concentration to below 0.5 mg l-1 to ensure anoxic conditions in the reactors37. The methanol was used as carbon source. The concentration of NO - N and methanol in the medium was varied at different stages of the study to maintain (methanol/NO-N) ratio. Operation of a Fluidized Bed Biofilm Reactor: Figure-1 shows schematic diagram of the FBBR which operated daily for denitrification, nearly for a year. The reactor was inoculated with domestic wastewater (as a source of denitrifying bacteria) and run by feeding synthetic medium for 15 days. After getting proper results, the reactor was run for 75 days to find out optimum methanol/NO- N ratio. For this, reactor was run for 15 days each for each methanol/NO- N ratio of 2.25, 2.50, 2.75, 3.00 and 3.25. Average NO- N removal efficiency obtained was 67.95%, 78.96%, 84.55%, 89.88% and 86.63% for methanol/NO- N ratios of 2.25, 2.50, 2.75, 3.00 and 3.25 respectively. Hence, the ratio of 3.00 was finalized for the study. For Experimental work, by maintaining constant methanol/NO- N ratio as 3.00, the synthetic wastewater samples were prepared for varying concentrations of NON of 10.00 mg l-1, 20.00 mg l-1, 30.00 mg l-1, 40.00 mg l-1, 50.00 mg l-1, 60.00 mg -1, 70.00 mg l-1, 80.00 mg l-1, 90.00 mg l-1 and 100.00 mg l-1. For these concentrations each, the reactor was run for 10 days and various characteristics of influent and effluent were measured at the end of each run (i.e. hydraulic retention time (HRT) of 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes and 30 minutes). The characteristics measured were temperature, pH, alkalinity, COD and NO-N. Analytical Methods: Samples were collected from the FBBR at regular intervals and tested for various characteristics. pH was measured by digital pH Meter. Alkalinity was determined by titration method according to APHA (2005)42. COD was International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 2(12), 42-51, December (2013) Int. Res. J. Environment Sci. International Science Congress Association 46 measured by reflux method according to APHA (2005)42. NON was measured by UV-Spectrophotometer (Schimadzu make, Model – UV 1650). Results and Discussion The experimental denitrification reactor was operated for 10 different concentrations and readings were recorded at various HRTs. The NO-N removal was determined on the basis of the results of analysis of medium entering and leaving the reactor for methanol/ NO-N ratio of 3.00. Average NO-N removal efficiency was found to be 59.01%, 83.22%, 86.10%, 88.13%, 89.92% and 90.90% for HRT of 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, and 30 minutes respectively. The results are shown graphically in figure-2, figure-3, figure-4, figure-5, figure-6, and figure-7. The experiment has shown a greater overall denitrification rate. Figure-2 NON Removal after 5 Minutes (HRT) for Different Concentrations of NON In this study, it was observed that, NO-Nremoval efficiency was in the increasing order for the increasing concentration of NO-Nup to 70 mg l-1, after this trend was declining. Average NO-N removal efficiency for HRT of 30 minutes for NO-N concentration of 10 mg l-1, 20 mg l-1, 30 mg l-1, 40 mg l-1, 50 mg -1, 60 mg l-1, 70 mg l-1 was 88.40%, 89.03%, 89.58%, 90.79%, 91.54%, 92.42%, 93.76% respectively while for concentrations of 80 mg l-1, 90 mg l-1, 100 mg l-1 itwas 92.10%, 91.01%, 90.33% respectively. Figure-8 shows graphical representation of NO-N removal % for different HRTs. From the figure, it was observed that, as the concentration of NO-N increases in the wastewater sample (i.e. from 10.00 mg l-1 to 70.00 mg l-1) there was a gradual increase in NO-N removal. But after this there was a slight decrease in NO-N removal. This might be due to less concentration of NO-N available to the denitrifying biomass present in the wastewater. Figure-9 shows the graphical representation of NO-N removal % for wastewater containing varying concentrations of NO-N at different HRTs. Figure-3 NO- N Removal after 10 Minutes (HRT) for Different Concentrations of NO-N Figure-4 NO- N Removal after 15 Minutes (HRT) for Different Concentrations of NO-N International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 2(12), 42-51, December (2013) Int. Res. J. Environment Sci. International Science Congress Association 47 Figure-5 NO- N Removal after 20 Minutes (HRT) for Different Concentrations of NO-N Figure-6 NO-N Removal after 25 Minutes (HRT) for Different Concentrations of NO-N Figure-7 NO- N Removal after 30 Minutes (HRT) for Different Concentrations of NO-N Figure-8 NO-N Removal (%) for Different HRTs for Different Concentrations of NO-N International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 2(12), 42-51, December (2013) Int. Res. J. Environment Sci. International Science Congress Association 48 Figure-9 NO-N Removal for Different Concentrations of NO-N at Different HRTs From the readings and figures, it was observed that most of the NO-N was removed at HRT of 10 minutes. There is a very little difference between NO-N removal % at HRT of 10 and 30 minutes. Thus HRT of 10 minutes can be considered as optimum condition. The nitrogen loading rates vary from 0.48 kg N m-3 d-1 to 28.80 kg N m-3 d-1. For these nitrogen loading rates, denitrification rates observed vary from 0.42 kg N m-3 d-1to 16.91 kg N m-3 d-1. Optimum (at optimum NO-N removal efficiency) nitrogen loading rate and denitrification rate observed were 10.08 kg N m-3 d-1 and 8.67 kg N m-3 d-1respectively. Rezaee et al43 in their study to investigate technical feasibility of biological nitrate removal in a packed bed reactor using microbial cellulose as biopolymer carrier, got denitrification rate of 4.70 kg NO-N m-3-1 for loading rate of 5.64 kg NO-N m-3-1. The biofilm reactors give high nitrate removal rate from 3.10 - 4.40 kg NO-N m-3-3 to 10.00 – 12.00 kg NO-N m-3-3 38. Rabah and Dahab37 presented the results of their study in comparison with the other studies in which fluidized bed reactors were reportedly used with methanol as the carbon source (table-1). Results mentioned by them were found to be in agreement with the results obtained in this study. Table-1 Comparison of some studies on denitrification using fluidized bed reactors Form of Nitrogen Temperature C) Concentration of Nitrogen (mg l-1) Denitrification Rate (kg N m-3 d) References NON 18-23 5 – 100 5.4 – 20.70 Jeris and Owens (1975) NON - 6.6 – 30 0.69 – 3.28 Hermanwicz and Cheng (1990) NON 30 15 – 300 3.23 – 18.70 Hirata and Meutia (1996) NON 20 20 3.5 MacDonald (1990) NON - 676 – 1500 11.8 – 17.7 Chen et al (1996) NON 23 1000 12 Rabah Fahid K. J., et al, (2004) NON 24.5 – 40.5 10 – 100 0.42 – 16.91 (Optimum 8.67) This Study Courtesy: Rabah and Dahab37. The study is carried out using locally available and low cost material as biofilm carrier media. By considering this, and other advantages of FBBR, and the results of the study, process adopted will prove to be the best option for biological denitrification. Heterotrophic denitrification causes a release of hydroxyl ions and raises alkalinity. Each mg of nitrate-N reduced to N causes an alkalinity increase of 3.57 mg CaCO17. In this study, average g of Alkali produced per g of NO-N removed was found to be 3.60 which is in agreement with the values found in literature. As alkalinity is produced, there is a rise in pH. pH of the influent was in the range of 6.56 – 7.15 and that of effluent observed was in the range of 6.76 – 8.07. The denitrification intensity depends on carbon availability. The carbon to nitrogen ratio in the biological reactor influent should be high enough to denitrify all nitrates arisen in the nitrification process. Komorowska, Majcherek and Klaczynski44 mentioned in their paper, many researchers’ work revealed the g COD/g N ratio as 3.5 – 4.5. In the present study, based on all the results, average g of COD consumed per g of NO-N removed is found to be 3.70. This is in confirmation with the results obtained by many researchers. International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 2(12), 42-51, December (2013) Int. Res. J. Environment Sci. International Science Congress Association 49 Conclusion The results obtained by various researchers are shown in table-1. Denitrification rate obtained in this study was comparatively quite good. Thus process adopted would prove to be a best option for the removal of nitrate from the water resources. The results of the investigation, demonstrated that the trend of the removal of NO-N is quite high up to HRT of 10 minutes. An average removal rate at this HRT observed was 86.03%. This means that this technology allows the achievement of rapid and efficient denitrification at relatively low HRTs. On the concentration basis, it was observed that for initial concentrations of NO-N upto 70 mg l-1, the NO-N removal rate was in increasing order but for higher concentrations, the trend was slightly declining. It indicates that for higher concentrations of NO-N, the process can be adopted efficiently by diluting the influents. Overall results of this study demonstrated conclusively that FBBR with fine glass granules as a biofilm carrier media can be used with great advantages for biological denitrification. This study provides the justification for the recommendation of FBBR for biological denitrification by many researchers. This study is carried out with the help of denitrifying microorganisms developed from the seeding of domestic wastewater. There is a future scope that same study can be carried out by using special culture of denitrifying organisms which may enhance the NO-N removal efficiency. References 1.Lucas A. De, Rodriguez L., Villasenor J. and Fernandez F. 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