Simulated Bardenpho ConfigurationTest for Nitrate AccumulationNutrient FeedSampling and TestingNitrogen Removal ProjectHJR IncorporatedHeather NelsonJeannette Harduby Rudi SchuechFor Sparkling Clean Water Every TimeFor Sparkling Clean Water Every TimeAbstractThe following research was performed by HJR Incorporated to model the efficiency of a Bardenpho style wastewater treatment reactor in the removal of nitrate. The Bardenpho cycle includes an anaerobic stage, an aerobic stage, and then a second anaerobic and aerobic stage. A lab scale sequencing batch reactor was set up to model theprocess, and nitrate concentrations were monitored during different stages of the cycle. HJR attempted to measure the effluent nitrate concentrations in order to test the relationship between different stage durations and NO3- removal efficiency. However, as the experiment progressed, HJR encountered difficulties in measuring nitrate concentrations. Two different methods were attempted, but the results were inaccurate in each case. The first method was performed according to Karlsson et al. (1995), in which samples of treated effluent were filtered and run through a spectrophotometer. The secondmethod used a cadmium-reduction test kit supplied by HACH. By the end of the experiment, no conclusive results were obtained, and HJR needs to investigate other waysto measure the nitrate concentrations in wastewater.IntroductionMost municipal wastewaters contain significant concentrations of nutrients, whichif not removed during treatment, can result in various environmental problems such as eutrophication of surface waters. This research focuses on the removal of nitrogen in a sequencing batch reactor (SBR), which approximates a series of specialized reactors. A SBR is much simpler and smaller than a series of reactors, and is ideal for lab-scale research.Most nitrogen in raw wastewater is in the form of proteins, complex organic molecules, and ammonia. The first step in the removal of this nitrogen is the metabolism of organic nitrogen by many species of both aerobic and anaerobic bacteria, which produce ammonia (NH3, NH4+) as a byproduct. This step is termed ammonification. Most of these same bacteria reduce biological oxygen demand (BOD) by oxidizing organic carbon sources. Next, this ammonia is further oxidized first to nitrite (NO2-) and then to nitrate (NO3-), mainly by the bacterial species Nitrosomonas spp. and Nitrobacter spp., respectively. The chemical equations are as follows:Nitrosomonas: NH4+ + 3/2O2 → NO2- + 2H+ + H2ONitrobacter: NO2- + 1/2O2 → NO3-Overall: NH4+ + 2O2 → NO3- + 2H+ + H2ONote that some ammonia nitrogen is also incorporated into cell tissue, but this fraction can usually be neglected. These autotrophic bacteria are strictly aerobic, and require a neutral or slightly basic pH to thrive. They also are reported to need solid surfaces to grow on, grow very slowly, and are actually inhibited by organic matter (Lawrence 2002). This suggests that most or all of the BOD present in the water must be degraded before nitrification will occur. The nitrification process uses 7.1 g alkalinity (as CaCO3) for every gram of ammonia nitrogen oxidized, so pH control may be important, as this process tends to acidify the water (Tchobanolglous 1991).The last step in this treatment process is the transformation of nitrate and nitrite tonitrogen gas (N2), which is relatively insoluble and will bubble out of the water.Denitrification is a series of chemical reactions, with nitrite and nitrogen oxides (NO and N2O) as intermediates. Unlike nitrification, this anaerobic process involves many heterotrophic bacterial species, which oxidize organic carbon using the oxygen in nitrate instead of free oxygen (O2) that would be present in an aerobic environment. These bacteria, predominately Pseudomonas spp. and Bacillus spp., are facultative aerobes, meaning they will use free oxygen whenever possible since aerobic metabolism yields much more energy than anaerobic “respiration.” Denitrification occurs extremely rapidly, as long as 1) there is virtually no dissolved oxygen, 2) there is a source of organiccarbon, and 3) there is nitrate present. Although the terms anaerobic and anoxic are oftenused interchangeably, denitrification is in fact an anoxic process, since the reaction pathways are similar to the ones used in the presence of oxygen.It must be noted that all of these reactions are highly dependent on temperature, and removal efficiencies will decrease as temperature decreases. Future research might focus on this aspect by placing a heater inside the reactor. The ambient temperature was approximately 22° C where the reactor was situated.HJR used a SBR to approximate the Bardenpho process for nitrogen removal. See Figure 1 for a graphical description of this process, which is normally implemented in either a single large tank or separate tanks in series, coupled with a clarifier.Figure 1. Bardenpho processThe first step in the Bardenpho process is anaerobic, where any nitrate or nitrite left over from the last stage should quickly be removed as long as there is BOD available. Some ammonia may also be produced. Methanol is usually used as a source of organic carbon used to encourage denitrification in full scale treatment plants. However, the Bardenpho process uses BOD present in the raw waste and organic carbon from decayed bacteria to accomplish denitrification (Tchobanolglous 1991). When a single, continuous flow tank is used, small amounts of raw waste can be strategically introduced in certain areas prone to anaerobic conditions to allow denitrification.The second aerobic cycle uses up BOD, creates ammonia, and also theoretically may oxidize ammonia to nitrite and then nitrate, although BOD may inhibit this process. In the depicted process, a recycle loop returns this effluent to the first stage, where any nitrate created should be removed.The third and fourth stages are anaerobic and aerobic respectively, and involve thesame processes as the first two. However, the amounts of BOD and each form of nitrogen will be different. The dependence of each step on the previous steps makes it difficult to predict exactly what will happen in each stage. There will always be small amounts of nitrate present in the final effluent because the last cycle will oxidize anyammonia to nitrate. However, careful tuning of the recycle flows has been shown to achieve 90% nitrogen