Nitrogen Removal from Wastewater Using Anammox Process - Term Paper Example

Ammonium oxidation process affiliation Contents Contents 2 2 Acknowledgements 3 Introduction 4 Anammox wastewater treatment 9 Characteristics of the bacteria 10 Chemical reactions involved 11 Physical parameters affecting anammox 11 Influence of salinity on the anammox process. 12 MATERIAL AND METHODS 13 Oxygen Uptake Rate 13 RESULTS AND DISCUSSION 14 Physical Parameters and discussion 14 Applications of ANAMMOX 15 Advantages of the ANAMMOX process 16 Feasibility and interest of treatment process 17 CONCLUSION 18 References 19 Abstract Anaerobic Ammonium Oxidation, also referred to as ANAMMOX is a new and revolutionary nitrogen cycle whereby NH4+ oxidation is coupled to the reduction of NO2- to produce N2. The very first discovery of ANAMMOX happened in a wastewater treatment plant back in the year 1995 (Kuypers et al., 2003). At the time, the process was attributed to bacteria belonging to the genus Planctomycetes. The initial finding was followed by more detection of the bacteria in oceanic zone water columns with the least amounts of oxygen, in anoxic marine sediments, arctic sea ice, estuaries, and freshwater lakes. Generally, this bacterial can be found almost everywhere. Findings have shown that the contribution of this bacterium on the removal of nitrogen in the environment can be immense. The process, said to be chemolithrophic, is a very new loop in the biogeochemical nitrogen cycle hitherto unknown to engineering (Dong & Sun, 2007). While there is very little, that is known about the ecology, genetics, or even the physiology of the bacteria, this research project will be very important in shedding some light on the community structure of the Anaerobic Ammonium Oxidation bacterial and all their involvement in environmental parameters that include nitrate, ammonium, and the salinity levels. This project discusses the effects of pH and salinity on the anammox process with results showing that the salinity is among the few factors that are really affecting the effectiveness of the whole process. Acknowledgements My thanks go to Mr. XXXX through whose guidance I have learned molecular techniques used for the investigation of bacteria. It is due to his patient and undying support that pushed this study through. A good and encouraging attitude and his excitement about this work encouraged me to explore deeper into learning as much as possible in the process. I wish to also thank Ms. YYYY who also made this research a success through teaching me about the most fundamental and traditional microbiology techniques. Mr. QQQQ introduced the isotope ratio mass spectrometer to me. He was also very encouraging and it was through his words of wisdom that the concept behind stable isotope geochemistry became one that I can handle well, and with ease. This research owes its completion to WWWW who collected the sediment samples from XXX Estuary. All the other members of the microbiology laboratory were very helpful throughout my visits to the lab. It was their long, well-informed discussions that made the research a success, and I will forever cherish such assistance. Special thanks go to my father and mother, Mr. and Mrs. XZXZ who helped me immensely throughout the way. They were not only patient but also always supportive. I know for sure though that this work seemed endless to them and that they missed me home. Introduction The importance of nitrogen in this planet equates to life itself. Nitrogen forms an important part in nucleic acids, proteins, and almost all other cellular components (Wetzel & Likens, 2000). Its biogeochemical cycle is very intricate with valence states of -3 to +5, and is significant in bringing out a variety of biotic and abiotic processes, which rely on nitrogen whether to form other gaseous states, liquid, or solid compounds. While plentiful on earth, lithosphere has about 96% of all the gas, which is found in biogeochemical cycle of nitrogen. Nitrogen Bioavailability is normally reliant on microorganisms that engage in the nitrogen cycle (Halama et al., 2010). There are a number of inorganic forms of nitrogen. These include nitrite, nitrate and, ammonia that play very crucial roles in geomicrobial processes. These processes are responsible for controlling primary and secondary productions of the gas in aquatic environments (Elser et al., 2007). In the nitrogen cycle, the primary processes are assimilation, nitrogen fixation, ammonification, nitrification, denitrification, and dissimilatory nitrate reduction to ammonia (DNRA). The nitrogen cycle Nitrogen fixation is the major biological process that is responsible for bringing back nitrogen into the biosphere. The O2-sensitive nitrogenase enzyme facilitates the process. The process involves the reduction of N2 to NH3. While it is largely deliberated that nitrogen (N) limits phytoplankton’s productivity in water bodies such as the lakes and the oceanic biome, a few known fixers of nitrogen relative to the plethora of them exist in lakes and estuaries. The fixation of nitrogen occurs in quite a number of prokaryotic organisms that are free either living or symbiotic (like seen in legumes) (Zahran, 1999). Bacteria for instance those in the genus Rhizobium and Bradyrhizobium institute a particular interdependent relationship with leguminous host plants. The presence of the bacteria leads to the formation of new organ structures known as root nodules. The nitrogen-fixing bacteria supply the host plant with combined nitrogen through reducing the atmospheric nitrogen to ammonia (Soberon et al., 1999). In other words, the nodules facilitate the maintaining of an anaerobic environment through reciprocity between the nitrogenase enzyme and the plant. Nitrogen fixation in legumes Tradition Nitrification/denitrification chemical reactions While the above information shows just how important nitrogen is, nitrogen is said to be the major sources of pollution in the world today that have contributed to some of the devastated effects seen on the environment. All forms of pollution and all the sources of pollution, whether industrial, agricultural, or even municipal must be managed so that the levels of pollution are reduce for the improvement of the quality of life of people. There is number of problems associated with the pollution nitrogen sources other than bad odor in the environment. They include a natural order imbalance (imbalance in the ecological systems and an surge in eutrophication), depletion of oxygen dissolved on the surface of the water thus leading to creation of septic conditions and ultimately killing marine life, and lastly the increase of NO3-N concentrations ground water posing a very significant threat of human life (Dinnes et al., 2002). Due to the above reasons, Nitrogen is regarded as unwelcome substance in all public water. While the compound occurs naturally in water bodies, increased levels result from human use of fertilizer near the water bodies and the improper disposal of animal and human waste. Since an increased level of nitrogen in drinking water can be very poisonous to human life, the United States Environmental Protection Agency (USEPA) maintain that 10 mg N03-N/L would be the highest contamination level of the compound in drinking water. This corresponds to the maximum accepted level in both Canada and the World Health Organization (WHO) (Ward, 2005). All the above issues have brought about the need to treat wastewater so that it can be used with no detrimental effects on human life. The treatment is usually divided into two major categories: biological treatment systems, and physical/chemical treatment systems. Physical treatments of nitrogen include sedimentation, filtration, screening, and flotation. Chemical treatments on the other hand include adsorption, disinfection, and precipitation. The chief biological processes used for the treatment of wastewater can be divided into 5 major groups: pond processes, anaerobic process, anoxic process, aerobic process, and lastly combined aerobic-anoxic-anaerobic processes. All the above methods are used for nitrification, phosphorous removal, denitrifiaction, waste stabilization, and the removal of carbonaceous organic matter in wastewater. 1.2. Conventional ways of nitrogen removal Today, there are many ways to get rid of nitrogen from waste water. These methods can be either physical, chemical, or biological. The biological treatment method is the least expensive, requires low energy, or nitrogen. The basic composition of nitrogen in the wastewater is in the form of ammonia and the conventional method of removal is biological denitrification/nitrification. As shown in figure 33. The biological method is currently the most common and popular and is used particularly when dealing with wastewater from landfill leachate, anaerobic digester effluents, and industrial wastewater that contains high concentrations of nitrogen. Anammox wastewater treatment The discovery of the ANAMMOX bacterial is definitely one that will see a thorough change in how wastewater is used. The process was found about 20 years ago. Nonetheless, it was believed that it has been taking place at least 30 years ago. The primary workability of the process is that under anaerobic condition, the anammox bacteria can consume ammonium and nitrites in wastewater releasing nitrogen gas. The following is the reaction involved. 2NH4+ + 3O2 → 2NO2- + 4H+ + 2H2O NH4+ + NO2- → N2 + 2 H2O The anammox reaction flow chart Characteristics of the bacteria The Anaerobic Ammonium Oxidation bacteria (ANAMMOX) belong to the phylum Planctomycetes. To date, there are five discovered genera Jettenia (which is all fresh water species), Kuenenia, Brocadia, Anammoxoglobus, and Scalindua (the marine species). The bacteria have several characteristics that are only specific to its species. All the bacteria in the five general possess an Anammoxosome (Woebek, 2008). This is a membrane-bound compartment found inside the cytoplasm, which is evidently, what the locus of ANAMMOX catabolism is. In addition to that, this bacterium membrane chiefly consists of ladderane lipids that are unique to the bacteria itself. Something that is of special interest to scientists is the conversion to hydrazine as an intermediate. The chemical is actually used as a high-energy rocket fuel and is normally poisonous to almost every living organism. Another characteristic of the bacteria that is different from that of other bacteria is that the ANAMMOX bacteria have an extremely slow growth rate. So slow that it takes the bacteria between 7 and 22 days to double. Nonetheless, the bacteria are still very effective in low concentrations. What makes these bacteria such effective is that it has a very high affinity for its substrates, nitrite (sub-micromolar range), and ammonia. The cells are filled with Cytochrome C type proteins, which are made up of about 30% protein complement. The cells also contain the enzymes that are responsible for performing the main catabolic reactions in the ANAMMOX process. This high numbers of the enzyme is what makes the cells extraordinarily red (Woebek, 2008). Initially, the ANAMMOX process was thought to occur only in temperatures ranging between 20 °C to 43 °C (Li et al., 2010). Recently, however, the process has been found to occur in hot spring temperatures that are as warm as 52 °C and in hydrothermal vents in the Mid-Atlantic Ridge, of which the temperatures are between 60 °C to 85 °C (Bryne et al., 2008). Chemical reactions involved The whole process involved in ANAMMOX lies squarely on the removal of ammonium in wastewater treatment (Dalsgaard, 2003). The process is made of two independent processes. In the first stage, partial nitrification occurs to half of the ammonium molecule to nitrate. Ammonia oxidizing bacteria carries out the whole process. Below is the process. 2NH4+ + 3O2 → 2NO2- + 4H+ + 2H2O After the above reaction takes place, the ANAMMOX process converts the resulting nitrite and ammonium to nitrogen gas and circa (which is 15% nitrate). The ANAMMOX bacteria do this. The circa is not shown in the reaction below. NH4+ + NO2- → N2 + 2 H2O Note that both of the above processes can take place in a single reactor. This happens with the bacteria form a guild of compact granules (Paredes, 2007). Physical parameters affecting anammox There are a number of factors affecting the performance of the anammox process. PH is the main factor since it affects the ammonium/ammonia and nitrite/nitrous acid. When the pH is below 7.5 or above 8, then the process is greatly affected. The pH is chiefly what runs the reactors. Dissolved oxygen also affects how well the anammox process does as it affects the stability of the bacteria. Since the partial oxidation highly relies on the presence of oxygen, a balance needs to be established in the reactor so that the production of nitrogen is not hindered. Thirdly, the anammox bacteria require that the temperatures be at an optimum. Their growth depends on the temperature of the reactor. Very high temperatures would result to destroying them and very low temperature may affect the bacteria’s effectiveness. Lastly, the anammox process is also affected by hydraulic time retention (HTR) whose value is usually inversely proportion to the flow rate of both outflow and inflow. Optimum HTR is very crucial in the efficiency of a reactor. Influence of salinity on the anammox process. Water salinity is a common phenomenon in wastewater. In fact, most factories are dumping very saline waste into water sources. The salinity can be a very important limiting factor. The activity of fresh water anammox is affected by the presence of salinity in wastewater; this means that salinity is a very important issue to handle, as it will affect the effectiveness of the anammox bacteria. MATERIAL AND METHODS A single reactor was used to measure the anammox process in two reactors in relation to salinity and the weight of the bottle. The two reactors had waste water and an equal amount of the bacteria. Oxygen Uptake Rate Since the rate at which oxygen is used in each reactor determines how much the anammox process is taking place, the following table was used to determine how the conditions affected the process. This is especially important when doing a full-scale anammox process. Table 1. The relationship between the salinity and weight inside the bottle Salinity (g/L) Density of buffer (g/L) Weight inside the bottle (g) 0 1,0 24 5 1,005 24,0 10 1,01 24,17 15 1,015 24,26 20 1,02 24,34 25 1,025 24,43 30 1,03 24,51 Pressure in the two bottles was also measured and changes in the pH observed. RESULTS AND DISCUSSION Reactions and discussion in the reactor The process was smooth until there was an increase in the salinity levels that demanded that the process takes an additional 3 weeks to complete. An additional of salinity by an extra 15g/L was so damaging to the reactors such that the anammox activity was zero. The graphs will be shown to illustrate this data. The vertical lines on the graphs were primarily used to divide the periods when there was an addition of salinity in the periods 0, 5, 15, 15g/L. Physical Parameters and discussion Since there was a high amount of ammonia consumed, it was expected that the pH level of the reactor fall. Nonetheless, the changes in the salinity levels affected the rates of reactions and more so how well the bacteria were working. During the whole period of increasing salinity, it is observed that the process undergoes a jumping amplitude where it then falls following increase in salinity. However, at a certain point, the pH level starts to drop. The explanation is because the bacteria needs sometime before it adapts to a certain environment and returns to its initial level of activity once it is stable in the environment. Applications of ANAMMOX While compared to the conventional nitrogen removal process, the ANAMMOX process seems to be the most convenient and cost effective. There are a number of plants already using the process as a method of water treatment regardless of the technique being considered a little new. Netherlands, for instance, built the first full scale plant for water treatment using the ANAMMOX process back in 2002 (Kuenen, 2008). Germany also has a plant in Hattingen that coincidently observes the ANAMMOX activity but the intention of building the plant was not to treat water using the ANAMMOX activity. By 2006, there were already three full-fledged process in The Netherlands. The first treatment plant in Rotterdam deals with municipal wastewater. There are then two on industrial effluent of which is a tannery while the second is a potato processing plant (Van der Star, 2007). Advantages of the ANAMMOX process To have a better picture of the advantages of using the ANAMMOX, it may require a comparison between the conventional wastewater treatment methods and the ANAMMOX process. ANAMMOX process Traditional water treatment method Requires only the ANAMMOX bacteria Requires an input of organic substances such as methanol Chemical reactions involved consume way less energy Consumes a lot of energy Autotrophic nature of both bacteria significantly reduce sludge production Associated with the production of excess sludge Significantly low emission of carbon dioxide gas. Produce high amounts of green-house gases such as N2O and CO2 and ozone-depleting NO The bacteria converts the compounds directly to gas, anaerobically Requires electron donors to convert the ammonia into gas Requires no aeration Requires aeration Reduced amount of oxygen required since half of the ammonia requires oxidation Consumes a lot of oxygen gas Cost effective, could reduce cost up to 60% Very expensive A comparison of the traditional and the Anammox processes of denitrification A summary of the ANAMMOX process Feasibility and interest of treatment process The ANAMMOX process as an energy-saving biotechnology offers the best alternative for the treatment of ammonium-rich wastewaters. After its success in the treatment of sludge digest liquids, it is understood that many countries should approach it as a water treatment method as its advantages by far outweigh its limitations. Its long start-up time is the well-known factor that limits its application. To significantly reduce this period will require more than the inoculation of pre-cultivated sludge. Selection of reactors should be done carefully and only those with effective biomass retention picked. An adjustment of the environmental conditions plus the nutrient balance is also an important thing to consider. Currently, the ANAMMOX process is still limited to animal wastewaters and sludge digestate. A wider application of the process may follow if there is a better way of largely enriching the biomass. CONCLUSION Nitrogen and carbon dioxide are among the most important gases but the fact that they may also have be very devastating effects on the environment for instance in water means that they need to be controlled. While both occur naturally in water, an excess amount of the compounds in ground water is said to be poisonous to humans and animals. Since pollution has been on the increase and somehow nitrates and ammonia have increasingly been dumped in water sources, it is evident that water treatment becomes a necessity and currently among the most important industrial processes today. Unfortunately, the traditional process in unusually expensive and one that poses a threat on marine life itself beside increasing the release of greenhouse gases such as carbon dioxide and nitrogen oxide into the atmosphere. The discovery of the eco-friendly process, ANAMMOX, involves Anaerobic Ammonium Oxidation which brings with it groundbreaking changes to traditional biological nitrogen removal in wastewater. The ANAMMOX process plays a unique role not only in the environment but also in the economy. As mentioned above, the processes involved are pocket-friendly and the emission of gases is significantly low. The starting up of the reactor is done from scratch since the process is relatively new and not every country has endorsed it. Nonetheless, it is feasible when considering the inoculation with enriched ANAMMOX sludge. To date, there are about 30 full-scale ANAMMOX systems that are up and running. There are other efficient methods through which the inoculation of the sludge can be done will be a very effective way of making the process more realistic. The lengthy period required for the bacterial to double, a period up to 22 days is one reason most countries are hesitant. References Byrne, N., Strous, M., Crépeau, V., Kartal, B., Birrien, J. L., Schmid, M., ... & Godfroy, A. (2008). Presence and activity of anaerobic ammonium-oxidizing bacteria at deep-sea hydrothermal vents. The ISME journal, 3(1), 117-123. Dalsgaard, T., Canfield, D. E., Petersen, J., Thamdrup, B., & Acuña-González, J. (2003). N2 production by the anammox reaction in the anoxic water column of Golfo Dulce, Costa Rica. Nature, 422(6932), 606-608. Dinnes, D. L., Karlen, D. L., Jaynes, D. B., Kaspar, T. C., Hatfield, J. L., Colvin, T. 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Microbiology and molecular biology reviews, 63(4), 968-989. Read More