Nitrogen removal from municipal wastewater with the application of deammonification process offers an operational cost reduction, especially if it is combined with a maximal use of organic content of wastewater for biogas production. In this thesis, two approaches for integration of the deammonification process into the municipal wastewater treatment scheme were studied. The first approach is based on ammonium concentration from municipal wastewater by ion exchange followed by biological removal of ammonium from the concentrated stream by deammonification process. Experiments with synthetic and real municipal wastewater showed that strong acid cation resin is suitable for ammonium concentration due to its high exchange capacity and fast regeneration. Since NaCl was used for regeneration of ion exchange materials, spent regenerant had elevated salinity. The deammonification biomass was adapted to NaCl content of 10-15 g/L by step-wise salinity increase. The technology was tested in batch mode with 99.9 % of ammonium removal from wastewater with ion exchange and up to 95 % of nitrogen removal from spent regenerant by deammonification process. The second studied approach was to apply anammox process to low-concentrated municipal wastewater in a moving bed biofilm reactor (MBBR) and integrated fixed film activated sludge (IFAS) system without a pre-concentration step. After a 5 months period of transition to mainstream wastewater the pilot plant was operated during 22 months and stable performance of one-stage deammonification was proven. Clear advantage of IFAS system was shown. The highest stable nitrogen removal efficiency of 70 % and a nitrogen removal rate of 55 g N/(m3·d) was reached. Moreover, the influence of operation conditions on competition between ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) was studied by literature review, batch tests and continuous pilot plant operation. / <p>QC 20170309</p>

O presente trabalho avaliou a remoção do nitrogênio amoniacal de liquido percolado de aterro sanitário através do processo de nitritação/desnitritação (via curta) utilizando a própria matéria orgânica presente no lixiviado como fonte de carbono para o processo de desnitritação. Foi também avaliada a remoção de nitrogênio amoniacal do lixiviado através do processo de stripping de amônia. Para o processo de stripping foram utilizados dois sistemas, o primeiro era constituído por um reator (R-2) com volume útil de 20L mantido sobre agitação mecânica (palheta) e o segundo era composto de uma coluna cilíndrica, com volume de lixiviado de 10L, mantida sob aeração. Além da remoção de nitrogênio houve também uma diminuição na concentração de DQO, DBO e COT durante os ciclos de stripping. A taxa volumétrica de remoção de amônia durante os ciclos de stripping variou entre 78 e 86,95 mg N-NH3/L.dia. Para a avaliação da remoção de nitrogênio através da via curta (via nitrito), foi utilizado um reator operado em bateladas seqüenciais (SBR- 1) com volume útil de 20 L. O reator foi operado por um período de aproximadamente 1 ano. A avaliação do processo de nitritação/desnitritação se deu em 4 fases distintas; na primeira fase o sistema foi alimentado com 2L de lixiviado bruto, na segunda fase o sistema R-1 foi alimentado com lixiviado pré tratado (NNH3lixiviado @ 1200 mg/L), na fase três o sistema foi também alimentado com 2 L de percolado pré-tratado (N-NH3lixiviado @ 900 mg/L) e por fim, na fase 4 o sistema foi alimentado com 4L de lixiviado pré-tratado (N-NH3lixiviado @ 900 mg/L ). Nas duas primeiras fases da pesquisa a remoção de nitrogênio foi relativamente eficiente, variando entre 80 e 90%, porém mesmo com a concentração de amônia livre variando entre 0,18 e 20,7 mg/L não houve a inibição da nitratação durante a etapa aerada dos ciclos de tratamento. Durante as fases 1 e 2, a fase anóxica foi relativamente longa sendo que, as taxas específicas de desnitritação variaram entre 0,0100 e 0,0148 Kg NO3 -, NO2 -/ Kg SSV.dia. Na fase 3, após a mudança na alimentação do sistema, o reator R-1 entrou em regime de equilíbrio e a inibição da nitratação foi praticamente total (acima de 95%). Mesmo com a completa inibição da nitratação, a etapa anóxica durante os ciclos de tratamento da fase 3 continuou sendo relativamente longa (72 h em média) remetendo assim, a uma falta de matéria orgânica para a redução do nitrito durante a fase anóxica. Na fase 4, apesar da não inibição da nitratação durante os primeiros ciclos, nos ciclos que se seguiram a inibição foi quase total, demonstrando claramente a adaptação do sistema às condições necessárias ao acúmulo de nitrito. A manutenção do pH da massa líquida próximo a 8,3 foi determinante para o acúmulo de nitrito durante todas as fases da pesquisa. Nas fases 1 e 2 houve a necessidade de controle do pH com adição de alcalinizante, já nas fases 3 e 4 esse controle não foi necessário. / The present work evaluates the biological ammonia removal of a landfill leachate, through nitritation/denitritation as well as the utilization of the organic compounds present in the landfill leachate, as carbon source to denitritation process. It also evaluates the ammonia removal of landfill leachate by the ammonia stripping process. It has been used two systems for the stripping process, the first one was constituted of a reactor (R-2) with 20L useful volume kept on mechanical shaking (vane) and the second one was composed of a cylindrical column, with a 10L of landfill leachate volume, kept on aeration. Beyond the biological ammonia removal it also had a reduction in the COD, BOD and TOC concentration during the stripping cycles. The ammonia removal volumetric rate during the stripping cycles have varied between 78 e 86,95 mg N-NH3/L.day. In order to evaluate the ammonia removal through the short cut (via nitrite) one has used a sequencing batch reactor (SBR-1) with a 20L useful volume. The reactor was been operated by a period of approximately 1 year. The assessment of nitritation/denitritation process has happened in 4 distinct phases: in the first one the system was fed on 2L of heavy landfill leachate; in the second the system R-1 was fed on pre-treated landfill leachate (N-NH3leachate @ 1200 mg/L); in the third phase the system was also fed on 2L of pre-treated landfill leachate (N-NH3leachate @ 900 mg/L); and finally, in the fourth phase it was fed on 4L of pre-treated landfill leachate (N-NH3leachate @ 900 mg/L). In the two first phases of this research the biological ammonia removal was been relatively efficient, varying between 80 and 90%, however, even with the free ammonia varying between 0,18 and 20,70 mg/L, it has not had nitratation inhibition during the aerated stage of the treatment cycles. During phases 1 and 2 the anoxic phase was relatively long and specific denitritation rates have varied between 0,0100 and 0,0148 Kg NO3 -, NO2 -/ Kg VSS.day. In phase 3, after the change of system feeding, the R-1 reactor has entered in balance regime and the nitratation inhibition has been practically total (above 95%). Even with the complete nitratation inhibition, the anoxic phase during the phase 3 treatment cycles have continued being relatively long (72h on average), thus sending to a lack of organic compounds for the nitrite reduction in this phase. In phase 4, although the not inhibition of nitratation during the first cycles, in the followed cycles the inhibition has been almost total, demonstrating clearly the system adaptation to the necessary conditions to the nitrite accumulation. The maintenance of pH of liquid mass next to 8,3 has been determinative for the accumulation of nitrite during all phases of this research. In phases 1 and 2 it have been necessary to control the pH alkalinizing the system, already in phases 3 and 4 this control has not been necessary.

by Lydia Chang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1989. / Bibliography: leaves 154-165.

Biological nitrogen removal (BNR) has been applied for more than a century in the interests of preserving and enhancing public health and the environment. But only during the last few decades has the development of molecular techniques using biomolecules such as nucleic acids (DNA and RNA) and proteins allowed the accurate description and characterization of the phylogenetic and functional diversity of microbial communities. Moreover, thanks to recent advances in genomics and next-generation sequencing technologies, microbial community analyses have initiated a new era of microbial ecology. Notwithstanding the fact that the efficiency and robustness of a wastewater treatment mainly depend on the composition and activity of BNR communities, research on the structural and functional microbial ecology of the engineered BNR process remains rare with respect to next-generation sequencing and bioinformatics. This dissertation aims to bridge high-priority knowledge gaps in determining and applying knowledge of microbial structure (who is there and how many?) and function (what are they doing? what else can they do?) to the practice of BNR processes, and to opening up the ‘black-box’ of energy and resource efficient engineered BNR processes using a systems biology approach. Specific objectives were to (1) selectively enrich Nitrospira spp. from a mixed environmental microbial consortium (such as activated sludge) in a continuously operated bioreactor and characterize the microbial ecology during the course of enrichment, determine key kinetic parameters of enriched Nitrospira spp., (2) examine the inhibitory effects of nitrogenous intermediates (such as hydroxylamine, presented herein) on the physiological and molecular responses of Nitrospira spp. in terms of both catabolism and anabolism, (3) characterize bacterial community composition and their dynamics by 16S rRNA gene amplicon sequencing under varying reactor operational conditions from full-scale WWTPs and identify process parameters that most significantly correlate with those dynamics, (4) interpret metagenomic (DNA-based) and metatranscriptomic (RNA-based) derived structure, metabolic function and activity of the full-scale BNR microbial communities, and (5) describe gene expression in the same full-scale BNR communities in response to alternating anoxic-aerobic conditions using a metatranscriptomic approach. First, planktonic Nitrospira spp. were successfully enriched from activated sludge in a sequencing batch reactor by maintaining sustained limiting extant nitrite and dissolved oxygen concentrations for a half year. The determined parameters collectively reflected not just higher affinities of this enrichment for nitrite and oxygen, respectively, but also a higher biomass yield and energy transfer efficiency relative to other NOB such as Nitrobacter spp. Used in combination, these kinetic and thermodynamic parameters can help toward the development and application of energy-efficient biological nutrient removal processes through effective Nitrospira out-selection. Second, using quantitative activity measurements (respirometrc rates) with functional gene expression profiles, this study demonstrated that N-intermediates such as hydroxylamine (NH¬2OH) can strongly inhibit the activity and expression of key anabolic (energy synthesis) and catabolic (biomass synthesis) pathways of Nitrospira spp. A strategy that relies upon the transient accumulation and consumption of such intermediates (such as transient aeration) could provide the platform for successful suppression of Nitrospira spp. in the next generation of energy efficient engineered BNR processes. Third, 16S rRNA gene amplicon sequencing revealed that microbial community structure and their dynamics significantly varied depending on seven differing wastewater treatment processes. The findings showed that five process parameters of wastewater influenced the dynamics of BNR communities; water temperature was correlated most strongly to the variance of bacterial communities, followed by effluent NH3, effluent NO3-, removed N, and effluent NO2-. The results provided insights into the underlying ecological pattern of community compositions and dynamics in full-scale WWTPs; and correlation with process parameters brought about distinct communities that enable different microbial activities. However, one of the greatest challenges was to elucidate the relationship between microbial structure and their “active” functions, which are related to reactor performance (This challenge continued into fourth study chapter summarized below). Fourth, continuing from the previous study, combined metagenomics and metatranscriptomics revealed far superior richness of information of not just microbial structure, but also potential (through metagenomics) and expressed function (through metatranscriptimics) within the complex activated sludge processes. Via independent analysis of whole-DNA and whole-RNA, the entire microbial community and its in situ active members, involved in nitrificaiton and denitrification, were compared. Active nitrifiers and denitrifiers obtained by RNA analysis exhibited relatively high abundances in DNA-derived communities. Further gene expression annotation on nitrogen removal revealed that the expressions of denitrification-related genes except nos were increased under anoxic conditions relative to aerobic conditions, while the expressions of nitrifying genes were decreased. Our findings led to an improved understanding of metabolic activities and roles of BNR microbial communities, and offer the first metatranscriptional insights on engineered nutrient removal in anoxic conditions relative to aerobic conditions in full-scale wastewater systems. In sum, next-generation sequencing as well as traditional molecular techniques shed light on microbial diversity and different functional genes in varying engineered BNR systems. Furthermore, this dissertation provides a wealth of knowledge on systematic explorations of the linkage between structure and function of BNR communities, and offers engineering applications to BNR processes including energy and resource efficient engineered systems. It is expected that the implementation and further expansion of this work will improve the design and operation of engineered BNR processes, eventually producing benefits for the global population and the environment.

O presente trabalho avaliou a remoção do nitrogênio amoniacal de liquido percolado de aterro sanitário através do processo de nitritação/desnitritação (via curta) utilizando a própria matéria orgânica presente no lixiviado como fonte de carbono para o processo de desnitritação. Foi também avaliada a remoção de nitrogênio amoniacal do lixiviado através do processo de stripping de amônia. Para o processo de stripping foram utilizados dois sistemas, o primeiro era constituído por um reator (R-2) com volume útil de 20L mantido sobre agitação mecânica (palheta) e o segundo era composto de uma coluna cilíndrica, com volume de lixiviado de 10L, mantida sob aeração. Além da remoção de nitrogênio houve também uma diminuição na concentração de DQO, DBO e COT durante os ciclos de stripping. A taxa volumétrica de remoção de amônia durante os ciclos de stripping variou entre 78 e 86,95 mg N-NH3/L.dia. Para a avaliação da remoção de nitrogênio através da via curta (via nitrito), foi utilizado um reator operado em bateladas seqüenciais (SBR- 1) com volume útil de 20 L. O reator foi operado por um período de aproximadamente 1 ano. A avaliação do processo de nitritação/desnitritação se deu em 4 fases distintas; na primeira fase o sistema foi alimentado com 2L de lixiviado bruto, na segunda fase o sistema R-1 foi alimentado com lixiviado pré tratado (NNH3lixiviado @ 1200 mg/L), na fase três o sistema foi também alimentado com 2 L de percolado pré-tratado (N-NH3lixiviado @ 900 mg/L) e por fim, na fase 4 o sistema foi alimentado com 4L de lixiviado pré-tratado (N-NH3lixiviado @ 900 mg/L ). Nas duas primeiras fases da pesquisa a remoção de nitrogênio foi relativamente eficiente, variando entre 80 e 90%, porém mesmo com a concentração de amônia livre variando entre 0,18 e 20,7 mg/L não houve a inibição da nitratação durante a etapa aerada dos ciclos de tratamento. Durante as fases 1 e 2, a fase anóxica foi relativamente longa sendo que, as taxas específicas de desnitritação variaram entre 0,0100 e 0,0148 Kg NO3 -, NO2 -/ Kg SSV.dia. Na fase 3, após a mudança na alimentação do sistema, o reator R-1 entrou em regime de equilíbrio e a inibição da nitratação foi praticamente total (acima de 95%). Mesmo com a completa inibição da nitratação, a etapa anóxica durante os ciclos de tratamento da fase 3 continuou sendo relativamente longa (72 h em média) remetendo assim, a uma falta de matéria orgânica para a redução do nitrito durante a fase anóxica. Na fase 4, apesar da não inibição da nitratação durante os primeiros ciclos, nos ciclos que se seguiram a inibição foi quase total, demonstrando claramente a adaptação do sistema às condições necessárias ao acúmulo de nitrito. A manutenção do pH da massa líquida próximo a 8,3 foi determinante para o acúmulo de nitrito durante todas as fases da pesquisa. Nas fases 1 e 2 houve a necessidade de controle do pH com adição de alcalinizante, já nas fases 3 e 4 esse controle não foi necessário. / The present work evaluates the biological ammonia removal of a landfill leachate, through nitritation/denitritation as well as the utilization of the organic compounds present in the landfill leachate, as carbon source to denitritation process. It also evaluates the ammonia removal of landfill leachate by the ammonia stripping process. It has been used two systems for the stripping process, the first one was constituted of a reactor (R-2) with 20L useful volume kept on mechanical shaking (vane) and the second one was composed of a cylindrical column, with a 10L of landfill leachate volume, kept on aeration. Beyond the biological ammonia removal it also had a reduction in the COD, BOD and TOC concentration during the stripping cycles. The ammonia removal volumetric rate during the stripping cycles have varied between 78 e 86,95 mg N-NH3/L.day. In order to evaluate the ammonia removal through the short cut (via nitrite) one has used a sequencing batch reactor (SBR-1) with a 20L useful volume. The reactor was been operated by a period of approximately 1 year. The assessment of nitritation/denitritation process has happened in 4 distinct phases: in the first one the system was fed on 2L of heavy landfill leachate; in the second the system R-1 was fed on pre-treated landfill leachate (N-NH3leachate @ 1200 mg/L); in the third phase the system was also fed on 2L of pre-treated landfill leachate (N-NH3leachate @ 900 mg/L); and finally, in the fourth phase it was fed on 4L of pre-treated landfill leachate (N-NH3leachate @ 900 mg/L). In the two first phases of this research the biological ammonia removal was been relatively efficient, varying between 80 and 90%, however, even with the free ammonia varying between 0,18 and 20,70 mg/L, it has not had nitratation inhibition during the aerated stage of the treatment cycles. During phases 1 and 2 the anoxic phase was relatively long and specific denitritation rates have varied between 0,0100 and 0,0148 Kg NO3 -, NO2 -/ Kg VSS.day. In phase 3, after the change of system feeding, the R-1 reactor has entered in balance regime and the nitratation inhibition has been practically total (above 95%). Even with the complete nitratation inhibition, the anoxic phase during the phase 3 treatment cycles have continued being relatively long (72h on average), thus sending to a lack of organic compounds for the nitrite reduction in this phase. In phase 4, although the not inhibition of nitratation during the first cycles, in the followed cycles the inhibition has been almost total, demonstrating clearly the system adaptation to the necessary conditions to the nitrite accumulation. The maintenance of pH of liquid mass next to 8,3 has been determinative for the accumulation of nitrite during all phases of this research. In phases 1 and 2 it have been necessary to control the pH alkalinizing the system, already in phases 3 and 4 this control has not been necessary.

A presente dissertação apresenta e discute os resultados do trabalho experimental cujo objetivo foi avaliar a remoção de nitrogênio na forma de mitrato (N-NO3-) pelo processo de desnitrificação biológica em reator anóxico horizontal de leito fixo (RAHLF) contendo matrizes de espuma de poliuretano, em escala de laboratório, utilizando gás metano como fonte de carbono e único doador de elétrons adicionado ao sistema. Para concentrações iniciais de N-NO3- de 20 mg/L e 40 mg/L no substrato sintético, foi possível obter diminuição das concentrações iniciais em 85% e 50%. No entanto, os altos níveis de redução de N-NO3-, obtidos sob condições limitantes de metano, deram suporte à hipótese de que parte da remoção do N-NO3- foi realizada mediante a utilização de compostos reduzidos de enxofre ou nitrogênio, tais como: S0, HS- ou NH4+, provavelmente formados sob condições anóxicas, simultaneamente com o processo de desnitrificação. Foi possível verificar, também, a influência da relação carbono (mg/L CH4 / nitrogênio (mg/L N-NO3-) no estabelecimento das rotas metabólicas de desnitrificação predominantes, quais sejam, a redução dissimilativa do nitrogênio à amônia (RDNA) ou a desnitrificação. Adicionalmente, foram realizados ensaios em reatores tipo batelada, com o objetivo de se medir o consumo de metano. Porém, os resultados não foram satisfatórios, provavelmente em razão da diversidade microbiana presente no inóculo. Foram realizadas análises de microscopia óptica e de fluorescência, assim como de DGGE, para avaliar a diversidade e as alterações nas populações microbianas ao longo do RAHLF e do tempo de experimento. Os diferentes sistemas utilizados apresentaram limitações relacionadas à baixa solubilidade do gás metano no meio líquido, à resistência à transferência de massa da fase gasosa para a líquida e desta última para a biomassa aderida à espuma. / This study presents and discusses experimental work results conducted with the purpose of evaluating nitrate - nitrogen (N-NO3-) removal by biological denitrification process in a lab scale horizontal flow fixed bed anoxic reactor (RAHLF), using methane gas as sole carbon source and electron donor. Support media for microorganisms were polyurethane foam matrixes. For initial N-NO3- concentrations of 20 mg/L and 40 mg/L present in synthetic substrate, it was possible to obtain 85% and 50% removal respectively. These high reduction rates, obtained under limiting conditions of methane, sustained the idea of part of the N-NO3- removal being accomplished by reductive sulfur or nitrogen species utilization, such as: S0, HS- or NH4+, probably formed under anoxic conditions simultaneously to denitrification process. It was possible to verify also carbon (mg/L CH4) / nitrogen (mg/L N-NO3-) ratio effect in denitrification metabolic paths establishment, i.e. dissimilative reduction of nitrogen to ammonia or denitrification itself. In addition, batch tests where conducted with methane consumption measuring purpose. Yet, results where not satisfactory probably due to great microbial diversity present in inoculum. Optical microscopy and fluorescence exams where developed, as well as, DGGE, in order to evaluate diversity and alterations in bacterial populations as a function of reactor\'s length and time. Different systems used in experimental work presented limitations due to low methane gas solubility in bulk liquid and mass transfer resistance from gas to liquid phase and from this to fixed biomass.

<p>This is a project about The Water Treatment System at Djupdalen. The leakage water comes to the Water Treatment System from a deposition plant through the land. The leakage water is characterized by a high concentration of nitrogen and the system is based on biological removing of the nitrogen in the water, by nitrifying and denitrifying bacteria. Four different problems are found in the system: 1. High level of nitrogen concentration in the outgoing water of the system. It should be due to the lack of phosphate in the water, that do not let the bacteria to grow. 2. Low temperature during the most part of the year. Nitrifying and denitrifying bacteria are temperature-dependent, that are very slow at low temperatures. 3. High oxygen concentration in one of the anoxic pond, where the denitrification process take place. This oxygen concentration is too high for denitrifying bacteria to work. 4. The nitrification and denitrification bacteria need to be “old” to work efficiently. They need a surface to attach, because if not they flow with the water and they leave the system. And four possible solutions for the system are presented: 1. Phosphate should be added to the system to let bacteria growth. 2. Store the water at a store pond during the winter months and transport it to the system when the temperature is optimum for the bacteria to work. 3. Add carbon matter to improve the carbon oxidation and to low down the oxygen levels at the anoxic ponds. 4. Two options are presented to improve the system, the first one is based on the construction of a dark wavy bottom in the channel system, which will give a surface for bacteria to attaché, it will produce oxygenation in the water, and it will also improve the water temperature; and the second one is based on the addition of panels made of black material, which will give to bacteria a surface to attach, and improve the water temperature.</p>

Nitrogen oxide in water was a critical factor of eutrophication. The poor tap-water quality in Taiwan was the result of ammonia nitrogen pollution. This research used manganese dioxide as the catalyst to degrade ammonia nitrogen content in water. Controlled factors in our experiment include basic test, optimal reaction condition test, and kinetics. Real water sample was drawn from the Love River for catalysis effect test. Results were then compared with the popularly used titanium dioxide. Significant findings in this research include: 1) when the manganese dioxide content in water was 2%, the ammonia nitrogen removal rates were 31.80% under UV irradiation, and 22.21 % without light interference; 2) under UV irradiation, manganese dioxide would not affect the catalysis effect due to pH changes; 3) silicate in the water had catalysis effect, while sulfate, phosphate, and nitrate had inhibition effect; 4) manganese dioxide had catalysis effect in seawater, yet the removal rate would decrease as the salt content increases; 5) the rise of water temperature would enhance the ammonia nitrogen removal rate; 6) manganese dioxide had catalysis effect on the treatment of the Love River water, and the ammonia nitrogen removal rate reached 89.50 %; 7) in the biological test, manganese dioxide could effectively degrade the ammonia nitrogen content in water, and improve the survival rate of larval shrimp; 8) comparing to titanium dioxide, manganese dioxide had advantages of low cost, with catalysis effect in both seawater and fresh water under no light condition. As a result, manganese dioxide has significant future application potentials. In the future, this research will conduct in-depth study on kinetics of degradability of manganese dioxide catalysis on ammonia nitrogen, and to design suitable catalytic reactor for water treatment. Moreover, it is of value to broadly research manganese dioxide related catalytic products, such as catalytic spray, catalytic paint, fluorescent tube, air filter, and catalytic fan...etc.

published_or_final_version / Civil Engineering / Master / Master of Philosophy

Η προστασία του περιβάλλοντος και της δημόσιας υγείας στις μέρες μας είναι επίκαιρες όσο ποτέ άλλοτε. Μία από τις κύριες αιτίες μόλυνσης η οποία μάλιστα συνεχώς αυξάνεται λόγω και τις ολοένα αυξανόμενης αστικοποίησης είναι η απόθεση των υγρών αποβλήτων. Γι αυτό το λόγο τα τελευταία χρόνια γίνονται ερευνητικές προσπάθειες με στόχο τη μείωση των ρυπαντικών φορτίων σε περιβαλλοντικά αποδεκτά επίπεδα, για να μπορέσουν τα λύματα να διατεθούν χωρίς να αλλοιώνουν σημαντικά τα χαρακτηριστικά του φυσικού αποδέκτη. Η βιολογική επεξεργασία λυμάτων είναι μία σύνθετη διαδικασία που πραγματοποιείται μέσω περίπλοκων βιολογικών, φυσικοχημικών και βιοχημικών αντιδράσεων. Η βιολογική απομάκρυνση του αζώτου πραγματοποιείται με τις διεργασίες της νιτροποίησης και της απονιτροποίησης. Η νιτροποίηση πραγματοποιείται κάτω από αερόβιες συνθήκες με την συνδρομή αυτότροφων βακτηρίων, που μετατρέπουν την αμμωνία σε νιτρώδες άζωτο και στη συνέχεια ακολουθεί οξείδωση των νιτρωδών σε νιτρικό άζωτο. Η απονιτροποίηση συνίσταται στην αναγωγή του νιτρικού αζώτου σε αέριο άζωτο, με τη βοήθεια προαιρετικά αερόβιων ετερότροφων μικροοργανισμών. Η προσομοίωση της διεργασίας σε Η/Υ με τη χρήση μαθηματικών μοντέλων, παίζει σημαντικό ρόλο στην περιγραφή, τον έλεγχο και την πρόβλεψη των αλληλεπιδράσεων των συστατικών που συμβαίνουν σε μια εγκατάσταση επεξεργασίας λυμάτων. Στην παρούσα εργασία έγινε η χρήση ενός τροποποιημένου μοντέλου με βάση το ASM3 για την ακρίβεια του ASM3 2N για την προσομοίωση μιας οξειδωτικής τάφρου. Σκοπός της παρούσας εργασίας είναι να διερευνηθούν μέσω προσομοιώσεων οι συνθήκες αερισμού σε μία τυπική εγκατάσταση οξειδωτικής τάφρου, κάτω από τις οποίες επιτυγχάνεται απομάκρυνση του αζώτου από τα απόβλητα σε τιμές εντός των επιτρεπτών ορίων της νομοθεσίας για διάθεση στο φυσικό αποδέκτη. Ειδικότερα μελετήθηκε η επίδραση των σημαντικών λειτουργικών παραμέτρων οι οποίες επηρεάζουν την απόδοση του συστήματος με σκοπό τον προσδιορισμό εκείνο μέσω του οποίου επιτυγχάνεται ελαχιστοποίηση του κόστους λειτουργίας μιας τέτοιας εγκατάστασης. / -