A ampla ocorrência de contaminação de águas por compostos de nitrogênio em concentrações superiores às recomendadas pela legislação tem suscitado interesse no desenvolvimento de tecnologias viáveis de remoção desses compostos. A remoção biológica de nitrogênio apresenta como principais vantagens os custos relativamente reduzidos e a possibilidade de maior eficiência. Compostos reduzidos de enxofre como sulfetos podem ser oxidados a enxofre elementar ou a sulfato por bactérias oxidantes de sulfeto que utilizam nitrato ou nitrito como receptor de elétrons. Esta desnitrificação reduz os requerimentos globais de carbono para a remoção de nutrientes, com menor produção de lodo, proporcionando grande economia. O objetivo desta pesquisa consistiu em contribuir para o conhecimento acerca dos aspectos microbiológicos do processo de desnitrificação com o uso de sulfeto. Foram avaliados os efeitos dos modos de operação dos reatores desnitrificantes sobre a biomassa em cada uma das diferentes configurações e monitorada a colonização microbiana por meio de técnicas de Biologia Molecular como PCR/DGGE, sequenciamento e análises filogenéticas. Os fragmentos do gene RNAr 16S foram relacionados aos gêneros Pseudomonas, Aeromonas, Acidobacteria, Chlroroflexi, Clostridium, Cupriavidus e Ralstonia. Filotipos dos clones para o sistema piloto foram associados a bactérias não cultiváveis e Firmicutes envolvidos na digestão anaeróbia em reatores tratando água residuária, Synergistetes, Deferribacteria e Proteobacteria. Foram identificados micro-organismos presentes nos reatores com reconhecida capacidade para desnitrificação: Pseudomonas, Desulfovibrio desulfuricans e Ralstonia. Amostras de ambos os reatores desnitrificantes apresentaram reações de amplificação positivas com primers específicos para bactérias semelhantes a Thiomicrospira associados a primers universais: 100% das amostras amplificaram com OST1F/1492R e 75% com EUB8F/OSTR1R. Para duas condições de operação do reator em escala de bancada foram identificados micro-organismos semelhantes a Sulfurimonas denitrificans, bactéria autotrófica redutora de nitrato e oxidadora de sulfeto. Chloroflexi também foram encontrados em digestores localizados em plantas de tratamento de águas residuárias recebendo essencialmente efluente doméstico e Propionibacterium foi associada a comunidade microbiana de reatores UASB tratando água residuária industrial. Bactérias em associações sintróficas com participação no ciclo do enxofre e/ou na digestão anaeróbia foram igualmente identificadas: Clostridium sulfidigenes e outros Firmicutes, Synergistetes, clones de bactérias de cultura de enriquecimento e bactérias do gênero Syntrophorhabdus. Os resultados deste trabalho proporcionaram associar a colonização microbiana com o desempenho e as características metabólicas de alguns micro-organismos com reatores desnitrificantes combinados para o tratamento de águas residuárias. / The widespread nitrate contamination in concentrations higher than recommended by legislation has raised interest in technologies for water and wastewater treatment. Biological nitrogen removal is relatively low cost and higher efficiency. Sulfide as electron donor can be oxidized to elemental sulfur or sulfate by sulfide oxidizing bacteria that can use nitrate or nitrite as electron acceptor. This type of denitrification reduces the overall requirements for removal of carbon nutrients and less sludge is produced. The aim of this research was to contribute to microbiological knowledge about denitrification using sulfide. The effects of operation conditions on the denitrifying biomass were monitored through molecular biology techniques such as PCR/DGGE, sequencing and phylogenetic analysis. 16S rRNA gene fragments were related to Pseudomonas, Aeromonas, Acidobacteria, Chlroroflexi, Clostridium, Cupriavidus and Ralstonia. Phylotypes of clones from samples of pilot-scale reactor were associated with non-cultivable bacteria and Firmicutes involved in anaerobic digestion of wastewater, Synergistetes, Deferribacteria and Proteobacteria. Microorganisms with ability to denitrification were identified in both reactors: Pseudomonas, Desulfovibrio desulfuricans and Ralstonia. Samples of denitrifying reactors showed positive amplification with specific primers for Thiomicrospira associated to universal primers: 100% of the samples amplified with OST1F/1492R and 75% EUB8F/OSTR1R. Sulfurimonas denitrificans-like were identified for two operational conditions of the bench scale reactor. Chloroflexi were also found in treatment plants digesters receiving domestic wastewater and Propionibacterium was associated with microbial community of UASB reactors treating industrial wastewater. Syntrophic bacteria participating in the sulfur cycle and/or anaerobic digestion were also identified: Clostridium sulfidigenes and other Firmicutes, Synergistetes, clone enrichment culture bacteria and Syntrophorhabdus. These results provide to associate this microbial colonization and metabolic characteristics of some microorganisms with performance of combined denitrifying reactors for treatment of wastewater.

O processo de nitrificação e desnitrificação simultâneas (NDS) permite alcançar a remoção combinada de matérias carbonácea e nitrogenada em uma única unidade. O reator de leito estruturado, com biomassa imobilizada e recirculação interna, apresenta características positivas para que estes processos envolvidos ocorram, tais como propiciar a formação de biofilme e evitar a colmatação do leito. Esta configuração tem sido estudada com êxito em reatores em escala de bancada para tratamento de esgoto. Nesta pesquisa foi utilizado um reator de leito estruturado em escala piloto com a finalidade de avaliar sua implantação, eficiência e estabilidade tratando esgoto doméstico em condições reais para futura aplicação em pequenas comunidades, condomínios residenciais entre outros como sistema descentralizado. O reator foi construído em fibra de vidro, de formato cilíndrico, com diâmetro interno de aproximadamente 0,80 m e 2,0 m de altura. O volume total foi de aproximadamente 0,905 m3 e o volume útil de 0,642 m3. A operação foi realizada sob condições de aeração contínua e intermitente e os tempos de detenção hidráulica (TDH) testados foram de 48, 36 e 24 horas. A remoção de DQO manteve-se acima de 90% com TDH de 48 e 36 horas. A melhor eficiência de remoção de nitrogênio total foi de 72,4 ± 6,4%, sob TDH de 48 horas e a aeração intermitente, com 2 horas de aeração e 1 hora não aerada. A concentração de oxigênio dissolvido (OD) média de 2,8 ± 0,5 mg.L-1 na fase aerada e temperatura média de 24,7 ± 1,0 °C. Nesse mesmo período, a eficiência média de remoção de DQO foi de 94 ± 4 %. Apesar das dificuldades apresentadas no controle da aeração, as eficiências das remoções obtidas indicaram que o reator de leito estruturado e aeração intermitente (LEAI) se apresenta como uma alternativa promissora em escala plena, requerendo ajustes para construção e incremento da estabilidade da NDS. / The simultaneous nitrification and denitrification (SND) process allow achieving a combined nitrogen and carbon removal in a single unit. The structured-bed reactor, with immobilized biomass and internal recirculation, presents positive characteristics for occurrence of these involved processes, such as providing biofilm formation and prevent clogging. This configuration have been study successfully in a bench scale for sewage treatment. In this research was used a structured-bed reactor in a pilot scale in order to evaluate its implantation, efficiency and stability treating sewage in real conditions to future application in small communities, residential condominium among others, as decentralized treatment. The reactor was constructed with cylindrical glass fiber modules, with internal diameter of 0.8 m and 2.0 m height. The total volume was about 0.905 m3 and 0.642 m3 working volume. It was worked under continuous and intermittent aeration conditions and the tested hydraulic retention times (HRT) were 48, 36 e 24 hours. The maximum total nitrogen removal was 72.4 ± 6.4% ; the HRT was 48 hours with intermittent aeration, in which 2 hours in aeration and 1-hour nonaeration. An average dissolved oxygen (DO) concentration of 2.8 ± 0.5 mg.L-1 in the aerated time and an average temperature of 24.7 ± 1.0°C. In the same period, the average COD removal was 94 ± 4%. Despite of the difficulties presented in aeration control, the obtained removals indicated the structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) can be a promising alternative in full scale, demanding adjustments to improve the reactor construction and the SND stability.

This doctoral research provides an advanced molecular approach for the investigation of microbial structure and function in response to operational conditions of biological nitrogen removal (BNR) processes, including those leading to direct production of a major greenhouse gas, nitrous oxide (N₂O). The wastewater treatment sector is estimated to account with 3% of total anthropogenic N₂O emissions. Nevertheless, the contribution from wastewater treatment plants (WWTPs) is considered underestimated due to several limitations on the estimation methodology approach suggested by the Intergovernmental Panel on Climate Change (IPCC). Although for the past years efforts have been made to characterize the production of N₂O from these systems, there are still several limitations on fundamental knowledge and operational applications. Those include lack of information of N₂O production pathways associated with control of aeration, supplemental organic carbon sources and adaptation of the microbial community to the repeated operational conditions, among others. The components of this thesis, lab-scale investigations and full-scale monitoring of N₂O production pathways and emissions in conjunction with meta-omics approach, have a combined role in addressing such limitations. Lab-scale experiments imposing short-term anoxic-aerobic cycling on partial- and full-nitrification based processes were conducted to investigate the microbial response to N₂O production. Interestingly, it was determined that full-nitrification systems could be a higher contributor to N₂O production and emissions than partial-nitrification. While it has been reported in the literature a higher contribution from the latter when the microbial community is not subjected to oxygen cycling conditions. Following the knowledge obtained with a single anoxic-aerobic cycle imposed to nitrifying communities, long-term adaptation of the microbial community to continued anoxic-aerobic cycling and its impact on N₂O production were investigated through a meta-omics approach. Long-term studies are particularly significant regarding engineered systems, where the microorganisms are continually subjected to cycling conditions again and again. A microbial adaptation at the RNA level was identified on both autotroph and heterotroph organisms. The transcripts of the metabolic pathways related to NO and N₂O production (nir, nor) and consumption (nor, nos) were initially induced followed by a gradual decline, leading to a parallel reduction in gaseous emissions over time. Other pathways not typically interrogated in conjunction with the nitrogen metabolism, such as electron transport chain and carbon fixation were also investigated and revealed a mechanism to overcome the imbalance in electron flow and generation of proton motive force (increased transcription of terminal oxidase genes, cco and cox) to uphold carbon fixation during continued cycling. The second part of this thesis focuses on full-scale WWTPs, where it is crucial to determine specific nuances of the systems’ dynamics and of the different types of treatment that may contribute to increased production and emissions of N₂O. For that purpose, two distinct BNR systems not usually considered and studied in terms of N₂O production and emissions were chosen. First, a separate centrate treatment (SCT) process employing glycerol as the supplemental carbon source was monitored. Significantly, this system was found to have one of the highest levels of N₂O production and emission report thus far. Glycerol revealed to foster a microbial community (i.e. Burkholderiales, Rhodobacterales and Sphingomonadales) that stores internal carbon and promote partial denitrification, leading to accumulation of nitrite and N₂O [7-11]. Second, both fixed- and moving-bed biofilm BNR systems were investigated. The overall N₂O emission fractions for the Integrated Fixed-Film Activated Sludge (IFAS)(0.09 – 1.1% infl-TKN) and denitrification filters (0.11 – 1.4% infl-TN) were similar to the reported emissions from suspended growth activated sludge systems [4-6]. For the IFAS system, aqueous and gaseous N₂O profiles paralleled the diurnal variability on influent nitrogen load. The production of N₂O was significantly correlated with ammonia concentration (p<0.05, r=0.91), suggesting the production through hydroxylamine oxidation pathway. Denitrification filters displayed a very peculiar pattern on N₂O emissions associated with intermittent operational cycles (i.e. nitrogen release cycle and backwash). These intrinsic operations of the denitrification filters contributed to transient oxygen conditions and nearly the entire N₂O emissions through gaseous stripping and production by inhibition of denitrification. Similarly to suspended growth systems, process design and operations demonstrated to also play an important role in N₂O emissions from attached growth processes. Finally, aeration strategies for energy efficient conventional nitrification based on the microbial community development and its associated performance was investigated in lab-scale. It was demonstrated that using the same air supply rate, continuous and intermittent aeration resulted in completely different microbial structure. Consequently, distinct kinetics and nitrification performance were observed. The aeration rate could be minimized (resulting in reduction in energy consumption) for high ammonia removal efficiency and lower N₂O emissions, as long as the process is designed accordingly to the microbial ecology developed in such conditions. In sum, the microbial structure, function and connection of metabolic pathways of complex engineered microbial communities as applicable to BNR systems and its operations were investigated in detail. From an engineering perspective, this dissertation provides an advancement on the molecular approach to characterize structure and function of microbial responses to engineered operations beyond the business-as-usual target genes, which can eventually result in better design and control of engineered BNR processes. This study offers more than an improved scientific understanding of the complex microbial environment and direct engineering applications. It connects sanitation with water quality and the greenhouse gas effect by prioritizing concurrent enhanced biological nitrogen removal and mitigation of N₂O production and emission. Ultimately the implications of the result presented herein can provide economical, environmental, health benefits for the society.

Population growth and aspects related to management water resources, make it extremely important to search for simple wastewater treatment systems, low cost and simplicity operational, capable of producing effluent with potential use for compatible many purposes. In this scenario, the use of aerated reactors as post-treatment of anaerobic effluent is shown quite promising for Brazilian reality. This work contributes to the development of new biofilter system for aerobic treatment of sewage, which is being developed at the Federal University of Rio Grande do Norte. The reactor uses corrugated conduit as cut filler, providing a high void ratio, and is capable of producing effluent with turbidity UT order of 1, 2 mg / L of TSS and COD of below 40 mg / L. IT IS objective of this work to investigate the nitrogen removal capacity by simultaneous nitrification and denitrification. The work was divided into four phases, in which has been changed air flow in the filters, and during step 4, introduced a supplementary source of carbon. The system proved to be effective regarding the removal of nitrogen. In the most efficient configuration It was able to remove 56% of the influent nitrogen, and the less efficient phase removal was 40%. The principal component analysis showed that the nitrification was the most important factor for the process. It was concluded that the system is able to remove nitrogen through nitrification and simultaneous denitrification. Furthermore, it is also important to mention that during the more than three years of the experiment duration was not required removal of retained sludge. / O crescimento da populaÃÃo e aspectos relacionados ao gerenciamento de recursos hÃdricos, fazem com que seja extremamente importante a busca por sistemas de tratamento de esgoto simples, de baixo custo e simplicidade operacional, capazes de produzir efluentes com potencial de utilizaÃÃo para diversos fins compatÃveis. Neste cenÃrio, a utilizaÃÃo de reatores aerados como pÃs-tratamento de efluente anaerÃbio mostra-se bastante promissor para a realidade brasileira. Este trabalho contribui para o desenvolvimento de novo sistema de biofiltros aerÃbios para tratamento de esgotos sanitÃrios, que està sendo desenvolvido na Universidade Federal do Rio Grande do Norte. O reator utiliza eletroduto corrugado cortado como material de enchimento, proporcionando elevado Ãndice de vazios, e à capaz de produzir efluente com turbidez da ordem de 1 UT, 2 mg/L de SST e DQO abaixo de 40 mg/L. à objetivo deste trabalho investigar a capacidade de remoÃÃo de nitrogÃnio pelo processo de nitrificaÃÃo e desnitrificaÃÃo simultÃnea. O trabalho foi dividido em quatro fases, nas quais foi alterada a vazÃo de ar nos filtros, e, durante a fase 4, introduzida uma fonte suplementar de carbono. O sistema mostrou-se eficiente em relaÃÃo à remoÃÃo de nitrogÃnio. Na configuraÃÃo mais eficiente foi capaz de remover 56% do nitrogÃnio afluente, e na fase menos eficiente a remoÃÃo foi de 40%. A anÃlise de componentes principais mostrou que a nitrificaÃÃo foi o fator mais relevante para o processo. Concluiu-se que o sistema à capaz de remover nitrogÃnio pelo processo de nitrificaÃÃo e desnitrificaÃÃo simultÃnea. AlÃm disso, à importante mencionar tambÃm que durante os mais de trÃs anos de duraÃÃo do experimento nÃo foi necessÃria a remoÃÃo do lodo retido.

Made available in DSpace on 2017-07-10T19:24:29Z (GMT). No. of bitstreams: 1 Lidiana de Andrade.pdf: 573128 bytes, checksum: aea6329b21b37790be3adaed5e1f2ec1 (MD5) Previous issue date: 2008-06-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Effluents from fish slaughterhouse are rich in nutrients, among other there is nitrogen that causes eutrophication in rivers. Nitrogen removal can be done in two parts: Nitrification and Denitrification. Nitrification is influenced by factors such as temperature, pH, alkalinity, C/N relation and other. This experiment aimed to test the influence of air flow and ammonia concentration in nitrification process in a sequential batch reactor with immobilized biomass. The reactor had volume of 2.5L, it was operated as rotational central composed design (DCCR), which were tested the factors: air flow (1 to 3L.min-1), initial concentration of ammonia nitrogen (40 to 100mgN.L-1). The results evaluated were conversion rate of ammonia to nitrate, nitrite percentage of accumulation, and capacity of microorganisms detention. The results showed with confidence interval of 95%, that the concentrations decrease of evaluated factors significantly increased the conversion percentage of ammonia to nitrate. The nitrite percentage of accumulation was influenced significantly by the increasing concentration of ammonia. And the biomass capacity of detention has not suffered significant influence from any factors considered. / Os efluentes de abatedouro de peixes são ricos em nutrientes e, entre eles, está o nitrogênio que causa a eutrofização dos corpos de água. A remoção do nitrogênio pode ser feita em duas etapas: nitrificação e desnitrificação. A nitrificação é influenciada por fatores como temperatura, pH, alcalinidade, relação C/N entre outros. Este experimento teve como objetivo testar a influência da vazão de ar e da concentração de nitrogênio amoniacal no processo de nitrificação em reator em batelada seqüencial com biomassa imobilizada. O reator com volume de 2,5L foi operado conforme delineamento composto central rotacional, em que foram avaliados os fatores: vazão de ar (de 1 e 3 L.min-1); e concentração inicial de nitrogênio amoniacal (de 40 e 100 mgN.L-1). As variáveis-resposta analisadas foram: porcentagem de conversão de nitrogênio amoniacal a nitrato, porcentagem de acúmulo de nitrito e capacidade de imobilização dos microrganismos. Os resultados mostraram, com intervalo de confiança de 95%, que a diminuição das concentrações dos fatores avaliados aumentou significativamente a porcentagem de conversão de nitrogênio amoniacal a nitrato. A porcentagem de acúmulo de nitrito foi influenciada de forma significativa somente com o aumento da concentração de nitrogênio amoniacal. E a capacidade de imobilização da biomassa não sofreu influencia significativa de nenhum dos fatores analisados.

O processo de nitrificação e desnitrificação simultâneas (NDS) permite alcançar a remoção combinada de matérias carbonácea e nitrogenada em uma única unidade. O reator de leito estruturado, com biomassa imobilizada e recirculação interna, apresenta características positivas para que estes processos envolvidos ocorram, tais como propiciar a formação de biofilme e evitar a colmatação do leito. Esta configuração tem sido estudada com êxito em reatores em escala de bancada para tratamento de esgoto. Nesta pesquisa foi utilizado um reator de leito estruturado em escala piloto com a finalidade de avaliar sua implantação, eficiência e estabilidade tratando esgoto doméstico em condições reais para futura aplicação em pequenas comunidades, condomínios residenciais entre outros como sistema descentralizado. O reator foi construído em fibra de vidro, de formato cilíndrico, com diâmetro interno de aproximadamente 0,80 m e 2,0 m de altura. O volume total foi de aproximadamente 0,905 m3 e o volume útil de 0,642 m3. A operação foi realizada sob condições de aeração contínua e intermitente e os tempos de detenção hidráulica (TDH) testados foram de 48, 36 e 24 horas. A remoção de DQO manteve-se acima de 90&#37; com TDH de 48 e 36 horas. A melhor eficiência de remoção de nitrogênio total foi de 72,4 &#177; 6,4&#37;, sob TDH de 48 horas e a aeração intermitente, com 2 horas de aeração e 1 hora não aerada. A concentração de oxigênio dissolvido (OD) média de 2,8 &#177; 0,5 mg.L-1 na fase aerada e temperatura média de 24,7 &#177; 1,0 &#176;C. Nesse mesmo período, a eficiência média de remoção de DQO foi de 94 &#177; 4 &#37;. Apesar das dificuldades apresentadas no controle da aeração, as eficiências das remoções obtidas indicaram que o reator de leito estruturado e aeração intermitente (LEAI) se apresenta como uma alternativa promissora em escala plena, requerendo ajustes para construção e incremento da estabilidade da NDS. / The simultaneous nitrification and denitrification (SND) process allow achieving a combined nitrogen and carbon removal in a single unit. The structured-bed reactor, with immobilized biomass and internal recirculation, presents positive characteristics for occurrence of these involved processes, such as providing biofilm formation and prevent clogging. This configuration have been study successfully in a bench scale for sewage treatment. In this research was used a structured-bed reactor in a pilot scale in order to evaluate its implantation, efficiency and stability treating sewage in real conditions to future application in small communities, residential condominium among others, as decentralized treatment. The reactor was constructed with cylindrical glass fiber modules, with internal diameter of 0.8 m and 2.0 m height. The total volume was about 0.905 m3 and 0.642 m3 working volume. It was worked under continuous and intermittent aeration conditions and the tested hydraulic retention times (HRT) were 48, 36 e 24 hours. The maximum total nitrogen removal was 72.4 &#177; 6.4&#37; ; the HRT was 48 hours with intermittent aeration, in which 2 hours in aeration and 1-hour nonaeration. An average dissolved oxygen (DO) concentration of 2.8 &#177; 0.5 mg.L-1 in the aerated time and an average temperature of 24.7 &#177; 1.0&#176;C. In the same period, the average COD removal was 94 &#177; 4&#37;. Despite of the difficulties presented in aeration control, the obtained removals indicated the structured-bed reactor subjected to recirculation and intermittent aeration (SBRRIA) can be a promising alternative in full scale, demanding adjustments to improve the reactor construction and the SND stability.

Made available in DSpace on 2017-05-12T14:47:47Z (GMT). No. of bitstreams: 1 Lidiana de Andrade.pdf: 573128 bytes, checksum: aea6329b21b37790be3adaed5e1f2ec1 (MD5) Previous issue date: 2008-06-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Effluents from fish slaughterhouse are rich in nutrients, among other there is nitrogen that causes eutrophication in rivers. Nitrogen removal can be done in two parts: Nitrification and Denitrification. Nitrification is influenced by factors such as temperature, pH, alkalinity, C/N relation and other. This experiment aimed to test the influence of air flow and ammonia concentration in nitrification process in a sequential batch reactor with immobilized biomass. The reactor had volume of 2.5L, it was operated as rotational central composed design (DCCR), which were tested the factors: air flow (1 to 3L.min-1), initial concentration of ammonia nitrogen (40 to 100mgN.L-1). The results evaluated were conversion rate of ammonia to nitrate, nitrite percentage of accumulation, and capacity of microorganisms detention. The results showed with confidence interval of 95%, that the concentrations decrease of evaluated factors significantly increased the conversion percentage of ammonia to nitrate. The nitrite percentage of accumulation was influenced significantly by the increasing concentration of ammonia. And the biomass capacity of detention has not suffered significant influence from any factors considered. / Os efluentes de abatedouro de peixes são ricos em nutrientes e, entre eles, está o nitrogênio que causa a eutrofização dos corpos de água. A remoção do nitrogênio pode ser feita em duas etapas: nitrificação e desnitrificação. A nitrificação é influenciada por fatores como temperatura, pH, alcalinidade, relação C/N entre outros. Este experimento teve como objetivo testar a influência da vazão de ar e da concentração de nitrogênio amoniacal no processo de nitrificação em reator em batelada seqüencial com biomassa imobilizada. O reator com volume de 2,5L foi operado conforme delineamento composto central rotacional, em que foram avaliados os fatores: vazão de ar (de 1 e 3 L.min-1); e concentração inicial de nitrogênio amoniacal (de 40 e 100 mgN.L-1). As variáveis-resposta analisadas foram: porcentagem de conversão de nitrogênio amoniacal a nitrato, porcentagem de acúmulo de nitrito e capacidade de imobilização dos microrganismos. Os resultados mostraram, com intervalo de confiança de 95%, que a diminuição das concentrações dos fatores avaliados aumentou significativamente a porcentagem de conversão de nitrogênio amoniacal a nitrato. A porcentagem de acúmulo de nitrito foi influenciada de forma significativa somente com o aumento da concentração de nitrogênio amoniacal. E a capacidade de imobilização da biomassa não sofreu influencia significativa de nenhum dos fatores analisados.

The ability of Nakivubo wetland (which has performed tertiary water treatment for Kampala city for the past 40 years) to respond to pollution and to protect the water quality of Inner Murchison Bay of Lake Victoria was investigated. The aim of this study was to assess the capacity of Nakivubo wetland to remove nitrogen from the wastewater after its recent encroachment and modification, in order to optimize biological nitrogen removal processes using constructed wetland technology. Field studies were performed to assess the hydraulic loading, stability and water quality of this wetland. The distribution and activity of ammonium-oxidizing bacteria (AOB) in Nakivubo channel and wetland were also investigated, and the significance of the different matrices in biological nitrogen transformations within the two systems elucidated. Studies to optimize nutrient removal processes were carried out at pilot scale level both in container experiments and in the field using substrate-free constructed wetlands (CWs) planted with Cyperus papyrus and Miscanthidium violaceum which were adapted to the local ecological conditions. Results showed that Nakivubo wetland performs tertiary treatment for a large volume of wastewater from Kampala city, which is characterised by large quantities of nutrients, organic matter and to a lesser extent metals. Mass pollutant loads showed that wastewater effluent from a sewage treatment plant constituted a larger proportion of nitrogen and phosphorus and biochemical oxygen demand (BOD) discharged into the wetland. The upper section of Nakivubo wetland exhibited high removal efficiencies for BOD, whereas little or no ammonium-nitrogen and metals except Lead were removed by wetland. Studies further showed that nitrifying bacteria existed in the wetland but their activity was limited by oxygen depletion due to the high BOD in the wastewater and heterotrophic bacteria from the sewage treatment plant. Distributional studies indicated the presence of more AOB in surface sediments than the water column of the lower section of Nakivubo channel, an indication that nitrifiers settled with particulate matter prior to discharge into the wetland, and thus did not represent seeding of the wetland. The significant reductions in concentrations of BOD compared to ammonium and total nitrogen in the channel and wetland wastewater confirmed this finding. Whereas suspended nitrifiers upstream of Nakivubo channel equally influenced total nitrogen balance as those in surface sediments, epiphytic nitrification was more important than that of sediment/peat compartments in the wetland, and thus highlighted the detrimental impacts of wetland modification on the water quality Inner Murchison Bay and Lake Victoria as a whole. Performance assessment of pilot-scale container experiments and field-based CWs indicated highly promising treatment efficiencies, notably in papyrus-based treatments. Plant biomass productivity, nutrient storage, and overall system treatment performance were higher in papyrusbased constructed wetlands, and resulted in effluent that met national discharge limits. Thus, papyrus-based CWs were found to be operationally efficient in removing pollutants from domestic wastewater. / QC 20101028

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

Combined treatment technologies for the removal of waste carbon, nitrogen, and/or sulfur under anoxic/anaerobic conditions have recently received considerable attention. It has been reported that nitrate and/or reduced N-oxides, such as nitrite (NO2-), nitric oxide (NO), and nitrous oxide (N2O), which are products of denitrification, suppress methanogenesis. Research was conducted to investigate the effect of N-oxides and sulfide on mixed, mesophilic (35oC) methanogenic cultures, along with the effect of the type of electron donor on the kinetics and pathway of nitrate reduction. Among all N-oxides tested, NO exerted the most and nitrate exerted the least inhibitory effect on the fermentative/methanogenic consortia. Long-term exposure of a methanogenic culture to nitrate resulted in an increase of N-oxide reduction and a decrease of methane production rates. Sulfide addition to sulfide-free enriched cultures resulted in inhibition of NO2-, NO, and N2O reduction causing accumulation of these intermediates, which in turn inhibited methanogenesis and fermentation. In nitrate-amended, sulfide-acclimated cultures, nitrate reduction occurred via dissimilatory nitrate reduction to ammonia (DNRA); thus, accumulation of N-oxides was avoided and inhibition of methanogenesis was prevented. The nitrate reduction rates in cultures fed with different electron donors followed the descending order: H2/CO2 > acetate > glucose > dextrin/peptone > propionate. Denitrification was observed in the propionate-, acetate-, and H2/CO2-fed cultures regardless of the COD/N value. Both denitrification and DNRA were observed in the dextrin/peptone- and glucose-fed cultures and the predominance of either of the two pathways was a function of the COD/N value. Nitrate reduction processes were incorporated into the IWA Anaerobic Digestion Model No. 1 (ADM1) in order to account for the effect of nitrate reduction processes on fermentation and methanogenesis. The extended ADM1 described the experimental results very well. Model simulations showed that process interactions during nitrate reduction within an overall methanogenic system cannot be explained based on only stoichiometry and kinetics, especially for batch systems and/or continuous-flow systems with periodic, shock nitrate loads. The results of this research are useful in predicting the fate of carbon-, nitrogen-, and sulfur-bearing waste material, as well as in understanding microbial process interactions, in both natural and engineered anoxic/anaerobic systems.