An in situ respirometric technique was applied to a sequential biofilm batch reactor treating a synthetic wastewater containing acetate. In this reactor, inoculated with mixed liquor from a wastewater plant, unglazed ceramic tiles were used as support media while maintaining complete mixing regime. A total of 8 kinetic and stoichiometric parameters were determined by pulse respirometry, namely substrate oxidation yield, biomass growth yield, storage yield, storage growth yield, substrate affinity constant, storage affinity constant, storage kinetic constant and maximum oxygen uptake rate. Additionally, biofilm growth was determined from support media sampling showing that the colonization process occurred during the first 40 days, reaching an apparent steady-state afterward. Similarly, most of the stoichiometric and kinetic parameters were changing over time but reached steady values after day 40. During the experiment, the respirometric method allowed to quantify the amount of substrate directed to storage, which was significant, especially at substrate concentration superior to 30 mg COD L-1. The Activated Sludge Model 3 (ASM3), which is a model that takes into account substrate storage mechanisms, fitted well experimental data and allowed confirming that feast and famine cycles in sequential batch reactor favor storage. These results also show that in situ pulse respirometry can be used for fixed-bed reactors characterization.
O objetivo deste trabalho incidiu no desenvolvimento de um processo multi-stage económico para a produção de polímeros biodegradáveis, polihidroxialcanoatos (PHA), por culturas microbianas mistas, usando como matéria-prima águas residuais de lagares de azeite. Neste processo foram utilizadas águas residuais de lagares de azeite pré-fermentadas, nas quais 60% do conteúdo de CQO (Carência Química de Oxigénio) solúvel foi convertido em ácidos gordos voláteis (AGV) que são substratos mais directos para a produção de PHA. Esta corrente rica em AGV foi utilizada como alimento na fase sucessiva do processo, efetuada num reator descontínuo sequencial (SBR) à escala laboratorial. O objetivo desta etapa foi a selecção e enriquecimento da cultura mista microbiana em microrganismos com capacidade de acumulação de PHA elevada e estável, recorrendo ao regime de “fome e fartura”. Foram testadas duas cargas orgânicas diferentes no SBR – 2.37 e 4.74 g L-1 d-1 (referentes a CQO solúvel) – diluindo as águas residuais pré-fermentadas com meio mineral. A resposta de acumulação da cultura selecionada com a carga orgânica mais elevada foi estudada na etapa seguinte, tendo como objetivo o aumento do conteúdo intracelular de polímero na biomassa...
Este trabalho abordou a valorização de um subproduto da indústria de lacticínios (soro de queijo) através da alteração do funcionamento de processos habitualmente utilizados no contexto do tratamento biológico. Foi avaliada a fermentação acidogénica deste subproduto para maximizar a conversão do seu elevado teor de matéria orgânica em ácidos orgânicos voláteis (AOV) que actualmente são produtos com elevada procura, nomeadamente para produção de polihidroxialcanoatos (PHA). Em ensaios descontínuos e semi-contínuos foi caracterizada a produção e composição de AOV a partir de soro de queijo variando a razão food-to-microorganism (F/M) e a concentração de alcalinidade. Recorrendo à modelação dos resultados através de superfícies de resposta, demonstrou-se que condições de F/M = 4 gCQO g-1SSV combinadas com uma adição elevada de alcalinidade (8 g L-1 expresso como CaCO3) resultaram na conversão de 72% da CQO alimentada em AOV. O acetato e o butirato foram os AOV predominantes (60%), mas elevadas razões F/M combinadas com elevadas alcalinidades promoveram o alongamento da cadeia carboxílica, tendo sido produzidos AOV de maior massa molecular (iso-valerato e n-caproato). O processo de fermentação acidogénica foi posteriormente desenvolvido em modo contínuo num reactor MBBR acidogénico operado a longo prazo. Cargas orgânicas entre 30 e 50 gCQO L-1d-1 permitiram obter um grau de acidificação máximo de 68% no efluente fermentado. Foi ainda demonstrado que uma adição dinâmica de alcalinidade (0 – 4...
Dissertação para obtenção do Grau de Mestre em
Engenharia Química e Bioquímica; Polyhydroxyalkanoates (PHAs) are polyesters of hydroxyl fatty acids, which are accumulated in microbial cells as carbon/energy reserves.
PHAs are bio-based and biodegradable and display a wide range of thermoplastic properties, being a promising alternative to conventional plastics.
Presently, industrial PHA production was primarily based on pure microbial cultures. Although this process has high PHA production efficiency, it presents high costs associated with the use of chemically-defined feedstocks, and to the need for sterility.
An attractive feature of mixed microbial cultures (MMCs) PHAs production is the ability to use waste/surplus feedstocks. Many industrial wastes are seasonally produced making it necessary find the best method of utilization of this feedstock on PHA production process. Two different approaches might be taken account: (1) stock of industrial wastes during their production for their use throughout the year. However, the high fermentability of these agro-industrial wastes makes them susceptible to degradation during storage period; (2) the use of different feedstocks over the year according its availability. It is thus important to study MMC’s response to different feedstocks. The aim of this work is study how MMC PHA production process is affected by a feedstock shift...
Oral bacterial microcosms, established using saliva inocula from three individuals, were maintained under a feast-famine regime within constant-depth film fermenters. Steady-state communities were exposed four times daily, postfeeding, to a chlorhexidine (CHX) gluconate-containing mouthwash (CHXM) diluted to 0.06% (wt/vol) antimicrobial content. The microcosms were characterized by heterotrophic plate counts and PCR-denaturing gradient gel electrophoresis (DGGE). CHXM caused significant decreases in both total anaerobe and total aerobe/facultative anaerobe counts (P < 0.05), together with lesser decreases in gram-negative anaerobes. The degree of streptococcal and actinomycete inhibition varied considerably among individuals. DGGE showed that CHXM exposure caused considerable decreases in microbial diversity, including marked reductions in Prevotella sp. and Selenomonas infelix. Pure-culture studies of 10 oral bacteria (eight genera) showed that Actinomyces naeslundii, Veillonella dispar, Prevotella nigrescens, and the streptococci were highly susceptible to CHX, while Lactobacillus rhamnosus, Fusobacterium nucleatum, and Neisseria subflava were the least susceptible. Determination of the MICs of triclosan, CHX, erythromycin, penicillin V...
Aerobic granular sludge is attractive for high-rate biological wastewater treatment. Biomass wash-out conditions stimulate the formation of aerobic granules. Deteriorated performances in biomass settling and nutrient removal during start-up have however often been reported. The effect of wash-out dynamics was investigated on bacterial selection, biomass settling behavior, and metabolic activities during the formation of early-stage granules from activated sludge of two wastewater treatment plants (WWTP) over start-up periods of maximum 60 days. Five bubble-column sequencing batch reactors were operated with feast-famine regimes consisting of rapid pulse or slow anaerobic feeding followed by aerobic starvation. Slow-settling fluffy granules were formed when an insufficient superficial air velocity (SAV; 1.8 cm s−1) was applied, when the inoculation sludge was taken from a WWTP removing organic matter only, or when reactors were operated at 30°C. Fast-settling dense granules were obtained with 4.0 cm s−1 SAV, or when the inoculation sludge was taken from a WWTP removing all nutrients biologically. However, only carbon was aerobically removed during start-up. Fluffy granules and dense granules were displaying distinct predominant phylotypes...
Microorganisms are constantly exposed to rapidly changing conditions, under natural as well as industrial production scale environments, especially due to large-scale substrate mixing limitations. In this work, we present an experimental approach based on a dynamic feast/famine regime (400 s) that leads to repetitive cycles with moderate changes in substrate availability in an aerobic glucose cultivation of Saccharomyces cerevisiae. After a few cycles, the feast/famine produced a stable and repetitive pattern with a reproducible metabolic response in time, thus providing a robust platform for studying the microorganism’s physiology under dynamic conditions. We found that the biomass yield was slightly reduced (−5%) under the feast/famine regime, while the averaged substrate and oxygen consumption as well as the carbon dioxide production rates were comparable. The dynamic response of the intracellular metabolites showed specific differences in comparison to other dynamic experiments (especially stimulus-response experiments, SRE). Remarkably, the frequently reported ATP paradox observed in single pulse experiments was not present during the repetitive perturbations applied here. We found that intracellular dynamic accumulations led to an uncoupling of the substrate uptake rate (up to 9-fold change at 20 s.) Moreover...
Fonte: Universidade do MinhoPublicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 01/01/2013ENG
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Understanding of metabolic robustness and regulation from system biology approaches will allow for more designbased
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Polyhydroxyalkanoates (PHA) production using mixed microbial cultures (MMC) requires a multi-stage process involving the microbial selection of PHA-storing microorganisms, typically operated in sequencing batch reactors (SBR), and an accumulation reactor. Since low-cost renewable feedstocks used as process feedstock are often nitrogen-deficient, nutrient supply in the selection stage is required to allow for microbial growth. In this context, the possibility to uncouple nitrogen supply from carbon feeding within the SBR cycle has been investigated in this study. Moreover, three different COD:N ratios (100:3.79, 100:3.03 and 100:2.43) were tested in three different runs which also allowed the study of COD:N ratio on the SBR performance.
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