Tratamento de soro de queijo no ASBR: influência da estratégia de alimentação

Avaliou-se o desempenho do reator anaeróbio em batelada seqüencial com biomassa imobilizada (ASBBR) no tratamento de soro de queijo quanto submetido a diferentes estratégias de alimentação e cargas orgânicas volumétricas (COV). O reator operou com agitação mecânica através de impelidor do tipo hélice na rotação de 500 rpm. Um volume de 2 litros foi alimentado por ciclo com 1 litro de volume residual, totalizando 3 litros. O substrato utilizado foi soro de queijo desidratado reconstituído. Suplementou-se o sistema com NaHCO3 na razão de 50% NaHCO3/DQO. Foram testadas as seguintes COVs: 2, 4, 8 e 12 gDQO/l.d. Para ciclos de 8 horas e em cada COV, três estratégias de alimentação foram testadas: (a) operação em batelada com ciclo de 8 horas, (b) batelada alimentada de 2 horas (c) batelada alimentada de 4 horas. Na COV de 2 gDQO/l.d, a conversão de matéria orgânica como DQO em amostras filtradas foi de 92, 96 e 91% para as estratégias de alimentação (a), (b) e (c), respectivamente. Para a COV de 4 gDQO/l.d, o desempenho foi de 94, 97 e 93%, respectivamente. Para a COV de 8 gDQO/l.d houve redução nas eficiências de conversão a 83, 85 e 86%, respectivamente. O aumento da COV para 12 gDQO/l.d, resultou na redução em eficiências de 72, 73 e 81%, respectivamente. Os perfis durante os ciclos da concentração de ácidos voláteis totais mostraram que, apesar do aumento gradual com o tempo de enchimento aumentando, nenhuma diferença significativa foi detectada em termos dos seus valores máximos. Foi observada a redução de ácido propiônico como conseqüência do aumento do tempo de enchimento. Assim, para COV de 2 e 4 gDQO/l.d, a estratégia de alimentação (b) proporcionou maiores eficiências de conversão e estabilidade operacional, enquanto que este comportamento foi observado na estratégia de alimentação (c) para os valores de COV de 8 e 12 gDQO/l.d.

Degradação anaeróbia de fenol sob diferentes condições nutricionais

A tecnologia anaeróbia tem sido utilizada com sucesso no tratamento de água residuária contendo compostos fenólicos. Recentes pesquisas incluem tais compostos entre aqueles que podem ser degradados através desse processo. O objetivo desse trabalho foi avaliar a degradação do fenol em diferentes condições nutricionais, com ênfase na redução do sulfato. Os experimentos foram realizados com meio de cultura específico para esses microrganismos anaeróbios. Foram realizados ensaios de degradação em reatores em batelada alimentados nas seguintes condições: (1) fenol e sulfato, a diferentes concentrações, com inóculo previamente enriquecido; (2) fenol, sulfato e co-substratos e; (3) fenol, sulfato e extrato de levedura. Todos os ensaios foram realizados em temperatura de 30 graus Celsius, sob agitação de 150 rpm. Foi avaliado o consumo de fenol e sulfato e, produção de metano, em função do tempo, para diferentes concentrações iniciais de fenol e sulfato. Nos ensaios com reatores alimentados com fenol (329,3 mg/l); fenol (307,3 mg/l) e sulfato (160 mg/l); fenol (322.3 mg/l), sulfato (160 mg/l) e lactato (478,16 mg/l); fenol (332,1 mg/l), sulfato (150 mg/l) e etanol (129,76 mg/l), a remoção foi de, respectivamente, 99,8%, 98,2%, 98,8% e 98,8%. Os reatores alimentados com fenol (239,7 mg/l) obtiveram 100% de eficiência na degradação em apenas 11 dias e, os reatores alimentados com fenol (234,3 mg/l) e sulfato (162,5 mg/l) e fenol (256,0 mg/l) e sulfato (500 mg/l) tiveram eficiências de degradação de, respectivamente, 98,8% e 99,3% com 17 dias de operação. Tais eficiências foram obtidas pelo acréscimo de extrato de levedura nos reatores, no início dos ensaios. A caracterização morfológica foi realizada através de microscopia óptica. A diversidade microbiana referente aos Domínios Bacteria e Archaea, além do grupo de bactérias redutoras de sulfato foi avaliada através da técnica de PCR DGGE, onde foram observadas alterações nas populações microbianas, em função das condições nutricionais. Para o Domínio Archaea não foram observadas diferenças nos ensaios realizados. Para o Domínio Bacteria e Grupo das BRS essas diferenças foram, mais facilmente, percebidas com relação ao inóculo e entre os diversos reatores. A alteração na diversidade microbiana pode ter sido decorrente da composição do meio que, nesse caso, foi específico para BRS e a composição do inóculo que continha parte previamente adaptada às BRS. Essas condições adequadas puderam propiciar surgimento e desenvolvimento de populações microbianas capazes de degradar fenol, utilizando sulfato.

A novel wastewater treatment process: Simultaneous nitrification, denitrification and phosphorus removal

Simultaneous nitrification and denitrification (SND) via the nitrite pathway and anaerobic-anoxic enhanced biological phosphorus removal (EBPR) are two processes that can significantly reduce the COD demand for nitrogen and phosphorus removal. The combination of these two processes has the potential of achieving simultaneous nitrogen and phosphorus removal with a minimal requirement for COD. A lab-scale sequencing batch reactor (SBR) was operated in alternating anaerobic-aerobic mode with a low dissolved oxygen concentration (DO, 0.5 mg/L) during the aerobic period, and was demonstrated to accomplish nitrification, denitrification and phosphorus removal. Under anaerobic conditions, COD was taken up and converted to polyhydroxyalkanoates (PHA), accompanied with phosphorus release. In the subsequent aerobic stage, PHA was oxidized and phosphorus was taken up to less than 0.5 mg/L at the end of the cycle. Ammonia was also oxidised during the aerobic period, but without accumulation of nitrite or nitrate in the system, indicating the occurrence of simultaneous nitrification and denitrification. However, off-gas analysis found that the final denitrification product was mainly nitrous oxide (N2O) not N-2. Further experimental results demonstrated that nitrogen removal was via nitrite, not nitrate. These experiments also showed that denitrifying glycogen.-accumulating organisms rather than denitrifying polyphosphate-accumulating organisms were responsible for the denitrification activity.

Determination of external and internal mass transfer limitation in nitrifying microbial aggregates

In this article we present a study of the effects of external and internal mass transfer limitation of oxygen in a nitrifying system. The oxygen uptake rates (OUR) were measured on both a macro-scale with a respirometric reactor using off-gas analysis (Titrimetric and Off-Gas Analysis (TOGA) sensor) and on a micro-scale with microsensors. These two methods provide independent, accurate measurements of the reaction rates and concentration profiles around and in the granules. The TOGA sensor and micro-sensor measurements showed a significant external mass transfer effect at low dissolved oxygen (DO) concentrations in the bulk liquid while it was insignificant at higher DO concentrations. The oxygen distribution with anaerobic or anoxic conditions in the center clearly shows major mass transfer limitation in the aggregate interior. The large drop in DO concentration of 22 - 80% between the bulk liquid and aggregate surface demonstrates that the external mass transfer resistance is also highly important. The maximum OUR even for floccular biomass was only attained at much higher DO concentrations ( approximate to 8 mg/L) than typically used in such systems. For granules, the DO required for maximal activity was estimated to be > 20mg/L, clearly indicating the effects of the major external and internal mass transfer limitations on the overall biomass activity. Smaller aggregates had a larger volumetric OUR indicating that the granules may have a lower activity in the interior part of the aggregate. (C) 2004 Wiley Periodicals, Inc.

The effect of pH on the competition between polyphosphate-accumulating organisms and glycogen-accumulating organisms

In enhanced biological phosphorus removal (EBPR) processes, glycogen-accumulating organisms (GAOs) may compete with polyphosphate-accumulating organisms (PAOs) for the often-limited carbon substrates, potentially resulting in disturbances to phosphorus removal. A detailed investigation of the effect of pH on the competition between PAOs and GAOs is reported in this study. The results show that a high external pH (similar to 8) provided PAOs with an advantage over GAOs in EBPR systems. The phosphorus removal performance improved due to a population shift favouring PAOs over GAOs, which was shown through both chemical and microbiological methods. Two lab-scale reactors fed with propionate as the carbon source were subjected to an increase in pH from 7 to 8. The phosphorus removal and PAO population (as measured by quantitative fluorescence in situ hybridisation analysis of Candidatus Accumulibacter phosphatis) increased in each system, where the PAOs appeared to out-compete a group of Alphaproteobacteria GAOs. A considerable improvement in the P removal was also observed in an acetate fed reactor, where the GAO population (primarily Candidatus Competibacter phosphatis) decreased substantially after a similar increase in the pH. The results from this study suggest that pH could be used as a control parameter to reduce the undesirable proliferation of GAOs and improve phosphorus removal in EBPR systems. (c) 2005 Elsevier Ltd. All rights reserved.

Efficient and stable nitritation and denitritation of ammonium-rich sludge dewatering liquor using an SBR with continuous loading

Separate treatment of dewatering liquor from anaerobic sludge digestion significantly reduces the nitrogen load of the main stream and improves overall nitrogen elimination. Such ammonium-rich wastewater is particularly suited to be treated by high rate processes which achieve a rapid elimination of nitrogen with a minimal COD requirement. Processes whereby ammonium is oxidised to nitrite only (nitritation) followed by denitritation with carbon addition can achieve this. Nitrogen removal by nitritation/denitritation was optimised using a novel SBR operation with continuous dewatering liquor addition. Efficient and robust nitrogen elimination was obtained at a total hydraulic retention time of 1 day via the nitrite pathway. Around 85-90% nitrogen removal was achieved at an ammonium loading rate of 1.2 g NH4+-N m(-3) d(-1). Ethanol was used as electron donor for denitritation at a ratio of 2.2gCODg(-1) N removed. Conventional nitritation/denitritation with rapid addition of the dewatering liquor at the beginning of the cycle often resulted in considerable nitric oxide (NO) accumulation during the anoxic phase possibly leading to unstable denitritation. Some NO production was still observed in the novel continuous mode, but denitritation was never seriously affected. Thus, process stability can be increased and the high specific reaction rates as well as the continuous feeding result in decreased reactor size for full-scale operation. (c) 2006 Elsevier Ltd. All rights reserved.

Putative glycogen-accumulating organisms belonging to the Alphaproteobacteria identified through rRNA-based stable isotope probing

Deterioration of enhanced biological phosphorus removal (EBPR) has been linked to the proliferation of glycogen-accumulating organisms (GAOs), but few organisms possessing the GAO metabolic phenotype have been identified. An unidentified GAO was highly enriched in a laboratory-scale bioreactor and attempts to identify this organism using conventional 16S rRNA gene cloning had failed. Therefore, rRNA-based stable isotope probing followed by full-cycle rRNA analysis was used to specifically identify the putative GAOs based on their characteristic metabolic phenotype. The study obtained sequences from a group of Alphaproteobacteria not previously shown to possess the GAO phenotype, but 90% identical by 16S rRNA gene analysis to a phylogenetic clade containing cloned sequences from putative GAOs and the isolate Defluvicoccus vanus. Fluorescence in situ hybridization (FISH) probes (DF988 and DF1020) were designed to target the new group and post-FISH chemical staining demonstrated anaerobic-aerobic cycling of polyhydroxyalkanoates, as per the GAO phenotype. The successful use of probes DF988 and DF1020 required the use of unlabelled helper probes which increased probe signal intensity up to 6.6-fold, thus highlighting the utility of helper probes in FISH. The new group constituted 33% of all Bacteria in the lab-scale bioreactor from which they were identified and were also abundant (51 and 55% of Bacteria) in two other similar bioreactors in which phosphorus removal had deteriorated. Unlike the previously identified Defluvicoccus-related organisms, the group identified in this study were also found in two full-scale treatment plants performing EBPR, suggesting that this group may be industrially relevant.

Bioreaction and separation in batch chromatographic columns

The objective of this work has been to study the behaviour and performance of a batch chromatographic column under simultaneous bioreaction and separation conditions for several carbohydrate feedstocks. Four bioreactions were chosen, namely the hydrolysis of sucrose to glucose and fructose using the enzyme invertase, the hydrolysis of inulin to fructose and glucose using inulinase, the hydrolysis of lactose to glucose and galactose using lactase and the isomerization of glucose to fructose using glucose isomerase. The chromatographic columns employed were jacketed glass columns ranging from 1 m to 2 m long and the internal diameter ranging from 0.97 cm to 1.97 cm. The stationary phase used was a cation exchange resin (PUROLITE PCR-833) in the Ca2+ form for the hydrolysis and the Mg2+ form for the isomerization reactions. The mobile phase used was a diluted enzyme solution which was continuously pumped through the chromatographic bed. The substrate was injected at the top of the bed as a pulse. The effect of the parameters pulse size, the amount of substrate solution introduced into the system corresponding to a percentage of the total empty column volume (% TECV), pulse concentration, eluent flowrate and the enzyme activity of the eluent were investigated. For the system sucrose-invertase complete conversions of substrate were achieved for pulse sizes and pulse concentrations of up to 20% TECV and 60% w/v, respectively. Products with purity above 90% were obtained. The enzyme consumption was 45% of the amount theoretically required to produce the same amount of product as in a conventional batch reactor. A value of 27 kg sucrose/m3 resin/h for the throughput of the system was achieved. The systematic investigation of the factors affecting the performance of the batch chromatographic bioreactor-separator was carried out by employing a factorial experimental procedure. The main factors affecting the performance of the system were the flowrate and enzyme activity. For the system inulin-inulinase total conversions were also obtained for pulses sizes of up to 20 % TECV and a pulse concentration of 10 % w/v. Fructose rich fractions with 100 % purity and representing up to 99.4 % of the total fructose generated were obtained with an enzyme consumption of 32 % of the amount theoretically required to produce the same amount of product in a conventional batch reactor. The hydrolysis of lactose by lactase was studied in the glass columns and also in an SCCR-S unit adapted for batch operation, in co-operation with Dr. Shieh, a fellow researcher in the Chemical Engineering and Applied Chemistry Department at Aston University. By operating at up to 30 % w/v lactose feed concentrations complete conversions were obtained and the purities of the products generated were above 90%. An enzyme consumption of 48 % of the amount theoretically required to produce the same amount of product in a conventional batch reactor was achieved. On working with the system glucose-glucose isomerase, which is a reversible reaction, the separation obtained with the stationary phase conditioned in the magnesium form was very poor although the conversion obtained was compatible with those for conventional batch reactors. By working with a mixed pulse of enzyme and substrate, up to 82.5 % of the fructose generated with a purity of 100 % was obtained. The mathematical modelling and computer simulation of the batch chromatographic bioreaction-separation has been performed on a personal computer. A finite difference method was used to solve the partial differential equations and the simulation results showed good agreement with the experimental results.

Biosynthesis and separation of dextran fructose mixtures in a chromatographic reactor

A literature review of work carried out on batch and continuous chromatographic biochemical reactor-separators has been made. The major part of this work has involved the development of a batch chromatographic reactor-separator for the production of dextran and fructose by the enzymatic action of the enzyme dextransucrase on sucrose. In this reactor, simultaneous reaction and separation occurs thus reducing downstream processing and isolation of products as compared to the existing industrial process. The chromatographic reactor consisted of a glass column packed with a stationary phase consisting of cross linked polysytrene resin in the calcium form. The mobile phase consisted of diluted dextransucrase in deionised water. Initial experiments were carried out on a reactor separtor which had an internal diameter of 0.97cm and length of 1.5m. To study the effect of scale up the reactor diameter was doubled to 1.94cm and length increased to 1.75m. The results have shown that the chromatographic reactor uses more enzyme than a conventional batch reactor for a given conversion of sucrose and that an increase in void volume results in higher conversions of sucrose. A comparison of the molecular weight distribution of dextran produced by the chromatographic reactor was made with that from a conventional batch reactor. The results have shown that the chromatographic reactor produces 30% more dextran of molecular weight greater than 150,000 daltons at 20% w/v sucrose concentration than conventional reactors. This is because some of the fructose molecules are prevented as acting as acceptors in the chromatographic reactor due to their removal from the reaction zone. In the conventional reactor this is not possible and therefore a greater proportion of low molecular weight dextran is produced which does not have much clinical use. A theoretical model was developed to describe the behaviour of the reactor separator and this model was simulated using a computer. The simulation predictions showed good agreement with experimental results at high eluent flowrates and low conversions.

Characterisation of a cavity transfer mixer as a chemical reactor

This research project examined the feasibility of using a cavity transfer mixer (CTM) as a continuous reactor to perform reactions between either solid or liquid reagents and polymer melt; reactions which have previously been typically carried out in batch reactor systems. Equipment has been developed to allow uniform and reproducible introduction of reagents into the polymer melt. Reactions have also been performed using batch processing equipment to enable comparison with the performance of the CTM. It was concluded that: a) there are certain reactions which cannot be carried out in a CTM, but which can be performed in a batch system such as a mill or a sigma blade mixer. This was found to be the case for some neutralisation reactions where the product was quasi crosslinked. b) the reactions that can be carried out in a CTM are performed more efficiently in a CTM than on a batch process. For example, when monomers were to be grafted onto polymers, this was more safely and efficiently performed in the CTM than in a mill or a sigma blade mixer. Residence time distributions (RTDs) for three CTMs were studied in order to gain an insight into the effect of CTM geometry on RTD, polymer melt flow pattern and reactor performance. A mathematical model has been developed to predict the influence of process parameters on RTD and the results compared with experimentally observed trends. The comparison was good. A programme of research has been drawn up to form the basis of an industrially based sponsored development project of the CTM reactor. This work programme was successfully marketed to companies with commercial interest in modified rubber and plastics as an integral part of the research programme of this thesis and the sponsored research programme has paralleled the work reported here.

Coupling of Heck and hydrogenation reactions in a continuous compact reactor

A continuous multi-step synthesis of 1,2-diphenylethane was performed sequentially in a structured compact reactor. This process involved a Heck C-C coupling reaction followed by the addition of hydrogen to perform reduction of the intermediate obtained in the first step. Both of the reactions were catalysed by microspherical carbon-supported Pd catalysts. Due to the integration of the micro-heat exchanger, the static mixer and the mesoscale packed-bed reaction channel, the compact reactor was proven to be an intensified tool for promoting the reactions. In comparison with the batch reactor, this flow process in the compact reactor was more efficient as: (i) the reaction time was significantly reduced (ca. 7 min versus several hours), (ii) no additional ligands were used and (iii) the reaction was run at lower operational pressure and temperature. Pd leached in the Heck reaction step was shown to be effectively recovered in the following hydrogenation reaction section and the catalytic activity of the system can be mostly retained by reverse flow operation. © 2009 Elsevier Inc. All rights reserved.

Eliminação/valorização de resíduos de frutas (kiwi) por digestão anaeróbia

Este estudo tem como objetivo a valorização económica de resíduos agroindustriais, nomeadamente resíduos de kiwi, por digestão anaeróbia de forma a otimizar a produção de biogás e a sua qualidade (% CH4). Trata-se de uma pesquisa experimental que consistiu na avaliação da produção de biogás usando diferentes proporções de substrato e inóculo, quatro valores distintos para a razão C:N, inóculo de diferentes digestores e colheita do inóculo em épocas distintas do ano. Os ensaios foram desenvolvidos num reator batch em condições mesofílicas, sendo o processo acompanhado por monitorização dos parâmetros: pH, Alcalinidade, Ácidos Gordos Voláteis (AGV), Sólidos Totais (ST), Sólidos Voláteis (SV), Carência Química de Oxigénio (CQO) e Carbono. Para a totalidade dos ensaios, o valor de pH no reator praticamente não apresentou variação, mantendo-se em torno de 7,0; a alcalinidade do meio, 1500 mg CaCO3/L, revelou-se adequada uma vez que no final do processo de DA a concentração de AGV (400-600 mg/L), nunca excede os valores considerados críticos. Os resultados obtidos apresentam valores interessantes para um número considerável de ensaios. Das 10 experiências realizadas, em duas foram obtidos resultados muito significativos em relação à literatura; o ensaio com 1% de substrato (experiência 2) registou uma produção de biogás de 1628 L/kg SV com uma %CH4 de 57% e o biogás de maior qualidade, 85% de metano, foi obtido no ensaio com 5% de resíduo de kiwi (experiência 10). As experiências em que se avaliou o efeito da razão C:N foram as menos produtivas, possivelmente devido à inibição da atividade da população microbiana pelo KNO3. A qualidade do inóculo revelou-se determinante num conjunto de ensaios, nomeadamente quando a sua colheita foi realizada no inverno, com o digestor a apresentar temperaturas bastante baixas. De acordo com os valores mais favoráveis para a produção de biogás, por tonelada de resíduo de kiwi poderá ser obtido um valor monetário bruto de 102 €, resolvendo-se um problema de eliminação deste resíduo, com valorização energética simultaneamente.

Effect of impeller type and mechanical agitation on the mass transfer and power consumption aspects of ASBR operation treating synthetic wastewater

The effect of flow type and rotor speed was investigated in a round-bottom reactor with 5 L useful volume containing 2.0 L of granular biomass. The reactor treated 2.0 L of synthetic wastewater with a concentration of 800 mgCOD/L in 8-h cycles at 30 degrees C. Five impellers, commonly used in biological processes, have been employed to this end, namely: a turbine and a paddle impeller with six-vertical-flat-blades, a turbine and a paddle impeller with six-45 degrees-inclined-flat-blades and a three-blade-helix impeller. Results showed that altering impeller type and rotor speed did not significantly affect system stability and performance. Average organic matter removal efficiency was about 84% for filtered samples, total volatile acids concentration was below 20 mgHAc/L and bicarbonate alkalinity a little less than 400 mgCaCO(3)/L for most of the investigated conditions. However, analysis of the first-order kinetic model constants showed that alteration in rotor speed resulted in an increase in the values of the kinetic constants (for instance, from 0.57 h(-1) at 50 rpm to 0.84 h(-1) at 75 rpm when the paddle impeller with six-45 degrees-inclined-flat-blades was used) and that axial flow in mechanically stirred reactors is preferable over radial-flow when the vertical-flat-blade impeller is compared to the inclined-flat-blade impeller (for instance at 75 rpm, from 0.52 h(-1) with the six-flat-blade-paddle impeller to 0.84 h(-1) with the six-45 degrees-inclined-flat-blade-paddle impeller), demonstrating that there is a rotor speed and an impeller type that maximize solid-liquid mass transfer in the reaction medium. Furthermore, power consumption studies in this reduced reactor volume showed that no high power transfer is required to improve mass transfer (less than 0.6 kW/10(3) m(3)). (C) 2008 Elsevier Ltd. All rights reserved.

Ozone oxidation of pulp and paper wastewater and its impact on molecular weight distribution of organic matter

The impact of ozone oxidation on removing high molecular weight (HMW) organics in order to improve the biodegradability of alkaline bleach plant effluent was investigated using a semi-batch reactor under different initial pH (12 and 7). After the ozonation process, the ratio of BOD5/COD increased from 0.07 to 0.16 and 0.22 for initial pH 12 and 7, respectively. Also, the effluent color decreased by 48% and 61% at initial pH 12 and pH 7, respectively. These changes were primarily driven by reductions of the HMW fractions of the effluent during ozonation.

BIOLOGICAL NITROGEN REMOVAL OVER NITRITATION/DENITRITATION USING PHENOL AS CARBON SOURCE

A laboratory scale activated sludge sequencing batch reactor was operated in order to obtain total removal of influent ammonia (200; 300 and 500 mg NH(3)-N.L(-1)) with sustained nitrite accumulation at the end of the aerobic stages with phenol (1,000 mg C(6)H(5)OH.L(-1)) as the carbon source for denitrifying microorganisms during the anoxic stages. Ammonia removal above 95% and ratios of (NO(2)(-)-N / (NO(2)(-)-N + NO(3)(-)-N)) ranging from 89 to 99% were obtained by controlling the dissolved oxygen concentration (1.0 mg O(2).L(-1)) and the pH value of 8.3 during the aerobic stages. Phenol proved to be an adequate source of carbon for nitrogen removal via nitrite with continuous feeding throughout part of the anoxic stage. Nitrite concentrations greater than 70.0 mg NO(2)(-)-N.L(-1) inhibited the biological denitritation process.