1,721,201 research outputs found
Polyhydroxyalkanoates production in aerobic sequential processes by mixed microbial cultures
Full text linkThe current emphasis on sustainability, eco-efficiency and green chemistry has led to intensive search for renewable and environmentally friendly resources. Thus, sustainable development is recognized to be essential for the growth of the economy and industrial productivity. Since global petroleum reserves are finite, there is a need for additional new sources of durable materials. Renewable materials from microorganisms can provide a source of sustainable alternative to petroleum derived chemicals including polymers. Polyhydroxyalkanoates (PHA) are one of the relatively newer families of biodegradable polymers that have great potential in the future due to their variability in properties, they are polyesters of hydroxyalkanoic acids that have received extensive attention due to their inherent biocompatibility and biodegradability. The most widely applied strategy for PHA production is to cultivate one wild-type or genetically recombinant bacterial strain with a renewable but refined substrate. At the same time, some of the bacteria naturally occurring in open mixed microbial cultures (activated sludge) treating wastewaters are able to store PHA. In the wastewater treatment plant, carbon storage in the form of PHA can be enhanced under dynamic conditions respect to microbial substrate. In this way, while the wastewater treatment is applied favoring the PHA storing bacteria, a biopolymer can be harvested as a value-added resource from wastewater treatment system. The research activities of the thesis has been divided in 3 fundamental steps:
a) under new dynamic feeding condition (feast-famine) in Sequencing Batch Reactor (SBR), the process performance was investigated in the early days after start up, performing the PHA-accumulation stage in batch, under pulse feeding condition. The new process concept was evaluated in terms of specific storage rate and yield, PHA biomass content and PHA productivity;
b) the more traditional steady-state approach has been applied at fixed operating parameters (OLR, HRT, pH, T) with the exception of the frequency of the alternation of the feast and famine phases. Microbial community analysis, based on denaturing gradient gel electrophoresis (DGGE) was carried out in order to evaluate if the cycle length plays a main role on the microbial speciation within the SBR;
c) based on the results obtained at the point (b), a continuous system (SBR and accumulation) was developed. The PHA-saturated biomass was daily collected and treated with quenching reagent for PHA extraction; then the stored polymer was purified and characterized via lyophilization and chloroform purification;
d) the last part of the experimental program consists in the optimization of the accumulation stage in terms of nutrient content of wastewaters used as substrate, in particular the nitrogen and phosphorous concentration; the COD/N and COD/P ratios covered a wide range of values, changing from starvation to excess condition in the growth medium.
The achieved results open new perspectives and solutions for further investments and technology applications, in particular its integration within public services like the traditional wastewater treatment plants and anaerobic digestion plants
A method to partition the measured atmospheric CO2 based on oxygen measurements
No full textThe atmospheric greenhouse gas CO2 has been increasing since the 18thcentury. To predict future CO2 levels it is necessary to understand the global carbon cycle. Systematic measurements of the atmospheric CO2 together with atmospheric oxygen measurements are a useful tool to deduce and disentangle carbon fluxes due to surface exchange and atmospheric transport processes.
This thesis presents measurements of atmospheric oxygen and associated tracers performed with different analysis techniques.
An analyzer system for continuous O2 and CO2 measurements was developed and installed in a large airfreight container with automated instruments for measurement of atmospheric gases and trace compounds, operated on a monthly basis onboard a Lufthansa International Airways during long-distance flights within a EU founded project named CARIBIC (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container). The analysis principle for oxygen is based on the fuel cell technique whereas the common infrared absorption technique is used for carbon dioxide. Aspects of experiments regarding the optimal performance, reproducibility and data evaluation as well as measurements are discussed. Several problems were experienced during the flights, in particular for the oxygen determination which revealed variations in the order of about 150 per meg, still significantly above the expected range, and are therefore difficult to be interpreted. Flight CO2 measurements exhibited variations linked to the cruise altitude changes, to stratospheric air intrusion and to mixing of air masses carrying different CO2 concentrations.
Within the European projects AEROCARB and CARBOEUROPE IP flask samples of atmospheric air from the high-altitude site Jungfraujoch, Switzerland, the mountain site Puy de Dôme, France, as well as from aircraft based vertical profiles at Griffin Forest, UK, were analyzed by isotope ratio mass spectrometry.
The observations on flask samples collected at the Jungfraujoch station show, since the year 2003, an enhancement of the oxygen trend which amounts to about 45 per meg/yr with a corresponding CO2 increase of around 2.4 ppm/yr. This enhancement is also comparable with that observed at the Puy de Dôme station where oxygen, since mid 2002, has decreased with a rate of about 50 per meg/yr whilst the CO2 increase was of around 1.7 ppm/yr but exhibiting a higher variability compared to the Jungfraujoch CO2. The apparent slopes calculated from correlation plots between detrended CO2 and δO2/N2 records as well as between corresponding trends are significantly larger than the observed terrestrial exchange and fossil fuel emission slopes indicating a strong oceanic influence.
Observations from a four years campaign of regular aircraft flights over the Griffin forest show decreasing oxygen trends which amount to about 49±9 per meg/yr with a corresponding CO2 increase rate varying from 2.9±1 ppm/year to 1.9±0.9 ppm/yr according to the sampling altitude. For the period 2004.2-2006.9 the seasonal co-variances of O2 and CO2 indicate an oceanic influence on the δO2/N2 trends or the predominance of natural gas as fuel, which is rather unrealistic.
The cycle amplitudes decrease with the height for CO2 while for δO2/N2 they show a different behavior decreasing from 800 m to 1100 m and than remaining constant at the higher sampling heights. The land biogenic exchange accounts for more than 70% of the δO2/N2 seasonal cycle at 800 m and for 27% to 46% at the higher altitudes. Vertical δO2/N2 and CO2 profiles do not show only typical distinct summer-winter structures with regular monotonic decrease (or increase) with the sampling height. They rather exhibit contrasting shapes and their O2:CO2 exchange ratios vary from -1.0±0.1 and -4.5±1.2 mol O2/mol CO2.
A one-year time series of atmospheric CO2 measurements from Bern, Switzerland, together with the atmospheric tracers 222Rn, δAr/N2, δO2/N2, δ29N2, δ34O2 and stable isotopes of CO2 is also presented. Using the correlation from short-term fluctuations of CO2 and 222Rn, we estimated a mean CO2 flux density between February 2004 and April 2004 in the region of Bern of 95±39 tCKm−2month−1. Nighttime δ13C and δ18O of CO2 show a considerable variance throughout the year with generally lower values in winter compared to summertime. The O2:CO2 oxidation ratio during the nighttime build-up of CO2 varies between -0.96 and -1.69 mol O2/mol CO2. Furthermore, δAr/N2measurements showed that artifacts like thermal fractionation at the air intake are relevant for high precision measurements of atmospheric O2
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Pilot scale polyhydroxyalkanoates-production from organic fraction of municipal solid waste by Hydrogenophaga species
No full textPlastic pollution represents a worldwide threat to environment, nevertheless during last decades promising alternatives to conventional plastics have been investigated. The use of biodegradable polymers produced by microorganisms, such as polyhydroxyalkanoates (PHA), are of high interest due to their thermo-plastic properties. Recently, the PHA-production from the Organic Fraction of Municipal Solid Waste (OFMSW) was successfully reported at pilot scale. In particular, this work is aimed at evaluating the microbial community dynamics during plant operation (around 200 days) and correlating the occurrence of specific PHA accumulating bacteria to process parameters (e.g. temperature, Volatile Fatty Acids composition, PHA content, Organic Loading Rate). Temporal changes in microbial community composition were described by high-throughput 16S rRNA gene sequencing and the outputs of the analysis were validated by applying
specific FISH oligonucleotide probes. The Nile blue staining, specific for the detection of intracellular lipid inclusions, confirmed that the whole biomass was able to store PHA granules. Members of Hydrogenophaga genus were main PHA accumulating bacteria and found associated to the maximum PHA storage capacity.
This genus strongly increased overtime together with the appearance of functional gene (phaC) coding for PHA synthase
Produzione di Poliidrossialcanoati (PHA) dal trattamento dei fanghi e delle acque di scarico municipali
No full textL’ approccio proposto in questo lavoro, nel programma del progetto europeo ROUTES FP7, è mirato a collocare la produzione di polimeri biodegradabili (poliidrossialcanoati, PHA) nell’ambito del trattamento delle acque di scarico municipali e della minimizzazione dei fanghi prodotti nel processo stesso. Diversamente dallo schema di processo di produzione di PHA ampiamente studiato, in cui i reflui fermentati ricchi in VFA venivano utilizzati sia per la selezione del consorzio microbico misto (attraverso cicli feast-famine), che per la successiva fase di produzione di PHA (accumulo intracellulare), in questo processo innovativo, lo step di selezione viene eseguito utilizzando reflui urbani non fermentati in un processo a fanghi attivi creato ad-hoc. I reflui ricchi in VFA, provenienti dalla fermentazione acidogenica di fanghi primari, vengono invece utilizzati unicamente nello stadio di accumulo, evitandone lo spreco nella fase di selezione. Questo tipo di processo produttivo offre dunque la possibilità di trattamento delle acque reflue municipali e di rimozione del carbonio, simultaneamente alla produzione di un
consorzio microbico misto abile a produrre PHA. Inoltre, il fango primario può essere fortemente ridotto, convertendone i solidi organici in VFA attraverso la fermentazione acidogenica; il fango secondario, con una migliorata capacità di stoccaggio di PHA, può essere completamente convogliato dalla fase di selezione alla fase di accumulo, recuperando parte di esso come PHA, prodotto finale ad alto valore aggiunto.
Il processo complessivo è stato valutato sia in scala di laboratorio che in scala pilota, utilizzando acque di scarico municipali (sintetiche e reali) per lo stadio di selezione; e substrati ad alto contenuto in VFA (fanghi primari fermentati, fanghi primari sottoposti a processi di wet-oxidation, fanghi primari miscelati con la frazione organica dei rifiuti solidi municipali) per la fase di accumulo. I risultati hanno dimostrato la fattibilità dell’approccio innovativo proposto, con rendimenti finali di stoccaggio e contenuto intracellulare di PHA fino a 0.38 COD/COD e 34% (w/w) rispettivamente
Tannery sludge valorization through zeolite-assisted anaerobic process for short-chain fatty acids (SCFAs) production
No full textTannery sludge, a challenging waste, was utilized as a substrate for the production of Short-Chain Fatty Acids (SCFAs) through a series of six thermophilic Continuous Stirred-Tank Reactor runs. The sludge was subjected to a mild thermal pre-treatment and incorporated zeolites (chabazite in run II, and clinoptilolite in run III) in the acidification process. Results highlighted zeolites' impact on chromium concentration and the SCFAs/CODSOL ratio. Ammonia release remained consistent at around 47 % and 51 % for run I and II, respectively, but surpassed 60% in run III, suggesting limited zeolite effectiveness in NH4 absorption. Chromium release in the liquid fraction, due to thermal pretreatment, reached 335 mg/L. While in tests without zeolite, complete removal proved challenging, in zeolite-amended runs, complete removal was achieved, showcasing the materials' heavy metal absorption capacity. SCFA concentrations reached 20260 mgCOD/L, with acidification efficiency varying; runs I and III had ratios around 0.70 COD/COD, while run II showed substantial improvement (0.92) with chabazite. Anaerobic fermentation-digestion mass balance indicated a 41% reduction in landfill sludge mass, reducing its environmental footprint while yielding valuable byproducts like biogas and SCFAs. These findings underscore zeolites' potential in heavy metal absorption and acidification process enhancement, paving the way for applications with tannery sludge
Effect of culture residence time on substrate uptake and storage by a pure culture of Thiothrix (CT3 strain) under continuous or batch feeding
No full textA pure culture of the filamentous bacterium Thiothrix, strain CT3, was aerobically cultured in a chemostat under continuous acetate feeding at three different culture residence times (RT 6, 12 or 22 d) and the same volumetric organic load rate (OLR 0.12 gCOD/L/d).
Cells cultured at decreasing RT in the chemostat had an increasing transient response to acetate spikes in batch tests. The maximum specific acetate removal rate increased from 25 to 185 mgCOD/gCOD/h, corresponding to a 1.8 to 8.1 fold higher respective steady-state rate in the chemostat. The transient response was mainly due to acetate storage in the form of poly(3-hydroxybutyrate) (PHB), whereas no growth response was observed at any RT. Interestingly, even though the storage rate also decreased as the RT increased, the storage yield increased from 0.41 to 0.50 COD/COD. This finding does not support the traditional view that storage plays a more important role as the transient response increases.
The transient response of the steady-state cells was much lower than in cells cultured under periodic feeding (at 6 d RT, from 82 to 247 mgCOD/gCOD/h), with the latter cells showing both storage and growth responses. On the other hand, even though steady-state cells had no growth response and their storage rate was also less, steady-state cells showed a higher storage yield than cells cultured under dynamic feeding. This suggests that in Thiothrix strain CT3, the growth response is triggered by periodic feeding, whereas the storage response is a constitutive mechanism, independent from previous acclimation to transient conditions
Feed frequency in a Sequencing Batch Reactor strongly affects the production of polyhydroxyalkanoates (PHAs) from volatile fatty acids
No full textThe production of polyhydroxyalkanoates (PHAs) by activated sludge selected in a sequencing batch reactor (SBR) has been investigated. Several SBR runs were performed at the same applied organic load rate (OLR), hydraulic retention time (HRT) and feed concentration (8.5gCODL-1 of volatile fatty acids, VFAs) under aerobic conditions. The effect of the feeding time was only evaluated with a cycle length of 8h; for this particular cycle length, an increase in the storage response was observed by increasing the rate at which the substrate was fed into the reactor (at a fixed feeding frequency). Furthermore, a significantly stronger effect was observed by decreasing the cycle length from 8h to 6h and then to 2h, changing the feed frequency or changing the organic load given per cycle (all of the other conditions remained the same): the length of the feast phase decreased from 26 to 20.0 and then to 19.7% of the overall cycle length, respectively, due to an increase in the substrate removal rate. This removal rate was high and similar for the runs with cycle lengths of 2h and 6h in the SBR. This result was due to an increase in the selective pressure and the specific storage properties of the selected biomass. The highest polymer productivity after long-term accumulation batch tests was 1.7gPHAL-1d-1, with PHA content in the biomass of approximately 50% on a COD basis under nitrogen limitation. The DGGE profiles showed that the good storage performance correlated to the development of Lampropedia hyalina, which was only observed in the SBR runs characterized by a shorter cycle length. © 2013 Elsevier B.V
Quick start up of biological sequencing batch reactor (SBR) for Polyhydroxyalkanoates production from renewable resources
No full textIn recent years, a lot of research has been dedicated on the production of biodegradable polymers (e.g. polyhydroxyalkanoates, PHAs) from renewable resources. Presently, industrial processes for PHA production are primarily based on the use of pure cultures of specific microorganisms, batch cultivation conditions and ad hoc formulated substrates (usually based on the unbalance between carbon and nitrogen). In order to reduce the PHA production costs and further increase their
environmental sustainability, alternative processes have been proposed based on the use of fermented organic waste as a substrate and of microbial mixed cultures previously selected under periodic feeding. Typically, the proposed process includes three stages: the first stage, acidogenic fermentation of organic waste or wastewater (e.g. food farming industry), produces a concentrated mixture of organic acids needed to feed second and third stages. The second stage is performed under periodic feeding at a medium organic load in order to select and produce a biomass with a high storage response. After each feeding cycle, a portion of the selected biomass is extracted, to be used in the third stage at a higher load for the synthesis of the polymer. A key point of the overall process is the appropriate selection of biomass in the second stage, through its cultivation under alternating excess and lack of substrate conditions, usually done in a sequencing batch reactor (SBR). The SBR is usually inoculated by an activated sludge from wastewater treatment plants, which ability to produce PHAs is progressively increased during SBR operation through several mechanisms (physiological adaptation, selection and enrichment); hence, the process start up and the time needed for reaching the steady-state are also key factors for obtaining a good process performances.
For these reasons, in the present study, we investigated the process performances in the early days after SBR start up (from two to ten days from the SBR inoculation). By taking the biomass from the SBR during start up and performing the third accumulation stage in batch experiments, it was possible to compare the ability to store PHAs of the biomass after short acclimation with the one of a fully acclimated biomass, obtained after quite longer operation in the same operating conditions of SBR reactor (OLR 8.5gCOD L-1 d-1, pH = 7.5, cycle time 2 h). As expected, during start up the SBR performances was found highly dependent on the used inoculum (four different runs were performed) and highly unstable in terms of yield and rate of PHA formation. The tests carried out after two-three days after start up (just over 30 operating cycles) did not give satisfying results, probably because of too short selective pressure imposed to the biomass. However, already after four-five days operation, the SBR showed good performance and the selected biomass was able to store PHAs at comparable (though slightly lower) rate and yield with those obtained in batch tests carried out with fully acclimated biomass. It was also shown that the time needed for substrate depletion in the SBR cycles was the key parameter to be monitored for ascertain when the biomass had been selected enough and was ready for the next accumulation stage: under chosen operating conditions, a substrate depletion time equal or less than 15% of the cycle length was enough to obtain a good storage performance. These results could open a new perspective for a different arrangement of a semi-continuous process, where the SBR is started up with a new activated sludge inoculums and the selection is operated for the shortest time possible; then the whole amount of selected biomass is used in the accumulation stage
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