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J Carrera

Publications and source records attributed to J Carrera.

At least 19 recordsLinked to original sources
PubMed2006

Improving the start-up of an EBPR system using OUR to control the aerobic phase length: a simulation study.

The enhanced biological phosphorus removal (EBPR) process is based on enriching the sludge with polyphosphate accumulating organisms (PAO) which are scarce in conventional non-EBPR wastewater treatment plant sludge. Hence, the start-up of EBPR systems (i.e. enriching the sludge with PAO) can be very slow and complex. A simulation study of a possible improvement of the start-up of an EBPR system in a sequencing batch reactor is presented in this work. The improvement is based on reducing the length of the aerobic phase so that it coincides with the depletion of orthophosphate from the medium. This improvement, though verified by simulation to be very successful, requires a good on-line orthophosphate sensor. To avoid this technical limitation, a link between oxygen uptake rate (OUR) measurements and orthophosphate presence is proposed. This link allows the control of the aerobic phase length with OUR as a measured variable and, consequently, a considerable improvement with respect to the conventional fixed aerobic phase length operation. An improvement of 95% in the ratio of PAO to heterotrophs and an increase of 30% in the final amount of PAO in sludge is achieved with this control strategy. The kinetic mod for simulations was a modification of the Activated Sludge Model 2d.

Aerobiosis↗
PubMed2006

Observation and mathematical description of the acceleration phenomenon in batch respirograms associated with ammonium oxidation.

Two-step nitrification models are generally calibrated using short-term respirometric batch experiments. Important discrepancies appear between model predictions and experimental observations just after the pulse addition since a fast transient in the OUR profile is experimentally observed. Acceleration of the OUR appears ongoing between the substrate addition and attainment of the maximum OUR value. Among the several phenomena that could contribute to this observation, the most probable cause is the limitation of reducing equivalents required for maximal ammonia monooxygenase activity at the time of substrate addition. Ignoring acceleration would result in large parameter estimation errors from respirometric batch experiments. This work proposes a simple methodology to successfully describe (not to explain) the acceleration phenomenon estimating only two parameters. This methodology consists of introducing a Gaussian-like expression in the model.

Ammonia↗
PubMed2005

Limitations of ASM1 and ASM3: a comparison based on batch oxygen uptake rate profiles from different full-scale wastewater treatment plants.

The two most popular models for the description of the biological COD removal are ASM1 and ASM3. However, some numerical inconsistencies arise when using these models to interpret the data obtained in short-term respirometric batch experiments. In this study, both models are fitted to four different respirometric batch profiles obtained with biomass from different WWTP. The parameter estimation results and the practical (local) identifiability are analysed, and the limitations of both models are discussed. The growth yield obtained by fitting ASM1 to the short-term respirometric batch profiles is higher than the default one, as well as the storage yield obtained by fitting ASM3 is lower than the default one. Based on these values, possible improvements to the modelling of the biological COD removal, such as the inclusion of simultaneous growth and storage on external substrate, are proposed.

Biodegradation, Environmental↗
PubMed2004

Improving the biological nitrogen removal process in pharmaceutical wastewater treatment plants: a case study.

The Biological Nitrogen Removal (BNR) process of some pharmaceutical wastewater treatment plants has important operational problems. This study shows that, in order to solve these problems, the design of industrial BNR processes should start by analysing three key parameters: the characteristics of the wastewater load, the determination of the maximum TKN removal rate and the detection of toxic or inhibitory compounds in the wastewater. A case study of this analysis in pharmaceutical wastewater is presented here. In this case, the conventional TKN analytical method does not make an accurate characterisation of the wastewater load because it measures a concentration of 100 mg TKN l(-1) whereas the real concentration, determined with a modified TKN analytical method, is 150-500 mg TKN l(-1). Also, the TKN removal of the treatment system is insufficient in some periods because it falls below legal requirements. This problem might be a consequence of the wrong characterisation of wastewater during the design process. The maximum TKN removal at 27 degrees C (24 mg N g VSS(-1) d(-1) or 197 mg N l(-1) d(-1)) was evaluated in a pilot-scale plant. This value is six times greater than the average NLR applied in the full-scale plant. Finally, some of the components of the wastewater, such as p-phenylenediamine, might have inhibitory or toxic effects on the biological process. P-phenylenediamine causes a large decrease in the nitrification rate. This effect was determined by respirometry. This methodology shows that the effect is mainly inhibitory with a contact time of 30 min and if the contact time is longer, 14 hours, a toxic effect is observed.

Bioreactors↗
PubMed2003

Biological nitrogen removal of high-strength ammonium industrial wastewater with two-sludge system.

The biological nitrogen removal (BNR) process is the most common method for removing low quantities of ammonium from wastewater, but this is not the usual treatment for high-strength ammonium wastewater. The capacity to biologically remove the nitrogen content of a real industrial wastewater with a concentration of 5000 g N-NH(4)(+) L(-1) is demonstrated in this work. The experimental system used is based on a two-sludge system, with a nitrifying activated sludge and a denitrifying activated sludge. This system treated real industrial wastewater for 450 days, and during this period, it showed the capacity for oxidizing all the ammonium at average nitrification rates between 0.11 and 0.18 g N-NH(4)(+)g VSS(-1)d(-1). Two key process parameters were evaluated: the maximum nitrification rate (MNR) and the maximum denitrification rate (MDR). MNR was determined in continuous operation at three different temperatures: 15 degrees C, 20 degrees C and 25 degrees C, obtaining values of 0.10, 0.21 and 0.37 g N-NH(4)(+) g VSS(-1)d(-1), respectively. Complete denitrification was achieved using two different industrial carbon sources, one containing mainly ethanol and the other one methanol. The MDR reached with ethanol (0.64 g N-NO(x)(-) g VSS(-1)d(-1)) was about 6 times higher than the MDR reached with methanol (0.11g N-NO(x)(-)g VSS(-1)d(-1)).

Bioreactors↗
PubMed2003

An off-line respirometric procedure to determine inhibition and toxicity of biodegradable compounds in biomass from an industrial WWTP.

Determining whether a certain compound is toxic (or inhibitor) or not to a biomass of a WWTP is crucial in order to avoid WWTP malfunction. Respirometric techniques have been commonly used to assess the toxicity of a certain compound by evaluating the oxygen uptake rate (OUR) profile obtained when a pulse of substrate is added to endogenous biomass and comparing it with the OUR profile obtained when the pulse is a mixture of substrate and the possible toxic or inhibitor (PTI). However, when using this method with biodegradable compounds some difficulties arise because the PTI consumption implies oxygen consumption as well. In this study, a modified procedure for toxicity assessment using respirometry is developed which overcomes the difficulties caused by the toxic biodegradability. This procedure is based on the comparison of different respirograms obtained with pulses of control substrate before and after adding the PTI and with a pulse of PTI and control substrate together. Moreover, some examples are shown with p-phenylenediamine and phenol as an example of toxic and inhibitor for nitrifying biomass.

Biodegradation, Environmental↗
PubMed2001

On the behavior of approaches to simulate reactive transport.

Two families of approaches exist to simulate reactive transport in groundwater: The Direct Substitution Approach (DSA), based on Newton-Raphson and the Picard or Sequential Iteration Approach (SIA). We applied basic versions of both methods to several test cases and compared both computational demands and quality of the solution for varying grid size. Results showed that the behavior of the two approaches is sensitive to both grid size and chemistry. As a general rule, the DSA is more robust than the SIA, in the sense that its convergence is less sensitive to time step size (any approach will converge given a sufficiently small time step). Moreover, the DSA leads to a better simulation of sharp fronts, which can only be reproduced with fine grids after many iterations when the SIA is used. As a consequence, the DSA runs faster than SIA in chemically difficult cases (i.e., highly non-linear and/or very retarded), because the SIA may require very small time steps to converge. On the other hand, the size of the system of equations is much larger for the DSA than for the SIA, so that its CPU time and memory requirements tend to be less favorable with increasing grid size. As a result, the SIA may become faster than the DSA for very large, chemically simple problems. The use of an iterative linear solver for the DSA makes its CPU time less sensitive to grid size.

Calcium Carbonate↗
PubMed2001

Effect of different operational parameters in the enhanced biological phosphorus removal process. Experimental design and results.

The uncontrolled dumping of phosphorus into a water environment creates serious problems of eutrophication, affecting water quality and causing grave problems in the aquatic ecosystem. European legislation demands drastic reduction of phosphorus dissolved in wastewater. Enhanced Biological Phosphorus Removal (EBPR) is the current tendency in wastewater treatment. This biological process depends on a multiplicity of variables, but its three main factors are: influent COD/P ratio, anaerobic fraction and sludge retention time (SRT). The aim of this work is to statistically determine the effect of these three parameters in EBPR through a response surface methodology. The objective function that has been chosen is phosphorus removed per unit biomass formed. This function provides ample information on BPR, since the quantity of phosphorus removed depends on the accumulative capacity of the microorganisms present. Two levels were chosen for the SRT (5 and 10 days), two for the anaerobic fraction (0.1 and 0.2), and six for levels of the influent COD/P ratio (between 16 and 87). The experiments were undertaken at pilot scale (100 litres) with an A2/O configuration, with simultaneous nitrogen and phosphorous removaL The wastewater used is a synthetic mixture of complex sources of carbon and nitrogenwithout volatile fatty acids. The empirical model obtained indicates that the factor most influencing the EBPR process is the influent COD/P ratio, whilst the anaerobic fraction is that which has least influence. Additionally, there is an optimum in the influent COD/P ratio that is to be found between 41 and 48.

Biodegradation, Environmental↗
PubMed2000

Teaching through clinical cases: a good method to study bioethics. Experience at the Lleida Faculty of Medicine.

This paper summarises our experience in the teaching of bioethics during the final course in medicine at the Universitat de Lleida. Teaching has been based on the discussion of real clinical cases, the ethical implications of which have been extracted and presented by the professor, and analysed under his supervision. We present here the objectives, the programme and the course and evaluation methodology used, as well as the results of an inquiry carried out among the 55 students attending the course. The acceptance level was 92% and the attendance 95%. We believe the methodology used to be successful, since it makes possible the introduction of theoretical aspects of bioethics in order to solve actual cases, as well as encourage wide discussion. At the same time it emphasises that the students discover the values involved.

Attitude of Health Personnel↗
PubMed1999

Recurrent molecular abnormalities in type VII collagen in Southern Italian patients with recessive dystrophic epidermolysis bullosa.

In this study we searched for mutations in the type VII collagen gene (COL7A1) in 10 families from Southern Italy with severe generalised recessive dystrophic epidermolysis bullosa using PCR amplification of genomic DNA, heteroduplex analysis and direct nucleotide sequencing. Our principal aim was to identify any recurrent mutations in COL7A1 that might facilitate future mutation detection strategies in this population. Three recurrent COL7A1 mutations were delineated in six of the 10 families: a frameshift mutation in exon 4, 497insA, was detected in three affected individuals from three families, a deletion mutation at the acceptor splice site of intron 114/exon 115, 8441-14del21, was found in five patients in three of the families, and an intron 49 acceptor splice site mutation, 4783-1 G-to-A, was identified in three subjects in two families (GenBank accession no, L02870). Haplotype analyses showed evidence for propagation of common ancestral mutant COL7A1 alleles for each of these recurrent mutations. These results contribute significantly to understanding the nature of COL7A1 pathology in patients from Southern Italy and in designing future approaches to mutation detection.

Alleles↗
PubMed1999

Massive fetomaternal hemorrhage: how long should children with good evolution be controlled? A case report.

We report on a term infant with a severe fetomaternal hemorrhage that caused a serious anemia that was surmounted after several transfusions. After the initial complications, such as persistent pulmonary circulation, severe anemia and thrombocytopenia, the outcome was good. We discuss the importance of a long-term follow-up of affected children, as well as their mothers. No clear parameters for a real prognosis are available. A follow-up is needed in order to detect possible complications in neurological development.

Adult↗
PubMed1997

Microsurgical reconstruction of the Achilles tendon with a fascia lata flap.

A case of total reconstruction of the Achilles tendon is reported. A compound free musculocutaneous unit of fascia lata was used to supply the absent tendon and soft tissues, achieving excellent cosmetic and functional results. This technique is suggested as an alternative for combating infection, providing soft-tissue cover, and bridging the gap in the tendon.

Achilles Tendon↗
PubMed1995

[Evaluation of serum adenosine deaminase as a prognostic marker in the treatment of human immunodeficiency virus infection with zidovudine].

BACKGROUND: Adenosine deaminase (ADA) is a key enzyme in cellular immunity. It catalyses the reaction 2'deoxyadenosine to 2'deoxiinosine, a critical step in the production of essential metabolites for the synthesis of nucleic acids. Its main physiological activity occurs in T cells of lymphoid tissue. The advanced HIV infection is characterized by a severe and progressive cellular immunity compromise. Partial positive results have been obtained with Zidovudine (AZT), a drug which Serum adenosine deaminase has been proposed as a useful marker for the assessment of the therapy response in these patients. METHODS: Serum ADA activity was determined in patients infected with HIV in stage II, before and after four months of therapy with AZT, regarding variations in its activity with improvements in biological parameters--CD4 and CD8 lymphocytes. RESULTS: Patients infected with HIV showed a significant increase in ADA activity compared with patients in the control group: 21.6 +/- 5.4 vs. 10.4 +/- 2.3 U/l (p < 0.001). Therapy with AZT decreased ADA activity: 21.6 +/- 5.4 vs. 15.2 +/- 4.3 U/l (p < 0.001) and correlated with an increase in CD4 counts: 187 +/- 105 vs. 353 +/- 145/mm3 (p < 0.001) and in CD4/CD8 ratio: 0.188 +/- 0.10 vs. 0.382 +/- 0.18 (p < 0.001). CONCLUSIONS: The detection of a decrease in ADA correlates significantly with a favourable outcome in immunological parameters in individuals infected with HIV in stage II of disease treated with AZT.

Adenosine Deaminase↗
PubMed1983

[Acute brucellosis: our experience over a 3-year period].

Authors, based on objectives data of large incidence of acute Brucellosis in their job area in the last years, get in every patient coming in their Medicine Internal Department suffering from it through three years. They analyse mainly the epidemiological, clinic-biological and therapeutics aspects of this acute pathology. The epidemiological conclusions established on the objective analysis of the series issue make known great interest. The increase of this illness does not happen to be because of infection in animal farms, but for the existence of food channels that are not under sanitary control.

Adolescent↗