Biomedical subjects

X Flotats

Publications and source records attributed to X Flotats.

6 recordsLinked to original sources

PubMed2007

Anaerobic digestion of solid material: multidimensional modeling of continuous-flow reactor with non-uniform influent concentration distributions.

A new multidimensional (3 and 2D) anaerobic digestion model for cylindrical reactor with non-uniform influent concentration distributions was developed to study the way in which mixing intensity affects the efficiency of continuous-flow anaerobic digestion. Batch experiments reported and simulated earlier by Vavilin and Angelidaki (2005) were used to modernize a kinetic scheme and to obtain the corresponding kinetic coefficients. In the new models, hydrolytic microorganisms were included using Contois kinetics for the hydrolysis/acidogenesis degradation of municipal solid waste (MSW). Monod kinetics was applied for description of methanogenesis. Both hydrolytic and methanogenic microorganisms were assumed to be inhibited by high volatile fatty acids (VFA) concentration. According to the new distributed models, the mixing level reduction expressed by increasing dimensionless Peclet number may improve the continuous flow reactor performance at the relatively low influent methanogenic biomass concentration. In the continuously stirred tank reactor (CSTR) there are two steady states with and without methane production at slightly different values of initial methanogenic biomass concentration. In the system, the threshold methanogenic biomass concentration existed because of inhibition by high VFA concentration. High methanogenic biomass concentration is required for efficient anaerobic digestion of MSW in order to avoid possible inhibition due to high VFA build-up. Thus, CSTR configuration might have unstable dynamics at high organic loading as shown in earlier experiments carried out by Stroot et al. (2001). A gradual increase of organic loading during the start up of a completely mixed digester causing an accumulation of methanogenic biomass is a solution to prevent a probable digester failure. According to the distributed models a plug-flow reactor with non-uniform influent concentration distributions where methanogenic and hydrolytic microorganisms are separated has significant methane production and solids removal at the relatively low influent methanogenic biomass concentration.

Anaerobiosis↗

PubMed2006

Identifiability study of the proteins degradation model, based on ADM1, using simultaneous batch experiments.

The objective of the present study is to analyse kinetic and stoichiometric parameter values of gelatine anaerobic degradation at thermophilic range, based on an experiment designed to elucidate if volatile fatty acids (VFA) are inhibitors of the hydrolysis process. Results showed that VFA are not inhibiting the hydrolysis process. The ADM1 model adequately expressed the consecutive steps of hydrolysis and acidogenesis, with estimated kinetic values corresponding to a fast acidogenesis and slower hydrolysis. The hydrolysis was found to be the rate limiting step of anaerobic degradation. Estimation of yield coefficients based on the relative initial slopes of VFA profiles obtained in a simple batch experiment produced satisfactory results. From the identification study, it was concluded that it is possible to determine univocally the related kinetic parameter values for protein degradation if the evolution of amino acids is measured in simultaneous batch experiments, with different initial protein and amino acids concentrations.

Algorithms↗

PubMed2004

Environmental engineering education in Spain.

There is a growing demand for engineers and technologists who show multidisciplinary expertise to deal with environmental issues. As a result of this demand, most countries are adapting their old university programs on environmental engineering education. In Spain an official environmental engineering degree does not yet exist, but the Council of Universities is working to present a proposal, based on Bologna agreement concepts. The paper summarizes not only the future perspectives of environmental engineering education in Spain, but also the evolution of the approach during the last decades, which includes the role of the private initiative, the environmental sciences degree, and the intensification in different traditional engineering degrees. Finally, the paper briefly details and compares the syllabus developed in the only four Spanish universities where environmental engineering is offered as a non-official post-graduate course lasting two years.

Curriculum↗

PubMed2003

A method for livestock waste management planning in NE Spain.

A method of decision-making on livestock wastes management in areas with nutrient surplus due to high livestock density is applied in Catalonia (NE Spain). Nutrient balance is made considering soil nitrogen application as the limiting factor. Special attention is paid to the centralized treatment option. The method presented consists of: 1. minimizing livestock waste generation (at farm scale) as a step previous to any other, both in amount and limiting components, 2. applying the nitrogen balance method at regional and municipal scale and providing enough storage capacity in order to apply wastes in an agronomically correct way, 3. spatially refining the results of the nitrogen balance by a proposed method that allows precisely pinpointing the hotspots of livestock waste generation, where centralized treatment might be an interesting option, and 4. deciding on the waste treatment objectives, provided that treatments be necessary. Knowledge about the wastes, meeting the interests and merging the efforts of the various actors, as well as an adequate budget are necessary ingredients for the success of any waste management plan.

Animals↗

PubMed2003

Concentration of pig slurry by evaporation: anaerobic digestion as the key process.

Nutrient redistribution between areas with a structural pig slurry surplus and those with a shortage, is limited by the high cost of transportation and spreading, due to the high water content in slurry (more than 90%) and its relative low nutrient concentration. Water can be removed from slurry by evaporation, through the application of waste heat from a power plant or from other processes. Apart from obtaining a concentrate with an obviously higher nutrient concentration than the original slurry, another objective is to obtain clean water as condensate. The objective of this work was to study the batch vacuum evaporation of pig slurry liquid fraction, to evaluate the economic feasibility and to evaluate condensate quality as a function of both pH (4, 5 and 6) and pig slurry type (fresh slurry and anaerobically digested slurry). Results showed that condensate characteristics (ammonia nitrogen, VFA, COD) were strongly dependent on these variables. Previous anaerobic digestion presented clear advantages: it provided a fraction of the required energy and it removed organic matter, preventing its volatilisation in the evaporation process and providing higher quality condensates. These advantages make the combined treatment strategy economically more feasible than the evaporation process alone.

Animals↗

PubMed2001

Study of thermal hydrolysis as a pretreatment to mesophilic anaerobic digestion of pig slurry.

Feasibility of anaerobic digestion of pig slurry is dependent, among other factors, on the biogas production rate, which is low compared with other organic wastes, and on the profitable uses of surplus thermal energy produced, a limiting factor in warm geographical areas. The objectives of this work are determining whether low temperature thermal pretreatment (< 90 degrees C) improves pig slurry anaerobic digestion, and determining whether organic matter degradation during the thermal pretreatment is due to thermal phenomena (80 degrees C) or to enzymatic ones (60 degrees C). The thermal degradation tests showed that hydrolysis occurring during the thermal pretreatment is due to thermal phenomena. The increase in soluble substances were significantly larger at 80 degrees C than at 60 degrees C (both during 3 h). Two types of slurry were used in the batch anaerobic digestion tests. The effect of thermal pretreatment differed with the type of slurry: it was positive with almost non-degraded slurries containing low NH4(+)-N concentration, and negative (inhibition of the anaerobic digestion process) when using degraded slurries with high NH4(+)-N content.

Agriculture↗