DETAILED MODELING OF UPFLOW ANAEROBIC FIXED FILM REACTORS

Upflow anaerobic fixed film reactors with high retention time or discontinuously loaded may result in rather large microbial aggregate fragments that are retained in the reactor. A structured model, based on the dynamics of a discrete bivariant distribution of sizes of bacterial aggregates and gas bubbles, has been developed which offers a methodological way to formulate hypothesis, detect some limit situations and achieve a mathematical syn- thesis of empirical knowledge about the considered phenomena. Experimental validation of the model has been carried out with satisfactory results

PIG SLURRY TREATMENT STRATEGY IN A HIGH LIVESTOCK CONCENTRATION AREA: ANAEROBIC DIGESTION AS THE KEY PROCESS

Abstract A pig slurry treatment strategy must include processes with the aim of reducing volatile organic compound emissions, controlling odours, mineralising nutrients, improving its fertilising proprieties, and recovering energy, when it is possible. In this sense, anaerobic digestion fulfils all this requirements. However, in areas with high animal farming density and a structural nutrient surplus, it is necessary to include other processes, which favour nutrient redistribution. The objective of this paper is to study the importance of including anaerobic digestion process in the treatment strategy when the main objective is to recover nitrogen by means of ammonia air stripping at 80ºC, or by vacuum evaporation in order to reduce volume and to favour redistribution. Two types of pig slurry (fresh and anaerobically digested slurry) were used and the initial pH was chosen as the control variable. Apart from producing part of the required thermal energy, previous anaerobic digestion presented several clear advantages: The consumption of volatile fatty acids and volatile organic compounds during anaerobic digestion reduced the volatilisation of organic matter in the stripping and vacuum evaporation processes. This fact resulted in high quality condensate when vacuum evaporation is applied and an ammonia salt with low organic matter contamination when nitrogen is recovered with stripping / absorption process. In this case, high ammonia removal efficiency is possible, over 96%, without modifying the pH

Modelling inhibitory effects of long chain fatty acids in the anaerobic digestion process

Mathematical modelling of anaerobic digestion process has been used to give new insights regarding dynamics of the long chain fatty acids (LCFA) inhibition. Previously published experimental data, including batch tests with clay mineral bentonite additions, were used for parameter identification. New kinetics were considered to describe the bio-physics of the inhibitory process, including: i) adsorption of LCFA over granular biomass and ii) specific LCFA substrate (saturated/unsaturated) and LCFA-degrading populations. Furthermore, iii) a new variable was introduced to describe the state of damage of the acetoclastic methanogens in order to account for the loss of cell-functionality (inhibition) induced by the adsorbed LCFAs. The proposed model modifications are state compatible and easy to be integrated into the International Water Association’s Anaerobic Digestion Model N1 (ADM1) framework. Practical identifiability of model parameters was assessed with a global sensitivity analysis, while calibration and model structure validation were performed on independent data sets. A reliable simulation of the LCFA-inhibition process can be achieved, if the model includes the description of the adsorptive nature of the LCFAs and the LCFA-damage over specific biomass. The importance of microbial population structure (saturated/unsaturated LCFA-degraders) and the high sensitivity of acetoclastic population to LCFA are evidenced, providing a plausible explanation of experimental based hypothesis.This work was funded by the Spanish Ministry of Science and Innovation (projects CTM 2010-18212 and PSE-120000-2009-27)

Influence of adsorption and anaerobic granular sludge characteristics on long chain fatty acids inhibition process

The impact of LCFA adsorption on the methanogenic activity was evaluated in batch assays for two anaerobic granular sludges in the presence and absence of bentonite as synthetic adsorbent. A clear inhibitory effect at an oleate (C18:1) concentration of 0.5 g(C18:1) L(-1) was observed for both sludges. Palmitate (C16:0) was confirmed to be the main intermediate of C18:1 degradation in not adapted sludge and its accumulation was further evidenced by fluorescence staining and microscopy techniques. LCFA inhibition could be decreased by the addition of bentonite, reducing the lag-phase and accelerating the kinetics of LCFA degradation, concluding in the importance of the adsorptive nature of the LCFA inhibitory process. Granule morphology and molecular profiling of predominant microorganisms revealed that biomass adaptation to LCFA could modify the intermediates accumulation profiles and process rates.This work was funded by the Spanish Ministry of Science and Innovation (projects ENE 2007-65850 and CTM 2010-18212), and was partially supported by a grand from the Department of Universities, Research and Media Society of Catalonia Government (BE-DGR 2008 BE1 00261). We would like to thank Lucia Neves, Ana Nicolau, Madalena Vieira, and Ana Julia Cavaleiro, from University of Minho, for their assistance in microscopic observations and analytical methods. We also thank Miriam Guivernau (IRTA) for assistance in the PCR-DGGE profiling and ribotype sequencing. We are also grateful to David Bedoya (MWH) and Francesc Prenafeta (IRTA) for the revision and critical reading of the manuscript

Parameter Identification of thermophilic anaerobic degradation of valerate

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Modeling of thermophilic anaerobic digestion of sorted household solid waste

Two mathematical models (structured and simplified) were developed and calibrated with experimental data for anaerobic biodegradation of source-sorted household solid wastePostprint (published version

Digestión anaerobia de purines de cerdo y codigestión con residuos de la industria alimentaria

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