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I Angelidaki

Publications and source records attributed to I Angelidaki.

At least 19 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

Operational strategies for thermophilic anaerobic digestion of organic fraction of municipal solid waste in continuously stirred tank reactors.

Three operational strategies to reduce inhibition due to ammonia during thermophilic anaerobic digestion of source-sorted organic fraction of municipal solid waste (SS-OFMSW) rich in proteins were investigated. Feed was prepared by diluting SS-OFMSW (ratio of 1:4) with tap water or reactor process water with or without stripping ammonia. Three continuously stirred tank reactors were operated at 55 degrees C with 11.4 gVS d(-1) loading rate and 15 d retention time. Total ammonia nitrogen (TAN) level in the reactor fed with recirculated water alone was spiked to 3.5 and 5.5 g-N l(-1) through ammonium bicarbonate additions. Dilution of SS-OFMSW with fresh water showed a stable performance with volatile fatty acids of < 1g l(-1) and methane yield of 0.40 m3 kg(-1) volatile solids (VS). Use of recirculated process water after stripping ammonia showed even better performance with a methane yield of 0.43 m3 kg(-1) VS. Recirculation of process water alone on the other hand, resulted in process inhibition at both TAN levels of 3.5 and 5.5 g-N l(-1). However, after a short period, the process recovered and adapted to the tested TAN levels. Thus, use of recirculated process water after stripping ammonia would not only evade potential inhibition due to ammonia but could avoid the use of fresh water for dilution of high solids protein-rich SS-OFMSW.

Ammonia↗
PubMed2006

Lessons learnt from 15 years of ICA in anaerobic digesters.

Anaerobic digestion plants are highly efficient wastewater treatment processes with inherent energy production. Despite these advantages, many industries are still reluctant to use them because of their instability confronted with changes in operating conditions. There is therefore great potential for application of instrumentation, control and automation (ICA) in the field of anaerobic digestion. This paper will discuss the requirements (in terms of on-line sensors needed, modelling efforts and mathematical complexity) but also the advantages and drawbacks of different control strategies that have been applied to AD high rate processes over the last 15 years.

Automation↗
PubMed2006

Enhanced biogas recovery by applying post-digestion in large-scale centralized biogas plants.

The main objective of this study was to investigate the degradation efficiency of centralized biogas plants and provide guidance for the design of more efficient digester and post-digestion systems. These centralized biogas plants in Denmark digest manure together with organic waste from the food industry to generate biogas, which is used for electricity and thermal energy. A total of 20 such plants are currently active in Denmark, most of which were included in the investigation. From the plants, samples were obtained from various steps of the process. Samples were analysed and the residual biogas potential determined by batch post-digestion at various temperature levels. Results were correlated with plant characteristics and production statistics in order to judge the efficiency of various digestion concepts. A simplified model based on a two-step biogas production process was developed and experimental data were used to determine kinetic constants. Experimental results and analysis combined with model simulations showed that the residual biogas potential in the main digestion step effluent is originating mainly from undegraded particulate matter in the biomass. For thermophilic plants 93% of the residual biogas potential was originating from particulate matter and 88% for the mesophilic biogas plants. This indicates that the residual biogas potential is mainly due to insufficient retention time in the main digestion step for hydrolysis of particulate material and that the hydrolysis step is the methane yield limiting factor, while conversion of soluble material such as VFA is the rate limiting factor critical for achieving a stable process.

Denmark↗
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↗
PubMed2005

Strategies for changing temperature from mesophilic to thermophilic conditions in anaerobic CSTR reactors treating sewage sludge.

Thermophilic anaerobic digestion presents an advantageous way for stabilization of sludge from wastewater treatment plants. Two different strategies for changing operational process temperature from mesophilic (37 degrees C) to thermophilic (55 degrees C) were tested using two continuous flow stirred tank reactors operated at constant organic loading rate of 1.38 g VS/l reactor/day and hydraulic retention time of 20 days. In reactor A, the temperature was increased step-wise: 37 degrees C-->42 degrees C-->47 degrees C-->51 degrees C-->55 degrees C. While in reactor B, the temperature was changed in one-step, from 37 degrees C to the desired temperature of 55 degrees C, The results showed that the overall adaptation of the process for the step-wise temperature increment took 70 days in total and a new change was applied when the process was stabilized as indicated by stable methane production and low volatile fatty acids concentrations. Although the one-step temperature increase caused a severe disturbance in all the process parameters, the system reached a new stable operation after only 30 days indicating that this strategy is the best in changing from mesophilic to thermophilic operation in anaerobic digestion plants.

Bacteria, Anaerobic↗
PubMed2005

Anaerobic degradation of solid material: importance of initiation centers for methanogenesis, mixing intensity, and 2D distributed model.

Batch anaerobic codigestion of municipal household solid waste (MHSW) and digested manure in mesophilic conditions was carried out. The different waste-to-biomass ratios and intensity of mixing were studied theoretically and experimentally. The experiments showed that when organic loading was high, intensive mixing resulted in acidification and failure of the process, while low mixing intensity was crucial for successful digestion. However, when loading was low, mixing intensity had no significant effect on the process. We hypothesized that mixing was preventing establishment of methanogenic zones in the reactor space. The methanogenic zones are important to withstand inhibition due to development of acids formed during acidogenesis. The 2D distributed models of symmetrical cylinder reactor are presented based on the hypothesis of the necessity of a minimum size of methanogenic zones that can propagate and establish a good methanogenic environment. The model showed that at high organic loading rate spatial separation of the initial methanogenic centers from active acidogenic areas is the key factor for efficient conversion of solids to methane. The initial level of methanogenic biomass in the initiation centers is a critical factor for the survival of these centers. At low mixing, most of the initiation methanogenic centers survive and expand over the reactor volume. However, at vigorous mixing the initial methanogenic centers are reduced in size, averaged over the reactor volume, and finally dissipate. Using fluorescence in situ hybridization, large irregular cocci of microorganisms were observed in the case with minimal mixing, while in the case with high stirring mainly dead cells were found.

Acids↗
PubMed2005

Effect of operating conditions and reactor configuration on efficiency of full-scale biogas plants.

A study on 18 full-scale centralized biogas plants was carried out in order to find significant operational factors influencing productivity and stability of the plants. It was found that the most plants were operating relatively stable with volatile fatty acids (VFA) concentration below 1.5 g/l. VFA concentration increase was observed in occasions with dramatic overloading or other disturbances such as operational temperature changes. Ammonia was found to be a significant factor for stability. A correlation between increased residual biogas production and high ammonia was found. When ammonia was higher than approx. 4g-N/l the degradation efficiency of the plant decreased and as a consequence, the residual methane potential was high. Decrease of the residual methane potential with increasing hydraulic retention time was found. Digestion temperature was very important for effective post-digestion. Post-digestion for recovering the residual methane potential at temperatures below 15 degrees C was very inefficient.

Ammonia↗
PubMed2005

Online headspace chromatographic method for measuring VFA in biogas reactor.

A headspace chromatographic method has been applied to measure volatile fatty acids in anaerobic digesters using gas phase extraction at pH less than 2 and temperature higher than 65 degrees C. The concentration of volatile fatty acids in liquid and gas phase can be correlated in the form of Henry's coefficient. Analysis of different factors in the batch indicated that pH, temperature, and salt addition had a strong impact on apparent solubility, while liquid/gas volume ratio and organic acid concentration had little impact. Larger liquid volume had a positive impact on extraction efficiency, while increased gas headspace had a negative impact, indicating that the system was total mass-limited. The best conditions were at pH < 2.0, and temperatures above 75 degrees C. The advantage of an automated gas-extraction system for organic acid analysis, compared to an automated liquid system is that it contains no filter element, which is 4 susceptible to fouling in manure samples or samples with high solid content. An automated system which included a valerate pulse to the parent reactor was implemented, and operated for a short period.

Animals↗
PubMed2004

Anaerobic bioprocessing of sewage sludge, focusing on degradation of linear alkylbenzene sulfonates (LAS).

Anaerobic degradation of sludge amended with linear alkylbenzene sulfonates (LAS) was tested in a one stage continuous stirred tank reactor (CSTR) and a two stage reactor system consisting of a CSTR as first step and upflow anaerobic sludge bed (UASB) reactor as the second step. Anaerobic removal of LAS was only observed at the second step but not at the first step. Removal of LAS in the UASB reactors was approx. 80% where half was due to absorption and the other half was apparently due to biological removal as shown from the LAS mass balance. At the end of the experiment the reactors were spiked with 14C-LAS which resulted in 5.6% 14CO2 in the produced gas. Total mass balance of the radioactivity was however not achieved. In batch experiments it was found that LAS at concentrations higher than 50 mg/l is inhibitory for most microbial groups of the anaerobic process. Therefore, low initial LAS concentration is a prerequisite for successful LAS degradation. The results from the present study suggest that anaerobic degradation of LAS is possible in UASB reactors when the concentration of LAS is low enough to avoid inhibition of microorganisms active in the anaerobic process.

Absorption↗
PubMed2004

Improved nitrogen removal in upflow anaerobic sludge blanket (UASB) reactors by incorporation of Anammox bacteria into the granular sludge.

Upflow anaerobic sludge blanket reactors may offer a number of advantages over conventional mixed-tank, SBR, and biofilm reactors, including high space-loading, low footprint, and resistance to shocks and toxins. In this study, we assessed the use of upflow anaerobic sludge blanket (UASB) reactor technology as applied to anaerobic ammonia removal, or Anammox. Four 200 ml UASB reactors were inoculated with 50% (by volume) anaerobic granular sludge and 50% flocular sludge from different sources (all with the potential for containing Anammox organisms). Tools used to assess the reactors included basic analyses, fluorescent in-situ hybridisation, and mathematical modelling, with statistical non-linear parameter estimation. Two of the reactors showed statistically identical Anammox activity (i.e., identical kinetic parameters), with good ammonia and nitrite removal (0.14 kgNHx m(-3) reactor day(-1), with 99% ammonia removal). The third reactor also demonstrated significant Anammox activity, but with poor identifiability of parameters. The fourth reactor had no statistical Anammox activity. Modelling indicated that poor identifiability and performance in the third and fourth reactors were related to an excess of reduced carbon, probably originating in the inoculum. Accumulation of Anammox organisms was confirmed both by a volume loading much lower than the growth rate, and response to a probe specific for organisms previously reported to mediate Anammox processes. Overall, the UASB reactors were effective as Anammox systems, and identifiability of the systems was good, and repeatable (even compared to a previous study in a rotating biological contactor). This indicates that operation, design, and analysis of Anammox UASB reactors specifically, and Anammox systems in general, are reliable and portable, and that UASB systems are an appropriate technology for this process.

Ammonia↗
PubMed2004

Removal of polycyclic aromatic hydrocarbons (PAHs) from sewage sludge by anaerobic degradation.

Due to the hydrophobic nature of the polyaromatic hydrocarbons (PAHs) they are mostly bound to the sludge and escape aerobic treatment in a wastewater treatment plant. They therefore proceed directly to the anaerobic post treatment, terminate in the sludge, and can be released to the environment if land spreading is used. PAH degradation in anaerobic methanogenic systems has only recently been shown to occur. In this study we have assessed several factors of anaerobic PAH degradation by evaluating thermodynamic feasibility of degradation, assessing degradation at different temperatures, and investigating the enriched cultures using fluorescent in-situ hybridization (FISH). Thermodynamic calculations indicated that PAH degradation was possible under methanogenic conditions, in the presence of hydrogen utilizing methanogens. Removal of naphthalene and 1-methyl naphthalene depended both on temperature and the initial inoculum. Inocula sourced from contaminated land sites were the most effective. The enrichments were all a mixture of Bacteria, and Archaea, and the Archaea were generally identified as Methanobacteriales, using an order-specific probe. The bacteria were not specifically identified. The results indicate a syntrophic culture, with the bacteria oxidizing the naphthalene, and the Archaea converting the hydrogen produced by oxidation, to methane.

Bacteria, Anaerobic↗
PubMed2003

Kinetics of thermophilic, anaerobic oxidation of straight and branched chain butyrate and valerate.

The degradation kinetics of normal and branched chain butyrate and valerate are important in protein-fed anaerobic systems, as a number of amino acids degrade to these organic acids. Including activated and primary wastewater sludge digesters, the majority of full-scale systems digest feeds with a significant or major fraction of COD as protein. This study assesses the validity of using a common kinetic parameter set and biological catalyst to represent butyrate, n-valerate, and i-valerate degradation in dynamic models. The i-valerate degradation stoichiometry in a continuous, mixed population system is also addressed, extending previous pure-culture and batch studies. A previously published mathematical model was modified to allow competitive uptake of i-valerate, and used to model a thermophilic manure digester operated over 180 days. The digester was periodically pulsed with straight and branched chain butyrate and valerate. Parameters were separately optimized to describe butyrate, i-valerate, and n-valerate degradation, as well as a lumped set optimized for all three substrates, and nonlinear, correlated parameter spaces estimated using an F distribution in the objective function (J). Each parameter set occupied mutually exclusive parameter spaces, indicating that all were statistically different from each other. However, qualitatively, the influence on model outputs was similar, and the lumped set would be reasonable for mixed acid digestion. The main characteristic not represented by Monod kinetics was a delay in i-valerate uptake, and was compensated for by a decreased maximum uptake rate (k(m)). Therefore, the kinetics need modification if fed predominantly i-valerate. Butyrate (i- and n-) and n-valerate could be modeled using stoichiometry consistent with beta-oxidation degradation pathways. However, i-valerate produced acetate only, supporting the stoichiometry of a reaction determined by other researchers in pure culture. Therefore, lumping i-valerate stoichiometry with that of n-valerate will not allow good system representation, especially when the feed consists of proteins high in leucine (which produces i-valerate), and the modified model structure and stoichiometry as proposed here should be used. This requires no additional kinetic parameters and one additional dynamic concentration state variable (i-valerate) in addition to the variables in the base model.

Acetates↗
PubMed2002

Anaerobic biodegradation of spent sulphite liquor in a UASB reactor.

Anaerobic biodegradation of fermented spent sulphite liquor, SSL, which is produced during the manufacture of sulphite pulp, was investigated. SSL contains a high concentration of lignin products in addition to hemicellulose and has a very high COD load (173 g COD l(-1)). Batch experiments with diluted SSL and pretreated SSL indicated a potential of 12-22 l methane per litre SSL, which corresponds to 0.13-0.22 l methane (g VS)(-1) and COD removal of up to 37%. COD removal in a mesophilic upflow anaerobic sludge blanket, UASB. reactor ranged from 10% to 31% at an organic loading rate, OLR, of 10-51 g (1 d)(-1) and hydraulic retention time from 3.7 to 1.5 days. The biogas productivity was 3 1 (l(reactor d)(-1), with a yield of 0.05 l gas (g VS)(-1). These results suggest that anaerobic digestion in UASB reactors may provide a new alternative for the treatment of SSL to other treatment strategies such as incineration. Although the total COD reduction achieved is limited, bioenergy is produced and readily biodegradable matter is removed causing less load on post-treatment installations.

Anaerobiosis↗
PubMed2002

A novel in-situ sampling and VFA sensor technique for anaerobic systems.

A key information for understanding and controlling the anaerobic biogas process is the concentration of Volatile Fatty Acids (VFA). However, access to this information has so far been limited to off-line measurements by manual time and labour consuming methods. We have developed a new technique that has made it possible to monitor VFA on-line in one of the most difficult media: animal slurry or manure. A novel in-situ filtration technique has made it possible to perform microfiltration inside the reactor system. This filter enables sampling from closed reactor systems without large scale pumping and filtering. Using this filtration technique together with commercially available membrane filters we have constructed a VFA sensor system that can perform automatic analysis on animal slurry at a frequency as high as every 15 minutes. The VFA sensor has been tested for a period of more than 60 days with more than 1000 samples on both a full-scale biogas plant and lab-scale reactors. The measuring range covers specific measurements of acetate, propionate, iso-/n-butyrate and iso-/n-valerate from 0.1 to 50 mM (6-3,000 mg).

Automation↗
PubMed2002

The IWA Anaerobic Digestion Model No 1 (ADM1).

The IWA Anaerobic Digestion Modelling Task Group was established in 1997 at the 8th World Congress on Anaerobic Digestion (Sendai, Japan) with the goal of developing a generalised anaerobic digestion model. The structured model includes multiple steps describing biochemical as well as physicochemical processes. The biochemical steps include disintegration from homogeneous particulates to carbohydrates, proteins and lipids; extracellular hydrolysis of these particulate substrates to sugars, amino acids, and long chain fatty acids (LCFA), respectively; acidogenesis from sugars and amino acids to volatile fatty acids (VFAs) and hydrogen; acetogenesis of LCFA and VFAs to acetate; and separate methanogenesis steps from acetate and hydrogen/CO2. The physico-chemical equations describe ion association and dissociation, and gas-liquid transfer. Implemented as a differential and algebraic equation (DAE) set, there are 26 dynamic state concentration variables, and 8 implicit algebraic variables per reactor vessel or element. Implemented as differential equations (DE) only, there are 32 dynamic concentration state variables.

Bioreactors↗
PubMed2002

Anaerobic treatment of sludge: focusing on reduction of LAS concentration in sludge.

Anaerobic degradation of linear alkylbenzene sulfonates (LAS) was tested in continuous stirred tank reactors (CSTR). LAS12 was used as a model compound and was spiked on sewage sludge. The experiments clearly showed that transformation of LAS12 occurred under anaerobic conditions. The degree oftransformation varied between 14% and 25%. HPLC analysis showed that disappearance of LAS12 was followed by the formation of a metabolite. The experiments indicated that there is a clear correlation between degradation of organic matter contained in sludge and transformation of LAS 12. When the reduction degree of the organic matter increased from 22% to 28%, the transformation degree of LAS12 also increased, from 14% to 20%. Decreasing the total solids concentration of the influent sludge or increasing the spiked concentration of LAS12 did not alter the degree of LAS12 transformation significantly. A clear correlation between transformed and bioavailable LAS12 was found, indicating that it is merely the bioavailable fraction of LAS12 that is transformed by anaerobic digestion. The results from the present study are promising and indicate that a great potential for biological degradation of LAS is possible even at anaerobic conditions.

Alkanesulfonic Acids↗