Investigations on the changes in anaerobic biodegradability and biotoxicity of an industrial microbial biomass induced by a thermochemical pretreatment

2000 ◽  
Vol 41 (3) ◽  
pp. 137-144 ◽  
Author(s):  
J.P. Delgèns ◽  
V. Penaud ◽  
M. Torrijos ◽  
R. Moletta
Keyword(s):  
Anaerobic Digestion ◽  
Microbial Biomass ◽  
Operating Conditions ◽  
Thermochemical Pretreatment ◽  
Anaerobic Microorganisms ◽  
Rate Limiting Step ◽  
The Poor ◽  
Anaerobic Biodegradability ◽  
Physico Chemical ◽  
Rate Limiting

In the anaerobic digestion of solid wastes, hydrolysis is the rate limiting step and physico-chemical pretreatment is often required to promote solubilization of organic matter. As an illustration, anaerobic digestion was limited by the substrate solubilization step during continuous cultures performed with an industrial microbial biomass. In optimal operating conditions determined for the hydrolysis-acidogenesis step (T=35°C; pH=8.5; OLR=5.4 g COD/l.d) 50.6% COD solubilization was achieved. A thermochemical pretreatment based on sodium hydroxide addition, was used in order to enhance COD solubilization. Optimal conditions for COD solubilization were pH=12, T=140°C for 30 minutes. In these conditions, 70% COD solubilization was achieved. However, anaerobic biodegradability of the pretreated substrate was not improved and remained near 40%. The poor anaerobic biodegradability performances were attributed to the soluble molecules generated during the thermochemical pretreatment that were refractory and/or inhibitory to anaerobic microorganisms. Fractionation of the soluble pretreated microbial biomass by two methods (treatment with adsorbent resins and precipitation by pH adjustment) demonstrated that high molecular weight compounds (>100 kDa) are involved in the poor biodegradability and in the biotoxicity observed. Partial decolorization through resin use and acid precipitation remove these compounds. The consequence of their removal was an increase of the production of biogas.

Characteristics of carbohydrate degradation and the rate-limiting step in anaerobic digestion

1985 ◽  
Vol 27 (10) ◽  
pp. 1482-1489 ◽  
Author(s):  
Tatsuya Noike ◽  
Ginro Endo ◽  
Juu-En Chang ◽  
Jun-Ichi Yaguchi ◽  
Jun-Ichiro Matsumoto
Keyword(s):  
Anaerobic Digestion ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Carbohydrate Degradation ◽  
Rate Limiting

Potential of anaerobic digestion of complex waste(water)

2001 ◽  
Vol 44 (8) ◽  
pp. 115-122 ◽  
Author(s):  
G. Zeeman ◽  
W. Sanders
Keyword(s):  
Waste Water ◽  
Anaerobic Digestion ◽  
Order Relation ◽  
Organic Substrates ◽  
Reactor Technology ◽  
Rate Limiting Step ◽  
Treatment Technologies ◽  
Transport Complex ◽  
Rate Limiting ◽  
Hydrolysis Of

Although they differ greatly in origin complex waste(water)s mainly consist of proteins, lipids, carbohydrates and sometimes lignin in addition. Hydrolysis is the first and generally rate-limiting step in the process of anaerobic digestion of particulate organic substrates. Hydrolysis of particulate polymers can be described by Surface Based Kinetics, but for use in practice the empirical first order relation is advised. Unlike the hydrolysis of protein and carbohydrate, lipid hydrolysis is hardly occurring in the absence of methanogenesis. The latter is probably a physical rather than a biological process and affects the choice for either a one- or a two-step (phase) anaerobic reactor. In the chain of collection and transport, complex wastes often become complex wastewaters simply because of dilution. Dilution not only changes the reactor technology to be applied but also complicates the post-treatment and possibilities for resource recovery. Combining concentrated with diluted waste streams will almost always end up in much more complicated treatment technologies.

Anaerobic digestion of solid animal waste in an accumulation system at mesophilic and thermophilic conditions, start up

2003 ◽  
Vol 48 (4) ◽  
pp. 217-220 ◽  
Author(s):  
H.M. El-mashad ◽  
G. Zeeman ◽  
W.K.P. van Loon ◽  
G.P.A. Bot ◽  
G. Lettinga
Keyword(s):  
Anaerobic Digestion ◽  
Minor Effect ◽  
Mixing Conditions ◽  
Rate Limiting Step ◽  
Start Up ◽  
Accumulation System ◽  
Filling Time ◽  
Thermophilic Conditions ◽  
A Minor ◽  
Rate Limiting

The anaerobic digestion of solid animal wastes has been studied in an accumulation system (AC) at a filling time of 60 days followed by about 50 days batch digestion at 40 and 50°C. Poor mixing conditions during anaerobic digestion of solid wastes promote stratification of the substrate and intermediate products along the reactor height. The effect of layers stratification has also been followed in the AC system. The results showed a pronounced stratification of both CODdis and VFA concentrations along the AC system height. The temperature had a minor effect on the methane yield. The results also showed that methanogenesis was rate limiting in the AC system while the hydrolysis was the rate-limiting step during batch digestion.

scholarly journals Direct Benzyl Alcohol and Benzaldehyde Synthesis from Toluene over Keggin-Type Polyoxometalates Catalysts: Kinetic and Mechanistic Studies

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Allam Djaouida ◽  
Mansouri Sadia ◽  
Hocine Smaïn
Keyword(s):  
Benzyl Alcohol ◽  
Partial Oxidation ◽  
Product Distribution ◽  
Operating Conditions ◽  
Catalyst Composition ◽  
Rate Limiting Step ◽  
Ft Ir ◽  
Keggin Polyoxometalate ◽  
Catalyst Systems ◽  
Rate Limiting

The catalytic activity of various Keggin polyoxometalate catalysts has been investigated in the gas-phase partial oxidation of toluene to produce benzyl alcohol and benzaldehyde. The catalyst systems HPMo12O40, HPMo11VO40, FePMo12O40, and PMo11FeO39 were prepared and characterized by FT-IR, UV-visible, SEM, XRD, TGA, and cyclic voltammetry. The acid/base properties were evaluated using the decomposition of isopropanol. Catalytic studies were carried under atmospheric pressure and over the temperature range 200°C–350°C, using carbon dioxide as a mild oxidant. Toluene conversion and product distribution depend mainly on the catalyst composition and operating conditions. In addition to benzaldehyde, benzyl alcohol is obtained with a high selectivity on the PMo11FeO39 catalyst. The kinetic data show that the reoxidation of the reduced catalyst is the rate-limiting step for the partial oxidation reaction of toluene.

Enhancement of the conventional anaerobic digestion of sludge: comparison of four different strategies

2011 ◽  
Vol 64 (2) ◽  
pp. 375-383 ◽  
Author(s):  
S. I. Pérez-Elvira ◽  
M. Fdz-Polanco ◽  
F. Fdz-Polanco
Keyword(s):  
Anaerobic Digestion ◽  
Thermal Hydrolysis ◽  
General Increase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Key Factor ◽  
Thermophilic Digestion ◽  
Pre Treatment ◽  
Treatment Alternatives ◽  
Rate Limiting

Anaerobic digestion (AD) is the preferred option to stabilize sludge. However, the rate limiting step of solids hydrolysis makes it worth modifing the conventional mesophilic AD in order to increase the performance of the digester. The main strategies are to introduce a hydrolysis pre-treatment, or to modify the digestion temperature. Among the different pre-treatment alternatives, the thermal hydrolysis (TH) at 170 °C for 30 min, and the ultrasounds pre-treatment (US) at 30 kJ/kg TS were selected for the research, while for the non-conventional anaerobic digestion, the thermophilic (TAD) and the two-stage temperature phased AD (TPAD) were considered. Four pilot plants were operated, with the same configuration and size of anaerobic digester (200 L, continuously fed). The biogas results show a general increase compared to the conventional digestion, being the highest production per unit of digester for the process combining the thermal pre-treatment and AD (1.4 Lbiogas/Ldigester·day compared to the value of 0.26 obtained in conventional digesters). The dewaterability of the digestate became enhanced for processes TH + AD and TPAD when compared with the conventional digestate, while it became worse for processes US + AD and TAD. In all the research lines, the viscosity in the digester was smaller compared to the conventional (which is a key factor for process performance and economics), and both thermal pre-treatment and thermophilic digestion (TAD and TPAD) assure a pathogen free digestate.

scholarly journals Probing Differences in Mass-Transfer Coefficients in Beaker and Stirrer Digestion Systems and the USP Dissolution Apparatus 2 Using Benzoic Acid Tablets

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2168
Author(s):  
Timothy A. G. Langrish ◽  
Chao Zhong ◽  
Lizhe Sun
Keyword(s):  
Mass Transfer ◽  
Benzoic Acid ◽  
Reynolds Numbers ◽  
Operating Conditions ◽  
External Mass Transfer ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Rate Limiting Step ◽  
Dissolution Apparatus ◽  
Rate Limiting

Measurements of external mass-transfer coefficients for dissolution have been made with benzoic acid tablets with a diameter of 13 mm and approximately 3 mm thick, using two different dissolution systems. One system has been a beaker with a platform for the tablet and either 80 mL or 120 mL of water, with three different types of stirrers, and the other has been a USP dissolution apparatus 2 (paddle) with either 200 mL or 900 mL water. Various stirring speeds have also been used in the different pieces of equipment. The same mass-transfer coefficient may potentially be obtained from the same tablet by adjusting the operating conditions in the two different devices. The ranges of the external mass-transfer coefficients measured in both devices overlapped significantly, with the range being 0.193–4.48 × 10−5 m s−1 in the beaker and stirrer system and 0.222–3.45 × 10−5 m s−1 in the USP dissolution apparatus 2. Dimensional analysis of the results, using Sherwood and Reynolds numbers, shows that the Ranz–Marshall correlation provides a lower bound for estimates of the Sherwood numbers measured experimentally. Calculations of time constants for mass transfer suggest that mass transfer may be a rate-limiting step for dissolution and food digestion under some circumstances. The range of mass-transfer coefficients measured here is representative of other measurements from the literature, and the use of the Ranz–Marshall correlation supports the suggestion that this range of values should be generally expected in most situations.

A Kinetic Study on the Methanogenesis Process in Anaerobic Digestion

1989 ◽  
Vol 21 (4-5) ◽  
pp. 175-186 ◽  
Author(s):  
C. Y. Lin ◽  
T. Noike ◽  
H. Furumai ◽  
J. Matsumoto
Keyword(s):  
Anaerobic Digestion ◽  
Substrate Concentration ◽  
Volatile Fatty Acid ◽  
Kinetic Mechanism ◽  
High Concentration ◽  
Two Phase ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
The Relationship ◽  
Rate Limiting

Results obtained from experiments on two-phase anaerobic digestion using a high concentration of a volatile fatty acid (VFA) mixture were used to elucidate the kinetic mechanism of the methanogenesis process. The mixture consisted of the major intermediate products of anaerobic digestion, i.e., acetic acid (HAc), propionic acid (HPr) and butyric acid (HBu). The relationship between the rate of substrate utilization and substrate concentration in the digesters was in the form of a Michaelis-Menten equation. The rate-limiting step of the methanogenesis process, i.e., the conversion of HAc to methane, was speeded up in the digesters and this was proved kinetically. A method for determining kinetic constants for substrate-specific microorganisms was suggested. A simulation model for predicting the effluent substrate concentration was demonstrated. The effluent substrate concentration of an anaerobic digester fed by a multisubstrate was found to be simulatively predictable from its influent component substrates.

Influence of the size reduction of organic waste on their anaerobic digestion

2000 ◽  
Vol 41 (3) ◽  
pp. 155-162 ◽  
Author(s):  
L.M. Palmowski ◽  
J.A. Müller
Keyword(s):  
Particle Size ◽  
Anaerobic Digestion ◽  
Organic Waste ◽  
Gas Production ◽  
Size Reduction ◽  
Particle Size Reduction ◽  
Rate Limiting Step ◽  
Organic Solid ◽  
Rate Limiting ◽  
Positive Effect

The rate-limiting step in anaerobic digestion of organic solid waste is generally their hydrolysis. A size reduction of the particles and the resulting enlargement of the available specific surface can support the biological process in two ways. Firstly, in case of substrates with a high content of fibres and a low degradability, their comminution yields to an improved digester gas production. This leads to a decreased amount of residues to be disposed of and to an increased quantity of useful digester gas. The second effect of the particle size reduction observed with all the substrates but particularly with those of low degradability is a reduction of the technical digestion time. Furthermore, the particle size of organic waste has an influence on the dewaterability after codigestion with sewage sludge. The presence of organic waste residues improves the dewaterability measured as specific resistance to filtration but this positive effect is attenuated if the particle size of the solids is reduced.

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