“…This buffering protects against possible acidification of the reactor, giving a pH of the same order as the optimal for methanogenic microorganisms (11). The pH and buffering capacity protects against acidification of the reactor, which could be caused by a sudden overloading reactor, an abrupt change in operating temperature, or the presence of toxic compounds or inhibitors in the substrate (13,14).…”
Section: Resultsmentioning
confidence: 99%
“…This buffering protects against possible acidification of the reactor, giving a pH of the same order as the optimal for methanogenic microorganisms (). The pH and buffering capacity protects against acidification of the reactor, which could be caused by a sudden overloading reactor, an abrupt change in operating temperature, or the presence of toxic compounds or inhibitors in the substrate ( , ). 1 Variation in pH, alkalinity, volatile acidity, and volatile acidity/alkalinity ratio in the effluents of the reactor as a function of the load added, S T0 (grams of COD). 2 Variation in the volume of methane accumulated ( G ) as a function of time for loads of ( A ) 1.5, 2.0, 2.5, and 3.0 g of COD and ( B ) 3.5, 4.0, 4.5, and 5.0 g of COD. 3 Variation in the specific rate constant, K G , with the initial COD ( S T0 ). 4 Comparison between experimental maximum methane production ( G T ) values and theoretical values ( G m ) predicted by eq 1. 5 Variation in experimental maximum methane volume produced ( G T ) with the COD consumed to obtain the methane yield coefficient of the process. 6 Amount of substrate removed against substrate added for all of the experiments carried out to obtain the percentage biodegradability of the waste.…”
Section: Resultsmentioning
confidence: 99%
“…The pH and buffering capacity protects against acidification of the reactor, which could be caused by a sudden overloading reactor, an abrupt change in operating temperature, or the presence of toxic compounds or inhibitors in the substrate (13,14).…”
Section: Control Parameters and Reactor Stabilitymentioning
A study of the anaerobic digestion of wastewater from the pressing of orange peel generated in orange juice production was carried out in a laboratory-scale completely stirred tank reactor at mesophilic temperature (37 degrees C). Prior to anaerobic treatment the raw wastewater was subjected to physicochemical treatment using aluminum sulfate as a flocculant and to pH reduction using a solution of sulfuric acid. The reactor was batch fed at COD loads of 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 g of COD. The process was very stable for all of the loads studied, with mean pH and alkalinity values of 7.5 and 3220 mg of CaCO3/L, respectively. The anaerobic digestion of this substrate was found to follow a first-order kinetic model, from which the specific rate constants for methane production, K(G), were determined. The K(G) values decreased considerably from 0.0672 to 0.0078 L/(g h) when the COD load increased from 1.5 to 5.0 g of COD, indicating an inhibition phenomenon in the system studied. The proposed model predicted the behavior of the reactor very accurately, showing deviations of <5% between the experimental and theoretical values of methane production. The methane yield coefficient was found to be 295 mL of CH4 STP/g of COD removed, whereas the mean biodegradability of the substrate (TOC) was 88.2%. A first-order kinetic model for substrate (TOC) consumption allowed determination of the specific rate constants for substrate uptake, K(C), which also decreased with increasing loading, confirming the above-mentioned inhibition process. Finally, the evolution of the individual volatile fatty acid concentrations (acetic, C2; propionic, C3; butyric, C4; isobutyric, iC4; valeric, C5; isovaleric, iC5; and caproic, C6) with digestion time for all loads used was also studied. The main acids generated were acetic and propionic for all loads studied, facilitating the conversion into methane.
“…This buffering protects against possible acidification of the reactor, giving a pH of the same order as the optimal for methanogenic microorganisms (11). The pH and buffering capacity protects against acidification of the reactor, which could be caused by a sudden overloading reactor, an abrupt change in operating temperature, or the presence of toxic compounds or inhibitors in the substrate (13,14).…”
Section: Resultsmentioning
confidence: 99%
“…This buffering protects against possible acidification of the reactor, giving a pH of the same order as the optimal for methanogenic microorganisms (). The pH and buffering capacity protects against acidification of the reactor, which could be caused by a sudden overloading reactor, an abrupt change in operating temperature, or the presence of toxic compounds or inhibitors in the substrate ( , ). 1 Variation in pH, alkalinity, volatile acidity, and volatile acidity/alkalinity ratio in the effluents of the reactor as a function of the load added, S T0 (grams of COD). 2 Variation in the volume of methane accumulated ( G ) as a function of time for loads of ( A ) 1.5, 2.0, 2.5, and 3.0 g of COD and ( B ) 3.5, 4.0, 4.5, and 5.0 g of COD. 3 Variation in the specific rate constant, K G , with the initial COD ( S T0 ). 4 Comparison between experimental maximum methane production ( G T ) values and theoretical values ( G m ) predicted by eq 1. 5 Variation in experimental maximum methane volume produced ( G T ) with the COD consumed to obtain the methane yield coefficient of the process. 6 Amount of substrate removed against substrate added for all of the experiments carried out to obtain the percentage biodegradability of the waste.…”
Section: Resultsmentioning
confidence: 99%
“…The pH and buffering capacity protects against acidification of the reactor, which could be caused by a sudden overloading reactor, an abrupt change in operating temperature, or the presence of toxic compounds or inhibitors in the substrate (13,14).…”
Section: Control Parameters and Reactor Stabilitymentioning
A study of the anaerobic digestion of wastewater from the pressing of orange peel generated in orange juice production was carried out in a laboratory-scale completely stirred tank reactor at mesophilic temperature (37 degrees C). Prior to anaerobic treatment the raw wastewater was subjected to physicochemical treatment using aluminum sulfate as a flocculant and to pH reduction using a solution of sulfuric acid. The reactor was batch fed at COD loads of 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 g of COD. The process was very stable for all of the loads studied, with mean pH and alkalinity values of 7.5 and 3220 mg of CaCO3/L, respectively. The anaerobic digestion of this substrate was found to follow a first-order kinetic model, from which the specific rate constants for methane production, K(G), were determined. The K(G) values decreased considerably from 0.0672 to 0.0078 L/(g h) when the COD load increased from 1.5 to 5.0 g of COD, indicating an inhibition phenomenon in the system studied. The proposed model predicted the behavior of the reactor very accurately, showing deviations of <5% between the experimental and theoretical values of methane production. The methane yield coefficient was found to be 295 mL of CH4 STP/g of COD removed, whereas the mean biodegradability of the substrate (TOC) was 88.2%. A first-order kinetic model for substrate (TOC) consumption allowed determination of the specific rate constants for substrate uptake, K(C), which also decreased with increasing loading, confirming the above-mentioned inhibition process. Finally, the evolution of the individual volatile fatty acid concentrations (acetic, C2; propionic, C3; butyric, C4; isobutyric, iC4; valeric, C5; isovaleric, iC5; and caproic, C6) with digestion time for all loads used was also studied. The main acids generated were acetic and propionic for all loads studied, facilitating the conversion into methane.
“…On the other hand, with the diminishing supply of natural gas and other fossil fuels, bacterial conversion of liquid (or solid) wastes to methane and stabilized byproducts through anaerobic digestion would be beneficial (Goodwin and Hickey, 1988;Hickey and Goodwin, 1989;Borja et al, 1995a). These by-products could subsequently serve as food or fertilizer and generally be disposed of with fewer problems (easier dewatering, smaller amounts).…”
New obligately anaerobic bacteria are being discovered at an accelerating rate and it is becoming very evident that the diversity of anoxic biotransformations has been greatly underestimated. Furthermore, among contemporary anaerobes there are many that thrive in extreme environments including, for example, an impressive array of both archaebacterial and eubacterial hyperthermophiles. Free energy for growth and reproduction may be conserved not only via fermentations but also by anoxygenic photophosphorylation and other modes of creating transmembrane proton potential. Thus forms of anaerobic respiration in which various inorganic oxidants (or indeed carbon dioxide) serve as terminal electron acceptors have greatly extended the natural habitats in which such organisms may predominate. Anaerobic bacteria are, however, often found in nature as members of close microbial communities (consortia) that, although sustained by syntrophic and other relations between component species, are liable to alter their composition and character in response to environmental changes, e.g., availability of terminal oxidants. It follows that the biotechnological exploitation of obligately anaerobic bacteria must be informed by knowledge both of their biochemical capacities and of their normal environmental roles. It is against this background that illustrative examples of the activities of anaerobic bacteria are considered under three heads: 1. Biodegradation/Bioremediation, with special reference to the anaerobic breakdown of aromatic and/or halogenated organic substances; 2. Biosynthesis/Bioproduction, encompassing normal and modified fermentations; and 3. Biotransformations, accomplished by whole or semipermeabilized organisms or by enzymes derived therefrom, with particular interest attaching to the production of chiral compounds by a number of procedures, including electromicrobial reduction.
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