Anaerobic acidogenesis of a complex wastewater: I. The influence of operational parameters on reactor performance

Abstract

The influence of operational, parameters, such as hydraulic retention time, organic loading rate, influent substrate concentration, pH, and temperature, on the performance of the first phase of anaerobic digestion has been investigated. A complex substrate based on beef extract was used, and six series of experimental runs were conducted, each one showing the effect of one operational variable. The predominant fermentation products were always acetic and propionic acid, independent of the values of the operational parameters. For initial COD concentrations and hydraulic retention times above the critical values identified as 3 g/L and 6 h, respectively, the degree of acidification achieved was between 30 and 60%. The degree of acidification was found to increase with the hydraulic retention time and decrease with the influent substrate concentration and organic loading rate, while the opposite held true for the rate of product formation. Furthermore, it has been demonstrated that acidification is primarily determined by the hydraulic retention time and the rate of product formation by the influent substrate concentration. The concentration of the acetic acid produced was found to depend on the operational parameters. However, the concentration of propionic acid produced depended only on the substrate availability with a consistent proportion of 8% initial COD converted to it. The optimum pH and temperature were 7 and 40 degrees C, respectively. The percentage of acetic acid as a proportion of the total volatile fatty acids produced was found to increase with increasing pH and temperature, while the percentage of propionic acid seemed to decrease accordingly. Finally the effect of the temperature on the rate of acidification followed an Arrhenius type equation with an activation energy equal to 4739 cal/mol.

Performance of an Innovative Two-Stage Process Converting Food Waste to Hydrogen and Methane

“…The distribution of metabolites formed during H 2 fermentation is often a crucial signal in assessing the efficiency of H 2 -producing cultures. [22][23][24] At initial D of 4.5 days Ϫ1 (days 1-2), VFA concentration was higher than ethanol. Butyrate (45.2-49.7%) and acetate (12.9 -15.4%) were the two major components of VFAs in the first two days, though lactate composition was high on day 1.…”

Comparative performance of mesophilic and thermophilic acidogenic upflow reactors

“…The overall performance of an acidogenic reactor can be evaluated using the term 'degree of acidification', which is quantified by comparing the COD equivalent of the acidogenic products, i.e. VFA/alcohols plus hydrogen and methane in the biogas, to the influent COD [7]. Table 2 lists that the degree of acidification decreased with an increase of OLR, from 59.1% at 4 gCOD/l d to 28.2% at 24 gCOD/l d for the mesophilic reactor, and from 60.8% at 4 gCOD/l d to 27.1% at 24 gCOD/l d for the thermophilic reactor.…”

“…Specific VFA/alcohol production rate, defined as the rate of VFA/alcohol production per day per unit amount of VSS in the reactor (g/gVSS d), can also be used to evaluate the VFA/alcohol generating capability of an acidogenic reactor [2,7]. The specific VFA/alcohol production rate, as shown in Table 2 24 gCOD/l d for the thermophilic reactor.…”

“…Therefore, it has been proposed that the two phases are physically separated by using two reactors in series: one for VFA production and another for methane production [3]. A two-phase anaerobic process has been successfully applied to the treatment of municipal sludge [3] and various wastewaters, including trout processing wastewater [4], cafeteria wastewater [5], olive oil mill effluent [6], and vegetable-processing wastewater [7]. However, nearly all of these studies have been focused on mesophilic acidogenesis, while information for the thermophilic acidogeneses is very limited [8].…”

Anaerobic Hydrogen Production from Sucrose Using an Acid‐Enriched Sewage Sludge Microflora

“…It has been shown that HRT and substrate concentration caused a shift in the metabolic pathways obvious from the shift in the formation of fermentation products [19,22±24]. Under low HRT values, HBu is the predominant metabolite indicating the presence of clostridia [28]. The low B/Ac ratios experienced at the HRTs of 10 and 12 h hinted at the possible presence of HPr and HBu-degrading acidogens.…”