Acidogenic fermentation of lactose

Cheese whey is the main component of waste streams from cheese manufacturing plants. Whey is a high biochemical oxygen demand (BOD) effluent that must be reduced before the streams are sent to the sewer. It is proposed in this article that the production of methane by anaerobic fermentation would be the best use of this stream, especially for small plants. Single-stage fermentation of lactose, the main component of whey, results in a very low pH and a stalled process. Two-phase fermentation will eliminate this problem. The acidogenic stage of fermentation has been studied at pH of between 4 and 6.5. The nature of the main products of the reaction have been found to be pH dependent. Below a pH of 4.5 a gas (CO(2) and H(2)) is produced along with ethanol, acetate, and butyrate. Above a pH of 4.5 no gas was produced, and the liquid products included less ethanol and butyrate and more acetate. A separate study on the conditions for gas formation showed that if the pH dropped for a short time below 4.5 gases were formed at all subsequent pH. This would indicate a change in population distribution due to the period at a low pH. By assuming that the desired products from the acidogenic stage were butyrate, acetate, and no gases, the optimum pH range was found to be between 6.0 and 6.5.     

Acidogenic fermentation of corn stover

Corn stover was fermented by anaerobic acidogenic bacteria to produce volatile (C₂–C₆) organic acids. Mild pretreatment with dilute alkali solutions produced a two-fold increase in fermentability. A mixture of lime and sodium carbonate was found to be a better pretreatment agent than sodium hydroxide. Methane generation was inhibited by low temperature (? 25°C) and high solids [≥ 2.5% (w/v)] fermentation. Volatile acid yields of 0.5–0.55 g acetic acid equiv/g dry ash-free (DAF) stover could be obtained in batch fermentations. Several extractants and extraction solvents for organic acids were found to be nontoxic to acidogenic fermentation. The data show that acidogenic fermentation can produce useful volatile fatty acids in high yields from a complex lignocellulosic feedstock. These fermentations are nonsterile, need no stirring, and are easy to run. Moreover, cellulose, pentosans, and other carbohydrates are directly utilized by acidogenic bacteria. Hence, acidogenic fermentation could be useful in converting biomass to chemical feedstocks and fuel.     

On-line fluorescence-monitoring of the methanogenic fermentation

On-line in situ fluorescence measurements of the methanogenic fermentation were conducted with reactors receiving either glucose or a mixture of volatile fatty acids as the substrate. The reactors were perturbed from steady-state conditions in order to assess the response of fluorescencemonitoring probes. Two fluorescence-monitoring probes were evaluated over a period of 8 months; they performed in a consistent manner, and their response was not significantly affected by the changes in pH and redox potential encountered during routine reactor operation. A commercially available probe, designed to measure NAD(P)H, demonstrated particular promise for detecting imbalance caused by the entry of air, inhibitor addition and was capable of distinguishing between different substrates. This fluorescence-monitoring probe detected imbalance more rapidly than other on-line measurements such as pH, Eh, or gas production, or off-line measurements such as volatile fatty acid concentration or gas composition. An experimental fluorescence-monitoring probe, designed to measure coenzyme F(420), also showed some promise in this regard. The response of the fluorescence-monitoring probes also revealed details of the metabolic routes in the reactors and the probes represent a useful research tool. For example, a failure to observe the characteristic response of the NAD(P)H-monitoring probe to formate addition during the metabolism of acetate, propionate, or glucose strongly suggests that any formate liberated during their catabolism is degraded via a different route to exogenously added formate.     

Kinetics of the methanogenic fermentation of acetate

Inhibition of the fermentation of acetate to methane and carbon dioxide by acetate was analyzed with an acetate-acclimatized sludge and with Methanosarcina barkeri Fusaro under mesophilic conditions. A second-order substrate inhibition model, q(ch(4) ) = q(m)S/[K(s) + S + (S/K(i))], where S was the concentration of undissociated acetic acid, not ionized acetic acid, could be applicable in both cases. The analysis resulted in substrate saturation constants, K(s), of 4.0 muM for the acclimatized sludge and 104 muM for M. barkeri. The threshold concentrations of undissociated acetic acid when no further acetate utilization was observed were 0.078 muM (pH 7.50) for the acclimatized sludge and 4.43 muM (pH 7.45) for M. barkeri. These kinetic results suggested that the concentration of undissociated acetic acid became a key factor governing the actual threshold acetate concentration for acetate utilization and that the acclimatized sludge in which Methanothrix spp. appeared dominant could utilize acetate better and survive at a lower concentration of undissociated acetic acid than could M. barkeri.     

Acidogenic fermentation of source separated mixtures of vegetables and fruits wasted from supermarkets

A pilot scale mesophilic anaerobic acidogenic fermenter was fed with mixtures of vegetables and fruits shredded by a hammer mill and mixed in a stock tank, in order to produce a liquid phase suitable as RBCOD source in denitrification and EBPR processes. Different operative conditions were studied working with a HRT in the range 1–:12 days. The effluent coming from the fermenter was screw pressed, and the solid phase was recycled adopting different ratios to the fermenter, in order to define its effect on the final liquid phase composition. The variations of the VFA, lactate, methyl and ethyl alcohol concentrations, TCOD, SCOD and pH during more than one year were analysed and discussed both with reference to the fresh feed, and to the content of the fermenter. It was found that almost all the organic matter in the liquid phase inside the fermenter was represented by VFA (mainly acetate), lactate (in particular) and methyl and ethyl alcohols when HRT was longer than 6 days.     

Control/promotion of the refuse methanogenic fermentation

Although practiced for more than 7 millennia, the landfill disposal of refuse has, as yet, with few exceptions, been merely regarded as a low-cost disposal option and its exploitation potential has been largely ignored. Today, however, a number of possibilities are under consideration including the production of energy, chemical feedstock, value-added chemicals, carbon dioxide and protein; the use of refuse as an anaerobic filter for the co-disposal of industrial wastewater and sludge; and the restoration of impoverished soils by fresh or composted refuse addition. Development of these technologies, however, necessitates a comprehensive understanding of the fundamental microbiology and biochemistry of refuse catabolism. Existing fundamental knowledge underpinning these technologies will be considered in a series of review articles. In the first, control/exploitation of the solid-state refuse methanogenic fermentation is examined with specific reference to the effects of first-tier variable manipulations.     

Semisolid fermentation of ryegrass straw

Candida utilis, Aureobasidium pullulans, and Trichoderma viride were grown on pretreated ryegrass straw. The pretreatment consisted of hydrolysis of straw with 0.5 N H₂SO₄ (water-substrate, 3:1) at 121 C, 100 C, and room temperature and adjustment of the hydrolysate to pH 4.5 to 5.0 with 5 N NH₄OH. The 121 C pretreatment yielded a material containing 30% sugar and 2.3% N. The fermentation was carried on semisolid substrate (moisture level, 75%) in rotating jars for 2 to 3 days at room temperature. The organisms grew rapidly during the period from 18 to 42 h of incubation. During this period the number of microbial cells increased by 20- to 200-fold, and the level of NH₃-N decreased from 1.3 to 0.9%. The fermentation resulted in a fourfold increase in protein, fivefold increase in crude fat, and 40% increase in the digestibility of straw. The best result in terms of increasing protein and digestibility of straw was obtained when C. utilis was grown on straw preheated at 121 C.     

Pilot-scale semisolid fermentation of straw

Semisolid fermentation of ryegrass straw to increase its animal feed value was successfully performed on a pilot scale. The pilot plant, which could handle 100 kg of straw per batch, was designed so that all major operations could take place in one vessel. The straw was hydrolyzed at 121 degrees C for 30 min with 0.5 N H2SO4 (7:3 liquid:solid), treated with ammonia to raise the pH to 5.0, inoculated with Candida utilis, and fermented in a semisolid state (70% moisture). During fermentation the straw was held stationary with air blown up through it. Batch fermentation times were 12 to 29 h. Semisolid fermentation did not require agitation and supported abundant growth at 20 to 40 degrees C even at near zero oxygen tensions. Fermentation increased the protein content, crude fat content, and in vitro rumen digestibility of the straw.     

A comprehensive model of simultaneous denitrification and methanogenic fermentation processes

The denitrification process was incorporated into the IWA Anaerobic Digestion Model No. 1 (ADM1) in order to account for the effect of denitrification on the methanogenic fermentation process. The model was calibrated and optimized using previously published experimental data and kinetic parameter values obtained with a mixed, mesophilic (35°C) methanogenic culture. Model simulations were used to predict the effect of nitrate reduction on the methanogenic fermentation process in batch, semi‐continuous, and continuous flow reactors experiencing operational changes and/or system disturbances. The extended model clearly revealed the importance of substrate competition between denitrifiers and non‐denitrifiers as well as the impact of N‐oxide inhibition on process interactions between fermentation, methanogenesis, and denitrification. Biotechnol. Bioeng. 2010;105: 98–108. © 2009 Wiley Periodicals, Inc.     

Acidogenic fermentation of proteinaceous solid waste and characterization of different bioconversion stages and extracellular products

The purpose of this study was to investigate hydrolysis of animal fleshing (ANFL), a predominant tannery solid waste and to characterize the acetogenic fermentation products of anaerobic digestion. The acidogenic digestibility of the tannery solid wastes were evaluated up to 120 h using batch anaerobic digestion tests performed under mesophilic condition at 37 degrees C. The degradation of ANFL starts with non-fibrillar proteins and proceeds with fibrillar proteins. The release of aliphatic amino acid in the early stages of hydrolysis (24 h) and followed by aromatic amino acids (24-72 h) were evidenced by HPLC analysis. The maximum production of propionic and valeric acid were observed in 72 h followed by rapid increase in acetic acid in 96 h using GC-MS. Breakdown of ANFL and formations of other metabolites were evidenced by FT-IR and (1)H-NMR spectroscopy.     

Acidogenic fermentation of pectin by a mixed population of bacteria in continuous culture

Summary Pectin, dissolved in a mineral salts solution, was degraded anaerobically by a mixed population of bacteria in chemostat cultures (pH=6, T=30°C). At a dilution rate of 0.3 h^–1, the specific volume activity was 45.7 (g substrate). (l reactor)^–1.d^–1.     

Acidogenic fermentation of vegetable based market waste to harness biohydrogen with simultaneous stabilization

Vegetable based market waste was evaluated as a fermentable substrate for hydrogen (H₂) production with simultaneous stabilization by dark-fermentation process using selectively enriched acidogenic mixed consortia under acidophilic microenvironment. Experiments were performed at different substrate/organic loading conditions in concurrence with two types of feed compositions (with and without pulp). Study depicted the feasibility of H₂ production from vegetable waste stabilization process. H₂ production was found to be dependent on the concentration of the substrate and composition. Higher H₂ production and substrate degradation were observed in experiments performed without pulp (23.96 mmol/day (30.0 kg COD/m³); 13.96 mol/kg COD_R (4.8 kg COD/m³)) than with pulp (22.46 mmol/day (32.0 kg COD/m³); 12.24 mol/kg COD_R (4.4 kg COD/m³)). Generation of higher concentrations of acetic acid and butyric acid was observed in experiments performed without pulp. Data enveloping analysis (DEA) was employed to study the combined process efficiency of system by integrating H₂ production and substrate degradation.     

Pilot-scale semisolid fermentation of straw.

Semisolid fermentation of ryegrass straw to increase its animal feed value was successfully performed on a pilot scale. The pilot plant, which could handle 100 kg of straw per batch, was designed so that all major operations could take place in one vessel. The straw was hydrolyzed at 121 degrees C for 30 min with 0.5 N H2SO4 (7:3 liquid:solid), treated with ammonia to raise the pH to 5.0, inoculated with Candida utilis, and fermented in a semisolid state (70% moisture). During fermentation the straw was held stationary with air blown up through it. Batch fermentation times were 12 to 29 h. Semisolid fermentation did not require agitation and supported abundant growth at 20 to 40 degrees C even at near zero oxygen tensions. Fermentation increased the protein content, crude fat content, and in vitro rumen digestibility of the straw.     

Kinetics of rice straw methane fermentation

Summary The kinetics of anaerobic fermentation of rice straw to methane were studied. Rice straw was the only carbon source at influent volatile solid concentrations of 18.9 and 37.8 g/l. Semicontinous runs were carried out at 37°C in laboratory scale perfectly mixed reactors. The Contois' kinetic model constants were calculated from the experimental data. Arefrac tory coefficient was measured (R=0.374) to account for the nonbiodegradable portion of the organic matter of rice straw and incorporated into the kinetic equations. The predicted values of effluent substrate concentration, volumetric methane yield, volumetric methane production rate, and biodegradable conversion efficiency fit well with those measured experi mentally.Percent destruction values of feed constituents were measured.     

Fermentation pattern of methanogenic degradation of rice straw in anoxic paddy soil

The anaerobic degradation of different fractions of rice straw in anoxic paddy soil was investigated. Rice straw was divided up into stem, leaf sheath and leaf blade. The different straw fractions were mixed with paddy soil and incubated under anoxic conditions. Fermentation of straw components started immediately and resulted in transient accumulation of acetate, propionate, butyrate, isobutyrate, valerate, isovalerate and caproate with much higher concentrations in the presence than in the absence of straw. Also some unidentified compounds with UV absorption could be detected. The maximum concentrations of these compounds were different when using different straw fractions, suggesting differences in the degradation pathway of these straw fractions during the early phase of incubation, i.e. with Fe(III) and sulfate serving as oxidants. When concentrations of the intermediates decreased to background values, CH(4) production started. Rates of CH(4)unamended soil. During the methanogenic phase, the percentage contribution of fermentation products to CH(4) production was determined by inhibition with 2-bromoethanesulfonate (BES). Acetate (48-83%) and propionate (18-28%) were found to be the main intermediates of the carbon flow to CH(4), irrespective of the fraction of the rice straw or its absence. Mass balance calculations showed that 84-89% of CH(4) was formed via acetate in the various incubations. Radiotracer experiments showed that 11-27% of CH(4) was formed from H(2)/CO(2), thus confirming that acetate contributed 73-89% to methanogenesis. Our results show that the addition of rice straw and the fraction of the straw affected the fermentation pattern only in the early phase of degradation, but had no effect on the degradation pathway during the later methanogenic phase.     

Solid-state refuse methanogenic fermentation: control and promotion by water addition

The efficacy of single water additions to promote the solid-state refuse methanogenic fermentation was examined with laboratory batch cultures. Initially, acidogenesis increased with increasing water addition although product inhibition was also apparent, particularly in low moisture content samples. With refuse columns, a moisture content increase from 55 to 75% (w/w) effected a 2.4-fold increase in the total volume of methane evolved during a 95-day incubation period although reduced evolution was apparent at the elevated moisture content of 80% (w/w). In general, the methane content of the evolved gases increased in response to increased water addition.     

Characteristics of granular methanogenic sludge grown on phenol synthetic medium and methanogenic fermentation of phenolic wastewater in a UASB reactor

The growth of granules on a phenol synthetic medium and the methanogenic fermentation of industrial phenolic wastewater from a steel factory in an upflow anaerobic sludge blanket (UASB) reactor were investigated. Total granular sludge concentration retained in the UASB reactor was 6.7 g MLSS/l (6.0 g MLVSS/l) during the 10 months' operation on the phenol synthetic medium. This realized a maximum phenol removal rate of 2.2 g/l·d (phenol concentration of influent = 500 mg/l), which corresponded to 5.2 g COD/l·d at space velocity (SV) of 4.4 d⁻¹. The granules formed were of relatively small size ranging from 0.61 to 0.77 mm, and had a relatively low density of 0.013–0.023 g MLVSS/cm³ and low specific gravity (1.11) due to very low ash content (8.7–11.9%). Electron microscopic analysis showed that Methanothrix spp. appeared dominantly on the granule surface as well as within it. The specific metabolic activities of bacterial trophic groups were the highest for H₂ followed by acetate, benzoate, phenol, and propionate. In the case of industrial phenolic wastewater, although phenol efficiency was only 50% at SV of 0.4 d⁻¹, when the wastewater was diluted twofold and the treated wastewater was recycled at SV of 7.3 d⁻¹, the removal efficiencies of phenol and CODcr were restored to 90% (influent=400 mg/l) and 80% (influent=5,000 mg/l), respectively. It was suggested that recycling of the treated wastewater might be improved by partly degrading unknown toxic compounds contained in phenolic wastewater.