On-line automated monitoring and control systems for CO2 and O2 in aerobic and anaerobic solid-state fermentations

Solid-state culture of Azospirillum brasilense: a reliable technology for biofertilizer production from laboratory to pilot scale

A biofertilizer of Azospirillum brasilense was produced in solid-state culture (SSC) from laboratory to pilot scale. Similar operation conditions (continuous aeration and mild intermittent mixing) and two dimensionless numbers with similar L/D ratio and a similar working volume were applied to reach a scale-up factor of 75. An innovative bioreactor with rotating helical ribbons (15 kg wet matter) was used at pilot scale. A mathematical model was proposed and validated to evaluate the respirometry trends at laboratory and pilot scale exhibiting similar behavior. The cell viability was (1.3 ± 0.4) × 10⁹ and (1.3 ± 0.3) × 10⁹ colony-forming units per gram of initial dry mass at laboratory and pilot scale, at 36 and 43 h, respectively. A. brasilense maintains its viability twelve months of storage at 4 and 30 °C. This is the first report of A. brasilense being cultivated in SSC under controlled conditions. SSC processes involving unicellular microorganisms with tolerance to agitation are a promising technology to produce biofertilizers.

Biosurfactants: The green generation of speciality chemicals and potential production using Solid-State fermentation (SSF) technology

Surfactants are multipurpose products found in most sectors of contemporary industry. Their large-scale manufacturing has been mainly carried out using traditional chemical processes. Some of the chemical species involved in their production are considered hazardous and some industrial processes employing them categorised as "having potential negative impact on the environment". Biological surfactants have therefore been generally accepted worldwide as suitable sustainable greener alternatives. Biosurfactants exhibit the same functionalities of synthetic analogues while having the ability to synergize with other molecules improving performances; this strengthens the possibility of reaching different markets via innovative formulations. Recently, their use was suggested to help combat Covid-19. In this review, an analysis of recent bibliography is presented with descriptions, statistics, classifications, applications, advantages, and challenges; evincing the reasons why biosurfactants can be considered as the chemical specialities of the future. Finally, the uses of the solid-state fermentation as a production technology for biosurfactants is presented.

Dynamic mathematical modeling of heat and mass transfer incorporating with the local nutrient and biomass limitation of growth in a packed-bed solid-state bioreactor

This research develops on our previous semi-mechanistic model that describes the dynamic physical and biochemical processes taking place in a packed-bed bioreactor to analyze the relationship of nutrient limitation, biomass accumulation, metabolic heat generation, and mathematical description of packed-bed porous media. The experimental and simulation data proved that glucose concentration gradients in the biofilm could be neglected due to small biofilm thickness and high diffusivity of glucose in the biofilm. The prediction results also showed that an increase in the initial substrate concentration leads to a rise in the temperature gradient in the bed. The model proposes that if the diameter of substrate particle is too large (r > 0.1 cm), the growth rate will decrease significantly due to the high biomass accumulation in the biofilm, and temperature gradients decrease in the column. This can be used as a strategy to control the overheating problem in the bed.

Effect of stirring on growth and cellulolytic enzymes production by Trichoderma harzianum in a novel bench-scale solid-state fermentation bioreactor

A novel bench-scale stirred bioreactor for solid-state fermentation was used to determine the effect of the stirring rate on growth and enzymes production by Trichoderma harzianum PBLA. Lab-scale static tubular bioreactors were first used to assess the effect of bioreactor diameter on heat accumulation, growth, and production of cellulases and xylanases. The increased diameters (1.8-4.2 cm) led to increases in temperature up to 36 °C (at a rate of 1.08 °C/cm), which negatively affected the growth and enzyme production. Afterward, in the bench-scale bioreactor operated at rates up to 3.0 rpm, maximum xylanases production (107 ± 0.3 U/g dm) was attained at rates of 0.5 and 1.0 rpm, reaching a maximum of 34 ± 0.3 °C. Cellulases production was reduced (up to 79%) due to stirring. Therefore, the production of xylanases by T. harzianum can be performed in this cross-flow stirred SSF bioreactor at rates up to 1.0 rpm, avoiding heat accumulation and damage on metabolic activity.

On-line monitoring of Aspergillus niger GH1 growth in a bioprocess for the production of ellagic acid and ellagitannase by solid-state fermentation

The present work describes the monitoring of CO₂ production by Aspergillus niger GH1 in a bioprocess for the production of ellagitannase (EAH) and ellagic acid by solid state fermentation. Pomegranate ellagitannins, mainly punicalagin, were used as carbon source and EAH inducer. A second condition, using ellagitannins and maltose as growth promoting carbon source, was tested. The ellagic acid production was quantified and the EAH activity was assayed. The accumulated metabolites were identified by HPLC-ESI-MS/MS. Higher CO₂ production (7.79mg/grams of dry material) was reached in media supplemented with maltose. Short-time lag phase (7.79h) and exponential phase (10.42h) were obtained using only ellagitannins, despite its lower CO₂ production (3.79mg/grams of dry material). Without the use of maltose lower ellagic acid (11.85mg/L/h) and EAH (21.80U/L/h) productivities were reached. The use of maltose enhances the productivity of EA (33.18mg/L/h) and EAH (33.70U/L/h). Besides of punicalin and ellagic acid, two unknown compounds with mass weight of 702 and 290g/mol (ions 701 and 289m/z in negative mode, respectively) were identified and characterized by HPLC-ESI-MS/MS analysis.

Derivation of an Upscaled Model for Mass Transfer and Reaction for Non-Food Starch Conversion to Bioethanol

In this paper, we derive mathematical models for mass transfer and reaction taking place in first-generation bioreactors to convert non-food starch into bioethanol. Given the hierarchical nature of the system, we identified three scale levels ranging from inside bagasse fibers (the pore scale) where the reaction occurs, up to the bioreactor itself (macroscopic scale) where the various products obtained from this reaction are monitored. We derive a macroscopic model at the reactor scale by systematically upscaling the relevant information from the pore scale using the method of volume averaging. A salient feature of the model is that the effective medium coefficients involved are predicted by solving ancillary closure problems in representative unit cells of the different levels of scale. The predictions of the model in terms of CO2 production as well as cellular growth were validated with a close agreement with available experimental data. This work enhances our understanding of the relevance of transport phenomena taking place at the different scales in a bioreactor and may become an aid in design and operation applications of bioethanol production systems.

Production of Conidia by the Fungus Metarhizium anisopliae Using Solid-State Fermentation

This chapter describes the production of conidia by Metarhizium anisopliae using solid-state fermentation. Before production of conidia, procedures for strains conservation, reactivation, and propagation are essential in order to provide genetic stability of the strains. The strain is conserved in freeze-dried vials and then reactivated through insect inoculation. Rice is used as a substrate for the conidia production in two different bioreactors: plastic bags and tubular bioreactor. The CO2 production in the tubular bioreactors is measured with a respirometer; this system allows calculating indirect growth parameters as lag time (tlag) (25-35 h), maximum rate of CO2 production (rCO2 max) (0.5-0.7 mg/gdm h), specific rate of CO2 production (μ) (0.10-0.15 1/h), and final CO2 production (CO2) (100-120 mg/gdm). Conidial yield per gram of dry substrate (gdm) should be above 1 × 10(9) conidia/gdm after 10 days of incubation. Germination and viability of conidia obtained after 10 days of incubation should be above 80 % and 75 %, respectively. Bioassays using of Tenebrio molitor as a host insect should yield a final mortality above 80 %.

Better One-Eyed than Blind--Challenges and Opportunities of Biomass Measurement During Solid-State Fermentation of Basidiomycetes

Filamentous fungi, especially basidiomycetes, produce a wide range of metabolites, many of which have potential biotechnological and industrial applications. Solid-state fermentation (SSF) is very suitable for the cultivation of basidiomycetes since it mimics the natural habitat of these fungi. Some of the major advantages of SSF are the robustness of the process, the use of low-cost residual materials as substrates, and the reduced usage of water. However, monitoring key variables is difficult, which makes process control a challenge. Specifically, it is very difficult to determine the biomass during SSF process involving basidiomycetes. This is problematic, as the biomass is normally a key variable in mass and energy balance equations. Further, the success of fungal SSF processes is often evaluated, in part, based on the growth of the fungus. Direct determination of the dry weight of biomass is impossible and indirect quantification techniques must be used. Over the years, various determination techniques have been developed for the quantification of fungal biomass in SSF processes. The current review gives an overview of various direct and indirect biomass determination methods, discussing their advantages and disadvantages.

Rapid mineralisation of the Organic Fraction of Municipal Solid Waste

The effect of pH, C/N ratio, addition of a microbial consortium (MC) and temperature upon mineralisation of Organic Fraction of Municipal Solid Waste (OFMSW) was studied; mineralisation was measured through the CO2 production rate and total CO2 formation. Through this process up to 432.9mg of CO2g(-1) initial dry matter (IDM) after 2days of treatment was obtained. It was found that under a slightly acidic pH (5-6) and C/N of 30, the mineralisation process was accelerated. Moreover, temperature (27-50°C) had no effect on the total CO2 produced. The highest CO2 production rate (5.28d(-1)) was observed at 27°C, C/N ratio of 30 and 8% of microbial consortium; it is at least 3.52 times higher than that reported (1.5d(-1)). The highest release of reducing sugars was determined at 50°C, possibly due to an increase in hydrolytic enzymes. Results suggest the potential use of rapid mineralisation of OFMSW for further friendly environmental processes.

Removal of polycyclic aromatic hydrocarbons from soil: a comparison between bioremoval and supercritical fluids extraction

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic substances which are resistant to environmental degradation due to their highly hydrophobic nature. Soils contaminated with PAHs pose potential risks to human and ecological health, therefore concern over their adverse effects have resulted in extensive studies on their removal from contaminated soils. The main purpose of this study was to compare experimental results of PAHs removal, from a natural certified soil polluted with PAHs, by biological methods (using bioaugmentation and biostimulation in a solid-state culture) with those from supercritical fluid extraction (SFE), using supercritical ethane as solvent. The comparison of results between the two methods showed that maximal removal of naphthalene, acenaphthene, fluorene, and chrysene was performed using bioremediation; however, for the rest of the PAHs considered (fluoranthene, pyrene, and benz(a)anthracene) SFE resulted more efficient. Although bioremediation achieved higher removal ratios for certain hydrocarbons and takes advantage of the increased rate of natural biological processes, it takes longer time (i.e. 36 d vs. half an hour) than SFE and it is best for 2-3 PAHs rings.

Lipases production by solid-state fermentation: the case of Rhizopus homothallicus in perlite

Lipases are widely used in the industry for different purposes. Although these enzymes are mainly produced by submerged fermentation, lipase production by solid-state fermentation (SSF) has been gaining interest due to the advantages of this type of culture. Major advantages are higher production titers and productivity, less catabolite repression, and use of the dried fermented material as biocatalyst. This chapter describes a traditional methodology to produce fungal (Rhizopus homothallicus) lipases by SSF using perlite as inert support. The use of different devices (glass columns or Erlenmeyer flasks) and type of inoculum (spores or growing mycelium) is considered so that lipase production by SSF could be easily performed in any laboratory.

Biodegradation of heavy crude oil Maya using spent compost and sugar cane bagasse wastes

Experiments were carried out to evaluate the use of some agroindustrial wastes as supports in solid state cultures for the biodegradation of crude oil Maya in static column reactors over 15-20 days periods. Spent compost and cane bagasse wastes showed superior qualities over peat moss waste as support candidates with the advantage that they contain appreciable densities of autochthonous microorganisms in the order of 10(2) cfu g(-1). Mercuric chloride (2%) was able to completely inhibit growth of these microfloras. Biodegradation was enhanced in the presence of the IMP consortium and highest when microflora from cane bagasse only was the bioaugmentation partner (180.7 mg kg(-1) day(-1)). Combination of these waste materials (3:1 ratio, respectively) was observed to significantly biodegrade the crude oil by approximately 40% in 15 days from an initial concentration of 10,000 mg kg(-1) with a four order of magnitude increase in microbial density during this period. Spent compost and cane bagasse wastes are veritable solid support candidates for use in the biodegradation of crude oil polluted systems.

Kinetic properties of a commercial and a native inoculum for aerobic milk fat degradation

The aerobic fat biodegradation potential and growth characteristics of a commercial and a native inoculum (activated sludge from a dairy wastewater treatment pond), were evaluated. Batch tests were conducted with a medium based on butter oil, as the sole source of carbon, and mineral salts. Residual fat, biomass and CO(2) production were measured. Overall fat removal values were above 78% for both inocula. The growth kinetics of the commercial and native inocula followed Haldane and Monod models respectively. Both inocula showed a similar behaviour when butter oil concentration was under 360 mg/l; at higher values, the difference between the growth rates increased as a consequence of the inhibition exhibited by the commercial inoculum. The selection of an inoculum for bioaugmentation of bioreactors in the wastewater treatment requires a comprehensive knowledge of their degradation ability and tolerance to fluctuating compounds and of the operational conditions that will be utilized.

Biodegradation of high concentrations of hexadecane by Aspergillus niger in a solid-state system: kinetic analysis

Solid-state microcosms were used to assess the influence of constant and variable C/N ratios on the biodegradation efficiency by Aspergillus niger at high hexadecane (HXD) concentrations (180-717 mg g-1). With a constant C/N ratio, 100% biodegradation (33-44% mineralization) was achieved after 15 days, at rates increasing as the HXD concentration increased. Biomass yields (YX/S) remained almost independent (approximately 0.77) of the carbon-source amount, while the specific growth rates (mu) decreased with increasing concentrations of HXD. With C/N ratios ranging from 29 to 115, complete degradation was only attained at 180 mg g-1, corresponding to 46% mineralization. YX/S diminished (approximately 0.50 units) as the C/N ratio increased. The highest values of mu (1.08 day-1) were obtained at low C/N values. Our results demonstrate that, under balanced nutritional conditions, high HXD concentrations can be completely degraded in solid-state microcosms, with a negligible (<10%) formation of by-products.

PCB biodegradation in aged contaminated soil: interactions between exogenous Phanerochaete chrysosporium and indigenous microorganisms

This work investigated whether the interaction between the white-rot fungus Phanerochaete chrysosporium and indigenous microorganisms could enhance polychlorinated biphenyl (PCB) removal from historically contaminated soil in aerobic microcosms. The PCB mixture was composed mainly of 14% tri-, 20% tetra-, 9% penta-, 17% hexa-, 26% hepta-, 11% octa-, and 3% nona-chlorobiphenyl (CB) congeners, determined by GC/MS. The fungus, which was grown on sugarcane bagasse and added via this solid substrate, successfully colonized the contaminated soil. The added fungi and the indigenous soil community biodegraded most PCB congeners, with removing efficiencies ranging from 13% to 100% for the 45-day incubation period. The interaction between the fungus and the microorganisms present in the added bagasse inhibited both heterotrophic activity (measured by CO2 evolution) and PCB degradation, suggesting a possible antagonism. In contrast, analysis of variance (ANOVA) inferred a synergistic effect between fungus and soil microorganisms, which resulted in a heterotrophic activity above 2.5 mg-CO2/g-initial dry matter/day. The statistical analyses also showed that the presence of fungus alone was particularly beneficial for the removal of penta- and hepta-CB.

An automated test for measuring polymer biodegradation

The biodegradability of polymer materials as evaluated by the modified Sturm test is labor-intensive, cumbersome and costly and also tends to cumulate errors. An automated system for the measurement of carbon dioxide would overcome many of these disadvantages. We describe here a method in which CO2 was determined by IR spectroscopy. We compared the results with those from trapping CO2 in a solution of barium hydroxide (Ba(OH)2) followed by manual titration. The automated system was more reproducible, less costly and more compact. The automated system could also be employed to measure the biodegradability of other substances such as oils and detergents.

Respiration studies of penicillin solid-state fermentation

An earlier work showed that when the bagasse content (BC) of the solid medium was decreased within a wide range of values, penicillin production by solid-state fermentation was always increased. Respiration studies were performed to understand how BC controls the secondary metabolism in this culture system. CO2 production of solid cultures with different compositions was monitored. In cultures of series A, the initial moisture content was increased and this variation was compensated by decreasing the nutrient and BC of the medium. In series B the initial moisture content was increased while BC was decreased and the nutrient content increased. In addition, penicillin production and respiration was also studied in extreme media (dry and concentrated and humid and diluted), with high and low BC. Criteria for the interpretation of respiration kinetics of the idiophase were established for the first time in this work. For the cumulative form (total CO2/g dry matter vs t) as well as for derivative (CO2/g dm/h vs t) respiration kinetics, the CO2 production rate (Q(CO2)) was determined by calculating the slope of the cumulative curve. Results indicate that Q(CO2) of the tropho- and idiophases was directly related to the BC of the solid medium (and inversely related to penicillin yields). These conclusions were confirmed by analysis of the derivative form, the results of which indicate that a lower but stable metabolic activity is essential for obtaining high penicillin yields in solid-state fermentation (SSF). The results indicate that the derivative CO2 production kinetics proved to be a more precise and sensitive indicator of the culture metabolic activity during idiophase than the cumulative respiration kinetics.

The molecular biology of Schwanniomyces occidentalis klocker

This review describes the molecular studies of Schwanniomyces occidentalis (Debaryomyces occidentalis) concerning transformation, genome, gene cloning, gene structure, gene expression and its characteristics to application. Schw. occidentalis appears to have at least five or seven chromosomes and no native plasmid from the yeast has been reported. Four transformation systems based on complement of Schw. occidentalis auxotrophic mutants were established. Vectors with the replicon of 2-micron plasmid and autonomous replication sequences (ARS) of Saccharomyces cerevisiae and Schw. occidentalis ARS replicated extrachromosomally in Schw. occidentalis transformants, without modification of the transformed vector DNA. So far, at least 21 Schw. occidentalis genes encoding 14 different proteins have been cloned. Most of the Schw. occidentalis genes have shown homologies (45 to 91%) with the corresponding genes of other organisms, especially of S. cerevisiae. However, some Schw. occidentalis genes possess other unique structures for their operators, promoters, transcription initiation sites, and terminators. Some foreign genes were expressed in Schw. occidentalis, while Schw. occidentalis genes functioned in other yeasts and bacteria, Escherichia coli, and Streptomyces lividans. Due to a strong ability of secretion and low level of glycosylation, Schw. occidentalis might be a promising host to produce heterologous proteins.