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Carbonic anhydrase has proven to be an excellent candidate for recombinant biocatalysts production. Its ubiquitous nature and the diversity of its forms available in various microorganisms, enable the exploitation of thermophilic, psychrophilic and halophilic properties of the native enzymes. Consolidated technologies for enzyme immobilization on solid supports disclose utilization in continuous bioreactors, opening up new opportunities to use carbonic anhydrase (Russo et al., 2013; Yoshimoto and Walde, 2018). These perspectives are perfectly framed in one of the most challenging targets of modern chemical reaction engineering: developing feasible and efficient CO2 capture and utilization processes. The principles of green chemical engineering promote the use of sustainable solvents and biocatalysts by rethinking conventional processes and mining waste streams, including flue gases. For these reasons, studies focused on post-combustion CO2 capture have been increasingly directed toward using carbonic anhydrase as a biocatalyst to enhance the CO2 absorption rate in reactive absorption processes. The present contribution addresses key methodologies for carbonic anhydrase immobilization aimed to develop heterogeneous biocatalysts for CO2 capture and utilization. Advantages and drawbacks of covalent attachment on fine granular solids, immobilization into cross-linked enzyme aggregates as well as 'in vivo' immobilization methods will be addressed (Fabbricino et al., 2021). How the characterization of biocatalyst can be exploited for a CO2 capture unit design will be discussed, showing the most effective techniques (Peirce et al., 2018). Perspectives on how enzymatic reactive CO2 absorption can be applied to carbon capture and utilization will eventually be presented with a particular focus on biocatalytic CO2 fixation pathways.

Carbonic anhydrase (CA) is an excellent candidate for novel biocatalytic processes based on the capture and utilization of CO

Biorefinery processes for the production of second generation biofuels and bio-commodities are based on the use of waste lignocellulosic biomasses as a renewable feedstock. The sugar-based biorefinery platform includes biomass pretreatment and hydrolysis of structural polysaccharides as the first steps of the feedstock transformation. Hydrolysis of cellulose and hemicellulose in real biomass can be catalyzed by cellulase enzymes cocktails. The process has been developed up to industrial scale even though the scientific community is still active in investigating several critical issues in order to reduce costs of the process. The process allows obtaining a concentrated sugar aqueous solution (hydrolysate) from the heterogeneous conversion of the complex substrate (biomass) by the catalytic action of cellulases and beta-glucosidase dissolved in the liquid phase. The issues related to the reactor design include multi-scale phenomena affecting reaction kinetics, hydrodynamics as well as mass transfer of the biphasic system. The recent literature has been reviewed in order to highlight the state of the art about modelling of enzyme-catalyzed cellulose hydrolysis kinetics[1, 2], modelling of hydrolysis reactors[3], and optimization of process strategies[4]. Moreover, in the framework of the project Waste2Fuels (H2020-LCE-11-2015 g.a. n°654623), semi-mechanistic models of agro-food waste enzymatic hydrolysis have been assessed in order to obtain quantitative tools for bioreactor modelling. The effect of biomass pretreatment in terms of delignification degree has been quantified through the assessment of kinetic parameters of two agro-food wastes (apple pomace and coffe silverskin). References [1] Jeoh T., Cardona M., Karuna N., Mudinoor A.R., Nill J. (2017) Mechanistic Kinetic Models of Enzymatic Cellulose Hydrolysis--A Review, Biotechnology and Bioengineering, 114 (7), 1369-1385 [2] Bansal P., Hall M., Realff M.J., Lee J.H., Bommarius A.S. (2009) Modeling cellulase kinetics on lignocellulosic substrates, Biotechnology Advances 27, 833-848

Torrefaction is a relatively new biomass pretreatment technology where the feedstock is heated (typically < 50 °C/min) in an inert environment up to a temperature of about 200-300 °C for a relatively long reactor residence time (from 30 min to 120 min, depending on the specific feedstock). The resulting torrefied material has low moisture content, high calorific values, increased resistance to moisture, and improved grinding properties [1]. Even though, torrefaction was originally developed as a treatment to improve the properties of biomass intended as a feedstock for thermochemical conversion pathways (i.e. combustion, pyrolysis and gasification) recently, it has also attracted some interest as a potential pretreatment of lignocellulosic biomass intended as feedstock for biorefinery (mainly for fermentable sugar production by enzymatic hydrolysis) [2-4]. A first attempt by Chiaramonti et al. [2] demonstrated that olive pruning debris torrefied under mild conditions (180-220°C) results into materials which can be enzymatically hydrolyzed and fermented into ethanol with yields close to those of the raw biomass. Again, Sheikh et al. [4] highlighted that, as long as the torrefaction conditions are not too severe (160-260 °C for 20-60 min), the saccharification yield of torrefied rice straw is much higher than that of untreated rice straw, thus resulting in a greater sugar release and an improved enzymatic digestibility. In order to confirm and strengthen the promising outcomes of these early studies, the potential to combine biomass torrefaction with biochemical conversion technologies (such as enzymatic hydrolysis and fermentation) has been further explored in the present work. In particular, two different agro-industrial residues, namely coffee silvers skin and brewery's spent grain, have been subjected to torrefaction under mild conditions of temperature (160-220 °C) and time (10-60 min), in both packed and fluidized bed reactors and then used as substrate for enzymatic hydrolysis tests. References [1] Nhuchhen, D.R., Basu, P., Acharya, B. A Comprehensive Review on Biomass Torrefaction. IJRER 2014 (2014) 1-56. [2] Chiaramonti, D., Rizzo A.M., Prussi, M., Tedeschi, S., Zimbardi, F., Braccio, G., Viola, E., Taddei Pardelli, P., 2nd generation lignocellulosic bioethanol: is torrefaction a pos-sible approach to biomass pretreatment?. Biomass Conv. Bioref. 1 (2011) 9-15. [3] Normark, M., Pommer, L., Grasvik, J., Hedenstrom, M., Gorzsas, A., Winestrand, S., Jonsson, L.J. Biochemical conversion of torrefied Norway spruce after pretreatment with acid or ionic liquid. Bioenerg. Res. 9 (2016), 355-368. [4] Sheikh, M.M., Kim, C.H., Park, H.J., Kim, S.H., Kim, G.C., Lee, J.Y., Sim, S.W., Kim, J.W. Effect of torrefaction for the pretreatment of rice straw for ethanol production. J. Sci. Food Agric. 93 (2013) 3198-204.

1. Introduction Post-combustion CO2 capture strategy asks for novel processes avoiding the use of polluting solvents and aimed at CO2 utilization. CO2 absorption processes based on the enhancement of capture rate by the enzyme carbonic anhydrase (CA) (EC - 4.2.1.1) have been deeply investigated [1]. CA is able to catalyze the CO2 hydration reaction and its thermophilic and halophilic forms are active into aqueous alkaline solvents [2]. In addition, the use of carbonate aq solvents and CA allows the exploitation of the bicarbonate enriched solvent for CO2 utilization processes based on the cultivation of high value microalgae biomass [3, 4]. This contribution reports on recent efforts for the development of three techniques for the production of CA biocatalysts: two different CA immobilization techniques were developed and compared with a whole cell biocatalyst where CA is present on the outer membrane of engineered Eschierichia coli cells [5]. 2. Methods Thermostable CA was (Novozymes) and immobilized in the form of Cross Liked Enzyme Aggregates (CLEA) [6] and covalently attached on magnetic nanoparticles (MNP) [7]. Whole cell biocatalyst bearing CA on outer surface of cell membrane were prepared according to Del Prete et al. [5]. Kinetic characterization of CA based biocatalyst was performed through CO2 absorption tests in a stirred cell lab scale bioreactor [6, 7]. 3. Results and discussion Figure 1 shows the immobilization yields (mass of immobilized enzyme/initial mass of enzyme) and the enzyme loadings (mass of enzyme/mass of biocatalyst) after preparation of CA CLEA and MNP with attached CA. CLEA shows remarkable improvement of these characteristics with respect to CA covalently attached on MNP. On the other hand, large CLEA size (low biocatalyst effectiveness) did not allow kinetic characterization [6]. MNP and free CA apparent kinetics were fully characterized under industrially relevant conditions [7]. Whole cell biocatalyst showed active CA on its membrane [5] and its kinetic characterization is ongoing through CO2 absorption tests used for CLEA and MNP characterization [6, 7]. Figure 1. Comparison between CA immobilized on magnetic nanoparticles (MNP)and cross linked enzyme aggregates (CLEA). 4. Conclusions Three technologies have been developed to produce CA-biocatalysts for the development of CO2 capture processes oriented through aq phase CO2 utilization [3, 4]. Table 1 reports pros and cons about each investigated biocatalyst. Among these, MNP biocatalyst is ready to further scale-up tests since assessed kinetic parameters have been used for an absorption column design study [8]. Table 1 Comparison between possible strategies for CA use as promoter of enzymatic reactive absorption for CO2 capture. References [1]M. E. Russo, G. Olivieri, A. Marzocchella, P. Salatino, P. Caramuscio, C. Cavaleiro, Sep Pur Technol, 107 (2013) 331-339. [2]M. Leimbrink, S. Tlatlik, S. Salmon, A. K. Kunze, T. Limberg, R. Spitzer, A. Gottschalk, A. Górak, M. Skiborowski, Int J Greenhouse Gas Control, 62 (2017) 100-112. [3]Z. Chi, J. V O'Fallon, S. Chen, Trends Biotechnol. 29 (2011) 537-41. [4]B. Gris, E. Sforza, L. Vecchiato, A. Bertucco, Ind. Eng. Chem. Res. 53 (2014) 16678-16688. [5]S. Del Prete, R. Perfetto, M. Rossi, F. A. S. Alasmary, S. M. Osman, Z. AlOthman, C. T. Supuran, C. Capasso, J. Enz Inihib Medicinal Chem, 32 (2017) 1120-1128 [6]S. Peirce, M.E. Russo, R. Isticato, R.F. Lafuente, P. Salatino, A. Marzocchella, Biochem. Eng. J. 127 (2017) 188-195. [7]S. Peirce, M.E. Russo, R. Perfetto, C. Capasso, M. Rossi, R. Fernandez-Lafuente, P. Salatino, A. Marzocchella, Biochem. Eng. J. 138 (2018) 1-11. [8]M. E. Russo, P. Bareschino, F. Pepe, A. Marzocchella, P. Salatino, Chem. Eng. Transact. 69 (2018)

Recently the use of lignocellulosic feedstock as source of fermentable sugars has been extensively investigated in order to develop biorefinery processes to produce liquid biofuels and bio-commodities. In particular, second generation biofuels have been proposed as the result of the conversion of sugars from residual biomass such as agriculture and food industry by-products. An example of liquid biofuel produced through sugar-based biorefinery is bio-butanol [1]. The possibility to produce butanol from low cost feedstocks, such as lignocellulosic food wastes, has been recently explored [2]. This process, as well as all the second generation biorefinery processes, asks for physical or chemical pretreatments of the lignocellulose (e.g., acid hydrolysis, alkaline wet oxidation and steam explosion) in order to mitigate the hindrance effect of lignin that limits the accessibility of carbohydrates to the hydrolytic enzymes. Despite the progress made in developing innovative biomass delignification processes [3], some drawbacks still exist that need to be faced. Further efforts are therefore needed in order to identify biomass pretreatments that are able to break up the lignocellulosic structure, to decrease the cellulose crystallinity, and at the same time to provide a high hemicellulose recovery while limiting the formation of inhibitory compounds [4]. Moreover, most of the pretreatment processes requires large water, solvents or energy consumption and are typically implemented at large scale as first operation in the biorefinery sites. More versatile processes that might be locally applied for distributed production and collection of lignocellulosic feedstock are required in order to develop 'intermediate' carbon vectors in the form of stable and ready-to-use resources. To this aim, the investigation of mild thermochemical processes such as torrefaction can offer wide opportunities. Torrefaction is a mild thermo-chemical treatment where biomass is heated in an inert environment up to a temperature ranging between 200 and 300 °C. It is characterized by low particle heating rate (< 50 °C/min) and a relatively long reactor residence time (5 -120 min) [5]. Even though, so far, torrefaction has been mostly adopted as a biomass pretreatment technology for thermochemical conversion pathways (i.e. combustion, pyrolysis and gasification), there are evidence in the pertinent literature [6] that torrefied feedstocks can be enzymatically hydrolyzed for lignocellulosic bioethanol production. Brachi et al. (2017) [7] have also found that torrefaction promote the conversion of crystalline cellulose into an amorphous state, the latter being more susceptible to the enzymatic hydrolysis than the former. Among the other effects, torrefaction improves the grindability of fibrous materials [5], which may reduce the energy demand for grinding the feedstock before hydrolysis, and turned out to be a suitable pretreatment to improve the fuel properties of lignin residues resulting from enzymatic hydrolysis [8]. In the light of the abovementioned benefits, the potential of combining biomass torrefaction with enzymatic hydrolysis for lignocellulosic butanol and isopropanol production has been preliminary investigated in the present paper by using coffee silverskin as a feedstock. In more details, thermogravimetric runs and lab-scale fixed bed torrefaction tests have been carried out to identify the process temperature, which allows minimizing the content of lignin in the torrefied solid, while preserving the original amount of cellulose and hemicellulose. The basic idea is to exploit the different thermal stability and reactivity that hemicellulose, cellulose and lignin exhibit because of their different composition and structure.

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Within the framework of lignocellulose biorefinery, main issues related to the upstream processes include the drastic temperature and pressure usually required for efficient delignification of the biomass and the cost of the cellulase enzymes used to obtain monomeric sugars from cellulose hydrolysis. Several studies address the optimization of lignin removal with novel pretreatment (e.g. green solvents) with respect to the resulting sugar yields from enzymatic hydrolysis of the pretreated biomass performed at fixed conditions [1]. Among studies related to characterization of enzymatic hydrolysis, the use of semi-mechanistic models have been adopted to describe the kinetics of heterogeneous conversion of cellulose from lignocellulosic biomass into glucose [2, 3]. To investigate the effect of biomass composition resulting from different chemical and enzymatic delignification pretreatments, kinetic characterization of commercial cocktail Cellic CTec2 (Novozymes) has been carried out adopting apple industrial residues pretreated with NaOH, HCl and laccases.

Carbon dioxide capture by absorption in carbonates solutions supplemented with the enzyme carbonic anhydrase (CA) has been studied as a novel strategy alternative to the amine based absorption. The enzyme immobilized on fine dispersed solids promotes the heterogeneous biocatalysis of CO2 hydration reaction and the enhancement of CO2 absorption rate. In the present work, a theoretical model of a slurry absorption unit for CO2 capture in CA supplemented K2CO3 solutions was developed and solved using the commercial software package Comsol Multiphysics®. The model was developed through the 'tanks-in-series' approach applied to both the gas and liquid phases; the slurry biocatalyst was modelled as pseudo-homogeneous fine dispersed solids. The reversible Michaelis and Menten kinetics described CO2 conversion by the slurry biocatalyst. The role of mass transfer rate and heterogeneous enzyme catalysis on the CO2 capture rate and on the CO2 concentration profiles in the liquid boundary layer was investigated. Simulation results showed that the CO2 capture rate poorly increased when dissolved CA was used within the enzyme solubility limit, and that in the presence of CA immobilized on fine particles the CO2 absorption rate was enhanced about three fold with respect to carbonate solvent. Support from grant PON03PE_00157_1 'Smart generation' is gratefully acknowledged.

This paper shows the coimmobilization of b-galactosidase from Aspergillus oryzae (b-gal) and lipase B from Candida antarctica (CALB). The combi-biocatalyst was designed in a way that permits an optimal immobilization of CALB on octyl-agarose (OC) and the reuse of this enzyme after b-gal (an enzyme with lower stability and altogether not very stabilized by multipoint covalent attachment) inactivation, both of them serious problems in enzyme co-immobilization. With this aim, OC-CALB was coated with polyethylenimine (PEI) (this treatment did not affect the enzyme activity and even improved enzyme stability, mainly in organic medium). Then, b-gal was immobilized by ion exchange on the PEI coated support. We found that PEI can become weakly adsorbed on an OC support, but the adsorption of PEI to CALB was quite strong. The immobilized b-gal can be desorbed by incubation in 300 mM NaCl. Fresh b-gal could be adsorbed afterwards, and this could be repeated for several cycles, but the amount of PEI showed a small decrease that made reincubation of the OC-CALB-PEI composite in PEI preferable in order to retain the amount of polymer. CALB activity remained unaltered under all these treatments. The combi-catalyst was submitted to inactivation at 60 C and pH 7, conditions where b-gal was rapidly inactivated while CALB maintained its activity unaltered. All b-gal activity could be removed by incubation in 300 mM NaCl, however, SDS analysis showed that part of the enzyme b-gal molecules remained immobilized on the OC-CALC-PEI composite, as the inactivated enzyme may become more strongly adsorbed on the ion exchanger. Full release of the b-gal after inactivation was achieved using 1 M NaCl and 40 C, conditions where CALB remained fully stable. This way, the proposed protocol permitted the reuse of the most stable enzyme after inactivation of the least stable one. It is compatible with any immobilization protocol of the first enzyme that does not involve ion exchange as only reason for enzyme immobilization

The reduction of polyphenols content in olive mill wastewater (OMW) is a major issue in olive oil manufacturing. Although researchers have pointed out the potential of white-rot fungus in dephenolizing OMW, the results available in the literature mainly concern pretreated (sterilized) OMW. This paper deals with the reduction of polyphenols content in untreated OMW by means of a white-rot fungus, Pleurotus ostreatus. Dephenolization was performed both in an airlift bioreactor and in aerated flasks. The process was carried out under controlled non-sterile conditions, with different operating configurations (batch, continuous, biomass recycling) representative of potential industrial operations. Total organic carbon, polyphenols concentration, phenol oxidase activity, dissolved oxygen concentration, oxygen consumption rate, and pH were measured during every run. Tests were carried out with or without added nutrients (potato starch and potato dextrose) and laccases inducers (i.e., CuSO4). OMW endogenous microorganisms were competing with P. ostreatus for oxygen during simultaneous fermentation. Dephenolization of raw OMW by P. ostreatus under single batch was as large as 70%. Dephenolization was still extensive even when biomass was recycled up to six times. OMW pre-aeration had to be provided under continuous operation to avoid oxygen consumption by endogenous microorganisms that might spoil the process. The role of laccases in the dephenolization process has been discussed. Dephenolization under batch conditions with biomass recycling and added nutrients proved to be the most effective configuration for OMW polyphenols reduction in industrial plants (42–68% for five cycles).

Effects of liquid properties on the hydrodynamics of gas-liquid systems were investigated in lab-scale bubble column (BC) and internal loop airlift (ILA). Alginate solutions, a glycerol solution and a Boger fluid were adopted to separately address the effects of viscosity and of surface tension for Newtonian fluids, and the effects of relaxation time for Non-Newtonian fluid characterized by approximately constant viscosity (low shear thinning). Hydrodynamic regimes were characterized in terms of overall gas hold-up, gas-liquid mass transfer coefficient, drift-flux and liquid circulation velocity. The superficial gas velocities at the transition between hydrodynamic regimes (homogenous regime – vortical-spiral regime – heterogeneous regime) as a function the liquid viscosity was characterized by a maximum. The same behaviour was observed for the maximum stable gas hold-up and gas-liquid mass transfer coefficient in BC. Viscosity enhances homogeneous regime stability for viscosity < 4.25 mPa•s, in BC, and viscosity < 7.68 mPa•s, in ILA. For Non-Newtonian fluids the transition velocity increases with liquid elasticity. The stabilization mechanism related to the relaxation time of Boger fluids has been discussed.

An assessment of the growth kinetics of acidogenic cells of Clostridium acetobutylicum DSM 792 is reported in the paper. Tests were carried out in a continuous stirred tank reactor under controlled conditions adopting a complex medium supplemented with lactose as carbon source to mimic cheese whey. The effects of acids (acetic and butyric), solvents (acetone, ethanol and butanol) and pH on the growth rate of acidogenic cells were assessed. The conversion process was characterized under steady-state conditions in terms of concentration of lactose, cells, acids, total organic carbon and pH. The growth kinetics was expressed by means of a multiple product inhibition and interacting model including a novel formulation to account for the role of pH. The model has the potential to predict microorganism growth rate under a broad interval of operating conditions, even those typical of solvents production.

This paper reports on the assessment of two enzyme-based processes for the conversion of synthetic dyes. A crude laccase mixture from Pleurotus ostreatus was immobilised on EUPERGIT C 250L©, an acrylic resin with epoxy functionalities. This biocatalyst was used in the conversion of the anthraquinonic dye Remazol brilliant blue R. Two different fixed bed reactors were used to assay the solid biocatalyst activity and to characterize the dye conversion kinetics. The immobilisation procedure was optimized providing a maximum immobilisation yield of 7% of the initial laccase activity in solution. The kinetics of dye conversion was in line with a product-inhibited kinetic model. The biocatalyst underwent moderate deactivation along with conversion. The kinetic models were implemented to describe dye conversion in a continuous fixed bed reactor (CFBR), operated with immobilised laccases, and in a stirred tank reactor (STR), operated with free laccases. The CFBR option enables the remediation of a wastewater volume larger than the one processed in the STR under comparable operating conditions. The better performance of CFBR results from the balanced effect of an improved stability of immobilised laccases and of a loss of activity following immobilisation.

This work reports the results of a series of tests on the specific butanol production rate by Clostridium acetobutylicum continuous cultures. The tests were carried out using lactose as carbon source to mimic cheese-whey. A continuous stirred tank reactor equipped with a microfiltration unit was used. The dilution rate (D) ranged between 0.02 and 0.15 h−1 and the ratio R of the permeate stream rate to the stream fed to the reactor ranged between 14% and 95%. For each set of D and R values, the continuous cultures were characterized in terms of concentration of cells, acids and solvents. Results were processed to assess the concentration of acidogenic cells, solventogenic cells, spores and the specific butanol production rate. The max butanol productivity was 0.5 g L−1 h−1 at D = 0.1 h−1 and R = 95%. The butanol productivity referred to solventogenic cells was expressed as a function of concentration of lactose, acids and butanol.

A biomimetic strategy for CO2 capture was recently proposed and extensively reviewed in the literature [1]. It is based on the use of Carbonic Anhydrase (CA) as biocatalyst to increase CO2 absorption rate in aqueous solutions. Kinetic characterization of CA forms is one of the key issues for the design of the absorption unit. The kinetics should be assessed under operating conditions as close as possible to those used in industrial processes. However, the CA kinetic assessment asks for rapid mixing techniques (e.g. stopped flow) because of the exceptional turnover (ranging between 104 and 106 s-1). Indirect measurement strategies of the CO2 absorption rate under controlled conditions of mass transfer rate were used by several authors [2, 3]. These strategy allowed to investigate the effects of temperature, solvent ionic strength and pH over wide ranges. The present contribution concerns the characterization of a protein mixture containing recombinant CA. The indirect measurements strategy was based on time-resolved measurements of gas pressure decay in a batch stirred reactor (Figure 1). The absorption rate of pure CO2 into carbonate solutions was assessed by processing the pressure timeseries. The aim of the study were: - t he assessment of the second order kinetic constant kcat/Km at 25 and 40°C. Initial carbonate concentration and carbonate conversion were changed to simulate actual solvent composition in CO2 capture units. - the protein mixture characterization in terms of long term stability at temperature between 40 and 70°C. - the role of precipitated enzyme aggregates that may be observed at enzyme concentrations larger that its solubility limit in the selected solvent Concerning the latter aim, it has been inspired by two evidences: if the time scale of enzyme precipitation is slower than that of denaturation of its structure, the protein aggregates are made by active enzymes; the contribution of dissolved CA at concentration lower than 100 mg/L is not satisfactory [4]. Hence, it is worth to try to control the activity of CA precipitated aggregates as a reliable alternative to increase enzyme loading in the reactor. Preliminary results showed that the CA kcat/Km ratio was 0.9 L/(mg s) at 25°C in NaHCO3/Na2CO3 buffer at pH 9.6. This value is similar to those assessed in previous works for bovine CA and larger than that assessed for the thermostable recombinant CA from the bacterium Sulphurhydrogenibium sp. YO3AOP1 [2]

The biomimetic CO2 capture strategy is based on the enhancement of CO2 absorption rate into aqueous solvents catalyzed by the enzyme Carbonic Anhydrase (CA). This strategy may provide an environmental friendly alternative to the amine-based CO2 capture process. Key issues for the development of biomimetic CCS process include the development of the biocatalysts to be confined into the absorption unit, immobilizing the enzyme is the most promising option. This issue is a mandatory requirement in the case of both solvent regeneration (aimed at CO2 storage) and of solvent processing (aimed at CO2 utilization). The design of the absorption unit must ensure absorption enhancement by the heterogeneous biocatalyst. The immobilization of CA on fines and the occurrence of biocatalysis at the gas-liquid interface may provide absorption rate enhancement [1, 2]. The present contribution reports the theoretical study of a slurry absorption unit for CO2 capture into K2CO3 aqueous solvent assisted by CA. Main assumptions were: i) the absorption unit described according to the tanks-in-series model; ii) counter-current flow of gas and liquid streams; iii) CO2 chemical absorption described according to the two films theory; iv) slurry phase modelled according to the pseudo-homogeneous approach [3]. The model was based on: a) mass balances on the dissolved species CO2, HCO3 - and CO3 2-; b) charge balance and solvent dissociation equilibrium condition extended to both the liquid boundary layer and the liquid bulk; c) the overall mass balance on carbon. For fine dispersed biocatalysts, the model included an analytical relation between the reactant concentrations, the Thiele modulus and the effectiveness factor of the biocatalyst particles . A staged bubble column was selected as potential configuration for counter-current gas-liquid equipment able to handle slurry phase. The mass transfer coefficient were retrieved from the literature [4]. Model computation was performed using the commercial software COMSOL Multiphysics. Results pointed out an increase of the CO2 capture in the presence of dissolved CA. The concentration profiles for CO2 in the liquid boundary layer highlighted the beneficial effect of enzyme catalysis on CO2 absorption rate even though the advantages were strongly limited by the enzyme solubility (about 100 mg/L). Simulations carried out for CA immobilized on fines showed that absorption rate enhancement increased with respect to that obtained by homogeneous enzyme catalysis. The sensitivity analysis to the CA turnover number was carried out to take into account its spectrum depending on the primary CA form and on the immobilization technique.

Novel post-combustion treatments include carbon capture and sequestration processes based on biomimetic strategies. These strategies include CO2 absorption into aqueous solution assisted by enzyme catalysis. Carbonic anhydrase catalyses CO2 hydration and it has been proposed as industrial biocatalyst for Carbon Capture and Storage (CCS) post-combustion processes. The recombinant enzyme SspCA, isolated from the thermophile bacterium Sulfurhydrogenibium sp. was characterized as potential biocatalyst for CO2 capture processes based on regenerative absorption into alkaline solutions. This paper reports results of a preliminary study focused on the immobilization of carbonic anhydrase on granular solids to improve biocatalyst stability at the typical operating conditions of the CO2 absorption processes. This study included the selection of solid supports and of the immobilization technique. Granular fine silica particles were adopted as enzyme carriers. Two classes of solids were investigated: 120 and 9 micronm d50 diameter. Bovine carbonic anhydrase was used as enzyme model in order to optimize immobilization procedure and activity assay for immobilized carbonic anhydrase. Enzyme-carrier covalent bonding was adopted as immobilization technique. In particular, solids were silanized and activated with respect to the enzyme by means of glutaraldehyde branches. For 120 micronm particles, the maximum enzyme loading resulted 40.3 mg of bovine CA per g of solids and the maximum yield resulted about 66.5% for initial CA concentration between 1.4 and 4 mg/mL. Copyright �� 2013, AIDIC Servizi S.r.l.

This research work reports on the feasibility of bio-butanol production by fermentation of cheese whey in a continuous packed bed reactor (PBR). The anaerobic solventogenic bacterium Clostridium acetobutylicum DSM 792 was adopted for the fermentation processes and commercial cheese whey powder was adopted as substrate. The fermentation plant consisted of a PBR, liquid pumps, a thermostatic unit, and a pH control unit. The PBR was a 4 cm ID, 16 cm high glass tube with a 8 cm bed of 3 mm Tygon rings, as carriers. The pH ranged between 4.5 and 5.5, the dilution rate (D) between 0.4 h-1 and 0.64 h-1. The PBR feedstock was a solution of deproteinized cheese whey powder. Results show that the best performance (butanol productivity 2.66 g/Lh, butanol concentration 4.93 g/L, butanol yield 0.26 g/g, butanol selectivity of the overall solvents production 82%w) was at D=0.54 h-1. Copyright �� 2013, AIDIC Servizi S.r.l.

An assessment of both the growth and the metabolism of acidogenic cells Clostridium acetobutylicum DSM 792 is reported in the paper. Tests were carried out in a CSTR under controlled pH conditions. Cultures were carried out using a semi-synthetic medium supplemented with lactose as carbon source. Acids and solvents, that represent products of the ABE process, have been purposely added in controlled amounts to the culture medium to investigate their effects on the product yields. The mass fractional yield of biomass and products were expressed as a function of the specific growth rate taking into account the Pirt model. The maximum ATP yield and the maintenance resulted 29.1 g DM /mol ATP and 0.012 mol ATP /g DM h, respectively. Quantitative features of the C. acetobutylicum growth model were in good agreement with experimental results. The model proposes as a tool to estimate the mass fractional yield even for fermentations carried out under conditions typical of the solventogenesis.

A mathematical model of an aerobic biofilm reactor is presented to investigate the bifurcational patterns and the dynamical behavior of the reactor as a function of different key operating parameters. Suspended cells and biofilm are assumed to grow according to double limiting kinetics with phenol inhibition (carbon source) and oxygen limitation. The model presented by Russo et al. is extended to embody key features of the phenomenology of the granular-supported biofilm: biofilm growth and detachment, gas-liquid oxygen transport, phenol, and oxygen uptake by both suspended and immobilized cells, and substrate diffusion into the biofilm. Steady-state conditions and stability, and local dynamic behavior have been characterized. The multiplicity of steady states and their stability depend on key operating parameter values (dilution rate, gas-liquid mass transfer coefficient, biofilm detachment rate, and inlet substrate concentration). Small changes in the operating conditions may be coupled with a drastic change of the steady-state scenario with transcritical and saddle-node bifurcations. The relevance of concentration profiles establishing within the biofilm is also addressed. When the oxygen level in the liquid phase is

Microorganism kinetic growth characterized by substrate inhibition was investigated by means of a continuous stirred tank reactor equipped with a feedback controller of the medium feeding flow rate. The aerobic growth of Pseudomonas sp. OX1 with phenol as carbon/energy source was adopted as a case study to test a new control strategy using dissolved oxygen concentration as a state variable. The controller was successful in steadily operating bioconversion under intrinsically unstable conditions. A simple model of the controlled system was proposed to set the feedback controller. The specific growth rate of Pseudomonas sp. OX1 was successfully described by means of the Haldane model. The regression of the experimental data yielded μM = 0.26 h−1, KPh = 5 × 10−3 g/L and KI = 0.2 g/L. The biomass-to-substrate fractional yield as a function of the specific growth rate did not change moving from substrate-inhibited to substrate-deficient state. The data was modelled according to the Pirt model: m = 1.7 × 10−2 g/(g h), Y X / Ph Th = 1.3 g/g . The specific growth rates calculated for batch and continuous growth were compared.

Dyes adsorption on granular particles of lyophilised Cunninghamella elegans was characterized in terms of adsorption isotherm and kinetics. The study refers to dyes of an acid bath for wool: Acid Blue 62, Acid Red 266 and Acid Yellow 49. The dye concentration in model solutions – containing a single dye or the three dyes all together in order to mimic the wastewater – was increased up to about 500 mg/L. Tests showed that the maximum adsorption capacity of the biomass ranges between 300 and 600 mgdye/gDM. Mutual interferences among dyes caused the reduction of the adsorption capacity of the biomass towards the model wastewater. An experimental procedure for the assessment of biosorption kinetics was developed in order to control the effects of the interphase mass transfer on the biosorption rate. The biosorption kinetics were described by both pseudo-first order and pseudo-second order models, depending on the saturation level of the sorbent, and was characterized by a time scale of 1–10 min. The role of the molecular structures of the dyes was discussed. In particular, both kinetics and equilibrium tests confirm that the biomass is more selective towards AR266, probably for the high negative charge density of the –CF3 functional group that can interact with –NHx active sites of the biomass.

In this study, we report on a butanol production process by immobilized Clostridium acetobutylicum in a continuous packed bed reactor (PBR) using Tygon rings as a carrier. The medium was a solution of lactose (15-30 g/L) and yeast extract (3 g/L) to emulate the cheese whey, an abundant lactose-rich wastewater. The reactor was operated under controlled conditions with respect to the pH and to the dilution rate. The pH and the dilution rate ranged between 4 and 5, the dilution rate between 0.54 and 2.4 h(-1) (2.5 times the maximum specific growth rate assessed for suspended cells). The optimal performance of the reactor was recorded at a dilution rate of 0.97 h(-1): the butanol productivity was 4.4 g/Lh and the selectivity of solvent in butanol was 88%(w).

A dynamical model of a continuous biofilm reactor is presented. The reactor consists of a three-phase internal loop airlift operated continuously with respect to the liquid and gaseous phases, and batchwise with respect to the immobilized cells. The model has been applied to the conversion of phenol by means of immobilized cells of Pseudomonas sp. OX1 whose metabolic activity was previously characterized (Viggiani, A., Olivieri, G., Siani, L., Di Donato, A., Marzocchella, A., Salatino, P., Barbieri, P., Galli, E., 2006. An airlift biofilm reactor for the biodegradation of phenol by Pseudomonas stutzeri OX1. Journal of Biotechnology 123, 464-477). The model embodies the key processes relevant to the reactor performance, with a particular emphasis on the role of biofilm detachment promoted by the fluidized state. Results indicate that a finite loading of free cells establishes even under operating conditions that would promote wash out of the suspended biophase. The co-operative/competitive effects of free cells and immobilized biofilm result in rich bifurcational patterns of the steady state solutions of the governing equations, which have been investigated in the phase plane of the process parameters. Direct simulation under selected operating conditions confirms the importance of the dynamical equilibrium establishing between the immobilized and the suspended biophase and highlights the effect of the initial value of the biofilm loading on the dynamical pattern.

The huge emission of greenhouse gases from fossil-fuelled power plants is emphasizing the need for efficient Carbon Capture and Storage (CCS) technologies. The biomimetic CO2 absorption in aqueous solutions has been recently investigated as a promising innovative alternative for post-combustion CCS. The carbonic anhydrase (CA) - a broad group of ubiquitous enzymes - may catalyse the CO2 hydration reaction and then to promote CO2 absorption rate into aqueous solutions. Nevertheless the research on this issue is quite active, the reliable designing of absorption units still requires more details. The present study proposes the design of a random packing absorption column operated with alkaline solvents supplied with CA. The height of the packed bed to fulfil the 80% of CO2 abatement from a flue gas stream was as large as 15-20 m. A comprehensive discussion of effects of operating conditions and of CA features on unit performance is reported.

The concerns regarding energy and environmental issues have revalued the interest in the use of biomass as a renewable energy source. According to this scenario, studies have bloomed in the scientific literature regarding the production of energy vectors from a wide spectrum of biomass. Solvent-producing clostridia could produce acetone, butanol, and ethanol (ABE) from several biomasses such as palm oil waste (Lee et al., 1995), agro-industrial waste(water)s (Raganati et al., 2013), and agricultural crops (Qureshi et al., 2001). The remarkable features of the butanol – e.g. hydrophobicity, high energy density, storage and transportation consistent with current structures – make this alcohol a potential substitute and/or supplement of gasoline (Table 1) (Cascone, 2008; Masiero et al., 2011).