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Sustainable recycling of lignocellulosic biomass includes utilization of all carbohydrates present in its hydrolysates. Since wheat straw is a xylose-rich raw material, utilization of xylose from obtained liquid part (liquor) of hydrolysates improves overall bioprocess efficiency. In this work, dilute acid pre-treatment of wheat straw was performed in high-pressure reactor at different temperatures (160 °C – 200 °C), residence times (1 min – 10 min), and acids (H2SO4 and H3PO4) concentrations. During dilute acid pre-treatment, hemicellulose is degraded to pentose sugars that cannot be used by industrial ethanol- producing yeasts. Therefore, genetically engineered Saccharomyces cerevisiae strain that can utilize xylose was used. Fermentations were performed on different xylose-rich liquor wheat straw hydrolysates in shake-flasks and in horizontal rotating tubular bioreactor. The efficiency of fermentations carried out in shake flasks using xylose- rich liquor wheat straw hydrolysates were in the range of 19.61 – 74.51 %. However, the maximum bioprocess efficiency (88.24 %) was observed during fermentation in the HRTB on the liquor wheat straw hydrolysate obtained by pre-treatment with 2 % w/w phosphoric acid. This work is licensed under a Creative Commons Attribution 4.0 International License.

BACKGROUND: Sugar beet pulp (SBP) is a promising feedstock for the production of 2nd generation biofuels, but efficient enzymatic hydrolysis remains a key challenge; therefore, new process designs and/or bioreactor designs are crucial to overcome this hurdle. In this regard, horizontal rotating tubular bioreactors (HRTB) offer the advantage of high substrate loadings while minimizing the space and energy demand compared with conventional stirred tank reactors. Here, a statistical approach is used to optimize the hydrolysis of sugar beet pulp in laboratory experiments, and it is shown that such a process can be implemented in a HRTB. RESULTS: Using the design of experiments (DOE) method, the reaction conditions of four commercial enzyme mixtures (Ultrazym AFP‐L, Viscozyme L, Pectinase and Cellulase) was optimized for the degradation of SBP in small‐scale experiments. Using Ultrazym AFP‐L as the most efficient mixture, a 10 L scale conversion was performed in a HRTB. At a substrate loading of 135 g L⁻¹ and optimized conversion parameters (enzyme load, pH and rotating speed of the reactor), 0.525 W dm⁻³ were needed to achieve solubilisation of 30% of the total mass of initial SBP after 24 h. CONCLUSION: DOE was found to be an easy‐to‐apply method that allowed optimizing the conditions for enzymatic hydrolysis of SBP, resulting in a higher sugar yield. The results could be transferred to an HRTB, which is a suitable system for enzymatic conversion and efficient saccharification of semi‐solid or solid substrates with relatively low energy consumption. © 2016 Society of Chemical Industry

The conventional ethanol fermentation is a typically product inhibiting process leading to low productivity and yield. This problem can be alleviated by continuous removal of ethanol during the fermentation. In-situ ethanol separation increases the productivity of the fermentation and reduces the amount of water added to the distillation feed stream. In this study, a novel vacuum assisted in-situ gas striping recovery system for ethanol removal from a column bioreactor was tested. With the aim to increase the ethanol production from sugar beet pulp we apply a three step process comprising the hydrolysation, fermentation and in-situ gas stripping with a vacuum assisted recovery system. Following a statistical analysis, the recycling and vacuum ratio had the strongest impact on ethanol production. Using Pareto charts, we showed that the recycling ratio is the most important variable affecting the hydrolysation step, and that the pressure ratio is the most important variable affecting the vacuum stripping step. The herein established mathematical models that describe these hydrolysation/fermentation processes can be further used for the ethanol production optimisation. Additionally, these results can be utilised for the development of an integrated simultaneous fermentation and in-situ gas striping vacuum distillation process. Future trends of this research may also address the scale-up for industrial bioethanol production.

In this research, the impact of chemical agents on the growth of Euglena gracilis and contaminants (S. cerevisiae and B. subtilis) in different cultivation media was studied. E. gracilis was cultivated on modified Hutner and complex medium in Erlenmeyer flasks and a stirred tank bioreactor. H2O2 and antimycin were used as suppressors of contaminant growth activities during algae cultivation. The use of antimycin as a chemical suppressor of contaminants is not recommendable because of its significant impact on the E. gracilis growth. At a H2O2 concentration of 5 mg L-1 contaminant growth activities were almost completely suppressed. In these conditions, E. gracilis is capable to grow, but a further increase of H2O2 concentration is related to significant reduction of algae growth. H2O2 as a suppressor of contaminants has great potential for industrial application, but its optimal concentration for a particular bioprocess has to be determined in order to obtain the maximal bioprocess efficiency.

The adaptation of commercially available ion- selective electrodes (ISEs) for use in wastewater matrices was demonstrated using multivariate analysis and optimization with the Microsoft Excel Solver tool. The electrodes were characterized in pure analyte solutions, and their parameters were estimated using multivariate analysis and Solver optimization. The ammonium, nitrate, and nitrite ions were measured in model systems that were designed to simulate wastewater. The accuracy of the measurements (95.3% - 101.0%) was satisfactory for the determination of ammonium, nitrate, and nitrite in complex matrices. The adapted ISEs were then successfully used for bioprocess (synthetic wastewater treatment) dynamics and efficiency studies in a horizontal rotating tubular bioreactor (HRTB) by monitoring the concentrations of the substrates and intermediates in the samples collected from the bioreactor. The simultaneous determination of ammonium, nitrate, and nitrite in the samples through the use of adapted ISEs considerably shortened the time required for ion determination.

Fossil fuels are still major energy sources, but the search for renewable energy sources has been encouraged. Bioethanol has been recognized as an alternative to fossil fuels and nowadays it represents more than 90% of the global biofuel production. Bioethanol production from raw sugar beet cossettes as a semi-solid substrate was studied. The study was carried out in the horizontal rotating tubular bioreactor (HRTB) with Saccharomyces cerevisiae as a microbial production strain. The impact of different combinations of HRTB operational parameters such as, rotation speed (5-15 min(-1)), rotation type [constant or interval (3-15 min h(-1))] and working volume (ratio V (W)/V (T) = 0.2-0.7) on the bioethanol production was examined. In this study, the highest bioprocess efficiency parameters ( = 0.47 g g(-1), E = 87.36% and Pr = 0.618 g L-1 h(-1)) were observed at 0.20 V (W)/V (T), interval rotation of 12 min h(-1) and rotation speed of 15 min(-1). It has to be pointed out that bioethanol production efficiency in the HRTB was on the similar level as observed by bioethanol production from the raw sugar beet juice. Naturally present microorganisms of sugar beet could have a significant impact on bioethanol production. Higher yeast inoculation rate could reduce contaminant activities and, consequently, the bioethanol production efficiency would be improved.

In this work, the heterotrophic cultivation of bacterium Paracoccus denitrificans has been studied in a horizontal rotating tubular bioreactor (HRTB).After development of a microbial biofilm on the inner surface of the HRTB, conditions for one-step removal of acetate and ammonium ion were created. The effect of bioreactor process parameters [medium inflow rate (F) and bioreactor rotation speed (n)] on the bioprocess dynamics in the HRTB was studied. Nitrite and nitrogen oxides (NO and N_2O) were detected as intermediates of ammonium ion degradation. The biofilm thickness and the nitrite concentration were gradually reduced with increase of bioreactor rotation speed when the medium inflow rate was in the range of 0.5– 1.5 l h^– 1. Further increase of inflow rate (2.0– 2.5 l h^– 1) did not have a significant effect on the biofilm thickness and nitrite concentration along the HRTB. Complete acetate consumption was observed when the inflow rate was in the range of 0.5– 1.5 l h^– 1 at all bioreactor rotation speeds. Significant pH gradient (cca 1 pH unit) along the HRTB was only observed at the highest inflow rate (2.5 l h^– 1). The results have clearly shown that acetate and ammonium ion removal by P. denitificans can be successfully conducted in a HRTB as a one-step process.

BacteriumParacoccus denitrificansis capable to obtain metabolic energy by oxidation of ammonia (chemolitotrophic metabolism) and organic compounds (chemoorganotrophic or heterotrophic metabolism). It can also perform nitrate and nitrite respiration. When cultivated in certain conditions P. denitrificans can conduct the complete transformation of ammonia into gaseous nitrogen and consequently the whole nitrogen removal process can be carried out in one step. These characteristics make it suitable for successful treatment of wastewater with high nitrogen content. In this work the heterotrophic cultivation of P. denitrificans was studied in continuous stirred tank reactor (CSTR) and in horizontal rotating tubular bioreactor (HRTB). Bioprocess dynamics, efficiency and stability in both bioreactors were examined at different dilution rates (D = 0.0333‐0.1667 h � 1 ). In both cases, bioprocess dynamics was monitored by the analysis of biomass, substrate and metabolites concentrations in the liqiud outflow. The bioprocess efficiencyand stability was much higher in HRTB than in CSTR. Advantages of HRTB over CSTR were more obvious at higher dilution rates as a consequence of bacterial biofilm formation on the inner surface of HRTB that enabled better biomass retention. # 2006 Elsevier Ltd. All rights reserved.

The performance of a horizontal rotating tubular bioreactor (HRTB) was investigated with a biological system under non-sterile conditions. A spontaneously developed microbial culture was cultivated in a simple glucose/yeast extract medium. A fermentative bioconversion was examined by different combinations of process parameters (bioreactor rotation speed 5 - 30 min^-1 and medium inflow rate 1 - 10 litre h^-1). Bioconversion dynamics in HRTB was monitored by withdrawing the samples from five positions along the bioreactor. Investigation in HRTB showed a rapid and an efficient glucose conversion into different products of metabolism. Glucose consumption rate along the HRTB depended on medium inflow rate, while bioreactor rotation speed did not have a significant influence. Complete glucose conversion in HRTB was observed at inflow rates of up to 6.5 litre h^-1. The pH gradient along the HRTB was detected at higher medium inflow rates (6.5 and 10 litre h^-1), but did not significantly influence substrate conversion efficiency. A discussion of its potential use and a comparison of HRTB with other bioreactors are also presented.

In this research heterotrophic cultivation of photosynthetic protist Euglena gracilis was carried out on synthetic (Hutner medium) and complex cultivation media in order to produce -1, 3-glucan (paramylon). For preparation of complex media various industrial by-products (e.g. molasses, corn steep solid, yeast and beef extract) with or without addition of pure compounds [glucose, galactose, fructose, lactose, maltose, sucrose and (NH4)2HPO4] were used. Heterotrophic cultivation of E. gracilis was performed in Erlenmeyer flasks and additionally confirmed during research in the stirred tank bioreactor. The results of this research clearly show that E. gracilis could easily metabolize glucose and fructose (compared to other sugars used in this research) as carbon sources and corn steep solid as complex nitrogen and growth factors source for biomass growth and paramylon synthesis during cultivation in heterotrophic conditions. Furthermore, it was also proved that addition of (NH4)2HPO4 (source of nitrogen and phosphorus), beef extract (source of nitrogen compounds and vitamin B12) or gibberellic acid (plant growth hormone) did not have significant impact on the biomass growth and paramylon synthesis. After optimization of complex medium composition and verification of these results during E. gracilis cultivations in the stirred tank bioreactor it was concluded that medium composed of glucose (20 g/L) and corn steep solid (25 g/L) is the most suitable complex cultivation medium for industrial production of paramylon.

Industrial wastewaters polluted with toxic heavy metals are serious ecological and environmental problem. Therefore, in this study multi-heavy metals (Fe(2+), Cu(2+), Ni(2+) and Zn(2+)) removal process with mixed microbial culture was examined in the horizontal rotating tubular bioreactor (HRTB) by different combinations of process parameters. Hydrodynamic conditions and biomass sorption capacity have main impact on the removal efficiency of heavy metals: Fe(2+) 95.5-79.0%, Ni(2+) 92.7-54.8%, Cu(2+) 87.7-54.9% and Zn(2+) 81.8-38.1%, respectively. On the basis of experimental results, integral mathematical model of removal heavy metals in the HRTB was established. It combines hydrodynamics (mixing), mass transfer and kinetics to define bioprocess conduction in the HRTB. Mixing in the HRTB was described by structured cascade model and metal ion removal by two combined diffusion-adsorption models, respectively. For Langmuir model, average variances between experimental and simulated concentrations of metal ions were in the range of 1.22-10.99 × 10^(-3) and for the Freundlich model 0.12-3.98 × 10^(-3), respectively. On the basis of previous facts, it is clear that developed integral bioprocess model with Freundlich model is more efficient in the prediction of concentration of metal ions in the HRTB. Furthermore, the results obtained also pointed out that the established model is at the same time accurate and robust and therefore it has great potential for use in the scale-up procedure.

Mixed microbial culture was isolated from heavy metal-contaminated ground soils located inside iron, vinyl and cement factory area. Isolated mixed microbial culture was used for the heavy metal ions (Fe2+, Cu2+, Ni2+ and Zn2+) removal process in horizontal rotating tubular bioreactor (HRTB). In this research, the effect of bioreactor process parameters on the bioprocess dynamics in the HRTB was studied. Results of this research have shown that profiles of heavy metals concentration were gradually reduced along HRTB at all combinations of bioreactor process parameters [inflow rates (0.5-2.0 L h^-1) and rotation speed (5-30 min^-1)]. Hydrodynamic conditions and biomass sorption capacity have main impact on the metal ions removal efficiency that was varied in the range of 38.1% to 95.5%. Notable pH gradient (cca 0.7 pH unit) along the HRTB was only observed at the inflow rate of 2.0 L h^-1. On the basis of obtained results, it is clear that medium inflow rate (F) has higher impact on the heavy metal removal process than bioreactor rotation speed (n) due to the fact that increase of inflow rate was related to the reduction of equilibrium time for all examined metal ions. Furthermore, equilibrium times for all metal ions are significantly shorter than medium residence times at all examined combinations of bioreactor process parameters. The main impact on the biofilm sorption capacity has covalent index of metal ions and biofilm volumetric density. The sorption capacity of suspended microbial biomass is closely related to its concentration. Results of this research have also shown that the removal of heavy metals ion can be successfully conducted in an HRTB as a one-step process.

The aim of this work was to investigate the possibility to conduct continuous aerobic bioprocess in a horizontal rotating tubular bioreactor (HRTB). Aerobic oxidation of acetate by the action of a mixed microbial culture was chosen as a model process. The microbial culture was not only grown in a suspension but also in the form of biofilm on the interior surface of HRTB. Efficiency of the bioprocess was monitored by determination of the acetate concentration and chemical oxygen demand (COD) along HRTB. While acetate inlet concentration and feeding rate influenced efficiency of acetate oxidation significantly, the bioreactor rotation speed did not influence the bioprocess dynamics significantly. Gradients of acetate concentration and pH along HRTB were more pronounced at lower feeding rates. Volumetric load of acetate proved to be the most significant parameter. High volumetric loads (above 2 g acetate l^-1 h^-1) gave poor acetate oxidation efficiency (only 17 to 50%). When volumetric load was in the range of 0.60-1.75 g acetate l^-1 h^-1, acetate oxidation efficiency was 50-75%. At lower volumetric loads (0.14-0.58 g acetate l^-1 h^-1), complete acetate consumption was achieved. On the basis of obtained results, it can be concluded that HRTB is suitable for conducting the aerobic continuous bioprocesses

A horizontal rotating tubular bioreactor (HRTB) is a plug flow bioreactor whose interior is provided with O-ring-shaped partition walls that serve as carriers for microbial biomass. During this investigation, microbial biomass was grown in suspension and on the bioreactor inner surface as a microbial biofilm with average mass that was considerably higher than suspended biomass. The dynamics of bioprocess in HRTB was studied by different combinations of process parameters (bioreactor rotation speed and mean residence time) and it was monitored by withdrawing the samples from five positions along the bioreactor. During this investigation it was also observed that mean residence time had a more pronounced effect on the bioprocess dynamics than bioreactor rotation speed. For the description of bioprocess kinetics in HRTB an unstructured kinetic model was established that defines biomass growth, product formations and substrate consumption rate by using a modified Monod (Levenspiel) model. This kinetic model defines changes in suspension and in microbial biofilm, and it shows relatively good agreement with experimental data.

A horizontal rotating tubular bioreactor (HRTB) is designed as the combination of a thin-layer bioreactor and a biodisc reactor. The investigation of mixing in HRTB was done by the temperature step method in a wide range of process conditions [residence time (t_Z = 3600 - 36000 s) and bioreactor rotation speed (n = 0.083 - 0.917 s^-1)]. In all experiments heat losses were detected. A mathematical model based on tank in series concept was developed to described the mixing in HRTB - a spiral flow model (SFM) which has incorporated heat losses. However, the simulations of SFM could be used for calculation of temperature response curves for the case when there is no heat losses. These corrected curves were used then to estimate Bodenstein number as a parameter of standard dispersion model (SDM). Obtained Bodenstein numbers were in the range 10 - 17. The simulations had shown that SFM was more capable to describe the mixing in HRTB giving better fitting with experimental measurements then SDM, indicating that mixing pattern in HRTB is to complex to be described with this relatively simple, one-parameter model.

A horizontal rotating tubular bioreactor (HRTB) is a combination of a “thin-layer bioreactor” and a “biodisc” reactor. Its interior is divided by O-ring shaped partition walls. Mixing properties of this new type of the bioreactor were investigated by using a temperature step method. The mixing simulations were done by Runge-Kutta-Fehlberg numerical integration. Adjustable parameters of the “spiral flow” model were optimised by Monte-Carlo method. In this investigation, the structured “spiral flow” model (containing four adjustable parameters) was tested in a wide range of experimental conditions. The results show that the structured “spiral flow” model is capable to describe the mixing in HRTB in the whole range of both bioreactor operational parameters (n and D).

A horizontal rotating tubular bioreactor (HRTB) was designed as a combination of a “thin-layer bioreactor” and a “biodisc” reactor whose interior was divided by O-ring shaped partition walls. For the investigation of mixing in HRTB the temperature step method was applied. Temperature changes in the bioreactor were monitored by six Pt-100 sensors (t 90 response time 0.08 s and resolution 0.002 °C) which were connected with an interface unit and a personal computer. In this work a modified “tank in series” concept was used to establish a mathematical model. The heat balance of the model compartments was established according to the physical model and the “spiral flow” pattern. Numerical integration was done by the Runge-Kutta-Fehlberg method. The mathematical mixing model called “spiral flow” model contained four adjustable parameters (N1, Ni, F cr and F p) and five parameters which characterized the plant and experimental conditions. The “spiral flow” model was capable to describe the mixing in HRTB properly, and its applicability was much better than with the “simple flow” model, presented earlier.