This review explores the impact of the COVID-19 pandemic on the renewable energy (RE) sector, especially in countries with the highest RE capacities, e.g., the USA, China, India, and the EU. It highlights stimulus packages put in place by governments worldwide and their sustainability to cushion the RE sector. Commissioning of RE projects has stalled due to lack of funding allocation and interruptions in the supply of equipment and components due to lockdown measures. Despite the need to fund COVID-19 vaccination programs and other related health services, the world must not neglect other sectors of the economy, creating more problems, such as worsening the climate change situation in the long run. This review aims to present the information needed to sustain future energy during the COVID-19 global pandemic.

This work is aimed at analyzing demand dynamics for hydrocarbon fuels from March 2020 and developing a forecast model for the near future. Based on the method of artificial neural network with feedforward and backpropagation learning, a model is proposed for forecasting oil demand and passenger mobility during a pandemic for the United States, Russia, and India. The results of the calculations showed that road and air transport dynamics strongly depend on the application of measures to limit and ban and the level of COVID-19 incidence in a country. The proposed method can be used to make forecasts during pandemics and unforeseen situations to regulate the price policy for hydrocarbon fuels and the safety of passenger traffic in the future.

A comprehensive description of the barium sulfate precipitation process in a wide range of supersaturations is presented. By using an additive to stabilize the particles, the decoupling of the primary from the secondary processes, as well as the agglomeration from aggregation was possible. By being able to study the two processes independently, a model describing the agglomeration of barium sulfate in the range of high supersaturations was validated experimentally for the first time. The proposed model has proven to describe the experiments with a high degree of accuracy in the whole range of supersaturations investigated. Additionally, by comparing agglomeration kernels of various complexity, ranges where simplifications are possible were identified, thus enabling the future development of models with better performance.

The partial molar volume of lysozyme and bovine serum albumin in aqueous solutions at different pH values and in aqueous solutions containing sodium chloride, ammonium chloride, sodium sulfate, or ammonium sulfate at different concentrations at pH 7.0 was investigated experimentally at 298.15 K and 1 bar. It was found that the influence of the pH value and the salts on the partial molar volume of the proteins is small, but trends were measurable. Furthermore, the partial molar volume of lysozyme in pure water at different pH values and in aqueous solutions with different sodium chloride concentrations at pH 7.0 was predicted by molecular simulations. The predictions are in good agreement with the experimental data.

For the first time, a two-stage decision support framework for equipment selection, applied to biomass separation, is presented. In the first stage, the framework evaluates from a number of equipment based on the process requirements and outputs only those that offer a technically feasible separation. In the second stage, the analytic hierarchy process is applied for performing a multicriteria decision analysis to select amongst the feasible equipment based on separation performance and energy consumption criteria. This approach systematically considers the relative importance of those different alternatives and selection criteria by pairwise comparisons. The output of the framework is an overall ranking of equipment as well as a sensitivity analysis of the results for different weighting of the criteria. These results can be used to equip practitioners in the field of bioseparations with a tool for making more consistent and better-informed equipment selection decisions.

A common focus of fermentation process optimization is the product titer. Different strategies to boost fermentation titer target whole-cell biocatalyst selection, process control, and medium composition. Working at higher product concentrations reduces the water that needs to be removed in the case of aqueous systems and, therefore, lowers the cost of downstream separation and purification. Different approaches to achieve higher titer in fermentation are examined. Energy and water consumption data collected from different Cargill fermentation plants, i.e., ethanol, lactic acid, and 2-keto--gulonic acid, confirm that improvements in fermentation titer play a decisive role in downstream economics and environmental footprint.

Analyses and simulations of a lab-scale device for determining floc strength are presented together with simulations of two different hermetic disc-stack centrifuge inlets. Two methods for determining the turbulent shear stresses on flocs in hermetic centrifuge inlets are described. A model for the average shear rate in a hermetic centrifuge inlet is proposed. A correlation for estimating the floc size of the centrifuge feed after passing the high-shear zone of the inlet is derived.

Rheological characterization of the solids phase in bio-industry disc-stack centrifuges is considered. Three discriminatory properties of the solids phase are investigated, namely, the particle settling velocity, the angle of repose, and the solids phase viscosity. The solids phase produced in disc-stack centrifuges in the food or biopharmaceutical industry possesses both liquid-like and solid-like properties which can be quantified by means of these test methods. The resulting rheological characterization can be used for diagnostic purposes in the selection process of industrial centrifuges and for optimization of centrifuge solids handling in biomass processing of suspension systems.

The solid-liquid equilibrium (SLE) in the ternary system 2-keto--gulonic acid (HKGA) + -ascorbic acid (vitamin C) + water was investigated experimentally at temperatures between 276 K and 308 K at ambient pressure, i.e., under conditions that are of particular interest for industrial applications. Phase diagrams with one eutonic point were obtained for all temperatures. The dissociation constant and the solubility constant of vitamin C were determined as a function of temperature. Based on an extended version of the Debye-Hückel theory, a physicochemical model was developed that describes the SLE in the ternary system. The agreement between experimental data and results from the model is excellent.

The chromatographic recovery of monosaccharides and lignin from lignocellulosic hydrolysates was studied at laboratory and pilot scale. A weak cation-exchange resin in sodium form and a water eluent gave good separation efficiency. Scale-dependent phenomena, especially viscous fingering resulting from the large viscosity and density differences between the hydrolysate feed and eluent, were observed. The issue was resolved in the pilot scale with appropriate selection of the flow direction, and a high productivity was achieved at 95 % recovery yield. The pH value of the feed was found to have no effect on the actual separation; however, the resin was significantly less colored at a higher pH value.

The optimization of an organic acid production process downstream of fermentation is presented. Sodium salt solution of the organic acid (Na salt) solution is the product in the industrial fermentation process for the organic acid production and until today, it has not been attempted to directly crystallize/isolate the Na salt under these circumstances. Evaporation crystallization of Na salt directly from the solid-free fermentation broth without purification can be realized with high product purity. Parameters limiting the crystallization/separation process are identified and discussed. The above points are considered as a function of viscosity, crystal size, and product purity. Comparison with the existing process completes this evaluation. The impact on the process design and alternatives are illustrated. The modification of hybrid processes using crystallization also as a purification step is investigated.

Complex streams in bio-based industries require efficient downstream processing units. Simulated moving-bed (SMB) chromatography is known to improve process efficiency by reducing resin and buffer requirement, but it can be further enhanced by technology hybridization. In the current experiments, an SMB system has been integrated with a bipolar electrodialysis (BPED) system. SMB purified -aminobutyric acid (GABA) from a clarified fermentation broth while BPED processed the product-containing eluent stream into recyclable eluent and purified product streams. The continuous operation did not result in any impurity accumulation.

Expanded-bed adsorption (EBA) is an efficient downstream technology that enhances the techno-economic potential of bio-based industries. However, application of EBA for bulk biochemicals requires the use of industrial resins. Therefore, two cation exchangers, namely, gel-type CS16GC and porous IRC747, were tested to purify -aminobutyric acid (GABA) from unclarified fermentation broth. Experiments compared the impact of gel-type and macroporous resin properties on the EBA process performance. As an outcome, the gel-type resin exhibited higher GABA binding capacity of compared to that of macroporous resin. This was due to improved hydrodynamics and uniform flow distribution in the case of gel-type resin. Further, CS16GC effectively removed ≥ 99 % of impurities and achieved ≥ 97 % GABA yield.

Small hydrocyclones are an attractive technology for biomass separation from fermentation processes. The interactive effect of design parameters on the performance of mini-hydrocyclones is, however, not fully explored and studies are often limited by the challenges in manufacturing such small units. Here, 10-mm mini-hydrocyclones are produced by 3D printing and the impact of spigot diameter, vortex finder diameter and height on separation performance is studied. A central composite rotatable design was adopted to obtain information on the relation between the variables and their influence on concentration ratio and recovery of yeast from a highly diluted system. A Pareto front for separation performance was generated and shown to be suitable to select an optimal design for a set of process constraints.

Wood hydrolysates contain sugars that can be used as feedstock in fermentation processes. For that purpose, the hydrolysate must be concentrated and inhibitors that harm fermentation must be removed. Herein, the integration of these tasks with the recovery of inhibitors is studied. The wood hydrolysate is represented as a mixture of water, xylose, acetic acid, and furfural. Acetic acid and furfural are two frequently occurring inhibitors and valuable chemicals, and thus, their recovery is studied. Furfural is recovered from the vapors by heteroazeotropic distillation. It is shown that this can be achieved without additional energy. The recovery of acetic acid by distillation is also possible, but not attractive. The new process is simulated by using a thermodynamic model based on experimental data.

Chemicals produced using biotechnological methods like fermentation processes are obtained as complex diluted aqueous mixture, which still contains the production organism. Centrifugation is a commonly used technology for biomass separation. By flocculation, the settling velocity of microorganisms can be increased. Here, a laboratory flocculant screening method tailored for the separation of flocculated biomass in a fully hermetic disc stack centrifuge is described. The specific requirements of this process, namely, floc formation, floc stability, sliding behavior in the disc stack, and flowability of the sludge, were transferred to lab scale and validated in pilot tests. The qualitative results of the laboratory screening were in agreement with the processes at industrial scale.

Bio-based industries need efficient downstream solutions to process complex streams. This was addressed through a technology integration approach, where expanded-bed adsorption (EBA) is integrated with simulated moving-bed (SMB) technology. Current work involved adaptation of an SMB apparatus and control principle to implement expanded-bed level control. As an outcome, EBA-SMB technology was successfully applied for purification of -aminobutyric acid (GABA). This resulted in two-fold increase in productivity and a GABA purity ≥ 92 % in one step from unclarified fermentation broth, compared to ≥ 93 % purity in case of clarified broth and packed-bed SMB. These results proved that EBA-SMB technology is able to enhance process efficiency and economics of bioprocesses.

One intention of the PRODIAS (processing diluted aqueous systems) project is to develop and establish a toolbox of innovative and tailored separation technologies applicable to design energy-efficient water removal and product recovery techniques. Within this project, the recovery of -aminobutyric acid (GABA) was investigated. Using both synthetic as well as fermented solutions, reactive extraction of GABA with the solvent di-(2-ethylhexyl)phosphoric acid + isododecane was performed. For back extraction, different mineral acids were examined. Multistage countercurrent reactive extraction using pH adjustments along the stages to increase extraction efficiency as well as back extraction were then run on pilot-plant scale with fermented GABA solutions. The resulting GABA salt from back extraction was finally split by means of bipolar electrodialysis.

In order to close the technology gap between membrane technologies and spray/freeze-drying ideally with a technology that avoids thermal stress to sensitive enzyme solutions, the limits of freeze concentration for this application have been investigated. On laboratory scale it was found that average crystal sizes are > 300 µm despite high viscosity and ice separation is possible up to 42 % solids and > 1000 mms viscosity. No activity loss was observed during concentration. A combination of two-stage freeze concentration with a filter and wash column for ice liquid separation in an integrated setup with ultrafiltration has the greatest potential and was shown to be economically feasible in three out of four cases studied.

A sharp reduction of the energy consumption of a high-speed centrifuge was obtained following several design changes, while still maintaining separation capacity. This reduction is necessary for making some applications commercially interesting, e.g., large-volume flow rates in the growing biopharma industry. The reduction was achieved by modifying flow paths of the rotor, i.e., reducing the outlet radius to minimize angular momentum losses and lowering the pressure drop of the internal flow. Further, removing air outside the rotor reduced aerodynamic losses, and using a direct drive motor, losses encountered with gear or belt drives were eliminated. This way, an average energy reduction of 50 % was obtained.

The identification of the main flow regime boundaries in bubble columns is essential since the degrees of mixing and mass and heat transfer vary with the flow regime. In this work, a new statistical parameter was extracted from the time series of the cross-sectional averaged gas holdup. The measurements were performed in bubble columns by means of conductivity wire-mesh sensors at very high sampling frequency. The columns were operated with an air/deionized water system under ambient conditions. As a flow regime indicator, a new dimensionless statistical parameter called "relative maximum number of visits in a region" was introduced. This new parameter is a function of the difference between the maximum numbers of visits in a region, calculated from two different division schemes of the signal range.