Enzymes – an alternative cleaning agent for membranes in biorefineries?
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The pulp and paper industry is among the world most important industrial sectors. At present it focuses on the production of cellulose pulp fibers and electricity but transforming pulp mills into biorefineries can reduce the use of fossil fuel resources. Adjusting the processes and converting lignocellulosic materials into new environmental friendly products will enable the production of biochemicals, biofuels and advanced materials for a future bio-economy. The widely used thermomechanical pulping (TMP) process produces large quantities of process water containing cellulose, lignin, hemicellulose and extractives. An efficient separation of these wood chemicals is crucial for the pulp biorefinery concept. The pressure-driven membrane processes microfiltration (MF) and ultrafiltration (UF) are high potential technologies for the separation task. In this application MF and UF are confronted with membrane fouling resulting in flux reduction and retention alteration which have a major impact on the separation process economy. Using suitable cleaning agents can recover flux and retention leading to a sustainable process. During the separation of hemicellulose from TMP process water, severe membrane fouling occurred due to the presence of polysaccharides and proteins. A typical cleaning protocol in pulp biorefineries often includes the use of strong alkaline solutions at high temperatures resulting in short membrane life cycles. The use of enzymatic cleaning is environmental friendly and requires less harsh conditions. The aim of this work is to demonstrate the feasibility of cleaning membranes fouled by TMP process water with enzymes to recover flux and retention. Furthermore, the impact of different enzymatic cocktails as cleaning agents to enhance the efficiency of the cleaning step is discussed. Effective membrane cleaning is a key for the transformation of pulp mills into biorefineries. Overall, this presentation will show that enzymes are an alternative to common cleaning agents, resulting in longer membrane life cycle and less environmental impact. (Less)Keywords:
Hemicellulose
Nanofiltration
Ultrafiltration (renal)
Cleaning agent
Membrane Fouling
Pulp mill
Environmentally Friendly
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The development and wide spread acceptance of production facilities for biofuels, biochemicals and biomaterials is an important condition for reducing reliance on limited fossil resources and transitioning towards a global biobased economy. Pulp and paper mills in North America are confronted with high energy prices, high production costs and intense competition from emerging economies and low demand for traditional products. Integrated forest biorefineries (IFBR) have been proposed as a mean to diversify their product streams, increase their revenue and become more sustainable. This is feasible because they have access to forest biomass, an established feedstock supply chain and wood processing experience. In addition, the integration of a biorefinery process that can share existing infrastructure and utilities on the site of pulp mill would significantly lower investment cost and associated risks. Kraft pulping mills are promising receptor processes for a biorefinery because they either possess a prehydrolysis step for extracting hemicelluloses sugars prior to wood pulping or it can be added by retrofit. The extracted hemicelluloses could be subsequently transformed into a wide range of value added products for the receptor mill. To successfully implement hemicelluloses biorefinery, novel processes that are technically and economically feasible are required. It is necessary to identify products that would be profitable, develop processes that are energy efficient and the receptor mill should be able to supply the energy, chemicals and material demands of the biorefinery unit. The objective of this thesis is to develop energy efficient and economically viable hemicelluloses biorefineries for integration into a Kraft pulping process. A dissolving pulp mill was the reference case study. The transformation of hemicellulosic sugars via a chemical and biochemical conversion pathway, with furfural and ethanol as representative products for each pathway was studied. In the first part of this work, the feasibility of concentrating prehydrolysate solution with a reverse osmosis membrane was studied. The concentration step is required to reduce the energy demand of the subsequent conversion processes and the size of process equipments. Reconstituted prehydrolysate solutions containing different concentrations of glucose, xylose acetic acid, syringaldehyde and furfural was used to determine the feasibility of concentrating with a reverse osmosis membrane. The effect of the solution composition and operating conditions (cross flow velocity, temperature and pressure) on the selectivity of the membrane and
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Nanofiltration
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Membrane separation processes have been deployed for downstream applications in biorefineries. This article discusses the challenges of membrane technology in purification of biofuels such as bioethanol, biodiesel and biogas. The significance of membrane technology are discussed towards the fractionation of lignocellulosic biomass for biofuel production. The membrane reactors for biodiesel production were also studied. Limitation with respect to each individual processes on biofuel purification were also reported. The major limitation in membrane separation are membrane fouling and concentration polarization. Membrane engineering and process optimization are the viable tools to enhance the performance of membrane. Recently, inorganic nanofillers has significant control in alteration of polymeric membrane characteristics for the improvement of permeability and selectivity. This article would be an insight for researchers to understand the challenges of biorefinery membrane separation.
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Biorefineries are integrated biotech facilities aiming on full utilization of feedstock for the simultaneous production of e.g. food, biofuels and biochemicals. This presentation will provide an overview supported by case and application studies on the integration of membrane processes into biorefineries. Starting with the pre-treatment of the raw material e.g. wood biomass or starch, micro- (MF) and ultrafiltration (UF) can be integrated in the extraction and polishing of the raw materials followed by the conversion of the raw materials into sugar. These sugars can then be polished by a decanter – UF synergy process and - if diluted - concentrated by reverse osmosis (RO) before fermentation. During fermentation, the biofuels/biochemicals are produced and can be continuously removed by e.g. MF/UF/pervaporation (PV) to prevent product inhibitions from stopping the fermentation. Subsequently, MF, UF, nanofiltration (NF), RO and PV can be used for concentration/polishing of the biofuels/biochemicals. Furthermore, membranes can be used to close the water loop of biorefineries by e.g. using RO for evaporator condensate polishing or membrane bioreactors (MBRs) for the end-of-pipe treatment. Overall this presentation will highlight the opportunities of membrane processes in biorefineries, a key concept in solving future’s energy and environmental challenges. (Less)
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1. Introduction„White biotechnology“- the third and latest wave of biotechnology - is aiming to replace the well-established C2/C3 chemistry based on oil and gas, by biological processes. The backbone of biotechnology is to make the conversion by fermentation which is widely established in the production of antibiotics, enzymes, bioethanol and organic acids. One of the key concepts related to “white biotechnology” are so-called bio-refineries. In analogy to petroleum refineries, bio-refineries are aiming to make full utilization of biomass for the simultaneous production of biofuels, biochemicals, heat and power [1]. Cross-flow membrane processes have established themselves as low-energy and highly selective separation processes in the downstream processing of fermentation products for recovery and purification since the beginning of the 1970’s, and it can be expected that this role will extend into the new concept of bio-refineries. 2. Membrane processes in bio-refineriesThe concept and complexity of a bio-refinery depends upon its feed stock. In sugar-based bio-refineries the feedstock can be directly utilized in the fermentation steps. Starch-based bio-refineries require a hydrolysis step to convert the starch into sugars, while cellulosic based bio-refineries include pre-treatment steps to break down the cellulosic matrix and release the cellulose, lignin and hemicellulose components. Ultrafiltration (UF) can be used as part of the pre-treatment to concentrate hemicellulose and separate it from lignin [2]. Further, after hydrolysis, a decanter – UF synergy process can be used to polish the sugars by removing impurities such as enzymes and starch residues before fermentation, see Figure 1. A feature to this synergy process includes the option to recycle enzymes back to the hydrolysis step. In the case where the sugar streams are very diluted, reverse osmosis (RO) can be used for the concentration of the sugars before the fermentation step. A limiting factor for the RO concentration process is the osmotic pressure of the sugars which approaches 50 bar at sugar concentrations between 15o and 25o Brix. During the fermentation step, the biofuels/biochemicals are produced and can be continuously removed by, for example, microfiltration (MF)/UF/pervaporation (PV) to prevent product inhibitors from stopping the fermentation. The membrane processes can be either operated submerged in the fermenter or placed as a side-stream directly connected to the fermenter. The major challenge is to select low-fouling membranes and open-channel modules to avoid channel blockage. In the case where MF/UF is used for the separation of the biofuels/biochemical from the fermentation broth, the permeate stream will also contain sugars. Applying nanofiltration (NF) /RO e.g. in the case of alcohols and organic acids production, these sugars can be concentrated and recycled back to the fermenter. In the purification section of the production process, distillation can be combined with PV in a hybrid process to concentrate the biofuels/biochemicals. The water loop is one of the key loops in bio-refineries. Membrane processes are well-established to upgrade in-take water i.e. in a cascade process consisting of UF as a pre-filtration step followed by RO. Additionally, membrane processes can be used for in-process water recycling i.e. using RO as an evaporator condensate polisher or they can be integrated in the wastewater treatment plants as membrane bioreactor units for end-of-pipe treatment. 4. Outlook and conclusionsMembrane processes as highly selective and energy-saving separation processes have the potential to become key units of operation in the concept of bio-refineries. The potential application range covers key steps from the initial feed stock pre-treatment steps to the concentration of the final products and includes further applications within the water loop, ranging from in-take water preparation to end-of-pipe treatment. Current R&D efforts are focusing on up-scaling of these potential applications from laboratory to pilot and ultimately full production scale. (Less)
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Bio refinery is defined as the sustainable processing of biomass into a spectrum of marketable products and energy. The biomass is any biological material derived from living organisms, such as animals and plants. Whether bio-derived feedstock based on biomass is more environmentally friend is still controversial. It is anyway clear that, in the coming decades, it will play an important role as integrative feedstock source. Drivers for this growth include, carbon emission taxation, development of fast growing plants and with limited water demand, development of low energy demanding separation processes, energy supply to remote off-grid places. Challenges for bio-derived feedstock sustainability include, suitable and efficient transformation processes (such as trans esterification, esterification, hydrolysis), efficient and selective separation techniques for downstream processing, use of less energy for separation and formulation, use of clean technologies to produce co-products, process flexibility and modularity to be adapted for different products of interest, water removal, biodiesel viscosity control.
Membrane-based processes best suit these requirements and can promote breakthroughs in the implementation of bio refinery. In this lecture, advances of membranes and membrane devices in terms of chemical, physical, mechanical and fluid dynamics properties will be discussed. Their use in integrated membrane operations for the sustainable processing of agro-food wastes into valuable marketable products and energy will be presented. Pressure driven membrane operations have been applied to purify water and recover enriched fractions of biophenols. These valuable components have been further processed by membrane contactors, i.e. they have been concentrated by osmotic distillation and used to formulate water-in-oil emulsions by membrane emulsification. Bio catalytic membrane reactors have been used to produce a powerful anti-inflammatory, i.e. oleuropein aglycon. The organic biomass recovered in the first steps of pre-treatment and in the microfiltration retentate was suitable for production of biogas via anaerobic digestion. The biogas can be processed by membrane operations to obtain methane suitable for the energy grid and food grade CO2.
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1. IntroductionThe end of the 20th century was marked by the start of the third and so far final wave of biotechnology, the so-called white biotechnology, aiming to substitute chemical processes based on C2/C3 chemistry of oil and gas by biotechnological processes. The standard conversion process in biotechnology is fermentation, which is used to produce a wide range of bulk products such as antibiotics, enzymes, bioethanol and organic acids. Cross-flow membrane processes were introduced for downstream processing of fermentation products in the 1970ies and since then became a standard unit of operation for the recovery and purification of fermentation products. This presentation will provide a brief overview on the current status of membrane processes in the bulk fermentation industry looking on the established applications such as antibiotics, enzymes and organic acids plus the latest trend in this industry - biorefineries. Details on the different processes and process conditions will be given. 2. Current statusThe use of membrane processes in the production of bulk fermentation products such as antibiotics, enzymes and organic acids is widely established. At the front-end of the production, the combination of MF/UF with diafiltration can be used for separation of the active ingredients from the fermentation broth. After this separation, membrane processes such as UF, NF, and RO are used for concentration and purification of the active ingredients. An example of a production line for antibiotics with membrane opportunities is shown in Figure 1. [figure1] 3. Future biorefineriesBiorefineries are integrated biotech facilities aiming on full utilization of feedstock for the simultaneous production of e.g. food, biofuels and biochemicals. Examples are the integrated production of biofuels and/or biopolymers from sugar and/or cellulose-based feedstock as part of sugar factories or pulp mills. In all these new concepts, membranes can play a significant role as highly selective and low-energy separation processes. Depending on the raw material, the initial step is the pre-treatment and conversion of the raw material, e.g. wood biomass, to sugars. Based on this conversion the sugars might be at very low concentration. The diluted sugar stream can then be concentrated by RO and polished by MF/UF before the fermentation step. During the fermentation step, the biofuels/biochemicals are produced and continuously removed by membrane processes such as MF/UF/PV to prevent product inhibitions from stopping the fermentation process. Subsequently, membrane processes like MF, UF, NF, RO and PV can be used for concentration and polishing of the biofuels/biochemicals. In Figure 2, an overview of different membrane opportunities is given. [figure2] 4. OutlookOverall, this paper shows that cross-flow membrane processes have established themselves in the bulk fermentation industry and further have a great potential in future biorefineries. (Less)
Diafiltration
Commodity chemicals
Membrane Technology
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The pulp and paper industry is one of the most important industrial sectors worldwide. The focus of current pulp mills is on the production of cellulose pulp fibres and electricity. By converting traditional pulp mills into biorefineries they can be a keystone in a future bioeconomy based on renewable resources instead of fossil fuels. In order to achieve this, pulp mills have to close their loops and focus on the optimal utilisation of the lignocellulosic raw material not only for fibres but also for the production of biochemicals, biofuels and other advanced materials.Thermomechanical pulping (TMP) is one of most widely used pulping processes. However, its current concept results in large quantities of process water containing very diluted lignocellulosic components such as cellulose, lignin, hemicellulose and extractives and are today send for biological wastewater treatment. An efficient separation and concentration of these wood chemicals could be fundamental in utilising the TMP process in future pulp mill biorefineries. The pressure-driven membrane processes microfiltration (MF) and ultrafiltration (UF) have been identified as high potential processes for the separation and concentration of lignocellulosic components. During the separation process, MF and UF are experiencing membrane fouling resulting in flux reduction and changes in membrane retention, which have both a negative impact on the process economy. However, flux and retention can be recovered by regular cleaning but improved cleaning protocols and new cleaning agents are required to obtain a sustainable process.Therefore, this study focus on the cleaning of polymeric membranes used for the separation of hemicellulose from TMP process water which are severely fouled due to the presence of polysaccharides and proteins. Typical conventional cleaning protocols for such fouling include generally the use of strong alkaline solutions with added detergents at high temperatures resulting in a reduced membrane life cycles, Anton et al. (2015). Alternatively, enzymatic membrane cleaning protocols could be adopted which are more sustainable since they have a lower environmental impact and require less harsh conditions with regard to temperature and pH. Thus, the aim of this work is to compare different conventional and enzymatic cleaning protocols with regard to flux and retention recovery of the membranes fouled by TMP process water.This work will show that on the one hand polysaccharide degrading enzymes can help to enhance the cleaning of membranes fouled with TMP process water and thus resulting in a longer membrane life cycle and less environmental impact, but on the other hand it will also reveal that there is still further development of cleaning agents and protocols required to obtain a complete environmental friendly replacement for current cleaning agents and protocols. Overall, this study will highlight that effective and sustainable membrane cleaning is a key for the true transformation of pulp mills into biorefineries. (Less)
Hemicellulose
Pulp mill
Nanofiltration
Ultrafiltration (renal)
Organosolv
Lignocellulosic Biomass
Membrane Technology
Membrane Fouling
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1. IntroductionThe starting point of modern biotechnology is often defined by the production of lactic acid by Pasteur in 1857 and the discovery of penicillin by Fleming in 1928. During this first wave of biotechnological processes moved production of e.g. antibiotics and amino acids from laboratory to industrial scale. The second wave of biotechnological processes started with the discovery of the DNA structure by Crick and Watson in 1953 which opened the doors for molecular engineering allowing to recombine DNA. The end of the 20th century marked the beginning of the third wave of biotechnology focusing on the replacement of chemical processes using C2/C3 chemistry based on oil and gas by biotechnological processes. Membranes have been successfully integrated into biotechnology production processes since the invention of the phase inversion membrane by Sidney and Sourirajan in the 1960ies and are under investigation to become key separation processes in the development of future biorefineries. 2. Future biorefineriesBiorefineries are integrated biotech facilities aiming on full utilization of feedstock for the simultaneous production of e.g. food, biofuels and biochemical (1). Examples are the integrated production of biofuels and/or biopolymers from sugar and/or cellulose-based feedstock as part of sugar/starch factories or pulp mills. In these biorefineries the applications of membranes can be both in the production or water loop of the process. 2.1 Production loopDepending on the raw material, e.g. wood biomass or starch, the initial step is the pre-treatment and conversion to sugars. The sugars - if diluted - can then be concentrated by reverse osmosis and polished by microfiltration/ultrafiltration before fermentation. During fermentation, the biofuels/biochemicals are produced and can be continuously removed by e.g. microfiltration/ultrafiltration/pervaporation to prevent product inhibitions from stopping the fermentation. Subsequently, microfiltration, ultrafiltration, nanofiltration, reverse osmosis and pervaporation can be used for concentration and/or polishing of the biofuels/biochemicals. In Figure 1, an overview of different membrane opportunities is given. Figure 1:Membrane opportunities in biorefineries for biochemical and biofuel production loop (2).2.2 Water loop Another important loop in bio-refineries is the water loop. Since membrane processes are already well-established to upgrade in-take water in other industries e.g. using a cascade process consisting of ultrafiltration as pre-filtration step followed by reverse osmosis, it can be foreseen that membrane will also establish themselves also in biorefineries for this position. Additionally, membrane processes can be used for in-process water recycling e.g. using reverse osmosis as evaporator condensate polisher or they can be integrated in the wastewater treatment plants membrane bioreactor for end-of-pipe treatment. Hence, membrane processes can be an important tool in the water loop of biorefineries maximizing water utilization and minimizing water discharge. 3. Concluding outlookOverall, membrane processes have a great potential to become key separation unit in the concept of biorefineries considering their highly selectivity and low energy consumption. Potential key applications can be found in both the production and water loop of biorefineries and main R&D efforts in the industry are currently focusing on scaling these potential applications from laboratory to pilot and ultimately full-scale. (Less)
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Utilization of renewable resources is becoming increasingly important, and only sustainable processes that convert such resources into useful products can achieve environmentally beneficial economic growth. Wastewater from the pulp and paper industry is an unutilized resource offering the potential to recover valuable products such as lignin, pigments, and water [1]. The recovery of lignin is particularly important because it has many applications, and membrane technology has been investigated as the basis of innovative recovery solutions. The concentration of lignin can be increased from 62 to 285 g∙L(-1) using membranes and the recovered lignin is extremely pure. Membrane technology is also scalable and adaptable to different waste liquors from the pulp and paper industry.
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