The existence of deep eutectic solvents (DESs) has improved the process of biomass transformation and valorization due to its ability to break down the recalcitrant structure of biomass via delignification. However, the high viscosity of DES is one of the factors that restraints its effectiveness in delignification of biomass. The addition of water was expected to reduce the viscosity of DES and improve the process consequently. This study investigated the effects of water content in the DES (choline chloride:urea in 1:2 M ratio) on delignification of oil palm fronds (OPF), which are underutilized but available abundantly in Malaysia. The pretreatment was carried out at 120 degrees C for 4h using DES at a solid-to-liquid ratio of 1:10 (w/v). In terms of lignin removal, 30 vol% of distilled water in DES was determined to achieve the optimal result at 16.31% in delignification of OPF. Delignification of OPF was further confirmed via a series of characterization tests. In comparison with pure DES, the aqueous DES enabled more favorable improvement of lignin removal in a biomass pretreatment. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Among next generation bio-fuels, bio-butanol produced by the Acetone-Butanol-Ethanol (ABE) fermentation [1] can be obtained from renewable carbon sources such as agro-food wastes. This biorefinery approach will beneficiate of both the advanced fermentation technologies for butanol production and of the exploitation of resources different from food-feed crops. Maximization of the sugar yield and reduction of the operating costs of the biomass pretreatment/hydrolysis process are among the main aims of the current research. The present study proposes an attempt of integration between two enzymatic steps of biomass delignification and hydrolysis that may offer effective and costs saving alternative to the conventional mechanical/physical pretreatments and acid hydrolysis of biomass. Bubble column has been adopted as lab-scale reactor with pneumatic mixing to perform tests on laccase lignin degradation and sequential cellulose hydrolysis by commercial cellulase cocktail using apple pomace residues as substrate.

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.

Coffee is the second largest traded commodity after oil and large amounts of by-products are generated in the coffee industry every year. In particular, coffee silverskin (CS) and spent coffee grounds (SCG) are the main coffee industry residues. CS is about 4.2% (w/w) of coffee beans and the valorisation of this waste through the biorefinery approach may boost the circular economy development. In the present contribution, CS was pretreated with one of the mainly investigated biomass pretreatment reported in literature: alkaline hydrolysis in NaOH solutions. After enzymatic hydrolysis of the pretreated CS, the obtained sugars were used as carbon source to produce butanol and isopropanol by Clostridium beijerinckii DSM 6423. Moreover, fermentation tests were also carried out with synthetic media to investigate the effects of the alkaline pretreatment on the fermentation process. When pretreated CS was used as feedstock, the largest yields were 0.16 and 0.31 gsolvent/gsugars isopropanol and butanol, respectively. The reported results foster further studies regarding the reuse of CS for solvents production through fermentation processes.

Background: Waste biomass from agro-food industries are a reliable and readily exploitable resource. From the circular economy point of view, direct residues from these industries exploited for production of fuel/chemicals is a winning issue, because it reduces the environmental/cost impact and improves the eco-sustainability of productions. Results: The present paper reports recent results of deep eutectic solvent (DES) pretreatment on a selected group of the agro-industrial food wastes (AFWs) produced in Europe. In particular, apple residues, potato peels, coffee silverskin, and brewer's spent grains were pretreated with two DESs, (choline chloride-glycerol and choline chloride-ethylene glycol) for fermentable sugar production. Pretreated biomass was enzymatic digested by commercial enzymes to produce fermentable sugars. Operating conditions of the DES pretreatment were changed in wide intervals. The solid to solvent ratio ranged between 1:8 and 1:32, and the temperature between 60 and 150 °C. The DES reaction time was set at 3 h. Optimal operating conditions were: 3 h pretreatment with choline chloride-glycerol at 1:16 biomass to solvent ratio and 115 °C. Moreover, to assess the expected European amount of fermentable sugars from the investigated AFWs, a market analysis was carried out. The overall sugar production was about 217 kt yr-1, whose main fraction was from the hydrolysis of BSGs pretreated with choline chloride-glycerol DES at the optimal conditions. Conclusions: The reported results boost deep investigation on lignocellulosic biomass using DES. This investigated new class of solvents is easy to prepare, biodegradable and cheaper than ionic liquid. Moreover, they reported good results in terms of sugars' release at mild operating conditions (time, temperature and pressure).

In the general effort to produce chemicals and fuels from renewable resources there is new interest in the biotechnological route to produce butanol. Acetone-Butanol-Ethanol (ABE) fermentation leads to low product yield because butanol is toxic to microorganisms. Selecting an efficient technology to recover butanol from low concentration butanol (about 2%) solutions is key to a successful implementation of this butanol production process on an industrial scale. Adsorption has been suggested as a potential technology for butanol recovery. This paper reports a systematic investigation of the adsorption of the metabolites that are typically present in the ABE fermentation broth: acetone, butanol, ethanol, acetic acid, butyric acid, yeast extract. The effect of glucose as a carbon source for the ABE fermentation was also investigated. Three adsorbents were characterized: Amberlite XAD-4, Amberlite XAD-7 and Zeolite Y. Batch tests under a wide interval of operating conditions were carried out for the assessment of the adsorption capacities of the three adsorbents. The selectivity of the three adsorbent materials towards the main components of ABE broths was also investigated. These tests were carried out using both dilute model solutions and real fermentation broths. The tests show that Amberlite XAD-7 has the highest affinity for butanol adsorption. The co-presence of all the metabolites in the solution - synthetic broth and real broth - changes the distribution in the adsorbed phase remarkably. The distribution of the concentration of the adsorbed components can be affected by pH. The presence of glucose does not affect butanol adsorption. Amberlite XAD-7 has a great potential as an adsorbent in ABE fermentation coupled with in situ recovery product removal techniques.

The Acetone-Butanol-Ethanol (ABE) fermentation was a consolidate process to produce butanol during the first half of the last century but its modern industrial success is hindered by several issues. The selection of a technology for recovering low-concentration butanol from fermentation broth that is characterized by high recovery/selectivity performance and low energy request is a key issue for a successful bio-butanol production process. Several recovery processes were analysed in the literature and the adsorption was found to be very promising. This contribution reports on the butanol recovery by means of adsorption. The focus was on the selection of the adsorbent to maximize the butanol recovery. Three materials were characterized in terms of solvent adsorption capacity: Amberlite XAD7, Amberlite XAD4 and Zeolite Y.

In the last years, first generation biofuels (FGBs) have been overtaken by second generation biofuels (SGBs). Among the difference between FGBs and SGBs, the severity of biomass pretreatment step has been addressed in order to design environmental friendly and energy saving processes aimed at the recovery of sugar fractions from the lignocellulosic feedstock. Moreover, the issue related to the biomass availability in European countries has been addressed by several reviews in the literature even though, to our knowledge, no studies related to the amount of organic waste coming from the food industrial sector have been published so far. Among the novel green processes proposed for biomass pretreatment, lignin extraction with Deep Eutectic Solvents (DESs) seems to be a promising alternative for biomass dissolution and fermentable sugars recovery thanks to their physicochemical properties similar to that of ionic liquids (IL). In addition, use of DESs is less energy consuming and they are more environmental friendly and inexpensive than ILs. This paper reports a survey of several industrial Agro-Food Wastes (AFWs) available in Europe for the production of butanol as SGB. Data on biomass availability and composition were retrieved for each AFW and combined with experimental results reported in the literature on the butanol yield obtained after AFW pretreatment with DES and ABE fermentation of the sugar fraction. The results provided the potential butanol production rate for the whole set of AFW considered and were compared to the European biofuel demand.

The effective hydrolysis of lignocellulosic biomass catalysed by cellulase cocktails is a crucial step of the biorefinery approach towards the production of fuels and chemicals from fermentable sugars. Enzymatic hydrolysis of biomass is a heterogeneous process involving cellulases as biocatalysts that can be inhibited by produced sugars (glucose and cellobiose). The heterogeneous process includes the enzyme interaction with biomass and the subsequent cellulose and hemicellulose enzymatic hydrolysis, it can be characterized by more or less complex techniques depending on the final purpose [1,2]. Process design asks for reliable tools for cellulase kinetics modelling that can be applied to different cellulase cocktails provided by the continuous research efforts aimed at the selection of more active and stable enzyme forms. Semimechanistic models can be adopted in process design in order to take into account the effect of external mass transfer, of enzyme and substrate (biomass) concentration as well as of product inhibition [3]. The present contribution reports on part of the study included in the research project Waste2Fuels funded in the framework of the European Horizon 2020 work programme. The aim is the development of an experimental procedure to assess kinetics of cellulase cocktails under reliable conditions not limited by the liquid-solid mass transfer rate. Preliminary results concern the design and set up of a lab scale batch reactor that is equipped with a packed column loaded with biomass granules and a stirred buffer tank. The liquid buffer, supplemented with the enzymes, was recirculated through the packed column and the tank so that the entire unit was operated as a Stirred Tank Reactor (STR). Liquid recirculation rate was varied to assess the minimum liquid superficial velocity that correspond to not limiting mass transfer rate between the liquid phase and the biomass granules in the packed column. Under the selected kinetic regime, further experiments will be carried out to assess cellulase kinetics in terms of dependence on enzyme and substrate concentration.

Waste biomasses from agro-food industry may be adopted as cellulose rich feedstock for biorefinery [1]. Effective biomass pretreatment must be developed to overcome some issues related with conventional mechanical and chemical-physical pretreatments. Environmental and economic issues related with the use of solvents and with the energy demand for biomass pretreatment should be addressed. The use of green solvents for lignin extraction from biomass is a promising strategy, among these Deep Eutectic Solvents (DESs) have been proposed [2]. DES is a fluid made by two or three ionic compounds that forms eutectic mixture. DESs have physicochemical properties similar to ionic liquids and in addition, they are much environmental friendly and cheaper than ILs. The present contribution reports on part of the study included in the research project Waste2Fuels funded by the European Horizon 2020 work program. The biomass pretreatment with DES was optimized by testing two solvent compositions (CholineChloride-Glycerol and CholineChloride-Ethylenglycole) on four agro-food wastes: potato peels, apple residues, brewery spent grains, coffee silverskin. The adopted biomass to solvent ratio and the temperature were varied between 1:8 - 1:32 and 60-150°C, respectively. The pretreated biomass was hydrolyzed using a commercial cellulase cocktail, then samples were characterized in terms of residual lignin, cellulose and hemicellulose content, concentrations of sugars and of inhibitors in the hydrolysate. Hydrolysis glucose yields (percentage of the glucan content in the raw biomass) was about 90% after ChCl-Gly pretreatment at 150°C of all the agro-food wastes. Fermentation inhibitors in the hydrolyzate were negligible. Furthermore, structural changes of the pretreated biomass were characterized by X-Ray Diffraction and Scanning Electron Microscopy.

Waste lettuce leaves - from the "fresh cut vegetable" industry - were pretreated with the deep eutectic solvent (DES) made of choline chloride - glycerol. Reaction time (3-16 h) and the operation temperature (80-150 °C) were investigated. Enzymatic glucose and xylose yields of 94.9% and 75.0%, respectively were obtained when the biomass was pretreated at 150 °C for 16 h. Sugars contained in the biomass hydrolysate were fermented in batch cultures of Clostridium acetobutylicum DSMZ 792. The energy consumption and the energy efficiency related to the DES pretreatment were calculated and compared to the most common lignocellulosic pretreatment processes reported in the literature. The DES pretreatment process was characterized by lower energy required (about 28% decrease and 72% decrease) than the NAOH pretreatment and steam explosion process respectively. The Net Energy Ratio (NER) value related to butanol production via DES biomass pretreatment was assessed.

The hydrolysis of lignocellulosic biomass catalysed by cellulases is a crucial step of the biorefinery approach for the production of fuels and chemicals. It is a heterogeneous process involving cellulases as biocatalysts that can be inhibited by produced sugars (glucose and cellobiose). The heterogeneous process includes the enzyme interaction with biomass and the subsequent cellulose and hemicellulose enzymatic hydrolysis. In this study a kinetic characterization of the commercial cellulase cocktail Cellic CTec2 (Novozymes) was carried out. Industrial apple residues were pretreated with NaOH1 hydrolysis and lignin conversion by laccases2. After the pretreatment step the kinetic characterization of the enzymatic hydrolysis step was carried out in term of effect of mixing rate, substrate and enzyme concentrations. The experimental results were described through pseudo-homogeneous Michaelis-Menten, modified Michaelis-Menten and Chrastil's models3. Parameters of the Michaelis-Menten models describe the mutual affinity between the enzyme and the biomass, they were lower (Km=6g L-1, Ke=5 g L-1) for alkaline pretreated biomasses than for biomass pretreated with laccases (Km=9g L-1, Ke=7g L-1). The n parameter of the Chrastil's model shows the apparent order of reaction and n<0.6 shows apparent reaction rates limited by diffusion. It resulted 0.17 and 0.4 for alkaline and laccase pretreated biomass, respectively, thus it suggests a quite large effect of the unspecific alkaline pretreatment on biomass structure. Accordingly, a lower lignin content was obtained after NaOH pretreatment with respect to the lignin content obtained after laccases pretreatment. The reported results show how these kind of studies can provide useful information to optimize the enzymatic hydrolysis step depending on the biomass composition after the pretreatment step.

Development of biorefinery platform asks for efficient, cost saving, and green processes for lignocellulosic biomass saccharification. Novel biomass pretreatments aimed at lignin dissolution and reduction of cellulose crystallinity are currently studied. Among these, processes based on Deep Eutectic Solvents (DESs) draw scientific and industrial research's attention. The present work reviews main results available in the literature on the recent findings on DES pretreatment of lignocellulosic biomass. Moreover, some open issues related with process optimization and integration of pretreatment and enzymatic hydrolysis for fermentable sugar recovery are discussed.

Coffee silverskin (CSS) is an agro-food processing waste (AFW) largely produced in roasting factories at almost constant rate over the year. The CSS can be used as a source of fermentable sugars within a biorefinery approach for its exploitation. Pretreatment process and enzymatic hydrolysis are required to efficiently recovery monomeric fermentable sugars from AFWs such as CSS. Current research is focused on the selection of novel processes for biomass pretreatments able to provide effective lignin removal, to minimize the production of by-products that may inhibit the fermentation of the produced sugars, and to be cost saving with respect to conventional pretreatments. The aim of the present study was to investigate the effect of the ultrasound (US) assisted dilute acid pretreatment on the effective separation of lignin and polysaccharides of CSS. The effects of two operating conditions - biomass loading and sulphuric acid concentration - were studied to assess their effects on the sugar yields after enzymatic hydrolysis. The production of typical species that may inhibit the fermentation of the hydrolysate was monitored. Inhibitors like furfural, 5-hydroxymethyl furfural (HMF), ferulic and p-coumaric acid were present at concentrations lower than 1 mg/L after enzymatic hydrolysis of the pretreated CSS. As a result, the hydrolysate of US dilute acid pretreated CSS may be used for fermentation without detoxification step.

The residue of the fresh-cut vegetable packaging process is a major environmental concern for food industries. Actually 50% of the processed vegetables must be disposed of. But the lettuce fraction sorted and deemed unsuitable to be bagged may be used as feedstock for butanol production because it is rich in sugars. In this work acetone butanol ethanol (ABE) was produced from enzymatic-hydrolysed Lactuca sativa leaves. The lettuce leaves were first pre-treated with NaOH and then hydrolysed. The NaOH concentration was increased up to 200 kg m-3, Cellic CTec 2 (Novozymes) was used for the hydrolysis. The sugars contained in the biomass hydrolysate were fermented in batch cultures of Clostridium acetobutylicum DSMZ 792. The fermentation process was characterized in terms of sugar conversion and ABE production. The hydrolysate of the NaOH-pre-treated lettuce contained glucose and xylose (about 50/50). Under optimal conditions the sugar concentration after the enzymatic hydrolysis was 19.5 g L-1, the ABE concentration was 1.44 g L-1 and the butanol concentration was 1.1 g L-1. Some tests were also carried out with synthetic mixtures of glucose and xylose to investigate the effects of the alkaline pre-treatment on the fermentation process

This paper reports a study of potential feedstock for butanol production via the biotechnological route. Several waste(water) streams rich in sugars and lignocellulosic biomass were studied: cheese-whey, leftovers of high sugar-content beverages, food lost or wasted, agriculture residues. The maximum butanol production rate from each type of feedstock was assessed according to the parameters indicated in the literature: feedstock availability rate, feedstock average composition and butanol yield. In Europe the potential biotechnological production of butanol from the feedstock studied was assessed to be about 39 Mt yr-1, which would be enough to meet the current European demand of biofuels. The potential butanol production at local level was also assessed taking into account the concentration of feedstock suppliers in the Campania region.

The feedstock of the Acetone-Butanol-Ethanol (ABE) fermentation is a key issue for the economic success of the biotechnological route to produce biobutanol. Residues from agro-alimentary industries are particularly interesting as renewable substrates for the ABE fermentation because they are abundant and un-competitive with food sources. The residues are also a pressing issue for industries because more than 50% of the processed feedstocks are discharged and their disposal is particularly expensive. However, the high fraction of sugars of the residues makes them a promising interesting feedstock for the production of butanol. This contribution is about the characterization of the ABE fermentation by Clostridium acetobutylicum DSM 792 using sugars from fruit peels. Apple and pear peel extracts were tested as substrate for the fermentation. Batch tests were carried out under a wide interval of peels to water mass ratio. The conversion process was characterized in terms of metabolites and cell production, sugars conversion, specific rate of butanol production and of sugar consumption, butanol and cell yields. The fermentation tests with feedstock peels to water mass ratios lower than 1/6 were characterized by total sugar conversion and low butanol concentration (<8.5 g/L). Tests with feedstock peels to water ratios higher than 1/8 were characterized by high butanol production (about 14 g/L) and incomplete sugar conversion.