The application of green solvent in a biorefinery using lignocellulosic biomass as a feedstock.

The high dependence on crude oil for energy utilization leads to a necessity of finding alternative sustainable resources. Solvents are often employed in valorizing the biomass into bioproducts and other value-added chemicals during treatment stages. Unfortunately, despite the effectiveness of conventional solvents, hindrances such as expensive solvents, unfavourable environmental ramifications, and complicated downstream separation systems often occur. Therefore, the scientific community has been actively investigating more cost-effective, environmentally friendly alternatives and possess the excellent dissolving capability for biomass processing. Generally, 'green' solvents are attractive due to their low toxicity, economic value, and biodegradability. Nonetheless, green solvents are not without disadvantages due to their complicated product recovery, recyclability, and high operational cost. This review summarizes and evaluates the recent contributions, including potential advantages, challenges, and drawbacks of green solvents, namely ionic liquids, deep eutectic solvents, water, biomass-derived solvents and carbon dioxide in transforming the lignocellulosic biomass into high-value products. Moreover, research opportunities for future developments and potential upscale implementation of green solvents are also critically discussed.

Combined antioxidant-biofuel production from coffee silverskin.

Biorefinery concept asks for an integrated processing approach to exploit all biomass components. The self-sustainability target may be approached if molecules characterized by high added value and fermentable sugars are produced simultaneously. In the present study, sequential (i) mild hydrothermal pretreatment to produce antioxidants and (ii) NaOH pretreatment to produce a fermentable sugar solution were carried out on coffee silverskin. Twenty-minute treatment and biomass to liquid ratio 1:30 (g mL-1) were identified as optimal operating conditions to extract bioactive compounds characterized by antioxidant activity (22.2 mgGAE/gCSS; 13.9 mgTE/gCSS). Twenty-minutes and biomass to liquid ratio of 1:20 (g mL-1) were identified as optimal operating conditions to maximize sugar recovery and ABE production (solvent yield YABE/Sugars and ABE productivity of 0.21 g g-1 and 0.12 g L-1 h-1 were obtained, respectively). The study marks the highly economic potential of the process aimed to exploit the CSS as feesdstock for antioxidant and biofuel production.

Utilization of salt-rich by-products from the dairy industry as feedstock for recombinant protein production by Debaryomyces hansenii.

The dairy industry processes vast amounts of milk and generates high amounts of secondary by-products, which are still rich in nutrients (high Chemical Oxygen Demand (COD) and Biochemical Oxygen Demand (BOD) levels) but contain high concentrations of salt. The current European legislation only allows disposing of these effluents directly into the waterways with previous treatment, which is laborious and expensive. Therefore, as much as possible, these by-products are reutilized as animal feed material and, if not applicable, used as fertilizers adding phosphorus, potassium, nitrogen, and other nutrients to the soil. Finding biological alternatives to revalue dairy by-products is of crucial interest in order to improve the utilization of dry dairy matter and reduce the environmental impact of every litre of milk produced. Debaryomyces hansenii is a halotolerant non-conventional yeast with high potential for this purpose. It presents some beneficial traits - capacity to metabolize a variety of sugars, tolerance to high osmotic environments, resistance to extreme temperatures and pHs - that make this yeast a well-suited option to grow using complex feedstock, such as industrial waste, instead of the traditional commercial media. In this work, we study for the first time D. hansenii's ability to grow and produce a recombinant protein (YFP) from dairy saline whey by-products. Cultivations at different scales (1.5, 100 and 500 ml) were performed without neither sterilizing the medium nor using pure water. Our results conclude that D. hansenii is able to perform well and produce YFP in the aforementioned salty substrate. Interestingly, it is able to outcompete other microorganisms present in the waste without altering its cell performance or protein production capacity.

Deep Eutectic Solvents pretreatment of agro-industrial food waste.

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).

Low-energy biomass pretreatment with deep eutectic solvents for bio-butanol production.

Waste lettuce leaves - from the "fresh cut vegetable" industry - were pretreated with the deep eutectic solvent (DES) made of choline chloride - glycerol. Reaction time (3-16h) 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 16h. 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.

Renewable feedstocks for biobutanol production by fermentation.

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.

Continuous lactose fermentation by Clostridium acetobutylicum--assessment of solventogenic kinetics.

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 0.15h(-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 0.5gL(-1)h(-1) at D=0.1h(-1) and R=95%. The butanol productivity referred to solventogenic cells was expressed as a function of concentration of lactose, acids and butanol.

Continuous xylose fermentation by Clostridium acetobutylicum--Assessment of solventogenic kinetics.

This work deals with the specific butanol production rate of Clostridium acetobutylicum using xylose--a relevant fraction of lignocellulosic feedstock for biofuel production--as carbon source. The tests were carried out in a CSTR equipped with a microfiltration unit. The dilution rate (D) ranged between 0.02 and 0.22 h(-1) and the ratio R between the permeate stream rate and the stream fed to the reactor ranged between 14% and 88%. The biomass present in the broth was identified as a heterogeneous cell population consisting of: acidogenic cells, solventogenic cells and spores. The results were processed to assess the concentration of acidogenic cells, solventogenic cells and spores. The specific butanol production rate was also assessed. The max butanol productivity was 1.3 g L(-1) h(-1) at D = 0.17 h(-1) and R = 30%. A comparison between the results reported in a previous work carried out with lactose was made.

Deep eutectic solvent pretreatment and subsequent saccharification of corncob.

Ionic liquid (ILs) pretreatment of lignocellulosic biomass has attracted broad scientific interest, despite high costs, possible toxicity and energy intensive recycling. An alternative group of ionic solvents with similar physicochemical properties are deep eutectic solvents (DESs). Corncob residues were pretreated with three different DES systems: choline chloride and glycerol, choline chloride and imidazole, choline chloride and urea. The pretreated biomass was characterised in terms of lignin content, sugars concentration, enzymatic digestibility and crystallinity index. A reduction of lignin and hemicellulose content resulted in increased crystallinity of the pretreated biomass while the crystallinity of the cellulose fraction could be reduced, depending on DES system and operating conditions. The subsequent enzymatic saccharification was enhanced in terms of rate and extent. A total of 41 g fermentable sugars (27 g glucose and 14 g xylose) could be recovered from 100g corncob, representing 76% (86% and 63%) of the initially available carbohydrates.

Continuous xylose fermentation by Clostridium acetobutylicum--kinetics and energetics issues under acidogenesis conditions.

The paper reports the assessment of the growth kinetics of Clostridium acetobutylicum DSM 792 adopting xylose as carbon source. Xylose is the fundamental component of hemicellulose hydrolysis, a relevant fraction of lignocellulosic feedstocks for biofuel production. Tests were carried out in a CSTR operated under controlled pH. The effects of acids (acetic and butyric) and solvents (acetone, ethanol and butanol) on the fermentation were investigated. The conversion process was characterized under steady-state conditions in terms of concentration of xylose, cells, acids, and pH. The growth kinetics was expressed by means of a multiple product inhibition and it was able to predict microorganism growth rate under a broad interval of operating conditions, even those typical of solvents production. The mass fractional yield of biomass and products were expressed as a function of the specific growth rate taking into account the Pirt model.