Recovering rhamnogalacturonan-I pectin from sugar beet pulp using a sequential ultrasound and microwave-assisted extraction: Study on extraction optimization and membrane purification.

This research focuses on the integrated recovery of rhamnogalacturonan-I (RG-I) pectin from sugar beet pulp (SBP). First, the extraction of RG-I pectin through sequential ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) was assessed. Optimization using a response surface methodology identified the optimal conditions as initial pH 4, 10 min of UAE, and 157 °C for MAE, achieving a 66.0 % recovery of pectooligosaccharides (POS). Additionally, purification through continuous diafiltration and concentration via ultrafiltration of the POS using membranes with different molecular weight cut-offs (MWCO) was explored. In contrast to previous research using discontinuous diafiltration, the use of continuous diafiltration allowed a decrease in the extract viscosity and obtained higher yields using a higher MWCO membrane. The refined RG-I pectin solids exhibited a high global yield (39-40 g pectin/100 g SBP), and high-methoxyl characteristics, as well as purity levels (70-80 %) similar to commercial prebiotics.

Efficient recovery and characterization of humic acids from municipal and manure composts: A comparative study.

The recovery of humic acids from low-quality compost obtained in municipal solid waste treatment plants provides opportunities for its valorization. This study compares the recovery and properties of the humic acids obtained from municipal mixed waste compost (MMWC) and manure compost. The effects of temperature, time, and KOH concentration on the ratio of humic acids in the extracted liquid and the content of organic carbon of the precipitates were investigated by response surface methodology. Optimal conditions were 30 °C and 24 h for both composts, with a KOH concentration of 0.53 M for MMWC and 0.25 M for manure compost. The manure compost provided a liquid extract richer in humic acids than MMWC (76.6 % vs. 33.7 %), but the precipitates presented similar organic carbon contents (38.1 % vs. 42.4 %). Regarding composition, both humic acids presented higher organic carbon and nitrogen contents than the composts used as feedstock. The extraction and further precipitation of humic acids reduced the concentration of heavy metals. Humic acids from manure compost have a slightly higher average molecular weight (2650 Da) than those from MMWC (1980 Da), while both present similar C/N ratios and degree of aromaticity. Most contaminants of emerging concern present in the original composts were not detected in the humic acids. Thus, it was demonstrated that MMWC constitutes an attractive source of humic acids with properties similar to those obtained from a high-quality compost and, therefore, with potential economic value.

Carrot Discard as a Promising Feedstock to Produce 2,3-Butanediol by Fermentation with P. polymyxa DSM 365.

The valorization of fruit and vegetable residues (such as carrot discard) and their microbial conversion into 2,3-butanediol (BDO) can be considered as a very interesting way to reduce food waste and sustainably originate high value-added products. This work analyzes the valorization of carrot discard as feedstock for 2,3-butanediol (BDO) production by Paenibacillus polymyxa DSM 365. The influences of stirring and the presence of tryptone (nitrogen source) are studied. Furthermore, in order to evaluate the influence of the pre-culture medium (nitrogen source, nutrients, and pH) and the substrate, fermentation assays in simple and mixture semi-defined media (glucose, fructose, and/or galactose) were also carried out. As a result, 18.8 g/L BDO, with a BDO yield of 0.43 g/g (86% of its theoretical value), could be obtained from carrot discard enzymatic hydrolysate at 100 rpm, no tryptone, and pre-culture Häßler medium. No hydrothermal pre-treatment was necessary for BDO production from carrot discard, which increases the profitability of the process. Therefore, 18.8 g BDO, as well as 2.5 g ethanol and 2.1 g acetoin by-products, could be obtained from 100 g of carrot discard (dry matter).

Liquid fertilizer production from organic waste by conventional and microwave-assisted extraction technologies: Techno-economic and environmental assessment.

The use of mineral fertilizers in agriculture has significantly increased to support the growing global food demand. Organic fertilizers are produced from renewable waste materials to overcome the drawbacks of inorganic fertilizers. The development of novel production processes of organic fertilizers entails a significant advance towards the circular economy that reincorporates waste materials into the production cycle. In this work, the economic and environmental feasibility of an industrial plant with a treatment capacity of 300 kg/h of organic waste for the production of liquid fertilizers has been performed. Two extraction technologies (conventional and microwave) and two solvents (water and alkaline) have been compared to select the most sustainable and profitable scenario for scaling-up. The extraction process consists of 2 steps: extraction followed by a concentration stage (necessary only if water extraction is applied). The resolution of the mass balances shows that the fertilizer production under alkaline conditions is ten times higher than for water-based extraction. The economic analysis demonstrated that the total investment cost of microwave technology (>3.5 M€) is three times higher compared to the conventional extraction technology (<1.5 M€), mainly due to the higher complexity of the equipment. These facts directly impact the minimum selling price, because the fertilizers obtained by conventional extraction with alkaline solvent would have a lower selling price (about 1 €/L). As for environmental assessment, the indicators show that the environmental impact produced by water-based extraction is higher than alkaline-solvent extraction, mainly due to the necessity of a concentration stage of the liquid extract to meet the requirements of European regulations. In view of the results obtained in the economic and environmental evaluation, it could be concluded that the most favourable scenario for scaling up the production of liquid fertilizers from organic waste is the conventional extraction under alkaline conditions.

Ideal conditions of microwave-assisted acid pretreatment of sugarcane straw allow fermentative butyric acid production without detoxification step.

Sugarcane straw (SCS) was pretreated with dilute sulfuric acid assisted by microwave to magnify fermentable sugars and to minimize the concentration of inhibitors in the hydrolysates. The optimum conditions for maximum recovery of sugars were 162 °C and 0.6% (w/v) H2SO4. The low level of inhibitors, such as acetate (2.9 g/L) and total phenolics (1.4 g/L), in the SCS slurry from the pretreatment stage allowed the enzymatic hydrolysis and fermentation steps to occur without detoxification. Besides consuming the total sugar content (31.0 g/L), Clostridium beijerinckii Br21 was able to use acetate from the SCS hydrolysate, to give butyric acid at high conversion factor (0.49 g of butyric acid /g of sugar). The optimized pretreatment conditions spared acid, time, and the detoxification stage, making bio-butyric acid production from SCS extremely attractive.

Efficient biobutanol production by acetone-butanol-ethanol fermentation from spent coffee grounds with microwave assisted dilute sulfuric acid pretreatment.

The integral valorization of potential sugars (cellulosic and hemicellulosic) from spent coffee grounds (SCG), a lignocellulosic residue, is proposed in this work. With this aim, the microwave assisted dilute sulfuric acid pretreatment has been optimized, leading to a hemicellulosic sugar recovery in the pretreatment liquid (HSRL) and an enzymatic hydrolysis yield of 79 and 98%, respectively, at 160.47 °C and 1.5% H2SO4. Moreover, the complete digestibility of cellulose (enzymatic hydrolysis yield = 100%) was also discovered for non-pretreated SCG, which is very interesting. Secondly, the production of biobutanol, an advanced biofuel, is also proposed from pretreated SCG enzymatic hydrolysate and pretreatment liquid achieved under optimal conditions. These were fermented by Clostridium beijerinckii, yielding 95 kg butanol/t SCG (dry matter) and 151 kg acetone-butanol-ethanol/t SCG (dry matter).

Biobutanol production from brewer's spent grain hydrolysates by Clostridium beijerinckii.

Brewer's spent grain (BSG) is a promising feedstock for ABE fermentation. Sulfuric acid pretreatment of BSG at pH 1, 121°C and different solid loadings (5-15% w/w) was investigated. Enzymatic hydrolysis and ABE fermentation by Clostridium beijerinckii DSM 6422 of non-washed and washed pretreated BSG were performed to compare monosaccharide release and butanol production. Pretreatment at 15% w/w BSG resulted in higher availability of sugars in both the enzymatic hydrolysates and pretreatment liquid, and overall yields of 75gbutanol/kg BSG and 95gABE/kg BSG were obtained. When the enzymatic hydrolysate from the washed pretreated BSG was fermented, butanol (6.0±0.5g/L) and ABE (7.4±1.0g/L) concentrations were lower compared with 7.5±0.6g/L butanol and 10.0±0.8g/L ABE from a control. The fermentation of the liquid released in the pretreatment at 15% w/w resulted in a butanol production of 6.6±0.8g/L with a total ABE of 8.6±1.3g/L after overliming.

Efficient acetone-butanol-ethanol production by Clostridium beijerinckii from sugar beet pulp.

Sugar beet pulp (SBP) has been investigated as a promising feedstock for ABE fermentation by Clostridium beijerinckii. Although lignin content in SBP is low, a pretreatment is needed to enhance enzymatic hydrolysis and fermentation yields. Autohydrolysis at pH 4 has been selected as the best pretreatment for SBP in terms of sugars release and acetone and butanol production. The best overall sugars release yields from raw SBP ranged from 66.2% to 70.6% for this pretreatment. The highest ABE yield achieved was 0.4g/g (5.1g/L of acetone and 6.6g/L butanol) and 143.2g ABE/kg SBP (62.3g acetone and 80.9g butanol) were obtained when pretreated SBP was enzymatically hydrolyzed at 7.5% (w/w) solid loading. Higher solid loadings (10%) offered higher acetone and butanol titers (5.8g/L of acetone and 7.8g/L butanol). All the experiments were carried out under not-controlling pH conditions reaching about 5.3 in the final samples.

Acetone-butanol-ethanol (ABE) production by Clostridium beijerinckii from wheat straw hydrolysates: efficient use of penta and hexa carbohydrates.

ABE fermentation by Clostridium beijerinckii of steam-exploded and ozonated wheat straw hydrolysates was investigated. In steam-exploded hydrolysates, highest yields of 0.40 g/g ABE yield and 127.71 g ABE/kg wheat straw were achieved when the whole slurry from the pretreatment was used. In ozonated hydrolysates, 0.32 g/g ABE yield and 79.65 g ABE/kg wheat straw were obtained from washed ozonated wheat straw. Diverse effects were observed in steam explosion and ozonolysis of wheat straw which resulted in hemicellulose removal and acid insoluble lignin solubilization, respectively. SEM analysis showed structural differences in untreated and pretreated biomass. Depending on the operational strategy, after pretreatment and enzymatic hydrolysis, the glucose recovery ranged between 65.73-66.49% and 63.22-65.23% and the xylose recovery ranged between 45.19-61.00% and 34.54-40.91% in steam-exploded and ozonated hydrolysates, respectively. The effect of the main inhibitory compounds found in hydrolysates (oxalic acid, acetic acid, 5-hydroxymethylfurfural and furfural) was studied through ABE fermentation in model media.

Evaluation of Fenton method and ozone-based processes for colour and organic matter removal from biologically pre-treated swine manure.

This work evaluates the efficiency of different advanced oxidation processes (Fenton method, O3, H2O2 and O3/H2O2) for removing total COD (TCOD) and colour from biologically pre-treated swine manure. The Fenton process with a dosage of 100 mg L(-1) of Fe(2+) and 800 mg L(-1) of H2O2 resulted in about 78% TCOD and 96% colour reductions at an initial pH=3 after a reaction time of 30 min. Coagulation, rather than oxidation process, was identified as a crucial mechanism for removing pollutants. Otherwise, single ozonation achieved only 27-30% TCOD and 53-88% colour removals for ozone dosages ranging between 0.7 and 4.3 g O3 h(-1) at the original wastewater pH (pH=8.1) after 30 min reaction time. The combined treatment with O3/H2O2 at pH=8.1 did not produce any significant TCOD or colour reduction improvement. Therefore, direct reactions with ozone rather than radical reactions were elucidated as the main removal mechanisms in the ozone-based processes. Finally, a rough estimation of the operational costs involved in each process was also performed to compare their economic feasibility. The findings suggested that the Fenton process was more suitable than ozonation for reducing TCOD and colour from the biologically pre-treated swine manure.

Sugarcane bagasse ozonolysis pretreatment: effect on enzymatic digestibility and inhibitory compound formation.

Sugarcane bagasse was pretreated with ozone to increase lignocellulosic material digestibility. Bagasse was ozonated in a fixed bed reactor at room temperature, and the effect of the two major parameters, ozone concentration and sample moisture, was studied. Acid insoluble and total lignin decreased whereas acid soluble lignin increased in all experiments. Pretreatment barely attacked carbohydrates, with cellulose and xylan recovery rates being >92%. Ozonolysis increased fermentable carbohydrate release considerably during enzymatic hydrolysis. Glucose and xylose yields increased from 6.64% and 2.05%, for raw bagasse, to 41.79% and 52.44% under the best experimental conditions. Only xylitol, lactic, formic and acetic acid degradation compounds were found, with neither furfural nor HMF (5-hydroxymethylfurfural) being detected. Washing detoxification provided inhibitor removal percentages above 85%, increasing glucose hydrolysis, but decreasing xylose yield by xylan solubilization. SEM analysis showed structural changes after ozonization and washing.

Influence of aeration on bioethanol production from ozonized wheat straw hydrolysates using Pichia stipitis.

The influence of aeration on ethanol production by Pichia stipitis was studied in wheat straw hydrolysates subjected to ozone pretreatment for the first time. In a first stage, different aeration rates ranging from 0.03 to 0.50 L air/min, which corresponds to a volumetric oxygen transfer coefficient from 1.1 to 9.6 h(-1), were applied to model glucose/xylose substrates. The most promising value was found to be 3.3 h(-1) (0.1 L air/min) leading to better xylose utilization, an ethanol yield of 0.40 g ethanol/g sugars and complete depletion of sugars at 72 h. In a second stage, the effect of aeration was analyzed in ozonized wheat straw hydrolysates. Sugars were completely depleted at 96 h and ethanol yield reached a value of 0.41 g ethanol/g sugars. The addition of controlled oxygen (K(L)a=3.8 h(-1)) enhances the efficiency of the process causing an increase of 29.1% in ethanol production and a considerable reduction of 42.9% in fermentation time as compared to non-aerated hydrolysates.

An analysis of lignin removal in a fixed bed reactor by reaction of cereal straws with ozone.

The chemical pretreatment with ozone of rye and wheat straws was carried out in a fixed bed reactor. The effect of ozone pretreatment time on lignin removal was determined. Glucose and xylose concentrations in the hydrolysates were also measured after the subsequent enzymatic hydrolysis step. Acid insoluble lignin reacts with ozone within the first 90 min reaction. Insoluble lignin reduction was about 50%. The higher hydrolysis yields were obtained after 120 min ozonation: the glucose yield ranged from 40% to 50% for rye straw and from 34% to 39% for wheat straw, whereas xylose yields were about 30%, independently of the cereal straw. The glucose yields corresponding to the untreated raw straws were considerably lower, about 10%. Longer ozonation time sharply reduced the production of monosaccharides, probably due to the formation of side products. The kinetic model, with the reaction parameters estimated, predicted reasonably well the experimental data.

Effect of inhibitors formed during wheat straw pretreatment on ethanol fermentation by Pichia stipitis.

The inhibitory effect of the main inhibitors (acetic acid, furfural and 5-hydroxymethylfurfural) formed during steam explosion of wheat straw was studied through ethanol fermentations of model substrates and hydrolysates from wheat straw by Pichia stipitis. Experimental results showed that an increase in acetic acid concentration led to a reduction in ethanol productivity and complete inhibition was observed at 3.5 g/L. Furfural produced a delay on sugar consumption rates with increasing concentration and HMF did not exert a significant effect. Fermentations of the whole slurry from steam exploded wheat straw were completely inhibited by a synergistic effect due to the presence of 1.5 g/L acetic acid, 0.15 g/L furfural and 0.05 g/L HMF together with solid fraction. When using only the solid fraction from steam explosion, hydrolysates presented 0.5 g/L of acetic acid, whose fermentations have submitted promising results, providing an ethanol yield of 0.45 g ethanol/g sugars and the final ethanol concentration reached was 12.2 g/L (10.9 g ethanol/100 g DM).

Production of biomass by Spirulina maxima using sugar beet vinasse in growth media.

Cultivation of Spirulina maxima in media containing vinasse from beet molasses fermentation has been studied in both batch cultures and a photobioreactor. The results obtained in batch tests showed that S. maxima was able to grow in Schlösser media containing up to 5 g/L of vinasse or alkaline diluted vinasse (5 g/L). Biomass concentrations ranging from 3.5 and 4.8 g/L, productivities from 0.15 to 0.24 (g/L d) and specific growth rates about 0.1 d⁻¹ were found. Betaine, an organic nitrogenous compound present in vinasse, was completely consumed. The continuous operation in a tubular photobioreactor with Schlösser medium supplemented with 2g/L of vinasse led to S. maxima concentrations about 8 g/L and productivities of 0.7 g/L d for an hydraulic retention time of 11 d using a light intensity of 3000 lux, slightly higher than those achieved with Schlösser medium, showing that the addition of vinasse presents a positive effect on the growth of the microalgae.

Effect of ozonolysis pretreatment on enzymatic digestibility of wheat and rye straw.

Wheat and rye straws were pretreated with ozone to increase the enzymatic hydrolysis extent of potentially fermentable sugars. Through a 2(5-1) factorial design, this work studies the influence of five operating parameters (moisture content, particle size, ozone concentration, type of biomass and air/ozone flow rate) on ozonization pretreatment of straw in a fixed bed reactor under room conditions. The acid insoluble lignin content of the biomass was reduced in all experiments involving hemicellulose degradation. Near negligible losses of cellulose were observed. Enzymatic hydrolysis yields of up to 88.6% and 57% were obtained compared to 29% and 16% in non-ozonated wheat and rye straw respectively. Moisture content and type of biomass showed the most significant effects on ozonolysis. Additionally, ozonolysis experiments in basic medium with sodium hydroxide evidenced a reduction in solubilization and/or degradation of lignin and reliable cellulose and hemicellulose degradation.

Continuous ozonation of biologically pretreated molasses fermentation effluents.

In this work, continuous chemical oxidation processes (single ozonation and ozone combined with hydrogen peroxide) of biologically pretreated wastewaters from a beet molasses fermentation factory have been studied. Oxidation processes were carried out in a stirred tank reactor at the natural pH of the wastewater and 25 degrees C, analyzing the effect of the hydraulic residence time and applied ozone mass flow on color and organic matter removals. Ozone consumption was also measured in each experiment. The results show that continuous ozonation was effective for decolorization of molasses wastewater. Operating with a hydraulic residence time of 45 minutes and an applied ozone mass flow of 1.7 g/h, color and chemical oxygen demand (COD) reductions were about 80% and 14%, respectively. Increasing the hydraulic residence time or ozone mass flow led to a considerably increase in the ozone consumption, with similar color and organic matter reduction percentages. Slightly higher removal percentages were obtained combining ozone with hydrogen peroxide, attaining 83% color reduction and 20% COD removal. As consequence of the oxidation processes, biodegradability of the decolorized effluent increased about 40-50% and the ratio BOD5/COD was twofold higher.