Ozonolysis, as a lignocellulosic biomass pretreatment, goes back to 80s; however, in the last years it is becoming widespread again owing to its efficiency and mild operation conditions. Ozone reacts preferably with lignin than carbohydrates, promoting biomass destructuration and delignification, and so the sugar release by enzymatic hydrolysis.The hydrolysate from pretreated biomass has being used as sugars source for secondgeneration fuels production, mainly ethanol, methane and hydrogen. Short-chain carboxylic acids are the main inhibitory compounds generated, being properly removed by water washing. The most common inhibitory compounds reported for other pretreatments, furfural and HMF (5-hydroxymethylfurfural) † , are not found in ozonepretreated hydrolysates. Composition of pretreated biomass and ozone consumption depends on several process parameters: reactor design, moisture content, particle size, pH, reaction time, ozone/air flow and ozone concentration. Additional studies are necessary to clarify process parameters effect and to optimize the process to achieve high yields with economic feasibility.

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An enzymatic method for the carbohydrate hydrolysis of different microalgae biomass cultivated in domestic (DWB) † and pig manure (PMWB) wastewaters, at different storage conditions (fresh, freeze-dried and reconstituted), was evaluated. The DWB provided sugars yields between 40 and 63%, although low xylose yields (< 23.5%).Approximately 2% of this biomass was converted to byproducts as succinic, acetic and formic acids. For PMWB, a high fraction of the sugars (up to 87%) was extracted, but mainly converted into acetic, butyric and formic acids, which was attributed to the bacterial action. In addition, the performance of an alkaline-peroxide pretreatment, conducted for 1 hour, 50ºC and H 2 O 2 concentrations from 1 to 7.5% (w/w), was essayed. The hydrolysis of pretreated microalgae supported a wide range of sugars extraction for DWB (55-90%), and 100% for PMWB. Nevertheless, a large fraction of these sugars (~30% for DWB and 100% for PMWB) was transformed to byproducts. HighlightsTested biomass showed different behaviours depending on the algae/bacteria ratio.Enzymatic hydrolysis of DWB yielded high glucose and low xylose extraction.Sugars from PMWB were completely released by enzymatic hydrolysis but oxidized.Acetic, formic and succinic acids were the main byproducts from released sugars.Pretreatment enhanced enzymatic hydrolysis performance for almost all biomass tested. † Abbreviations: DWB, domestic wastewater biomass; PMWB, pig manure microalgae biomass; HRT, hydraulic retention time; SRT, sludge retention time; CO 2 , carbon dioxide; CH 4 , methane. Keywords: Enzymatic hydrolysis; Glucose; Xylose; Wastewater; Alkaline-peroxide pretreatment IntroductionWorld human population and industrial activity have exponentially increased during last decades, with a concomitant raise in global energy demand. This growth has been traditionally based on fossil fuels, whose side effects have turned this dependence environmentally unsustainable (Chisti, 2007). New renewable fuel sources and biorefinery approaches for designing cost-effective and "green" processes are expected to create more efficient and sustainable economies (Daroch et al., 2013). During the past decade, microalgae have experimented a continuous and positive development due to their wide range of practical applications: wastewater treatment, nitrogen and phosphorous recovery, biogas upgrading, production of biofuels, biofertilizers, animal and fish feed, etc. Despite Oswald and co-workers were pioneers in introducing the microalgae biorefinery concept in the 60's, the combination and optimization of processes for the valorisation of microalgae biomass obtained from wastewaters treatment remains a challenge nowadays (Acién et al, 2014).Microalgae biomass is mainly composed of proteins (6% -52%), lipids (5% -23%) and carbohydrates (7% -23%) (Tijani et al., 2015). This content may vary within microalgae strains and is highly dependent on cultivation conditions, especially under nutrients-deprivation scenarios. Among them, carbohydrates are one of th...

The influence of three variables on key parameters of the protein extraction process (an alkaline hydrolysis followed by an acidic precipitation) for biomass from innovative photo-bioreactors for pig manure treatment was evaluated. Alkaline hydrolysis provided high solubilisation values (up to 66.5% of the biomass), augmenting with increasing values of the three studied variables (NaOH concentration, temperature and time). Nevertheless, moderate total (13.2%) and protein extraction yields (16.9%) were obtained, which was attributable to protein denaturation or to the low effectivity of the precipitation method. Extracts rich in proteins (53.5%-77.9%) with suitable amino acid profiles were obtained, but significant amounts of the initial lipids (up to 44.6%) were co-extracted probably due to fatty acids saponification. These results establish the first step for future studies in enhancing cell wall disruption and protein recovery by coupling alkaline hydrolysis with other mechanical pre-treatments, while considering alternative separation and purification methods. Highlights  Protein recovery by pH-shift from a consortium microalgae-bacteria biomass.  ANOVA of NaOH concentration, temperature and time effect on process parameters.  Intermediate alkaline concentration (0.5M NaOH) provided maxima extraction yields.  High solubilisation by alkaline hydrolysis but low acidic precipitation efficiency.  Co-extraction of lipids increased with process intensity.

Steam explosion (150-200 °C, 5-30 min) was performed on a commercial cellulose presented in two configurations (fiberized and compact sheet) and its effect on their chemical and physical properties was studied, along with the influence of two different preservation methods (acetone drying and freezing) after pretreatment. No degradation compounds were produced during pretreatment, although solid recovery (R) decreased with temperature from 90% to 62%. Similar particle size and surface conditions (increased porosity) were found for both types of pretreated samples despite the extremely different initial configuration. Crystallinity diminished for 150 °C samples, but 200 °C pretreatment promoted recrystallization. Pretreatment also reduced polymerization degree, although enzymatic accessibility did not improve. Both acetone and freezing processes extremely affected cellulose properties. Acetone drying counterbalanced crystallinity and enzymatic accessibility variations of pretreated samples, while decreasing polymerization degree. Freezing dramatically decreased enzymatic accessibility of pretreated samples down to 15.8%.

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This study evaluated the effects of three chemical pretreatments of biomass sorghum (BS): dilute alkaline (PTA1 and PTA2), dilute acid (PTB1 and PTB2) and alkaline hydrogen peroxide (PTC1 and PTC2) in the enzymatic hydrolysis and ethanol production. Among the six investigated conditions, the pretreatment with 7.36% H2O2 (PTC2) was the most efficient in the lignin removal and preservation of the polysaccharide fraction. After the enzymatic hydrolysis, increases in the glucose and xylose concentrations were observed in the pretreated BS hydrolysates, mainly in PTB1 and PTC1. All the hydrolysates obtained low concentrations of inhibitors. In the alcoholic fermentations with Pichia stiptis, the greatest ethanol yield was HIGHLIGHTS  Alkaline, acid and alkaline peroxide pretreatments were evaluated in biomass sorghum hydrolysis. Acid and H2O2 pretreatments were the best in holocellulose protection and lignin removal. Highest monosaccharide yields were in hydrolysis of PTB1 (HCl 0.34%) and PTC1 (5% H2O2).  Greatest ethanol yield was obtained in PTB1 hydrolysate (16.15%).dos Santos, B.V; et al.