Please cite this article as: Martín Juárez, J., Riol Pastor, E., Fernández Sevilla, J.M., Muñoz Torre, R., García-Encina, P.A., Bolado Rodríguez, S., Effect of pretreatments on biogas production from microalgae biomass grown in pig manure treatment plants, Bioresource Technology (2018), doi: https://doi.org/10. 1016/j.biortech.2018.02.063 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ABSTRACTMethane production from pretreated and raw mixed microalgae biomass grown in pig manure was evaluated. Acid and basic pretreatments provided the highest volatile solids solubilisation (up to 81%) followed by alkaline-peroxide and ultrasounds (23%).Bead milling and steam explosion remarkably increased the methane production rate, although the highest yield (377 mL CH 4 /g SV) was achieved by alkali pretreatment.Nevertheless, some pretreatments inhibited biogas production and resulted in lag phases of 7-9 days. Hence, experiments using only the pretreated solid phase were performed, which resulted in a decrease in the lag phase to 2-3 days for the alkali pretreatment and slightly increased biomass biodegradability of few samples. The limiting step during the BMP test (hydrolysis or microbial inhibition) for each pretreatment was elucidated using the goodness of fitting to a first order or a Gompertz model. Finally, the use of digestate as biofertilizer was evaluated applying a biorefinery concept. Highlights Pretreatments solubilised volatile solids but also inhibited biogas production. Alkali pretreatment increased 2.3 times the methane production of the raw material. The removal of pretreated liquids did not improve the global methane production. Gompertz model fitted the results of methane production controlled by inhibition. Composition of digestates allows their possible valorisation as fertilizers.

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...

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Relación de artículos pertenecientes a la tesis y contribución………………………….11 List of publications The publications cited below are presented as a part of the current thesis. All papers were published in international journals indexed in ISI web of Knowledge (Papers I, III, and IV). Paper II have been submitted for publication in Algal Research and Paper V is being prepared.