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• Valorization of macroalgal residues by anaerobic digestion. • Knife milling and alkaline pretreatment enhanced methane production. • In semi-continuous reactors, alkaline pretreatment enhanced methane by 20%. • Digestates did not exhibit phytotoxicity. • Digestate from codigestion with sludge led to the highest tomato plant growth. The aim of this paper is to investigate the impact of pretreating macroalgal residue (MAR) from agar-agar extraction and its co-digestion with sewage sludge on methane production and the agronomic quality of the digestates produced. First, different pretreatments were assessed on BMP tests. Among milling technologies used, knife milling with a 4 mm-screen improved methane production by 25%. The MAR was then knife milled before alkaline, acid and thermal pretreatment. KOH pretreatment (5% TS basis, 25 °C for 2 days) led to the highest methane improvement. It was applied to semi-continuous anaerobic digestion and methane production achieved 237 Nml/gVS which was 20% higher than the control (198 Nml/gVS). In comparison to MAR mono-digestion, co-digestion with thickened activated sludge produced less methane (184 Nml/gVS) but reduced H 2 S emission by 91%. None of the digestates was toxic for the germination or growth of wheat and tomato plants. Particularly, co-digestion had the highest impact on tomato plant dry weight (+94% compared to soil alone) mainly due to the phosphorous brought by sludge. However, the impact of alkaline pretreatment on plant growth was not significant. [ABSTRACT FROM AUTHOR]

Biogas plants for waste treatment valorization are presently experiencing rapid development, especially in the agricultural sector, where large amounts of digestate are being generated. In this study, we investigated the effect of vibro-ball milling (VBM) for 5 and 30 min at a frequency of 20 s-1 on the physicochemical composition and enzymatic hydrolysis (30 U g-1 total solids (TS) of cellulase and endo-1,4-xylanase from Trichoderma longibrachiatum) of dry and wet solid separated digestates from an agricultural biogas plant. We found that VBM of dry solid digestate improved the physical parameters as both the particle size and the crystallinity index (from 27% to 75%) were reduced. By contrast, VBM of wet solid digestate had a minimal effect on the physicochemical parameters. The best results in terms of cellulose and hemicelluloses hydrolysis were noted for 30 min of VBM of dry solid digestate, with hydrolysis yields of 64% and 85% for hemicelluloses and cellulose, respectively. At the condition of 30 min of VBM, bioethanol and methane production on the dry solid separated digestate was investigated. Bioethanol fermentation by simultaneous saccharification and fermentation resulted in an ethanol yield of 98 geth kg-1 TS for raw solid digestate. Finally, in terms of methane potential, VBM for 30 min lead to an increase of the methane potential of 31% compared to untreated solid digestate. [ABSTRACT FROM AUTHOR]

Hydrothermal pretreatment of five lignocellulosic substrates (i.e. wheat straw, rice straw, biomass sorghum, corn stover and Douglas fir bark) were conducted in the presence of CO 2 as a catalyst. To maximize disintegration and conversion into bioenergy (methane and hydrogen), pretreatment temperatures and subsequent pressures varied with a range of 26–175 °C, and 25–102 bars, respectively. Among lignin, cellulose and hemicelluloses, hydrothermal pretreatment caused the highest reduction (23–42%) in hemicelluloses while delignification was limited to only 0–12%. These reductions in structural integrity resulted in 20–30% faster hydrolysis rates during anaerobic digestion for the pretreated substrates of straws, sorghum, and corn stover while Douglas fir bark yielded 172% faster hydrolysis/digestion due to its highly refractory nature in the control. Furans and phenolic compounds formed in the pretreated hydrolyzates were below the inhibitory levels for methane and hydrogen production which had a range of 98–340 ml CH 4 /g volatile solids (VS) and 5–26 ml H 2 /g VS, respectively. Results indicated that hydrothermal pretreatment is able to accelerate the rate of biodegradation without generating high levels of inhibitory compounds while showing no discernible effect on ultimate biodegradation. [ABSTRACT FROM AUTHOR]

Mechanical size reduction is considered as a primordial step of current and future lignocellulosic biorefinery. In this sense, it is of high interest to understand who are the biochemical and structural features of the lignocellulosic biomass, which affect the Specific Energy Requirement (SER), and in consequence the cost of mechanical size reduction processes. First, it was shown that the initial moisture content of the lignocellulosic biomass affect the SER and the final particle size distribution. The highest the moisture content gives raise the highest SER. Then, at fixed initial moisture content (≈7% DW), structural and biochemical features of lignocellulosic biomass that can affect the SER were determined. It was noticed that both arabinose/xylose ratio and accessible surface area lead to increasing the SER. On the contrary, the content of cellulose, lignin, crystallinity and p -coumaric acids links were found to have a positive effect on the reduction of the SER. [ABSTRACT FROM AUTHOR]

Because of their rich composition in carbohydrates, lignocellulosic residues represent an interesting source of biomass to produce biohydrogen by dark fermentation. Nevertheless, pretreatments should be applied to enhance the solubilization of holocelluloses and increase their further conversion into biohydrogen. The aim of this study was to investigate the effect of thermo-alkaline pretreatment alone and combined with enzymatic hydrolysis to enhance biohydrogen production from sunflower stalks. A low increase of hydrogen potentials from 2.3 ± 0.9 to 4.4 ± 2.6 and 20.6 ± 5.6 mL of H2 g–1 of volatile solids (VS) was observed with raw sunflower stalks and after thermo-alkaline pretreatment at 55 °C, 24 h, and 4% NaOH and 170 °C, 1 h, and 4% NaOH, respectively. Enzymatic pretreatment alone showed an enhancement of the biohydrogen yields to 30.4 mL of H2 g–1 of initial VS, whereas it led to 49 and 59.5 mL of H2 g–1 of initial VS when combined with alkaline pretreatment at 55 and 170 °C, respectively. Interestingly, a diauxic effect was observed with sequential consumption of sugars by the mixed cultures during dark fermentation. Glucose was first consumed, and once glucose was completely exhausted, xylose was used by the microorganisms, mainly related to Clostridium species. [ABSTRACT FROM AUTHOR]

Abstract: Dilute-acid pretreatments are commonly used to solubilize holocelluloses of lignocellulosic materials and represent a promising route to enhance biohydrogen production by dark fermentation. Besides the soluble sugars released, furan derivatives, such as furfural and 5-HMF, as well as phenolic compounds can accumulate in dilute-acid hydrolyzates and that may affect fermentative microbial populations. In this study, biohydrogen production from glucose (5 g VS L− 1) in batch tests was investigated in presence of increasing volumes (0% – control, 3.75%, 7.5%, 15% and 35% (v/v)) of dilute acid hydrolyzate generated from sunflower stalks (170 °C, 1 h, 4 g HCl/100 gTS). A sharp decrease of the hydrogen yield was observed from 2.04 mol H2 mol− 1 eq. hexose initial in the control to 0 mol H2 mol− 1 eq. hexose initial for volumes higher than 15% of added hydrolyzate. Although acetate and butyrate were the main end-products found in the control, ethanol and lactate accumulated accordingly with the increasing addition of hydrolyzate. A clear shift of dominant microbial populations from Clostridium sp. to Sporolactobacillus sp. was concomitantly observed, suggesting a specific inhibition of the biohydrogen-producing bacteria by adding increasing volumes of hydrolyzates. [Copyright &y& Elsevier]

Production of energy from lignocellulosic biomass or residues is receiving ever-increasing interest. Among the different processes, dark fermentation for producing biohydrogen and anaerobic digestion for producing biomethane present considerable advantages. However, they are limited by the accessibility of holocelluloses that are embedded in the lignin network. The authors propose a review of works on the conversion of biomass into biohydrogen and biomethane with the comprehensive description of (a) biomass composition and features that may impact on its anaerobic conversion and (b) the impact of different kinds of pretreatment on these features and on the performance of biohydrogen and methane production. [ABSTRACT FROM PUBLISHER]

Abstract: The conversion of sunflower oil cake (SOC) into methane by mesophilic anaerobic digestion was the object of this study. The effect of a combined dilute acid-thermal pretreatment (acid concentration and temperature) on solubilisation and methane potential was investigated using a central composite design (CCD). For temperatures up to 170°C, solubilisation of each parameter (total organic carbon, sugars and proteins) increased with the severity of the pretreatment (high temperature and high acid concentration). Methane production was higher for pre-treated samples than for the untreated samples (195mL CH4/gVS). The highest yield (302±10mL CH4/gVS) was obtained after acid pretreatment at 170°C. At this temperature, acid concentrations lower than 1% had no significant impact on methane production in comparison to thermal treatment alone. The volume of methane produced by the soluble fraction reached more than 60% of total methane production. An increase in methane production was correlated to the concentration of organic carbon in the liquid phase of samples pretreated at 130–170°C with acid. At temperatures higher than 170°C, some recalcitrant compounds were formed in the liquid phase. [Copyright &y& Elsevier]

In an integrated biorefinery concept, biological hydrogen and methane production from lignocellulosic substrates appears to be one of the most promising alternatives to produce energy from renewable sources. However, lignocellulosic substrates present compositional and structural features that can limit their conversion into biohydrogen and methane. In this study, biohydrogen and methane potentials of 20 lignocellulosic residues were evaluated. Compositional (lignin, cellulose, hemicelluloses, total uronic acids, proteins, and soluble sugars) as well as structural features (crystallinity) were determined for each substrate. Two predictive partial least square (PLS) models were built to determine which compositional and structural parameters affected biohydrogen or methane production from lignocellulosic substrates, among proteins, total uronic acids, soluble sugars, crystalline cellulose, amorphous holocelluloses, and lignin. Only soluble sugars had a significant positive effect on biohydrogen production. Besides, methane potentials correlated negatively to the lignin contents and, to a lower extent, crystalline cellulose showed also a negative impact, whereas soluble sugars, proteins, and amorphous hemicelluloses showed a positive impact. These findings will help to develop further pretreatment strategies for enhancing both biohydrogen and methane production. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effect of extrusion at high solid loading on corn stover (CS) properties and its enzymatic hydrolysis. This biomass was extruded under different screw speeds and different solid loadings and the impact of these parameters on the physicochemical properties was evaluated. It was found that lignocellulosic components were not significantly affected by the pretreatment, while the surface area increased with solid loading and rotation speed. Different enzyme cocktails were used for the enzymatic hydrolysis of extruded and untreated CS. Overall, mild twin‐extrusion enhanced the enzymatic hydrolysis of CS through an increase in glucose and xylose yields by 134–212% and 214–294%, respectively, when using Trichoderma longibrachiatum cellulase. The highest sugar content was obtained from CS extruded under 400 g total solids per liter and 200 rpm. The energy efficiency of the pretreatment was also assessed and was found to be maximal at 400 g total solids per liter and 200 rpm. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Hydrolysates resulting from the lignocellulosic biomass pretreatment in bioethanol production may be used to produce biogas. Such hydrolysates are rich in xylose but also contain lignin polymers or oligomers as well as phenolic and furan compounds, such as syringaldehyde, vanillin, HMF, furfural. The aim of this study was to investigate the impact of these byproducts on biomethane production from xylose. The anaerobic digestion of the byproducts alone was also investigated. No inhibition of the anaerobic digestion of xylose was observed and methane was obtained from furans: 430mLCH4/g of furfural and 450mLCH4/g of HMF; from phenolic compounds: 453mLCH4/g of syringaldehyde and 105mLCH4/g of vanillin; and, to a lesser extent, from lignin polymers: from 14 to 46mLCH4/gMV. The use of different natural polymers (lignosulfonates, organosolv and kraft lignins) and synthetic dehydrogenative polymers showed that higher S/G ratios and lower molecular weights in lignin polymers led to greater methane production. [Copyright &y& Elsevier]

After press separation of the liquid and solid digestate from an agricultural biogas plant, pyrolysis of solid anaerobic digestate was carried out (i.e., at 500 °C, 1h, and 10 °C/min) to produce biochar (37.6 wt%), bio-oil (33.7 wt%) and syngas (29.3 wt%). The organic phase of bio-oil and syngas exhibited high and low heating values of 28.4 MJ/kg and 12.9 MJ/Nm3, respectively. Then, the synergy of coupling biochar with liquid digestate for agronomic purposes was investigated by leaching experiment and growth plant tests on wheat. Leaching experiments using combination of liquid digestate (170 kg N/ha) and biochar demonstrated that biochar addition increases the cumulative leaching of all nutrients, except nitrate, that have a significant decrease of 82% and 91%, respectively at 50 and 100 t/ha, compared to soil treated only with liquid digestate. The co-application of biochar with liquid digestate on growth wheat plant tests demonstrated that biochar application at 50 t/ha did not exhibit a negative impact on the relative seed germination and improved aerial dry biomass production (up to 27.5%) compared to soil with only liquid digestate addition. Image 1 • Pyrolysis of the solid digestate increased the energy recovery from the solid digestate. • Adding biochar to the soil increases the gravimetric water retention. • Coupling of biochar and liquid digestate (LD) reduces the loss of nitrate by leaching. • Coupling of biochar and LD improves the growth of wheat plants compared to LD only. [ABSTRACT FROM AUTHOR]

This study aims at investigating how organic waste co-digestion coupled with alkaline pretreatment can impact the methane production and agronomic value of produced digestates. For this purpose, sludge alone and mixed with olive pomace or macroalgal residues were subjected to anaerobic digestion with and without alkaline pretreatment. In addition, co-digestion of pretreated sludge with raw substrates was also carried out and compared to the whole mixture pretreatment. KOH pretreatment enhanced methane production by 39%, 15% and 49% from sludge, sludge mixed with olive pomace and sludge mixed with macroalgal residues, respectively. The digestates were characterised according to their physico-chemical and agronomic properties. They were then applied as biofertilizers for tomato growth during the first vegetative stage (28 days of culture). Concentrations in chlorophyll a and carotenoids in tomato plants, following sludge digestate addition, rose by 46% and 41% respectively. Sludge digestate enhanced tomato plant dry weight by 87%, while its nitrogen content increased by 90%. The impact of nitrogen and phosphorus contents in the digestate was strongest on tomato plant dry weight, thus explaining the efficiency of sludge digestate relative to other types of digestate. However, when methane production is considered, the combination of pre-treatment with co-digestion of macroalgal residues and sludge appears most beneficial for maximizing energy recovery and for biofertilizer generation. Unlabelled Image • In mono-digestion, KOH pretreatment of sludge led to 39% higher methane yield. • Highest yield 281 N ml/g VS from pretreated mixture of sludge and macroalgal residue • Enhancement of dry weight reached up to 87% due to digestate application. • Sludge digestate enhanced chlorophyll a of tomato plant by 84%. • Dry weight of tomato was highly correlated with N and P content in digestate. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the efficiency of a mechano-enzymatic deconstruction of two macroalgae species for sugars and bioethanol production, by using a new enzymatic cocktail (Haliatase) and two types of milling modes (vibro-ball: VBM and centrifugal milling: CM). By increasing the enzymatic concentration from 3.4 to 30 g/L, the total sugars released after 72 h of hydrolysis increased (from 6.7 to 13.1 g/100 g TS and from 7.95 to 10.8 g/100 g TS for the green algae U. lactuca and the red algae G. sesquipedale, respectively). Conversely, total sugars released from G. sesquipedale increased (up to 126% and 129% after VBM and CM, respectively). The best bioethanol yield (6 geth/100 g TS) was reached after 72 h of fermentation of U. lactuca and no increase was obtained after centrifugal milling. The latter led to an enhancement of the ethanol yield of G. sesquipedale (from 2 to 4 g/100 g TS). [ABSTRACT FROM AUTHOR]

Large amounts of produced water are extracted by the Oil and Gas energy sector since the industrial revolution. This available water, often salty, can be used to dilute liquid digestate from the anaerobic digestion process, a promising source of nutrients for microalgae cultivation. The study investigates the growth of halotolerant microalgae and their associated bacteria in column photobioreactors (PBRs) and open raceway pond (RWP), to treat industrial wastewaters while producing biomass for energy valorisation. Microalgae were cultured in mixtures of saline artificial produced water (7–44 %v/v), liquid digestate (5 %v/v using PBRs, 29–63 %v/v using RWP) and seawater. Nannochloropsis oceanica and Tetraselmis suecica strains were firstly cultivated in 70 L PBRs in indoor conditions for 3 months and later in 1.1 m3 RWP operated in outdoor conditions for 5 months in spring-summer period. In PBRs, average productivity was 9.0 ± 4.2 gVSS·m−2·d−1 (102–153 mgVSS·L−1·d−1), with daily removal efficiencies for chemical oxygen demand, nitrogen and phosphorous up to 61.8, 31.6 and 97.2 %, respectively. In RWP, strong changes in the microalgae populations were observed. Productivity was 6.7 ± 5.2 gVSS·m−2·d−1 (30 ± 23 mgVSS·L−1·d−1), with daily removal efficiencies for chemical oxygen demand, nitrogen and phosphorous up to 48.4, 44.4 and 88.1 %, respectively. In parallel with the production of microalgae, a nitrifying microbial population grew in the RWP despite the high salinity (70 g L−1). Over these periods of several months, microalgae production was maintained using a culture medium containing high salt concentration, metals and harmful aromatic compounds. [Display omitted] • Halotolerant microalgae were cultivated in column photobioreactors and raceway pond. • Similar areal productivities (7-9 gVSS·m−2·d−1) were obtained using both systems. • Up to 62% COD, 32% nitrogen and 98% phosphorous removed using column photobioreactors. • Up to 48% COD, 44% nitrogen and 88% phosphorous removed using raceway pond. • High nitrification was observed despite the high salinity of the culture medium. [ABSTRACT FROM AUTHOR]

Highlights: [•] Innovative dry NaOH chemo-mechanical pretreatment was developed. [•] Dry (TSdry) and dilute (TSdilute) NaOH chemo-mechanical pretreatment were compared. [•] TSdilute consumed higher amounts of water and energy compared to TSdry. [•] Energy efficiency obtained for TSdilute was 0.417kg glucose kWh−1 and 0.888 for TSdry. [ABSTRACT FROM AUTHOR]

[Display omitted] • Saline microalgae biomass was used to investigate saline anaerobic digestion. • Inoculum used to treat non-saline sewage sludge was acclimated to 14 g·L-1 salinity. • CH 4 production was not impacted by salinity after 10 weeks of semi-continuous test. • Salinity causing 50 % inhibition of CH 4 production was 27 g·L-1 after acclimation. • The population of methylotrophic methanogens increased with salt acclimation. The aim of this study was to acclimate anaerobic prokaryotes to saline microalgae biomass. Semi-continuous experiments were conducted using two 1.5 L mesophilic reactors for 10 weeks, (hydraulic retention time of 21 days). The first reactor was solely fed with sewage sludge (control), while the second received a mixture of sewage sludge and microalgal biomass (80/20 %w/w) cultivated at 70 g·L-1 salinity. The in-reactor salinity reached after the acclimation phase was 14 g·L-1. Biomethane production was comparable between the control and acclimated reactors (205 ± 29 NmL Methane ·g VolatileSolids -1). Salinity tolerance assessment of methanogenic archaea revealed that salinity causing 50% inhibition of methane production increased from 10 to 27 g·L-1 after acclimation. Microbial diversity analyses revealed notable changes in methanogenic archaea populations during co-digestion of saline microalgae biomass, particularly methylotrophic (+27%) and acetotrophic (-26%) methanogens. This study has highlighted the possibility of treating efficiently saline microalgae in co-digestion with sewage sludge in future industrial biogas plants. [ABSTRACT FROM AUTHOR]

Anaerobic digestion for the valorization of organic wastes into biogas is gaining worldwide interest. Nonetheless, the sizing of the biogas plant units require knowledge of the quantity of feedstock, and their associated methane potentials, estimated widely by Biochemical Methane Potential (BMP) tests. Discrepancies exist among laboratories due to variability of protocols adopted and operational factors used. The aim of this study is to verify the influence of some operational factors (e.g., analysis frequency, trace elements and vitamins solution addition and flushing gas), feedstock conservation and the source of inoculum on BMP. Among the operational parameters tested on cellulose degradation, only the type of gas used for flushing headspace of BMP assays had shown a significant influence on methane yields from cellulose. Methane yields of 344 ± 6 NL CH4 kg-1 VS obtained from assays flushed with pure N2 and N2/CO2 (60/40 v/v). The origin of inoculum (fed in co-digestion) only significantly affected the methane yields for straw, 253 ± 3 and 333 ± 3 NL CH4 kg-1 VS. Finally, freezing/thawing cycle effect depended of the substrate (tested on biowaste, manure, straw and WWTP sludge) with a possible effect of water content substrate. [ABSTRACT FROM AUTHOR]

In this study, the effect of thermo‐alkaline pretreatment and recycling of the liquid fraction (black liquor) for successive pretreatment steps on chemical composition and methane yields from horse manure was investigated. At first, horse manure was subjected to alkaline pretreatment at 70 °C for 1 h (8.6 g NaOH/100 g total solids). Pretreated biomass was then separated into solid and liquid fractions (black liquor). In the subsequent stages, black liquor was mixed with 20% (v/v) of fresh NaOH and was reused to pretreat subsequent batches of horse manure (cycles 1–4). Chemical analyses showed that thermo‐alkaline pretreatment was effective in the delignification and solubilization of organic matter and thereby increased the holocellulose (cellulose and hemicelluloses) content in the solid fraction of horse manure. On comparison with untreated horse manure methane yields (225 ± 1 L CH4 kg−1 VSadded), thermo‐alkaline pretreatment improved the methane yields of horse manure by 39% (313 ± 16 L CH4 kg−1 VSadded). However, the effectiveness of black liquor recycling on methane production decreased (from 39 to 12%) with an increase in the number of recycling steps (from 1 to 4). Nevertheless, recycling of black liquor reduced the consumption of NaOH (40%) and water use (60%). Thus, thermo‐alkaline pretreatment with liquor recycling was found to be an effective pretreatment with an economic gain of 2.4 to 10.4 compared to pretreatment without recycling. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

The following study investigates the possibility of growing the Spirulina platensis (S. platensis) cyanobacteria on two agro-industrial anaerobic digestion (AD) digestates diluted with geothermal water. The two digestates (FAWD: Food and Agricultural Wastes Digestate and CDD: Cheese Diary Digestate) were selected based on their different chemical characteristics, attributed to the type of feedstock and the operating conditions used during the AD process. In the first part of the study, a screening experiment was performed in 200 mL glass tubes to evaluate the appropriate dilution factor to generate the maximum S. platensis growth using both AD digestates individually and geothermal water as sustainable alternative dilution agent. Based on the different growth parameters measured, dilution rates of 5x and 40x were chosen for CDD and FAWD respectively, as a trade-off between growth performances and quantity of water to use. Volumetric productivities of 33 ± 1 mg/L/d and 56 ± 8 mg/L/d combined with maximal concentrations of 0.52 ± 0.02 g/L and 0.69 ± 0.02 g/L were achieved when cultivating S. platensis on CDD and FAWD, respectively. In the second part, the selected experimental results were scaled-up to 6 L flat panels bioreactors and S. platensis biomass productivities of 71 and 101 mg/L/d were obtained for CDD and FAWD, respectively using sodium bicarbonate as inorganic carbon source. When regulating the pH to 8.5 with carbon dioxide (CO 2) injection, cultures were able to produce up to 1.13 g/L and 0.79 g/L of S. platensis corresponding to biomass productivities of 81 and 136 mg/L/d for CDD and FAWD, respectively. In addition, S. platensis properly assimilated the ammonium present in the digestate-based culture media, with removal efficiency up to 98% in the case of the CDD substrate. The characterization of the final S. platensis biomass revealed the presence of high concentration of carbohydrates (48.6–70.3 % of dry weight) in the culture supplemented with both AD digestates. The experimental findings show the potential of reusing liquid digestate, CO 2 as well as geothermal water for the sustainable production of carbohydrate-rich S. platensis biomass. [Display omitted] • Geothermal water was successfully used to prepare digestate-based culture media. • Experiments were scaled up from 200 mL culture tubes to 6 L flat panels bioreactors. • Ammonia stripping was reduced by controlling the pH during S. platensis cultivation. • The harvested S. platensis biomass showed high carbohydrate content. • The use of geothermal water reduced the water footprint of the bioremediation process. [ABSTRACT FROM AUTHOR]

Interest is growing in the production of biohydrogen from algae through dark fermentation, as alternative to fossil fuels. However, one of the limiting steps of biohydrogen production is the conversion of polymeric carbohydrates into monomeric sugars. Thus, physical, chemical and biological pretreatments are usually employed in order to facilitate carbohydrates de-polymerization and enhancing biohydrogen production from algae. Considering the overall process, biohydrogen production through dark fermentation leads generally to negative net energy balances of the difference between the energy produced as biohydrogen and the direct ones (heat and electricity) consumed to produce it. Thus, to make the overall process economically feasible, dark fermentation of algae must be integrated in a biorefinery approach, where the outlets are valorized into bioenergy or value added biomolecules.The present study reviews recent findings on pretreatments and biohydrogen production through dark fermentation of algae looking at the perspectives of integrating side streams of dark fermentation from algal biomass, according to a biorefinery approach. [ABSTRACT FROM AUTHOR]

During the last decade, the application of pretreatment has been investigated to enhance methane production from lignocellulosic biomass such as wheat straw (WS). Nonetheless, most of these studies were conducted in laboratory batch tests, potentially hiding instability problems or inhibition, which may fail in truly predicting full-scale reactor performance. For this purpose, the effect of an alkaline pretreatment on process performance and methane yields from WS (0.10 g NaOH g−1 WS at 90 °C for 1 h) co-digested with fresh wastewater sludge was evaluated in a pilot-scale reactor (20 L). Results showed that alkaline pretreatment resulted in better delignification (44%) and hemicellulose solubilization (62%) compared to untreated WS. Pilot-scale study showed that the alkaline pretreatment improved the methane production (261 ± 3 Nm3 CH4 t−1 VS) compared to untreated WS (201 ± 6 Nm3 CH4 t−1 VS). Stable process without any inhibition was observed and a high alkalinity was maintained in the reactor due to the NaOH used for pretreatment. The study thus confirms that alkaline pretreatment is a promising technology for full-scale application and could improve the overall economic benefits for biogas plant at 24 EUR t−1 VS treated, improve the energy recovery per unit organic matter, reduce the digestate volume and its disposal costs. [ABSTRACT FROM AUTHOR]