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In this study, the production of fermentable sugars and biogas from thermally pretreated brewer's spent grains (BSGs) was investigated. There were two autohydrolysis conditions (C1-1S: 180 ºC, 30 min, 5 mL H2O g BSG −1 and C2-1S: 180 ºC, 60 min, 5 mL H2O g BSG −1) which were evaluated, with and without a previous low severity pretreatment (80 ºC, 10 min, 10 mL H2O g BSG −1). The highest specific methane production (302.4 NL CH4 kg COD −1) and enzymatic hydrolysis yield (EHY of 98%, 50 FPU g BSG −1) were obtained from the two-stage pretreatment, with the second stage operated at 180 °C for 60 min, 5 mL H2O g BSG −1. However, in the integrated process, the two-stage pretreatment with the second stage performed at 180 °C for 30 min, and 5 mL H2O g BSG −1 was the best condition to produce fermentable sugars from enzymatic hydrolysis of pretreated BSGs, using a lower enzyme loading (EHY of 93%, 25 FPU g BSG −1). The burning of biogas produced from an anaerobic digestion of liquid fractions (hydrolysates) generated after two-stage thermal pretreatment in a combined heat and power system can produce a net thermal energy of 1.71 MJ kg BSG dry basis −1 and electrical energy of 0.392 kW h kg BSG dry basis −1. [Display omitted] • Co-production of fermentable sugars and biogas from BSGs proved to be promising. • Two-stage thermal pretreatment of BSGs improved the enzymatic hydrolysis yield (EHY). • C1-2S condition (180 ºC, 30 min, 5 mL H2O g BSG −1) showed an EHY of 93%. • The biogas produced by C1-1S could generate 1.71 MJ kg BSG −1 and 0.392 kW h kg BSG −1. • BSG pretreatment showed potential to add value to it in a circular biobased economy. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the production of biobased volatile fatty acids (VFAs) from pretreated olive mill solid waste (OMSW). Three hydrothermal pretreatment (HP) conditions (D1: 125 ºC, 53 min; D2: 161 ºC, 62 min; D3: 191 ºC, 83 min) were selected. The pretreated olive mill solid fraction (OMSF), pretreated olive mill liquid fraction (OMLF), and pretreated OMSW were evaluated as potential substrates for acidification in the anaerobic digestion (AD) in liquid (L-AD), semi-solid (Ss-AD), and solid (S-AD) phases. The best acidification efficiency (AE) observed in this study was 65%, for L-AD and HP condition D2 (161 ºC, 62 min). However, the HP condition D2 applied to the Ss-AD provided a VFA concentration of 18218 mg L−1, about 6-fold higher than that observed in the L-AD system. Polyphenols changed the profile of VFAs, increasing the production of longer chain VFAs in the L-AD and S-AD systems. Also, the influence of the typology of the AD system and HP severity on the microbial community was evaluated. Proteobacteria and Firmicutes were the most representative phyla in acidogenic fermentation of OMSW substrates and the genera Enterobacter , Pseudomonas , Achromobacter , Clostridium , Ochrobactrum , and Peptoclostridium played an important role in the pretreated OMSW fermentation and, consequently, in the VFAs production profile. ga1 • HP applied to Ss-AD had the best potential profitability: US$ 130 per ton of raw OMSW. • The best AE was 65% for L-AD and HP condition D2 (161 ºC, 62 min). • Type of AD system and HP severity had great influence on VFAs production profile. • Phenolics changed the metabolic pathway for the production of longer chain VFAs. • Proteobacteria and Firmicutes were the dominant phyla in AD of the solid wastes. [ABSTRACT FROM AUTHOR]

This study evaluated the potential of energy generation using a combined heat and power co-generation system (CHP) from biogas produced during the anaerobic digestion of coffee husks (CH) pretreated with steam explosion. Pretreatment conditions assessed were time (1, 5, 15 and 60 min) and temperature (120, 180 and 210 °C). Polysaccharides solubilisation and biogas production were not correlated. While pretreatment with severities higher than 4 resulted in a highest solubilisation of cellulose, hemicelluloses and lignin; however, furans concentration in those cases hindered biomass biodegradation. Considering a CHP, all pretreatment conditions were worthwhile when compared to non-pretreated CH. The best condition was 120 °C for 60 min, in which a 2.37 severity showed the highest methane yield (144.96 NmL CH 4 g COD −1 ) and electricity production (0.59 kWh kg CH −1 ). However, even better results could be achieved using 120 °C for only 5 min, which would lead to a larger amount of CH daily processed. [ABSTRACT FROM AUTHOR]

In the context of a sugarcane biorefinery, sugarcane bagasse produced may be pretreated generating a solid and liquid fraction. The solid fraction may be used for 2G bioethanol production, while the liquid fraction may be used to produce biogas through anaerobic digestion. The aim of this study consisted in evaluating the anaerobic digestion performance of hemicellulose hydrolysate produced after hydrothermal pretreatment of sugarcane bagasse. For this, hydrothermal pretreatment was assessed in a continuous upflow anaerobic sludge blanket (UASB) reactor operated at a hydraulic retention time (HRT) of 18.4 h. Process performance was investigated by varying the dilution of sugarcane bagasse hydrolysate with a solution containing xylose and the inlet organic loading rate (OLR). Experimental data showed that an increase in the proportion of hydrolysate in the feed resulted in better process performance for steps using 50% and 100% of real substrate. The best performance condition was achieved when increasing the organic loading rate (OLR) from 1.2 to 2.4 g COD/L·d, with an organic matter removal of 85.7%. During this period, the methane yield estimated by the COD removal would be 270 L CH 4 /kg COD. Nonetheless, when further increasing the OLR to 4.8 g COD/L·d, the COD removal decreased to 74%, together with an increase in effluent concentrations of VFA (0.80 g COD/L) and furans (115.3 mg/L), which might have inhibited the process performance. On the whole, the results showed that anaerobic digestion of sugarcane bagasse hydrolysate was feasible and may improve the net energy generation in a bioethanol plant, while enabling utilization of the surplus sugarcane bagasse in a sustainable manner. [ABSTRACT FROM AUTHOR]

This study described the anaerobic degradation of the azo dye Remazol Golden Yellow RNL (RGY-RNL) using cellulose-immobilized riboflavin (MC 3) as the redox mediator. This new solid support containing immobilized riboflavin was synthesized from succinylated mercerized cellulose, and was characterized by elemental analysis, FTIR, and solid-state 13 C NMR. MC 3 was resistant to pH 2–9, and anaerobic degradation of RGY-RNL using MC 3 in the presence of anaerobic sludge yielded a zero order degradation rate constant ( k 0,obs ) equal to 0.189 mg/L h, which was 56% better than experiments carried out without a redox mediator. Color removal efficiency after 48 h of degradation averaged 89.4% in experiments with MC 3 and 72% without the addition of a redox mediator. These results showed that MC 3 can be used to immobilize redox mediators, allowing reduction of wastewater treatment costs. [ABSTRACT FROM AUTHOR]

This study evaluated the pretreatment of sugarcane bagasse (SCB) with dilute citric acid solution for biogas production. The black liquor (BL) from pretreatment and residual solid fraction (RSF) obtained after enzymatic hydrolysis were used as substrates for the biogas production. After saccharifications of the pretreated solid fractions performed with Cellic® CTec 3 cocktail, the highest concentration of total reducing sugars (TRS) was in the range of 10.7–184.8 g L−1 and the sugar yields were in the range of 3.5–88.8%. For BL, the contents of glucose, xylose, and arabinose were in the range of 1.9–8.9 g L−1, 4.0–24.7 g L−1, and 0.2–5.4 g L−1, respectively. Biogas production from BL and RSF resulted, respectively, in maximum values of 563.6 and 57.8 NmL g COD −1, indicating the feasibility of using dilute citric acid pretreatment coupled to biogas production in biorefineries. Brief energy and economic assessment were carried out considering the energy balance (thermal energy generated by burning biogas - thermal energy spent in the pretreatment), as well as revenue from a possible sale of electricity generated in a combined heat and power system. [Display omitted] [ABSTRACT FROM AUTHOR]

This study investigates the production of volatile fatty acids (VFAs) from anaerobic digestion of raw brewer's spent grains (RBSG) and the solid fraction of brewer's spent grains pretreated by alkaline extraction (PBSG). The variables pH (5−9) and temperature (20–50 ºC) were optimized using Doehlert experimental design. The maximum concentrations of VFAs obtained were 8126.6 ± 108.8 mg L−1 for RBSG and 8005.3 ± 267.9 mg L−1 for PBSG. Protein removal did not affect the fermentative production of VFAs from BSG. However, the type of substrate influenced the VFAs profile and the microbial community. Clostridiaceae and Peptostreptococcaceae were the most abundant members in the reactors fed with raw BSG. On the other hand, Bacteroidaceae and Oscillospiraceae played important roles in the anaerobic digestion of pretreated BSG, accounting for more than 52% of the identified microorganisms. A multiproduct biorefinery with protein removal and subsequent VFAs production had a higher potential revenue (US$ 37,909.00 per ton of RBSG), compared to VFAs production according to a single product model (US$ 258.80 per ton of RBSG) (pH 8 and temperature of 20 ºC). This study provides insights from physicochemical, biological, and engineering perspectives, paving the way for future research focused on utilizing RBSG and PBSG for VFAs production. [Display omitted] • Volatile fatty acids (VFAs) produced by fermentation of raw and pretreated BSG. • The operating parameters pH and temperature were optimized using a Doehlert design. • Carbon-to-nitrogen ratio affected VFAs profile and bacterial composition. • The production of valeric acid is correlated with the presence of protein. • Multiproduct biorefinery was more profitable than the single product layout. [ABSTRACT FROM AUTHOR]

Ozone pretreatment of coffee husks (CH) was evaluated to generate hydrolysates for biogas production and to preserve cellulose of the solid phase for 2G ethanol production. Pretreatment variables included liquid-to-solid ratio ( LSR ), pH and specific applied ozone load ( SAOL ). Considering single-stage anaerobic digestion (AD), the highest methane production (36 NmL CH 4 /g CH) was achieved with the hydrolysate generated in the experiment using LSR 10 mL/g, pH 11 and SAOL 18.5 mg O 3 /g CH, leading to 0.064 kJ/g CH energy recovery. Due to the presence of toxic compounds in the hydrolysate, the addition of powdered activated carbon (4 g/L) to the reactor enhanced biogas production, leading to 86 NmL CH 4 /g CH yield and 0.58 kJ/g CH energy recovery. When two-stage AD was applied, methane production resulted in 49 NmL CH 4 /g CH, with additional 19 NmL H 2 /g CH production, resulting in a net 0.26 kJ/g CH energy recovery. [ABSTRACT FROM AUTHOR]

The present study investigated the potential of UASB inoculum, by itself or mixed to nitrogenous residue (fresh bovine manure – FBM) or to adapted microorganisms (bovine rumen – BR), for biomethanation of raw and pretreated sugarcane bagasse (SB) by solid-state anaerobic digestion. The influence of autohydrolysis and organosolv pretreatment conditions on the efficiency of biomethanation process was also evaluated by means of kinetic parameters. Akaike Information Criterion was used to statistically evaluate methane production, and the multi-stage model exhibited the highest fit among the models tested. FBM addition resulted in improvements in the C/N ratio, higher yield (143.3NL CH4 kg VS −1 ) and higher rate constant (3.05NL CH4 kg VS −1 day −1 ) for CH 4 production from raw SB without any lag phase when compared to UASB inoculum itself which exhibited 5.6 days of lag phase. The FBM also led to a better inoculum adaptation to substrates which contained inhibitors such as xylooligomers and lignin fragments, and had lower C5 sugar content. [ABSTRACT FROM AUTHOR]

In the present study, the ozonation of sugarcane bagasse (SB) at different operational conditions (pH, time, liquid-to-solid ratio ( LSR )) was evaluated with the aim of generating a soluble liquid fraction (SLF) suitable for biogas production (CH 4 and H 2 ) via anaerobic digestion and a solid fraction prone to enzymatic hydrolysis and 2G ethanol production. The SLFs obtained were characterized for sugars, total organic carbon (TOC), soluble lignin, furans and other components identified by GC/MS. The results showed that it was possible to solubilize 45.2% of lignin, 48.3% of hemicelluloses and 40.7% of cellulose with the use of ozone (8 mg min −1 ) at pH 11 for 15 min, employing a LSR of 13.3 mL g −1 . The best results of biochemical methane potential (BMP) and biochemical hydrogen potential (BHP) were 2.6 Nm 3 of CH 4 and 0.18 Nm 3 of H 2 per kg of TOC, respectively. An energy balance for the best pretreatment conditions indicates that the combustion of such biogas led to an energy surplus of 0.1 MJ kg −1 SB for methane and to an energy deficit of 0.191 MJ kg −1 SB for hydrogen. Potentially inhibitory compounds for anaerobic digestion such as oxalic acid, butanal, xylitol, furanone, benzaldehyde, d -erythrotetrofuranose, d -erythro-pentofuranose and 2,5-furandione were identified in the hydrolysates, which negatively affected the anaerobic digestion and the energy balance. Nevertheless, the energy generated from the hydrolysates (as biogas) and from the ozonized solid fraction (as 2G ethanol) offsets the ozonation energy input and led to positive energy balance. [ABSTRACT FROM AUTHOR]

This study aimed at optimizing the net energy recovery from hydrogen and methane production through anaerobic digestion of the hemicellulose hydrolysate (HH) obtained by desirable conditions (DC) of autohydrolysis pretreatment (AH) of sugarcane bagasse (SB). Anaerobic digestion was carried out in a two-stage (acidogenic-methanogenic) batch system where the acidogenic phase worked as a hydrolysis and biodetoxification step. This allowed the utilization of more severe AH pretreatment conditions, i.e. T = 178.6 °C and t = 55 min (DC3) and T = 182.9 °C and t = 40.71 min (DC4). Such severe conditions resulted in higher extraction of hemicelluloses from SB (DC1 = 68.07%, DC2 = 48.99%, DC3 = 77.40% and DC4 = 73.90%), which consequently improved the net energy balance of the proposed process. The estimated energy from the combustion of both biogases (H 2 and CH 4 ) accumulated during the two-stage anaerobic digestion of HH generated by DC4 condition was capable of producing a net energy of 3.15 MJ·kg SB −1 dry weight . [ABSTRACT FROM AUTHOR]

This study aimed to optimize through design of experiments, the process variables (temperature – T , time – t and solid-to-liquid ratio – SLR ) for sugarcane bagasse (SB) autohydrolysis (AH) to obtain hemicellulose hydrolyzates (HH) prone to anaerobic digestion (AD) and biochemical methane production (BMP). The results indicated that severe AH conditions, which lead to maximum hemicelluloses dissolution and sugar content in the HH, were not the best for BMP, probably due to the accumulation of toxic/recalcitrant compounds (furans and lignin). Mild AH conditions (170 °C, 35 min and SLR = 0.33) led to the highest BMP (0.79 Nm 3 kg TOC −1 ), which was confirmed by the desirability tool. HH produced by AH carried out at the desired condition DC2 (178.6 °C, 43.6 min and SLR = 0.24) showed the lowest accumulation of inhibitory compounds and volatile fatty acids (VFA) and highest BMP (1.56 Nm 3 kg TOC −1 ). The modified Gompertz model best fit the experimental data and led to a maximum methane production rate ( R ) of 2.6 mmol CH 4 d −1 in the best condition. [ABSTRACT FROM AUTHOR]

• The proposed SB fractionation strategy led to substantial savings of H 2 O 2. • Alkaline extraction after hydrothermal pretreatment led to high delignification. • The higher accessibility of pretreated SB led to an enzymatic conversion of 88.9%. • 190.8 L ethanol ton SB −1 were produced by fermentation using S. cerevisiae LBCM1047. • The anaerobic digestion of residual liquid streams produced 27.46 Nm3 CH4 ton SB −1. The fractionation of sugarcane bagasse (SB) by hydrothermal pretreatment (HP, autohydrolysis) followed by alkaline extraction (AE) and advanced oxidative pretreatment (AOP) for production of second-generation ethanol and biogas was investigated. The AOP of SB was optimized using a Doehlert design, varying the applied H 2 O 2 load, liquid-to-solid ratio (LSR), and time. The responses evaluated were yield (Y), residual cellulose (RC), delignification (DE), and enzymatic conversion (EC). The AE of SB pretreated by HP led to 61.8% DE (using 0.2 mol L−1 NaOH). This high lignin removal enabled substantial savings of H 2 O 2 in the AOP. The optimized AOP conditions led to 78% Y , 82.2% RC , 42.7% DE , and 88.9% EC (overall glucose yield of 60.9%). Fermentation of the enzymatic hydrolysate with Saccharomyces cerevisiae yielded 190.8 L ethanol ton SB −1. Biogas production by anaerobic digestion of residual liquid streams of the pretreatment steps yielded 27.46 NL CH4 kg SB −1. An energy balance was estimated for the SB fractionation. [ABSTRACT FROM AUTHOR]