Lignocellulosic residues are a widely available energy resource, but their conversion into biogas through biomethanation may be hindered by a chemical structure with strong bonds. A strategy based on temperature-phased anaerobic digestion (TPAD) is here applied to optimize anaerobic digestion of artichoke as a representative lignocellulosic waste. The experiments consist of a first thermophilic stage conducted at 55 °C (7 and 5 days), followed by a second mesophilic stage at 35 °C. In addition, for comparison, single-stage temperature trials are carried out within the most common conditions for biomethanation (mesophilic at 35 °C, and thermophilic at 55 °C), as well as at the intermediate range (42 °C). In general, biomethanation of artichoke residues under TPAD configuration provides better performance than single-stage systems. Particularly, the best performance is observed for the TPAD arrangement using a thermophilic phase of 7 days. Thus, at this optimal configuration, volatile solids (VS) removal of 54%, and biogas and methane yields of 442 mL/g-VS and 375 mL-CH4/g-VS were reached, respectively. Moreover, a kinetic model coupling biogas generation and substrate consumption has been applied. Good agreement is found for both variables in each system tested. The calculated non-biodegradable substrate (S¿) is lower in TPAD systems (mean 49.6%) compared with that of single-stages (average 53.9%).

In this paper, the use of techniques such as TGA, FTIR-ATR and XRD has provided valuable information about the lignocellulosic wastes in anaerobic digestion (AD) processes. A deep study of their break-down in solid state could improve the management of these recalcitrant substrates. Representative wastes (artichoke -ART-, asparagus -ASP-, the co-digestion of both -AcoD-and pure cellulose -CELL-) were assessed in batch. The main obtained results were related to biochemical parameters. As the biomethanization progressed, hemicellulose, cellulose and lignin were weakened as shown by TGA, and cellulose crystallinity decreased as demonstrated by XRD. Additionally, results from FTIR-ATR allowed hypothesizing that the formation of acetate in solid state did not always lead to its solubilisation, thus hindering biogas formation. AcoD and CELL were the most successful in releasing the newly formed acetate from the solid fraction to the aqueous medium, increasing its bioavailability, which was supported by the higher biogas production.

Barley malt and sloe are two raw materials used in the production of beer and pacharan (a Spanish spirit drink), respectively. These organic wastes have been used as substrate of anaerobic digestion to assess the effect of temperature (35 degrees C and 55 degrees C) and thermal pretreatment (80 degrees C for 1.5 h). Viable microbiological isolates have also been identified through metabolic tests and a kinetic model which includes biogas generation and volatile solids (VS) removal has been proposed. Temperature studies on barley malt yielded higher productivities at 55 degrees C (the ratio of produced biogas volume per VS consumed was 119% higher than that at 35 degrees C), but similar VS removal (0.9% less elimination at 55 degrees C). On the other hand, sloe digestion was more effective at 35 degrees C (biogas/VS-consumed ratio 252% higher than that at 55 degrees C), while VS elimination can be considered the same. Attending to the effect of thermal pretreatment on productivity, barley malt showed no improvement while sloe was enhanced (144% at 35 degrees C and 160% at 55 degrees C). Kinetic modelling fits to the experimental results, showing differences in maximum specific growth rate of biomass according with the temperature conditions. In all cases the adjustment was good (R-2 > 0.96). Microbiological characterization identified bacterial population, both strict and facultative anaerobes.

Different wastes treated together can be the supplement of nutritional deficiencies for the microorganisms involved in anaerobic codigestion (AcoD). In this study, the presence of macromolecules and trace elements on AcoD of agricultural waste was assessed. An extra nutrients solution that plays a key role in the microbiological metabolism was used at three different conditions: mesophilic (35 degrees C), intermediate (42 degrees C) and thermophilic (55 degrees C). The main results showed that at 35 degrees C in the presence of nutrients, biogas production reached 1.5-fold the production of biogas without them. Additionally, productivity was 1.9 times higher than that for the process without nutrients. Also, 42 degrees C without nutrients posed an interesting approach due to the uncommon use of this intermediate temperature, which has been demonstrated to be worth considering (55% of VS removal and 7.4 L-biogas). The AcoD at 55 degrees C showed that biogas production also surpassed 10.2 L with nutrients and that mL-CH4/g-VS were 1.2-fold of that obtained for the process without extra solution. Results for each temperature indicate that the nutrients solution contributes to AcoD. Furthermore, 35 degrees C, the most widespread temperature range at industrial scale, was the temperature at which the impact of nutrients was more remarkable. A deeper knowledge of AD nutritional limitations according to temperatures can optimize the industrial process in order to get better biogas yields and biomass removal. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Microbial dynamics in an upgrading biogas reactor system undergoing a more than two years-period at stable operating conditions were explored. The carbon dioxide generated during biomass degradation in the first reactor of the system was converted to methane into the secondary reactor by addition of external hydrogen. Considering the overall efficiency, the long-term operation period resulted in an improved biogas upgrading performance (99% methane content). However, a remarkable accumulation of acetate was revealed, indicating the enhancement of homoacetogenic activity. For this reason, a shift in the anaerobic digestion microbiome was expected and evaluated by 16S rRNA amplicon analysis. Results demonstrated that the most abundant archaeal species identified in the first time point, Candidatus Methanoculleus thermohydrogenotrophicum, was replaced by Methanothermobacter thermautotrophicus, becoming dominant after the community adaptation. The most interesting taxonomic units were clustered by relative abundance and six main long-term adaptation trends were found, characterizing functionally related microbes (e.g. homoacetogens).

Agricultural lignocellulosic waste can generate serious environmental problems if not properly managed. Biodegradation, through anaerobic digestion (AD), is a cost-effective strategy for biogas production. However, studies on the biodegradation of lignocellulose show that the substrate is recalcitrant to microbiological hydrolysis, which reduces the efficiency of converting organic matter into biogas. The main reasons are its complex structure and slow biodegradation. The appropriate performance of biomethanization suggests a deep knowledge of substrate composition. Typically, the composition is about 10% to 25% lignin, 20% to 30% hemicellulose, and 40% to 50% cellulose. This book chapter will summarize the AD process and rate-limiting steps, compositional properties (focusing especially on pretreatment strategies applied to lignocellulosic biomass to improve methane yield), and overall AD performance. The most common pretreatments applied to organic substrates will be studied: physical, chemical, biological, and a combination of them. Additionally, the new trends in pretreatments will be exposed.

Anaerobic codigestion has shown to be feasible to manage organic waste. Different wastes treated together can be the supplement of nutritional deficiencies for the microorganisms involved. In this study, the presence of acromolecules and trace elements on anaerobic codigestion of agricultural waste has been assessed. An extra nutrients solution containing elements, which play a key role in the anaerobic microbiological metabolism, was used at three different temperature conditions: mesophilic (35°C), intermediate (42°C) and thermophilic (55°C). The main results showed that at 35°C in the presence of nutrients, biogas production reached 6.2L, almost 1.5-fold the production of biogas without them. Additionally, productivity was 359.3mL-CH4 / g-VS, which is 1.9 times higher than that for the process without nutrients. At 42°C up to 55% of VS were eliminated and more than 10.0L-biogas were produced, while biomethanization without extra nutrients solution only reached 7.4L. The anaerobic codigestion at 55°C showed that biogas production also surpassed 10.2L in the presence of nutrients and 146.99mL-CH4 / g-VS were obtained, being these results 1.2-fold those obtained for the process without extra solution. Results for each temperature showed that the nutrients solution could contribute to the biomethanization process of codigestion waste. Furthermore, 35°C was the temperature range at which the impact of nutrients was more remarkable.

Anaerobic digestion (AD) is becoming one of the most feasible and efficient options for agroindustrial waste management. However, this kind of waste can contain certain substances from the industrial activity, which could potentially inhibit or, at least, modify the biomethanization process. Pesticides are widely used in agricultural activities. Mancozeb is an ethylene dithiocarbamate fungicide with broad spectrum used in crops. It reacts with and inactivates sulfhydryl groups of aminoacids and enzymes of fungal cells, disrupting of respiration, lipid metabolism and production of energy. Tefluthrin is a synthetic pyrethroid insecticide used to control a wide range of soil pests. It causes neurotoxicity and is a sodium channel modulator. This paper assesses the influence of the presence of mancozeb and tefluthrin on thermophilic (55°C) anaerobic co-digestion (carrot, cabbage, green pea, artichoke and fava and broad bean) of synthetic agroindustrial waste. The main results show that the pesticides improve the biomethanization process referred to generation of biogas (123%), consumption of volatile solid -VS- (18%), removal of chemical oxygen demand (5%) and yield of biogas measured like mL biogas/ VS consumed (117%), between other parameters. Anaerobic codigestion on presence of pesticides seems feasible and improved in comparison with the codigestion without these substances.