To reduce the impact on the environment and enhance the sustainability of resources, it is necessary to promote and strengthen the use of landrace cultivars that advocate regenerative agriculture. In ...this study, the growth and development as well as the anaerobic digestion (AD) of six different landrace cultivars, two commercial hybrids cultivars and a public genotype of Sorghum bicolor have been evaluated. The landrace cultivars, in general, presented greater heights, biomass yields and compactness shoots as well as similar or an improvement in grain production compare to the commercial varieties. The AD of the different sorghum straws was performed in batch mode at mesophilic temperature (35°C). The landrace cultivar Zahina (ZH) obtained the highest final methane yield (413 ± 79 NL CH4 kg−1 VS, volatile solids) but the landrace cultivars Zahina gigante (ZHG) and Trigomillo (TG) were the ones that obtained the highest methane per biomass production (13.7 and 12.7 NL CH4 shoot unit−1, respectively). By contrast, the commercial varieties were the ones that obtained the lowest methane yields. Two mathematical models, first‐order kinetics and the Transference Function model, were used to fit the experimental data with the aim of describing and simulating the anaerobic biodegradation of these S. bicolor straw varieties and obtaining the kinetic constants. Both models allowed for adequately fitting the experimental results of methane production with time. In particular, the fastest biomethanization occurred using the commercial variety PR88Y20 (PR88) (specific rate constant k = 0.148 ± 0.008 days−1), while the slowest one was obtained from Panizo (PAN) variety (k = 0.064 ± 0.005 days−1). In addition, the highest values of the maximum methane production rate, Rm, were attained for the varieties ZH and PR88, which were 87.1% and 71.3% higher than that achieved for the PAN variety, which exhibited the lowest value.
Landrace cultivars presented greater biomass, compactness and grain production. Zahina (landrace cultivar) obtained the highest final methane yield: 413 NL CH4 kg−1 VS. Zahina gigante and Trigomillo (landrace cultivars) achieved the highest methane per biomass production.
The table olive industry produces a high quantity of wastewater annually. These wastewaters are very problematic because of their characteristics of high organic matter, high phenolic content, high ...salinity and conductivity. The quantities in which they are produced are also a serious problem. The worldwide production of table olives reached 2,550,000 tons in the last five campaigns, with the European Union contributing to 32% of total production. The problem of these wastewaters is focused on the Mediterranean area where the highest quantity of table olives is produced and to a lesser extent on the United States and South America. Countries like Spain produce around 540,000 tons of these wastewaters. At present, there is no standard treatment for these wastewaters with acceptable results and which is applied in the industry. Currently, the most common treatment is the storage of these wastewaters in large evaporation ponds where, during the dry season, the wastewater disappears due to evaporation. This is not a solution as the evaporation ponds depend completely on the climatology and have a high number of associated problems, such as bad odors, insect proliferation and the contamination of underground aquifers. Different studies have been carried out on table olive wastewater treatment, but the reality is that at the industrial level, none has been successfully applied. New and promising treatments are needed. The current review analyzes the situation of table olive wastewater treatment and the promising technologies for the future.
The brown marine alga Rugulopteryx okamurae (R. okamurae) has quickly spread through the Mediterranean coasts since it was firstly spotted in the area in 2015. This alien species has already ...colonized a great part of the Mediterranean western coasts and displaced the local biota, disrupting the natural and autochthonous marine ecosystem. Moreover, the related ‘green’ tides also provoke environmental problems ashore that need to be addressed. Comprehending the potential of this unwanted biomass could be of vital importance to lessen its ecological impact. In this study, the ashore R. okamurae was assessed for its potential as raw material for the extraction of reducing sugars and polyphenolic compounds with antioxidant capacities. The extraction process was evaluated and optimized using the response to surface methodology (RSM) combined with a modified Box-Behnken design. Initially, 2 key operational factors were identified as the most influential parameters (i.e. drying temperature and milling time). However, the type of solvent and the use of zeolite were included in the design as factors that potentially could have a significant impact on the process. The analyzed responses were the extraction yields for total phenolic compounds (TPC) and reducing sugars (RS). For the extraction of TPC the optimized methodology was based on the use of ethanol as solvent, a drying temperature of 60 °C and a zeolite-assisted milling time of 60 s, reaching a maximum yield of 15.33 ggallic acid kg−1. For the extraction of RS the optimized methodology was based on the use of water as solvent, a drying temperature of 100 °C and a zeolite-absence milling time of 50s, reaching a maximum yield of 10.42 gglucose kg−1.
•Extraction of R. okamurae compounds optimized via response surface methodology.•Aqueous extracts presented higher reducing sugar extraction yields.•Ethanol extracts presented higher total phenolic compound extraction yields.•Biomass drying temperature and milling time are the most influential factors.
This study shows, for the first time, how the natural biodegradation of the Phaeophyceae Rugulopteryx okamurae (R.o.) affects its methane yield, by biochemical methane potential assays, and the ...methane production kinetics. Additionally, a mechanical (zeolite-assisted milling) and a thermal (120 °C, 45 min) pretreatments were assessed. The highest methane yield was obtained from the mechanically pretreated fresh ashore biomass (219 (15) NLCH4 kgVS−1), which presents the use of zeolite during milling as an economical alternative for heavy metal toxicity reduction. Moreover, no significant differences were observed between the other tests (with the exception of the lowest value obtained for the mechanically pretreated fresh R.o.). Low methane yields were linked to the heavy metal content. However, an increase of 28.5 % and 20.0 % in the k value was found for the untreated fresh R.o. biomass and fresh ashore biomass, respectively, when subjected to thermal pretreatment. Finally, an enhancement of 80.5 % in the maximum methane production rate was obtained for the fresh ashore biomass milled with zeolite compared to the untreated fresh ashore biomass.
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•The mechanical pretreatment of FAR increased methane yield by 37.5 %.•The thermal pretreatment of FAR increased the kinetic constant value by 20 %.•All the methane production vs. time curves fitted a first-order and a TF model.•Heavy metal toxic limits were observed in all the studied cases.
The invasive alien seaweed Rugulopteryx okamurae (R.o.) has spread quickly through the Mediterranean Sea causing an unprecedented ecological impact. A solution integrated into a circular economy ...model is needed in order to curb the negative effects of its presence. Anaerobic digestion (AD) is proposed as a feasible process able to transform biomass into renewable energy. Nevertheless, in order to improve the methane yield and surpass the drawbacks associated with AD processes, this research proposes a thermal pretreatment and a new developed method where the macroalgae is mechanically pretreated with zeolite. Chemical and microstructure characterization of the algal biomass after pretreatments involved scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The highest methane yields of 240 (28) and 250 (20) NLCH4 kg−1 VSadded were obtained with the new mechanical pretreatment and the thermal pretreatment at 120 °C for 45 min without zeolite, achieving a 35 % improvement against the non-pretreated algae. A direct relationship between the crystallinity index of the samples and methane production was observed. The experimental data of methane production versus time were found to be in accordance with both first-order kinetic and Transference Function mathematical models.
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•AD is an efficient method to reduce the impact of the invasive alien R. okamurae.•The newly developed mechanical pretreatment increased methane yield by 35 %.•Cellulose crystallinity index showed a strong positive relationship with methane.•The sole mechanical pretreated assay showed a two-substrate first-order kinetics.
This study evaluates the comprehensive valorization of the byproducts derived from the two-phase olive oil elaboration process i.e., olive washing water (OWW), olive oil washing water (OOWW), and ...olive mill solid waste (OMSW) in a closed-loop process. Initially, the microalga Raphidocelis subcapitata was grown using a mixture of OWW and OOWW as the culture medium, allowing phosphate, nitrate, sugars, and soluble chemical oxygen demand removal. In a second step, the microalgal biomass grown in the mixture of washing waters was used as a co-substrate together with OMSW for an anaerobic co-digestion process. The anaerobic co-digestion of the combination of 75% OMSW–25% R. subcapitata enhanced the methane yield by 7.0 and 64.5% compared to the anaerobic digestion of the OMSW and R. subcapitata individually. This schedule of operation allowed for integration of all of the byproducts generated from the two-phase olive oil elaboration process in a full valorization system and the establishment of a circular economy concept for the olive oil industry.
This research evaluates the anaerobic digestion (AD) process of the residue generated in a new olive-oil manufacturing process for cold-pressed olive, a residue consisting of a mixture of the ...wastewater and solid waste obtained from this process. Additionally, in order to assess the possible influence of the level of ripening of the olives on the performance of anaerobic processing, olives of the Picual variety were collected at two stages, i.e., green olives and olives in veraison. The AD processes of the residues obtained from the cold-pressing process and the process without pressure (control) were comparatively assessed by means of biochemical methane potential (BMP) assays conducted at mesophilic temperature (35 ± 1 °C). Maximum values for methane yield (390 ± 1 NL CH4/kg VSadded) and biodegradability (84.5%) were obtained from the cold-pressed green olive residues. For the rest of the wastes studied, biodegradability also reached high values, ranging from 79.1 to 79.6%. The logistic model adequately fit the experimental data and allowed for the assessment of the anaerobic biodegradation of these wastes and for obtaining the kinetic parameters for each case studied. The theoretical values for ultimate methane production predicted from this model showed less than a 1% deviation from the experimental values. A decrease was detected for both types of olives tested in the rate of maximum methane production, Rm, during the cold-pressing process, from 44.3 ± 0.1 to 30.1 ± 1.3 L CH4/(kg VS·d) (green olives) and from 43.9 ± 1.5 to 38.7 ± 1.6 L CH4/(kg VS·d) (olives in veraison). Finally, the highest energy output result was detected in the waste from cold-pressed green olives (15.7 kJ/g VSremoved), which coincided with its high methane yield.
Microalgae are photosynthetic organisms able to grow faster than land plants and produce biomass with relatively high energy potential. Accumulated high-value compounds like lipids, minerals, or ...proteins have focused the attention of scientists due to the potential production of biofuels and other value-added products. However, several drawbacks regarding both the biochemical structure of these organisms and technological difficulties have prevented the industry for implementing a comprehensive low-cost process regarding energy and environmental contamination. Among these technologies, anaerobic digestion (AD) has greatly increased research attention because of its simplicity and the ability to produce easily recycle by-products. Moreover, anaerobic co-digestion (AcoD) has shown promising results as a method to bypass the AD problems of microalgae as a sole substrate. This review is focused on the recent trends and comparison of the AcoD process to maximize energy recovery from microalgae biomass and agro-industrial wastes. The yield of methane gas among the studied bibliography is compared and a critical review of published data and methods used is included.
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