Supercritical Fluid Extraction of Fucoxanthin from the Diatom Phaeodactylum tricornutum and Biogas Production through Anaerobic Digestion.

Phaeodactylum tricornutum is the marine diatom best known for high-value compounds that are useful in aquaculture and food area. In this study, fucoxanthin was first extracted from the diatom using supercritical fluid extraction (SFE) and then using the extracted diatom-like substrate to produce bioenergy through anaerobic digestion (AD) processes. Factors such as temperature (30 °C and 50 °C), pressure (20, 30, and 40 MPa), and ethanol (co-solvent concentration from 10% to 50% v/v) were optimized for improving the yield, purity, and recovery of fucoxanthin extracted using SFE. The highest yield (24.41% w/w) was obtained at 30 MPa, 30 °C, and 30% ethanol but the highest fucoxanthin purity and recovery (85.03mg/g extract and 66.60% w/w, respectively) were obtained at 30 MPa, 30 °C, and 40%ethanol. Furthermore, ethanol as a factor had the most significant effect on the overall process of SFE. Subsequently, P.tricornutum biomass and SFE-extracted diatom were used as substrates for biogas production through AD. The effect of fucoxanthin was studied on the yield of AD, which resulted in 77.15 ± 3.85 LSTP CH4/kg volatile solids (VS) and 56.66 ± 1.90 LSTP CH4/kg VS for the whole diatom and the extracted P.tricornutum, respectively. Therefore, P.tricornutuman can be considered a potential source of fucoxanthin and methane and both productions will contribute to the sustainability of the algae-biorefinery processes.

Evaluation and modelling of methane production from corn stover pretreated with various physicochemical techniques.

Lignocellulosic by-products from agricultural crops represent an important raw material for anaerobic digestion and clean renewable, which is a key component of the circular economy. Lignocellulose is recalcitrant to biodegradation and pretreatments are required to increase methane yield during anaerobic digestion. In this work, the efficacy of different physicochemical pretreatments was compared using corn stover biomass as substrate. Anaerobic digestion of untreated and pretreated corn stover was performed in batch mode at mesophilic temperature (38°C) and organic matter solubilization of pretreated substrates was also investigated. The highest organic matter solubilization occurred in autoclave pretreatment (soluble chemical oxygen demand = 5630 ± 42 mg O2 L-1). However, the highest methane yield was obtained using alkaline pretreatment (367 ± 35 mL CH4 g-1 VSadded). Alkaline pretreatment increased methane yield by 43.3% compared to untreated control (256 ± 15 mL CH4 g-1 VSadded). Two mathematical models (i.e. first-order kinetics and transfer function) were utilized to fit the experimental data with the aim of assessing anaerobic biodegradation and to obtain the kinetic constants in all cases studied. Both models adequately fit the experimental results. The kinetic constant, k, of the first-order model increased by 92.8% when stover was pretreated with sulphuric acid compared with control. The transfer function model revealed that the maximum methane production rate, Rm, was obtained for the sulphuric acid treatment, which was 63.5% higher compared to control.

Screening of biomethane production potential from dominant microalgae.

The use of microalgae for biomethane production has been considerably increasing during the recent years. In this study, four dominant species belonging to the genera Scenedesmus, Chlorella, Dunaliella and Nostoc were selected. The influence of different genera with several morphological, structural and physicochemical characteristics on methane production was assessed in biochemical methane potential (BMP) tests. The ultimate methane yield values were 332 ± 24, 211 ± 2, 63 ± 17 and 28 ± 10 mL CH4/g VSadded for Scenedesmus obliquus, Chlorella sorokiniana, Dunaliella salina and Nostoc sp., respectively. The highest methane production was achieved by microalga species that had no complex cell wall or wall basically composed by proteins and simple sugars such as in S. obliquus, whereas lower methane yields were found for D. salina and Nostoc sp., due to the salinity effects and cell wall composition in terms of complex polysaccharide and glycolipid layers, respectively. Kinetic constant values obtained in the BMP tests ranged between 1.00 ± 0.08 and 0.097 ± 0.005 days(-1) for D. salina and S. obliquus, respectively.

Anaerobic digestion of spring and winter wheat: Comparison of net energy yields.

Anaerobic digestion of wheat was investigated under batch conditions. The article compares the potential net energy yield between a winter wheat (sown in the autumn) and a spring wheat (sown in the spring) grown in the same year and harvested at the same growth stage in the same farm. The spring wheat had a slightly higher biochemical methane potential and required lower energy inputs in cultivation, but produced a lower dry biomass yield per hectare, which resulted in winter wheat providing the best overall net energy yield. The difference was small; both varieties gave a good net energy yield. Spring sowing may also offer the opportunity for growing an additional over-winter catch crop for spring harvest, thus increasing the overall biomass yield per hectare, with both crops being potential digester feedstocks.

Assessment of the anaerobic acidogenesis of wet olive cake from a two-phase olive oil mill.

A study of the anaerobic acidogenesis of wet olive cake or olive mill solid waste (OMSW) from the two-phase olive oil mill industry was carried out. Eight different hydraulic retention times (HRTs) ranging from 50.0-10.7 days were studied. An increase of 935.7 % in total volatile fatty acids (VFA) over the initial acidic concentration in the OMSW (1.4 g L(-1) expressed as acetic acid) was achieved. The results showed a maximum total VFA generation rate of 5.05 g COD L(-1)d(-1), this rate being achieved at the same hydraulic retention time as the maximum acetic acid production (8.2 g L(-1)) and as the maximum acidification degree (34.4 %).

Feasibility of sunflower oil cake degradation with three different anaerobic consortia.

Sunflower oil cake (SuOC) is the solid by-product from the sunflower oil extraction process and an important pollutant waste because of its high organic content. For the anaerobic digestion of SuOC three different industrial reactors were compared as inoculum sources. This was done using a biochemical methane production (BMP) test. Inoculum I was a granular biomass from an industrial reactor treating soft-drink wastewaters. Inoculum II was a flocculent biomass from a full-scale reactor treating biosolids generated in an urban wastewater treatment plant. Inoculum III was a granular biomass from an industrial reactor treating brewery wastes. The highest kinetic constant for methane production was achieved using inoculum II. The inoculum sources were analyzed through PCR amplification of 16S rRNA genes and fingerprinting before (t = 0) and after the BMP test (t = 12 days). No significant differences were found in the bacterial community fingerprints between the beginning and the end of the experiments. The bacterial and archaeal communities of inoculum II were further analyzed. The main bacteria found in this inoculum belong to Alphaproteobacteria and Chloroflexi. Of the Archaea detected, Methanomicrobiales and Methanosarcinales made up practically the whole archaeal community. The results showed the importance of selecting an appropriate inoculum in short term processes due to the fact that the major microbial constituents in the initial consortia remained stable throughout anaerobic digestion.

Biochemical methane potential of winter wheat (Triticum aestivum L.): Influence of growth stage and storage practice.

The effect of growth stage at harvest and of storage practice on the biochemical methane potential (BMP) of winter wheat was investigated using batch-fed stirred mesophilic digesters. The wheat used was a single variety sown at the same time (autumn) and harvested at 3 different stages in its growth: medium milk (A), soft dough (B) and Caryopsis (C). Wheats (A and B) were ensiled whilst the later harvested material (C) with a higher dry matter content was treated by the alkalage process. The BMP values expressed on the basis of volatile solids (VS) were 0.360 + or - 0.030, 0.346 + or - 0.006 and 0.311 + or - 0.016l CH(4) g(-1) VS(added) for A, B and C, respectively. A simple first order kinetic model gave only a poor fit to the experimental data but a close match was obtained using a modified first order pseudo-parallel model which explains the methane production curve on the basis of differences in biodegradability of the plant material.

Kinetics for substrate utilization and methane production during the mesophilic anaerobic digestion of two phases olive pomace (TPOP).

A kinetic study of the anaerobic digestion process of two phases olive pomace (TPOP) was carried out in a laboratory-scale completely stirred tank reactor at mesophilic temperature (35 degrees C). The reactor was operated at influent substrate concentrations of 34.5 (substrate I), 81.1 (substrate II), 113.1 (substrate III), and 150.3 g COD/L (substrate IV). The hydraulic retention times (HRT) ranged between 8.3 and 40.0 days for the most diluted substrate (I) and between 10 and 50 days for the other three influent substrate concentrations used (substrates II-IV). The results obtained demonstrated that the rates of substrate uptake and methane production were correlated with the concentration of biodegradable total chemical oxygen demand (COD), through equations of the Michaelis-Menten type. A mass (COD) balance around the reactor allowed the methane yield coefficient and cell maintenance coefficient to be obtained, which gave values of 0.25 L CH(4)/g COD(t) and 0.25 days(-1), respectively. The first one was coincident to that obtained through experimental data of methane production and substrate consumption. The kinetic equations obtained and the proposed mass balance were used to simulate the anaerobic digestion process of TPOP and to obtain the theoretical COD of the reactor and methane production rates. The small deviations obtained (equal or lower than 10%) between the values calculated through the model and experimental ones suggest that the proposed model predicts the behavior of the reactor very accurately.