Semi-continuous Regime Research Articles

Integration of subcritical water pretreatment and anaerobic digestion technologies for valorization of açai processing industries residues

The objective of this work was to study the valorization of residual biomass and wastewater from açai fruit processing to obtain energy products and higher added value from such residues, through the integration between subcritical waterpretreatment and anaerobic digestion technologies. Subcritical watertechnology was performed to pretreat the residual biomass. For this process, the reactorwas feed with 5 g of açai residue and a solvent to biomass mass ratio of 80 g of water per gram of açai residue was used. The process was carried out at 170 and 200 °C, during 20 min, using water flow of 20 mL min−1 (15 Mpa system). Then, the residual biomass was submitted to the anaerobic digestion process using a reactor with pretreatment (integration) and a control reactor, both in semi-continuous regime and under mesophilic conditions (35 °C). The açai stone had a high carbohydrate concentration including 43.81% cellulose and 25.89% hemicellulose. For the evaluated conditions, subcritical water pretreatment at 200 °C gave the bestresultsforyield of reducing sugars, total reducing sugars and monosaccharide concentration. Anaerobic digestion experiments resulted in analkalinity between 150 and 1537 mgCaCO3.L−1 for the control reactor and between 249 and 491 mgCaCO3.L−1 for the reactor integration.Acetic acid was the main volatile fatty acid produced in both reactors, but butyric acid also had a very high concentration in the control reactor. The methane composition in the biogas for the integration reactor in the stabilization phase was between 60 and 80%, whilefor the control reactor it was in the range between 40 and 60%.The accumulated biogas yield was 7.79 and 791.81 L.KgTVS−1 for the control and integration reactor, respectively. Anaerobic digestion using the açai hydrolysate obtained by subcritical water pretreatment showed a significant advantage over the control digestion, resulting in30% more methane in the biogas and 100 times higheryield.

Sunflower oil transesterification with methanol using immobilized lipase enzymes.

The transesterification of sunflower oil with methanol, using immobilized lipase enzymes as catalysts, was studied. The process was carried out in a semi-continuous mode. Temperature (30-50°C), methanol flow (0.024-0.04ml/min), kind of enzyme (Lipozyme 62350, Lipozyme TL-IM, Novozym 435 and Pseudomonas cepacia Sol-Gel-AK) and enzyme concentrations (1.25-10% by weight) were the operating variables. The final product was characterized by the EN 14214 standard. All the parameters, except for cold filter plugging point, were similar to a diesel fuel. For low methanol flows, reaction rate was proportional to methanol concentration. High flows caused catalyst deactivation. Novozyme 435, Lipozyme TL-IM and Lipozyme 62350 showed similar maximum reaction rates, but Novozyme 435 was more resistant to deactivation. Pseudomonas cepacia hardly obtained 1% conversion. The catalyst concentration, up to 2.5%, had a positive effect on the reaction rate and conversion. The optimum temperature was 40°C. The initial reaction rate was in line with the Arrhenius law, up to 50°C. By differential and integral methods, the Michaelis-Menten, competitive inhibition and ping-pong bi-bi kinetic parameters were determined. The transesterification of sunflower oil in a semi-continuous regime of alcohol improved the results, compared to the discontinuous regime, and those were similar to the obtained ones in a discontinuous regime with step-by-step methanol addition. The lipase that showed the best yield and higher resistance to deactivation was Novozym 435. The kinetic models that forecast the deactivation of lipases by an inhibitor described the experimental behavior properly.

Photofermentative Poly-3-Hydroxybutyrate Production by Rhodopseudomonas sp. S16-VOGS3 in a Novel Outdoor 70-L Photobioreactor

In the present study, the performance of a 70 L photobioreactor, operating outdoors, was investigated using a purple bacterial strain as Rhodopseudomonas sp. S16-VOGS3 for producing poly-3-hydroxybutyrate (PHB). The novel photobioreactor was equipped with 5 rows L-shaped; the bottom of every row was placed in a stainless-steel tank containing water with controlled temperature. The photofermentation trials were carried out under fed-batch mode and under a semi-continuous regimen using lactic acid as the carbon source. The effect of the irradiance and the carbon/nitrogen ratio on the PHB accumulation was investigated, in order to evaluate the optimal bacterial growth. The results showed the feasibility of the prototype photobioreactor for the production of PHB by Rhodopseudomonas sp. S16-VOGS3 under the natural light/dark cycle. During the fed-batch growth (144 h long), the cumulative PHB increased quickly reaching a maximum value of 377 mg/L and decreased to 255 mg/L during the semi-continuous regimen (336 h long).

Methane potential of fruit and vegetable waste: an evaluation of the semi-continuous anaerobic mono-digestion

ABSTRACTThe anaerobic digestion (AD) of a high diversity blend of fruit and vegetable waste (FVW) generated in tropical conditions as a single substrate was performed. A continuously stirred tank reactor (CSTR) operated in semi-continuous regime was used for AD. The reactor performance was monitored with gradually increasing organic loading rates (OLRs) from 0.5 up to 5.0 gVS L–1 d–1. The biochemical methane potential (BMP) of FVW determined by batch bottles was 360 LN CH4 kgVS–1, with a biodegradability of 79%. A stable pH with an adequate level of buffering capacity was observed during the entire experiment. Methane yield indicated the best performance at an OLR of 3.0 gVS L–1 d–1, with 285 LN CH4 kgVS–1 added, reaching 79% of BMP. At an OLR over 3.0 gVS L–1 d–1 accumulation of volatile fatty acids (VFA) was detected; in particular, propionic acid was monitored, and a decreased methane yield was detected. Biogas production rate was 1.55 LN L–1 d–1 and showed linear increase according to increases in the OLR.

Codigestion of sludge and citrus peel wastes: Evaluating the effect of biochar addition on microbial communities

In this study, the effects on process performance and changes in microbial populations with the addition of biochar to the anaerobic digestion of sludge and orange peels were evaluated. Biochar had a positive influence in batch digestions, leading to a decrease in the lag phase and an increase in methane yields; this was even more evident for citrus peel wastes, which reached an increase of approximately 33% when 10 g L−1 of biochar was added and 56% when 30 g L−1 was added. Particle size analysis performed for the experiments shows greater surface area available in biochar systems for biomass immobilization.Analysis of the microbial communities by means of 16S rRNA gene pyrosequencing shows that the biochar addition favoured the electro-active microorganisms consortia creating a synthrophic metabolism between eubacterial and archaeal populations, which resulted in an improvement of the anaerobic digestion performance.The codigestion of the mixture under a semicontinuous regimen showed an improvement in methane yields of approximately 60% and at hydraulic retention times of 30–20 days (reaching methane production values above 500 L CH4 kg VS−1 at an OLR of 1.49 kg VS m−3 d−1). The enhancement observe in biochar supplemented fermentations may be explained by the adsorption of inhibitors and the relatively high surface area favoured the adhesion and growth of microorganisms.

Effect of nutritional status and concentration of Nannochloropsis gaditana as enrichment diet for the marine rotifer Brachionus sp

The development of strategies to improve the quality and to optimize the costs of rotifer production for fish larval feeding, particularly those related to microalgal supply, are highly desirable. In the present work, three different rations (80,000, 130,000 or 200,000 cells rotifer−1) of Nannochloropsis gaditana were assessed as enrichment diets for the marine rotifer Brachionus sp. The microalga was cultured in semi-continuous regime with two different daily renewal rates, 10% and 40%, which provided nutrient-depleted or nutrient-sufficient conditions respectively and resulted in strong differences in biochemical composition. Protein and arachidonic acid (ARA) content were twice higher and eicosapentaenoic acid (EPA) was three times higher in N. gaditana from nutrient-sufficient cultures. After 24-h enrichment, rotifers fed N. gaditana cultured in nutrient-sufficient conditions showed higher dry weight, as well as higher contents of protein, lipids and carbohydrates. Total polyunsaturated fatty acids (PUFAs) and ARA contents increased >50%, whereas EPA content doubled in rotifers fed N. gaditana from nutrient-sufficient conditions. As for feed ration, the increase from 80,000 to 130,000 cells individual−1 enhanced the accumulation of protein, lipids, carbohydrates, total PUFAs, ARA and EPA, but a further increase to 200,000 cells individual−1 only enhanced the accumulation of lipid content. Our results show that the nutritional quality of microalgae, rather than concentration, is the most important factor influencing biomass productivity and biochemical composition of rotifer cultures. Since microalgal biomass is in general a limited resource for aquaculture, the improvement of its nutritional value through the optimization of culture conditions should be considered as an adequate and cost-efficient strategy to produce high-quality live feed.

Effect of fed‐batch and semicontinuous regimen on Nannochloropsis oculata grown in different culture media to high‐value products

AbstractBACKGROUNDHigh cell density in cultures of microalgae is a key factor to recover biomass and extract metabolites of interest. A fed batch tubular reactor (FBTR) and semi‐continuous reactor (SCR) with f/2 Guillard Medium (f/2GM) and algal medium (AM) were evaluated. Both modes were operated under completely defined conditions to assess their effect on cell density, and lipid, protein and carbohydrate productivity of the microalgae Nannochloropsis oculata.RESULTSResults show that the FBTR promotes the highest cell density for both culture media, achieving 525 ± 1.84×106 cell mL‐1. With AM in the SCR, specific growth rate, productivities of biomass and lipids were the highest, as well as content of protein (48%), lipid (52.1%) and carbohydrates (17%). No significant differences were found in saturated fatty acids composition, whereas unsaturated fatty acids composition was affected by the operating regimen, this being higher in the FBTR.CONCLUSIONThe use of AM in both operating modes, FBTR and SCR, increased the cell density and improved the lipid content of N. oculata. A good option would be to combine both culture modes; first, use the FBTR to obtain high cell densities and then apply the SCR mode to increase lipid productivity; finally, an important quantity of high‐value products could be recovered. © 2017 Society of Chemical Industry

Anaerobic co-digestion of sugarcane press mud with vinasse on methane yield

The conversion efficiency of high solids waste digestion as sugarcane press mud (P) may be limited due to hydrolysis step. The option of co-digestion with vinasse, main liquid waste generated from ethanol production, was investigated under batch regime at mesophilic conditions (37.5±1°C) and the best mixture was evaluated under semicontinuous regime in stirred-tank reactors. The maximum values for methane yield in batch tests were for V75/P25 and V50/P50 mixtures (on basis of the chemical oxygen demand (COD) percentage added in the mixture), with an average value of 246NmL CH4g−1 CODfed, which was 13% higher than that of press mud alone. A highest methane production rate of 69.6NmL CH4g−1 CODfed−1d−1 was obtained for the mixtureV75/P25. During the experiment carried out in CSTR reactors, the organic loading rate (OLR) was increased from 0.5 up to 2.2gVSL−1d−1. Methane yields of 365L CH4 kg−1VS and biogas productivities of 1.6LL−1 were obtained in co-digestion, which was 64% higher in comparison to mono-digestion. The performance of the process in mono-digestion was less stable than in co-digestion, with a significant fall of methane yield to 1.8kgVSm−3d−1, and a partial inhibition of the methanogenic archaeas when the OLR was increased up to 2.2kgVSm−3d−1. The co-digestion of vinasse with press mud is a good option for the treatment of streams at the alcohol-sugar industry.

Mathematical Simulation of the Extraction of a Blending Agent from Cylindrical Bodies in the Semicontinuous Regime

A problem of the kinetics of extraction of a blending agent from cylindrical bodies in an apparatus of semicontinuous action (periodic for the solid phase and continuous for the liquid phase) in which the liquid phase is completely mixed was formulated and solved analytically. The kinetics of the indicated process at different specific flow rates of the liquid phase was analyzed with the use of a numerical method. Recommendations on the use of the solution obtained for calculating the kinetics of extraction of technological contaminants from textile materials in the process of their flushing are given

BioH2 photoproduction by means of Rhodopseudomonas palustris sp. cultured in a lab-scale photobioreactor operated in batch, fed-batch and semi-continuous modes

The present investigation deals with Rhodopseudomonas palustris sp. grown, using acetate, for purposes of hydrogen generation. All experiments were carried out using a lab-scale photobioreactor. The cultures were irradiated with a 150W (OSRAM power star HQI-TS) lamp impinging on the reactor surface an irradiance of 74W/m2. Three different growth regimens were compared: batch, fed-batch, and semi-continuous. In the third approach, two daily dilutions were applied, in order to operate the photobioreactor at two hydraulic retention times: 240h in the first semi-continuous regimen (SC240h) and 60h in the second (SC60h). The best performances were attained when operating the photobioreactor in fed-batch mode. A maximum hydrogen production rate of 15.21mL(H2)/Lh was achieved. The hydrogen yield (YH) was 1.60mol H2/mol acetic acid in SC240h; 1.42mol H2/mol acetic acid when the culture was operated in fed-batch mode, and 0.85mol H2/mol acetic acid under a batch growth regimen. YH decreased to 0.36mol H2/mol acetic acid in SC60h. Significant changes in the oxidation–reduction potential were noted among the selected growth regimens tested then and also over time.

PHYSIOLOGICAL CHARACTERISTICS OF Panax japonicus SUSPENSION CELL CULTURE DURING GROWTH SCALING-UP

A scaled-up cultivation from flasks to semi-industrial bioreactors (up to 630 l) of the Panax japonicus suspension cell culture under a semi-continuous regime has been performed. The cell population growth and biosynthetic characteristics during the scaling-up process were investigated. It was shown that the cultivation in bioreactors had less effect on the growth than on biosynthetic characteristics (ginsenoside formation). The decrease in the total content of major gingenosides in the cell biomass and also changes in the ratio of individual compounds were observed as a result of going to the bioreactor cultivation. The under-research strain is characterized by a wide variation of ginsenoside content under either conventional culturing in flasks or growing in a bioreactor. The regular chemical analysis showed, thad the total content of 7 major ginsenosides (Rf, Rbi, Rc, Rb 2 , Rd, Rgi and Re) in cell biomass can vary from 0.5% to 3.0 % of dry cell biomass.

Characterization of a model cyanobacterium Synechocystis sp. PCC 6803 autotrophic growth in a flat‐panel photobioreactor

We characterized the photoautotrophic growth of glucose‐tolerant Synechocystis sp. PCC 6803 in a flat‐panel photobioreactor running on a semicontinuous regime under various lights, temperatures, and influx carbon dioxide concentrations. The maximum reached growth rate was 0.135 h−1, which corresponds to a doubling time of 5.13 h—a growth speed never reported for Synechocystis before. Saturating red light intensity for the strain was 220–360 μmol(photons) m−2 s−1, and we did not observe any photoinhibition up to 660 μmol(photons) m−2 s−1. Synechocystis was able to grow under red light only; however, photons of wavelengths 405–585 and 670–700 nm further improved its growth. Optimal growth temperature was 35°C. Below 32°C, the growth rates decreased linearly with temperature coefficient (Q10) 1.70. Semicontinuous cultivation is known to be efficient for growth characterization and optimization. However, the assumption of correct growth rates calculation—culture exponential growth—is often not fulfilled. The semicontinuous setup in this study was operated as a turbidostat. Accurate online OD measurements with high time‐resolution allowed fast and reliable growth rates determination. Repeating diluting frequencies (up to 18 dilutions per day) were essential for rapid growth stability evaluation. The presented setup provides improvement to previously published semicontinuous characterization strategies by decreasing experimental time requirements and maintaining the culture in exponential growth phase throughout the entire characterization procedure.

Batch Growth of Chlorella Vulgaris CCALA 896 versus Semi-Continuous Regimen for Enhancing Oil-Rich Biomass Productivity

The aim of this study was to induce lipid accumulation in Chlorella cells by creating stressful growth conditions. Chlorella vulgaris CCALA 896 was grown under various batch growth modes in basal and modified BG-11 and Kolkwitz culture broths, using a continuous light regimen of 150 µE/m2/s, at 30 °C. In order to perform the experiments, two indoor photobioreactor shapes were used: a cylindrical glass photobioreactor (CGPBR) with a working volume of 350 mL, and a flat glass photobioreactor (FGPBR) with a working volume of 550 mL. Stress-eliciting conditions, such as nitrogen and phosphorous starvation, were imposed in order to induce lipid accumulation. The results demonstrated that more than 56% of the lipids can be accumulated in Chlorella biomass grown under two-phase batch growth conditions. The highest biomass productivity of 0.30 g/L/d was obtained at the highest nominal dilution rate (0.167 day−1) during a semi-continuous regimen, using a modified Kolkwitz medium. During the pH-stress cycles, the amount of lipids did not increase significantly and a flocculation of Chlorella cells was noted.

Enhancing neutral lipid content in Skeletonema marinoi through multiple phase growth in a bench photobioreactor

The continuing increase in fuel demand, the dramatic situation of climate changes and global warming are bringing worldwide attention to identification of alternative energy source that can replace fossil fuel. Among all the feedstock considered for biodiesel production, microalgae are the most promising. In particular, it has been demonstrated that microalgae enhance their neutral lipids content in stress conditions, such as nutrient starvation. However, this increase in neutral lipids content is often coupled with a strong biomass decrease. In this study, in order to limit this side effect, a novel three-phase growth strategy was tested on the diatom Skeletonema marinoi. After a first phase directed to biomass production the culture, during a second phase of semi-continuous regimen characterized with reduction of nitrate concentration, achieved a neutral lipids content per cell of 10% of dry weight with slight impact on biomass. After these two phases the cells, gradually acclimatized to low nitrogen concentration, were still able to grow in a third maturation phase performed in batch. During this last phase, the culture further increased neutral lipid content up to the 30 % of dry weight.

Dry thermophilic anaerobic digestion of the organic fraction of municipal solid wastes: Solid retention time optimization

The thermophilic temperature has showed operational advantages in the Anaerobic Digestion process (AD). The increasing of the rate of hydrolysis, which suppose an acceleration of the overall process, and a higher hygienization of the final digestate are one of them. Dealing with OFMSW (Organic Fraction of Municipal Solid Waste) from non-selective collection systems involves additional difficulties due to their heterogeneity. The AD process of OFMSW is conducted usually in the range of 20–35% TS (dry AD). The main objective of this study was to determine the optimum Solids Retention Time (SRT) for the dry thermophilic AD of OFMSW operating in semi-continuous regime. Thus, the following SRTs have been tested: 15, 10, 8, 6, 5, 4 and 3 days. The main results have showed that the process is feasible in SRTs lower that those found in literature. Probably the history of the reactor, joined to the lower organic content in the waste, can be a key factor and the progressive decreasing of SRT is a strategy that permits to maintain stable conditions for lower SRT. The best operating conditions for thermophilic semicontinuous systems ranged in 8–5 days, with a yield of 0.33–0.34 LCH4/gVSadded and a concentration of Volatile Fatty Acids (VFA) around 100 mg HAc/L. The process becomes unstable for SRTs lower than 4 days, showing a clear decrease in methane productivity (lower than 0.2 LCH4/gVSadded) and an accumulation of VFA (more than 500 mg HAc/L). In general, SRTs below 4 days were not suitable for single stage of dry AD of OFMSW.

NMR Characterization of Carbon Dioxide Chemical Absorption with Monoethanolamine, Diethanolamine, and Triethanolamine

The present work analyzes and compares the carbon dioxide absorption process in aqueous solutions of different amines (MEA, monoethanolamine; DEA, diethanolamine; TEA, triethanolamine). This study evaluates the influence of the reagents nature upon absorption using a semicontinuous regime in a bubble contactor. 13C and 1H nuclear magnetic resonance (NMR) spectroscopy has been used to analyze species (reagents and/or products) in the reaction medium. In this way, the influence of the amino group substitution degree and carbon dioxide loading upon the chemical absorption mechanism were analyzed.

Co-digestion of used oils and urban landfill leachates with sewage sludge and the effect on the biogas production

This paper evaluates the potential of mesophilic anaerobic digestion (AD) in the treatment of used oils and landfill leachates through co-digestion of the sludge produced in a wastewater treatment plant (WWTP). Biomethane potential (BMP) tests were performed on two different co-substrates and on WWTP sludge. The biogas production per kg of fresh matter of the sludge generated in a WWTP was only 6.1Nl/kg due to its low volatile solids concentration. Biogas production of landfill leachates per kg of fresh matter was found to be low (12.4Nl/kg). The biogas production per kg of fresh matter for the used oil over a period of 47days (not completely degraded) was 970.6Nl/kg. Used oil was selected as co-substrate according to these results. Anaerobic co-digestion of sludge and used oil was conducted in a pilot plant fed in semi-continuous regime in the mesophilic range (38°C) to obtain their adequate mixture in order to ensure the correct function of the process. The optimum oil percentage in the mixture was 19% (volatile solids basis). Once the appropriate mixture was obtained the co-digestion process was carried out in the digester of the Pobla de Farnals WWTP. The co-digestion process improved the performance of volatile matter removal (showing an 11% increase over the period without co-digestion) as well as the biogas production (a 23.5% increase over the period without co-digestion) without disturbing the anaerobic digestion process. The total production of biogas per day in the WWTP increased over the period without co-digestion.

In situ electric properties of Ag films deposited on rough substrates

Silver (Ag) films have been deposited on rough substrates (including frosted glass and silicone grease), and for comparison on flat glass, by DC-magnetron sputtering, and their sheet resistances measured in situ during deposition. It is found that the growth of Ag films proceeds through three distinct stages: discontinuous, semi-continuous, and continuous regimes. The sheet resistance on rough substrates jumps in the vicinity of the percolation threshold, whereas the resistance on flat substrates decreases monotonically during deposition. The abnormal in situ electric properties on rough substrates are well explained based on the differences of the growth mechanism and microstructure of Ag films on different substrates.

Hydrogen Photoproduction byRhodopseudomonas palustris42OL Cultured at High Irradiance under a Semicontinuous Regime

The main goal of this study was to increase the hydrogen production rate improving the culture technique and the photobioreactor performances. Experiments were carried out at a constant culture temperature of 30°C and at an average irradiance of 480 W m−2 using a cylindrical photobioreactor (4.0 cm, internal diameter). The culture technique, namely, the semicontinuous regime for growing Rhodopseudomonas palustris 42OL made it possible to achieve a very high daily hydrogen production rate of 594 ± 61 mL (H2) L−1 d−1. This value, never reported for this strain, corresponds to about 25 mL (H2) L−1 h−1, and it was obtained when the hydraulic retention time (HRT) was of 225 hours. Under the same growth conditions, a very high biomass production rate (496 ± 45 mg (dw) L−1 d−1) was also achieved. Higher or lower HRTs caused a reduction in both the hydrogen and the biomass production rates. The malic-acid removal efficiency (MAre) was always higher than 90%. The maximal hydrogen yield was 3.03 mol H2 mol MA−1 at the HRT of 360 hours. The highest total energy conversion efficiency was achieved at the HRT of 225 hours.

Assessment of carotenoid production by Dunaliella salina in different culture systems and operation regimes

The effect of operation regime and culture system on carotenoid productivity by the halotolerant alga Dunaliella salina has been analyzed. Operation strategies tested included batch and semi continuous regime, as well as a two-stage approach run simultaneously in both, open tanks and closed reactor. The best results were obtained with the closed tubular photobioreactor. The highest carotenoid production (328.8 mg carotenoid l −1 culture per month) was achieved with this culture system operated following the two-stage strategy. Also, closed tubular photobioreactor provided the highest carotenoid contents (10% of dry weight) in Dunaliella biomass and β-carotene abundance (90% of total carotenoids) as well as the highest 9-cis to all-trans β-carotene isomer ratio (1.5 at sunrise).