Average Volumetric Productivity Research Articles

Optimizing Continuous‐Flow Biocatalysis with 3D‐Printing and Inline IR Monitoring

AbstractEnzymatic biocatalysis typically generates less waste, uses less water, and minimizes energy consumption compared to traditional chemical methods. Efficient, cell‐free biosynthesis relies on the reuse of its valuable biocatalysts. Immobilization of enzymes on solid supports, such as enzyme carrier resins (ECRs), offers a reliable and widely deployed approach to maximize enzyme turnover in cell‐free biosynthesis. We focus on two major bottlenecks associated with optimizing cell‐free biocatalysis. First, we apply our lab's 3D‐printed labware to screen ECRs in 96‐well mini‐reactors to optimize enzyme immobilization conditions. Second, we introduce inline infrared spectroscopy to monitor bioreactor output and maximize enzyme productivity. Urease provides a model system for examining immobilization conditions and continuous assessment of biocatalyst performance. As required for the high substrate concentrations to improve process efficiency and minimize waste, urease was studied in unusually high concentrations of its substrate – molar concentrations of urea. The optimized reactor processed 3.24 L of 4.00 M urea at an average volumetric productivity of 13 g ⋅ L−1 ⋅ h−1 over 18 h and achieved an estimated productivity number of >17.4 kg urea processed per g of immobilized urease Type‐IX. This workflow can be generalized to most biocatalytic processes and could accelerate adoption of cell‐free biosynthesis for greater chemical sustainability.

Sulfate limitation increases specific plasmid DNA yield and productivity in E. coli fed-batch processes

Plasmid DNA (pDNA) is a key biotechnological product whose importance became apparent in the last years due to its role as a raw material in the messenger ribonucleic acid (mRNA) vaccine manufacturing process. In pharmaceutical production processes, cells need to grow in the defined medium in order to guarantee the highest standards of quality and repeatability. However, often these requirements result in low product titer, productivity, and yield. In this study, we used constraint-based metabolic modeling to optimize the average volumetric productivity of pDNA production in a fed-batch process. We identified a set of 13 nutrients in the growth medium that are essential for cell growth but not for pDNA replication. When these nutrients are depleted in the medium, cell growth is stalled and pDNA production is increased, raising the specific and volumetric yield and productivity. To exploit this effect we designed a three-stage process (1. batch, 2. fed-batch with cell growth, 3. fed-batch without cell growth). The transition between stage 2 and 3 is induced by sulfate starvation. Its onset can be easily controlled via the initial concentration of sulfate in the medium. We validated the decoupling behavior of sulfate and assessed pDNA quality attributes (supercoiled pDNA content) in E. coli with lab-scale bioreactor cultivations. The results showed an increase in supercoiled pDNA to biomass yield by 33% and an increase of supercoiled pDNA volumetric productivity by 13 % upon limitation of sulfate. In conclusion, even for routinely manufactured biotechnological products such as pDNA, simple changes in the growth medium can significantly improve the yield and quality.Graphical

Eucalyptus Growth Responses to Soil Water Storage Capacity in Arenosols and Acrisols Soils: Wood and Biomass Stock Modelling

Eucalyptus is the main fast-growing tree for biomass production in the tropics, providing resources for pulp and paper industries and bioenergy. The potential productivity of forest sites over an eight-year rotation in Brazil was evaluated by the Physiological Principles in Predicting Growth (3-PG) model for two soils, Acrisols and Arenosols, with high and low water storage, respectively, and distinct productive potential capacity. The model was parameterized by data-sets obtained in bimonthly forest inventories performed in stands with 33, 58 and 89 months-old trees, and edaphic surveys. The average volumetric productivity of wood and biomass of the main stem determined at the 89 months-old stand was 374 m3 ha−1 (177 Mg ha−1) for Acrisols and 272.3 m3 ha−1 (130.0 Mg ha−1) for Arenosols. The estimated volumetric production in the Arenosols had a high mean annual increment up to the age of 58 months, with a significant reduction in growth rates after this time. In Acrisols, high incremental rates in wood volume up to age of 89 months (MAIVW > 50 m3 ha−1 year−1) indicate that, under ideal soil conditions, the cutting cycle may exceed 8 years with no productivity impairment. The parameterized model matched well for forest yield (r2 > 0.9) and dendrometric variables (r2 > 0.78). The expected results of lower productivity in Arenosols occurred only after 58 months, while for Acrisols productivity remained high up to 89 months. The results showed the eucalyptus cycle should be shorter in Arenosols, since the lower cutting cycle can provide higher final productivity, when using the mean annual increment to evaluate productivity.

Optimization of feedstock and insulating strategies to enhance biogas production of solar-assisted biodigester system

Assisted by solar greenhouse, the temperature of the digestion liquid can be increased by solar radiation to promote the biogas production rate in cold climate. Due to the dynamic characteristics of solar radiation, air temperature and other variable parameters jointly affect the digestion process. A novel dynamic biogas production prediction model for solar-assisted biogas digestion is developed in this study. The model integrates soil heat transfer, feeding process and covering/uncovering of greenhouse insulation quilt, and coupled with biogas anaerobic digestion kinetic model. After validated by experimental results of an actual biogas project in rural area of Xuzhou, China, the feedstock process and insulating strategies for biogas plants are optimized based on prediction model. The results show a significant increase of 55% average volumetric biogas production rate could be achieved, it indicates that optimizing operation strategy of solar assisted biogas plants has a great potential for enhancing gas production in cold winter climates with sufficient solar radiation resources, which can promote biogas applications in rural North China. The models could be used for predicting biogas production rate of passive solar-assisted biogas digester, and could also help for energy savings and renewable energy utilization in China and other countries.

Shaping an Open Microbiome for Butanol Production through Process Control

The growing awareness of limited resource availability has driven production systems towards greater efficiencies, and motivated the transition of wastewater treatment plants to water resource recovery facilities. Open microbiome fermentation offers a robust platform for resource recovery, due to its higher metabolic versatility, which is capable of dealing with even dilute residual liquid streams. Organic matter, e.g., fatty acids, lost in these streams can potentially be recovered into higher value chemicals such as alcohols. This study aims to shape an open microbiome towards butanol production from butyrate and hydrogen through pH control and continuous hydrogen supply. Two sets of experiments were conducted in Scott bottles (1 L) and a lab-fermenter (3 L). The open microbiome produced up to 4.4 mM butanol in 1 L bottles. More promising conversions were obtained when up-scaling to a lab-fermenter with pH control and an increased hydrogen partial pressure of 2 bar; results included a butanol concentration of 10.9 mM and an average volumetric productivity of 0.68 mmol L−1 d−1 after 16 days. This corresponds to 2.98- and 4.65-fold increases, respectively, over previously reported values. Thermodynamic calculations revealed that product formation from butyrate was unfeasible, but energetically favorable from bicarbonate present in the inoculum. For the first time, this study provides insights regarding the community structure of an open microbiome producing butanol from butyrate and hydrogen. DNA sequencing combined with 16S rRNA gene amplicon analysis showed high correlation between Mesotoga spp. and butanol formation. Microbial diversity can also explain the formation of by-products from non-butyrate carbon sources.

Two-stage anaerobic digestion system for biotransformation of an azo dye in the presence of sulfate: Minimizing competition for reducing equivalents

Anaerobic treatment of azo dyes is particularly challenging in the case of wastewaters containing sulfate. We studied the use of multiple stage anaerobic system to minimize the impacts of sulfidogenesis and methanogenesis on the decolorization and biotransformation of an azo dye. The system was composed of a 1st-stage anaerobic structured-bed reactor (R1), designed for removal of color, followed by a 2nd-stage upflow anaerobic sludge blanket reactor (R2) intended for organic matter and sulfate removals. Results showed that near complete decolorization was achieved in R1 when a dye loading rate of 222 ± 9 mg L−1 d−1 was applied. Sulfidogenic activity in this reactor was negligible due to the low pH and did not impair reductive decolorization. After increasing dye load, decolorization efficiency in R1 decreased, but gradually recovered in the following weeks. R2 kept decolorization around 90% even when R1 presented decreased efficiencies, keeping up with overall performance. Residual organic matter in the system's final effluent consisted of aromatic amines and other dye fragments recalcitrant to anaerobic digestion (AD), whose concentrations further increased after treatment in R2. The average volumetric methane production rate achieved in R2 was 472 ± 111 mL L−1 d−1. The two-stage AD system provided enhanced removals of color, organic matter and sulfate by eliminating issues related to the competition for reducing equivalents.

High-Rate Sulfate Removal Coupled to Elemental Sulfur Production in Mining Process Waters Based on Membrane-Biofilm Technology.

It is anticipated that copper mining output will significantly increase over the next 20 years because of the more intensive use of copper in electricity-related technologies such as for transport and clean power generation, leading to a significant increase in the impacts on water resources if stricter regulations and as a result cleaner mining and processing technologies are not implemented. A key concern of discarded copper production process water is sulfate. In this study we aim to transform sulfate into sulfur in real mining process water. For that, we operate a sequential 2-step membrane biofilm reactor (MBfR) system. We coupled a hydrogenotrophic MBfR (H2-MBfR) for sulfate reduction to an oxidizing MBfR (O2-MBfR) for oxidation of sulfide to elemental sulfur. A key process improvement of the H2-MBfR was online pH control, which led to stable high-rate sulfate removal not limited by biomass accumulation and with H2 supply that was on demand. The H2-MBfR easily adapted to increasing sulfate loads, but the O2-MBfR was difficult to adjust to the varying H2-MBfR outputs, requiring better coupling control. The H2-MBfR achieved high average volumetric sulfate reduction performances of 1.7–3.74 g S/m3-d at 92–97% efficiencies, comparable to current high-rate technologies, but without requiring gas recycling and recompression and by minimizing the H2 off-gassing risk. On the other hand, the O2-MBfR reached average volumetric sulfur production rates of 0.7–2.66 g S/m3-d at efficiencies of 48–78%. The O2-MBfR needs further optimization by automatizing the gas feed, evaluating the controlled removal of excess biomass and S0 particles accumulating in the biofilm, and achieving better coupling control between both reactors. Finally, an economic/sustainability evaluation shows that MBfR technology can benefit from the green production of H2 and O2 at operating costs which compare favorably with membrane filtration, without generating residual streams, and with the recovery of valuable elemental sulfur.

Dynamic Effect of Operational Regulation on the Mesophilic BioMethanation of Grape Marc.

Wine production annually generates an estimated 11 million metric tonnes of grape marc (GM) worldwide. The diversion of this organic waste away from landfill and towards its use in the generation of renewable energy has been investigated. This study aimed to evaluate the effectiveness of operational parameters relating to the treatment regime and inoculum source in the extraction of methane from GM under unmixed anaerobic conditions at 35 °C. The study entailed the recirculation of a previously acclimated sludge (120 days) as downstream inoculum, an increased loading volume (1.3 kg) and a low substrate-to-inoculum ratio (10:3 SIR). The results showed that an incorporation of accessible operational controls can effectively enhance cumulative methane yield (0.145 m3 CH4 kg−1 VS), corresponding to higher amounts of digestible organics converted. The calculated average volumetric methane productivity equalled 0.8802 L CH4 LWork−1 d−1 over 33.6 days whilst moderate pollutant removal (43.50% COD removal efficiency) was achieved. Molecular analyses identified Firmicutes and Bacteroidetes phyla as core organisms for hydrolytic and fermentative stages in trophic relationships with terminal electron acceptors from the methane-producing Methanosarcina genus. Economic projections established that the cost-effective operational enhancements were sustainable for valorisation from grape marc by existing wineries and distilleries.

Outdoor cultivation of a novel isolate of the microalgae Scenedesmus sp. and the evaluation of its potential as a novel protein crop.

A Danish strain of the green microalgae Scenedesmus sp. was isolated, identified and characterized with respect to productivity under outdoor cultivation conditions at northern latitudes. The algae were cultivated outdoors in Denmark in closed tubular photobioreactors using only sunlight, simple inorganic nutrients and under ambient temperatures. The biomass composition was evaluated in terms of protein content and quality. The average volumetric and areal biomass productivity obtained for the Scenedesmus sp. isolate during outdoor cultivation was 0.083 g dry matter L-1 and 6.40 g dm m-2 day-1 , respectively. Thus, productivities are comparable to data reported in the literature under similar conditions. A strain-specific nitrogen to protein conversion factor of 5.5 was determined for the Scenedesmus sp. strain enabling more accurate protein estimations from simple nitrogen determination methods like Kjeldahl analysis in the future. The protein content was determined to be 52.4% of dried biomass for this Scenedesmus strain. The sum of essential amino acids was 42% which is high compared to other microalgae. The results are compared and discussed in comparison to other microalgae and soybean as a common plant protein source.

Fucoxanthin production from Tisochrysis lutea and Phaeodactylum tricornutum at industrial scale

Fucoxanthin is a xanthophyll carotenoid with high market value. Currently, seaweeds are the primary source for fucoxanthin industrial production. However, marine microalgae reach 5 to 10 times higher concentrations (2.24 to 26.6 mg g−1 DW) and are considered a promising feedstock. In this work, two marine microalgae were produced at industrial scale to evaluate biomass and fucoxanthin production: Phaeodactylum tricornutum for autumn/winter and Tisochrysis lutea for spring/summer. Both strains were grown in 15 m3 tubular flow-through photobioreactors; for 170 consecutive days of semi-continuous cultivation regime. The average volumetric biomass productivities of P. tricornutum and T. lutea were 0.11 and 0.09 g DW L−1 day−1. P. tricornutum reached higher maximum biomass concentration (2.87 g DW L−1) than T. lutea (1.47 g DW L−1). P. tricornutum fucoxanthin content ranged between 0.2 and 0.7% DW, while T. lutea between 0.2 and 0.6% DW. The fucoxanthin content was correlated with the irradiation (MJ m−2) and biomass concentration in the photobioreactor (g L−1). This is the first work in literature reporting a long-term industrial production of T. lutea. Overall, we showed possible scenarios for fucoxanthin production from microalgae, increasing the window to supply the industry with steady production throughout the year.

Влияние коэффициента рециркуляции эффлюента метантенка на выход биоводорода в двухстадийном процессе анаэробной биоконверсии жидких органических отходов

This paper considers the production of biohydrogen in a two-stage process of anaerobic bioconversion of organic matter (OM) of liquid waste with recirculation of digester effluent into an anaerobic bioreactor for dark fermentation (ARDF). The values of the average biohydrogen specific yield (BSY) and the average volumetric biohydrogen production rate (VBPR) were obtained at 4 recirculation ratios (RR) of the digester effluent (1, 1.1, 1.18, 1.25) and 2 hydraulic retention times (HRT) ( 1 and 2.5) in ARDF. Organic loading rate (olr) varied from 7.96 to 21.6 g OM / (l ∙ day). The pH value in ARDF practically did not depend on RR and HRT, and ranged from 3.8 to 4.16. The maximum BSY was 0.108 l / (day ∙ g OMin) with a RR of 1.11 and a HRT of 2.5 days. The maximum VBPR was observed at RR 1 and HRT 1 day and amounted to 1.67 l / (l ∙ day). The methane content in biohydrogen-containing biogas at modes providing maximum BSY and VBPR was no more than 0.01%, but it increased sharply at higher values of RR and HRT. The hydrogen content in biogas averaged 50-52% for all combinations of RR and HRT, but it sharply decreased to 46.7% with HRT 2.5 and RR 1.25. In general, with RR 1.11 and HRT 1 day, an increase in BSY by 9.05% was observed, while the VBPR decreased by 1.04% (compared with RR 1.0 and HRT 1 day). In general, the experi- mental data obtained allow us to speak of a RR equal to 1.11 as the most effective for both HRTs in the studied range of RR.

Experimental studies on the contribution of solar energy as a source for heating biogas digestion units

The main drawback of heating biogas digestion systems based on solar energy is its unavailability overnight and at different times (days and months). To circumvent this problem, a hybrid system(solar and electricity) powering the heat digester could provide the required mesophilic conditions. The present study aimed to evaluate the technical and design feasibility of using solar energy to assist in heating the digestion units. Also, measured and determined the contribution of solar energy to heat the system. This study was conducted in the central area of Coastal Delta, Egypt (30.5∘N, 30.6∘E; 8.5 m a.s.l.). Results show that the contribution of solar energy to biogas production was 75.21%, 60%, and 53.58% when using three settings temperature of (37, 40, and 45 °C) of the energy consumed via cattle dung solution heating. Furthermore, increasing the set temperature inside the horizontal and vertical digesters from 37 °C to 45 °C augmented their daily average volumetric biogas production by 87.12% and 59.45%, respectively. Finally, the current study says that solar energy has reduced energy consumption by 61.28%. Also, the economic analysis indicates that the estimated return profit was $ 177.41 (USD), which represents 45.15% of the total income per operation.

The synergistic effect of the thickened digestate treatment in the vortex layer apparatus prior to its recirculation into the reactor on the characteristics of anaerobic bioconversion of organic waste

For the first time, the effect of thickened digestate treatment in a vortex layer apparatus (VLA) prior to its recirculation into anaerobic reactor on the efficiency of anaerobic bioconversion of an organic substrate was investigated. At the hydraulic retention time of the recirculated digestate in VLA for 30 seconds, of the substrate in the anaerobic bioreactor for 8 days and the recirculation coefficient of 1.5, the average specific yield of biogas increased by 75.2%, and the average volumetric methane production – by 16.8%. There was no increase in methane concentration in biogas, while the average concentration of hydrogen sulfide in biogas decreased by 8 times.

Efficient in-situ separation design for long-term sophorolipids fermentation with high productivity

Until now, the production of microbial biosurfactants has been limited to the use of first-generation (food) substrates. Moreover, the results on sophorolipids yield and productivity reported by state-of-the-art fed-batch processes for sophorolipids production remain unsatisfactory and lead to a significantly high cost per kg of the product. With an aim to address these problems, this study demonstrates a long-term and high-efficiency sophorolipids production method using a semi-continuous integrated production-separation system which utilizes food waste as a substrate. An average volumetric productivity of 2.43 g L −1 h −1 and the overall sophorolipids yield on the substrate (i.e. the combination of glucose and oleic acid as carbon source) of 0.73 g g −1 was achieved within 240 h by fed-batch and separation fermentation. Moreover, the potential of sustaining high production efficiency during long-term fermentation times (480 h) was investigated. No reduction in process efficiency was observed, i.e. average volumetric productivity and an overall sophorolipids yield of 2.39 g L −1 h −1 and 0.73 g g −1 were obtained, respectively. Notably, a very high biomass concentration of 117.2 g L −1 was observed in fed-batch fermentation and separation, which is the highest cell density ever reported for Starmerella bombicola . The separation efficiency was also calculated to evaluate the in-situ separation performance of the developed process quantitatively. In 480-h fermentation, the average separation efficiency of 74.3% and overall separation efficiency of 93.0% was achieved after six separation cycles, suggesting that both separation design and process control were successful in laboratory-scale fermentation. These findings demonstrate the potential of the developed sophorolipids fermentation-separation system for application at industrial scale. • Food waste was used for sophorolipids (SL) fermentation. • Combination of fed-batch with an in-situ separation strategy was developed. • An average productivity of 2.4 g L −1 h −1 was obtained in 480 h fermentation. • A yield of 0.73 g g −1 of carbon added was achieved. • A cell density of 117.2 g L −1 and separation efficiency of 93.0% were achieved.

Continuous fermentation of recombinant Pichia pastoris Mut+ producing HBsAg: Optimizing dilution rate and determining strain-specific parameters

There is a growing interest in the biopharmaceutical industry to enhance production efficiency via shifting batch to continuous manufacturing. In the previous study, we demonstrated that under identical operation condition, continuous fermentation of recombinant Pichia pastoris (P. pastoris) Mut+ producing intracellular hepatitis B surface antigen (HBsAg) has considerably higher efficiency compared to the conventional fed-batch process. In the current work, by examining various dilution rates, we further optimized the process efficiency, and also determined some strain-specific parameters. According to the results, continuous operation at the dilution rate of 0.015 1/h demonstrated the highest performance compared to other dilution rates of 0.009, 0.02, 0.25, 0.03 and 0.0417 1/h. In the optimum dilution rate, the average HBsAg titer, yield, specific and volumetric productivity were 283.9mgHBsAg/L, 0.71mgHBsAg/g MeOH, 0.0097mgHBsAg/g wet cell weight (WCW)/h and 4.26mgHBsAg/L/h, respectively. Compared to the continuous fermentation in the previous study, the volumetric and specific productivities were improved by the factors of 2.0 and 2.5, respectively. Following Herbert-Pirt linear relation between specific growth rate and methanol consumption rate, the obtained biomass yield and maintenance coefficient in the continuous fermentation were 1.22 (g WCW/g MeOH) and 0.008 (g MeOH/g WCW/h), respectively. The consistency in the process condition and efficiency without any genetic instability and contamination in the one-month operation- in each fermentation run- suggests that the studied recombinant strain could be one of the potential candidates for continuous biomanufacturing of hepatitis B vaccine.

Metabolic fluxes-oriented control of bioreactors: a novel approach to tune micro-aeration and substrate feeding in fermentations

BackgroundFine-tuning the aeration for cultivations when oxygen-limited conditions are demanded (such as the production of vaccines, isobutanol, 2–3 butanediol, acetone, and bioethanol) is still a challenge in the area of bioreactor automation and advanced control. In this work, an innovative control strategy based on metabolic fluxes was implemented and evaluated in a case study: micro-aerated ethanol fermentation.ResultsThe experiments were carried out in fed-batch mode, using commercial Saccharomyces cerevisiae, defined medium, and glucose as carbon source. Simulations of a genome-scale metabolic model for Saccharomyces cerevisiae were used to identify the range of oxygen and substrate fluxes that would maximize ethanol fluxes. Oxygen supply and feed flow rate were manipulated to control oxygen and substrate fluxes, as well as the respiratory quotient (RQ). The performance of the controlled cultivation was compared to two other fermentation strategies: a conventional “Brazilian fuel-ethanol plant” fermentation and a strictly anaerobic fermentation (with ultra-pure nitrogen used as the inlet gas). The cultivation carried out under the proposed control strategy showed the best average volumetric ethanol productivity (7.0 g L−1 h−1), with a final ethanol concentration of 87 g L−1 and yield of 0.46 gethanol gsubstrate−1. The other fermentation strategies showed lower yields (close to 0.40 gethanol gsubstrate−1) and ethanol productivity around 4.0 g L−1 h−1.ConclusionThe control system based on fluxes was successfully implemented. The proposed approach could also be adapted to control several bioprocesses that require restrict aeration.

Metabolic engineering of Escherichia coli for the production of butyric acid at high titer and productivity

BackgroundSeveral anaerobic bacteria produce butyric acid, a commodity chemical with use in chemical, pharmaceutical, food and feed industries, using complex media with acetate as a co-product. Butyrate titer of various recombinant Escherichia coli did not exceed 10 g l−1 in batch fermentations in any of the media tested.ResultsA recombinant E. coli (strain LW393) that produced butyrate as the major fermentation product was constructed with genes from E. coli, Clostridium acetobutylicum and Treponema denticola. Strain LW393 produced 323 ± 6 mM (28.4 ± 0.4 g l−1) butyric acid in batch fermentations in mineral salt medium with glucose as C source at a yield of 0.37 ± 0.01 g (g glucose consumed)−1. Butyrate accounted for 90% of the total products produced by the culture. Supplementing this medium with yeast extract further increased butyric acid titer to 375 ± 4 mM. Average volumetric productivity of butyrate with xylose as C source was 0.89 ± 0.07 g l−1 h−1.ConclusionsThe butyrate titer reported in this study is about 2.5–3-times higher than the values reported for other recombinant E. coli and this is achieved in mineral salt medium with an expectation of lower purification and production cost of butyrate.

Dark fermentative biohydrogen production from synthetic cheese whey in an anaerobic structured-bed reactor: Performance evaluation and kinetic modeling

This study investigated the potential of dark fermentative hydrogen production from cheese whey in an acidogenic anaerobic structured-bed reactor (ASTBR). The reactor was operated at 25 °C with an organic loading rate (OLR) of 24 kg COD m−3 d−1 and a hydraulic retention time (HRT) of 24 h. The ASTBR had an average volumetric hydrogen production rate (VHPR) of 1.6 ± 0.7 L H2 L−1 d−1 and an average hydrogen yield (HY) of 1.4 ± 0.7 moL H2 mol−1 of consumed lactose. Batch experiments were performed with biomass from the ASTBR to characterize the main metabolic transformations involved in hydrogen production. An ADM1-based, unstructured kinetic model was developed and fitted to the obtained temporal profiles. The model allowed a satisfactory description of the process and indicated that hydrogen production from lactate and acetate could explain 74.5% of the total hydrogen volume produced. Because lactic-acid-producing bacteria are expected to ultimately colonize acidogenic reactors treating cheese whey, optimizing electron flow through this pathway may be a suitable strategy to enable long-term hydrogen production from cheese whey using mixed-culture fermentation.

Treating anaerobically digested piggery effluent (ADPE) using microalgae in thin layer reactor and raceway pond

The successful cultivation of microalgae on anaerobically treated wastewaters would not only allow for the bioremediation of the waste stream but also the cost effective production of algal biomass. In this study, the growth and bioremediation ability of a microalgal consortium of Chlorella sp. and Scenedesmus sp. for treating anaerobically digested piggery effluent (ADPE) was assessed and compared using a thin layer reactor (TLR) (0.5-cm depth, 350 L) and a conventional raceway pond (15-cm depth, 1500 L) with an initial ammonium concentration of 110 ± 10 mg N-NH4+ L−1. The ammonium removal rate of microalgae grown in the TLR (19.23 mg N-NH4+ L−1 d−1) was 1.4 times higher than that grown in the raceway pond. The ash-free biomass yield (0.84 g L−1) and the average volumetric biomass productivity (60 mg L−1 d−1) of the algal consortium in the TLR were 2.5 and 2 times higher than that achieved in the raceway pond, respectively. However, considering four times higher culture volume in the raceway pond, the average areal biomass productivity in the raceway pond (4.2 g m−2 s−1) was more than two times higher than the productivity achieved in the TLR (1.9 g m−2 s−1). As a result of this, the areal lipid productivity of the microalgae grown in the raceway pond was also 2.7 times higher than that grown in the TLR. Our results indicated that under the operational conditions evaluated in this study and based on areal biomass productivity, raceway pond performed better than the thin layer reactor for treating ADPE.

Recovery of unstable digestion of vegetable waste by adding trace elements using the bicarbonate alkalinity to total alkalinity ratio as an early warning indicator.

Vegetable waste (VW) is highly perishable and susceptible to acidification during anaerobic digestion, which inhibits biogas production. Effective process monitoring, diagnosis and control are necessary to maintain stable anaerobic digestion at a high organic loading rate (OLR). Continuous mesophilic digestion was conducted at OLRs of 0.5, 1.0, 1.5, 2.0, 3.0, 3.5 and 4.0g volatile solids (VS)/(Ld) with effluent recirculation (ER) in a reactor with total volume of 70L. The effectiveness of three early warning indicators was validated. The ability of trace elements (TEs) (Fe, Co and Ni) to recover unstable VW digestion systems was evaluated. The results showed that the ratio of bicarbonate alkalinity (BA) to total alkalinity (TA) was a more effective warning indicator than the ratios of methane (CH4) to carbon dioxide and volatile fatty acids (VFAs) to TA. When the ratio of BA/TA was lower than 0.9, the digestion system tended to be unstable. ER maintained a stable OLR of 1.5g VS/(Ld). The addition of TEs achieved a maximum stable OLR of 3.5g VS/(Ld) with an average volumetric biogas production rate of 1.91 L/(Ld). Severe VFAs accumulation and unrecoverable instability occurred at an OLR of 4.0g VS/(Ld). The supplementation of ammonium bicarbonate was not useful for the recovery of the unstable system when the OLR was greater than 3.5g VS/(Ld) for the digestion of VW. The specific methane production was approximately 340 L/kg VS during the stable period with a digestion efficiency of 85%.