Co-Fermentation of Cheese Whey and Crude Glycerol in EGSB Reactor as a Strategy to Enhance Continuous Hydrogen and Propionic Acid Production

Thermophilic and mesophilic anaerobic digestion of soybean molasses: A performance vs. stability trade-off

One of the factors that has a direct impact on anaerobic digestion is the applied organic loading rate (OLRA). Increasing OLRA can boost methane production but can also cause process failure. As a result, establishing the appropriate OLRA for the procedure is critical. This study evaluated the effect of increasing the OLRA using soybean molasses in a thermophilic anaerobic reactor (R-Thermo), as well as the effect of feeding strategy and co-processing with okara. Furthermore, the performance versus stability trade-off between R-Thermo and mesophilic anaerobic digestion (R-Meso) was investigated. The increase of OLRA from 10 to 15 and 20 kg-COD/m³/d led to a decrease in COD removal efficiency (90, 86, and 75%), methane yield (12.0, 11.6, and 9.9 mol-CH4/kg-COD) and an increase in total volatile acids concentration (251, 456, and 1393 mg-HAc/L, respectively). At 15 kg-COD/m³/d, R-Meso performed similarly to R-Thermo, and at 20 kg-COD/m3/d, R-Meso outperformed (81% COD removal efficiency, 9.3 mol-CH4/kg-CODrem and 154.5 mol-CH4/m3/d). Temperature greatly influenced the distribution of metabolic pathways, as shown by thermodynamic and kinetic analyses, thus impacting bacterial diversity. At 55 °C, amongst the bacterial genera, Tepidiphilus stood out (>28.2%), followed by Acetomicrobium, Coprothermobacter and Candidatus_Caldatribacterium. The OLRA clearly impacted the archaeal community; Methanothermobacter (77.4%) was favored over Methanosarcina (14.8%). Under thermophilic temperature, it seems that syntrophic acetate oxidation (SAO) bacteria might have competed for substrate with acetoclastic methanogens, while in R-Meso microorganisms responsible for the initial steps of organic matter breakdown, such as members of the Firmicutes and Proteobacteria phyla (at least 67%), were dominant. In summary, R-Meso, characterized by a more uniform distribution of metabolic pathways, as well as a diverse and well-adapted microbial consortium, have exhibited enhanced stability and outperformed R-Thermo at high-loads.

Integrated production of hydrogen and methane in a dairy biorefinery using anaerobic digestion: Scale-up, economic and risk analyses

Anaerobic digestion has emerged as the most appealing waste management strategy in biorefineries. Particularly, recent studies have highlighted the energy advantages of waste co-digestion in industrial biorefineries and the use of two-stage systems. However, there are some concerns about moving the system from laboratory testing to industrial scale. One of them is the high level of investment that is required. Therefore, this study carried out a techno-economic analysis (scale-up and energy production, economic and risk analysis, and factorial design) to assess the feasibility of single- and two-stage systems in the treatment of cheese whey and glycerin for the production of hydrogen and methane. Scenarios (S1 to S9) considered thermophilic and mesophilic single and two-stage systems with different applied organic loading rates (OLRA). The analyses of scale-up and energy production revealed that S3 (a thermophilic single-stage system operated at high OLRA 17.3 kg-COD.m-3.d-1) and S9 (a thermophilic-mesophilic two-stage system operated at high OLRA 134.8 kg-COD.m-3.d-1 and 20.5 kg-COD.m-3.d-1, respectively) were more compact and required lower initial investment compared to other scenarios. The risk analysis performed by a Monte Carlo simulation showed low investment risks (10 and 11%) for S3 and S9, respectively, being the electricity sales price, the key determining factor to define whether the project in the baseline scenario will result in profit or loss. Lastly, the factorial design revealed that while the net present value (NPV) is positively impacted by rising inflation and electricity sales price, it is negatively impacted by rising capitalization rate. Such assessments assist in making decisions regarding which system can be fully implemented, the best market circumstances for the investment, and how market changes may favorably or unfavorably affect the NPV and the internal rate of return (IRR).

Potential utilization of dairy industries by-products and wastes through microbial processes: A critical review

The dairy industry generates excessive amounts of waste and by-products while it gives a wide range of dairy products. Alternative biotechnological uses of these wastes need to be determined to aerobic and anaerobic treatment systems due to their high chemical oxygen demand (COD) levels and rich nutrient (lactose, protein and fat) contents. This work presents a critical review on the fermentation-engineering aspects based on defining the effective use of dairy effluents in the production of various microbial products such as biofuel, enzyme, organic acid, polymer, biomass production, etc. In addition to microbial processes, techno-economic analyses to the integration of some microbial products into the biorefinery and feasibility of the related processes have been presented. Overall, the inclusion of dairy wastes into the designed microbial processes seems also promising for commercial approaches. Especially the digestion of dairy wastes with cow manure and/or different substrates will provide a positive net present value (NPV) and a payback period (PBP) less than 10 years to the plant in terms of biogas production.

Propionic acid-rich fermentation (PARF) production from organic wastes: A review

Nowadays, increasing attention has been drawn to biological valorization of organic wastes. Wherein, propionic acid-rich fermentation (PARF) has become a focal point of research. The objective of this review is to make a thorough investigation on the potential of PARF production and give future outlook. By discussing the key factors affecting PARF including substrate types, pH, temperature, retention time, etc., and various improving methods to enhance PARF including different pretreatments, inoculation optimization and immobilization, a comprehensive summary on how to achieve PARF from organic waste is presented. Then, current application of PARF liquid is concluded, which is found to play an essential role in the efficient denitrification and phosphorus removal of wastewater and preparation of microbial lipids. Finally, the environmental performance of PARF production is reviewed through life cycle assessment studies, and environmentally sensitive sectors are summarized for process optimization, providing a reference for waste management in low carbon scenarios.

Biohydrogen production by co-fermentation of antibiotic fermentation residue and fallen leaves: Insights into the microbial community and functional genes

This investigation explored the co-fermentation of antibiotic fermentation residue (AFR) and fallen leaves for enhancing biohydrogen production, and analyzed the mechanism from the aspects of microbial activity, microbial community and functional genes. The results showed that the optimal mixing ratio of AFR to leaves was 25:75 (VS basis), which balanced the substrate condition and synergistically enhanced the biohydrogen productivity, and the hydrogen yield was 37.45 mL/g-VS_added, which was 438.8% and 9.2% higher compared to the sole AFR fermentation and the sole leaves fermentation, respectively. The co-fermentation also improved the organics utilization and induced a more effective metabolic pathway. Further microbiology analysis found that the co-fermentation promoted the microbial activity, enriched more hydrogen-producing bacteria (Clostridium sensu stricto 1), and enhanced the expression of hydrogen-producing functional genes (e.g. genes encoding ferredoxin hydrogenase (EC 1.12.7.2) and pyruvate-ferredoxin oxidoreductase (EC 1.2.7.1)), which were fundamentally responsible for the synergistic biohydrogen fermentation.

A strategy for successive feedstock reuse to maximize photo-fermentative hydrogen production of Arundo donax L

This study proposed a strategy to maximize the hydrogen yield by reusing feedstock of Arundo donax L. For this purpose, a successive 4-batch photo-fermentative hydrogen production (PFHP) was carried out to test the strategy. About 50% of total hydrogen yield was additionally obtained by reusing the Arundo donax L for successive 4 times in comparison to single 1st batch (161.4 mL/U. cell dry weight). In addition to the highest hydrogen yield, the maximum hydrogen production rate (6.0 mL/U. cell dry weight /h), and the highest volatile fatty acids (VFAs) concentration (32 mM) were also obtained from the 1st batch, while the 2nd batch gave the maximum substrate conversion efficiency (96.5%). Moreover, a positive relationship between the sum of acetic and butyric acids with hydrogen yields was observed. This strategy would help in enhancing hydrogen yield that coupled with cost reduction for biohydrogen production.

Insights into correlation between hydrogen yield improvement and glycerol addition in photo-fermentation of Arundo donax L

This study aimed to explore the correlation between hydrogen yield improvement of photo-fermentation of Arundo donax L. and glycerol addition. Different glycerol concentrations (g/L) (0, 10, 15, 20, and 30) were replenished to establish co-substrate system. And statistical analysis was introduced to evaluate the correlation. The maximum hydrogen yield improvement (294%) was obtained from glycerol addition of 15 g/L in comparison with mono-substrate system of Arundo donax L. Under the optimal glycerol addition (15 g/L), the glycerol/Arundo donax L. ratio, C/N ratio, initial medium redox potential (E_h), and solid/liquid ratio were 1:1, 25.1, 57 mV, and 1/68, respectively. In addition, canonical correlation analysis (CCA) indicated that initial and final medium redox potential (E_h) had the strongest relationship with yield improvement of photo-fermentation. Moreover, Pearson's correlation analysis claimed that Arundo donax L./glycerol ratio played a key role during the photo-fermentative hydrogen production (PFHP) process.

Sulfate and metals removal from acid mine drainage in a horizontal anaerobic immobilized biomass (HAIB) reactor

The acid mine drainage (AMD) can causes negative impacts to the environment. Physico-chemical methods to treat AMD can have high operational costs. Through passive biological methods, such as anaerobic reactors, sulfate reduction, and recovery of metals are promoted. This study evaluated the performance of a horizontal anaerobic immobilized biomass (HAIB) reactor for the treatment of synthetic AMD using polyurethane foam as support material, and anaerobic sludge as inoculum. Ethanol was used as an electron donor for sulfate reduction, resulting in an influent chemical oxygen demand (COD) in the range of 500-1,500 mg/L and COD/sulfate ratio at 1. A gradual increase of sulfate and COD concentration was applied that resulted in COD removal efficiencies higher than 78%, and sulfate removal efficiencies of 80%. Higher sulfate and COD concentrations associated with higher hydraulic retention times (36 h) proved to be a better strategy for sulfate removal. The HAIB reactor was able to accommodate an increase in the SLR up to 2.25 g SO₄^2-/L d^-1 which achieved the greatest performance on the entire process. Moreover, the reactor proved a suitable alternative for reaching high levels of metal removal (86.95 for Zn, 98.79% for Fe, and 99.59% for Cu).

Propionic Acid: Method of Production, Current State and Perspectives

During the past years, there has been a growing interest in the bioproduction of propionic acid by Propionibacterium. One of the major limitations of the existing models lies in their low productivity yield. Hence, many strategies have been proposed in order to circumvent this obstacle. This article provides a comprehensive synthesis and review of important biotechnological aspects of propionic acid production as a common ingredient in food and biotechnology industries. We first discuss some of the most important production processes, mainly focusing on biological production. Then, we provide a summary of important propionic acid producers, including Propionibacterium freudenreichii and Propionibacterium acidipropionici, as well as a wide range of reported growth/production media. Furthermore, we describe bioprocess variables that can have impact on the production yield. Finally, we propose methods for the extraction and analysis of propionic acid and put forward strategies for overcoming the limitations of competitive microbial production from the economical point of view. Several factors influence the propionic acid concentration and productivity such as culture conditions, type and bioreactor scale; however, the pH value and temperature are the most important ones. Given that there are many reports about propionic acid production from glucose, whey permeate, glycerol, lactic acid, hemicelluloses, hydrolyzed corn meal, lactose, sugarcane molasses and enzymatically hydrolyzed whole wheat flour, only few review articles evaluate biotechnological aspects, i.e. bioprocess variables.

Rhodotorula toruloides Single Cell Oil Production Using Eucalyptus urograndis Hemicellulose Hydrolysate as a Carbon Source

Microbial oil is a potential substitute for vegetable oils in the biodiesel industry. Efforts to obtain cheap carbon sources for the cultivation of lipid-producing microorganisms comprise an active research area. This work aimed to extract the hemicellulose fraction from Eucalyptus uograndis and to use its hydrolysate as a carbon source for Rhodotorula toruloides (an oleaginous yeast) cultivation for microbial oil production. Hemicellulose hydrothermal extractions were performed at different temperatures, times, and ratios of solid to liquid (S/L). Temperature and time showed a stronger effect on the solubilization of hemicellulose. Hemicellulose extraction at 155 °C, 195 min, and an S/L ratio of 1/2 resulted in a hydrolysate with a xylose content of 37.0 g/l. R. toruloides cultivation in this hydrolysate showed that initial pH had a strong influence on cell growth. At an initial pH of 6.2, cells grew to 6.0 g/l of biomass with a lipid content of 50%. Therefore, we believe that E. urograndis hemicellulose hydrolysate could be a potential substrate for R. toruloides for lipid production based on the biorefinery concept.

Controlling methane and hydrogen production from cheese whey in an EGSB reactor by changing the HRT

This study assessed the effects of hydraulic retention time (HRT; 8 h-0.25 h) on simultaneous hydrogen and methane production from cheese whey (5000 mg carbohydrates/L) in a mesophilic (30 °C) expanded granular sludge bed (EGSB) reactor. Methane production was observed at HRTs from 4 to 0.25 h. The maximum methane yield (9.8 ± 1.9 mL CH₄/g COD_ap, reported as milliliter CH₄ per gram of COD applied) and methane production rate (461 ± 75 mL CH₄/day L_reactor) occurred at HRTs of 4 h and 2 h, respectively. Hydrogen production increased as methane production decreased with decreasing HRT from 8 to 0.25 h. The maximum hydrogen yield of 3.2 ± 0.3 mL H₂/g COD_ap (reported as mL H₂ per gram of COD applied) and hydrogen production rate of 1951 ± 171 mL H₂/day L_reactor were observed at the HRT of 0.25 h. The decrease in HRT from 8 to 0.25 h caused larger changes in the bacterial populations than the archaea populations. With the decrease in HRT (6 h-0.25 h), the Shannon diversity index decreased (3.02-2.87) for bacteria and increased (1.49-1.83) for archaea. The bacterial dominance increased (0.059-0.066) as the archaea dominance decreased (0.292-0.201) with the HRT decrease from 6 to 0.25 h.

Bioprocessing of Biodiesel Industry Effluent by Immobilized Bacteria to Produce Value-Added Products

Biodiesel industrial effluent rich in crude glycerol (CG) was processed to produce value-added product. Under continuous culture system, Bacillus amyloliquefaciens strain CD16 immobilized within its biofilm, produced 3.2 L H₂/day/L feed, over a period of 60 days at a hydraulic retention time of 2 days. The effective H₂ yield by B. amyloliquefaciens strain CD16 was 165 L/L CG. This H₂ yield was 1.18-fold higher than that observed with non-biofilm forming Bacillus thuringiensis strain EGU45. Bioprocessing of the effluent released after this stage, by recycling it up to 25% did not have any adverse effect on H₂ production by strain EGU45; however, a 25% reduction in yield was recorded with strain CD16. Biofilm forming H₂ producers thus proved effective as self-immobilizing system leading to enhanced process efficiency.