A parametric response surface study of fermentative hydrogen production from cheese whey

Factor-based assessment of continuous bio-H2 production from cheese whey

Despite having been widely investigated, dark fermentative H₂ production from organic residues is still limited by process-related issues which may hamper the perspectives of full-scale process implementation. Such constraints are mainly due to the process complexity, which is largely affected by multiple and often mutually interacting factors. In the present work, the results of continuous fermentative H₂ production experiments using synthetic cheese whey as the input substrate were used to gain detailed knowledge of the process features and identify suitable and critical operating conditions. Specifically, innovative process interpretation involved a combination of analytical characterization of the fermentation broth, mass balance calculations and statistical methods (correlation and principal component analyses) to derive systematic considerations for process characterization and scale-up. The metabolic products mainly included acetate and butyrate, which however were likely to derive (in different proportions depending on the operating conditions) from both hydrogenogenic and competing pathways. For some tests, lactate and succinate were also found to have been formed. It was observed that the main features of the process (H₂ yield and rate, stability condition) were correlated with the operational and analytical parameters. The first three principal components identified by the statistical analysis were able to account for: 1) the effect of retention time and total metabolites produced; 2) biogas (H₂ and CO₂) generation, butyrate production and stability condition; and 3) organic loading rate and propionate production. The results suggested that the main features of hydrogenogenic fermentation can be described by a reduced set of factors that may be usefully adopted for both process monitoring and prediction purposes.

Simultaneous medium chain fatty acids production and process carbon emissions reduction in a continuous-flow reactor: Re-understanding of carbon flow distribution

Due to its wide application and high value, the production of medium chain fatty acids (MCFAs) from waste biomass has become one of the worldwide research hotspots. Increasing the carbon element participation from short-chain fatty acids to the form of MCFAs is also conductive to reduce the release of biogas from biological treatment process, because carbon is in the form of MCFAs instead of biogas which directly contribute to process carbon emissions reduction. However, many barriers limiting MCFAs production and application remain to be resolved. Aiming continuous MCFAs production from lactate-rich waste biomass, this study optimized the operation conditions and clarified the main limiting factors and possible mechanisms. The maximum caproic acid concentration of 2.757 g/L were obtained at the Upflow Velocity (ULV) of 1.15 m/h and pH 4.9-5.1. Caproiciproducens, Pseudoramibacter, norank_f_Eubacteriaceae, and Oscillibacter were identified to be the dominant microbial genus responsible for MCFAs production from lactate. The reduction of carbon emissions calculation was also studied in the present processes.

Fermentative molecular biohydrogen production from cheese whey: present prospects and future strategy

Waste-dependent fermentative routes for biohydrogen production present a possible scenario to produce hydrogen gas on a large scale in a sustainable way. Cheese whey contains a high portion of organic carbohydrate and other organic acids, which makes it a feasible substrate for biohydrogen production. In the present review, recent research progress related to fermentative technologies, which explore the potentiality of cheese whey for biohydrogen production as an effective tool on a large scale, has been analyzed systematically. In addition, application of multiple response surface methodology tools such as full factorial design, Box-Behnken model, and central composite design during fermentative biohydrogen production to study the interactive effects of different bioprocess variables for higher biohydrogen yield in batch, fed-batch, and continuous mode is also discussed. The current paper also emphasizes computational fluid dynamics-based simulation designs, by which the substrate conversion efficiency of the cheese whey-based bioprocess and temperature distribution toward the turbulent flow of reaction liquid can be enhanced. The possible future developments toward higher process efficiency are outlined.

The dairy biorefinery: Integrating treatment processes for cheese whey valorisation

With an estimated worldwide production of 190 billion kg per year, and due to its high organic load, cheese whey represents a huge opportunity for bioenergy and biochemicals production. Several physical, chemical and biological processes have been proposed to valorise cheese whey by producing biofuels (methane, hydrogen, and ethanol), electric energy, and/or chemical commodities (carboxylic acids, proteins, and biopolymers). A biorefinery concept, in which several value-added products are obtained from cheese whey through a cascade of biotechnological processes, is an opportunity for increasing the product spectrum of dairy industries while allowing for sustainable management of the residual streams and reducing disposal costs for the final residues. This review critically analyses the different treatment options available for energy and materials recovery from cheese whey, their combinations and perspectives for implementation. Thus, instead of focusing on a specific valorisation platform, in the present review the most relevant aspects of each strategy are analysed to support the integration of different routes, in order to identify the most appropriate treatment train.

Efficient repeated batch production of androstenedione using untreated cane molasses by Mycobacterium neoaurum driven by ATP futile cycle

The biotransformation of phytosterol to androstenedione (AD) by mycobacteria is a unique process accompanied by energy-producing. However, high intracellular ATP content can severely inhibit the efficient production of AD. In this study, a novel citrate-based ATP futile cycle (AFC) and pyruvate-based AFC were constructed for the first time. Application of AFCs reduced intracellular ATP and propionyl-CoA levels and increased NAD⁺/NADH ratios and cell viability. The forced consumption of ATP promotes the transcription of critical genes in propionyl-CoA metabolism. The synergistic effect of enhanced propionyl-CoA metabolism and AFC increased AD conversion yield from 60.6% to 97.3%. The AD productivity was further improved by repeated batch fermentation using untreated cane molasses. The maximum productivity was 181% higher than that of the original strain. Therefore, the strategy of combining AFC and repeated batch fermentation is a valuable tool for the efficient and low-cost production of AD and other steroidal pharmaceutical precursors.

Evaluation of texture of cheese by-products incorporated bread

Abstract This work aimed to develop new breads incorporating whey residue, “sorelho”, obtained from ewe’s milk after the production of Serra da Estrela Cheese. For this, we baked three types of bread: wheat bread (control sample), bread incorporating sorelho, and another version containing additional nutritional elements. The texture was evaluated with a texturometer, using compression and perforation tests. Results showed that sorelho can be successfully incorporated in bread. The best product was the bread with sorelho plus improved nutrition, which presented good textural characteristics during a period of 24 hours. This trend was observed for all properties evaluated: hardness, chewiness, resilience, cohesiveness, springiness (compression test) and external firmness, inner firmness, stickiness, adhesiveness (perforation test). Finally, factor analysis showed: FACTOR 1 – compression textural properties; FACTOR 2 – perforation firmness properties and FACTOR 3 – perforation adhering properties, which in total explained approximately 81% of total variance.

Control of fermentation duration and pH to orient biochemicals and biofuels production from cheese whey

Batch dark fermentation tests were performed on sheep cheese whey without inoculum addition at different operating pHs, relating the type and production yields of the observed gaseous and liquid by-products to the evolution of fermentation. Cheese whey fermentation evolved over time in two steps, involving an initial conversion of carbohydrates to lactic acid, followed by the degradation of this to soluble and gaseous products including short-chain fatty acids (mainly acetic, butyric and propionic acids) and hydrogen. The operating pH affected the production kinetics and yields, as well as the fermentation pathways. By varying the duration of the fermentation process, different cheese whey exploitation strategies may be applied and oriented to the main production of lactic acid, hydrogen or other organic acids.

State of the art and challenges of biohydrogen from microalgae

Biohydrogen from microalgae has attracted extensive attention owing to its promising features of abundance, renewable and self sustainability. Unlike other well-established biofuels like biodiesel and bioethanol, biohydrogen from microalgae is still in the preliminary stage of development. Criticisms in microalgal biohydrogen centered on its practicality and sustainability. Various laboratory- and pilot-scale microalgal systems have been developed, and some research initiatives have exhibited potential for commercial application. This work provides a review of the state of the art of biohydrogen from microalgae. Discussions include metabolic pathways of light-driven transformation and dark fermentation, reactor schemes and system designs encompassing reactor configurations and light manipulation. Challenges, knowledge gaps and the future directions in metabolic limitations, economic and energy assessments, and molecular engineering are also delineated. Current scientific and engineering challenges of microalgal biohydrogen need to be addressed for technology leapfrog or breakthrough.

Economical production of androstenedione and 9α-hydroxyandrostenedione using untreated cane molasses by recombinant mycobacteria

Production of androstenedione (AD) and 9α-hydroxyandrostenedione (9α-OH-AD) by recombinant mycobacteria using untreated cane molasses and hydrolysate of mycobacterial cells (HMC) was investigated for the first time. B-vitamins feeding experiment and reverse transcription-PCR analysis showed that propionyl-CoA carboxylase (PCC) plays an important role in the phytosterol biotransformation of mycobacteria. The respective AD and 9α-OH-AD conversion ratios were increased by 2.91 and 1.48 times through coexpression of PCC and NADH dehydrogenase. The highest conversion ratios of AD and 9α-OH-AD obtained by using a co-feeding strategy of cane molasses and HMC reached 96.38% and 95.04%, respectively, and the total costs of carbon and nitrogen sources for the culture medium were reduced by 29.89% and 49.49%, respectively. Taking the results together, untreated cane molasses and HMC can be used for the economical production of steroidal pharmaceutical precursors by mycobacteria. This study offers an economical and green strategy for steroidal pharmaceutical precursor production.

Biohydrogen and polyhydroxyalkanoate production from original hydrolyzed polyacrylamide-containing wastewater

This work aimed to study biohydrogen (H₂) and polyhydroxyalkanoate (PHA) production from original hydrolyzed polyacrylamide (HPAM)-containing wastewater. NH₄⁺-N from HPAM hydrolysis was removed efficiently through short-cut nitrification and anoxic ammonia oxidation (anammox). Carbon/Nitrogen (C/N) ratios of effluent reached 51-97, and TOC decreased only 2%-4%, providing potential for subsequent H₂ and PHA production. The maximum yields of H₂ (0.833 mL·mg^-1_substrate) and Volatile Fatty Acid (VFA) (465 mg·L^-1) occurred at influent C/N ratio of 51. Substrate removal increased linearly with the activities of dehydrogenase and hydrogenase (R² ≥ 0.990), and H₂ yield rose exponentially with enzyme activities (R² ≥ 0.989). The maximum PHA yield (54.2% VSS) occurred at the 42nd hour and influent C/N ratio of 97. PHA yield was positively correlated with substrate uptake. The change of H₂-producing, PHA-accumulating and HPAM-degradating bacteria indicated that those functional microorganisms had synergistic effects on H₂ production and substrate uptake, as well as PHA accumulation and substrate uptake.

Influence of the pH control strategy and reactor volume on batch fermentative hydrogen production from the organic fraction of municipal solid waste

Three different experimental sets of runs involving batch fermentation assays were performed to evaluate the influence of the experimental conditions on biological hydrogen production from the source-separated organic fraction of municipal solid waste collected through a door-to-door system. The fermentation process was operated with and without automatic pH control, at a pH of 5.5 and 6.5, food-to-microorganism ratios of 1/3 and 1/1 (wet weight basis) and with different working volumes (0.5 and 3 L). The experimental results showed that the pH control strategy and the reactor volume did not affect the final hydrogen production yield but played an important role in determining the time evolution of the process. Indeed, although the different experimental conditions tested yielded comparable hydrogen productions (with maximum average values ranging from 68.5 to 88.5 NLH₂ (kgTVS_OF)^-1), the automatic pH control strategy improved the process from the kinetic viewpoint resulting in a t₉₅ reduction from an average of 34.9 h without automatic pH control to an average of 19.5 h.

Fermentative H2 production from food waste: Parametric analysis of factor effects

Factorial fermentation experiments on food waste (FW) inoculated with activated sludge (AS) were conducted to investigate the effects of pH and the inoculum-to-substrate ratio (ISR [g VS_AS/g TOC_FW]) on biohydrogen production. The two parameters affected the H₂ yield, the fermentation rate and the biochemical pathways. The minimum and maximum yields were 41 L H₂/kg TOC_FW (pH = 7.5, ISR = 1.74) and 156-160 L H₂/kg TOC_FW (pH = 5.5, ISR = 0.58 and 1.74). The range of carbohydrates conversion into H₂ was 0.37-1.45 mol H₂/mol hexose, corresponding to 9.4-36.2% of the theoretical threshold. A second-order predictive model for H₂ production identified an optimum region at low pHs and high ISRs, with a theoretical maximum of 168 L H₂/kg TOC_FW at pH = 5.5 and ISR = 1.74. The Spearman's correlation method revealed several relationships between the variables, suggesting the potentially governing metabolic pathways, which turned out to involve both hydrogenogenic pathways and competing reactions.

Biochemical Hydrogen Potential Tests Using Different Inocula

Four inocula collected from different operating facilities were tested in their hydrogenic performances by means of two biochemical hydrogen potential test set-ups using sucrose and food waste as substrates, with the aim of evaluating the influence of inoculum media in batch fermentative assays. The selected inocula were: activated sludge collected from the aerobic unit of a municipal wastewater treatment plant, digested sludge from an anaerobic reactor treating organic waste and cattle manure, digested sludge from an anaerobic reactor treating agroindustrial residues, and digested sludge from an anaerobic reactor of a municipal wastewater treatment plant. Test results, in terms of specific hydrogen production, hydrogen conversion efficiency, and volatile solids removal efficiency, were significantly dependent on the type of inoculum. Statistical analysis showed different results, indicating that findings were due to the different inocula used in the tests. In particular, assays performed with activated sludge showed the highest performances for both substrates and both experimental set-ups.

Biohydrogen Production from Food Waste: Influence of the Inoculum-To-Substrate Ratio

In this study, the influence of the inoculum-to-substrate ratio (ISR) on dark fermentative hydrogen production from food waste (FW) was evaluated. ISR values ranging from 0.05 to 0.25 g VSinoculum/g VSsubstrate were investigated by performing batch tests at T = 39 °C and pH = 6.5, the latter being the optimal value identified based on a previous study. The ISR was found to affect the fermentation process, clearly showing that an adequate ISR is essential in order to optimise the process kinetics and the H2 yield. An ISR of 0.14 proved to optimum, leading to a maximum H2 yield of 88.8 L H2/kg VSFW and a maximum production rate of 10.8 L H2/kg VSFW∙h. The analysis of the fermentation products indicated that the observed highest H2 production mostly derived from the typical acetate/butyrate-type fermentation.