Assessing nitrous oxide emissions from algal-bacterial photobioreactors devoted to biogas upgrading and digestate treatment.

Nitrous oxide (N2O) emissions in High Rate Algal Ponds (HRAP) can negatively affect the sustainability of algal-bacterial processes. N2O emissions from a pilot HRAP devoted to biogas upgrading and digestate treatment were herein monitored for 73 days. The influence of the pH (7.5, 8.5, and 9.5), nitrogen sources (100 mg/L of N-NO2-, N-NO3-, and N-NH4+) and illumination on N2O emissions from the algal-bacterial biomass of the HRAP was also assessed in batch tests. Significantly higher N2O gas concentrations of 311.8 ± 101.1 ppmv were recorded in the dark compared to the illuminated period (236.9 ± 82.6 ppmv) in the HRAP. The batch tests revealed that the highest N2O emission rates (49.4 mmol g-1 TSS·h-1) occurred at pH 8.5 in the presence of 100 mg N-NO2-/L under dark conditions. This study revealed significant N2O emissions in HRAPs during darkness.

Functional link hybrid artificial neural network for predicting continuous biohydrogen production in dynamic membrane bioreactor.

Conventional machine learning approaches have shown limited predictive power when applied to continuous biohydrogen production due to nonlinearity and instability. This study was aimed at forecasting the dynamic membrane reactor performance in terms of the hydrogen production rate (HPR) and hydrogen yield (HY) using laboratory-based daily operation datapoints for twelve input variables. Hybrid algorithms were developed by integrating particle swarm optimized with functional link artificial neural network (PSO-FLN) which outperformed other hybrid algorithms for both HPR and HY, with determination coefficients (R2) of 0.97 and 0.80 and mean absolute percentage errors of 0.014 % and 0.023 %, respectively. Shapley additive explanations (SHAP) explained the two positive-influencing parameters, OLR_added (1.1-1.3 mol/L/d) and butyric acid (7.5-16.5 g COD/L) supports the highest HPR (40-60 L/L/d). This research indicates that PSO-FLN model are capable of handling complicated datasets with high precision in less computational timeat 9.8 sec for HPR and 10.0 sec for HY prediction.

Positive effect of phasin in biohydrogen production of non polyhydroxybutyrate-producing Clostridium acetobutylicum ATCC 824.

In this study, the goal was to enhance the tolerance of Clostridium acetobutylicum ATCC 824 to biomass-based inhibitory compounds for biohydrogen production and evaluate various known genes that enhance the production of biochemicals in various hosts. The introduction of phaP, the major polyhydroxyalkanoate granule-associated protein that has been reported as a chaperone-like protein resulted in increased tolerance to inhibitors and leads to higher levels of hydrogen production, cell growth, and glucose consumption in the presence of these inhibitors. It was observed that the introduction of phaP led to an increase in the transcription of the hydrogenase gene, whereas transcription of the chaperone functional genes decreased compared to the wild type. Finally, the introduction of phaP could significantly enhance biohydrogen production by 2.6-fold from lignocellulosic hydrolysates compared to that of wild type. These findings suggested that the introduction of phaP could enhance growth and biohydrogen production, even in non-polyhydroxyalkanoate-producing strains.

Efficient polyhydroxybutyrate production using acetate by engineered Halomonas sp. JJY01 harboring acetyl-CoA acetyltransferase.

Polyhydroxybutyrate (PHB) is a well-known biodegradable bioplastic synthesized by microorganisms and can be produced from volatile fatty acids (VFAs). Among VFAs acetate can be utilized by Halomonas sp. YLGW01 for growth and PHB production. In this study, Halomonas sp. JJY01 was developed through introducing acetyl-CoA acetyltransferase (atoAD) with LacIq-Ptrc promoter into Halomonas sp. YLGW01. The effect of expression of atoAD on acetate was investigated by comparison with acetate consumption and PHB production. Shake-flask study showed that Halomonas sp. JJY01 increased acetate consumption rate, PHB yield and PHB production (0.27 g/L/h, 0.075 g/g, 0.72 g/L) compared to the wild type strain (0.17 g/L/h, 0.016 g/g, 0.11 g/L). In 10 L fermenter scale fed-batch fermentation, the growth of Halomonas sp. JJY01 resulted in higher acetate consumption rate, PHB yield and PHB titer (0.55 g/L/h, 0.091 g/g, 4.6 g/L) than wild type strain (0.35 g/L/h, 0.067 h/h, 2.9 g/L). These findings demonstrate enhanced acetate utilization and PHB production through the introduction of atoAD in Halomonas strains.

Polyhydroxyalkanoate production from rice straw hydrolysate: Insights into feast-famine dynamics and microbial community shifts.

Activated sludge contains a versatile microbiome capable of converting wastes into valuable chemicals like polyhydroxyalkanoates (PHA). This study investigated the influence of repeated feast and famine phases on PHA production as well as the corresponding microbial population dynamics using waste activated sludge (WAS) as inoculum. Hydrolysate derived from rice straw was employed as a substrate for PHA production. The 16sRNA analysis results revealed that Corynebacteriaceae (40%), Bacillaceae (23%), and Pseudomonas (5%) were the primary contributors to PHA synthesis. Notably, Bacillaceae and Pseudomonas thrived in all the feast and famine phases. The achieved PHA concentration was 3.5 ± 0.2 g/L, and its structure and composition were assessed using Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR). The analysis revealed that the PHA consists of a copolymer of hydroxybutyrate (HB) and hydroxyvalerate (HV), specifically identified as Poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV).

Anaerobic digestion of sewage sludge using anaerobic dynamic membrane bioreactor under various sludge composition and organic loading rates.

This study investigates the effects of sludge compositions and organic loading rates (OLRs) on stable biogas production during sludge digestion. Batch digestion experiments evaluate the effects of alkaline-thermal pretreatment and waste activated sludge (WAS) fractions on the biochemical methane potential (BMP) of sludge. A lab-scale anaerobic dynamic membrane bioreactor (AnDMBR) is fed with a mixture of primary sludge and pretreated WAS. Monitoring of volatile fatty acid to total alkalinity (FOS/TAC) helps maintain operational stability. The highest average methane production rate of 0.7 L/L·d is achieved when the OLR, hydraulic retention time, WAS volume fraction, and FOS/TAC ratio are 5.0 g COD/L·d, 12 days, 0.75, and 0.32, respectively. This study finds functional redundancy in two pathways: hydrogenotrophic and acetolactic. An increase in OLR promotes bacterial and archaeal abundance and specific methanogenic activity. These results can be applied to the design and operation of sludge digestion for stable, high-rate biogas recovery.

Enhancement of biohydrogen production in Clostridium acetobutylicum ATCC 824 by overexpression of glyceraldehyde-3-phosphate dehydrogenase gene.

In the dark fermentation of hydrogen, development of production host is crucial as bacteria act on substrates and produce hydrogen. The present study aimed to improve hydrogen production through the development of Clostridium acetobutylicum as a superior biohydrogen producer. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which produces NADH/NADPH for metabolites and energy in primary pathways, was introduced to enhance hydrogen production. The strain CAC824-G containing gapC that encodes GAPDH showed a 66.3 % higher hydrogen production than the wild-type strain, with increased NADH and NADPH pools. Glucose consumption and other byproducts, such as acetone, butanol, and ethanol, were also high in CAC824-G. Overexpression of gapC resulted in increased hydrogen production with sugars obtained from different biomass, even in the presence of inhibitors such as vanillin, 5-hydroxymethylfufural, acetic acid, and formic acid. Our results imply that overexpression of gapC in Clostridium is possible to expand the production of the reported biochemicals to produce hydrogen.

Enhanced continuous biohydrogen production using dynamic membrane with conductive biofilm supporter.

The present study investigated the effect of a conductive biofilm supporter on continuous production of biohydrogen in a dynamic membrane bioreactor (DMBR). Two lab-scale DMBRs were operated: one with a nonconductive polyester mesh (DMBR I) and the other with a conductive stainless-steel mesh (DMBR II). The highest average hydrogen productivity and the yield were 16.8% greater in DMBR II than in DMBR I, with values of 51.64 ± 0.66 L/L-d and 2.01 ± 0.03 mol H2/mol hexoseconsumed, respectively. The improved hydrogen production was concurrent with a higher NADH/NAD+ ratio and a lower ORP (Oxidation-reduction potential). Metabolic flux analysis implied that the conductive supporter promoted H2-producing acetogenesis and repressed competitive NADH-consuming pathways, such as homoacetogenesis and lactate production. Microbial community analysis revealed that electroactive Clostridium sp. were the dominant H2 producers in DMBR II. Conclusively, conductive meshes may be useful as biofilm supporters of dynamic membranes during H2 production for selectively enhancing H2-producing pathways.

Unraveling Biohydrogen Production and Sugar Utilization Systems in the Electricigen Shewanella marisflavi BBL25.

Identification of novel, electricity-producing bacteria has garnered remarkable interest because of the various applications of electricigens in microbial fuel cell and bioelectrochemical systems. Shewanella marisflavi BBL25, an electricity-generating microorganism, uses various carbon sources and shows broader sugar utilization than the better-known S. oneidensis MR-1. To determine the sugar-utilizing genes and electricity production and transfer system in S. marisflavi BBL25, we performed an in-depth analysis using whole-genome sequencing. We identified various genes associated with carbon source utilization and the electron transfer system, similar to those of S. oneidensis MR-1. In addition, we identified genes related to hydrogen production systems in S. marisflavi BBL25, which were different from those in S. oneidensis MR-1. When we cultured S. marisflavi BBL25 under anaerobic conditions, the strain produced 427.58 ± 5.85 µl of biohydrogen from pyruvate and 877.43 ± 28.53 µl from xylose. As S. oneidensis MR-1 could not utilize glucose well, we introduced the glk gene from S. marisflavi BBL25 into S. oneidensis MR-1, resulting in a 117.35% increase in growth and a 17.64% increase in glucose consumption. The results of S. marisflavi BBL25 genome sequencing aided in the understanding of sugar utilization, electron transfer systems, and hydrogen production systems in other Shewanella species.

Predicting the impact of hydraulic retention time and biodegradability on the performance of sludge acidogenesis using an artificial neural network.

This study aimed to predict volatile fatty acids (VFAs) production from SDBS-pretreated waste-activated sludge (WAS). A lab-scale continuous experiment was conducted at varying hydraulic retention times (HRTs) of 7 d to 1 d. The highest VFA yield considering the WAS biodegradability was 86.8 % based on COD at an HRT of 2 d, where the hydrolysis and acidogenesis showed the highest microbial activities. According to 16S rRNA gene analysis, the most abundant bacterial class and genus at an HRT of 2 d were Synergistia and Aminobacterium, respectively. Training regression (R) for TVFA and VFA yield was 0.9321 and 0.9679, respectively, verifying the efficiency of the ANN model in learning the relationship between the input variables and reactor performance. The prediction outcome was verified with R2 values of 0.9416 and 0.8906 for TVFA and VFA yield, respectively. These results would be useful in designing, operating, and controlling WAS treatment processes.

Microalgae biomass deconstruction using green solvents: Challenges and future opportunities.

Microalgae enablefixation of CO2into carbohydrates, lipids, and proteins through inter and intracellularly biochemical pathways. These cellular components can be extracted and transformed into renewable energy, chemicals, and materials through biochemical and thermochemical transformation processes.However, recalcitrant cell wall andlack of environmentally benign efficient pretreatment processes are key obstacles in the commercialization of microalgal biorefineries.Thus,current article describes the microalgal chemical structure, type, and structural rigidity and summarizes the traditional pretreatment methods to extract cell wall constituents. Green solvents such as ionic liquid (ILs), deep eutectic solvents (DES), and natural deep eutectic solvents (NDESs) have shown interesting solvent characteristics to pretreat biomass with selective biocomponent extraction from microalgae. Further research is needed in task-specific IL/DES design, cation-anion organization, structural activity understanding of ILs-biocomponents, environmental toxicity, biodegradability, and recyclability for deployment of carbon-neutral technologies. Additionally, coupling the microalgal industry with biorefineries may facilitate waste management, sustainability, and gross revenue.

Machine learning in fermentative biohydrogen production: Advantages, challenges, and applications.

Hydrogen can be produced in an environmentally friendly manner through biological processes using a variety of organic waste and biomass as feedstock. However, the complexity of biological processes limits their predictability and reliability, which hinders the scale-up and dissemination. This article reviews contemporary research and perspectives on the application of machine learning in biohydrogen production technology. Several machine learning algorithems have recently been implemented for modeling the nonlinear and complex relationships among operational and performance parameters in biohydrogen production as well as predicting the process performance and microbial population dynamics. Reinforced machine learning methods exhibited precise state prediction and retrieved the underlying kinetics effectively. Machine-learning based prediction was also improved by using microbial sequencing data as input parameters. Further research on machine learning could be instrumental in designing a process control tool to maintain reliable hydrogen production performance and identify connection between the process performance and the microbial population.

Recent updates in biohydrogen production strategies and life-cycle assessment for sustainable future.

Biohydrogen (bio-H2) is regarded as a clean, non-toxic, energy carrier and has enormous potential for transforming fossil fuel-based economy. The development of a continuous high-rate H2 production with low-cost economics following an environmentally friendly approach should be admired for technology demonstration. Thus, the current review discusses the biotechnological and thermochemical pathways for H2 production. Thermochemical conversion involves pyrolysis and gasification routes, while biotechnological involves light-dependent processes (e.g., direct and indirect photolysis, photo/ dark fermentation strategies). Moreover, environmentally friendly technologies can be created while utilizing renewable energy sources including lignocellulosic, wastewater, sludge, microalgae, and others, which are still being developed. Lifecycle assessment (LCA) evaluates and integrates the economic, environmental, and social performance of H2 production from biomass, microalgae, and biochar. Moreover, system boundaries evaluation, i.e., global warming potential, acidification, eutrophication, and sensitivity analysis could lead in development of sustainable bioenergy transition with high economic and environmental benefits.

Effect of bioaugmentation using Clostridium butyricum on the start-up and the performance of continuous biohydrogen production.

This study aimed to mitigate the instability in the start-up and continuous performance of dark fermentative biohydrogen production using heat-treated sludge by the addition of an exogenous H2-producing strain. Continuous fermentation augmented with Clostridium butyricum showed the highest average biohydrogen production rate (HPR) as 50.35 ± 2.56 and 58.57 ± 5.03 L/L-d with H2-producing butyric and acetic acid pathways, whereas the fermenters without bioaugmentation showed the termination of biohydrogen production in 3 days of continuous operation with non H2-producing lactic acid pathway and H2-consuming propionic acid pathway. The bioaugmentation blocked the growth of the competitors for hexose such as Streptococcus, Lactobacillus and Megasphaera, and provided H2-producer dominated microbiome with not only Clostridium butyricum, but also Clostridium puniceum and Clostridium neuense originated from heat-treated sludge. Bioaugmentation of a H2-producing strain would be a reliable dissemination strategy for dark fermentative biohydrogen production by minimizing the influence of seed sludge population.

Effective recovery of microalgal biomass using various types of emulsion polymers.

Microalgae biomass has been considered as one of the potential feedstocks in biofuel production. Yet, biomass harvesting poses a challenge to the overall production cost due to its low cell density. Flocculation has been marked as one of the promising processes in microalgae harvesting technology. In this study, the first screening of two anionic (A-230, and A-330E) and five cationic polymers (C-810E, C-810EL, C-810EB, C-810ELH, and C-810EMB) followed by gravity settling with the mixed microalgae concentration of 2.24 gTSS/L revealed that anionic polymers are less effective. Whereas all cationic polymers achieved above 90% harvesting efficiency. Therefore, the maximum mass recovery of 98.7% with 86.8 gTSS/L sediment content was achieved by adjusting pH to 6-0.6 mL/L (115.178 mg/gbiomass) of C-810E followed by 15-min settling. The cationic polymer addition followed by settling would enable cost-effective downstream processing of microalgal biomass.

Synthesis of fatty acid-based ammonium ionic liquids and their application for extraction of Co(II) and Ni(II) metals ions from aqueous solution.

Leaching of cobalt and nickel into diverse water streams has become an environmental hazard and is continuously impacting human health through the food chain. Solvent extraction is the most widely accepted for separating these metals, but traditional extractants employed in conjunction with molecular diluents often lack selectivity and caused major environmental hurdles. Therefore, the development of cost-effective, environmentally friendly technologies for recovering these heavy metals has been strongly encouraged in recent years. Herein, two halogens free, low viscous, biocompatible fatty acid-based hydrophobic ionic liquids (ILs), i.e., methytrioctylammonium oleate, methytrioctylammonium linoleate were synthesized, analytically characterized and employed for recovery of cobalt, Co(II) and nickel, Ni(II) from their aqueous solutions. Extraction behaviour of Co(II) and Ni(II) was further evaluated by varying equilibrium time, ILs molar concentration, metal loading, and temperature. Thermodynamic parameters such as enthalpy change and Gibbs free energy change were also studied during extraction process. Slope analysis suggested that the extraction mechanism was an exothermic process that followed ion-transfer from the aqueous phase to the organic phase. Results showed that both fatty acid based-ILs were found to be capable of extracting >99% of Co(II) and Ni(II) from aqueous solutions at 298 K, in 15 min of shaking time using a 1:1 (org: aq.) ratio at low concentrations of 2.5-10 g L-1. Furthermore, for methyltrioctylammonium oleate IL, Co(II) extraction was selectively preferred over Ni(II) extraction when the metal concentration was increased to above to 10 g L-1. The stripping results showed that 2 M H2SO4, and 2 M HCl successfully stripped out >99% of Co(II) and Ni(II) from the organic phase, respectively compared to HNO3.

Acceleration of lactate-utilizing pathway for enhancing biohydrogen production by magnetite supplementation in Clostridium butyricum.

A conductive metal compound can be used as a catalyst for enhancing hydrogen production by dark fermentation. This study aimed to identify mechanisms of enhanced hydrogen production by magnetite supplementation. Experiments were performed with lactate and/or magnetite supplementation to confirm that the lactate-utilizing pathway is the key cause of enhanced hydrogen production. Also, ribonucleic acid sample was collected for monitoring gene regulation under each condition. Hydrogen production was significantly enhanced by approximately 25.6% and 58.9%, respectively, via magnetite alone and with lactate. Moreover, the expression of genes involved in hydrogen production, including pyruvate ferredoxin oxidoreductase, hydrogenase, and ferredoxin, via magnetite alone and with lactate was upregulated by 0.26, 0.71, and 3.50 and 1.06, 2.14, and 1.94 times, respectively.

Valorization of pretreated waste activated sludge to organic acids and biopolymer.

Polyhydroxybutyrate (PHB) is a natural polyester that may be made by utilizing volatile fatty acids (VFAs) as a substrate. VFA generated by continuous anaerobic fermentation of waste activated sludge (WAS) was fed into bioreactors for PHB synthesis in this work. Series of optimization tests were conducted to increase the biodegradability and hydrolysis of waste activated sludge. It was found out that 0.05 g/g TS of SDBS (sodium dodecylbenzene sulfonate), 70 °C (heat treatment) and 2hr (time) as pretreatment condition would give the highest solubilization. Impact of pH adjustment on the acidogenesis of pretreated WAS was evaluated in batch experiments at varying initial pH (4-10). The result indicated that when operational pH was between 7.5 and 8, the VFA yield was increased by 5.3-18.1%. Continuous acidogenic operation validated the SDBS pretreatment and pH adjustment warranted stable VFA conversion from WAS at a yield of 47% in COD basis. Firmicutes, Actinobacteria and Proteobacteria were affiliated as dominant bacterial phyla in the continuous acidogenesis. The effluent of the continuous acidogenesis was converted to biopolymer with the average yields of 0.23 g PHB-COD/g VFAadded-COD in the feast mode and 0.34 g PHB-COD/g VFAadded-COD in the famine mode. In feast and famine cycle, the average VFA utilization was 55% and 60% respectively. The sequential SDBS pretreatment, acidogenesis and PHB production would produce 162 g of PHB from 1 kg of WAS as COD basis.

Comparison of alkali and ionic liquid pretreatment methods on the biochemical methane potential of date palm waste biomass.

Date palm waste biomass is a readily accessible agricultural waste biomass that may be used to produce biogas. Because the complex structure of date palm waste biomass prevents the embedded holo-cellulosic sugars from biodegrading, pretreatment is required to increase methane (CH4) yield. The present investigation aimed to comparatively determine the impact of alkali and ionic liquid pretreatment on the biochemical methane potential (BMP) of different types of date palm waste biomass. The findings revealed that ionic liquid pretreated Palm and Fruit bunch showed the highest BMP (321.67 mL CH4/g-TS) and substrate conversion efficiency (68.01%), respectively, over other biomass samples. In alkali pretreatment, the highest BMP and substrate conversion efficiency were detected with Palm (309.76 mL CH4/g-TS) and Spathe (62.09%). The high BMP and substrate conversion efficiency of date palm waste biomass may be harnessed for bioenergy production when this ionic liquid pretreatment technology is used.