The hydraulic retention time influences the abundance of Enterobacter, Clostridium and Lactobacillus during the hydrogen production from food waste

Photosynthesizing carbonate/nitrate into Chlorococcum humicola biomass for biodiesel and Bacillus coagulans-based biohydrogen production

Biofuel can be generated by different organisms using various substrates. The green alga Chlorococcum humicola OQ934050 exhibited the capability to photosynthesize carbonate carbon, maybe via the activity of carbonic anhydrase enzymes. The optimum treatment is C:N ratio of 1:1 (0.2 mmoles sodium carbonate and 0.2 mmoles sodium nitrate) as it induced the highest dry mass (more than 0.5 mg.mL-1). At this combination, biomass were about 0.2 mg/mL-1 carbohydrates, 0.085 mg/mL-1 proteins, and 0.16 mg/mL-1 oil of this dry weight. The C/N ratios of 1:1 or 10:1 induced up to 30% of the Chlorococcum humicola dry mass as oils. Growth and dry matter content were hindered at 50:1 C/N and oil content was reduced as a result. The fatty acid profile was strongly altered by the applied C.N ratios. The defatted leftovers of the grown alga, after oil extraction, were fermented by a newly isolated heterotrophic bacterium, identified as Bacillus coagulans OQ053202, to evolve hydrogen content as gas. The highest cumulative hydrogen production and reducing sugar (70 ml H2/g biomass and 0.128 mg/ml; respectively) were found at the C/N ratio of 10:1 with the highest hydrogen evolution efficiency (HEE) of 22.8 ml H2/ mg reducing sugar. The optimum treatment applied to the Chlorococcum humicola is C:N ratio of 1:1 for the highest dry mass, up to 30% dry mass as oils. Some fatty acids were induced while others disappeared, depending on the C/N ratios. The highest cumulative hydrogen production and reducing sugar were found at the C/N ratio of 10:1.

Evaluation of individual and combined effect of lactic acid-consuming bacteria on mesophilic hydrogen production from lactic acid effluent from food waste treatment

Lactic acid has been applied as a precursor for hydrogen (H2) production from substrates rich in lactic acid bacteria (LAB), focusing on microbial interactions between producing and consuming LAB tested with model substrates. Therefore, this study evaluated the effect of single and combined lactic acid-consuming bacteria on mesophilic H2 production in batch tests from lactic acid from fermented food waste (FW). Megasphaera elsdenii, Clostridium beijerinckii, and Clostridium butyricum were inoculated at different ratios (v/v). Additionally, thermal pretreated sludge (TPS) was added to the strain mixtures. The highest production was obtained with M. elsdenii, C. beijerinckii, and C. butyricum (17:66:17 ratio), obtaining 1629.0 mL/Lreactor. The optimal mixture (68:32:0 of M. elsdenii and C. beijerinckii) enriched with TPS reached 1739.3 ± 98.6 mL H2/Lreactor, consuming 98 % of lactic acid added. M. elsdenii and Clostridium strains enhance H2 production from lactic acid as they persist in a microbial community initially dominated by LAB.

Biohythane production from two-stage anaerobic digestion of food waste: A review

The biotransformation of food waste (FW) to bioenergy has attracted considerable research attention as a means to address the energy crisis and waste disposal problems. To this end, a promising technique is two-stage anaerobic digestion (TSAD), in which the FW is transformed to biohythane, a gaseous mixture of biomethane and biohydrogen. This review summarises the main characteristics of FW and describes the basic principle of TSAD. Moreover, the factors influencing the TSAD performance are identified, and an overview of the research status; economic aspects; and strategies such as pre-treatment, co-digestion, and regulation of microbial consortia to increase the biohythane yield from TSAD is provided. Additionally, the challenges and future considerations associated with the treatment of FW by TSAD are highlighted. This paper can provide valuable reference for the improvement and widespread implementation of TSAD-based FW treatment.

The Potential of Digested Sludge-Assimilating Microflora for Biogas Production from Food Processing Wastes

Food processing wastes (FPWs) are residues generated in food manufacturing, and their composition varies depending on the type of food product being manufactured. Therefore, selecting and acclimatizing seed microflora during the initiation of biogas production is crucial for optimal outcomes. The present study examined the biogas production capabilities of digested sludge-assimilating and biogas-yielding soil (DABYS) and enteric (DABYE) microflorae when used as seed cultures for biogas production from FPWs. After subculturing and feeding these microbial seeds with various FPWs, we assessed their biogas-producing abilities. The subcultures produced biogas from many FPWs, except orange peel, suggesting that the heterogeneity of the bacterial members in the seed microflora facilitates quick adaptation to FPWs. Microflorae fed with animal-derived FPWs contained several methanogenic archaeal families and produced methane. In contrast, microflorae fed with vegetable-, fruit-, and crop-derived FPWs generated hydrogen, and methanogenic archaeal populations were diminished by repeated subculturing. The subcultured microflorae appear to hydrolyze carbohydrates and protein in FPWs using cellulase, pectinase, or protease. Despite needing enhancements in biogas yield for future industrial scale-up, the DABYS and DABYE microflorae demonstrate robust adaptability to various FPWs.

Dark fermentation and microalgae cultivation coupled systems: Outlook and challenges

The implementation of a sustainable bio-based economy is considered a top priority today. There is no doubt about the necessity to produce renewable bioenergy and bio-sourced chemicals to replace fossil-derived compounds. Under this scenario, strong efforts have been devoted to efficiently use organic waste as feedstock for biohydrogen production via dark fermentation. However, the technoeconomic viability of this process needs to be enhanced by the valorization of the residual streams generated. The use of dark fermentation effluents as low-cost carbon source for microalgae cultivation arises as an innovative approach for bioproducts generation (e.g., biodiesel, bioactive compounds, pigments) that maximizes the carbon recovery. In a biorefinery context, after value-added product extraction, the spent microalgae biomass can be further valorised as feedstock for biohydrogen production. This integrated process would play a key role in the transition towards a circular economy. This review covers recent advances in microalgal cultivation on dark fermentation effluents (DFE). BioH₂ via dark fermentation processes and the involved metabolic pathways are detailed with a special focus on the main aspects affecting the effluent composition. Interesting traits of microalgae and current approaches to solve the challenges associated to the integration of dark fermentation and microalgae cultivation are also discussed.

Unrevealing the role of metal oxide nanoparticles on biohydrogen production by Lactobacillus delbrueckii

The positive interaction between Clostridium sp. and lactic acid-producing bacteria (Lactobacillus sp) is commonly seen in various high-rate hydrogen production systems. However, the exact role of the hydrogen production ability of Lactobacillus sp in a dark fermentation production system is rarely studied. Lactobacillus delbrueckii was herein used for the first time, to the best of the author's knowledge, to demonstrate biohydrogen production under anaerobic conditions. At first, the pH condition was optimized, followed by the addition of nanoparticles for enhanced biohydrogen production. Under optimized conditions of pH 6.5, substrate concentration 10 g/L, and 100 mg/L of NiO/Fe₂O₃, the maximum hydrogen yield (HY) of 1.94 mol/mol hexose was obtained, which is 18 % more than the control. The enhanced H₂ production upon the addition of nanoparticles is supported via the external electron transfer (EET) mechanism, which regulates the metabolic pathway regulation with increased production of acetate and butyrate and reduced formation of lactate.

Influence of key operational parameters on biohydrogen production from fruit and vegetable waste via lactate-driven dark fermentation

This study aims at investigating the influence of operational parameters on biohydrogen production from fruit-vegetable waste (FVW) via lactate-driven dark fermentation. Mesophilic batch fermentations were conducted at different pH (5.5, 6.0, 6.5, 7.0, and non-controlled), total solids (TS) contents (5, 7, and 9%) and initial cell biomass concentrations (18, 180, and 1800 mg VSS/L). Higher hydrogen yields and rates were attained with more neutral pH values and low TS concentrations, whereas higher biomass densities enabled higher production rates and avoided wide variations in hydrogen production. A marked lactate accumulation (still at neutral pH) in the fermentation broth was closely associated with hydrogen inhibition. In contrast, enhanced hydrogen productions matched with much lower lactate accumulations (even it was negligible in some fermentations) along with the acetate and butyrate co-production but not with carbohydrates removal. At pH 7, 5% TS, and 1800 mg VSS/L, 49.5 NmL-H2/g VSfed and 976.4 NmL-H2/L-h were attained.

Prokaryotic population dynamics and interactions in an AnSBBR using tequila vinasses as substrate in co-digestion with acid hydrolysates of Agave tequilana var. azul bagasse for hydrogen production

AIMS

The purpose of this study was to characterize the prokaryotic community and putative microbial interactions between H₂ -producing bacteria (HPB) and non-HPB using two anaerobic sequencing batch biofilm reactors (AnSBBRs) fed with tequila vinasses in co-digestion with acid hydrolysates of Agave tequilana var. azul bagasse (ATAB).

METHODS AND RESULTS

Two AnSBBRs were operated for H₂ production to correlate changes in physicochemical and biological variables by principal component analysis (PCA). Results indicated that H₂ yield was supported by Ethanoligenens harbinense and Clostridium tyrobutyricum through the PFOR pathway. However, only E. harbinense was able to compete for sugars against non-HPB. Competitive exclusion associated with competition for sugars, depletion of essential trace elements, bacteriocin production and resistance to inhibitory compounds could be carried out by non-HPB, increasing their relative abundances during the dark fermentation (DF) process.

CONCLUSIONS

The global scenario obtained by PCA correlated the decrease in H₂ production with the lactate:acetate molar ratio in the influent. At the beginning of co-digestion, this ratio had the minimum value considered for a net gain of ATP. This fact could cause the reduction of the relative abundance of C. tyrobutyricum.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study that demonstrated the feasibility of H₂ production by Clostridiales from acid hydrolysates of ATAB in co-digestion with tequila vinasses.

Three-stage process for tequila vinasse valorization through sequential lactate, biohydrogen and methane production

This study evaluated a novel three-stage process devoted to the cascade production of lactate, biohydrogen and methane from tequila vinasse (TV), with emphasis on attaining a high and stable biohydrogen production rate (HPR) by utilizing lactate as biohydrogen precursor. In the first stage, tailored operating conditions applied to a sequencing batch reactor were effective in sustaining a lactate concentration of 12.4 g/L, corresponding to 89% of the total organic acids produced. In the second stage, the stimulation of lactate-centered dark fermentation which entails the decoupling of biohydrogen production from carbohydrates utilization was an effective approach enabling stable biohydrogen production, having HPR fluctuations less than 10% with a maximum HPR of 12.3 L/L-d and a biohydrogen yield of 3.1 L/L_TV. Finally, 1.6 L CH₄/L-d and 6.5 L CH₄/L_TV were obtained when feeding the biohydrogen fermentation effluent to a third methanogenic stage, yielding a global energy recovery of 267.5 kJ/L_TV.