Enhancement of hydrogen production and energy recovery through electro-fermentation from the dark fermentation effluent of food waste

To enhance hydrogen production efficiency and energy recovery,a sequential dark fermentation and microbial electrochemical cell(MEC)process was evaluated for hydrogen production from food waste.The hydrogen production,electrochemical performance and microbial community dynamics were investigated during startup of the MEC that was inoculated with different sludges.Results suggest that biogas production rates and hydrogen proportions were 0.83 L/L d and 92.58%,respectively,using anaerobic digested sludge,which is higher than that of the anaerobic granular sludge(0.55 L/L d and 86.21%).The microbial community were predominated by bacterial genus Acetobacterium,Geobacter,Desulfovibrio,and archaeal genus Methanobrevibacter in electrode biofilms and the community structure was relatively stable both in anode and cathode.The sequential system obtained a 53.8% energy recovery rate and enhanced soluble chemical oxygen demand(sCOD)removal rate of 44.3%.This research demonstrated an important approach to utilize dark fermentation effluent to maximize the conversion of fermentation byproducts into hydrogen.

Vacuum promotes metabolic shifts and increases biogenic hydrogen production in dark fermentation systems

The successful operation of any type of hydrogen-producing bioreactor depends on the performance of the microorganisms present in the system. Both substrate and partial gas pressures are crucial factors affecting dark fermentation metabolic pathways. The main objective of this study was to evaluate the impact of both factors on hydrogen production using anaerobic granular sludge as inoculum and, secondly, to study the metabolic shifts of an anaerobic community subjected to low partial gas pressures. With this goal in mind, seven different wastewater （four synthetic media, two industrial waste- water, and one domestic effluent） and the effect of applying vacuum on the systems were analyzed. The application of vacuum promoted an increase in the diversity of hydrogen-producing bacteria, such as Clostridium, and promoted the dominance of acetoclasticover hydrogenotrophic methanogens. The application of different media promoted a wide variety of metabolic pathways. Nevertheless, reduction of the hydrogen partial pressure by application of vacuum lead to further oxidation of reaction intermediates irrespective of the medium used, which resulted in higher hydrogen and methane production, and improved the COD removal. Interestingly, vacuum greatly promoted biogenic hydrogen production from a real wastewater, which opens possibilities for future application of dark fermentation systems to enhance biohydrogen yields.

Assess the Denitrification Performance of Fermented and Dark-fermented Biosolids as External Carbon Sources Using Sequence Batch Reactors （SBRS）

The study has assessed the denitrification performance of fermented and dark-fermented biosolids as external carbon sources using lab-scaled Sequencing Batch Reactors （SBRs）. This was done by adding fermented and dark-fermented biosolids into anoxic zones of two SBRs, and then assessing the change of effluent characteristics comparing to before adding and to a third controlled reactor. The results showed that by adding 150-170 mg rbCOD/L of either of the selected fermented biosolids, almost complete denitrification could be reached for tested SBRs （reduced from initial -20 mg NO3/L to 〈 1 mg NO3/L）. Finally, the experiment also found that the impact of NI-I4 components of fermented and dark-fermented biosolids onto the final effluent were much lesser than expected, where only less than 2.5 mg NH4/L were detected in the effluent, much lower than the added 5.0-5.7 mg/L.

Evaluating the impact of sulfamethoxazole on hydrogen production during dark anaerobic sludge fermentation

The impact of antibiotics on the environmental protection and sludge treatment fields has been widely studied.The recovery of hydrogen from waste activated sludge(WAS)has become an issue of great interest.Nevertheless,few studies have focused on the impact of antibiotics present in WAS on hydrogen production during dark anaerobic fermentation.To explore the mechanisms,sulfamethoxazole(SMX)was chosen as a representative antibiotic to evaluate how SMX influenced hydrogen production during dark anaerobic fermentation of WAS.The results demonstrated SMX promoted hydrogen production.With increasing additions of SMX from 0 to 500 mg/kg TSS,the cumulative hydrogen production elevated from 8.07±0.37 to 11.89±0.19 mL/g VSS.A modified Gompertz model further verified that both the maximum potential of hydrogen production(Pm)and the maximum rate of hydrogen production(R_(m))were promoted.SMX did not affected sludge solubilization,but promoted hydrolysis and acidification processes to produce more hydrogen.Moreover,the methanogenesis process was inhibited so that hydrogen consumption was reduced.Microbial community analysis further demonstrated that the introduction of SMX improved the abundance of hydrolysis bacteria and hydrogen-volatile fatty acids(VFAs)producers.SMX synergistically influenced hydrolysis,acidification and acetogenesis to facilitate the hydrogen production.

Improved energy recovery from dark fermented cane molasses using microbial fuel cells

A major limitation associated with fermenta- tive hydrogen production is the low substrate conversion efficiency. This limitation can be overcome by integrating the process with a microbial fuel cell （MFC） which converts the residual energy of the substrate to electricity. Studies were carried out to check the feasibility of this integration. Biohydrogen was produced from the fermen- tation of cane molasses in both batch and continuous modes. A maximum yield of about 8.23 mol Hz/kg CODremoved was observed in the batch process compared to 11.6 mol Hz/kg CODremoved in the continuous process. The spent fermentation media was then used as a substrate in an MFC for electricity generation. The MFC parameters such as the initial anolyte pH, the substrate concentration and the effect ofpre-treatment were studied and optimized to maximize coulombic efficiency. Reductions in COD and total carbohydrates were about 85% and 88% respectively. A power output of 3.02 W/m3 was obtained with an anolyte pH of 7.5 using alkali pre-treated spent media. The results show that integrating a MFC with dark fermentation is a promising way to utilize the substrate energy.

Biological Hydrogen Production:A Comprehensive Review for Converting Wastes into Wealth

Energy shortages have hindered global economic development.By utilizing waste as a substrate for microbial fermentation,hydrogen production can transform waste into a valuable resource,significantly reducing the cost of hydrogen production and addressing a significant hurdle in achieving large-scale production of microbial hydrogen.This approach has significant potential for future hydrogen-production applications.Two-stage indirect photohydrolysis has recently emerged as a promising and efficient method for hydrogen production using cyanobacteria and green algae.However,this method cannot be directly applied to organic wastewater for hydrogen production.In contrast,dark fermentation by bacteria,particularly ethanol-type fermentation,is highly efficient for producing hydrogen.Therefore,the combination of the indirect photohydrolysis of algae and dark fermentation by bacteria is expected to significantly enhance the hydrogen-production capacity of organic wastewater,laying the groundwork for future large-scale microbial hydrogen production.This study reviews the main types and technical principles of microbial hydrogen production from waste,available waste types,research progress in the microbial hydrogen-production process,strategies to improve the hydrogen-production rate,and challenges faced during industrialization.Future research directions for microbial-waste hydrogen production are also proposed.The aim of this study is to provide a valuable reference for large-scale biological hydrogen-production research.

Optimization of hydrogen production from agricultural wastes using mixture design

Hydrogen production from food waste,cattle manure,potato pulp and pig manure was optimized through using mixture design in this study.The synergic and antagonistic effects of the four substrates on hydrogen yield,substrate conversion efficiency and pH were evaluated.The results showed that the optimal proportion of food waste,cattle manure,potato pulp and pig manure were 61.6%,38.4%,0,and 0,respectively.Under the optimal condition,hydrogen yield of 21.0 mL/g VS with VS reduction of 29.4%and pH of 5 could be obtained.The interaction between food waste and cattle manure had strongest synergistic effects.Hydrogen was mainly produced by acetic-butyric metabolic pathway,and ammonification of protein played an important role in the maintenance of pH.

Effect of illumination on the hydrogen-production capability of anaerobic activated sludge

To investigate the influence of illumination on the fermentative hydrogen production system, the hydro- gen production efficiencies of two kinds of anaerobic activated sludge （floc and granule） from an anaerobic baffled reactor were detected under visible light, dark and light-dark, respectively. The 10 mL floc sludge or granular sludge was respectively inoculated to 100 mL diluted molasses （chemical oxygen demand of 8000 mg.L^-1） in a 250 mL serum bottle, and cultured for 24 h at 37℃ under different illumination conditions. The results showed that the floc was more sensitive to illumination than the granule. A hydrogen yield of 19.8 mL was obtained in the dark with a specific hydrogen production rate of 3.52mol.kgLMLVSS.d^-1 （floc）, which was the highest among the three illumination conditions. Under dark condition, the hydrogen yield of floc sludge reached the highest with the specific hydrogen production rate of 3.52mol.kg^-1MLVSS.d^-1, and under light-dark, light, the specific hydrogen production rate was 3.11 and 2.21mol.kg^-1 MLVSS.d-1, respectively. The results demonstrated that the illumination may affect the dehydrogenase activity of sludge as well as the activity of hydrogen-producing acetogens and then impact hydrogen production capacity.