Management of Dark Fermentation Broth via Bio Refining and Photo Fermentation

Abstract

Lignocellulose and starch-based raw materials are often applied in the investigations regarding biohydrogen generation using dark fermentation. Management of the arising post-fermentation broth becomes a problem. The Authors proposed sequential processes, to improve the efficiency of both hydrogen generation and by-products management carried under model conditions. During the proposed procedure, the simple sugars remaining in broth are converted into organic acids, and when these products are used as substrates for the photo fermentation process. To enhance the broth management also conditions promoting Deep Eutectic Solvents (DES) precursors synthesis are simultaneously applied. Application of Box-Behnken design allows defining of the optimal conditions for conversion to DESs precursors. During the procedure hydrogen was obtained, the concentration of hydrogen in the photo fermentation reached up to 819 mL H2/L medium/7 d, depending on the broth type, i.e., when the broth was optimized for formic acid concentration. The DESs precursors were separated and engaged in DESs synthesis. To confirm the formation of the DESs, FT-IR analyses were performed. The Chemical Oxygen Demand of post-fermentation broths after dark fermentation optimized for formic acid was reduced by ca. 82%. The proposed procedure can be successfully used as a method of post-fermentation broth management.

Efficient Extraction of Fermentation Inhibitors by Means of Green Hydrophobic Deep Eutectic Solvents

“…The shifts, which can be observed in the range of 3680–3027 cm −1 confirmed the in-situ DES formation. Similar results were also obtained in previous studies [ 14 ]. In addition, in the FT-IR spectra of Cam: OA (1:1) and Gu, shifts are visible in the ranges of around 1743–1581 and 904–500 cm −1 , which characterize the C–H bending bonds of the aromatic band.…”

“…In this method, pure solvent forms hydrogen bonds with individual fermentation inhibitors (FF, LA, HMF) which generates the four-component DES complex. This approach has been described in previous studies [ 14 ].…”

“…Therefore, dark fermentation and photo fermentation may significantly increase the hydrogen yield if carried as subsequent processes. Among chemical compounds occurring in the liquid phase due to lignocellulosic biomass pretreatment and subsequent fermentation processes, carboxylic acids, i.e., acetic acid, lactic acid, citric acid, gluconic acid; dicarboxylic acids, i.e., succinic acid, fumaric acid, malic acid, levulinic acid; polyols, i.e., glycerin, sorbitol, xylitol and other compounds, including butanol, acetone, isopropanol, furfural, 1,3-propanediol, levulinic acid, syringole, guiacol, vanillin, and 5-hydroxymethylfurfural should be mentioned [ 13 , 14 ]. Nowadays, the management of the mentioned substances must be considered during the process in order to improve the efficiency of the process.…”

“…Any work on improving the energy balance of the production of second-generation biofuels, both in terms of energy and reducing the emission of undesirable substances, leads to the development of this sector and increases the profitability of given processes. Therefore, since some of mentioned post-fermentation substances are known to be potential fermentation inhibitors, model research on inhibiting concentrations was carried out [ 14 ].…”

Processing of Biomass Prior to Hydrogen Fermentation and Post-Fermentative Broth Management

“…The most frequently tested dark fermentation feeds are hydrolysates based on glucose and sucrose. A review of the literature [ 26 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 ] showed that for most model studies, substrate concentrations of about 10 g/L were neutral towards the slightly acidic pH of the fermentation broths. Only a few studies [ 104 ] were carried out for a pH > 7; however, as it appears from the content of the study, this is only the starting pH, which drops during fermentation due to the formation of organic acids during fermentation in a continuous UASB reactor.…”