Selection of metabolic pathways for continuous hydrogen production under thermophilic and mesophilic temperature conditions in anaerobic fluidized bed reactors

Improved dark fermentation of cane molasses in mesophilic and thermophilic anaerobic fluidized bed reactors by selecting operational conditions

“…6,7 Han et al 6 reported that raising the OLR (24-32 kg COD/m 3 day) reduced the HPR from 326.1 to 228.0 mL/L bed Áh in a mesophilic (35 C) continuous stirred tank reactor (CSTR). Unlike an AFBR, where the cell detention time is dissociated from the HRT, 19 a CSTR can exhibit biomass washout under short HRTs, resulting in lower HPR. 7 Wang et al 7 observed that reducing the HRT (5-4 hours) of a mesophilic (35 C) CSTR decreased the HPR from 322.7 to 229.3 mL/L bed Áh and the H 2 % from 62.0% to 51.9%.…”

“…When looking at the performance of AFBRs for dark fermentation of sucrose-based synthetic wastewater in different temperatures, 19 the results reported are relatable to MR and TR. Ferreira et al 19 confirmed that the lower HRT of 1 hour raised the HPR from 72 to 344 mL/L bed Áh at 30 C and from 68 to 195 mL/L bed Áh at 55 C. However, the maximum HPR of the thermophilic AFBR fed with sucrose (195 mL/L bed Áh) was lower than the maximum HPR of the TR (303.4 mL/L bed Áh). These results differed from the observations of Tunçay et al, 47 who reported lower hydrogen production when using molasses as a substrate in comparison with sucrose because of greater susceptibility of homoacetogenesis on molasses dark fermentation.…”

“…31 Regarding the H 2 production, studies conducted at thermophilic conditions 19,22,32 reported superior performance to those carried out in the mesophilic conditions. 19,22,33 However, regarding the soluble metabolite production, the influence of temperature on the composition of metabolites is minimal. 26 Another parameter that influences both H 2 and soluble metabolite production is the HRT, associated with the organic loading rate (OLR).…”

“…The use of mixed cultures has been reported in studies on the fermentative H 2 production from synthetic [15][16][17][18][19] and complex substrates. [20][21][22] The biological hydrogen production is another alternative for the use of fossil resources and can generate H 2 as an energy carrier (34 kcal/g) 23 while also producing valuable chemicals as soluble metabolites.…”

“…35 Therefore, the growth of microorganisms unfavorable to H 2 production is hindered by lower HRT. In our previous study using synthetic wastewater based on sucrose, 19 the reduction of the HRT raised the hydrogen production rate (HPR) to 344 mL/L bed Áh at 30 C and 195 mL/L bed Áh at 55 C in anaerobic fluidized bed reactors (AFBRs). Also, the lower HRT hindered propionic acid production, favoring hydrogen-producing pathways.…”