Effect of initial substrate and biomass concentrations on anaerobic fermentative hydrogen production in batch reactors

The effects of initial substrate (5-60 g /L) and biomass concentration (0.5-3 g /L) on fermentative hydrogen production by mixed cultures were investigated in batch tests using glucose as substrate.The experimental results showed that the hydrogen production increases as the initial substrate concentration increases from 0 to 25 g /L.It indicated that the shift in the metabolic pathway or in the composition of the bacterial flora occurs.The maximum hydrogen yield of 1.78 mol /mol-glucose is obtained at the substrate concentration of 15 g /L.This study also shows that initial biomass concentration affects the hydrogen yield as the cumulative hydrogen production has been increased with the increase of initial cell concentration up to 1.5 g /L and reached the highest level.The maximum hydrogen yield is obtained at the cell concentration of 1.5 g /L.It indicated that the optimum biomass /substrate ratio,maximizing the hydrogen yield and the hydrogen production rate,is determined to be 0.1 g biomass /g glucose.

Delignification of disposable wooden chopsticks waste for fermentative hydrogen production by an enriched culture from a hot spring

Hydrogen （H2） production from lignocellulosic materials may be enhanced by removing lignin and increasing the porosity of the material prior to enzymatic hydrolysis. Alkaline pretreatment conditions, used to delignify disposable wooden chopsticks （DWC） waste, were investigated. The effects of NaOH concentration, temperature and retention time were examined and it was found that retention time had no effect on lignin removal or carbohydrate released in enzymatic hydrolysate. The highest percentage of lignin removal （41%） was obtained with 2% NaOH at 100℃, correlated with the highest carbohydrate released （67 mg/gpretreated DWC） in the hydrolysate. An enriched culture from a hot spring was used as inoculum for fermentative H2 production, and its optimum initial pH and temperature were determined to be 7.0 and 50℃, respectively. Furthermore, enzymatic hydrolysate from pretreated DWC was successfully demonstrated as a substrate for fermentative H2 production by the enriched culture. The maximum H2 yield and production rate were achieved at 195 mL H2/g total sugarsconsumed and 1 16 mL Hz/（L.day）, respectively.

Continuous biohydrogen production from diluted molasses in an anaerobic contact reactor

An anaerobic contact reactor (ACR) systemcomprising a continuous flow stirred tank reactor (CSTR)with settler to decouple the hydraulic retention time(HRT) from solids retention time (SRT) was developedfor fermentative hydrogen production from dilutedmolasses by mixed microbial cultures. The ACR wasoperated at various volumetric loading rates (VLRs) of20-44 kgCOD·m^(-3)·d^(-1) with constant HRT of 6 h undermesophilic conditions of 35°C. The SRTwas maintained atabout 46-50 h in the system. At the initial VLR of20 kgCOD·m^(-3)·d^(-1), the hydrogen production rate droppedfrom 22.6 to 1.58 L·d^(-1) as the hydrogen was consumed bythe hydrogentrophic methanogen. After increasing theVLR to 28 kgCOD·m^(-3)·d^(-1) and discharging the sludge for6 consecutive times, the hydrogentrophic methanogenswere eliminated, and the hydrogen content reached 36.4%.As the VLR was increased to 44 kgCOD·m^(-3)·d^(-1), thehydrogen production rate and hydrogen yield increased to42.1 L·d^(-1) and 1.40 mol H2·molglucose-consumed^(-1),respectively. The results showed that a stable ethanoltypefermentation that favored hydrogen production inthe reactor was thus established with the sludgeloading rate (SLR) of 2.0-2.5 kgCOD·kgMLVSS-1·d^(-1).It was found that the ethanol increased more than otherliquid fermentation products, and the ethanol/acetic acid(mol/mol) ratio increased from 1.27 to 2.45 when the VLRincreased from 28 to 44 kgCOD·m^(-3)·d^(-1), whereas thehydrogen composition decreased from 40.4% to 36.4%.The results suggested that the anaerobic contact reactorwas a promising bioprocess for fermentative hydrogenproduction.

Effects of nitrate concentration on biological hydrogen production by mixed cultures

The effects of nitrate on fermentative hydrogen production and soluble metabolites from mixed cultures were investigated by varying nitrate concentrations from 0 to 10 g N/L at 35℃ with an initial pH of 7.0.The results showed that the substrate degradation rate,hydrogen production potential,hydrogen yield,and average hydrogen production rate initially increased with increasing nitrate concentrations from 0 to 0.1 g N/L,while they decreased with increasing nitrate concentrations from 0.1 to 10 g N/L.The maximum hydrogen production potential of 305.0 mL,maximum hydrogen yield of 313.1 mL/g glucose,and maximum average hydrogen production rate of 13.3 mL/h were obtained at a nitrate concentration of 0.1 g N/L.The soluble metabolites produced by the mixed cultures contained only ethanol and acetic acid(HAc)without propionic acid(HPr)and butyric acid(HBu).This study used the Modified Logistic model to describe the progress of cumulative hydrogen production in batch tests.A concise model was proposed to describe the effects of nitrate concentration on average hydrogen production rate.