during batch and continuous H 2 production from industrial waste. Only LCFAs
could be obtained from renewable and sustainable sources (from food processing
wastewater), while BESA and chloroform are petroleum-based derivatives. Thus,
they represent a sustainable and renewable input. Mohan et al. [220] reported
that treating the inoculum with 0.2 g BESA/L for 24 h increased the H 2 yield from
dairy wastewater by a factor of 2.6 compared to heat shock (100
C; 1 h).
4.3 Organic Loading Rate (OLR)
The organic loading rate (OLR) is an important operation parameter which has to be
optimized to achieve the maximum yield per unit mass of inoculum. The OLR of
waste fed to dark fermentative H 2 production process has continued to be an
objective of the research. The OLR means the food/microorganism ratio which
affects the microbial growth; therefore, it needs to be within the optimum range to
support optimal microbial growth because H 2 production is a growth-associated
reaction. Han et al. [231] reported that increasing the OLR from 8 to 24 kg molasses/
m
3 /d increased the H 2 production rate and achieved a maximum value of
10.74 mmol/L/h in a CSTR. Similarly, the H 2 yield increased with the increase of
cow manure and waste milk OLR in thermophilic (55
C) batch reactors [204].
The OLR also affects the biogas composition in an upflow anaerobic sludge
blanket (UASB); the higher the OLR, the greater the biogas H 2 content [232]. On the
contrary, Bhaskar et al. [233] found that increasing the OLR of chemical wastewater
decreased the specific H 2 yield and the chemical oxygen demand (COD) removal
efficiency in biofilm-configured sequencing batch reactors (SBR). The substrate
concentration affects the H 2 production; increasing the substrate (hydrolysate)
concentration from 20% to 25% increased the lag phase of H 2 production in batch
reactors, from 11 to 38 h, and at a level of 30% inhibited the H 2 fermentation
[234]. The variation in the findings regarding the effects of the OLR on the rate,
yield, and the gas composition can be due to the type and quality of the substrate fed
despite that two substrates can be fed at the same OLR (based on the COD) and their
metabolism rate can be different. In conclusion, the OLR needs to be optimized on a
case-by-case basis.
4.4 Comparative Studies on the Effects of Pretreatments
Several studies investigated the effect of some culture pretreatments on the preparation of inoculum for the conversion of corn stover hydrolysate, dairy wastewater,
palm oil mill effluent, and biodiesel production waste (glycerol) (Table 8.11).
However, the results reported were conflicting and inconclusive. The ranking of
the effect of several pretreatment on the H 2 yields (mmol H 2 /g sugar utilized) from
corn stover hydrolysate was as follows: heat (5.03) > base (4.5) > acid
352
A. Hajizadeh et al.
could be obtained from renewable and sustainable sources (from food processing
wastewater), while BESA and chloroform are petroleum-based derivatives. Thus,
they represent a sustainable and renewable input. Mohan et al. [220] reported
that treating the inoculum with 0.2 g BESA/L for 24 h increased the H 2 yield from
dairy wastewater by a factor of 2.6 compared to heat shock (100
C; 1 h).
4.3 Organic Loading Rate (OLR)
The organic loading rate (OLR) is an important operation parameter which has to be
optimized to achieve the maximum yield per unit mass of inoculum. The OLR of
waste fed to dark fermentative H 2 production process has continued to be an
objective of the research. The OLR means the food/microorganism ratio which
affects the microbial growth; therefore, it needs to be within the optimum range to
support optimal microbial growth because H 2 production is a growth-associated
reaction. Han et al. [231] reported that increasing the OLR from 8 to 24 kg molasses/
m
3 /d increased the H 2 production rate and achieved a maximum value of
10.74 mmol/L/h in a CSTR. Similarly, the H 2 yield increased with the increase of
cow manure and waste milk OLR in thermophilic (55
C) batch reactors [204].
The OLR also affects the biogas composition in an upflow anaerobic sludge
blanket (UASB); the higher the OLR, the greater the biogas H 2 content [232]. On the
contrary, Bhaskar et al. [233] found that increasing the OLR of chemical wastewater
decreased the specific H 2 yield and the chemical oxygen demand (COD) removal
efficiency in biofilm-configured sequencing batch reactors (SBR). The substrate
concentration affects the H 2 production; increasing the substrate (hydrolysate)
concentration from 20% to 25% increased the lag phase of H 2 production in batch
reactors, from 11 to 38 h, and at a level of 30% inhibited the H 2 fermentation
[234]. The variation in the findings regarding the effects of the OLR on the rate,
yield, and the gas composition can be due to the type and quality of the substrate fed
despite that two substrates can be fed at the same OLR (based on the COD) and their
metabolism rate can be different. In conclusion, the OLR needs to be optimized on a
case-by-case basis.
4.4 Comparative Studies on the Effects of Pretreatments
Several studies investigated the effect of some culture pretreatments on the preparation of inoculum for the conversion of corn stover hydrolysate, dairy wastewater,
palm oil mill effluent, and biodiesel production waste (glycerol) (Table 8.11).
However, the results reported were conflicting and inconclusive. The ranking of
the effect of several pretreatment on the H 2 yields (mmol H 2 /g sugar utilized) from
corn stover hydrolysate was as follows: heat (5.03) > base (4.5) > acid
352
A. Hajizadeh et al.