H 2 /g VSS/h from molasses-processing wastewater have been reported [172]. A yield
of 166.8 mL H 2 /g COD and H 2 production rate of 26.7 mL H 2 /g VSS/h have been
obtained from fructose-processing wastewater in a CSTR operated at 55
C [172].
3.3.2 Palm Oil Mill Effluent (POME)
Palm oil mill effluent (POME) is a good substrate for H 2 production [177] and has
COD and BOD of 15–100 and 10–44 g/L, respectively [6]. H 2 production rates and
yields, from POME-extracted olive pulp, were better at thermophilic conditions
compared to mesophilic conditions [178]. Olive mill waste (OMW) has COD and
BOD of 40–220 and 23–100 g/L [39, 40], respectively, with around 2–8% sugar, but
it contains a high fraction of oil and grease plus some polyphenols (1–2.4%) [39];
these compounds are inhibitory to methanogens at high concentrations. Hamdi [40]
reported 5–80 g/L of polyphenols and 23 g/L of fats in olive mill wastewater
(Table 8.7).
3.4 Biodiesel Industrial Waste
Glycerol is a by-product or waste of the rapidly growing biodiesel industry due to the
interest in green biofuels. It is a nontoxic simple sugar alcohol compound soluble in
water. Thus it is an excellent substrate for H 2 production by mixed dark fermentation. The reported H 2 yield from glycerol ranged between 0.3 and 0.4 mol/mol
glycerol or 38 and 72 mL H 2 /g COD glycerol for mesophilic conditions (Table 8.8).
Since the theoretical H 2 yield has been estimated at 1.0 mol H 2 /mol glycerol based
on the reaction of glycerol conversion to H 2 , CO 2 , and ethanol [188, 189], then there
is a need to optimize the fermentation conditions to achieve the theoretical yield
perhaps by selecting a proper co-substrate or enriching specific microorganisms.
3.5 Dairy Wastewater and Cheese Whey
Wastewater from dairy industry processing such as cheese production contains
readily fermentable sugars such as lactose. For example, cheese whey contains
about 15% lactose [190]. Because the waste is mainly composed of a single
substrate, then adding a co-substrate such as livestock manure can supplement the
required nutrients for the growth of microorganisms and increase the H 2 yield, as
reported in Table 8.9 [197]. Cheese whey wastewater has been used for the H 2
production using CSTR [195] and produced a yield between 0.8 and 0.9 mol H 2 /mol
344
A. Hajizadeh et al.
of 166.8 mL H 2 /g COD and H 2 production rate of 26.7 mL H 2 /g VSS/h have been
obtained from fructose-processing wastewater in a CSTR operated at 55
C [172].
3.3.2 Palm Oil Mill Effluent (POME)
Palm oil mill effluent (POME) is a good substrate for H 2 production [177] and has
COD and BOD of 15–100 and 10–44 g/L, respectively [6]. H 2 production rates and
yields, from POME-extracted olive pulp, were better at thermophilic conditions
compared to mesophilic conditions [178]. Olive mill waste (OMW) has COD and
BOD of 40–220 and 23–100 g/L [39, 40], respectively, with around 2–8% sugar, but
it contains a high fraction of oil and grease plus some polyphenols (1–2.4%) [39];
these compounds are inhibitory to methanogens at high concentrations. Hamdi [40]
reported 5–80 g/L of polyphenols and 23 g/L of fats in olive mill wastewater
(Table 8.7).
3.4 Biodiesel Industrial Waste
Glycerol is a by-product or waste of the rapidly growing biodiesel industry due to the
interest in green biofuels. It is a nontoxic simple sugar alcohol compound soluble in
water. Thus it is an excellent substrate for H 2 production by mixed dark fermentation. The reported H 2 yield from glycerol ranged between 0.3 and 0.4 mol/mol
glycerol or 38 and 72 mL H 2 /g COD glycerol for mesophilic conditions (Table 8.8).
Since the theoretical H 2 yield has been estimated at 1.0 mol H 2 /mol glycerol based
on the reaction of glycerol conversion to H 2 , CO 2 , and ethanol [188, 189], then there
is a need to optimize the fermentation conditions to achieve the theoretical yield
perhaps by selecting a proper co-substrate or enriching specific microorganisms.
3.5 Dairy Wastewater and Cheese Whey
Wastewater from dairy industry processing such as cheese production contains
readily fermentable sugars such as lactose. For example, cheese whey contains
about 15% lactose [190]. Because the waste is mainly composed of a single
substrate, then adding a co-substrate such as livestock manure can supplement the
required nutrients for the growth of microorganisms and increase the H 2 yield, as
reported in Table 8.9 [197]. Cheese whey wastewater has been used for the H 2
production using CSTR [195] and produced a yield between 0.8 and 0.9 mol H 2 /mol
344
A. Hajizadeh et al.