3 Industrial Wastewater Characterization
Converting waste to biohydrogen generates income and offsets some waste disposalassociated costs. However, a question that needs to be answered is whether a waste
stream is suitable for biohydrogen production. Generally, waste streams rich in
carbohydrates are ideal substrates for H 2 because they are readily degradable,
renewable, and sustainable and can be obtained at low cost. However, the suitability
of a feedstock for CH 4 and H 2 production by anaerobic digestion depends on several
factors. These factors include the feedstock’s physical-chemical properties, organic
content (mainly carbohydrate), cost, availability, the extent of biodegradability,
absence or presence of inhibitors and toxic compounds, requirements of
pretreatment, and sufficient concentration which makes the process energetically
favorable [69, 89]. Wastes rich in sugar monomers or polymers such as glucose,
xylose, sucrose, lactose, starch, cellulose, and hemicellulose could serve as substrates for H 2 production because they are easily biodegradable. Many waste streams
such as olive and palm mill effluent contain ethanol, acetate, butyrate, and propionate; these compounds can be consumed by microorganisms in H 2 -producing
bioreactions. Therefore, these waste streams were frequently reported as suitable
for biological H 2 production [90].
When assessing the suitability of industrial waste to anaerobic digestion, it must
be noticed that industrial waste may contain toxic compounds. These toxic compounds include oxidizing agents (disinfectant), long-chain fatty acids (LCFAs),
antibiotics, ammonia, detergents, pharmaceuticals, metal ions, and aromatic compounds from plants (lignin, tannins, phenolic compound, and pigments). The decision of whether waste containing these compounds is suitable for CH 4 or H 2
production depends on the extent to which these toxic compounds are inhibitory to
acidogens or methanogens. For example, LCFAs are inhibitory to methanogens but
not to acidogens. Therefore, they could be used as a co-substrate to inhibit
methanogens in mixed culture dark fermentation. Recently, it was reported that
moderate concentrations of ammonia increased the hydrogen yield from alkalinepretreated sludge [10]. Upon increasing the initial NH 4
+
-N concentration from 36 to
266 mg/L, the maximum hydrogen yield from alkaline (pH 9.5)-pretreated sludge
increased from 7.3 to 15.6 mL per gram of volatile suspended solids (VSS) under the
standard condition [10].
3.1 Food Waste
Food waste obtained from food catering facilities has been investigated for its
potential to produce H 2 by mixed culture dark fermentation. An advantageous
characteristic of such waste is that it has undergone chopping, soaking, and cooking
which decreased their particle size, lowered the degree of crystallinity, and increased
the soluble fraction. Careful examination of Table 8.3 reveals that wide variation
exists in the yield of H 2 reported for food waste. Indeed, food waste is a
8 Biohydrogen of Industrial Waste
335
Converting waste to biohydrogen generates income and offsets some waste disposalassociated costs. However, a question that needs to be answered is whether a waste
stream is suitable for biohydrogen production. Generally, waste streams rich in
carbohydrates are ideal substrates for H 2 because they are readily degradable,
renewable, and sustainable and can be obtained at low cost. However, the suitability
of a feedstock for CH 4 and H 2 production by anaerobic digestion depends on several
factors. These factors include the feedstock’s physical-chemical properties, organic
content (mainly carbohydrate), cost, availability, the extent of biodegradability,
absence or presence of inhibitors and toxic compounds, requirements of
pretreatment, and sufficient concentration which makes the process energetically
favorable [69, 89]. Wastes rich in sugar monomers or polymers such as glucose,
xylose, sucrose, lactose, starch, cellulose, and hemicellulose could serve as substrates for H 2 production because they are easily biodegradable. Many waste streams
such as olive and palm mill effluent contain ethanol, acetate, butyrate, and propionate; these compounds can be consumed by microorganisms in H 2 -producing
bioreactions. Therefore, these waste streams were frequently reported as suitable
for biological H 2 production [90].
When assessing the suitability of industrial waste to anaerobic digestion, it must
be noticed that industrial waste may contain toxic compounds. These toxic compounds include oxidizing agents (disinfectant), long-chain fatty acids (LCFAs),
antibiotics, ammonia, detergents, pharmaceuticals, metal ions, and aromatic compounds from plants (lignin, tannins, phenolic compound, and pigments). The decision of whether waste containing these compounds is suitable for CH 4 or H 2
production depends on the extent to which these toxic compounds are inhibitory to
acidogens or methanogens. For example, LCFAs are inhibitory to methanogens but
not to acidogens. Therefore, they could be used as a co-substrate to inhibit
methanogens in mixed culture dark fermentation. Recently, it was reported that
moderate concentrations of ammonia increased the hydrogen yield from alkalinepretreated sludge [10]. Upon increasing the initial NH 4
+
-N concentration from 36 to
266 mg/L, the maximum hydrogen yield from alkaline (pH 9.5)-pretreated sludge
increased from 7.3 to 15.6 mL per gram of volatile suspended solids (VSS) under the
standard condition [10].
3.1 Food Waste
Food waste obtained from food catering facilities has been investigated for its
potential to produce H 2 by mixed culture dark fermentation. An advantageous
characteristic of such waste is that it has undergone chopping, soaking, and cooking
which decreased their particle size, lowered the degree of crystallinity, and increased
the soluble fraction. Careful examination of Table 8.3 reveals that wide variation
exists in the yield of H 2 reported for food waste. Indeed, food waste is a
8 Biohydrogen of Industrial Waste
335