of POME in 2008 [36]. In 2016, the total production of oil palm fruits was about
300 million tonnes [37]. Olive mill waste (OMW) is produced annually in large
quantities; around 5.4 Â 10
6 m
3 of OMW are produced annually worldwide
[38]. OMW has COD and BOD of 40–220 and 23–100 g/L [39, 40], respectively,
with around 2–8% sugar.
1.2 General Description of Anaerobic Digestion
Anaerobic digestion is a well-established bioprocess for treating organic waste and
producing methane. In this process, a series of biochemical reactions degrade and
convert reduced (rich in electrons) organic materials to CH 4 through the metabolic
interactions of various anaerobic microorganisms (Fig. 8.2). Several groups of
trophically distinct microorganisms work together to degrade the organic material
and produce CH 4 , carbon dioxide (CO 2 ) and water in four successive stages
[42]. Anaerobic digestion depends on a balanced symbiotic relationship between
metabolically distinct microbial groups [43]. The major groups of microorganisms
are as follows [44]:
1. Hydrolytic and fermentative (acidogenic) bacteria
2. Hydrogen-producing acetogenic bacteria
3. Methanogenic Archaea (both acetoclastic and hydrogenotrophic)
Fig. 8.1 Comparative fractions of non-utilized raw material in food processing wastes which could
be used as substrates for H 2 production. (Adapted from [32])
328
A. Hajizadeh et al.
300 million tonnes [37]. Olive mill waste (OMW) is produced annually in large
quantities; around 5.4 Â 10
6 m
3 of OMW are produced annually worldwide
[38]. OMW has COD and BOD of 40–220 and 23–100 g/L [39, 40], respectively,
with around 2–8% sugar.
1.2 General Description of Anaerobic Digestion
Anaerobic digestion is a well-established bioprocess for treating organic waste and
producing methane. In this process, a series of biochemical reactions degrade and
convert reduced (rich in electrons) organic materials to CH 4 through the metabolic
interactions of various anaerobic microorganisms (Fig. 8.2). Several groups of
trophically distinct microorganisms work together to degrade the organic material
and produce CH 4 , carbon dioxide (CO 2 ) and water in four successive stages
[42]. Anaerobic digestion depends on a balanced symbiotic relationship between
metabolically distinct microbial groups [43]. The major groups of microorganisms
are as follows [44]:
1. Hydrolytic and fermentative (acidogenic) bacteria
2. Hydrogen-producing acetogenic bacteria
3. Methanogenic Archaea (both acetoclastic and hydrogenotrophic)
Fig. 8.1 Comparative fractions of non-utilized raw material in food processing wastes which could
be used as substrates for H 2 production. (Adapted from [32])
328
A. Hajizadeh et al.