83
Similarly, a study by Shen et al. (2018) on the effect of organic loading rate on
anaerobic codigestion of rice straw and pig manure showed that after biological
pretreatment, the substrate was optimally fermented at an organic loading rate of
2.5 kg COD m
−3
day
−1
. This pretreatment achieved the optimum volumetric methane production rate of 640 L CH 4 m
−3
day
−1
, and a methane yield of 456 L CH 4 kg
−1
COD removed, which were 62.4 and 37.8% higher than those of the control under
the same organic loading rate.
Using aerobic and anaerobic fungi as pretreatment agents resulted in increased
biodegradability of rice straw (Ghosh and Bhattacharyya 1999; Cann et al. 1994).
Methane production from rice straw AD was increased 31–46% when pretreating it
with white-rot fungus and brown-rot fungus (Polyporus ostreiformis using a strawto- fungi ratio of 14:1 and then digested in batch reactors at 30 °C after a 3-week
incubation period. Cann et al. (1994) reported that the anaerobic fungi from the
rumen consistently increased the digestibility of rice straw when compared with
fermenters where the fungi were inhibited. Haruta et al. (2002) also presented the
enhancements by a microbial community formed by mixing rice straw, chicken
feces, pig feces, cattle feces, and sugarcane dregs. This degraded 60% of the rice
straw within 4 days.
Momayez et al. (2018) presented an investigation using effluent of biogas digestate to pretreat rice straw. The straw was pretreated at different temperatures (130,
60, and 190 °C) at different pretreatment times (30 and 60 min). The pretreated
straw was subjected to different processes, including liquid anaerobic digestion
(L-AD) and dry anaerobic digestion (D-AD). The highest methane yields were
obtained through L-AD and D-AD of straw pretreated at 190 °C and 30 min, resulting in 24 and 26% increases in methane produced as compared with L-AD and
D-AD using untreated straw. Mustafa et al. (2016) showed that rice straw pretreated
with fungi (Pleurotus ostreatus and Trichoderma reesei) and used as feedstock for
AD improved the methane yield by 120 and 78.3%, respectively, as compared with
untreated straw. These points of view show that biological pretreatment studies have
a huge potential, considering that there were only a few fungi species that were
studied. There are still millions of fungi species that are yet to be studied.
The results of the previous research mentioned above are shown in Fig. 5.6.
5.3.2 Current Practices of Rice Straw AD
Continuous farm-scaled AD with a plastic digester was assessed and reported by
Tran et al. (2015). Figure 5.7a, b show the schematic diagram of the rice straw AD
system using a biogas bag developed by Can Tho University in Vietnam. The 6-m
3
household digester is made of high-density polyethylene (HDPE). Rice straw was
cut in 20-cm lengths and ensilaged about 5 days before feeding into the digester.
The cofeeding of rice straw and pig dung with the mixed ratio was 1:1 based on the
organic dry matter (ODM). The daily feed of rice straw was 4.75 kg dry weight
(DW) corresponding to 4.17 kg DW of pig dung. Retention time of rice straw in this
5 Anaerobic Digestion of Rice Straw for Biogas Production
Similarly, a study by Shen et al. (2018) on the effect of organic loading rate on
anaerobic codigestion of rice straw and pig manure showed that after biological
pretreatment, the substrate was optimally fermented at an organic loading rate of
2.5 kg COD m
−3
day
−1
. This pretreatment achieved the optimum volumetric methane production rate of 640 L CH 4 m
−3
day
−1
, and a methane yield of 456 L CH 4 kg
−1
COD removed, which were 62.4 and 37.8% higher than those of the control under
the same organic loading rate.
Using aerobic and anaerobic fungi as pretreatment agents resulted in increased
biodegradability of rice straw (Ghosh and Bhattacharyya 1999; Cann et al. 1994).
Methane production from rice straw AD was increased 31–46% when pretreating it
with white-rot fungus and brown-rot fungus (Polyporus ostreiformis using a strawto- fungi ratio of 14:1 and then digested in batch reactors at 30 °C after a 3-week
incubation period. Cann et al. (1994) reported that the anaerobic fungi from the
rumen consistently increased the digestibility of rice straw when compared with
fermenters where the fungi were inhibited. Haruta et al. (2002) also presented the
enhancements by a microbial community formed by mixing rice straw, chicken
feces, pig feces, cattle feces, and sugarcane dregs. This degraded 60% of the rice
straw within 4 days.
Momayez et al. (2018) presented an investigation using effluent of biogas digestate to pretreat rice straw. The straw was pretreated at different temperatures (130,
60, and 190 °C) at different pretreatment times (30 and 60 min). The pretreated
straw was subjected to different processes, including liquid anaerobic digestion
(L-AD) and dry anaerobic digestion (D-AD). The highest methane yields were
obtained through L-AD and D-AD of straw pretreated at 190 °C and 30 min, resulting in 24 and 26% increases in methane produced as compared with L-AD and
D-AD using untreated straw. Mustafa et al. (2016) showed that rice straw pretreated
with fungi (Pleurotus ostreatus and Trichoderma reesei) and used as feedstock for
AD improved the methane yield by 120 and 78.3%, respectively, as compared with
untreated straw. These points of view show that biological pretreatment studies have
a huge potential, considering that there were only a few fungi species that were
studied. There are still millions of fungi species that are yet to be studied.
The results of the previous research mentioned above are shown in Fig. 5.6.
5.3.2 Current Practices of Rice Straw AD
Continuous farm-scaled AD with a plastic digester was assessed and reported by
Tran et al. (2015). Figure 5.7a, b show the schematic diagram of the rice straw AD
system using a biogas bag developed by Can Tho University in Vietnam. The 6-m
3
household digester is made of high-density polyethylene (HDPE). Rice straw was
cut in 20-cm lengths and ensilaged about 5 days before feeding into the digester.
The cofeeding of rice straw and pig dung with the mixed ratio was 1:1 based on the
organic dry matter (ODM). The daily feed of rice straw was 4.75 kg dry weight
(DW) corresponding to 4.17 kg DW of pig dung. Retention time of rice straw in this
5 Anaerobic Digestion of Rice Straw for Biogas Production