87
reservoir and then converted to electric power by a generator. The digestate after AD
is used for processing organic fertilizers.
5.4 Utilization of Bioslurry
Applications of bioslurry on crops have been investigated since the 1940s. Gurung
(1997) showed that bioslurry had a better effect on crops compared to farmyard
manure. This study also revealed that AD converts 25–30% of the organic part of
fecal matter into biogas, while 70–75% goes to the effluent or bioslurry.
Nutrients (N-P-K) and micronutrients (zinc, iron, manganese, and copper) in
bioslurry are needed for plant growth (Tripathi 1993 as cited by Gurung 1997).
Bunyeth and Preston (2004) and Sophea and Preston (2001) reported that water
spinach yield responded linearly to increasing levels of nitrogen in bioslurry with
pig manure. The yield of leaf mustard fertilized by the codigester effluent was 2.2
times higher compared to the inorganic fertilizer treatment. In addition to increasing
the yield, the effluent can help retain more nutrients in the soil layer, accelerate
flower formation, and shorten cultivation time (Nguyen et al. 2015).
Using bioslurry for fisheries was also reported in several studies. Kaur et al.
(1987) presented that the growth rate of carp was 3.5 times higher in the bioslurry
tank than in the control tank with raw cow dung. Increases in fish growth rate using
biogas effluent were also revealed by Balasubramanian and Bai (1994) and Sophin
and Preston (2001).
5.5 Conclusions and Recommendations
This review of the AD process, including AD systems from different countries, provides an overview of the current practices and trends. It should be noted that there
is no such thing as a best digester design as the technology is often highly localized.
An AD technology may work well in one country but not in another because of different conditions.
With regards to the use of rice straw for AD, studies have shown that it is a feasible and sustainable technology, especially when rice straw is codigested with
other biological wastes such as animal manure. Using the optimum pretreatment,
conditions, and operational parameters and a mixture proportion with other substrates, methane production from AD of rice straw can be maximized. In addition,
the digestate byproduct can be processed to produce biofertilizer.
To increase the adoption of AD technologies, awareness of the technology must
be increased and the rice straw and biogas value chain must be upgraded. AD technologies that are easy to adopt, such as the use of hermetic bags for AD, can be
useful to farmers. Subsequent increase in demand for biogas and biofertilizers can
be supported by larger scale technologies such as the two-stage AD.
5 Anaerobic Digestion of Rice Straw for Biogas Production
reservoir and then converted to electric power by a generator. The digestate after AD
is used for processing organic fertilizers.
5.4 Utilization of Bioslurry
Applications of bioslurry on crops have been investigated since the 1940s. Gurung
(1997) showed that bioslurry had a better effect on crops compared to farmyard
manure. This study also revealed that AD converts 25–30% of the organic part of
fecal matter into biogas, while 70–75% goes to the effluent or bioslurry.
Nutrients (N-P-K) and micronutrients (zinc, iron, manganese, and copper) in
bioslurry are needed for plant growth (Tripathi 1993 as cited by Gurung 1997).
Bunyeth and Preston (2004) and Sophea and Preston (2001) reported that water
spinach yield responded linearly to increasing levels of nitrogen in bioslurry with
pig manure. The yield of leaf mustard fertilized by the codigester effluent was 2.2
times higher compared to the inorganic fertilizer treatment. In addition to increasing
the yield, the effluent can help retain more nutrients in the soil layer, accelerate
flower formation, and shorten cultivation time (Nguyen et al. 2015).
Using bioslurry for fisheries was also reported in several studies. Kaur et al.
(1987) presented that the growth rate of carp was 3.5 times higher in the bioslurry
tank than in the control tank with raw cow dung. Increases in fish growth rate using
biogas effluent were also revealed by Balasubramanian and Bai (1994) and Sophin
and Preston (2001).
5.5 Conclusions and Recommendations
This review of the AD process, including AD systems from different countries, provides an overview of the current practices and trends. It should be noted that there
is no such thing as a best digester design as the technology is often highly localized.
An AD technology may work well in one country but not in another because of different conditions.
With regards to the use of rice straw for AD, studies have shown that it is a feasible and sustainable technology, especially when rice straw is codigested with
other biological wastes such as animal manure. Using the optimum pretreatment,
conditions, and operational parameters and a mixture proportion with other substrates, methane production from AD of rice straw can be maximized. In addition,
the digestate byproduct can be processed to produce biofertilizer.
To increase the adoption of AD technologies, awareness of the technology must
be increased and the rice straw and biogas value chain must be upgraded. AD technologies that are easy to adopt, such as the use of hermetic bags for AD, can be
useful to farmers. Subsequent increase in demand for biogas and biofertilizers can
be supported by larger scale technologies such as the two-stage AD.
5 Anaerobic Digestion of Rice Straw for Biogas Production