Abstract
Dry anaerobic digestion technology (DADT) is considered a highly feasible way to treat agricultural straw waste; however, most practical operations are always in low efficiency, due to the poor fluidity behavior and complex lignocellulosic structure of straw, which is not easily decomposed by anaerobic bacteria. Hence, it is necessary to further investigate the operation boundary, in order to increase biogas production efficiency for effective applications. In this paper, typical DADTs are reviewed and their suitability for application in China is analyzed. The advantages and disadvantages of different anaerobic digestion processes are evaluated considering pretreatment, organic loading rate, anaerobic digestion temperature, and homogenization of the feedstock and inoculate. The suitability of the DADTs is evaluated considering the accessibility of straw resources and the convenience of biogas use. It is concluded that batch anaerobic digestion processes would be more suitable for the development of southern China due to the prevalence of small-scale agriculture, while continuous anaerobic digestion would be preferable in the north where large-scale agriculture is common. However, the DADTs discussed here need to broad application in China.
Highlights
In China, approximately 0.9 billion tons of agricultural straw was generated in 2015, which is considered as one of the most abundant sources for producing renewable energy [1]
In order to be considered for technical applications, Dry anaerobic digestion technology (DADT) must meet the optimal straw digestion parameters, which is the key point for operation efficiency and biogas production
Straw is a kind of lignocellulosic material consisting of three major components: Cellulose, hemicellulose, and lignin, where most of the cellulose is combined with lignin and hemicellulose [21]
Summary
In China, approximately 0.9 billion tons of agricultural straw was generated in 2015, which is considered as one of the most abundant sources for producing renewable energy [1]. Biogas seems to be a more effective way, compared with other renewable ways, such as bioethanol, to treat agricultural straw and produce renewable energy simultaneously [7]. It could be feasible at many scales from a household to large biogas plants, its energy yield could be much higher for energy crops since 2005, the Chinese government has initiated demonstration projects in 11 provinces [8]. In order to overcome the disadvantages discussed above, technologies are considered preferable for treating straw, as these processes have a lower water input, smaller digestion volume, and higher TS content of the digestion waste compared to wet processes [19]. The remaining sections of this article are arranged as follows: Section 2 describes the evaluation indicators, which would affect the stability and efficiency of the dry anaerobic digestion process, and introduces the various types of DADTs, including operating principle and technical features; Section 3 analyzes DADT applications in China according to the amount of resources, geological conditions and biogas utilization; and Section 4 presents the main conclusions and recommendations
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