34
3.1 Overview of Composting Technology
Composting converts organic mass, such as rice straw, other agricultural byproducts, digestive, animal wastes, etc., into a more decomposed product, called
compost. Composting is necessary because it can help to increase significantly the
quality of the compost product based on the optimized nutrient factors and the
decomposition process (Diaz et al. 2007). Compost is used as a soil improver or
directly as a planting substrate. Application of compost results in an increase in, not
only crop yield, but also soil fertility (Goyal et al. 2009; Vo-Van-Binh et al. 2014).
Compost quality is strongly affected by the factors happening during the composting process, such as temperature, pH, carbon-to-nitrogen ratio (C/N), etc. These
factors can be controlled through bio-, chemical-, and physical methods or a combination of these to optimize the composting processes and products. This chapter
provides an overview of the main factors including temperature, pH, C/N ratio,
moisture content, and properties of the feedstock.
3.1.1 Properties of Materials
In composting, waste products are mixed followed by creating conditions to enable
biological decomposition to result in a higher-quality organic resource. The speed
of the composting process and the quality of compost depend on the type, quality,
and chemical and physical properties of the raw materials, conditions, and environment during the process. Typical physical and chemical properties of different raw
materials for composting are shown in Table 3.1.
3.1.2 Temperature
Temperature effects on the composting process can be divided into the four phases,
(1) mesophilic, (2) thermophilic, (3) cooling, and (4) maturing. During the initial
phase of decomposition and break down of compounds, heat is generated due to the
bio-oxidative microbial degradation (Diaz et al. 2007). This phase is facilitated by
mesophilic bacteria, which become less competitive as temperature increases up to
approximately 40 °C when thermophilic bacteria become predominant. At about
55 °C, destruction of plant pathogens occurs (Shilev et al. 2007) and then complete
hygienization takes place at temperatures of 60 °C and above (Shilev et al. 2007).
However, temperatures exceeding 65 °C should be avoided as they may harm even
useful microbes (Shilev et al. 2007). According to Haug (1980), the composting
temperature has to be above 55 °C for three consecutive days to kill the pathogens.
The temperature of compost reaches 60 °C after 10 days and lowers to ambient
temperature from 60 to 90 days of composting (Jusoh et al. 2013). Temperature
N. T. Nghi et al.
3.1 Overview of Composting Technology
Composting converts organic mass, such as rice straw, other agricultural byproducts, digestive, animal wastes, etc., into a more decomposed product, called
compost. Composting is necessary because it can help to increase significantly the
quality of the compost product based on the optimized nutrient factors and the
decomposition process (Diaz et al. 2007). Compost is used as a soil improver or
directly as a planting substrate. Application of compost results in an increase in, not
only crop yield, but also soil fertility (Goyal et al. 2009; Vo-Van-Binh et al. 2014).
Compost quality is strongly affected by the factors happening during the composting process, such as temperature, pH, carbon-to-nitrogen ratio (C/N), etc. These
factors can be controlled through bio-, chemical-, and physical methods or a combination of these to optimize the composting processes and products. This chapter
provides an overview of the main factors including temperature, pH, C/N ratio,
moisture content, and properties of the feedstock.
3.1.1 Properties of Materials
In composting, waste products are mixed followed by creating conditions to enable
biological decomposition to result in a higher-quality organic resource. The speed
of the composting process and the quality of compost depend on the type, quality,
and chemical and physical properties of the raw materials, conditions, and environment during the process. Typical physical and chemical properties of different raw
materials for composting are shown in Table 3.1.
3.1.2 Temperature
Temperature effects on the composting process can be divided into the four phases,
(1) mesophilic, (2) thermophilic, (3) cooling, and (4) maturing. During the initial
phase of decomposition and break down of compounds, heat is generated due to the
bio-oxidative microbial degradation (Diaz et al. 2007). This phase is facilitated by
mesophilic bacteria, which become less competitive as temperature increases up to
approximately 40 °C when thermophilic bacteria become predominant. At about
55 °C, destruction of plant pathogens occurs (Shilev et al. 2007) and then complete
hygienization takes place at temperatures of 60 °C and above (Shilev et al. 2007).
However, temperatures exceeding 65 °C should be avoided as they may harm even
useful microbes (Shilev et al. 2007). According to Haug (1980), the composting
temperature has to be above 55 °C for three consecutive days to kill the pathogens.
The temperature of compost reaches 60 °C after 10 days and lowers to ambient
temperature from 60 to 90 days of composting (Jusoh et al. 2013). Temperature
N. T. Nghi et al.