into their intestinal tract through passage of the grind by gizzard in the foregut,
digestion by digestive enzymes in the midgut, and metabolism by microorganisms in
the hindgut. Finally, it is crushed by the anus and then discharged in the form of
granules (Curry and Schmidt 2007). This gut phase is also a critical factor affecting
the performance of vermicomposting products. The resulting casting is a microbial
agglomerate containing a granular surface with diverse functional microbial group
and chemical mucus from earthworm intestines. Once this agglomerate adheres to
the organic matter that has not been digested by the intestinal tract, it leads to the new
degradation and transformation of organic matter (commonly known as fecal digestion phase) (Domínguez et al. 2010). Besides, the drilling of earthworms in
vermicomposting can not only provide an aerobic environment but also disturb the
microbial agglomerate, which continuously flips them into all spaces of
vermicomposting, thus accelerating the degradation of organic matter (Meysman
et al. 2006). Consequently, these three ways of earthworms may directly or indirectly
affect the degradation and transformation of organic matter by regulating the
involved microorganisms in vermicomposting system.
In addition, sludge vermicomposting can be divided into four stages: pretreatment
stage, earthworm degradation stage, ammonification/nitrification stage, and decomposition stage (Fu et al. 2016). The methods of sludge pretreatment mainly include
air drying, airing, adding assistant materials, creating pellet, and so on. These
methods aim to remove excessive moisture content and ammonia from sludge and
to increase the carbon/nitrogen ratio or oxygen of substrate to provide a better
condition for earthworm’s survival. In the degradation stage, earthworm and microorganism corporately degrade organic matter of sludge. In this process, the content
of sludge organic matter is decreased gradually and the odor of sludge will disappear
quickly (Fu et al. 2016). In the ammonification/nitrification stage, the proteinoid-like
and microbial product-like substances decrease, while humic acid- and fulvic acidlike substances in organic matter are generated with the dominant microorganisms
such as actinomycetes, azotobacters, and ammoxidation bacteria (Huang et al.
2018). Moreover, the ammonia nitrogen and nitrate nitrogen rise rapidly in this
process. Therefore, when functional microorganisms are generated, earthworms can
be taken out of the vermi-reactor. After that, the vermicomposting products enter
into the maturity stage with much stronger nitrification and humification as well as
widener diversity of microorganisms (Fu et al. 2016; Huang et al. 2018).
4.4 Technological Conditions of Vermicomposting
for Municipal Sludge
4.4.1 Earthworm Species
Accordingly, more than 6000 kinds of earthworms are widely distributed in the
world. Based on the ecological function, it can be divided into three types: epigeic
60
K. Huang et al.
digestion by digestive enzymes in the midgut, and metabolism by microorganisms in
the hindgut. Finally, it is crushed by the anus and then discharged in the form of
granules (Curry and Schmidt 2007). This gut phase is also a critical factor affecting
the performance of vermicomposting products. The resulting casting is a microbial
agglomerate containing a granular surface with diverse functional microbial group
and chemical mucus from earthworm intestines. Once this agglomerate adheres to
the organic matter that has not been digested by the intestinal tract, it leads to the new
degradation and transformation of organic matter (commonly known as fecal digestion phase) (Domínguez et al. 2010). Besides, the drilling of earthworms in
vermicomposting can not only provide an aerobic environment but also disturb the
microbial agglomerate, which continuously flips them into all spaces of
vermicomposting, thus accelerating the degradation of organic matter (Meysman
et al. 2006). Consequently, these three ways of earthworms may directly or indirectly
affect the degradation and transformation of organic matter by regulating the
involved microorganisms in vermicomposting system.
In addition, sludge vermicomposting can be divided into four stages: pretreatment
stage, earthworm degradation stage, ammonification/nitrification stage, and decomposition stage (Fu et al. 2016). The methods of sludge pretreatment mainly include
air drying, airing, adding assistant materials, creating pellet, and so on. These
methods aim to remove excessive moisture content and ammonia from sludge and
to increase the carbon/nitrogen ratio or oxygen of substrate to provide a better
condition for earthworm’s survival. In the degradation stage, earthworm and microorganism corporately degrade organic matter of sludge. In this process, the content
of sludge organic matter is decreased gradually and the odor of sludge will disappear
quickly (Fu et al. 2016). In the ammonification/nitrification stage, the proteinoid-like
and microbial product-like substances decrease, while humic acid- and fulvic acidlike substances in organic matter are generated with the dominant microorganisms
such as actinomycetes, azotobacters, and ammoxidation bacteria (Huang et al.
2018). Moreover, the ammonia nitrogen and nitrate nitrogen rise rapidly in this
process. Therefore, when functional microorganisms are generated, earthworms can
be taken out of the vermi-reactor. After that, the vermicomposting products enter
into the maturity stage with much stronger nitrification and humification as well as
widener diversity of microorganisms (Fu et al. 2016; Huang et al. 2018).
4.4 Technological Conditions of Vermicomposting
for Municipal Sludge
4.4.1 Earthworm Species
Accordingly, more than 6000 kinds of earthworms are widely distributed in the
world. Based on the ecological function, it can be divided into three types: epigeic
60
K. Huang et al.