sludge is converted into concentrated sludge and then submitted to be dewatered.
After sludge dewatering, the resulted sludge also needs the later disposal processes,
such as incineration, thermal dry, landfill, composting, vermicomposting, and anaerobic digestion (Yang et al. 2015; Zhang et al. 2017). However, the treatment and
disposal of dewatered sludge from wastewater treatment plant have always been a
headache in the world, due to the large amounts and unstable organic component in
sludge (Yang et al. 2015; Christensen et al. 2015; Qu et al. 2019). Given that lots of
nutrients and elements exist in dewatered sludge, the recycling of dewatered sludge
is considered as a sustainable approach for resolving this big problem.
Vermicomposting is a biochemical approach for converting the sludge into highvalued organic microbial fertilizer by the joint action of earthworms and microorganisms (Huang et al. 2018). Compared to composting, vermicomposting is low cost
and easy to handle for recycling of sludge. More importantly, vermicomposting
product displays a much more nutrient content and diverse microbial community
beneficial for soil improvement or plant growth (Bhat et al. 2018; Huang et al. 2018).
As a consequence, vermicompost is deemed as a gold microbial fertilizer, and
vermicomposting is becoming rapidly popular all over the world. Until now, plenty
of studies have reported that the municipal sludge could be vermicomposted by
earthworms (Gupta and Garg 2008; Suthar and Singh 2008; Domínguez-Crespo
et al. 2012; Ludibeth et al. 2012; Reddy et al. 2012; Lv et al. 2015; Das et al. 2015;
Xie et al. 2016; Zhao et al. 2018; Lv et al. 2018a, b; Bhat et al. 2018; Huang et al.
2018). However, among these previous publications, several different crafts of
vermicomposting for dewatered sludge were carried out, and different earthworms’
species were selected, which causes many controversies in vermicomposting of
sludge. Thus, it is necessary to summarize these vermicomposting methods to better
improve this green technology. In addition, it has been well understood that earthworms are the leaders of microorganisms in vermicomposting, which can significantly change the number, activity, and population of microorganisms directly or
indirectly and thus regulate the path and process of organic degradation (Domínguez
et al. 2010). However, the detailed mechanism regarding earthworms and microorganisms in vermicomposting still needs to be elaborated.
In a word, the objectives of this chapter were to compare the current methods for
municipal sludge treatment, to introduce the different crafts and operation conditions
of vermicomposting for dewatered sludge, and to illustrate the mechanisms of
vermicomposting for sludge.
4.2 Sewage Sludge Treatment and Disposal
4.2.1 Characteristics and Amounts of Sewage Sludge
Sewage sludge is a solid/semisolid sediment produced by primary setting tank and
secondary setting tank during the process of sewage treatment. The composition of
sludge is complex, which is generally regarded as a polymer composed of zoogloeal
56
K. Huang et al.
After sludge dewatering, the resulted sludge also needs the later disposal processes,
such as incineration, thermal dry, landfill, composting, vermicomposting, and anaerobic digestion (Yang et al. 2015; Zhang et al. 2017). However, the treatment and
disposal of dewatered sludge from wastewater treatment plant have always been a
headache in the world, due to the large amounts and unstable organic component in
sludge (Yang et al. 2015; Christensen et al. 2015; Qu et al. 2019). Given that lots of
nutrients and elements exist in dewatered sludge, the recycling of dewatered sludge
is considered as a sustainable approach for resolving this big problem.
Vermicomposting is a biochemical approach for converting the sludge into highvalued organic microbial fertilizer by the joint action of earthworms and microorganisms (Huang et al. 2018). Compared to composting, vermicomposting is low cost
and easy to handle for recycling of sludge. More importantly, vermicomposting
product displays a much more nutrient content and diverse microbial community
beneficial for soil improvement or plant growth (Bhat et al. 2018; Huang et al. 2018).
As a consequence, vermicompost is deemed as a gold microbial fertilizer, and
vermicomposting is becoming rapidly popular all over the world. Until now, plenty
of studies have reported that the municipal sludge could be vermicomposted by
earthworms (Gupta and Garg 2008; Suthar and Singh 2008; Domínguez-Crespo
et al. 2012; Ludibeth et al. 2012; Reddy et al. 2012; Lv et al. 2015; Das et al. 2015;
Xie et al. 2016; Zhao et al. 2018; Lv et al. 2018a, b; Bhat et al. 2018; Huang et al.
2018). However, among these previous publications, several different crafts of
vermicomposting for dewatered sludge were carried out, and different earthworms’
species were selected, which causes many controversies in vermicomposting of
sludge. Thus, it is necessary to summarize these vermicomposting methods to better
improve this green technology. In addition, it has been well understood that earthworms are the leaders of microorganisms in vermicomposting, which can significantly change the number, activity, and population of microorganisms directly or
indirectly and thus regulate the path and process of organic degradation (Domínguez
et al. 2010). However, the detailed mechanism regarding earthworms and microorganisms in vermicomposting still needs to be elaborated.
In a word, the objectives of this chapter were to compare the current methods for
municipal sludge treatment, to introduce the different crafts and operation conditions
of vermicomposting for dewatered sludge, and to illustrate the mechanisms of
vermicomposting for sludge.
4.2 Sewage Sludge Treatment and Disposal
4.2.1 Characteristics and Amounts of Sewage Sludge
Sewage sludge is a solid/semisolid sediment produced by primary setting tank and
secondary setting tank during the process of sewage treatment. The composition of
sludge is complex, which is generally regarded as a polymer composed of zoogloeal
56
K. Huang et al.